承受扭矩和剪切时开口多孔金属的孔棱失效

以高孔率的三维网状多孔金属(即开口多孔金属)为研究对象,建立其简化结构失效模型。分析多孔构件在扭转和剪切载荷形式作用下由于孔棱发生拉断、剪切和屈曲而引起的失效模式,系统地研究上述两种承载条件下这类多孔体构件受到载荷作用而导致孔棱失效时名义载荷与孔率的数理关系。在此基础上,进一步研究此类材料在不同载荷作用下发生各种孔棱失效模式的载荷条件。结果表明,这些失效模式与多孔金属的材质指标、孔率及承受的载荷大小等因素均有关系,这种关系也可以进行相应的具体数理表征。     

泡沫金属在单双向拉压载荷作用下的表征分析

探讨泡沫金属的单向压缩以及双向拉压行为,并研究了该材料单双向拉伸性能,进一步分析该材料在承受各种单双向拉压载荷时的不同响应方式.结果表明:在泡沫金属材料受到不同的单双向拉压载荷作用而产生破坏时,其承受的各向名义应力大小与多孔体的孔率都可表达为一个统一的数理关系;对于一个确定的多孔体材料,其单双向压缩负载能力要分别大于其单双向拉伸负载能力.     

多孔金属材料失效模式的数理分析

三维网状多孔金属材料已广泛应用于工程领域,本文借助于数理分析,综合介绍了此类材料在常见载荷形式作用下的失效模式,并对相关环节展开探讨.全面分析了该材料在单向压缩、双向压缩和三向压缩等压缩载荷形式下的失效行为,重点讨论了多孔产品在不同压缩载荷形式下的孔棱拉断和剪切断裂破坏模式,以及在三向压缩载荷形式下可能出现的孔棱屈曲失...     

泡沫金属在双向承载条件下的力学性能

根据各向同性三维网状泡沫金属的简化结构模型,建立该类材料的双向拉伸力学分析模型.利用该力学模型推出泡沫金属在双向拉伸破坏时两向名义应力与孔率3者的数学关系式,并在此基础上进一步得出该类材料在承受双向载荷时的安全判据.当双向承受的名义应力相等时,还可得到泡沫金属在双向等荷承载条件下的载荷强度与孔率的数学关系.这些关系式通过泡沫镍为例的有关实验数据证明是相当实用的.而由本理论体系可得出对多孔体双向承载条件的安全性判断,这似乎是Gibson和Ashby的有关模型理论所未触及或难以做到的.     

泡沫金属材料可压缩塑性力学研究进展

对泡沫金属材料的连续本构模型与可压缩性塑性力学进行了评述,并介绍了根据J2流动理论得到的可压缩塑性力学的本构关系,以及该本构关系在求解泡沫金属材料平面应力裂纹缓慢扩展问题中的应用,并将所得结果与一般幂硬化材料中的相应结果进行了比较,从而在一定程度上揭示了可压缩塑性力学与经典塑性力学之间的关系.     

泡沫金属在单、双向载荷作用下的拉伸破坏行为初探

采用低载拉伸试验机对多孔体的单、双向拉伸进行了系列实验，通过分析该材料的单向拉伸破坏机制，发现开孔泡沫金属材料的宏观断裂特点既不同于最大拉应力准则的横向断裂，也不同于最大剪应力准则的塑性流动破坏，而是表现为介于它们之间的一种复杂断裂形式；拉伸断裂过程中多孔体的延伸率主要由三维网络中的金属丝体发生的塑性偏转所造成。通过其双向承载时断裂形态的观测分析，发现泡沫体十字型样品在双向等速拉伸载荷作用下的应力场分布与双向异速拉伸载荷作用下的类似，且其应力场的最大应力线为靠近样品中央载荷区边缘的四次对称曲边四边形。     

泡沫金属双向等应力拉伸的不同理论应用

在已有的泡沫金属双向名义载荷强度与孔隙率关系的基础上，分析了该材料的双向等应力拉伸加载情形，探讨了泡沫金属在该情形下发生破坏的力学行为。研究结果显示，以“八面体模型”推导出来的有关力学关系，较好地表征了该材料在双向等载条件下的行为特点。     

