Development of Fluoride-free Mold Powders for Peritectic Steel Slab Casting

第35卷第2期V ol.35No.22021年3月March 2021木材科学与技术Chinese Journal of Wood Science and Technology人造板饰面装饰纸无醛化研究现状徐建峰1,2，龙玲1,2，刘如1（1.中国林业科学研究院木材工业研究所，北京100091；2.中国林业科学研究院林业新技术研究所，北京100091）摘要：概述人造板饰面装饰纸无醛化研究和发展现状，对装饰纸无醛化发展中存在的问题进行了分析；介绍中国林科院木材工业研究所在装饰纸无醛化方面的研究成果，并对该方向的研究与发展提出建议。

关键词：装饰纸；无醛；人造板饰面中图分类号：TS653；TS761.2文献标识码：A文章编号：2096-9694（2021）02-0001-05Research Status Review of Formaldehyde-Free Decorative Paper forWood-Based PanelsXU Jian-feng 1,2，LONG Ling 1,2，LIU Ru 1（1.Research Institute of Wood Industry ，Chinese Academy of Forestry ，Beijing 100091，China ；2.Research Institute of ForestryNew Technology ，Chinese Academy of Forestry ，Beijing 100091，China ）Abstract:This paper reviewed the research status and industry development of formaldehyde-free decorative paper for wood-based panels.The challenges in the development were analyzed.Furthermore,the research results in this field conducted at the Research Institute of Wood Industry,Chinese Academy of Forestry were presented;the suggestions for future research and development were proposed.Key words:decorative paper;formaldehyde-free;wood-based panel finish饰面装饰纸作为用途最广、使用量最多的一类人造板饰面材料，是由装饰原纸经浸渍或印刷处理而成的特种纸，其品质在很大程度上取决于装饰原纸和浸渍胶液质量[1]。

水上开花的实验英语作文Floating Flowers: An Intriguing Experiment in Hydroponics.In the realm of horticulture, where creativity and scientific inquiry intertwine, the concept of floating flowers has emerged as a captivating experiment that challenges conventional gardening practices. This innovative approach to plant cultivation unveils a fascinating world of possibilities, providing a unique glimpse into the intricate relationship between plants and their environment.Hydroponics, the art of growing plants in a nutrient-rich water solution without the use of soil, serves as the foundation for this experiment. By suspending flowers in aerated water, we create a controlled and customizable environment that empowers us to explore the specific nutritional requirements of each plant.Materials Required:Assorted flowers of various sizes and colors (e.g., roses, lilies, orchids)。

Die history1 Die position in industrial productionMold is a high-volume products with the shape tool, is the main process of industrial production equipment.With mold components, with high efficiency, good quality, low cost, saving energy and raw materials and a series of advantages, with the mold workpieces possess high accuracy, high complexity, high consistency, high productivity and low consumption , other manufacturing methods can not match. Have already become an important means of industrial production and technological development. The basis of the modern industrial economy.The development of modern industrial and technological level depends largely on the level of industrial development die, so die industry to national economic and social development will play an increasing role. March 1989 the State Council promulgated "on the current industrial policy decision points" in the mold as the machinery industry transformation sequence of the first, production and capital construction of the second sequence (after the large-scale power generation equipment and the corresponding power transmission equipment), establish tooling industry in an important position in the national economy. Since 1997, they have to mold and its processing technology and equipment included in the "current national focus on encouraging the development of industries, products and technologies catalog" and "to encourage foreign investment industry directory." Approved by the State Council, from 1997 to 2000, more than 80 professional mold factory owned 70% VAT refund of preferential policies to support mold industry. All these have fully demonstrated the development of the State Council and state departments tooling industry attention and support. Mold around the world about the current annual output of 60 billion U.S. dollars, Japan, the United States and other industrialized countries die of industrial output value of more than machine tool industry, beginning in 1997, China's industrial output value has exceeded the mold machine tool industry output.2 China's mold industry and its development trendDie & Mould Industry StatusDue to historical reasons for the formation of closed, "big and complete" enterprise features, most enterprises in China are equipped with mold workshop, in factory matching status since the late 70s have a mold the concept of industrialization and specialization of production. Production efficiency is not high, poor economic returns. Mold production industry is small and scattered, cross-industry,capital-intensive, professional, commercial and technical management level are relatively low.According to incomplete statistics, there are now specialized in manufacturing mold, the product supporting mold factory workshop (factory) near 17 000, about 600 000 employees, annual output value reached 20 billion yuan mold. However, the existing capacity of the mold and die industry can only meet the demand of 60%, still can not meet the needs of national economic development. At present, the domestic needs of large, sophisticated, complex and long life of the mold also rely mainly on imports. According to customs statistics, in 1997 630 million U.S. dollars worth of imports mold, not including the import of mold together with the equipment; in 1997 only 78 million U.S. dollars export mold. At present the technological level of China Die & Mould Industry and manufacturing capacity, China's national economy in the weak links and bottlenecks constraining sustainable economic development. 2.1 Research on the Structure of industrial products moldIn accordance with the division of China Mould Industry Association, China mold is divided into 10 basic categories, which, stamping die and plastic molding two categories accounted for the main part. Calculated by output, present, China accounts for about 50% die stamping, plastic molding die about 20%, Wire Drawing Die (Tool) about 10% of the world's advanced industrial countries and regions, the proportion of plastic forming die die general of the total output value 40%.Most of our stamping die mold for the simple, single-process mode and meet the molds, precision die, precision multi-position progressive die is also one of the few, die less than 100 million times the average life of the mold reached 100 million times the maximum life of more than accuracy 3 ~ 5um, more than 50 progressive station, and the international life of the die 600 million times the highest average life of the die 50 million times compared to the mid 80s at the international advanced level. China's plastic molding mold design, production technology started relatively late, the overall level of low. Currently a single cavity, a simple mold cavity 70%, and still dominant. A sophisticated multi-cavity mold plastic injection mold, plastic injection mold has been able to multi-color preliminary design and manufacturing. Mould is about 80 million times the average life span is about, the main difference is the large deformation of mold components, excess burr side of a large, poor surface quality, erosion and corrosion serious mold cavity, the mold cavity exhaust poor and vulnerable such as, injection mold 5um accuracy has reached below the highest life expectancy has exceeded 20 million times, the number has more than 100 chamber cavity, reaching the mid 80s to early 90s the international advanced level.2.2 mold Present Status of TechnologyTechnical level of China's mold industry currently uneven, with wide disparities. Generally speaking, with the developed industrial countries, Hong Kong and Taiwan advanced level, there is a large gap.The use of CAD / CAM / CAE / CAPP and other technical design and manufacturemolds, both wide application, or technical level, there is a big gap between both. In the application of CAD technology design molds, only about 10% of the mold used in the design of CAD, aside from drawing board still has a long way to go; in the application of CAE design and analysis of mold calculation, it was just started, most of the game is still in trial stages and animation; in the application of CAM technology manufacturing molds, first, the lack of advanced manufacturing equipment, and second, the existing process equipment (including the last 10 years the introduction of advanced equipment) or computer standard (IBM PC and compatibles, HP workstations, etc.) different, or because of differences in bytes, processing speed differences, differences in resistance to electromagnetic interference, networking is low, only about 5% of the mold manufacturing equipment of recent work in this task; in the application process planning CAPP technology, basically a blank state, based on the need for a lot of standardization work; in the mold common technology, such as mold rapid prototyping technology, polishing, electroforming technologies, surface treatment technology aspects of CAD / CAM technology in China has just started. Computer-aided technology, software development, is still at low level, the accumulation of knowledge and experience required. Most of our mold factory, mold processing equipment shop old, long in the length of civilian service, accuracy, low efficiency, still use the ordinary forging, turning, milling, planing, drilling, grinding and processing equipment, mold, heat treatment is still in use salt bath, box-type furnace, operating with the experience of workers, poorly equipped, high energy consumption. Renewal of equipment is slow, technological innovation, technological progress is not much intensity. Although in recent years introduced many advanced mold processing equipment, but are too scattered, or not complete, only about 25% utilization, equipment, some of the advanced functions are not given full play.Lack of technology of high-quality mold design, manufacturing technology and skilled workers, especially the lack of knowledge and breadth, knowledge structure, high levels of compound talents. China's mold industry and technical personnel, only 8% of employees 12%, and the technical personnel and skilled workers and lower the overall skill level. Before 1980, practitioners of technical personnel and skilled workers, the aging of knowledge, knowledge structure can not meet the current needs; and staff employed after 80 years, expertise, experience lack of hands-on ability, not ease, do not want to learn technology. In recent years, the brain drain caused by personnel not only decrease the quantity and quality levels, and personnel structure of the emergence of new faults, lean, make mold design, manufacturing difficult to raise the technical level.2.3 mold industry supporting materials, standard parts of present condition Over the past 10 years, especially the "Eighth Five-Year", the State organization of the ministries have repeatedly Material Research Institute, universities and steel enterprises, research and development of special series of die steel, molds and othermold-specific carbide special tools, auxiliary materials, and some promotion. However, due to the quality is not stable enough, the lack of the necessary test conditions and test data, specifications and varieties less, large molds and special mold steel and specifications are required for the gap. In the steel supply, settlement amount and sporadic users of mass-produced steel supply and demand contradiction, yet to be effectively addressed. In addition, in recent years have foreign steel mold set up sales outlets in China, but poor channels, technical services support the weak and prices are high, foreign exchange settlement system and other factors, promote the use of much current.Mold supporting materials and special techniques in recent years despite the popularization and application, but failed to mature production technology, most still also in the exploratory stage tests, such as die coating technology, surface treatment technology mold, mold guide lubrication technology Die sensing technology and lubrication technology, mold to stress technology, mold and other anti-fatigue and anti-corrosion technology productivity has not yet fully formed, towards commercialization. Some key, important technologies also lack the protection of intellectual property.China's mold standard parts production, the formation of the early 80s only small-scale production, standardization and standard mold parts using the coverage of about 20%, from the market can be assigned to, is just about 30 varieties, and limited to small and medium size. Standard punch, hot runner components and other supplies just the beginning, mold and parts production and supply channels for poor, poor accuracy and quality.3 Die trend3.1 mold CAD / CAE / CAM being integrated, three-dimensional, intelligent and network direction(1) mold software features integratedDie software features of integrated software modules required relatively complete, while the function module using the same data model, in order to achieve Syndicated news management and sharing of information to support the mold design, manufacture, assembly, inspection, testing and production management of the entire process to achieve optimal benefits. Series such as the UK Delcam's software will include a surface / solid geometric modeling, engineering drawing complex geometry, advanced rendering industrial design, plastic mold design expert system, complex physical CAM, artistic design and sculpture automatic programming system, reverse engineering and complex systems physical line measurement systems. A higher degree of integration of the software includes: Pro / ENGINEER, UG and CATIA, etc.. Shanghai Jiaotong University, China with finite element analysis of metal plastic forming systems and Die CAD / CAM systems; Beijing Beihang HaierSoftware Ltd. CAXA Series software; Jilin Gold Grid Engineering Research Center of the stamping die mold CAD / CAE / CAM systems .(2) mold design, analysis and manufacture of three-dimensionalTwo-dimensional mold of traditional structural design can no longer meet modern technical requirements of production and integration. Mold design, analysis, manufacturing three-dimensional technology, paperless software required to mold a new generation of three-dimensional, intuitive sense to design the mold, using three-dimensional digital model can be easily used in the product structure of CAE analysis, tooling manufacturability evaluation and CNC machining, forming process simulation and information management and sharing. Such as Pro / ENGINEER, UG and CATIA software such as with parametric, feature-based, all relevant characteristics, so that mold concurrent engineering possible. In addition, Cimatran company Moldexpert, Delcam's Ps-mold and Hitachi Shipbuilding of Space-E/mold are professional injection mold 3D design software, interactive 3D cavity, core design, mold base design configuration and typical structure . Australian company Moldflow realistic three-dimensional flow simulation software MoldflowAdvisers been widely praised by users and applications. China Huazhong University of Science have developed similar software HSC3D4.5F and Zhengzhou University, Z-mold software. For manufacturing, knowledge-based intelligent software function is a measure of die important sign of advanced and practical one. Such as injection molding experts Cimatron's software can automatically generate parting direction based parting line and parting surface, generate products corresponding to the core and cavity, implementation of all relevant parts mold, and for automatically generated BOM Form NC drilling process, and can intelligently process parameter setting, calibration and other processing results.(3) mold software applications, networking trendWith the mold in the enterprise competition, cooperation, production and management, globalization, internationalization, and the rapid development of computer hardware and software technology, the Internet has made in the mold industry, virtual design, agile manufacturing technology both necessary and possible. The United States in its "21st Century Manufacturing Enterprise Strategy" that the auto industry by 2006 to achieve agile manufacturing / virtual engineering solutions to automotive development cycle shortened from 40 months to 4 months.3.2 mold testing, processing equipment to the precise, efficient, and multi-direction(1) mold testing equipment more sophisticated, efficientSophisticated, complex, large-scale mold development, testing equipment have become increasingly demanding. Precision Mould precision now reached 2 ~ 3μm, more domestic manufacturers have to use Italy, the United States, Japan and other countries in the high-precision coordinate measuring machine, and with digital scanning. Such as Dongfeng Motor Mould Factory not only has the capacity3250mm ×3250mm Italian coordinate measuring machine, also has a digital photography optical scanner, the first in the domestic use of digital photography, optical scanning as a means of spatial three-dimensional access to information, enabling th e establishment from the measurement of physical → model output of engineering drawings → → the whole process of mold making, reverse engineering a successful technology development and applications. This equipment include: second-generation British Renishaw high-speed scanners (CYCLON SERIES2) can be realized and contact laser probe complementary probe, laser scanner accuracy of 0.05mm, scanning probe contact accuracy of 0.02 mm. Another German company GOM ATOS portable scanners, Japan Roland's PIX-30, PIX-4 desktop scanner and the United Kingdom Taylor Hopson's TALYSCAN150 multi-sensor, respectively Three-dimensional scanner with high speed, low-cost and functional composite and so on.(2) CNC EDMJapan Sodick linear motor servo drive using the company's AQ325L, AQ550LLS-WEDM have driven fast response, transmission and high positioning accuracy, the advantages of small thermal deformation. Switzerland Chanmier company NCEDM with P-E3 adaptive control, PCE energy control and automatic programming expert systems. Others also used the powder mixed EDM machining technology, micro-finishing pulse power and fuzzy control (FC) technologies.(3) high-speed milling machine (HSM)Milling is an important means of cavity mold. The low-temperature high-speed milling with the workpiece, cutting force is small, smooth processing, processing quality, processing efficiency (for the general milling process 5 to 10 times) and can process hard materials (<60HRC) and many other advantages. Thus in the mold processing more and more attention. Ruishikelang company UCP710-type five-axis machining center, machine tool positioning accuracy up to 8μm, home-made closed-loop vector control spindle with a maximum speed 42000r/min. Italy RAMBAUDI's high-speed milling, the processing range of up to 2500mm × 5000mm × 1800mm, speed up 20500r/min, cutting feed speed of 20m/min. HSM generally used large, medium-sized mold, such as motor cover mold, die casting mold, large plastic surface machining, the surface precision up to 0.01mm.3.3 mold materials and surface treatment technology developed rapidly Industry to the level of mold, material application is the key. Due to improper selection and use of materials, causing premature die failure, which accounts for more than 45% failure die. In the mold material, commonly used cold work tool steel with CrWMn, Cr12, Cr12MoV and W6Mo5Cr4V2, flame hardened steel (such as Japan, AUX2, SX105V (7CrSiMnMoV), etc.; used a new type of hot work die steel American H13, Sweden QRO80M, QRO90SUPREME, etc.; used a pre-hardened plastic mold steel (such as the U.S. P20), age-hardening steel (such as the U.S. P21, Japan NAK55, etc.), heat treatment hardened steel (such as the United States, D2,Japan, PD613, PD555, Sweden wins the White 136, etc.), powder die steel (such as Japan KAD18 and KAS440), etc.; panel drawing die used HT300, QT60-2, Mo-Cr, Mo-V cast iron, large-scale mold with HT250. more regular use of Precision Die Hard Steel Results YG20 and other alloys and carbide. in the mold surface treatment, the main trends are: the infiltration of a single element to the multi-element penetration, complex permeability (such as TD method) development; by the general diffusion to the CVD, PVD, PCVD, ion penetration , the direction of ion implantation, etc.; can use the coating are: TiC, TiN, TiCN, TiAlN, CrN, Cr7C3, W2C, etc., while heat from the air treatment means to the development of vacuum heat treatment. In addition, the current strengthening of the laser, glow plasma Nitriding and electroplating (plating) enhanced anti-corrosion technologies are also more and more attention.3.4 mold industry new techniques, new ideas and new models have been gradually recognizedIn the forming process, the main function of composite stamping die, superplastic forming, plastic precision molding technology, plastic mold gas-assisted injection technology and hot runner technology, high-pressure injection molding technology. On the other hand, with the continuous development of advanced manufacturing technology and raise the level of mold industry as a whole, in the mold industry, there are some new design, production, management ideas and models. Concrete are: to adapt to the characteristics of mold-piece production flexible manufacturing technologies; to create the best management and effective teamwork, lean production; to enhance rapid response capabilities of Concurrent Engineering, Virtual Manufacturing and global agile manufacturing, manufacturing of new production networks philosophy; extensive use of standard parts common parts of the division of work mode of production; meet the environmental requirements of sustainable development and green design and manufacturing.SummaryThe 21st century, in the new situation of economic globalization, with capital, technology and labor market re-integration of equipment manufacturing in China after joining the WTO will become the world's equipment manufacturing base. In the modern manufacturing industry, no matter which industry, engineering equipment, are increasingly used to provide the products from the mold industry. In order to meet the user's high-precision mold manufacturing, short delivery time, the urgent demand low-cost, mold industry is extensive application of modern advanced manufacturing technology to speed up the mold industry, technological progress, to meet the basic sectors of the mold process equipment urgent needs.模具的发展1模具在工业生产中的地位模具是大批量生产同形产品的工具，是工业生产的主要工艺装备。

Bull Earthquake Eng(2008)6:645–675DOI10.1007/s10518-008-9078-1ORIGINAL RESEARCH PAPERNumerical analyses of fault–foundation interactionI.Anastasopoulos·A.Callerio·M.F.Bransby·M.C.R.Davies·A.El Nahas·E.Faccioli·G.Gazetas·A.Masella·R.Paolucci·A.Pecker·E.RossignolReceived:22October2007/Accepted:14July2008/Published online:17September2008©Springer Science+Business Media B.V.2008Abstract Field evidence from recent earthquakes has shown that structures can be designed to survive major surface dislocations.This paper:(i)Describes three differentfinite element(FE)methods of analysis,that were developed to simulate dip slip fault rupture propagation through soil and its interaction with foundation–structure systems;(ii)Validates the developed FE methodologies against centrifuge model tests that were conducted at the University of Dundee,Scotland;and(iii)Utilises one of these analysis methods to conduct a short parametric study on the interaction of idealised2-and5-story residential structures lying on slab foundations subjected to normal fault rupture.The comparison between nume-rical and centrifuge model test results shows that reliable predictions can be achieved with reasonably sophisticated constitutive soil models that take account of soil softening after failure.A prerequisite is an adequately refined FE mesh,combined with interface elements with tension cut-off between the soil and the structure.The results of the parametric study reveal that the increase of the surcharge load q of the structure leads to larger fault rupture diversion and“smoothing”of the settlement profile,allowing reduction of its stressing.Soil compliance is shown to be beneficial to the stressing of a structure.For a given soil depthH and imposed dislocation h,the rotation θof the structure is shown to be a function of:I.Anastasopoulos(B)·G.GazetasNational Technical University,Athens,Greecee-mail:ianast@civil.ntua.grA.Callerio·E.Faccioli·A.Masella·R.PaolucciStudio Geotecnico Italiano,Milan,ItalyM.F.BransbyUniversity of Auckland,Auckland,New ZealandM.C.R.Davies·A.El NahasUniversity of Dundee,Dundee,UKA.Pecker·E.RossignolGeodynamique et Structure,Paris,France123(a)its location relative to the fault rupture;(b)the surcharge load q;and(c)soil compliance.Keywords Fault rupture propagation·Soil–structure-interaction·Centrifuge model tests·Strip foundation1IntroductionNumerous cases of devastating effects of earthquake surface fault rupture on structures were observed in the1999earthquakes of Kocaeli,Düzce,and Chi-Chi.However,examples of satisfactory,even spectacular,performance of a variety of structures also emerged(Youd et al.2000;Erdik2001;Bray2001;Ural2001;Ulusay et al.2002;Pamuk et al.2005).In some cases the foundation and structure were quite strong and thus either forced the rupture to deviate or withstood the tectonic movements with some rigid-body rotation and translation but without damage(Anastasopoulos and Gazetas2007a,b;Faccioli et al.2008).In other cases structures were quite ductile and deformed without failing.Thus,the idea(Duncan and Lefebvre1973;Niccum et al.1976;Youd1989;Berill1983)that a structure can be designed to survive with minimal damage a surface fault rupture re-emerged.The work presented herein was motivated by the need to develop quantitative understan-ding of the interaction between a rupturing dip-slip(normal or reverse)fault and a variety of foundation types.In the framework of the QUAKER research project,an integrated approach was employed,comprising three interrelated steps:•Field studies(Anastasopoulos and Gazetas2007a;Faccioli et al.2008)of documented case histories motivated our investigation and offered material for calibration of the theoretical methods and analyses,•Carefully controlled geotechnical centrifuge model tests(Bransby et al.2008a,b)hel-ped in developing an improved understanding of mechanisms and in acquiring a reliable experimental data base for validating the theoretical simulations,and•Analytical numerical methods calibrated against the abovefield and experimental data offered additional insight into the nature of the interaction,and were used in developing parametric results and design aids.This paper summarises the methods and the results of the third step.More specifically: (i)Three differentfinite element(FE)analysis methods are presented and calibratedthrough available soil data.(ii)The three FE analysis methods are validated against four centrifuge experiments con-ducted at the University of Dundee,Scotland.Two experiments are used as a benchmark for the“free-field”part of the problem,and two more for the interaction of the outcrop-ping dislocation with rigid strip foundations.(iii)One of these analysis methods is utilised in conducting a short parametric study on the interaction of typical residential structures with a normal fault rupture.The problem studied in this paper is portrayed in Fig.1.It refers to a uniform cohesionless soil deposit of thickness H at the base of which a dip-slip fault,dipping at angle a(measured from the horizontal),produces downward or upward displacement,of vertical component h.The offset(i.e.,the differential displacement)is applied to the right part of the model quasi-statically in small consecutive steps.123hx O:“f o c u s ”O ’:“e p i c e n t e r ”Hanging wallFootwallyLW –LW hx O:“fo c u s ”O ’:“e p i c e n t e r ”Hanging wallFootwallyL W –LWq BStrip Foundation s(a )(b)Fig.1Definition and geometry of the studied problem:(a )Propagation of the fault rupture in the free field,and (b )Interaction with strip foundation of width B subjected to uniform load q .The left edge of the foundation is at distance s from the free-field fault outcrop2Centrifuge model testingA series of centrifuge model tests have been conducted in the beam centrifuge of the University of Dundee (Fig.2a)to investigate fault rupture propagation through sand and its in-teraction with strip footings (Bransby et al.2008a ,b ).The tests modelled soil deposits of depth H ranging from 15to 25m.They were conducted at accelerations ranging from 50to 115g.A special apparatus was developed in the University of Dundee to simulate normal and reverse faulting.A central guidance system and three aluminum wedges were installed to impose displacement at the desired dip angle.Two hydraulic actuators were used to push on the side of a split shear box (Fig.2a)up or down,simulating reverse or normal faulting,respectively.The apparatus was installed in one of the University of Dundee’s centrifuge strongboxes (Fig.2b).The strongbox contains a front and a back transparent Perspex plate,through which the models are monitored in flight.More details on the experimental setup can be found in Bransby et al.(2008a ).Displacements (vertical and horizontal)at different123Fig.2(a)The geotechnicalcentrifuge of the University ofDundee;(b)the apparatus for theexperimental simulation of faultrupture propagation through sandpositions within the soil specimen were computed through the analysis of a series of digital images captured as faulting progressed using the Geo-PIV software(White et al.2003).Soil specimens were prepared within the split box apparatus by pluviating dry Fontainebleau sand from a specific height with controllable massflow rate.Dry sand samples were prepared at relative densities of60%.Fontainebleau sand was used so that previously published laboratory element test data(e.g Gaudin2002)could be used to select drained soil parameters for thefinite element analyses.The experimental simulation was conducted in two steps.First,fault rupture propagation though soil was modelled in the absence of a structure(Fig.1a),representing the free-field part of the problem.Then,strip foundations were placed at a pre-specified distance s from the free-field fault outcrop(Fig.1b),and new tests were conducted to simulate the interaction of the fault rupture with strip foundations.3Methods of numerical analysisThree different numerical analysis approaches were developed,calibrated,and tested.Three different numerical codes were used,in combination with soil constitutive models ranging from simplified to more sophisticated.This way,three methods were developed,each one corresponding to a different level of sophistication:(a)Method1,using the commercial FE code PLAXIS(2006),in combination with a simplenon-associated elastic-perfectly plastic Mohr-Coulomb constitutive model for soil; 123Foundation : 2-D Elastic Solid Elements Elastic BeamElementsInterfaceElements hFig.3Method 1(Plaxis)finite element diecretisation(b)Method 2,utilising the commercial FE code ABAQUS (2004),combined with a modifiedMohr-Coulomb constitutive soil model taking account of strain softening;and(c)Method 3,making use of the FE code DYNAFLOW (Prevost 1981),along with thesophisticated multi-yield constitutive model of Prevost (1989,1993).Centrifuge model tests that were conducted in the University of Dundee were used to validate the effectiveness of the three different numerical methodologies.The main features,the soil constitutive models,and the calibration procedure for each one of the three analysis methodologies are discussed in the following sections.3.1Method 13.1.1Finite element modeling approachThe first method uses PLAXIS (2006),a commercial geotechnical FE code,capable of 2D plane strain,plane stress,or axisymmetric analyses.As shown in Fig.3,the finite element mesh consists of 6-node triangular plane strain elements.The characteristic length of the elements was reduced below the footing and in the region where the fault rapture is expected to propagate.Since a remeshing technique (probably the best approach when dealing with large deformation problems)is not available in PLAXIS ,at the base of the model and near the fault starting point,larger elements were introduced to avoid numerical inaccuracies and instability caused by ill conditioning of the element geometry during the displacement application (i.e.node overlapping and element distortion).The foundation system was modeled using a two-layer compound system,consisting of (see Fig.3):•The footing itself,discretised by very stiff 2D elements with linear elastic behaviour.The pressure applied by the overlying building structure has been imposed to the models through the self weight of the foundation elements.123Fig.4Method1:Calibration of constitutive model parameters utilising the FE code Tochnog;(a)oedometer test;(b)Triaxial test,p=90kPa•Beam elements attached to the nodes at the bottom of the foundation,with stiffness para-meters lower than those of the footing to avoid a major stiffness discontinuity between the underlying soil and the foundation structure.•The beam elements are connected to soil elements through an interface with a purely frictional behaviour and the same friction angleϕwith the soil.The interface has a tension cut-off,which causes a gap to develop between soil and foundation in case of detachment. Due to the large imposed displacement reached during the centrifuge tests(more than3m in several cases),with a relative displacement of the order of10%of the modeled soil height, the large displacement Lagrangian description was adopted.After an initial phase in which the geostatic stresses were allowed to develop,the fault displacement has been monotonically imposed both on the right side and the right bottom boundaries,while the remaining boundaries of the model have beenfixed in the direction perpendicular to the side(Fig.3),so as to reproduce the centrifuge test boundary conditions.3.1.2Soil constitutive model and calibrationThe constitutive model adopted for all of the analyses is the standard Mohr-Coulomb for-mulation implemented in PLAXIS.The calibration of the elastic and strength parameters of the soil had been conducted during the earlier phases of the project by means of the FEM code Tochnog(see the developer’s home page ),adopting a rather refined and user-defined constitutive model for sand.This model was calibrated with a set of experimental data available on Fontainebleau sand(Gaudin2002).Oedometer tests (Fig.4a)and drained triaxial compression tests(Fig.4b)have been simulated,and sand model parameters were calibrated to reproduce the experimental results.The user-defined model implemented in Tochnog included a yielding function at the critical state,which corresponds to the Mohr-Coulomb failure criterion.A subset of those parameters was then utilised in the analysis conducted using the simpler Mohr-Coulomb model of PLAXIS:•Angle of frictionϕ=37◦•Young’s Modulus E=675MPa•Poisson’s ratioν=0.35•Angle of Dilationψ=0◦123hFoundation : Elastic Beam ElementsGap Elements Fig.5Method 2(Abaqus)finite element diecretisationThe assumption of ψ=0and ν=0.35,although not intuitively reasonable,was proven to provide the best fit to experimental data,both for normal and reverse faulting.3.2Method 23.2.1Finite element modeling approachThe FE mesh used for the analyses is depicted in Fig.5(for the reverse fault case).The soil is now modelled with quadrilateral plane strain elements of width d FE =1m.The foun-dation,of width B ,is modelled with beam elements.It is placed on top of the soil model and connected through special contact (gap)elements.Such elements are infinitely stiff in compression,but offer no resistance in tension.In shear,their behaviour follows Coulomb’s friction law.3.2.2Soil constitutive modelEarlier studies have shown that soil behaviour after failure plays a major role in problems related to shear-band formation (Bray 1990;Bray et al.1994a ,b ).Relatively simple elasto-plastic constitutive models,with Mohr-Coulomb failure criterion,in combination with strain softening have been shown to be effective in the simulation of fault rupture propagation through soil (Roth et al.1981,1982;Loukidis 1999;Erickson et al.2001),as well as for modelling the failure of embankments and slopes (Potts et al.1990,1997).In this study,we apply a similar elastoplastic constitutive model with Mohr-Coulomb failure criterion and isotropic strain softening (Anastasopoulos 2005).Softening is introduced by reducing the mobilised friction angle ϕmob and the mobilised dilation angle ψmob with the increase of plastic octahedral shear strain:123ϕmob=ϕp−ϕp−ϕresγP fγP oct,for0≤γP oct<γP fϕres,forγP oct≥γP f(1)ψmob=⎧⎨⎩ψp1−γP octγP f,for0≤γP oct<γP fψres,forγP oct≥γP f⎫⎬⎭(2)whereϕp andϕres the ultimate mobilised friction angle and its residual value;ψp the ultimate dilation angle;γP f the plastic octahedral shear strain at the end of softening.3.2.3Constitutive model calibrationConstitutive model parameters are calibrated through the results of direct shear tests.Soil response can be divided in four characteristic phases(Anastasopoulos et al.2007):(a)Quasi-elastic behavior:The soil deforms quasi-elastically(Jewell and Roth1987),upto a horizontal displacementδx y.(b)Plastic behavior:The soil enters the plastic region and dilates,reaching peak conditionsat horizontal displacementδx p.(c)Softening behavior:Right after the peak,a single horizontal shear band develops(Jewelland Roth1987;Gerolymos et al.2007).(d)Residual behavior:Softening is completed at horizontal displacementδx f(δy/δx≈0).Then,deformation is accumulated along the developed shear band.Quasi-elastic behaviour is modelled as linear elastic,with secant modulus G S linearly incre-asing with depth:G S=τyγy(3)whereτy andγy:the shear stress and strain atfirst yield,directly measured from test data.After peak conditions are reached,it is assumed that plastic shear deformation takes placewithin the shear band,while the rest of the specimen remains elastic(Shibuya et al.1997).Scale effects have been shown to play a major role in shear localisation problems(Stone andMuir Wood1992;Muir Wood and Stone1994;Muir Wood2002).Given the unavoidableshortcomings of the FE method,an approximate simplified scaling method(Anastasopouloset al.2007)is employed.The constitutive model was encoded in the FE code ABAQUS(2004).Its capability toreproduce soil behaviour has been validated through a series of FE simulations of the directshear test(Anastasopoulos2005).Figure6depicts the results of such a simulation of denseFontainebleau sand(D r≈80%),and its comparison with experimental data by Gaudin (2002).Despite its simplicity and(perhaps)lack of generality,the employed constitutivemodel captures the predominant mode of deformation of the problem studied herein,provi-ding a reasonable simplification of complex soil behaviour.3.3Method33.3.1Finite element modeling approachThefinite element model used for the analyses is shown for the normal fault case in Fig.7.The soil is modeled with square,quadrilateral,plane strain elements,of width d FE=0.5m. 123Fig.6Method 2:Calibration ofconstitutive model—comparisonbetween laboratory direct sheartests on Fontainebleau sand(Gaudin 2002)and the results ofthe constitutive modelx D v3.3.2Soil constitutive ModelThe constitutive model is the multi-yield constitutive model developed by Prevost (1989,1993).It is a kinematic hardening model,based on a relatively simple plasticity theory (Prevost 1985)and is applicable to both cohesive and cohesionless soils.The concept of a “field of work-hardening moduli”(Iwan 1967;Mróz 1967;Prevost 1977),is used by defining a collection f 0,f 1,...,f n of nested yield surfaces in the stress space.V on Mises type surfaces are employed for cohesive materials,and Drucker-Prager/Mohr-Coulomb type surfaces are employed for frictional materials (sands).The yield surfaces define regions of constant shear moduli in the stress space,and in this manner the model discretises the smooth elastic-plastic stress–strain curve into n linear segments.The outermost surface f n represents a failure surface.In addition,accounting for experimental evidence from tests on frictional materials (de 1987),a non-associative plastic flow rule is used for the dilatational component of the plastic potential.Finally,the material hysteretic behavior and shear stress-induced anisotropic effects are simulated by a kinematic rule .Upon contact,the yield surfaces are translated in the stress space by the stress point,and the direction of translation is selected such that the yield surfaces do not overlap,but remain tangent to each other at the stress point.3.3.3Constitutive model parametersThe required constitutive parameters of the multi-yield constitutive soil model are summari-sed as follows (Popescu and Prevost 1995):a.Initial state parameters :mass density of the solid phase ρs ,and for the case of porous saturated media,porosity n w and permeability k .b.Low strain elastic parameters :low strain moduli G 0and B 0.The dependence of the moduli on the mean effective normal stress p ,is assumed to be of the following form:G =G 0 p p 0 n B =B 0 p p 0n (4)and is accounted for,by introducing two more parameters:the power exponent n and the reference effective mean normal stress p 0.c.Yield and failure parameters :these parameters describe the position a i ,size M i and plastic modulus H i ,corresponding to each yield surface f i ,i =0,1,...n .For the case of pressure sensitive materials,a modified hyperbolic expression proposed by Prevost (1989)and Griffiths and Prévost (1990)is used to simulate soil stress–strain relations.The necessary parameters are:(i)the initial gradient,given by the small strain shear modulus G 0,and (ii)the stress (function of the friction angle at failure ϕand the stress path)and strain,εmax de v ,levels at failure.Hayashi et al.(1992)improved the modified hyperbolic model by introducing a new parameter—a —depending on the maximum grain size D max and uniformity coefficient C u .Finally,the coefficient of lateral stress K 0is necessary to evaluate the initial positions a i of the yield surfaces.d.Dilation parameters :these are used to evaluate the volumetric part of the plastic potentialand consist of:(i)the dilation (or phase transformation)angle ¯ϕ,and (ii)the dilation parameter X pp ,which is the scale parameter for the plastic dilation,and depends basically on relative density and sand type (fabric,grain size).With the exception of the dilation parameter,all the required constitutive model parameters are traditional soil properties,and can be derived from the results of conventional laboratory 123Table1Constitutive model parameters used in method3Number of yield surfaces20Power exponent n0.5Shear modulus G at stress p1 (kPa)75,000Bulk modulus at stress p1(kPa)200,000Unit massρ(t.m−3) 1.63Cohesion0 Reference mean normal stressp1(kPa)100Lateral stress coefficient(K0)0.5Dilation angle in compression (◦)31Dilation angle in extension(◦)31Ultimate friction angle in compression(◦)41.8Ultimate friction angle inextension(◦)41.8Dilation parameter X pp 1.65Max shear strain incompression0.08Max shear strain in extension0.08Generation coefficient in compressionαc 0.098Generation coefficient inextensionαe0.095Generation coefficient in compressionαlc 0.66Generation coefficient inextensionαle0.66Generation coefficient in compressionαuc 1.16Generation coefficient inextensionαue1.16(e.g.triaxial,simple shear)and in situ(e.g.cone penetration,standard penetration,wave velocity)soil tests.The dilational parameter can be evaluated on the basis of results of liquefaction strength analysis,when available;further details can be found in Popescu and Prevost(1995)and Popescu(1995).Since in the present study the sand material is dry,the cohesionless material was modeled as a one-phase material.Therefore neither the soil porosity,n w,nor the permeability,k,are needed.For the shear stress–strain curve generation,given the maximum shear modulus G1,the maximum shear stressτmax and the maximum shear strainγmax,the following functional relationship has been chosen:For y=τ/τmax and x=γ/γr,withγr=τmax/G1,then:y=exp(−ax)f(x,x l)+(1−exp(−ax))f(x,x u)where:f(x,x i)=(2x/x i+1)x i−1/(2x/x i+1)x i+1(5)where a,x l and x u are material parameters.For further details,the reader is referred to Hayashi et al.(1992).The constitutive model is implemented in the computer code DYNAFLOW(Prevost1981) that has been used for the numerical analyses.3.3.4Calibration of model constitutive parametersTo calibrate the values of the constitutive parameters,numerical triaxial tests were simulated with DYNAFLOW at three different confining pressures(30,60,90kPa)and compared with the results of available physical tests conducted on the same material at the same confining pressures.The parameters are defined based on the shear stress versus axial strain curve and volumetric strain versus axial strain curve.Figure8illustrates the comparisons between numerical simulations and physical tests in terms of volumetric strain and shear stress versus123Table2Summary of main attributes of the centrifuge model testsTest Faulting B(m)q(kPa)s(m)g-Level a D r(%)H(m)L(m)W(m)h max(m) 12Normal Free—field11560.224.775.723.53.1528Reverse Free—field11560.815.175.723.52.5914Normal10912.911562.524.675.723.52.4929Reverse10919.211564.115.175.723.53.30a Centrifugal accelerationFig.9Test12—Free-field faultD r=60%Fontainebleau sand(α=60◦):Comparison ofnumerical with experimentalvertical displacement of thesurface for bedrock dislocationh=3.0m(Method1)and2.5m(Method2)[all displacements aregiven in prototype scale]Structure Interaction(FR-SFSI):(i)Test14,normal faulting at60◦;and(ii)Test29,reverse faulting at60◦.In this case,the comparison is conducted for all of the developed numerical analysis approaches.The main attributes of the four centrifuge model tests used for the comparisons are syn-opsised in Table2,while more details can be found in Bransby et al.(2008a,b).4.1Free-field fault rupture propagation4.1.1Test12—normal60◦This test was conducted at115g on medium-loose(D r=60%)Fontainebleau sand,simu-lating normal fault rupture propagation through an H=25m soil deposit.The comparison between analytical predictions and experimental data is depicted in Fig.9in terms of vertical displacement y at the ground surface.All displacements are given in prototype scale.While the analytical prediction of Method1is compared with test data for h=3.0m,in the case of Method2the comparison is conducted at slightly lower imposed bedrock displacement: h=2.5m.This is due to the fact that the numerical analysis with Method2was conducted without knowing the test results,and at that time it had been agreed to set the maximum displacement equal to h max=2.5m.However,when test results were publicised,the actually attained maximum displacement was larger,something that was taken into account in the analyses with Method1.As illustrated in Fig.9,Method2predicts almost correctly the location of fault out-cropping,at about—10m from the“epicenter”,with discrepancies limited to1or2m.The deformation can be seen to be slightly more localised in the centrifuge test,but the comparison between analytical and experimental shear zone thickness is quite satisfactory.The vertical displacement profile predicted by Method1is also qualitatively acceptable.However,the123Method 2Centrifuge Model TestR1S1Method 1(a )(b)(c)Fig.10Test 12—-Normal free-field fault rupture propagation through H =25m D r =60%Fontainebleau sand:Comparison of (a )Centrifuge model test image,compared to FE deformed mesh with shear strain contours of Method 1(b ),and Method 2(c ),for h =2.5mlocation of fault rupture emergence is a few meters to the left compared with the experimen-tal:at about 15m from the “epicenter”(instead of about 10m).In addition,the deformation predicted by Method 1at the ground surface computed using method 1is widespread,instead of localised at a narrow band.FE deformed meshes with superimposed shear strain contours are compared with an image from the experiment in Fig.10,for h =2.5m.In the case of Method 2,the comparison can be seen to be quite satisfactory.However,it is noted that the secondary rupture (S 1)that forms in the experiment to the right of the main shear plane (R 1)is not predicted by Method 2.Also,experimental shear strain contours (not shown herein)are a little more diffuse than the FE prediction.Overall,the comparison is quite satisfactory.In the case of Method 1,the quantitative details are not in satisfactory agreement,but the calculation reveals a secondary rupture to the right of the main shear zone,consistent with the experimental image.4.1.2Test 28—reverse 60◦This test was also conducted at 115g and the sand was of practically the same relative density (D r =61%).Given that reverse fault ruptures require larger normalised bedrock123Fig.11Test28—Reversepropagation through H=15mD r=60%Fontainebleau sand:Comparison of numerical withexperimental verticaldisplacement of the surface forbedrock dislocation h=2.0m(all displacements are given inprototype scale)displacement h/H to propagate all the way to the surface(e.g.Cole and Lade1984;Lade et al.1984;Anastasopoulos et al.2007;Bransby et al.2008b),the soil depth was set at H=15m.This way,a larger h/H could be achieved with the same actuator.Figure11compares the vertical displacement y at the ground surface predicted by the numerical analysis to experimental data,for h=2.0m.This time,both models predict correctly the location of fault outcropping(defined as the point where the steepest gradient is observed).In particular,Method1achieves a slightly better prediction of the outcropping location:−10m from the epicentre(i.e.,a difference of1m only,to the other direction). Method2predicts the fault outbreak at about−7m from the“epicenter”,as opposed to about −9m of the centrifuge model test(i.e.,a discrepancy of about2m).Figure12compares FE deformed meshes with superimposed shear strain contours with an image from the experiment,for h=2.5m.In the case of Method2,the numerical analysis seems to predict a distinct fault scarp,with most of the deformation localised within it.In contrast,the localisation in the experiment is clearly more intense,but the fault scarp at the surface is much less pronounced:the deformation is widespread over a larger area.The analysis with Method1is successful in terms of the outcropping location.However,instead of a single rupture,it predicts the development of two main ruptures(R1and R2),accompanied by a third shear plane in between.Although such soil response has also been demonstrated by other researchers(e.g.Loukidis and Bouckovalas2001),in this case the predicted multiple rupture planes are not consistent with experimental results.4.2Interaction with strip footingsHaving validated the effectiveness of the developed numerical analysis methodologies in simulating fault rupture propagation in the free-field,we proceed to the comparisons of experiments with strip foundations:one for normal(Test14),and one for reverse(Test29) faulting.This time,the comparison is extended to all three methods.4.2.1Test14—normal60◦This test is practically the same with the free-field Test12,with the only difference being the presence of a B=10m strip foundation subjected to a bearing pressure q=90kPa.The foundation is positioned so that the free-field fault rupture would emerge at distance s=2.9m from the left edge of the foundation.123。

Development of a Structural FEM for Road Surfacing SealsM. Huurman1, T.I. Milne2, M.F.C. van de Ven1, A. Scarpas1SummaryIn many countries with limited average inhabitants per square km road surfacing seals are widely used. Such a seal may consist of a layer of binder in which a single layer of larger mineral grains is embedded.From a structural point of view the seal basically serves two purposes, namely the protection of the base from moisture, so that it can't become saturated (a saturated base will loose it load bearing capacity with structural failure as a result), and to protect the base from direct contact with tyres. (the action of tyres result in local shear stresses, which when carried by the base surface, loss of material occurs).Apart from the structural functions, a seal also has some important functional purposes. It should offer skid resistance and a smooth road surface.Seals tend to fail due to the following types of damage under load : punching and rotation of seal stone, low temperature cracking and adhesion failure i.e. ravellingAt present there are no mechanistic design tools available and insight into seal behaviour is fully based on experience and empirical considerations. To improve insight into seal behaviour a micro mechanical Finite Element Model (FEM) for seal design purposes was developed and is discussed in this paper. It is shown that the model has all the properties required to get a better insight into seal behaviour.IntroductionIn many countries with limited average inhabitants per square km road surfacing seals are widely used. Such a seal may consist of a layer of bitumen binder in which a single layer of larger mineral grains is embedded. As a result the seal is too thin to give any contribution to the vertical load bearing capacity. The seal is placed over a base layer. This base layer gives the pavement it's structural value.From a structural point of view the seal basically serves two purposes: to protect the base from moisture, so that it can't become saturated (a saturated base will loose it's load bearing capacity with structural failure as a result), and to protect the base from direct contact with tyres. (the action of tyres results in local shear stresses, which when carried by the base loss of material will occur).Apart from the structural functions, a seal also has some important functional purposes. It should offer skid resistance and a smooth road surface.Seals are currently, to the authors' knowledge, designed on the basis of experience and empirical considerations. There are no mechanistic methods for seal design available. Insight into seal behaviour is however much needed (Milne,2003).1Faculty of Civil Engineering & Geosciences,Delft University of Technology, PO Box 5048, 2600 GA, Delft, The Netherlands2 Africon Engineering International (Pty) Ltd, PO Box 11126, Hatfield, 0028, South AfricaWith the modern trend in increased traffic loading, varying oil sources and related refining processes and the rapid introduction of new types of modified bitumen, it is the strong believe of the authors that seal design may strongly benefit from a better insight into seal behaviour. For that reason the University of Stellenbosch and the Delft University of Technology combined their human resources for the development of a Finite Element Model (FEM) that enables the examination of seal behaviour at a scale of individual grains (micro mechanics). In this paper first results towards the development of such a model are discussed.Model RequirementsPavements with a seal only may show various types of damage. From literature (CSRA,1997) it is known that the main causes of damage in pavements with a seal surfacing are : punching and rotation of seal stone, early rutting, low temperature cracking, moisture damage to the base and adhesion failure i.e. ravelling.A distinction should be made between damages that follow from base layer failure and damages that follow from seal failure. Since the seal has a limited thickness and novertical bearing capacity it is only logical that all damages that have to do with limited bearing capacity cannot be prevented by better seal design methods.Tacking into account the above a model for seal surfacing design should give insight into the mechanical mechanisms that lie behind the following types of damage: punching and rotation of seal stone, low temperature cracking and adhesion failure i.e. ravelling.A seal consists of a layer of stones embedded in a layer of binder, which cannot be considered a homogenous material. When insight into seal behaviour is to be obtained the micro-structure of the material should be addressed. On this scale the seal becomes a structure. It might be obvious that punching and rotation of seal stones and adhesion failure are types of damage that develop on the scale of individual grains. Low temperature cracking is damage that may either take place in the binder itself (lack of cohesion) or in the contact area between stone and binder (lack of adhesion). All types of damage that are relevant thus develop on the scale of grains and a FEM for seal surfacing should thus also be on this scale.It is believed that the orientation and the shape of grains may have a larger effect on damage development in seals. A rough stone is expected to have a stronger bond with the binder than a smooth stone. In the case of a rough stone mechanical bond will add up to the chemical and physical bond between stone and binder. The orientation of stones will effect the stresses involved with stone rotation. As a result the model should incorporate stone orientation.In the next section a FEM for seal surfacing as it exists today is discussed. This model complies to most of the demands discussed above and is the basis for further developments.Seal Surfacing ModelIn Figure 1 the basic layout of the model is presented. Various shades refer to different materials. As is shown by Figure 1, the model is made up of modules that consist of individual stones encompassed by bitumen. By adding modules together, the model can easily be made as large as can be handled by the available computers.Figure1: Basic layout of the FEM for seal surfacings with interface elementsGiven the importance of the adhesion between stone and binder, for both cracking and ravelling damage, each grain is placed in a bowl of interface elements. These elements, also shown in Figure 1,may be used to model the bond between stone and binder.As discussed in the previous section it is expected that grain shape and grain orientation may effect the behaviour of the seal surfacing. For that reason the model is parameterised. The model-parameters may be used to alter the basic topology of the model: average grain size in three directions (grain orientation), number of grains per unit area, thickness of the binder layer below the grains, and volume of binder.Apart from these fixed parameters the model is made so that a random generator may be used to vary the above parameters per grain. Grains with various sizes may be placed in the model as a result of this. Since grain shape is also considered to be an issue, a random generator may also be used to