Characterization of fatigue behavior of long fiber reinforced thermoplastic (LFT) composites

工 程 塑 料 应 用ENGINEERING PLASTICS APPLICATION第49卷，第6期2021年6月V ol.49，No.6Jun. 2021118doi:10.3969/j.issn.1001-3539.2021.06.021聚四氟乙烯压缩蠕变行为测试与表征雷淼，周健，李孟茹，晁敏，颜录科(长安大学材料科学与工程学院，西安 710064)摘要：为研究聚四氟乙烯(PTFE)压缩蠕变行为，自行设计制造压缩蠕变试验装置，分别对其常温与高温压缩蠕变性能进行测试，建立PTFE 压缩蠕变模型和蠕变方程，对所得压缩蠕变性能数据进行非线性拟合分析。

结果表明，自制高温压缩蠕变测试仪实现了由室温到250℃范围内、不同载荷作用下材料长期压缩蠕变性能测试的自动化操作；PTFE 在压缩蠕变过程中并不表现出黏性流动形变，但当其表现出与一般材料相同的典型蠕变行为时，推迟时间要比其它条件下大许多，当发生蠕变断裂时推迟时间将提高近一个数量级。

所建立的七元件蠕变模型能全面地反映PTFE 的压缩蠕变行为，可预测PTFE 的长时力学行为、使用寿命以及疲劳与失效等。

蠕变拟合曲线与测试数据吻合良好，拟合精度高。

关键词：聚四氟乙烯；复合材料；压缩蠕变；测试；表征中图分类号：TQ327.3 文献标识码：A 文章编号：1001-3539(2021)06-0118-07Testing and Characterization of Compressive Creep Behavior in PolytetrafluoroethyleneLei Miao ， Zhou Jian ， Li Mengru ， Chao Min ， Yan Luke(School of Materials Science & Engineering ， Chang ’an University ， Xi'an 710064， China)Abstract ：In order to study the compression creep behavior of polytetrafluoroethylene (PTFE)，the compression creep test device was designed and manufactured by ourselves ，the normal temperature and high temperature compression creep properties of PTFE were tested ，and the PTFE compression creep model and creep equation were established ，and then nonlinear fitting analysis was performed on the obtained compression creep performance data. The results show that the self-made high-temperature compression creep tester realizes the automatic operation of the long-term compression creep performance test of materials under different loads from room temperature to 250℃. PTFE does not exhibit viscous flow deformation during compression and creep ，but when it exhibits the same typical creep behavior as general materials ，the delay time is much longer than under other conditions ，and when creep rupture occurs ，the delay time increases by nearly one order of magnitude. The established seven-element creep model can fully reflect the compression creep behavior of PTFE ，and can predict the long-term mechanical behavior ，service life ，fatigue ，and failure of PTFE. The creep fitting curve is in good agreement with the test data ，and the fitting accuracy is high.Keywords ：polytetrafluoroethylene ；composite ；compressive creep ；testing ；characterization几乎所有材料都会发生蠕变，而塑料材料特别显著，在常温下就会有明显的蠕变。

Characterization MethodIntroductionCharacterization method refers to the process of determining and analyzing the properties, qualities, and features of a particular object or system. It plays a crucial role in various fields, including materials science, chemistry, biology, and engineering. By employing appropriate characterization techniques, researchers can gain valuable insights into the structure, composition, behavior, and performance of different materials and systems. This article aims to provide an overview of different characterization methods commonly used inscientific research.Types of Characterization MethodsCharacterization methods can be broadly categorized into two types: physical characterization methods and chemical characterization methods.1. Physical Characterization MethodsPhysical characterization methods focus on examining the physical properties and behavior of materials. Some commonly used physical characterization techniques include:•Microscopy: Microscopy techniques such as optical microscopy, electron microscopy (scanning electron microscopy (SEM) andtransmission electron microscopy (TEM)), atomic force microscopy(AFM), and scanning probe microscopy (SPM) enable researchers tovisualize and study the microstructure of materials at differentscales.•Spectroscopy: Spectroscopic techniques involve the interaction of materials with electromagnetic radiation to analyze theircomposition and structure. Examples include infrared spectroscopy (IR), Raman spectroscopy, ultraviolet-visible spectroscopy (UV-Vis), X-ray photoelectron spectroscopy (XPS), nuclear magneticresonance spectroscopy (NMR), and mass spectrometry.•X-ray Diffraction: X-ray diffraction (XRD) is a powerful technique for determining the crystal structure of materials byanalyzing the diffraction patterns produced when X-rays interactwith a sample. It provides information about crystal phaseidentification, lattice parameters, crystallite size, textureanalysis, etc.•Thermal Analysis: Thermal analysis techniques such asdifferential scanning calorimetry (DSC) and thermogravimetricanalysis (TGA) measure changes in material properties as afunction of temperature. These methods help in understanding phase transitions, thermal stability, decomposition behavior, and otherthermal properties of materials.•Mechanical Testing: Mechanical testing methods, including tensile testing, compression testing, hardness testing, and impact testing, evaluate the mechanical properties of materials such as strength,elasticity, hardness, toughness, and fatigue resistance.2. Chemical Characterization MethodsChemical characterization methods focus on identifying and analyzing the chemical composition of materials. Some commonly used chemical characterization techniques include:•Chromatography: Chromatographic techniques such as gaschromatography (GC), liquid chromatography (LC), and high-performance liquid chromatography (HPLC) separate and analyze thecomponents of a mixture based on their differential affinities fora stationary phase and a mobile phase.•Mass Spectrometry: Mass spectrometry (MS) is a technique that ionizes molecules and measures their mass-to-charge ratio. Itprovides information about the molecular weight, structure,composition, and fragmentation pattern of compounds.•Nuclear Magnetic Resonance: Nuclear magnetic resonance (NMR) spectroscopy detects the magnetic properties of atomic nuclei todetermine molecular structures. It is widely used for structuralelucidation and identification of organic compounds.•Electrochemical Analysis: Electrochemical techniques such as cyclic voltammetry (CV), electrochemical impedance spectroscopy(EIS), and potentiostatic/galvanostatic measurements investigatethe electrochemical behavior and properties of materials invarious environments.Application AreasCharacterization methods find applications in numerous scientific disciplines and industries. Some notable application areas include:1.Materials Science: Characterization methods play a vital role instudying the structure-property relationships of materials. Theyare used to analyze material composition, crystal structuredetermination, defect analysis, surface morphology examination,and mechanical property evaluation.2.Chemistry: Chemical characterization techniques are extensivelyemployed in organic and inorganic chemistry for compoundidentification, purity analysis, reaction monitoring, andstructure elucidation.3.Biology: Characterization methods help biologists understand thestructure and function of biological molecules such as proteins,nucleic acids, and carbohydrates. Techniques like X-raycrystallography, NMR spectroscopy, and mass spectrometry aid instudying biomolecular structures and interactions.4.Pharmaceuticals: Characterization methods are crucial in drugdevelopment and quality control processes. They ensure the purity, stability, and efficacy of pharmaceutical compounds by analyzingtheir chemical composition, crystallinity, dissolution behavior,and formulation characteristics.5.Environmental Science: Characterization methods are used toanalyze pollutants in air, water, soil samples to assessenvironmental quality. Techniques like gas chromatography-massspectrometry (GC-MS), atomic absorption spectroscopy (AAS), and X-ray fluorescence (XRF) help identify and quantify contaminants.ConclusionCharacterization methods provide valuable insights into the properties, composition, behavior, and performance of materials and systems across various scientific disciplines. By employing a combination of physical and chemical characterization techniques, researchers can gain a comprehensive understanding of their samples. These insights drive advancements in fields such as materials science, chemistry, biology, pharmaceuticals, and environmental science. Continuous development ofnew characterization methods further enhances our ability to explore the microscopic world and unravel the mysteries of nature.Note: The content provided above is a general overview of characterization methods. It is not an exhaustive list or detailed explanation of each technique.。

2219-T87铝合金TIG焊缝摩擦塞补焊接头组织及性能杜波;杨新岐;孙转平;王东坡【摘要】采用摩擦塞补焊工艺,对8,mm厚的2219-T87铝合金TIG焊缝进行焊接实验,采用光学显微镜、扫描电子显微镜观察接头的焊缝成型、显微组织和强化相转变,通过硬度测试、拉伸试验、断口观测研究接头的力学性能和断裂特征.结果表明:摩擦塞补焊接头可分为塞棒区、塞棒热力影响区、再结晶区、热力影响区、热影响区和母材区/TIG焊缝区6部分;接头热影响区和热力影响区的强化相粗化,发生局部软化,垂直于TIG焊缝方向的最低硬度(95.1,HV)出现在热力影响区,平行于TIG 焊缝方向的最低硬度(75.3,HV)出现在热影响区;接头的抗拉强度可达321.3,MPa,断后伸长率可达2.8％,,分别为母材的72.2％,和28.0％,;拉伸试样断裂位置为热力影响区,断口呈剪切韧窝,属于塑性断裂.【期刊名称】《天津大学学报》【年(卷),期】2018(051)012【总页数】6页(P1303-1308)【关键词】摩擦塞补焊;2219-T87铝合金;TIG焊缝;微观组织;力学性能【作者】杜波;杨新岐;孙转平;王东坡【作者单位】天津大学天津市现代连接技术重点实验室,天津 300350;天津大学天津市现代连接技术重点实验室,天津 300350;天津大学天津市现代连接技术重点实验室,天津 300350;天津长征火箭制造有限公司,天津 300451;天津大学天津市现代连接技术重点实验室,天津 300350【正文语种】中文【中图分类】TK453.92219铝合金是我国新一代运载火箭贮箱结构材料，搅拌摩擦焊已成功应用于火箭贮箱筒段纵缝的焊接，但受到贮箱体积和焊接条件的影响，运载火箭贮箱环焊缝及角焊缝的连接目前仍采用VPTIG焊接工艺．研究表明，2219铝合金采用VPTIG 焊接时，接头容易产生气孔缺陷，严重降低接头的力学性能，需要对气孔缺陷进行补焊，以满足贮箱的使用要求．摩擦塞补焊(friction plug welding，FPW)是英国焊接研究所于1995年发明的一种新型固相补焊技术[1]．该技术可用于搅拌摩擦焊尾孔的消除及焊接缺陷的修复，在火箭贮箱结构的制造过程中具有重要应用．国外对FPW进行了大量的实验和工艺优化工作[2-4]；国内对FPW的研究起步较晚[5-10]，与2219-T87铝合金TIG焊缝FPW相关的研究鲜有报道．本文对火箭贮箱结构用2219-T87铝合金TIG焊缝和2A14-T6铝合金塞棒进行了FPW工艺实验，焊后对接头的焊缝成型、微观组织、显微硬度、抗拉强度及拉伸断口进行了观察和测试．研究结果对FPW工艺应用于火箭贮箱制造中TIG焊缝缺陷的修复具有重要的理论和工程意义．实验板材料为2219-T87铝合金TIG焊缝，规格为200,mm×80,mm×8,mm，塞棒材料为2A14-T6铝合金．实测2219-T87铝合金TIG焊缝的抗拉强度为232.2,MPa，断后伸长率为1.23%,．2219-T87铝合金和2A14-T6铝合金的主要化学成分见表1．TIG焊缝的摩擦塞补焊工艺实验在天津大学自主设计研制的大功率摩擦柱塞焊接系统上完成，塞棒和塞孔的形状尺寸设计如图1(a)所示．通过前期的工艺实验，在优化的焊接工艺下进行实验(焊接转速5,000,r/min，焊接压力40,kN，顶锻压力45,kN，保压时间5,s，塞棒压入量6,mm)．金相试样采用线切割切取，经磨光、抛光后用Keller试剂腐蚀并在OLYMPUSGX51 光学显微镜下观察其显微组织．使用432SVD自动转塔数显维式硬度计测量接头的硬度分布，载荷1,000,g，加载时间10,s．依据国家标准《焊接接头拉伸试验方法》(GB/T 2651—2008)进行FPW接头的拉伸实验，拉伸试样尺寸如图1(b)所示．拉伸测试在CSS-44100电子万能实验机上进行，加载速率3,mm/min．使用Hitachi-S4800扫描电镜观察拉伸断口的宏观与微观形貌．图2(a)、2(b)分别为FPW接头平行和垂直于TIG焊缝方向的截面形貌．从图2中可以看出，由于焊接过程中连接界面附近塑性材料的流动，FPW接头的上表面形成飞边，下表面形成挤出端．两个截面的整体形貌比较相近，但由于TIG焊缝的焊核区硬度较低，流动性较好，平行于TIG焊缝方向飞边翻卷程度明显比垂直于TIG焊缝方向大．根据接头的组织特征，可将接头分为塞棒区(plug metal，PM)、塞棒热力影响区(plug thermo-mechanically affected zone，PTMAZ)、再结晶区(recrystallized zone，RZ)、热力影响区(thermo-mechanically affected zone，TMAZ)、热影响区(heat affected zone，HAZ)和母材区(base metal，BM)/TIG焊缝区(TIG weld)6个部分．图3为图2(a)中标注位置的显微组织．在平行于TIG焊缝方向截面上，塞棒中心只受到了焊接热循环的影响，保持了原始的细长晶粒形态(如图3(a)所示)；连接界面处发生了剧烈的热力耦合作用，此处的组织再结晶形成均匀细小的等轴晶组织(如图3(c)所示)；紧邻RZ两侧的TMAZ和PTMAZ发生了部分再结晶，但晶粒尺寸比RZ的大(如图3(c)所示)；而远离RZ的TMAZ和PTMAZ则只是发生了较大的塑性变形，且越靠近RZ变形越大(如图3(b)、3(d)和3(e)所示)；HAZ和TIG焊缝区均为尺寸较大的等轴晶粒，晶粒尺寸约为100～200,μm(如图3(f)所示)．由于预钻塞孔时，原来TIG焊缝的焊核区及其周围的组织已被去除，所以接头垂直于TIG焊缝方向截面的显微组织与母材FPW接头基本一致，之前的研究中已做过详细介绍，故不再赘述[8-10]．图4为扫描电镜下图2(a)中标注位置强化相的形态及分布特征．塞棒中心只受到焊接热的影响，而未受到力的作用，强化相沿塞棒拉拔的方向呈线状分布(如图4(a)所示)；RZ发生动态再结晶，强化相在剧烈的热力作用下得到细化(如图4(c)所示)；靠近RZ的PTMAZ和TMAZ发生部分再结晶，强化相也得到一定程度细化，但尺寸比RZ的大(如图4(c)所示)；稍远离RZ的PTMAZ和TMAZ中的强化相在热力作用下发生明显变形(如图4(b)、4(d)和4(e)所示)；HAZ和TIG焊缝中的强化相在FPW过程中未受到力的作用，强化相均匀分布(如图4(f)所示)．强化相在焊接过程中的演变与接头各区硬度的变化密切相关．TMAZ、HAZ和TIG焊缝中的强化相经历TIG焊接热循环的影响，TMAZ和HAZ又再次经历FPW焊接热循环的影响，这3个区域的组织发生严重过时效，强化相粗化，数量也明显比PM和PTMAZ多．图5(a)、图5(b)分别为FPW接头平行和垂直于TIG焊缝方向截面的硬度分布．硬度测试间距为0.5,mm．实测2219-T87铝合金板的平均硬度为146.5,HV，2A14-T6铝合金棒的平均硬度为133.6,HV．在平行于TIG焊缝方向截面上，TMAZ、HAZ和TIG焊缝区先后经历了TIG和FPW焊接热循环影响，所以这3个区域的硬度都比较低，约为75～80,HV，最低硬度出现在HAZ，最低值为75.3,HV；PM的硬度较高，硬度在122～130,HV范围内波动；PTMAZ的硬度比PM略高，约为135～140,HV，这是由于PTMAZ 发生了部分再结晶，晶粒得到一定程度的细化，从而使硬度得到小幅提高．在垂直于TIG焊缝方向截面上，PM和PTMAZ的硬度基本与平行于TIG焊缝方向截面上的分布一致；硬度自TMAZ开始降低，经过影响区后开始缓慢增加，最低硬度出现在TMAZ，最低值为95.1,HV．由于接头先后经过TIG和FPW焊接过程，TIG焊接过程热输入比较大，HAZ较宽，预钻塞孔时HAZ未能完全被去除，部分保留到了FPW接头中，所以硬度测试结果显示接头出现了较宽的软化区．由此可见，采用FPW工艺修复TIG焊接缺陷，去除了原始TIG焊缝软化严重的区域，降低了接头软化的程度，因此，FPW工艺有利于补焊焊缝力学性能的提高．图6为FPW接头和TIG接头的应力-应变曲线．由图6可知，由于TIG焊过程中较大的热输入和气孔缺陷，接头的力学性能较差，抗拉强度仅为232.2,MPa，断后伸长率为1.23%,，分别为母材的52.2%,和12.3%,；相比之下，TIG焊缝FPW 接头的抗拉强度可达321.3,MPa，断后伸长率可达2.8%,，分别为母材的72.2%,和28.0%,，远远超过TIG接头的抗拉强度和断后伸长率，说明通过FPW工艺对TIG焊缝进行缺陷修复是可行的，且具有明显的优势．图7为TIG焊缝FPW接头拉伸试样的断口形貌．拉伸试样的断裂位置在TMAZ，说明软化的TMAZ是整个接头的薄弱区域．由低倍断口形貌可以看出，拉伸断口呈现韧窝形貌，但韧窝有两种不同形态，即颜色较深的区域A和颜色较浅的区域B，区域A和区域B韧窝均呈现大小韧窝相间分布的特征，大韧窝的底部可清楚观察到强化相粒子；二者均呈现剪切韧窝的特征，区域A剪切韧窝特征更为明显．由FPW接头的断口形貌可知，接头属于塑性断裂，并且FPW过程中TMAZ 的强化相粒子发生聚集和长大．(1) 采用摩擦塞补焊工艺，实现了对8,mm厚2219-T87铝合金TIG焊缝的补焊，并获得了无缺陷的FPW接头．(2) FPW接头由塞棒区、塞棒热力影响区、再结晶区、热力影响区、热影响区和母材区/TIG焊缝区6个部分组成．(3) FPW接头TMAZ和HAZ的强化相严重粗化，发生局部软化，垂直于TIG焊缝方向的最低硬度(95.1,HV)出现在TMAZ；平行于TIG焊缝方向的最低硬度(75.3,HV)出现在HAZ．(4) FPW接头的抗拉强度可达321.3,MPa，断后伸长率可达2.8%,，分别为母材的72.2%,和28.0%,，远高于TIG接头．(5) FPW接头拉伸试样的断裂位置为TMAZ，说明TMAZ是FPW接头的薄弱区；拉伸断口呈剪切韧窝形貌，韧窝底部分布有强化相．【相关文献】［1］ Hartley P J. 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American character and habits[Abstract]Cultural differences, the first in customs. Culture shock is due to customs difference. Therefore, the United States to study cultural adaptation, the first to understand and adapt to American customs. Romans, can adapt to American culture, but also on various occasions that allow them to avoid making inappropriate moves, let you feel down or embarrassed. Arriving in the United States, nervous excitement is inevitable, and will be very excited; you hope to be able to quickly melt into American society. Asking someone else more for you to solve cultural barriers and see more and hear more can open imports to independent proactive attitude to overcome initial challenges. Make foreign friends, broaden their horizons, and improve English proficiency. The more opportunities to solve problems independently, English is also more rapid progress. Rights and obligations of the United States is a clear, customer-oriented society, and you try to express your displeasure, and correct their mistakes.[Key Words]American character; Habits; Get along with AmericanEvery nation has its own unique personality; people often talk about British modesty, French romance, Japanese Woman's supple, etc. Similarly, the American character has its distinctive features.Americans are generally cheerful, sociable, informal etiquette. The first meeting is not necessarily shake hands, sometimes just smile, and say "Hi" or "Hello" is even polite. Americans generally shake hands with women gently. In farewell, they just waved to you or said "goodbye", "See you tomorrow." But if others bow to them, they also use the appropriate etiquette, such as shaking hands, nodding, hugging, and salute and so on. When you first make an American friend, he will tell be talking with you even forever. More glances to strangers with no intention when you walk in the street, he might smiling nod to you, or call out "hello"; if your car broke down on the road, the enthusiastic people help you repair; if you got lost in the streets, and people were eager to help you.Americans do things fast-paced make visitors feel puzzled, and the first impression is probably all of them are Americans rush. It becomes very impatient even if they are blocking a moment, At first, you might think this is unfriendly to you. The bus drivers urge you; shop assistant hurried to treat you; Y ou buy something or go out to eat, no one told you joking greeting. Do not think that Americans are in such a hurry to you expressed unfriendly. Typically, outside the large cities have slower paceof life; in fact, other countries also have same phenomenon.They find out you were a stranger, most will be friendly and try to help you. If you need help or would like to ask what the problem is, you may find kind man, and say to him: "I was out of town, can you help me?"At this point, most people would stop and give you a smile pointing way or reply to your question. But you have to let them know you need help, otherwise they will probably come from your side. Occasionally you will encounter a hurry to act them too busy or can not help you. In such circumstances, you do not be discouraged, just get somebody else. Most Americans are willing to help foreign visitors.Americans do not like to be subordinated to others when dealing with each other and do not like people too polite to compliment yourself. Americans are worried about the entry of others deemed unapproachable been isolated which mean loneliness campaign failed to politicians.Therefore, Americans make friends and hope to give people a good impression, but can often lack the kind of heart-familiar.The second feature of the American character is independent and enterprising. They do not like to depend on others, do not like people dependent on them; develop independently from the urine of Americans struggle; do not rely on their parents. On the street, every morning you can see eleven-year-old boy delivering newspapers door to door regardless of wind and thunder rain.They will come up the social life of great benefits. the results obtained by their own scholarships or work part time earn tuition. They have to leave their parents live on their own when they are in adulthood;Once you get married, they even move about independently, rely on their own ability in the United States. Y oung couples have children and tend completely on their own instead of expecting grandmother or grandmother to take care of grandchildren. However, these independent spirits in the United States tend to become old tragedy.A third characteristic of the American character is pragmatic.They did not like the French like rambling fantasy, like the British did not speak panache to face.They admired the kind of savvy stronger than man. They can solve many things on their own. Most Americans know how to use the machine, repair of electrical equipment, furniture, paint and stucco walls. They believe that doing these menial jobs in life is granted. On the contrary, those nerds, fake gentleman, talkative short lines will be made fun of.American way of thinking has a big difference from which we had. English is this expression: 1) Like to be different; 2) Agree to disagree; 3) Everything is above board."Disabled priority, ladies first, the elderly priority, children first" is the American habit. Because they are vulnerable, people deserve health care. Americans do things all in regulations. Therefore, the queue becomes their established habits. Y ou have to wait until he or she calls you when it's your turn, and you can cross the yellow line toreceive services. Otherwise you will be criticized.Americans dressed very casually. They usually wear very little when the weather is hot, and a windbreaker or denim fabric is wrapped when it is cold. Only in formal occasion wear suits, skirts and other more formal clothes.Therefore, important events should pay attention to the dress code on the invitation. If you are unsure clothing requirements, they may first ask the other participants.Americans love to develop a healthy habit. Americans would say when you are walking on the streets in the United States for a week, and your shoes do not rub. Y ou go to school, and feel thirsty, you can drink tap water. After eating, the customer will consciously take home in doggy bags. And try not to make noise when eat dinner. No littering, spitting chaos.Americans use body potential language than we do. Shrug and face with unhappy expression expresses surprise and shrugging and smiling means sure. Thumb and forefinger form the number "6", which means "consent." Americans speak, move the body all the time, but without losing the sense of humor, you have to pay attention. Speech, the body can not give back, not too far away from the speaker should face each other. Thumb and index finger rubbing beep expresses encouragement, support, or having a new idea. Hands crossed together or on the waist pledge to fight pose. A palm facing up to greet people coming back and forth movement represents.With American friends shaking hands should be hard not too small, otherwise there is impolite suspected. The Americans are language-rich, sometimes hand catch to your shoulders, which means that affirmation and encouragement. Chinese people are more conservative character and difficult to greet strangers, but a greeting after he thought had friendship with each other. As everyone knows, the greetings and friendship between Americans is nothing. Americans understand this custom, on the one hand to learn their culture greetings, good morning, good afternoon, good night, thank you, I'm sorry all day. We must also recognize that the United States is owned greetings and friendship.Generally speaking, Americans do not receive gifts. Some receiving gifts often seem somewhat embarrassed. But birthdays, weddings or patient visits, gifts or inevitable.In addition, the Americans believe that the singular is auspicious. Sometimes only get three pears not feel happy, it is unlike the Chinese people pay attention to pairs. Americans received a gift, be sure to immediately open----at the front of the giver's face -----appreciate gift or sample and immediately thanks to the giver.In the United States, if you want to visit, you must first make a call the appointment. If the owner please resumes your seat, you not sit down immediately in order to express polite, but will make the owner feel uneasy, thinking chair unclean or other inconveniences. When a guest is not free to watch the master table of the wordof paper or read files. Do not fondle indoor antique curios, not to ask the price of indoor appliances.Do not smoke. If you want to smoke, you should first ask here whether they mind if the owner initiative to invite you to smoke, even if they have a smoke, has to accept the owner's smoke, rather than reject each other and suck their own. Otherwise, the owner will think that you are looking down on him and feel very happy.Do not leave immediately after a meal and the owner should have a chat for a while, and then leave. If it is someone's home to go to a couple of guests, leave to stand by his wife first. In more formal banquet, if more guests, you should wait a bit high elderly guests or important ladies first left after he will leave. If guests need something to go ahead, the owner should ask forgiveness before leaving. If you are not familiar with the owner, then a stranger after a call to the owner should be thanked, or write a "thank you" sent to the owner of the short Cambodia, so that the more comprehensive the courtesy.More open exchanges between American men and women. Dating men and women sometimes do not have other meanings, does not mean that will become a special partner. Therefore, if you want to meet someone to talk or watch movies, eat, in order to enhance mutual friendship and spend a pleasant time, as proposed initiative generous, both men and women can take the initiative to offer. Of course, there are some rules of dating American men and women, especially in the beginning stages. If you want to invite an American girl eating alone, please be sure to point the different meanings lunch and dinner.In general, the more casual lunch, easily accepted; dinner more seriously, after a meal may be further developed. So the first invitation, it is best to eat lunch as easily. Chinese female students as male students invited by the United States, also pay attention to different lunch and dinner. If you do not want to go to each other's appointments or make you uncomfortable with the move, you can kind but surely declined. In the United States, mutual respect is the basic principles of engagement, but also rights.The United States obey law, human rights in the country. Their values are equal and free. Therefore, marriage depends on the foundation that equality, mutual respect and preservation of privacy. Americans can have their marriage before several heterosexual friends, but after they get married to each other do not want to get involved in each of the opposite sex friends, once found, the divorce was inevitable. According to the U.S. habit, all important social events, banquets or parties held between friends, the couple attended together. I have found that American couples have a double into the right, very loving. However, the American divorce rate is high, which about 60% of the world's highest divorce rate in the country. It was the Americans marriage summarized twenty words: romantic teenager, passionate youth, middle-aged faithful, tragically old age.Of course, the white-collar marriage isrelatively stable.About money, Americans and the Chinese people have different attitude. Americans are generous to themselves, but to others, Americans are surprisingly careful, and don’t want to spend even a penny. On the contrary, the Chinese people liking to save are famous, and often conscious of their spending, but perhaps due to face relationship, a friend has been more generous. Together with the Americans to eat outside, pay each general account, even though they are women is also true.Even if the Americans propose to dinner, but also do not think that he or she is going to treat, and it is often still their pay. The Chinese people "who suggested who pays" habits are very different.In the U.S., it is best not to borrow money,even if you have to, because it is often denied. Of course, a little money can still be borrowed. However, Americans do have the habit of donations; many Americans donated large sums of money each year. This is very different from the Chinese people.Americans are also very pragmatic in terms of money. So they respect labor and remuneration calculation clearly. Friends went out to dinner, which is usually the payment of money;Tipping although the behavior of free evaluation of evidence, but there is the customary one, it is best to ask customs before entry. Generally speaking, tipping is about ten to fifteen percent or so in restaurant.But do not need to eat in the cafeteria to tip, if someone poured tea and inquired diligently demand, then according to the number of discretionary tip. Evening dining tip needed more than during the day. Tipping is an assessment of service quality; some waiters to will show particularly enthusiastic for tips. Remember never to penny tip, when the penny thrown on the table, even though you pay a lot of tips, is likely to be dissatisfied with the waiter misunderstood as their service is a humiliating manner.Unless the service is really bad, never be placed in the tip of any penny. Of course, if you pay by credit card, and the amount will be rounded tips and dining, it is not in this case.Americans see work as part of life. Despite they are wealthy; they have to have their own job. Their work is very professional, work efficiency is high. They think that wasting time is not idle. Working time and leisure time are entirely different. Americans like to talk about "the dignity of work".America's leading CEOs such a class may participate in any physical labor. They will be respected by others rather than look down.Americans work and rest time is very distinct. Business should be completed within the time at work.Americans prefer face to face or on the table in the negotiations finalized.Friday night is the night of friends get together, they can enjoy singing, dancing, drinking, playing games and other recreational activities. On Saturday, they took a family member or three or five friends drove to the outside world to play.Most shops open Monday through Saturday, half past nine or ten o'clock to 5:00pm, or about six. Some of the shops in the mall is open until nine p.m. Sunday will be open from noon until six later.Banking hours are relatively short, mostly Monday to Friday nine o'clock to 3:30 pm, some banks will extend the hours until Friday 6:00 pm Saturday morning. Regardless of companies and business firms, shopping centers, schools, generally there is no lunch break. The students have the habit of taking a nap are more difficult to adapt. Everyday life in the United States, Email has become the most practical, the most common means of communication. Communication between teachers and students in school, class, and usually use it to change jobs. Schools are used Email meeting notice.Major holidays: New Y ear's, Martin Luther King Jr. Day, Presidents' Day (Commemorating U.S. President George Washington and Abraham Lincoln's birthday), National Day (Independence Day), Labor Day, Columbus Day, V eterans Day, Election Day, Thanksgiving Day, Christmas Day.Generally they are willing to entertain guests in their own homes, rather than customary dinner in a restaurant.Do not like steamed and braised dishes. Do not like too hot dishes like salt taste, avoid salty taste, slightly to the sweet side as well. Like to drink Coca-Cola, beer, ice, mineral water, whiskey, brandy and so on. Do not like the people in their own meal dish leftover food, which is considered impolite. Like China's Jiangsu, Sichuan, Cantonese cuisine.Do not put blacks in the United States called "Negro", preferably use "Black". Blacks on this call will readily accept. Negro mainly refers to trafficking to the United States from Africa as slaves’blacks. Otherwise, blacks will feel indemnity for his contempt.Understanding the Americans customs need daily accumulation. American universities or student research group often hold communicative activities or picnics, graduate had been invited. But the Chinese students often do not participate actively. In fact, this is not only an understanding of professors and students opportunity, but also a good occasion to understand American customs.If it is possible, and try to attend these activities. If you live in the United States home, there are more opportunities to exchanges with the Americans, and have a deeper understanding of the American way of life, customs, habits and values.In order to save the money, Chinese students often shared with others, many of whom are American roommate. This is also a good way to understand American culture.People often say: "do as the Romans."In fact, it is quite difficult to do. Some people suggested that Chinese students lose their cultural baggage, and adapt to the American culture, social and educational environment. Indeed, the vast majority of Chinese students to the United States, more or less have to do some cultural adjustments to adapt to the United States learning and living environment. But adapting to American culture completely, and give Chinese culture up, and may alsohave to be carefully considered. In fact, more than twenty years of the Chinese student in the United States, it is difficult to give up Chinese culture. The correct attitude is a positive awareness and understanding of Americans and American society, and do not need to give up your culture. Y ou're still a Chinese person, but an understanding of the United States, to know how to live in the United States.[Reference Materials]1、国人的性格(2012-01-04 10:23:22) 美国人尼亚加拉大瀑布夏威夷岛性格杂谈2、美国习俗礼仪：生活礼仪 2008年09月18日新浪教育美国人的生活礼仪3、美国人的生活习惯/syy/yywh/201107/22676.html。

JOURNAL OF MATERIALS SCIENCE33(1998)1421—1429Laser-shock processing of aluminium-coated55C1steel in water-confinement regime, characterization and application to high-cycle fatigue behaviourP.PEYRE,L.BERTHE,X.SCHERPEREEL,R.FABBROCLFA-LALP,Unite&mixte ETCA-CNRS,94114Arcueil,France55C1steel was irradiated with a high-power neodymium—glass laser with application to induce plastic shock waves within targets,through the expansion of a laser-induced surface ser-shock processing experiments were conduced in the plasma-confined regime with water to increase the laser-induced peak stresses.Physical,mechanical and processings aspects were reviewed,such as the characterization of stress waves in coated steels with a VISAR velocimeter system,and the mechanical changes induced in55Cl in terms of compressive residual stresses or work-hardening levels.With the use of convenient protective coatings,some7—8GPa peak stress levels could be achieved which authorized the generation of high compressive residual stress levels(nearly80%of the compressive yield strength),but preserved the surface integrity from detrimental roughening.Surfacemodifications performed under different shock conditions were shown to display some30% increase on the bending fatigue limits of55C1at R:0.1.©1998Chapman&Hall1.IntroductionIn thefield of surface treatments,laser sources are usually used asflexible heat sources in investigation of solid-phase transformations[1],surface remelting (crankshaft applications)or surface alloying[2]. Among the wide variety of surface treatments investi-gated for improving properties of materials,laser-shock processing(LSP)was developed about25years ago in the USA[3,4]with particular application to enhance fatigue properties of fastened joints for aero-nautical applications.Many industrial materials were investigated at this time,such as aluminium or tita-nium alloys,or stainless steels,but because of the lack of reliable pulsed-laser sources(high cadency—high power density)and despite the satisfactory mechanical improvements displayed in aluminium-or titanium-based alloys,no real industrial application was shown to emerge.Since1988,and with the support of auto-motive and aerospace partners,intensive work has been undertaken in France,including phenomenologi-cal and applied studies[5—9].However,some critical processing questions still remain unanswered or need to be highlighted,such as(i)the precise influence of absorptive coatings which can modify very strongly the stress loadings transmitted to the metal by type mismatch impedance effects,(ii)the role played by laser-spot diameters on the stress-wave generation and propagation and on the resulting surface modifications,(iii)the plasticflow limit characterization at very high strain rate and its influence on the residual stress generation.All three processing aspects were reviewed with the objective to improve the fatigue life of steels which is one of the possiblefields of application for LSP.This underlined the need to pay special attention to all the surface parameters influencing the fatigue behaviour, such as(i)the compressive residual stressfields(X-ray dif-fraction)including stress amplitude levels,surface homogeneity aspects,and plastically affected depths, (ii)the work-hardening levels with the use of X-ray peak broadening and Vickers hardness measurements, (iii)the surface morphology modifications which are known to influence fatigue crack initiation.In each case,experimental measurements were re-ported which allowed a state-of-the art to be drawn for LSP in a plasma-confined regime with water,and to evaluate its potential as a novel process to improve the properties of the near-surface region.On the other hand,the future potential of LSP was discussed,with attention focused on the emergence of new laser sour-ces.2.General trends in laser-shock processingof materialsLaser-shock processing(LSP)uses a high-energy (tenths of J)pulsed laser to irradiate a metallic surface0022—2461 1998Chapman&Hall1421Figure 1Laser-shock processing with a water-confinement regime.TABLE I Physical,acoustic (from [12])and mechanical properties of the materials MaterialsC S Z7E (g cm \ )(m s \ )(g cm \ s \ )(GPa)(GPa)Al-99.99%purity 2.75380 1.38 1.45.10 0.2700.29316L Stainless steel 7.94600 1.5 3.7.10 0.31950.2955C1steel7.845001.53.6.100.622100.29during very short times (a few nanoseconds).When the laser pulse is focused on the surface to reach a GW cm \ power density,it generates,through the expansion of a high-temperature (a few tens of thou-sands °C)—high-pressure (GPa range)surface plasma,a high-intensity shock wave which induces planar plastic strain in the metallic part.Conventional con-figuration,that was assessed in the 1968—1980[3—5]period in the Battelle Columbus Institute (OH,USA)consists in covering the metal to be treated with a pro-tective coating (to avoid thermal effects)and to im-merse the area to be treated below a water overlay to improve the mechanical coupling by a confining-like effect (Fig.1).Indeed,as the plasma is trapped be-tween the target and the overlying water,its amplitude and duration are increased by factors of 10(for the peak pressure level)and 3(for the pulse duration)compared with direct ablation mode.Thus,the irra-diated materials undergo no thermal process nor microstructural changes,except at very high pressures when pressure-induced phase transformations occur,such as P on stainless steels (above 11—15GPa)[7]or P on ferritic steels.Instead,the surface is submitted to uniaxial plastic strain,provided the stress-wave amplitude reaches a level superior to the shock yield strength of the target which is commonly termed the Hugoniot elastic limit (HEL).All the investigations reported on LSP have been carried out with Q -switched neodymium —glass lasers operating at "1.06 m with 40—100J output ener-gies,0.6—30ns pulse durations and repetition rates ranging between 1shot every 20—30minutes (Battelle,USA,1968—1980[3—5]and 1shot every 2—3minutes (LALP,France,1990—1996)[6,9—11].The power den-sity range is usually in the 1—100GW cm \ range with pulses that are Gaussian in shape or exhibit short rise times [9].Many processing aspects to be high-lighted and optimized to ensure the best laser-material coupling as possible in terms of the plasma generation and most of all the stress-wave transmission to thesubstrate target.For instance,dielectric breakdowns occurring in the water have been shown to reduce the amount of energy reaching the surface at high power densities by creating a parasitic absorptive plasma at the water/air interface [11].Above 10—15GW cm \ ,the breakdown phenomenon limits the shock pres-sures to 5—6GPa,shortens the pulse durations and,most of all,gives much more scattering to the peak-pressure values.Of all the parameters influencing the transmission of a high-intensity stress wave to the substrate target at a given power density,the thermoabsorptive coat-ing layer has been rarely investigated precisely,except by Fox [3].In terms of compressive residual stress fields,all the previous studies have shown that LSP not only could have an affect much deeper than other surface processings (up to 2mm depth),but also gen-erated stress levels close to those generated by shot-peening [8,10].In this paper we aim to draw,for the first time,correlations between the shock conditions stress load-ings,2),the surface modifications and the mechan-ical behaviour of surface-treated samples after LSP.3.MaterialsThree different materials were used during our invest-igations;two of them (pure thin aluminium and AISI 316L stainless steel foils)were provided by Goodfel-low SA,the last one was an industrial 55C1medium carbon steel often used in automotive parts.Physical,acoustic and mechanical properties of the starting materials are shown in Table I,whereis density,Cis bulk sound velocity,S is a material constant,Z is acoustic impedance is ,D " (C #S º), 7istensile yield strength (quasi-static value),and E , are elastic constants (Young’s modulus and anisotropy coefficient)4.Characterization of laser-induced stress waves with the VISAR technique4.1.The VISAR system for measuring backfree velocitiesThe major contributor to the surface modifications generated by LSP is the stress pulse, "f (t )gener-ated at the surface of materials by the plasma pressure while it represents the mechanical loading of the target (at the plasma —target interface we can write P ").Many techniques have already been used to describe these mechanical impulses.Among these,piezoelectric quartz [9]or electromagnetic volt-age (EMV)gauges [13]have provided very useful information,but limited by non-linear behaviour in1422Figure2Schematic illustration of free velocity measurement with a VISARsystem.Figure3 "f(º)curves for aluminium,steels and air(vacuum). Example of a3—4GW cm\ LSP(P"2.7GPa):free velocity value"330m s\ on aluminium alloys,"110m s\ on316L steel.the case of quartz and by some magneticfieldfluctu-ations in the case of EMV gauge.New piezoelectric copolymers also seem to be very promising but are still under investigation[14].To understand and predict LSP effects on the me-tallic surface modifications,a precise characterization of laser-produced shock waves was conducted with a Doppler-laser velocimeter system called a velocity in-terferometer system for any reflector(VISAR).This technique interferometry is a newly developed[15] method for measuring free velocities induced by shock waves behind thin metallic targets.It has already been used to characterize the conventional shock loadings, but an original device has been developed in our laboratory by Tollier et al.[16]to identify the spalla-tion thresholds in pure materials such as aluminium or copper(Fig.2).Using an argon-probe laser focused (200 m spot)at the back free surface of the targets, this system identifies the acceleration of interferencef-ringes,which are dependent on the back free surface velocity,ºD,through a Doppler-like effect[15].As-suming that shock and release parts of the Hugoniot curves are almost symmetrical(totally symmetrical when the stress level (2HEL),this velocity,ºD,is approximately twice the particle velocity,º,behind the shock front(ºD"2º)(Fig.3).Lastly,by the use of the classical Rankine—Hugoniot conservation for-mula,one can access easily the stress-time loading profiles at the surface of the targets withwhen (HEL" C ºwhen 'HEL" Dº#2/3 7" (C #Sº)º#2/3 7(1) where is the laser-induced peak stress,2/3 7is an elastic contributor corresponding to the deviatoric parts of the stress, the density,and C the longi-tudinal elastic velocity(6000m s\ on steels and 6500m s\ on aluminium alloys).4.2.Shock-wave simulationsSHYLAC-1D hydrodynamic code[17]was used to simulate laser-induced free velocity profiles.This code is based on the method offinite differences and allows simulation of a laser energy deposit(J cm\ )including the efficiency of the interaction, ,at the surface of the material in confined ablation mode.Coefficient is known to be the energy ratio involved in the pressure rise,so(1! )E is devoted to the plasma formation [6].During our simulations,this coefficient was esti-mated to0.2—0.25,to give a goodfitting with experi-mental measurements.This code includes a Mıe Gruneisen equation of state with reference to the Hugoniot curves of the materials(Fig.3).A purely elastic—plastic behaviour was used for all the materials to evaluate the evolution of shock parameters(particle velocity,º,stress,internal energy,2)in metallic targets.4.3.Characterization of laser-inducedloadings on aluminium-coated steels During a laser-material interaction in the GW cm\ range,the energy deposit and the ablation pheno-menon occur on a few micrometres thus creating heat penetration to depths ranging between10and20 m. Consequently,during a conventional laser-shock,sur-faces have to be protected by at least20 m thick coatings to provide only pure mechanical impulses to the targets.Irrespective of laser parameters(power density,pulse duration,pulse rise time,laser wavelength)which have been shown to influence the plasma pressure levels,the coating effects have to be estimated to precise laser-induced stress loadings sub-mitted to materials.Since the early works on LSP,many coatings have been used to ensure a thermal protection to metallic targets.These coatings can be metallic or organic paints or adhesives.Thefirst atomic layers of the coating not only protect the surface from thermal rise but also from the plasma in itself,indicating that they can play a fundamental role on the plasma properties and particularly the plasma pressure.Most of all,1423Figure 4(——)VISAR velocity measurements at 3—4GW cm \ fluence on uncoated 316L and pure aluminium 200 m foils.(——)SHYLAC-1D simulation (energy deposit "20J cm \).Figure 5Back free velocity measurements at 3—4GW cm \ on 200 m 316L foils coated with 130—140 m aluminium paint ((——)VISAR measurement and (——)SHYLAC-1D simulation).The stress level increases from 2.7GPa to 4.6GPa on 316L with surfacecoating.Figure 6(——)VISAR measurement and (——)SHYLAC-1D simulation of LSP 3—4GW cm \ on 200 m 316L coated with 100 m aluminiumadhesive.Figure 7Stress "f (power density)curve:influence of the coat-ings on the stress amplitude values.All measurements made with 3—4mm impacts except three stress determinations made with 1mm diameter spots.(᭺,᭹)Base materials (aluminium or steels),(᭿)316L #140 m aluminium paint,(5)316L #aluminium adhesive.differences of acoustic properties,Z (Table I),at the interface between the surface coating and the under-lying substrate can modify the stress loading by type mismatch impedance effects:if Z (Z,the peakstress increases when the shock wave comes from material 1to material 2.In this work,two of the usual protective coatings have been investigated:an alumi-nium-based paint with different thicknesses,and an aluminium-based adhesive of 100 m (including 20 m glue).Well-calibrated 200 m 316L foils were used instead of 55C1ones to draw general tendencies about LSP on aluminium-coated steels.At a given incident laser irradiance (about 4GW cm \ power densities),free velocity measurements were conducted on (i)bare 200 m aluminium foils,(ii)bare 200 m 316L stainless steel foils and (iii)200 m 316L #aluminium-based coatings at different thicknesses.Figs 4—7show the free velocity profiles as a function of time for each configuration.On aluminium foils impacted with 4GW cm \ (Fig.4),the maximal free velocity amplitude is shown to be 320$20m s \ (average value with at least three measurements)de-noting an impact pressure P "2.8$0.2GPa (asshown by SHYLAC simulation and evidenced in Fig.3).Pressure pulse duration at half maximum is close to 60ns which is nearly twice the laser pulse duration.Reverberations of shock and release waves on the front and rear faces of the 200 m foil give this oscillating aspect (successive velocity jumps)to the profile.On AISI 316L stainless steel,impedance mismatch effects occur and modify the profiles very strongly,as shown by a comparison between profiles of uncoated and coated steels (Figs 4—6).The free velocity ampli-tude is nearly 120m s \ on the bare steels,whereas it reaches 200—220m s \ with 140 m coatings by impe-dance mismatch-like effects.In terms of stress levels, ,submitted to the metal,it increases from nearly the same level indicated on aluminium foils (2.7$0.5GPa)up to 4.5$0.5GPa.This very huge increase (#50%)happens with a shortening of the first velocity jump.In Fig.6,the coating effects are also shown very clearly:for a lower coating thickness (90 m Al #10 m glue versus 140 m Al paint),the adhesive configuration displays almost the same velocity levels1424Figure 8VISAR:elastic precursor determination on steels at 5GW cm \ and (——)500 m 316L or (——)360 m 55C1coated with 90 m aluminium paint (estimated surface stress "6GPa).(close to 220m s \ "4.7GPa).This was ascribed to the acoustic properties of glue which tend to increase the stress amplitudes.The stress levels deduced (with Equation 1)from several velocity measurements on coated steels at different power densities,are reported in Fig.7and compared with measurements on bare materials.From this stress "f (power density)curve,we can conclude that coatings effects can play a very significant role in the case where their acoustic proper-ties differ from those of the substrate (aluminium-base coatings on steels).On steels,the large stress increases generated by aluminium-based coatings will have to be taken into account to optimize the shock conditions for materials hardening.ser spot-size effectsRecent investigations have shown that with a small impact configuration (0.5—1mm),plastically affected depths could be strongly reduced by two-dimensional effects (Fig.11below).Our objective was also to con-firm that surface stress levels were unmodified when reducing the impact sizes.We have reported in Fig.7,pressure measurements performed with 1mm im-pacts,where it is obvious that no detectable change has occurred with 1mm instead of 4or 5mm impacts.4.5.Determination of elastic —plastictransition during a laser-shock loadingLSP can be described as a planar compressive stress wave creating plastic strain in materials,provided the stress amplitude exceeds the shock yield strength un-der uniaxial loading (termed the Hugoniot limit HEL)of the base material.To optimize processing condi-tions,one must not only access the maximal stress level at the surface of the target,but also HEL values which depend on mechanical properties according to [18]:HEL "(1! )/(1!2 )(2)where is the anisotropy coefficient andthecompressive yield strength at high strain rate.In elas-tic —plastic solids,the stress waves transmitted through the specimen separate into two distinct waves:a lead-ing elastic wave of HEL amplitude,and a plastic wave.The only means of determining HEL values is to analyse the amplitude of the elastic precursors of shock-wave profiles.These precursors are generally constant in depth,except on steels where attenuations have been shown to occur by many authors [19]on conventional shock loadings.The aim of this third part was to determine HEL values on all the materials investigated and to compare them with static values.Two examples of precursor determination are shown in Fig.8on 55C1and 316L steels indicating that the free velocity values at the elastic —plastic inflection are close to 105m s \ on 55C1steel and 50m s \ on 316L.With the use of Equation 1below HEL (HEL " C º&#*),this leads us to HEL values of1.2GPa on 316L and2.5GPa on 55C1.When acomparison is made with static 7,HEL values giveinteresting information on the strain-rate depen-dence of the alloys.Indeed,as HEL "(1! )/(1!2 ) "1.75,one can easily deducefrom the precursor values with "HEL/1.75.Consequently,at 10 s \ ,we have (i)on 316LºD &#*"50m s \ :HEL "1.2GPa, "0.7GPa "2.3(ii)on 55C1ºD &#*"105m s \ :HEL "2.5GPa, "1.4GPa "2.3So it seems that both ferritic and austenitic steels are strain-rate dependent in the 10\ s \ (quasi-static)to 10 s \ range.Indeed,more than a factor 2was found between yield strengths values measured at 10\ s \ ( )and estimated at 10 s \ ()withelastic precursors.Moreover,as precursors tend to decrease in depth on steels [19],the HEL values are certainly underestimated by our VISAR stly,on 55Cl steel,a decrease behind the precur-sor was noticed (Fig.8).This phenomenon,already mentioned by many authors on steels [18]seems to be due to twin formations at the elastic —plastic transition.4.6.ConclusionIn this section,we have described laser-induced shock waves in a water-confining regime with the use of a Doppler velocimeter system and with particular attention paid to the influence of the thermal absorp-tive coatings on the stress profiles.It has been shown on aluminium-coated steels that,with thick enough coatings (more than 50 m),stress levels could be increased to a large scale,reaching #50%,as com-pared with stress levels obtained on bare materials.Moreover,confirmation was obtained that,even if small impacts can have detrimental effects on the shock-wave attenuation in depth,their surface stress1425Figure 9Laser-shock processing fatigue of notched samples withlarge or smallimpacts.Figure 10Average residual stress values determined at the surface of notched fatigue samples with different LSP conditions at 5GW cm \ in the water-confining regime:(1)6mm impacts #aluminium adhesive,(2)6mm impacts #aluminium paint,(3)1mm impacts #aluminium paint.level is kept constant when compared to larger im-pacts.Lastly,the elastic —plastic transition during shock loading was investigated and it was shown that steels are much more strain-rate dependent than aluminium alloys.5.Surface modifications induced by laser-shock processing on 55C1steel 5.1.Residual stressesResidual stresses (RS)are usually known to be the key to enhanced mechanical properties such as fatigue or wear resistance.Consequently,most of our investiga-tions have concentrated on determining surface and in-depth residual stresses induced by different shock configurations on different materials.In the case of LSP,they appear to be the result of a two-step mecha-nism:(1)a uniaxial compression during the laser-pulse generating tensile stretching of the surface layers,and (2)an opposite reaction of the surrounding zones (besides and below)which induces the compressive stress field.A recent calculation by Ballard et al .[8]has shown (Equations 2and 3)that the laser-induced plastic deformation, (and therefore,the surface stresses,),are linearly dependent on the ( :HEL)ratio.In fact,this ratio seems to be the most important parameter to optimize,but it necessitates a precise knowledge of and HEL (as was done in Section 4).Indeed,according to Ballard et al .[8],and consider-ing the case of a solid inclusion in a semi-infinite body with work-hardening effects taken as negligible,the maximum plastic deformations are achieved when 2HEL ( (2.5HEL.Plastically affected depths ‘¸’and maximum surface stresses,,are then cal-culated from [8]¸"2HELC CC !C(2) " 71!4(2 (1# )Lr(2(3)where ¸is the plastically affected depth (mm),CandCare elastic and plastic velocities (6000and 4500m s \ ,respectively,on steels), is the pressure pulse duration (nearly 50—60ns for a 20—25ns laser pulse),the residual surface stresses (MPa),andr the radius of the impact (mm).The X-ray diffraction technique by the sin method was used to determine the residual surface stresses (RSS)induced by LSP. -Fe (211)diffraction profiles were measured at 10 angles and only 1 di-rection with Cr K ?radiation at 2 "156°angle.Peakbroadenings were evaluated using full-width at half-maximum (FWHM)after removal of the K ?radi-ation.Indepth stresses were obtained after step-by-step electropolishing of the impacted areas.The two coating configurations previously investi-gated with VISAR were also used for the treatment of notched fatigue samples at the same power density (Fig.9).With the aluminium paint configuration,two impact diameters were also used to estimate the spot-size effects.Residual stress measurements performed down the notch roots (Fig.10)show that uncoated materials have very high tensile stress values even when confined with water.This was attributed to severe surface melting and confirms the overall influ-ence of coatings to preserve the surface integrity.Among the three classical (protective coating #con-fining water)configurations,that for small impacts displayed the highest stress level (up to !460MPa compared to !410MPa with largest impacts and !390MPa with aluminium adhesive).These stress levels are close to !0.75which is roughly themaximal ratio previously achieved on aluminium alloys [10]or chromium —molybdenum steels [8].On the other hand,the large impact configuration was shown to affect the metal at much greater depth than the small impact one as shown by measurements on plane samples exhibited in Fig.11.This is due to two-dimensional attenuation of shock waves in the case of small impacts that reduce the plastically affec-ted depths (800 m for 1mm impacts and 1200 m for 6mm impacts).It was also shown that LSP did not create any detectable X-ray peak broadenings after LSP (Fig.12),except on uncoated materials where structural modifications during melting and solidifi-cation were shown to harden the superficial layers,thus increasing the FWHM values (from 1.4to1426Figure 11In-depth residual stresses on 55C1-LSP 5GW cm \ .Influence of impact sizes on the affected depths:(——)1mm,(᭺)6mmimpacts.Figure 12LSP effects on X-ray diffraction peak broadening (inte-gral FWHMvalues).Figure 13Surface morphology modifications as a function of LSP conditions (4—5GW cm \).Figure 14Stress —strain laws of 55C1steel before and after LSP-5GW cm \ (extensometric measurements).1.85"#30%).This indicates that LSP generates low work-hardening levels and low densities of structural defects (dislocations,etc.)in 55C1.5.2.Surface morphology modificationsRoughness and waviness measurements were made in order to analyse the surface geometry changes as a function of processing parameters.It is shown in Fig.13that LSP in the water-confinement re-gime #coating (configurations 1,2,3)keeps the sur-face roughness,R,globally unchanged (except forsmall impacts where a small roughening occurs from0.03—0.1 m).However,surface undulations appear because of the ring-like pattern on the incident laser beam,and also because of overlapping regions.This phenomenon is clearly discernible in the case of small impacts where the average waviness parameter,¼,increases from 0.07 m to 1.25 m (a factor of 20).The last point to notice is that uncoated material not only has tensile residual stresses but also has a deleterious surface state (R"0.2 m)because of surface melting.6.Modifications of mechanical properties of 55C1steel with LSP6.1.Modifications of monotonic propertiesPlane 55C1samples were laser processed at 5GW cm \ to evaluate LSP effects on static proper-ties.Extensometric strain-gauges were stuck to plane samples to estimate,during four-point monotonic bending,the effects of LSP in the water-confined mode on the "f ( )curve of the impacted surface (Fig.14).After LSP,the 55C1elastic —plastic behaviour is slightly modified,showing:no modifications of Young’s modulus,E ;no detectable change in 7;a 10%increase in(800MPa to 890MPa)dueto an increase in the hardening modulus,h ,of the surface layers in the first plastic strain steps.However,because of the kinematic #isotropic hardening behaviour evidenced at the beginning of the plastic strain (curved aspect of the elastic —plastic transition),a quantitative evolution of h was difficult to calculate.In conclusion,the laser-induced changes in plastic flow limits seems to be very low as compared with classical surface treatments like shot-peening or carbo-nitriding,which are known to create much higher increases in 7but also a surface embrittlement [20].6.2.Modifications of fatigue propertiesFatigue tests were carried out on notched specimen having a stress concentration factor K"1.65atR " /"0.1and a frequency f "30Hz witha four-point monotonic bending system.Fatigue limits, ",were determined at 2;10 cycles.For the1427。

速度快并且容易中的材料类SCI期刊(更新中)推荐：1. Journal of alloy and compounds 影响因子IF 1点多，1个月给消息，容易中，现在几乎成为中国人的专刊了，哈哈；2. applied surface science 影响因子IF 1点多，发表容易，3. Materials Letter 1.7 速度快，快报一般都要求有新意（当然，新意太高可以投APL了）4. Materials & Design 影响因子不到1，很快，快点一个月就接受的！适合特别想要文章毕业或者评奖学金的。

5. Physica B 影响因子不到1，很快，我一个同学已经在上面发了2篇了，最快不到一个月就接受了，还是容易中的，最好是工作全面细致些。

6. Materials science and engineering B 影响因子1点多，从投稿到接受一般3-4个月，相对容易中。

7. Optoelectronics and Advanced Materials-Rapid Communications, 罗马尼亚期刊，影响因子0.2，很快，一个月可以搞定，适合灌水和急需文章。

8. Optical materials 发光材料期刊，影响因子1点多，相对容易中，速度也快。

9. Journal of Luminescence 发光方面专业期刊，老牌杂志，虽然影响因子只有1点多，但很多发光方面的经典文章出自此期刊，相对容易中，速度也可以。

10. Journal of Physics D: Applied physics 偏物理材料方面，影响因子2 左右，速度快，也不难中，中国人投稿还比较多。

黑名单：1. Thin solid films 影响因子1点多，但审稿巨慢，不推荐；2. Materials Characterization 影响因子不高，容易中，但速度慢，如果不急着要文章，也可以投的；3. Materials Chemistry and Physics 影响因子1点多，速度巨慢，我一个同学投稿半年还没消息，现在1年过去了还没查到这篇文章，估计没戏了吧。

【篇一】勤奋是智慧的双胞胎，懒惰是愚蠢的亲兄弟。

diligence is the twin of wisdom, lazy stupid brother.智慧和纯洁来自努力，无知和纵欲来自懒惰。

wisdom and purity from efforts, ignorance and sex from laziness.懒人的工作总是明天，而他的假日则是今天。

lazy to work is always tomorrow, and his holiday is today.懒惰行走得那么慢，以至贫穷很快就赶上了它。

lazy walking so slowly, that poverty soon caught up with it.天下事，以难而废者十之一，以惰而废者十之九。

what's going on in the world, with hard and which is one of the ten, which is of ten nine in idle.懒惰，会被万人揍，你痛苦时，还会选择懒惰吗？lazy, will be ten thousand people beat, your pain, will choose lazy?愿你贪吃不胖，愿你懒惰不丑，愿你深情不被辜负。

wishing you greedy not fat and lazy not ugly, i wish you a deep feeling will not be disappoint.你有一天将遭遇的灾祸是你某一段时间疏懒的报应。

one day you will encounter the evil is a certain period of time you indolent recompense.一只懒惰的羊连对自己身上长的毛也觉得负荷沉重。

a lazy sheep even felt heavy in his long hair too.懒惰是人的一个本性，也就是说懒惰是与生俱来的。

高等固体力学大作业学号：SY1413102姓名：刘冰河学院：交通科学与工程学院高温合金材料本构模型一．概述以上温度，高温合金于20世纪40年代问世，它指以铁、钴、镍为基体，能在600C一定应力条件下适应不同环境长时间或短时间使用的金属材料，具有较高的强度、塑性，良好的抗氧化、抗热腐蚀性能，良好的热疲劳性能，断裂韧性，良好的组织稳定性和使用可靠性。

其主要分为铁基高温合金、钴基高温合金和镍基高温合金[1, 2]。

本构关系广义上是指自然界作用与由该作用产生的效应两者之间的关系。

为确定物体在外部因素作用下的响应，除必须知道反映质量守恒、动量平衡、动量矩平衡、能量守恒等自然界普遍规律的基本方程外，还须知道描述构成物体的物质属性所特有的本构方程，才能在数学上得到封闭的方程组，并在一定的初始条件和边界条件下把问题解决。

因此，无论就物理或数学而言，刻画物质性质的本构关系是必不可少的。

目前应用较多的本构模型主要包括弹塑性力学中的经典本构模型，如理想弹塑性模型、线性强化弹塑性模型、幂强化力学模型和刚塑性力学模型。

然而塑性变形中应力-应变之间关系是非线性的，应变不仅与应力状态有关，而且和变形历史有关，因而研究者还提出增量理论和全量理论进行描述主要形成。

研究者在对金属材料的研究中不断提出新的本构模型，主要形成了两类本构模型：经验型本构模型，如Johnson －Cook 模型、Rusinek-Klepaczko 模型等；物理型的本构模型，如Hoge－Mukherjee模型、Zerilli－Armstrong 模型、MTS 模型等[3-5]。

二．几种本构模型介绍经典本构模型主要有理想弹塑性模型，线性强化模型，幂强化力学模型，以及刚塑性模型，如图一所示。

对于理想弹塑性模型来说, 在研究材料的应力应变关系时，分两个阶段。

第一阶段为弹性变形，第二阶段为塑性变形。

在塑性变形时，要考虑变形之前的弹性变形，而不考虑硬化的材料，也就是进入塑性状态后，应力不需要增加就可以产生塑性变形。