泡沫材料在多向拉伸载荷作用下的力学模型

以各向同性的三维网状高孔率泡沫金属为研究对象,根据其简化结构模型,推导得出该类材料在多向拉伸破坏时3个名义主应力与孔率四者之间的数理关系。通过推演得出的有关关系式,还可进一步得出泡沫金属在多向受力状态下使用时的强度设计判据。     

三维网状泡沫金属杨氏模量和泊松比的数理表征

杨氏模量和泊松比是工程材料最为基本的两个力学指标.多孔金属是一种兼具功能和结构双重属性的优秀工程材料,采用"八面体分析模型",研究了三维网状泡沫金属的这两个性能指标,发现其表观杨氏模量与多孔体的孔率有比较复杂的数理关系,而其表观泊松比则是一个与孔率无关的特征材料常数.     

铝合金在两种应力状态下损伤机理研究

铝合金汽车构件在撞击的过程中,构件的应力状态各点均不相同,而且在撞击的过程中各点的应力状态随着时间变化而变化.为了研究铝合金构件在不同应力状态下损伤机理,采取了两种代表性的三轴应力状态,即缺口拉伸与纯剪切所产生的应力状态.研究结果表明缺口拉伸试验中,缺口根部产生相对较高的三轴应力,而且缺口根部明显产生微孔洞,随着应力的不断升高,微孔洞的体积分数不断增大.当达到材料的临界孔洞体积分数时,试样断裂;纯剪切试验中,三轴应力几乎等于0,在材料内部几乎没有产生微孔洞而产生了剪切带.剪切带在切应力的作用下变形不断增大,当到达材料的等效塑性断裂应变时,试样发生断裂;用Gurson损伤模型和剪切失效分别模拟缺口拉伸和剪切试验,试验的工程应力-应变曲线与模拟的工程应力-应变曲线拟合的很好.     

复合Bi系超导多芯带材轴向荷载作用下的临界电流退化模型与分析

超导材料由于在外部载荷作用下表现出的超导性能退化效应严重制约了其工程实际应用。基于脆性纤维金属基增强复合材料损伤理论,应用Weibull分布函数建立了轴向荷载作用下的复合多芯Bi系超导带材的力学变形对临界电流影响的退化模型。给出了轴向加载和卸载过程超导带材临界电流随轴向应变的变化关系;并对超导带材不同初始损伤以及预应变情形下的临界电流随轴向应变的变化关系和退化进行了理论预测,能够给出与实验结果吻合良好的轴向应变对临界电流的退化影响。     

Analysis and specification of the crash behaviour of plastics/metal-hybrid composites by experimental and numerical methods

Plastics materials are nowadays used in many structural applications for the substitution of metals with respect to weight reduction. In order to utilize the high freedom of design and the light-weight potential of plastics materials in crash-relevant structural parts, so-called hybrid composites which combine the high rigidity and strength of steel with the advantages of plastics materials are investigated in the outlined research. Thereby, the joining of both materials as well as the design by means of numerical methods such as the finite element analysis (FEA) are challenges which have to be met. A new approach in joining is based on the modified arc welding process where metal pin structures are formed in one working step and subsequently welded onto the surface. The pins are formed with ball-shaped, cylindrical or spiky ends and produced directly from the welding wire without requiring additional pre-fabricated components such as studs or similar. This allows the small-scale surface structuring of metal components that can be adapted optimally for a form fit on the respective plastics structure. Subsequently, injection molding is used for the application of the plastics material onto the pin-structured metal part in order to generate a positive fit between metal and plastics in an intrinsic joining process. An additional joining process, which is carried out after injection molding, is not required. Within the framework of the research presented, comprehensive mechanical tests are presented to illustrate the suitability of pin-structured metal-hybrid composites in crash applications. In comparison to structures which are in particular exposed to static loads and therefore designed to exhibit maximum component strength, crash applications are designed to fail in a continuous process to achieve maximum energy consumption. The outlined research illustrates the enhanced failure behavior of pin-structured plastics/metal-hybrid composites and the increased energy consumption under impact loading. Moreover, a comparison between pin structuring and laser structuring with regard to the obtainable mechanical properties under impact loading is given. