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材料科学与技术英文版Materials Science and Technology: Paving the Way for InnovationsMaterials Science and Technology is a rapidly evolving field that plays a critical role in the advancement of technology and innovation in various sectors including aerospace, automotive, healthcare, electronics, and energy. The field deals with the study, development, and manufacturing of materials for various applications. Materials science encompasses chemistry, physics, and engineering to understand the properties of materials and how these properties can be manipulated to create new materials.The development of new materials often leads to breakthroughs in technology and innovation. For example, the discovery and development of composite materials, which are composed of two or more constituent materials with significantly different physical or chemical properties that, when merged,create a material with unique characteristics, has revolutionized many industries. Carbon fiber composites are lighter and stronger than traditional materials, making them ideal for use in aircraft and racing cars.Nanotechnology is another area where materials science is making significant contributions. By manipulating materials at the nanoscale, materials scientists can create new materials with unique properties. For instance, graphene, a one-atom-thick sheet of carbon atoms, is stronger than steel, flexible, and conducts electricity better than copper. Graphene's properties make it an ideal material for use in electronics, batteries, and sensors.The development of biodegradable materials is another area of focus within materials science. As awareness of environmental issues grows, there is a greater demand for materials that can decompose and reduce waste. Bioplastics, made from plant-based materials, are an example of biodegradable alternatives totraditional plastics that can help reduce environmental pollution.Additive manufacturing, or 3D printing, has also transformed the field of materials science and technology. This technology allows for the creation of complex shapes and designs with materials ranging from plastics to metals. It provides a flexible manufacturing process that can create custom parts and reduce waste compared to traditional manufacturing methods.Materials science and technology have a profound impact on society. By enabling innovation in various sectors, they contribute to advancements in medical devices, renewable energy, and sustainable living. The development of new materials continues to push the boundaries of what is possible, opening up new opportunities for technology and innovation.In conclusion, materials science and technology are at the forefront of innovation, driving advancements invarious fields and contributing to the development of solutions to global challenges. The ongoing research and development in this field will undoubtedly lead to more breakthroughs, shaping the future of technology and society.。

外文翻译硼化物涂层的滑动和磨粒磨损行为（C. Martini, G. Palombarini∗, G. Poli, D. Prandstraller）Institute of Metallurgy, University of Bologna, Viale Risorgimento 4, Bologna 40136, Italy摘要由Fe2B单内层和外层的FeB所构成的多相硼化物涂层对铁和经渗碳处理的中碳钢有着深远的影响。

根据滑动和磨损试验条件对样本的硼摩擦学行为进行了研究。

发现不同地区的涂料的磨损率有很大的不同。

铁硼化物晶体秩序解释了这些差异的原因。

薄，易碎的涂料层构成的无序晶体对两种类型的抗磨损行为影响不大。

然后，构成Fe2B单紧凑，高度有序的晶体的地区阻力增加到最高值。

耐干滑动样本的硼优于通过提交替代表面处理样本资料（如气体氮化）和含量较低的aWC钴硬质合金涂层。

关键词：硼；铁；钢；滑动摩擦；磨粒摩擦；择优取向；晶体秩序；1 导言日益增加的需求与令人满意的电阻材料磨损与腐蚀性能促进了迅速扩张表面改性领域技术的发展。

事实上，在许多应用中，这服务生活的组成部分是由表面特性所决定的。

在这重要的热化学处理的钢种扩散的领域，如碳、氮和硼，硼处于一种特殊地位。

一方面，即使在超过20个全球行动纲领，以及高耐磨性，经热化学处理的硼化物涂层涂料使普通钢材有了很高的硬度。

硼钢构件在机械工程和汽车几个摩擦学性能优良的工业中有很广泛的应用。

值得注意的是，最好的结果是由粘固获得，即工序使用含有粉末的混合物进行硼化组件（如碳化硼），活化剂（通常KBF4），并最终加入稀释剂以控制潜在的硼化方法。

然而，相对于气相渗硼，粉末渗硼在工业生产过程中：（一）比较复杂，费时和昂贵，（二）不适合过程控制和自动化，这种状况妨碍了充分传播渗硼处理工艺。

努力加快工业气体渗过程的进展，就双方的加工条件和组成，硼化物层的孔隙度控制的主要问题加以解决，特别是，对等离子体及有关金属表面的相互作用机制缺乏了解。

Internal curing of high-performance concrete with pre-soaked fine lightweight aggregate for prevention of autogenous shrinkage crackingDaniel Cusson ⁎,Ted HoogeveenNational Research Council Canada,Ottawa,Ontario,Canada K1A 0R6Received 19September 2007;accepted 8February 2008AbstractThe effectiveness of internal curing (IC)to reduce autogenous shrinkage cracking in high-performance concrete (HPC)was investigated using different levels of internal curing on four pairs of large-size prismatic HPC specimens tested simultaneously under free and restrained shrinkage.Internal curing was supplied by pre-soaked fine lightweight aggregate (LWA)as a partial replacement to regular sand.It was found that the use of 178kg/m 3of saturated LWA in HPC,providing 27kg/m 3of IC water,eliminated the tensile stress due to restrained autogenous shrinkage without compromising the early-age strength and elastic modulus of HPC.It was shown that the risk of concrete cracking could be conservatively estimated from the extent of free shrinkage strain occurring after the peak expansion strain that may develop at very early ages.Autogenous expansion,observed during the first day for high levels of internal curing,can significantly reduce the risk of cracking in concrete structures,as both the elastic and creep strains develop initially in compression,enabling the tensile strength to increase further before tensile stresses start to initiate later.Crown Copyright ©2008Published by Elsevier Ltd.All rights reserved.Keywords:Curing (A );High-performance concrete (E );Shrinkage (C );Creep (C );Mechanical properties (C )1.IntroductionProper curing of concrete structures is important to ensure they meet their intended performance and durability require-ments.In conventional construction,this is achieved through external curing,applied after mixing,placing and finishing [1].Internal curing (IC)is a very promising technique that can provide additional moisture in concrete for a more effective hydration of the cement and reduced self-desiccation [2].In-ternal curing implies the introduction of a curing agent into concrete that will provide this additional moisture.Currently,there are two major methods available for internal curing of concrete.The first method uses saturated porous lightweight aggregate (LWA)[3]in order to supply an internal source of water,which can replace the water consumed by chemical shrinkage during cement hydration.This internal curing water is naturally drawn during cement hydration from the relatively large pores of the lightweight aggregate into the smaller pores ofthe cement paste.The second method uses super-absorbent polymers (SAP)[4],as these particles can absorb a very large quantity of water during concrete mixing and form large inclu-sions containing free water,thus preventing self-desiccation during cement hydration.For optimum performance,the internal curing agent should possess high water absorption capacity and high water desorption rates.The quantity of internal curing water required to replace the mix water consumed by chemical shrinkage can be easily estimated,as suggested elsewhere [5,6].Detailed information on internal curing can be found in the new state-of-the-art report on internal curing of concrete from RILEM TC-196[2].Since the 1950's,internal curing had been inadvertently applied in lightweight concrete structures before its potential for reducing self-desiccation in high-performance concrete (HPC)structures was recognized later in the 1990's [7].Lightweight aggregates were primarily used to reduce the weight of concrete structures;however,these aggregates were usually saturated prior to use in concrete to ensure adequate workability,since it was recognized that dry porous aggregates could absorb some of the mix water in fresh concrete [8].These concrete structuresAvailable online at Cement and Concrete Research 38(2008)757–765⁎Corresponding author.E-mail address:Daniel.Cusson@nrc-cnrc.gc.ca (D.Cusson).0008-8846/$-see front matter.Crown Copyright ©2008Published by Elsevier Ltd.All rights reserved.doi:10.1016/j.cemconres.2008.02.001were found to achieve long-term durability from their excellent in-service performance observed in the field[9,10].More recently,lightweight aggregates have been used successfully in large construction projects for the purpose of internal curing of normal-density concrete structures.For example,in January 2005,about190000m3of internally-cured concrete was used in a paving project in Hutchins,Texas,which was likely the largest project in the world taking advantage of internal curing with pre-soaked LWA[11].Field observations reported marginal pave-ment cracking,and strength tests indicated that the7-dayflexural strengths reached90%to100%of the required28-day flexural strength due to an improved hydration.They also found that the compressive strengths of air-cured cylinders were similar to those of wet-cured cylinders at all ages,suggesting that internally-cured concrete is less sensitive to poor external curing practices or unfavourable ambient conditions.Especially in low permeability concrete,conventional external curing may not be effective in preventing self-desiccation at the center of thick concrete elements.The use of internal curing,however,does not replace recommended curing practices,as it is important to keep the concrete surface continuously moist during the curing process in order to prevent surface cracking due to plastic or drying shrinkage in hot,dry or windy weather.This paper presents experimental results from large-size prismatic internally-cured HPC specimens tested simultaneous-ly under free and restrained autogenous shrinkage.The main objectives of this study are to determine the required level of internal curing needed to eliminate autogenous shrinkage in high-performance concrete,and to demonstrate that the risk of cracking in concrete structures under restrained conditions can be effectively reduced.2.Experimental program2.1.MaterialsFour concrete mix designs were experimentally evaluated, including one reference concrete mix(Mix-0)with no internal curing,and three similar concrete mixes with different levels of internal curing,namely Mix-L,Mix-M and Mix-H with low, medium and high contents of pre-soaked LWA,respectively,as shown in Table1.This was achieved by replacing part of the normal-density sand with pre-soaked lightweight aggregate sand.In this study,each concrete mix had450kg/m3of ASTM Type1cement,a total water–cement ratio of0.34,and a cement–sand–coarse aggregate ratio of1:2:2by mass.The properties of the fine and coarse aggregates are provided in Table2.The expanded shale lightweight aggregate sand used for internal curing had a dry-bulk density of920kg/m3and water content of15%by mass of dry material.This LWA sand was slightly coarser than the normal-density sand,made of silica and quartz,and was in fact improving the particle size distribution of the aggregates in the concrete mix.As shown in Table1,the quantities of LWA used in these mixes did not significantly affect the volumetric mass of concrete,which was 2410kg/m3on average.It is important to observe that the total amount of water(mix water and IC water)was kept the same in these concrete mixes, resulting in a constant total water–cement ratio of0.34for all mixes.Based on the mix water immediately available to fresh concrete before setting,the effective water–cement ratio ranged from0.34for the control concrete to0.28for the Mix-H con-crete(Table1).The goal of maintaining a constant total amount of water in the concrete mixes was twofold:(i)to prevent possible strength and stiffness reductions with more water and lightweight material in concrete,and(ii)to make the test more severe for internal curing as far as autogenous shrinkage is concerned,since concretes with lower water–cement ratios usually experience more severe self-desiccation.The quantity of IC water needed to achieve maximum hy-dration in concrete was estimated from calculations based on the chemical shrinkage and maximum degree of hydration theo-retically achievable in normal cement paste,as follows[2]:wcic¼0:18wcfor w=c V0:36ð1Þwhere(w/c)ic is the mass ratio of internal curing water to cement,and w/c is the mass ratio of mix water to ing the effective w/c shown in Table1,the theoretical quantities of internal curing water required to ensure maximum cement hydration were estimated at:0.061for Mix-0;0.058for Mix-L;0.054for Mix-M;and0.050for Mix-H.Since different levels of internal curing were desired in this study,lower than required quantities of IC water were provided in Mix-0,Mix-L and Mix-M.For the mix designs presented in Table1,the percentage of IC water actually provided to that required in theory were:0%Table1Concrete mix formulations and fresh concrete propertiesConstituent QuantityMix-0Mix-L Mix-M Mix-H(No IC)(Low IC)(Medium IC)(High IC) Total water(kg)21.321.321.321.3 ASTM type1cement(kg)62.562.562.562.5Dry normal sand(kg)125.0117.5110.0100.0 LWA sand(kg,dry)0.07.515.025.0Dry coarse aggregate(kg)125.0125.0125.0125.0 Dry superplasticizer(kg) 2.1 2.5 2.1 2.7 Total w/c0.340.340.340.34 Effective w/c0.340.320.300.28IC water/cement0.000.020.040.06 LWA/total sand0.000.060.120.20 Slump(mm)215210140102Air content(%) 3.9 5.0 3.0 3.0V olumetric mass(kg/m3)2428239124202400Table2Aggregate propertiesName Type MaximumsizeDry-bulkdensityFinenessmodulusWatercontent(mm)(kg/m3)(%) Lightweight sand Expanded shale5920 3.315 Regular sand Silica,quartz51650 2.60.3 Coarse aggregate Limestone201430 6.70.2758 D.Cusson,T.Hoogeveen/Cement and Concrete Research38(2008)757–765for Mix-0(control);34%for Mix-L;74%for Mix-M;and120% for Mix-H.For each mix design,two large-size concrete specimens and additional small-size concrete samples were prepared from the same batch and sealed with plastic sheets to prevent external drying,since the focus of this study was on autogenous shrink-age prevention.2.2.Testing proceduresA complete testing system and analysis method were previously developed for studying restrained shrinkage and tensile creep of large-size HPC specimens[12].This approach, modified from existing approaches[13,14],presents new features including:(i)the use of large-size specimens,enabling the study of the mechanical behaviour of concrete made with large coarse aggregate and reinforcing bars;and(ii)the ability to impose a partial(or full)degree of restraint on the specimen through embedded reinforcing bars,which is representative of field conditions.An advantage of using a partial degree of restraint is that restrained shrinkage testing can be conducted without prematurely cracking those concrete specimens experi-encing large shrinkage deformations(in our case the control specimen).Fig.1presents the main setup used for testing free and restrained shrinkage of large-size prismatic concrete specimens (200×200×1000mm).For each restrained specimen,the axial strain was measured with electrical strain gauges(SG)centered on four10-mm reinforcing bars embedded in concrete.The test apparatus included a closed loop servo-hydraulic system to control the actuator using the rebar-mounted strain gauges as the feedback signal.The force,measured by a load cell,was transmitted to the concrete by the steel bars,which had their ends welded to the stiff end plates connected to the rigid test frame.For each concrete mix,an unrestrained companion specimen was prepared with no reinforcement.Free shrinkage was measured using LVDTs placed at both ends of the speci-men.Two relative humidity(RH)sensors were placed in the unrestrained specimen to assess the extent of internal drying due to self-desiccation,and thermocouples(TC)were distributed in concrete as shown in Fig.1.Detailed technical information on the test frame and test procedures is provided elsewhere[12].Additional tests were simultaneously conducted on smaller concrete samples made of the same batch of concrete,including the determination of the thermal expansion coefficient on75×75×295mm prisms,as well as the compressive strength, splitting tensile strength and compressive modulus of elasticity on100×200mm cylinders.The temperature was monitored for each type of sample,and maturity(equivalent age at25°C)was calculated for each sample size in order to use consistent sets of results in the calculations.Maturity was calculated as follows [15]:M tðÞ¼Z texpE aR1273þT refÀ1273þT tðÞdtð2Þwhere t is the time after initial setting of concrete;E a/R is the activation energy factor of the concrete(for which a value of 4000K was experimentally determined[16]);T is the average concrete temperature as a function of time;and T ref is the reference concrete temperature(taken here as25°C).3.Results and analyses3.1.Effect of internal curing on concrete temperature and relative humidityDuring the free and restrained shrinkage experiments,the concrete specimens were tested under realistic temperature regimes,as shown in Fig.2.Due to the heat produced bycement Fig.1.Experimental setup for testing restrained and free shrinkage of large concrete specimens.759D.Cusson,T.Hoogeveen/Cement and Concrete Research38(2008)757–765hydration,the average concrete temperature reached 41°C to 45°C at 12to 18h after casting,depending on the specimen.After the cooling period,their average concrete temperature reduced to values between 21°C and 24°C near the age of 2days,and remained constant thereafter (matching their re-spective ambient temperatures).It can be observed that when pre-soaked LWA sand is used for internal curing,the peak temperature is a few degrees higher and occurs a few hours earlier than for the control concrete with no LWA (sealed curing only),which may be due to the use of internal curing and a lower effective water –cement ratio.Fig.2also presents the relative humidity measured in these concrete specimens (each curve is an average from two distinct sensors).For the control specimen (sealed curing only),the RH decreased from 100%initially to 94%after 2days and to 92%after 7days.However,when a low level of internal curing was used (Mix-L specimen),the concrete RH was approximately 2%lower than in the control specimen at any given time.With further increases in the quantity of LWA used for internal curing (from Mix-L to Mix-H),the RH remained relatively higher in concrete,with an RH of 98%after 2days and 96%after 7days,which are well beyond the RH values measured in the control specimen at these times.Fig.3(modified from [17])gives a conceptual illustration of different pore systems in cement paste under various curing conditions.It may be used to explain the reduced relative humidity measured in Mix-L concrete (insufficient internal curing)compared to Mix-0concrete (sealed curing only).In the case of insufficient internal curing,hydration may have im-proved from sealed curing (with some reduction in pore sizes),however,all pores in LWA and some pores in the cement paste may be left empty after the small quantity of internal curing water is consumed by the cement hydration reaction,thus re-sulting in slightly lower RH in the system.In Fig.3,the case of sufficient internal curing likely represents Mix-H concrete,in which all pores in the cement paste are filled with water while the pores in LWA are empty after migration of IC water to the cement paste.3.2.Effect of internal curing on free shrinkage strain Fig.4presents the total strain measured in the unrestrained concrete specimens for 7days.This measurement includes free autogenous shrinkage and thermal strains (drying shrinkage prevented).Note that in this paper,negative strain values repre-sent a contraction (shrinkage)and positive strain values repre-sent an expansion.It can be readily seen that the addition of pre-soaked LWA for internal curing allowed early-age expansion to occur,which was due to autogenous swelling and thermal expansion,with peaks observed between 8and 12h of age.The extent of expansion increased with the quantity of pre-soaked LWA used in the concrete mix.Mix-H was the only concrete producing positive values of total strain after the first day until the end of testing at 7days.The thermal strain was calculated from the average concrete temperature measured in each concrete specimen as a function of time (Fig.2)and the coefficient of thermal expansion (CTE)determined on smaller concrete prisms (75×75×295mm).The equipment and procedures used for testing the CTE is described elsewhere [18],where it was found that:(i)CTE increases from a low value of 8×10−6/°C shortly after setting to a maximum value of 11×10−6/°C after 10days,and (ii)the use of internal curing did not affect the early-age CTE of concrete compared to sealed-cured concrete.Calibrated on experimental results [18],the following empirical model for thermalexpansionFig.3.Conceptual representation of cement paste pore systems under different curing conditions (modified from [17]).Fig.4.Total strain measured in unrestrained concretespecimens.Fig.2.Temperature and relative humidity measured in unrestrained concrete specimens.760 D.Cusson,T.Hoogeveen /Cement and Concrete Research 38(2008)757–765was therefore determined for the concrete used in the present study:a c t ðÞ¼8þ1:3LN t ðÞensuring that 8Â10À6=-C V a c V 11Â10À6=-Cð3Þwhere αc is the concrete CTE determined as a function of time tafter setting (days).The autogenous shrinkage strain was thus determined by subtracting the calculated thermal strain from the total strain measured in the unrestrained specimen,and is presented in Fig.5for each concrete specimen.It can be seen that most of the autogenous deformations occurred within 24to 48h,with only limited changes thereafter.This observation emphasizes an important requirement for the prevention of autogenous shrink-age in concrete structures:shrinkage prevention measures must be effective shortly after setting of concrete before significant tensile stresses develop in concrete during the cooling period.For each concrete specimen,a critical strain value of net au-togenous shrinkage was calculated at around 36h of age which,in each case,corresponded to the time with the highest net shrinkage strain to tensile strength ratio.These critical net shrinkage strains ranged from only −25×10−6for Mix-H con-crete to a much larger value of −250×10−6for Mix-0concrete.It should be noted that Mix-L concrete,which only had 6%LWA sand (relative to the total mass of sand),experienced 20%less shrinkage than the control concrete (from −250×10−6to −200×10−6).3.3.Effect of internal curing on restrained shrinkage stress Stress calculations based on preliminary shrinkage testing indicated a high risk of cracking in Mix-0concrete specimen if tested under full restraint (i.e.zero displacement).It was there-fore decided to test the restrained specimens under a partial restraint of 0.9(i.e.allowing only 10%of total shrinkage to take place),thus slightly reducing the tensile stresses developing in the restrained specimens.Fig.6presents the degree of restraint applied to each restrained concrete specimen during the 7-day period of testing,which was defined as:K t ðÞ¼1Àe R tot t ðÞe F tot t ðÞð4Þwhere εtotRis the total strain allowed in the restrained concrete specimen (depending on the preset degree of restraint);and εtot Fis the total strain measured in the free (unrestrained)companion specimen.For Mix-0,Mix-L and Mix-M specimens,the target value of 0.9was difficult to maintain during the first day of testing,at which time the concrete specimen expanded or contracted very rapidly.The high relaxation of concrete at very early age pre-vented any cracking in the specimens.For Mix-H specimen,the applied degree of restraint was temporarily slightly over 1.0during the first 3days (i.e.the loading system was actually pulling on the specimen),however,this caused no problem since Mix-H concrete had very small autogenous shrinkage deformations and high relaxation resulting in relatively low tensile stresses developing in concrete.Fig.7illustrates the tensile stress developing over time in each restrained concrete specimen.It can be observed that Mix-M and Mix-H specimens first experienced restrained expansion resulting in compressive stresses during the first day,followed by tensile stresses developing in the specimens due to restrained shrinkage.It is clear that the high level of internal curing in Mix-H specimen resulted in smaller tensile stresses compared to the other concrete specimens,even if Mix-H specimen was tested under a somewhat higher degree of restraint (see Fig.6).It should be emphasized that most of the tensile stresses produced in Mix-H concrete specimen was actually not due to restrained autogenous shrinkage but to restrained thermalcontractionFig.7.Concrete stress measured in restrained concretespecimens.Fig.6.Degree of restraint imposed on restrained concretespecimens.Fig.5.Autogenous shrinkage strain measured in unrestrained concrete specimens.761D.Cusson,T.Hoogeveen /Cement and Concrete Research 38(2008)757–765during the cooling period.As shown in Fig.5,it is recalled that the critical net autogenous shrinkage strain was rather small in Mix-H specimen compared to its thermal contraction strain,of which the extent may be assessed from Fig.4.3.4.Effect of internal curing on risk of concrete crackingConventional concrete starts shrinking near the time of initial setting,from which time shrinkage should be measured experi-mentally since,in actual concrete structures,tensile stresses will start to develop around that time if movement is restrained.In this case,all of the shrinkage strain will be responsible for the development of tensile stresses,depending on the visco-elastic properties of concrete.In structures made with concrete thatmay experience swelling at early ages,not all of the strain will produce tensile stresses if movement is restrained,as some of it will generate compressive stresses initially(as previously shown in Fig.7).In that particular case,when testing free shrinkage of concrete specimens to assess the potential risk of cracking in concrete structures,large underestimations may occur if the extent of shrinkage strain used to evaluate that risk is determined from the time of setting.To illustrate this point,Fig.8presents the development of the total strain(i.e.thermal+autogenous shrinkage strains)mea-sured in the unrestrained Mix-H concrete specimen(from Fig.4)and the development of the corresponding concrete stress measured in the companion specimen under restraint (from Fig.7).It is clearly shown that,although the measured total strain always remained positive(absolute expansion), the tensile stress in the concrete specimen reached a value of 2MPa in only2days.This is due to the fact that the beneficial expansion occurred when the modulus of elasticity was relatively small and the effect of creep was relatively large at very early ages,resulting in a low peak compressive stress (−1MPa),followed later by restrained thermal contraction with an increased modulus of elasticity and reduced creep resulting in the development of tensile stress.Ideally,the extent of shrinkage strain to consider when evaluating the risk of cracking in concrete structures should be the amount of strain developing after the time at which com-pressive stresses reverse into tensile stresses(i.e.afterεσ=0). For the data in Fig.8,an ideal net shrinkage strain of−125×10−6(εmin−εσ=0)would be obtained at3days,which is more meaningful than the absolute value of+50×10−6at3days.However,when testing shrinkage under a stress-free condition,such information(εσ=0)is not available.In this case,it issuggested to rely on the extent of free shrinkage strain(or netshrinkage strain)occurring after the peak of expansion(i.e.after εmax),which would result in a conservative assessment of the risk of cracking in concrete structures.The net shrinkage strainwas calculated as follows:e sh net tðÞ¼e sh tðÞÀe exp maxð5Þwhereεsh(t)is the shrinkage strain measured as a function of time after initial setting;εexp max is the peak strain value of the autogenous expansion,if any(εexp max=0if no expansion).From Fig.8,the critical value of net shrinkage strain wouldbe−160×10−6(i.e.εmin−εmax)at3days,which is actually the extent of shrinkage strain contributing to the increase in tensile stress in the restrained concrete specimen.This proposed definition of net shrinkage has the double advantage of being conservative and independent of the choice of Time Zero in shrinkage testing[19].Whether Time Zero is defined as‘time after casting’,‘time after setting’(preferred),or‘time after peak of expansion’,the critical or ultimate value of net shrinkage strain according to Eq.(5)will always remain unaffected.The risk of cracking in concrete structures also depends onthe rates at which tensile strength and modulus of elasticitydevelop(as illustrated in Fig.9).The tensile strength curveswere determined by linear regression of splitting tensilestrength Fig.10.Total,creep and elastic strains obtained for restrained Mix-0concretespecimen.Fig.9.Tensile strength and modulus of elasticity measured for different concretemixes.Fig.8.Total strain and resulting stress in Mix-H concrete specimens.762 D.Cusson,T.Hoogeveen/Cement and Concrete Research38(2008)757–765test results obtained at1,2,4,7and28days on100×200mm concrete cylinders(tested in triplicates).The curves for the tensile modulus of elasticity were determined by linear regres-sion of modulus values obtained at various times.These values were first determined from stress–strain data obtained during rapid partial unloading/reloading cycles conducted on the large-size concrete specimens during the restrained shrinkage experi-ments(vertical lines in Fig.7).The curves shown in Fig.9 provide no indication that internal curing compromises the development of either tensile strength or modulus of elasticity until an age of7days.3.5.Effect of internal curing on creep and elastic strainsFigs.10–13present the creep and elastic strains as well as the total strain and strain capacity calculated for each of the four concrete specimens tested under restrained shrinkage.The strain analysis was based on compatibility of strain:e tot tðÞ¼e el tðÞþe cr tðÞþe sh tðÞþe th tðÞð6Þwhereεtot is the total strain allowed in the restrained concrete specimen measured as a function of time t;εel is the elastic strain calculated by dividing the measured concrete stress(Fig.7)by the corresponding tensile modulus of elasticity(Fig.9)de-veloping in the restrained specimen;εcr is the creep strain of concrete;andεsh+εth are the shrinkage and thermal strains measured together(Fig.4)in the unrestrained concrete specimen (with a small correction to account for the internal restraint provided by the reinforcement in the restrained concrete speci-men[12]).Finally,the strain capacity presented in Figs.10–13 was calculated by dividing the concrete tensile strength(Fig.9) by the corresponding tensile modulus of elasticity(Fig.9).In Fig.10for the control concrete specimen with no internal curing,it can be seen that the elastic strain came very close to the strain capacity at an age of1.5days.It is clear that under full restraint(K=1.0),this specimen would have cracked,which would have ended the test prematurely.Similar behaviour and conclusion also apply to Mix-L concrete specimen in Fig.11, where the elastic strain almost reached the tensile strain capacity at an age of1.5days for a degree of restraint near0.9.On the other hand,with higher levels of internal curing Mix-M and Mix-H concrete specimens performed quite well(Figs.12and 13,respectively),with the elastic strain always lower than the strain capacity at any given time.Note that most of the elastic strain development was due to thermal contractions during the cooling period.For these two concrete specimens with restrained expansion in the first day(before cooling),the elastic strain went into the compressive range allowing the strain capacity to develop further by the time the elastic strain reversed into the tensile range,which actually reduced the risk of cracking.The creep strain also developed differently depending on the extent of restrained expansion occurring in the concrete specimens at early age.With an increased quantity of pre-soaked LWA used in the specimens,larger creep strains developed in compression due to more significant restrained expansion.During the cooling period and after,increments of tensile creep strain developed due to restrained contraction resulting in a reduction in compressive creep strain towards the tensile range.Regardless of the concrete mixes tested,it is clear from these curves that creep developed very rapidly during the first day with a gradually decreasing development rate there-after,as typically expected with normal concrete under load.4.Effectiveness of internal curing4.1.Effectiveness in shrinkage reductionFig.14illustrates the effectiveness of the LWA used for internal curing in reducing autogenous shrinkage of the concrete mixes tested in this study.It is shown that the reduction inthe Fig.13.Total,creep and elastic strains obtained for restrained Mix-H concretespecimen.Fig.12.Total,creep and elastic strains obtained for restrained Mix-M concretespecimen.Fig.11.Total,creep and elastic strains obtained for restrained Mix-L concretespecimen.763D.Cusson,T.Hoogeveen/Cement and Concrete Research38(2008)757–765。

国外材料科学英文书籍1. "Materials Science and Engineering: An Introduction" by William D. Callister, Jr. 这本书是材料科学与工程领域的经典教材，涵盖了材料的结构、性能、制备和应用等方面。

2. "Principles of Materials Science and Engineering" by Donald R. Askeland and Pradeep P. Phulé. 本书提供了材料科学的全面概述，包括晶体结构、热力学、相图、材料的力学行为等内容。

3. "Introduction to Materials Science for Engineers" by James F. Shackelford. 这本书是为工程师编写的材料科学入门教材，强调了材料的工程应用和设计。

4. "Materials Science and Technology" by R.W. Cahn and P. Haasen. 该书是材料科学领域的权威著作，涵盖了材料的结构、性能、制备和应用等方面，内容深入且广泛。

5. "Materials Characterization: Introduction to Microscopic and Spectroscopic Methods" by Michael F. Ashby and David R. H. Jones. 这本书介绍了材料表征的各种技术和方法，包括显微镜、光谱学和衍射技术等。

这些书籍都是材料科学领域的经典著作，可以帮助读者深入了解材料的结构、性能、制备和应用等方面的知识。

你可以根据自己的需求和兴趣选择适合的书籍进行阅读。

材料科学专业英语英语作文英文回答：Materials science is a rapidly evolving field that deals with the synthesis, characterization, and application of materials with tailored properties. It combines elements from chemistry, physics, and engineering to design and develop new materials for various applications in various industries, ranging from aerospace to electronics to healthcare.The field of materials science encompasses a wide range of subfields, including:Materials Synthesis: Involves developing new methods for synthesizing materials with specific properties and structures. This can include techniques such as chemical vapor deposition, molecular beam epitaxy, and sol-gel processing.Materials Characterization: Involves using advanced techniques to characterize the structure, composition, and properties of materials. This can include techniques suchas X-ray diffraction, electron microscopy, and spectroscopy.Materials Modeling: Involves using computational techniques to simulate and predict the behavior of materials. This can include simulating the atomic-level structure of materials, predicting their mechanical properties, and understanding their electronic properties.Materials Applications: Involves designing and developing new materials for specific applications. Thiscan include developing new materials for aerospace, electronics, energy storage, and healthcare.Materials science plays a crucial role in the development of new technologies and products, such as:Electronic devices: Materials science is essential for developing new materials for electronic devices, such as semiconductors, insulators, and conductors. These materialsenable the development of faster, smaller, and more efficient electronic devices.Aerospace materials: Materials science is essential for developing new materials for aerospace applications, such as lightweight, strong, and heat-resistant alloys. These materials enable the development of more efficient and safer aircraft and spacecraft.Energy storage materials: Materials science is essential for developing new materials for energy storage, such as batteries and capacitors. These materials enable the development of more efficient and sustainable energy storage systems.Healthcare materials: Materials science is essential for developing new materials for healthcare applications, such as biomaterials and drug delivery systems. These materials enable the development of new treatments and therapies for various diseases.The field of materials science is expected to continueto grow rapidly in the coming years, driven by the demandfor new materials for various applications. This growthwill be fueled by advances in computational techniques, characterization techniques, and materials synthesis methods.中文回答：材料科学是一个快速发展的领域，它涉及到合成、表征和应用具有定制性能的材料。

Design and thermal analysis of plastic injection mouldS.H. Tang , Y.M. Kong, S.M. Sapuan, R. Samin, S. SulaimanAbstractThis paper presents the design of a plastic injection mould for producing warpage testing specimen and performing thermal analysis for the mould to access on the effect of thermal residual stress in the mould. The technique, theory, methods as well as consideration needed in designing of plastic injection mould are presented. Design of mould was carried out using commercial computer aided design software Unigraphics, Version 13.0. The model for thermal residual stress analysis due to uneven cooling of the specimen was developed and solved using a commercial finite element analysis software called LUSAS Analyst, Version 13.5. The software provides contour plot of temperature distribution for the model and also temperature variation through the plastic injection molding cycle by plotting time response curves. The results show that shrinkage is likely to occur in the region near the cooling channels as compared to other regions. This uneven cooling effect at different regions of mould contributed to warpage.Keywords: Plastic Injection mould; Design; Thermal analysis1.IntroductionPlastic industry is one of the world’s fast est growing industries, ranked as one of the few billion-dollar industries. Almost every product that is used in daily life involves the usage of plastic and most of these products can be produced by plastic injection molding method [1]. Plastic injection molding process is well known as the manufacturing process to create products with various shapes and complex geometry at low cost[2].The plastic injection molding process is a cyclic process. There are four significant stages in the process. These stages are filling, packing, cooling and ejection. The plastic injection molding process begins with feeding the resin and the appropriate additives from the hopper to the heating/injection system of the injection plastic injection molding machine [3]. This is the “filling stage” in which the mould cavity is filled with hot polymer melt at injection temperature. After the cavity is filled, in the “packing stage”, additional polymer melt is packed into the cavity at a higher pressure to compensate the expected shrinkage as the polymer solidifies. This is followed by “cooling stage” where the mould is cooled until the part is sufficiently rigid to be ejected. The last step is the “ejection stage” in which the mould is opened and the part is ejected, after which the mould is closed again to begin the next cycle [4].The design and manufacture of injection molded polymeric parts with desired properties is a costly process dominated by empiricism, including the repeated modification of actual tooling. Among the task of mould design, designing the mould specific supplementary geometry, usually on the core side, is quite complicated by the inclusion of projection and depression [5].In order to design a mould, many important designing factors must be taken into consideration. These factors are mould size, number of cavity, cavity layouts, runner systems,gating systems, shrinkage and ejection system [6].In thermal analysis of the mould, the main objective is to analyze the effect of thermal residual stress or molded-in stresses on product dimension. Thermally induced stresses develop principally during the cooling stage of an injection molded part, mainly as a consequence of its low thermal conductivity and the difference in temperature between the molten resin and the mould. An uneven temperature field exists around product cavity during cooling [7].During cooling, location near the cooling channel experiences more cooling than location far away from the cooling channel. This different temperature causes the material to experience differential shrinkage causing thermal stresses. Significant thermal stress can cause warpage problem. Therefore, it is important to simulate the thermal residual stress field of the injection-molded part during the cooling stage [8]. By understanding the characteristics of thermal stress distribution, deformation caused by the thermal residual stress can be predicted.In this paper the design of a plastic injection mould for producing warpage testing specimen and for performing thermal analysis for the mould to access on the effect of thermal residual stress in the mould is presented.2.Methodology2.1. Design of warpage testing specimenThis section illustrates the design of the warpage testing specimen to be used in plastic injection mould. It is clear that warpage is the main problem that exists in product with thin shell feature. Therefore, the main purpose of the product development is to design a plastic part for determining the effective factors in the warpage problem of an injectionmoulded part with a thin shell.The warpage testing specimen is developed from thin shell plastics. The overall dimensions of the specimen were 120mmin length, 50mmin width and 1mmin thickness. The material used for producing the warpage testing specimen was acrylonitrile butadiene stylene (ABS) and the injection temperature, time and pressure were 210 ◦C, 3 s and 60MPa, respectively.2.2. Design of plastic injection mould for warpage testing specimenThis section describes the design aspects and other considerations involved in designing the mould to produce warpage testing specimen. The material used for producing the plastic injection mould for warpage testing specimen was AISI 1050 carbon steel.Four design concepts had been considered in designing of the mould including:i. Three-plate mould (Concept 1) having two parting line with single cavity. Not applicable due to high cost.ii. Two-plate mould (Concept 2) having one parting line with single cavity without gating system. Not applicable due to low production quantity per injection.iii.Two-plate mould (Concept 3) having one parting line with double cavities with gating and ejection system. Not applicable as ejector pins might damage the product as the product is too thin.Iv. Two-plate mould (Concept 4) having one parting line with double cavities withgating system, only used sprue puller act as ejector to avoid product damage during ejection.In designing of the mould for the warpage testing specimen, the fourth design concept had been applied. Various design considerations had been applied in the design.Firstly, the mouldwas designed based on the platen dimension of the plastic injection machine used (BOY 22D). There is a limitation of the machine, which is the maximum area of machine platen is given by the distance between two tie bars. The distance between tie bars of the machine is 254 mm. Therefore, the maximum width of the mould plate should not exceed this distance. Furthermore, 4mm space had been reserved between the two tie bars and the mould for mould setting-up and handling purposes. This gives the final maximum width of the mould as 250 mm. The standard mould base with 250mm×250mmis employed. The mould base is fitted to the machine using Matex clamp at the upper right and lower left corner of the mould base or mould platen.The mould had been designed with clamping pressure having clamping force higher than the internal cavity force (reaction force) to avoid flashing from happening.Based on the dimensions provided by standard mould set, the width and the height of the core plate are 200 and 250 mm, respectively. These dimensions enabled design of two cavities on core plate to be placed horizontally as there is enough space while the cavity plate is left empty and it is only fixed with sprue bushing for the purpose of feeding molten plastics. Therefore, it is only one standard parting line was designed at the surface of the product. The product and the runner were released in a plane through the parting line during mould opening.Standard or side gate was designed for this mould. The gate is located between the runner and the product. The bottom land of the gate was designed to have 20◦ slanting and has only 0.5mm thickness for easy de-gating purpose. The gate was also designed to have 4mm width and 0.5mm thickness for the entrance of molten plastic.In the mould design, the parabolic cross section type of runner was selected as it has the advantage of simpler machining in one mould half only, which is the core plate in this case. However, this type of runner has disadvantages such as more heat loss and scrap compared with circular cross section type. This might cause the molten plastic to solidify faster. This problem was reduced by designing in such a way that the runner is short and has larger diameter, which is 6mm in diameter.It is important that the runner designed distributes material or molten plastic into cavities at the same time under the same pressure and with the same temperature. Due to this, the cavity layout had been designed in symmetrical form.Another design aspect that is taken into consideration was air vent design. The mating surface between the core plate and the cavity plate has very fine finishing in order to prevent flashing from taking place. However, this can cause air to trap in the cavity when the mould is closed and cause short shot or incomplete part. Sufficient air vent was designed to ensure that air trap can be released to avoid incomplete part from occurring.The cooling system was drilled along the length of the cavities and was located horizontally to the mould to allow even cooling. These cooling channels were drilled on both cavity and core plates. The cooling channels provided sufficient cooling of the mould in the case of turbulent flow.In this mould design, the ejection system only consists of the ejector retainer plate, sprue puller and also the ejector plate. The sprue puller located at the center of core plate not only functions as the puller to hold the product in position when the mould is opened but it also acts as ejector to push the product out of the mould during ejection stage. No additional ejector is used or located at product cavities because the product produced is very thin, i.e. 1 mm. Additional ejector in the product cavity area might create hole and damage to the product during ejection.Finally, enough tolerance of dimensions is given consideration to compensate for shrinkage of materials.3.Results and discussion3.1. Results of product production and modificationFrom the mould designed and fabricated, the warpage testing specimens produced have some defects during trial run. The defects are short shot, flashing and warpage. The short shot is subsequently eliminated by milling of additional air vents at corners of the cavities to allow air trapped to escape. Meanwhile, flashing was reduced by reducing the packing pressure of the machine. Warpage can be controlled by controlling various parameters such as the injection time, injection temperature and melting temperature.After these modifications, the mould produced high quality warpage testing specimen with low cost and required little finishing by de-gating.3.2. Detail analysis of mould and productAfter the mould and products were developed, the analysis of mould and the product was carried out. In the plastic injection moulding process, molten ABS at 210 ◦C is injected into the mould through the sprue bushing on the cavity plate and directed into the product cavity. After cooling takes place, the product is formed. One cycle of the product takes about 35 s including 20 s of cooling time.The material used for producing warpage testing specimen was ABS and the injection temperature, time and pressure were 210 ◦C, 3 s and 60MPa res pectively. The material selected for the mould was AISI 1050 carbon steel. Properties of these materials were important in determining temperature distribution in the mould carried out using finite element analysis.Due to symmetry, the thermal analysis was performed by modeling only the top half of the vertical cross section or side view of both the cavity and core plate that were clamped together during injection.Modeling for the model also involves assigning properties and process or cycle time to the model. This allowed the finite element solver to analyze the mould modeled and plot time response graphs to show temperature variation over a certain duration and at different regions.For the product analysis, a two dimensional tensile stress analysis was carried using LUSAS Analyst, Version 13.5. Basically the product was loaded in tension on one end while the other end is clamped. Load increments were applied until the model reaches plasticity.4conclusionIn future, however, it is suggested that the product service condition should be determined so that further analysis may be carried out for other behaviors under various other loading. that affect warpage. The testing specimen was produced at low cost and involves only little finishing that is de-gating.The thermal analysis of plastic injection mould has provided an understanding of the effect of thermal residual stress on deformed shape of the specimen and the tensile stress analysis of product managed to predict the tensile load that the warpage testing specimen can withstand before experiencing failure.References[1] R.J. Crawford, Rubber and Plastic Engineering Design and Application, Applied Publisher Ltd., 1987, p. 110.[2] B.H. Min, A study on quality monitoring of injection-molded parts, J. Mater. Process. Technol. 136 (2002) 1.[3] K.F. Pun, I.K. Hui, W.G. Lewis, H.C.W. Lau, A multiple-criteria environmental impact assessment for the plastic injection molding process: a methodology, J. Cleaner Prod. 11 (2002) 41.[4] A.T. Bozdana, O¨. Eyerc´ıog˘lu, Development of an Expert System for the Determination of Injection Moulding Parameters of Thermoplastic Materials: EX-PIMM, J. Mater. Process. Technol. 128 (2002) 113.[5] M.R. Cutkosky, J.M. Tenenbaum, CAD/CAM Integration Through Concurrent Process and Product Design, Longman. Eng. Ltd., 1987, p. 83.[6] G. Menges, P. Mohren, How to Make Injection Molds, second ed., Hanser Publishers, New York, 1993, p 129.[7] K.H. Huebner, E.A. Thornton, T.G. Byrom, The Finite Element Method for Engineers, fourth ed., Wisley, 2001, p. 1.[8] X. Chen, Y.C. Lam, D.Q. Li, Analysis of thermal residual stress in plastic injection molding, J. Mater. Process. Technol. 101 (1999) 275.。

Advanced Engineering MaterialsTypes of MaterialsMaterials may be grouped in several ways. Scientists often classify materials by their state: solid, liquid, or gas. They also separate them into organic (once living) and inorganic (never living) materials. Today’s materials can be classified as metals and alloys, as polymers or plastics, as ceramics, or as composites; composites, most of which are man-made, actually are combinations of different materials.For industrial purposes, materials are divided into engineering materials or nonengineering materials. Engineering materials are those used in manufacture and become parts of products.Nonengineering materials are the chemicals, fuels, lubricants, and other materials used in the manufacturing process, which do not become part of the product.Engineering materials may be further subdivided into: ①Metal ②Ceramics ③Composite ④Polymers, etc.Metals and Metal AlloysMetals are elements that generally have good electrical and thermal conductivity. Many metals have high strength, high stiffness, and have good ductility. Some metals, such as iron, cobalt and nickel, are magnetic. At low temperatures, some metals and intermetallic compounds become superconductors.What is the difference between an alloy and a pure metal? Pure metals are elements which come from a particular area of the periodic table. Examples of pure metals include copper in electrical wires and aluminum in cooking foil and beverage cans.Alloys contain more than one metallic element. Their properties can be changed by changing the elements present in the alloy. Examples of metal alloys include stainless steel which is an alloy of iron, nickel, and chromium; and gold jewelry which usually contains an alloy of gold and nickel.Why are metals and alloys used? Many metals and alloys have high densities and are used in applications which require a high mass-to-volume ratio.Some metal alloys, such as those based on aluminum, have low densities and are used in aerospace applications for fuel economy. Many alloys also have high fracture toughness, which means they can withstand impact and are durable.What are some important properties of metals?Density is defined as a material’s mass divided by its volume. Most metals have relatively high densities, especially compared to polymers.Fracture toughness can be described as a material’s ability to avoid fracture, especially when a flaw is introduced. Metals can generally contain nicks anddents without weakening very much, and are impact resistant. A football player counts on this when he trusts that his facemask won’t shatter.Plastic deformation is the ability of bend or deform before breaking. As engineers, we usually design materials so that they don’t deform under normal conditions. You don’t want your car to lean to the east after a strong west wind.However, sometimes we can take advantage of plastic deformation. The crumple zones in a car absorb energy by undergoing plastic deformation before they break.The atomic bonding of metals also affects their properties. In metals, the outer valence electrons are shared among all atoms, and are free to travel everywhere. Since electrons conduct heat and electricity, metals make good cooking pans and electrical wires.It is impossible to see through metals, since these valence electrons absorb any photons of light which reach the metal. No photons pass through.Alloys are compounds consisting of more than one metal. Adding other metals can affect the density, strength, fracture toughness, plastic deformation, electrical conductivity and environmental degradation.Ceramics and GlassesA ceramic is often broadly defined as any inorganic nonmetallic material．By this definition, ceramic materials would also include glasses; however, many materials scientists add the stipulation that “ceramic” must also be crystalline.A glass is an inorganic nonmetallic material that does not have a crystalline structure. Such materials are said to be amorphous.Properties of Ceramics and GlassesSome of the useful properties of ceramics and glasses include high melting temperature, low density, high strength, stiffness, hardness, wear resistance, and corrosion resistance.Many ceramics are good electrical and thermal insulators. Some ceramics have special properties: some ceramics are magnetic materials; some are piezoelectric materials; and a few special ceramics are superconductors at very low temperatures. Ceramics and glasses have one major drawback: they are brittle.Ceramics are not typically formed from the melt. This is because most ceramics will crack extensively (i.e. form a powder) upon cooling from the liquid state. CompositesComposites are formed from two or more types of materials. Examples include polymer/ceramic and metal/ceramic composites. Composites are used because overall properties of the composites are superior to those of the individual components.For example: polymer/ceramic composites have a greater modulus than the polymer component, but aren’t as brittle as ceramics.Two types of composites are: fiber-reinforced composites and particle-reinforced composites.Fiber-reinforced CompositesReinforcing fibers can be made of metals, ceramics, glasses, or polymers that have been turned into graphite and known as carbon fibers. Fibers increase themodulus of the matrix material.The strong covalent bonds along the fiber’s length give them a very high modulus in this direction because to break or extend the fiber the bonds must also be broken or moved.Fibers are difficult to process into composites,making fiber-reinforced composites relatively expensive.Fiber-reinforced composites are used in some of themost advanced, and therefore most expensive sports equipment, such as a time-trial racing bicycle frame which consists of carbon fibers in a thermoset polymer matrix.Body parts of race cars and some automobiles are composites made of glass fibers (or fiberglass) in a thermoset matrix.Fibers have a very high modulus along their axis, but have a low modulus perpendicular to their axis. Fiber composite manufacturers often rotate layers of fibers to avoid directional variations in the modulus.Particle-reinforced compositesParticles used for reinforcing include ceramics and glasses such as small mineral particles, metal particles such as aluminum, and amorphous materials, including polymers and carbon black.Particles are used to increase the modulus of the matrix, to decrease the permeability of the matrix, to decrease the ductility of the matrix. An example of particle-reinforced composites is an automobile tire which has carbon black particles in a matrix of polyisobutylene elastomeric polymer.PolymersA polymer has a repeating structure, usually based on a carbon backbone. The repeating structure results in large chainlike molecules. Polymers are useful because they are lightweight, corrosion resistant, easy to process at low temperatures and generally inexpensive.Some important characteristics of polymers include their size (or molecular weight), softening and melting points, crystallinity, and structure. The mechanical properties of polymers generally include low strength and high toughness. Their strength is often improved using reinforced composite structures.Important Characteristics of PolymersSize. Single polymer molecules typically have molecular weights between 10,000 and 1,000,000g/mol—that can be more than 2,000 repeating units depending on the polymer structure!The mechanical properties of a polymer are significantly affected by the molecular weight, with better engineering properties at higher molecular weights.Thermal transitions. The softening point (glass transition temperature) and the melting point of a polymer will determine which it will be suitable for applications. These temperatures usually determine the upper limit for which a polymer can be used.For example, many industrially important polymers have glass transition temperatures near the boiling point of water (100℃, 212℉), and they are most useful for room temperature applications. Some specially engineered polymers can withstand temperatures as high as 300℃(572℉).Crystallinity. Polymers can be crystalline or amorphous, but they usually have a combination of crystalline and amorphous structures (semi-crystalline).Application of these materials depend on their properties; therefore, we need to know what properties are required by the application and to be able to relate those specification to the material.For example, a ladder must withstand a design load, the weight of a personusing the ladder. However, the material property that can be measured is strength, which is affected by the load and design dimension. Strength values must therefore be applied to determined the ladder dimensions to ensure safe use. Therefore, in general, the structures of metallic materials have effects on their properties.In a “tensile test” a sample is gradually elongated to failure and the tensile force required to elongate the sample is measured using a load cell throughout the test. The result is a plot of tensile force versus elongation.True stress and true strain provide the most accurate description of what actually happens to the material during testing and so are widely used in materials science. For engineering design, however, there are two problems.Firstly, true stress requires a knowledge of the value of A throughout the test, whereas in real world applications the designer of structures chooses an initial cross sectional area (A0). Secondly true strain is not very easy to visualize. Consequently for engineering applications an “engineering” stress (s) and strain (e) are used in place of true stress and true strain:s = F / A0 and e = (l1 - l0) / l0Stress has units of Pa (i.e. N m-2) and strain is dimensionless. The concept of a stress is clearly closely related to that of pressure. Using the definitions of stress and strain given above, the load versus elongation curve produced by the tensile test can be converted into true stress - strain or engineering stress - strain curves. Using these curves, it is now possible to describe the mechanical properties of metals and alloys.In true and engineering stress-strain relationships for a “typical” metal, linear portion of the stress strain curves the material is deforming elastically at the Initial.In other words, if the load were removed the material will return to its initial, undeformed condition. In the linear elastic region, the “stiffness” or “elastic modulus” is the amount of stress required to produce a given amount of strain.For a tensile test, stiffness is described by Young’s modulus (E), which is given by: E = s / e or E = s / eThe greater the value of the stiffness, the more difficult it will be to produce elastic deformation. Thus, for example, in selecting a material for the springs of a vehicle, stiffness would be a key engineering design criterion.On exceeding a certai n stress, known as the “yield stress” or “yield strength” (sy or sy in true and engineering stress respectively), the stress - strain curve ceases to be linear and the material begins to undergo permanent “plastic” deformation.In the plastic region of the stress - strain curve, it is apparent that the stressrequired to continue plastic deformation is higher than that required to make the material yield. This phenomenon is called “work hardening” or “strain hardening”.In the true stress - strain curve, it can be seen that work hardening actually continues right up until failure at the failure stress sf. In contrast the engineering stress - strain curve shows a maximum stress, the “ultimate ” (UTS), prior to final failure.。

Optimal mould design for the manufacture by compression moulding of high-precisionlensesM. Sellier†1, C. Breitbach†, H. Loch† and N. Siedow‡August 7, 2006† Schott AG, Hattenbergstrasse 10, 55122 Mainz, Germany‡ Fraunhofer-Institut fuer Techno- und Wirtschaftsmathematik (ITWM)Fraunhofer-Platz 1, 67663 Kaiserslautern, GermanyAbstractThe increasing need for low-cost, high-precision optical devices requires innovative manufacturing techniques or the optimization of existing ones. The present study focuses on the latter alternative and proposes a computer-aided, mould optimization algorithm for the manufacturing of high-precision glass lenses by compression moulding. The intuitive, yet very efficient, algorithm computes at each optimization loop the mismatch between the desired and deformed glass shapes and uses this information to update the mould design. To solve this optimal shape design problem, a finite element model representative of the real industrial process is developed and solved in the commercial package ABAQUS. This model solves the several stages involved in the process and includes the thermo-mechanical coupling, the varying mechanical contact between the glass and the mould, and the stress and structure relaxation in the glass. The algorithm is successfully tested for the mould design for a plano-concave and a bi-concave lens as the residual error between the deformed and desired glass profiles is decreased to a value of the order of one micron.Keywords: optimal shape design, compression moulding, glass forming, finite element model.1 mathieu.sellier@itwm.fhg.de1.IntroductionIn the competitive industry of optics manufacturing, there is a growing need for the mass production of high-precision glass parts. To date, however, there is still a conflict between the productivity and accuracy requirements. Indeed, existing techniques relying on the grinding and polishing of the moulded glass piece can achieve sub-micron accuracy but at a prohibitive cost. A much more time- and cost-effective alternative would be to predict directly the mould design which yields the net, desired glass shape at the end of the forming process without requiring further post-processing.The compression moulding process, illustrated in Figure 1, consists of three stages: heating of the glass preform/mould assembly to a temperature above the glass transition temperature, pressing of the softened glass to transfer the mould shape onto the glass and, cooling down to room temperature. The mould design in this process is a challenging task because of the deformations induced during cooling stage (thermal shrinkage, residual stresses). Although the profile of the mould might be perfectly transferred to the softened glass at the end of the pressing stage, a strategy is required to compensate for these deformations. Existing compensation techniques rely, according to Yi and Jain in [1], on a simple first-order theory of thermal expansion but such an approach comes to a limit when accuracy of the order of one micron is targeted. Other studies related to the computer-aided tool design for glass forming include, for example, that of Moreau et al. in [2] who optimize the press design in the forming of an automotive rear side panel, that of Lochegnies et al. in [3] who determine the required mould yielding a prescribed glass thickness distribution in the blow and blow process, or that of Agnon and Stokes in [4] who derive the former shape that produces a prescribed top surface curvature profile in the thermal replication process.The aim of the present work is to present a numerical algorithm to optimize the mould shape in the context of high-precision compression moulding and demonstrate its ability toproduce challenging lens designs with an accuracy of the order of one micron. The intuitive idea of the algorithm is to iteratively “test and correct”. The residuals giving a measure of the mismatch between the final and desired glass piece geometries are computed at each optimization loop and used to update the previous mould design.The next section is devoted to the description of the process and its modelling in the finite element package ABAQUS. The details of the computer-aided mould optimization algorithm follow. Lastly, results supporting the success of the method for the mould design for a plano-concave and a bi-concave lens shape are reported.2.Modelling of the processThe first requirement to tackle numerically the optimal shape design problem described above is to be able to model accurately the forward problem, i.e. “what is the final glass profile for a given mould design?” Modelling the entire process is a complicated task because of the many stages involved, the thermo-mechanical coupling, the varying mechanical contact between the glass and the mould, and the complex rheology of the glass. To reduce the computational cost, only a simplified model representative of the whole industrial process is considered. The model is solved in the commercial finite element package ABAQUS and user-defined subroutines were developed to implement the complex rheology of the glass. Since the forming temperature is slightly above the glass transition temperature, the glass is in the viscoelastic range and the combined effects of stress and structure relaxation must be accounted for in order to achieve the necessary accuracy. The glass behaviour is represented by the Tool-Narayanaswamy model, [5, 6]. This model has become a standard to handle stress relaxation in glassy materials under non-isothermal conditions. The interested reader is referred to [8] for a thorough description of the model and to [7] for an overview. It suffices here to say that the glass has a transition temperature of 505 °C. Other glass properties and relaxation parameters are not reported since the optimization method described is entirely based ongeometric considerations and its success is therefore independent of the precise material properties or operating conditions. The mould is modelled in ABAQUS as a rigid body since its stiffness is much greater than that of the glass.The finite element analysis is restricted to an axisymmetric geometry and only a two-dimensional radial cross section of the model is represented in Figure 2 for the plano-concave lens and in Figure 3 for the bi-concave one. The glass preform is enclosed in the upper and lower parts of the mould and the outer ring prevents it from flowing outwards during the pressing stage. The outer ring is simply represented in ABAQUS by a rigid surface since its influence on the overall process is minor. In the real industrial process, the glass preform is produced in a low-cost, low-precision, preliminary stage with a near optimal shape and volume. For the plano-concave case, the preform has a flat lower surface and a spherical, concave upper one of radius of 44 mm. This radius is 10% greater than that of the desired final lens design (40 mm). For the bi-concave lens design, the upper and lower preform surfaces are both spherical and concave with a radius of 44 mm which is again 10% greater than the radii of the desired lens design.The thermo-mechanical coupling is included in the three stages of the transient analysis (heating, pressing, and cooling) but the effects of radiative heat transfer are neglected. The required symmetry conditions are imposed along the axis and the nodal vertical displacements are prescribed to vanish on the lower side of the lower mould (see the boundary conditions on the left-hand side of Figures 2 and 3).The glass and both parts of the mould are initially in contact along the axis. Thermal boundary conditions of the Dirichlet-type are applied on the top of the upper and the bottom of the lower mould and the lateral walls of the moulds are assumed to be insulated. All other boundaries are grouped in contact pairs. For the two surfaces of a contact pair, which don’t necessarily have to be in contact, mechanical and thermal surface interaction models are defined. In this set-up two nodes of the contact pair surfaces 1 and 2 exchange heat fluxes perunit area taking into account surface to surface radiation and heat conduction through the air layer between the two surfaces.The heating stage consists of imposing a steadily increasing temperature on the upper side of the upper mould and the lower side of the lower one (time-dependent Dirichlet boundary conditions). The temperature rises from 50 °C to 600 °C in 180 s and then remains constant for 180 s to reach a uniform temperature field. This temperature is about 95 °C above the glass transition temperature, a sufficiently high temperature to shape the glass preform. During this stage, the upper mould is moved upwards by a small amount to allow the glass to expand freely.In the pressing stage, the temperature is held constant at 600 °C and a downward stroke is imposed on the upper mould. The value of the displacement is chosen so that the lens thickness at the centreline is equal to the desired one. The displacement is ramped linearly in a time interval of 360 s. At the end of the pressing stage, the mould shape is transferred onto the mould.Finally, the temperature at both ends of the glass and mould assembly is decreased from 600 °C to 20 °C in 360 s during the cooling stage. This steady cooling is followed by a period of 180 s during which the temperature is kept at 20 °C. The position of the mould is held constant during this stage and a gap between the glass and the mould appears and grows because of the thermal shrinkage and the residual stresses in the glass. The right-hand side of Figures 3 and 4 shows the glass/mould assembly at the very end of the forming process when the desired glass profile is given to the mould. Although the magnitude of the gap is small in magnitude, the consequent mismatch between the contour of the glass piece and the one of the closed mould needs to be compensated for if an accuracy of the order of one micron is targeted.3.Description of the mould optimization algorithmThe optimization algorithm described in the following ignores the very details of the compression moulding process. It simply considers it as an operator F which maps the initialmould contour j mC into the final glass shape j g C at iteration j (see Figure 4). Although the glass contour is a closed curve, the upper and lower curves are considered independently in the range[0]i r ,. The curves are represented, in the scientific computing program MATLAB, bycubic splines fitted through the nodes of the mesh. Introducing the arc-length s , the curves j mC and j g C are defined in parametric form by the points ()()()j j m m r s z s , and ()()()j j g g r s z s ,,respectively, in intervals of s to be defined. Moreover, the initial glass contour 0C and thatdesired d C are described by the points ()00()()r s z s , and ()()()d d r s z s ,, respectively. The total length of the initial glass contour in the r -range of interest ([0]i r ,) is denoted by i l and iscomputed according to 122001i r i dz l dr dr /⎛⎞⎛⎞=+.⎜⎟⎜⎟⎜⎟⎝⎠⎝⎠∫ (1) The end point of the initial glass contour ()00()()i i r l z l , is displaced to ()()()()000000()()()()()()j j e e i r i i i z i i r z r l u r l z l z l u r l z l ,=+,,+, in the deformed glass geometry, where ()()()j j r z u r z u r z ,,, is the displacement vector at the location ()r z , and iteration j . Thus, the length i l in the initial glass geometry becomes j e l in the deformed geometry with 12201e j r gj e dz l dr dr /⎛⎞⎛⎞⎜⎟=+.⎜⎟⎜⎟⎜⎟⎝⎠⎝⎠∫ (2) The curves j m C ,j g C ,d C , and 0C are now completely defined by the points ()[0]()()i j j m m s l r s z s ∈,,, ()[0]()()j e jj g g s l r s z s ∈,,,()[0]()()j e d d s l r s z s ∈,,, and ()00[0]()()is l r s z s ∈,,, respectively. These curves are split into N equal intervals and the optimization loop proceeds on the 1N + corresponding control points.Although the operator F can not be completely characterized, two features, illustrated in Figure 4, may be expected and assumed:1. A point i P initially located at ()00()()i i r s z s , on the glass surface will be locatedaround ()()()j j i g f g f G r s z s =, in the deformed glass geometry (here,i l i Ns i =, j e l f N s i = and the index i ranges from 0 to N ). For example, a point located halfway through the initial glass contour may be expected to be located halfway through the deformed glass contour providing the curves remain reasonably smooth.2. The modification of the mould at ()()()j j i m i m i M r s z s =, only has a local effect on the initial glass surface at ()00()()i i i P r s z s =,.Based upon these assumptions, one can build a one to one operator F between ()()()j j m i mi r s z s , and ()()()j j g f g f r s z s ,, i.e.:()()()()j j g f m i j j g f m i r s r s F z s z s ⎧⎫⎧⎫⎪⎪⇒,⎨⎬⎨⎬⎪⎪⎩⎭⎩⎭ (3)and construct an iterative scheme to identify the required mould geometry as follows 11()()()()j j j m i r f m j j j m i z f m r s s r z s s z +⎧⎫⎪⎪⎪⎪⎨⎬⎪+⎪⎪⎪⎩⎭⎧⎫+Δ⎪⎪=,⎨⎬+Δ⎪⎪⎩⎭(4)where()()()()()()j j r f d f g f j j z f d f g f s r s r s s z s z s ⎧⎫⎧⎫Δ−⎪⎪⎪⎪=,⎨⎬⎨⎬Δ−⎪⎪⎪⎪⎩⎭⎩⎭ (5)is the residual vector. After updating the location of the 1N + control nodes on the mould surface, the mesh of the upper and lower mould contour is reconstructed.4. Mould design resultsThe optimization algorithm is applied to identify the required mould design which yields the desired plano-concave and bi-concave lenses described in the previous section. The mould design is optimized up to a radius r i of 18 mm and the number of intervals N is chosen equal to20. The only requirement on the number of nodes is that the number of control nodes should be sufficient to describe the curves accurately. The desired glass profile at room temperature is chosen as a first guess for the required mould shape. At each optimization loop, the same downward displacement which yields the desired centreline thickness is imposed on the upper mould and all other forming parameters apart from the unknown required mould contours remain identical.Figures 5 and 6 plot the nodal distance from the desired to the deformed glass profiles, in the direction normal to the desired profile, for the bi-concave and the plano-concave lens designs, respectively. Of course, as the nodal residuals become smaller, the mismatch between the deformed and desired glass geometries decreases. These two figures confirm the success of the optimization algorithm since the best mould design from a total of 6 loops, allows a substantial drop in the average value of the nodal residuals and the micron target is almost achieved everywhere. Indeed for the flat surface of the plano-concave lens design, a reduction of the nodal residuals of almost two orders of magnitude is achieved. Iterating further does not reduce further the residuals as these become oscillatory, i.e. regions of decreasing and increasing residuals alternate. Finally, Figure 7 shows the lower profile of the plano-concave lens at the end of the process for each optimization loop. This figure clearly illustrates that this surface becomes flatter and flatter, and therefore gets closer and closer to the desired design, as the optimization algorithm proceeds.5.ConclusionsA computer-aided optimization algorithm is presented in this paper for the mould design in high-precision compression moulding. Only a simplified model representative of the real industrial process is solved in the commercial finite element package ABAQUS. This model takes into account the multi-stage nature of the process, the thermo-mechanical coupling, the varying mechanical contact between the glass and the mould, and the complex rheology of theglass. The intuitive concept of the algorithm consists of computing at each optimization loop the mismatch between the final and desired lens profiles and using this information to update the previous mould design. Results for the mould design for a plano-concave and a bi-concave lens design confirm the feasibility of the method and its fast convergence rate. Indeed, only a few iterations are necessary to reduce the mismatch between the deformed and desired glass shapes to the targeted value of one micron. Although the true success of the optimization algorithm can only be assessed when applied to the real industrial process, this could provide a valuable alternative to other mould compensation technique. AcknowledgementsThe authors gratefully acknowledge the funding of the European Union through the MAGICAL project.References[1] Yi, A.Y. and Jain, A. Compression molding of aspherical lenses-a combined experimental and numerical analysis. J. Am. Ceram. Soc., 2005, 88, 579-586.[2] Moreau, P., Lochegnies, D. and Oudin, J. Optimum tool geometry for flat glass pressing. Int. J. Form. Proc., 1999, 2, 81-94.[3] Lochegnies, D., Moreau, P. and Guibaut, R. A reverse engineering approach to the design of the blank mould for the glass blow and blow process. Glass Technol., 2005, 46, 116-120. [4] Agnon, Y. and Stokes, Y.M. An inverse modelling technique for glass forming by gravity sagging. Eur. J. Mech. B-Fluids, 2005, 24, 275-287.[5] Tool, A.G. Relation between inelastic deformation and thermal expansion of glass in its annealing range. J. Am. Ceram. Soc., 1946, 29, 240-253.[6] Narayanaswamy, O.S. A model of structural relaxation in tempering glass. J. Am. Ceram. Soc., 1971, 54, 491-498.[7] Scherer, G.W. Relaxation in glass and composites, Wiley, New York, 1986.[8] Sellier, M. Optimal process design in high-precision glass forming. Int. J. Form. Proc., 2006, 9, 61-78.Figure captionsFigure 1: Schematic view of the compression moulding process with the corresponding temperature treatmentFigure 2: Two-dimensional radial cross section of the finite element model of the glass/mould assembly for the plano-concave lens in the initial (left) and deformed (right) configurationsFigure 3: Two-dimensional radial cross section of the finite element model of the glass/mould assembly for the bi-concave lens in the initial (left) and deformed (right) configurationsFigure 4: Schematic description of the algorithm and the operator F which transforms the initial mould geometry into the final glass oneFigure 5: Normal distance (in mm) between the desired and deformed glass profiles in a direction normal to the desired profile for each of the control nodes and for the bi-concave lens designFigure 6: Normal distance (in mm) between the desired and deformed glass profiles in a direction normal to the desired profile for each of the control nodes and for the bi-concave lens designFigure 7: Lower lens profile at each optimization loop for the plano-concave designFigure 1: Schematic view of the compression moulding process with the corresponding temperaturetreatmentFigure 2: Two-dimensional radial cross section of the finite element model of the glass/mould assembly for the plano-concave lens in the initial (left) and deformed (right) configurationsthe bi-concave lens in the initial (left) and deformed (right) configurationsgeometry into the final glass oneFigure 5: Normal distance (in mm) between the desired and deformed glass profiles in a direction normal to the desired profile for each of the control nodes and for the bi-concave lens designFigure 6: Normal distance (in mm) between the desired and deformed glass profiles in a direction normal to the desired profile for each of the control nodes and for the bi-concave lens designFigure 7: Lower lens profile at each optimization loop for the plano-concave design。

材料科学专业毕业设计外文文献及翻译文献摘要为了适应不断发展的材料科学领域，毕业设计需要参考一些权威的外文文献。

在这里，我们提供了一些与材料科学专业相关的外文文献，并附带简要翻译。

---文献1: "石墨烯在材料科学中的应用"作者: John Smith, Mary Johnson: John Smith, Mary Johnson摘要::本文综述了石墨烯在材料科学中的应用。

石墨烯是一种单层碳原子结构，具有独特的物理和化学性质。

我们讨论了石墨烯的制备方法、其在电子学、能源存储和生物医学领域中的应用。

石墨烯在材料科学中具有巨大的潜力，可以为未来的材料研究和应用开辟新的道路。

---文献2: "纳米材料的合成与性能研究"作者: David Brown, Emma Lee: David Brown, Emma Lee摘要::本文讨论了纳米材料的合成方法及其性能研究。

纳米材料是具有纳米尺度结构的材料，具有与宏观材料不同的性质。

我们介绍了几种常见的纳米材料合成方法，例如溶液法和气相法，并讨论了纳米材料的晶体结构、表面性质和力学性能。

研究纳米材料的性能对材料科学的发展和应用具有重要意义。

---文献3: "高温合金的热稳定性研究"作者: Jennifer Zhang, Michael Wang: Jennifer Zhang, Michael Wang摘要::本文研究了高温合金的热稳定性。

高温合金是一种用于高温环境的特殊材料，具有优异的耐热性能。

我们通过实验研究了高温合金的热膨胀性、热导率和高温力学性能。

通过了解高温合金的热稳定性，我们可以提高材料的耐高温性能，从而推动高温环境下的应用和工程技术发展。

---以上是几篇关于材料科学的外文文献摘要及简要翻译，希望对毕业设计的参考有所助益。