effect the grain shape. This random generator acts on the radius of the grain. Figure 2 shows the effects of these random generators on the topology of the mesh. For the mesh parameters used to generate the meshes in Figures 1 and 2, reference is made to Table 1.Figure 2: Mesh of the seal surfacing generated with the use of random generatorsSome ResultsThe randomly generated geometry makes it possible to do some low-level probabilistic analysis and furthermore distinguish between physical/chemical adhesion (to be modelled in the behaviour of the interface) and mechanical adhesion (to be modelled in the random grain geometry).To get some idea of the behaviour of the mesh, two computations were made. Both computations refer to exactly the same situation. In one of the calculations the grains are all the same size and have a perfect shape (i.e. all st.devs are 0%) in the second calculation the grain size shows a st.dev. of 2% and the radius of the grains has a st.dev. of 5%. In the Table 1 more details about the meshes, the loading and material properties are given.Table 1: Model parameter inputCalculation #1 Calculation #2nominal stdev nominal stdevgrain length 12 mm 0% 12 mm 2%grain width 8 mm 0% 8 mm 2%grain height 6 mm 0% 6 mm 2%grain radius n.a. 0% n.a. 5%IF thickness 0.2 mm 0.2 mmIF shear stiff 100 N/mm3 100 N/mm3IF normal stiff 500 N/mm3 500 N/mm3Binder E 100 MPa 100 MPaBinder Pios 0.45 0.45z = 139.5 N z = 1 Mpa z = 139.5 N z = 1 Mpa Load on central grainsy = 139.5 N y = 1 Mpa y = 139.5 N y = 1 Mpa The load is applied as a force on the upper node of each loaded grain. This force is based on an assumed average contact pressure between tyre and road surface.In Figures 3 the deformed meshes are shown.Figure 3: Deformation (50x) of the meshes as per table 1In Figure 3 the interface elements become visible. This is a result of the properties of these elements which in these calculations are such that stones may rotate within their shell of physical/chemical adhesion. This property of the model may prove to be of importance to explain loss of adhesion and thus loss of stones (ravelling). It may also help to understand stone rotation.In figure 4 the deformed mesh is shown in combination with strain. The figure shows concentration of strain around the stones in the direction of the shear load component, and that tensile and compressive strains are located close to each other. Figure 5 shows the stresses that develop.Figure 4: Strain as it develops in the binder between stonesFigure 5: Stress as it develops in the binder between stonesBoth Figures 4 and56 show that stress and strain in the surfacing binder are not homogenous. Compression may exist directly adjacent to areas of tension and areas of highly stressed binder emerge. This type of information may prove to be of vital value when seal cracking is an issue.Of course the discussed plots only enable qualitative insight into the computations. A further impression of the effects of grain shape is shown in figure 6. In this figure a cross-section of the model is provided, where the rotations are shown for a mesh with the smooth stones, and the randomly shapedstones. The figure clearly shows that stone shape has an effect on stone rotation. This of course is again strain [-]-2 %0 %stress-3.5 MPa0 MPaa strong indication that the model will be able to distinguish between physical/chemical adhesion (interface -behaviour) and mechanical adhesion (grain shape).Figure 6: Comparisson between smooth and randomly shaped stonesConclusionsIt is concluded that a micro-mechanical model for seal surfacing is available. Of course, the model may be loaded by various loads (also temperature loading), and it may be used in combination with more realistic material models.On the basis of the linear calculations discussed here it is concluded the model will prove to give insight into seal behaviour and offers the following: distinction between physical/chemical adhesion (IF-behaviour) and mechanical adhesion (grain shape), of importance to better understand loss of adhesion and thus loss of stone, which is a prime cause of seal damage, and the model provides insight into stress and strain development in the binder, of importance in explaining various types of cohesive seal cracking, and deformation in the binder resulting in stone rotation -both types of damage are main causes of seal failure.This information will also give insight into bleeding which may be a result of temperature effects or penetration of stones into the binder as a result of viscous binder deformation.As a result of the above, insight into stresses in the stone/binder interface is obtained. This information might be of large importance in explaining adhesive seal cracking.Future WorkFuture work will include the addition of a base layer, to enable interaction between base and seal to accommodate punching of stones into the base.In addition, realistic material models will have to be developed to further refine computational output the model provides.ReferencesMilne,TI,2003.Towards a Performance Related Seal design Method, Draft PhD Thesis, University of Stellenbosch, South AfricaCSRA, 1997, Draft Technical Recommendations for Highwats, Surfacing Seals for Rural and Urban Roads and Compendium of design Methods for Surfacing Seals in RSA, DoT for CSRA。

The Development of SustainableBiofuels from AlgaeWith the world moving towards sustainable sources of energy, biofuels have become an increasingly popular option to replace traditional fossil fuels. Algae-based biofuels have emerged as a promising sustainable alternative, with the potential to replace petroleum-based fuels and significantly reduce greenhouse gas emissions. In this article, we will explore the development of sustainable biofuels from algae, its benefits and challenges.Understanding Algae-Based Biofuels:Algae-based biofuels are derived from the oil present in microscopic algae which are grown in freshwater, marine water or even wastewater. The oil content in algae is harvested and processed to produce biodiesel, ethanol, and other biofuel alternatives. Algae are considered ideal for biofuel production as they grow rapidly and can produce high amounts of oil in a short period. Additionally, algae can be grown in areas where traditional agricultural crops cannot be grown, utilizing non-productive land and reducing competition for food and water resources.Benefits of Algae-Based Biofuels:One of the significant advantages of algae-based biofuels is their environmental sustainability. These fuels are considered carbon neutral as they do not release additional carbon dioxide into the atmosphere when combusted. Additionally, the cultivation of algae can absorb carbon dioxide from the atmosphere, further reducing greenhouse gas emissions.Furthermore, algae-based biofuels have the potential to reduce dependence on fossil fuels, which are a finite resource. In the long run, this would help stabilize energy prices and provide energy security to nations.Challenges Associated with Algae-Based Biofuels:Despite the numerous benefits, there are certain challenges associated with the development of algae-based biofuels. One of the most significant challenges is the high production cost, primarily due to the need to maintain optimal growth conditions for the algae. Additionally, the harvesting and processing of algae to extract oil require advanced technology, making it a costly process.Furthermore, the environmental impact of commercial-scale algae production is not yet understood. The cultivation of algae requires significant amounts of water, which could exacerbate water scarcity concerns in regions prone to drought. Additionally, the use of fertilizers and pesticides in algae cultivation could potentially contaminate water bodies and affect local ecosystems.Conclusion:In conclusion, algae-based biofuels have significant potential to provide sustainable alternatives to traditional fossil fuels, aiding in the reduction of greenhouse gas emissions and dependence on non-renewable energy sources. However, the development and commercialization of algae-based biofuels will require continued research and development, as well as careful consideration of the potential environmental impacts. With advancements in technology, it is hoped that algae-based biofuels will become a significant contributor to the wor ld’s energy mix in the coming years.。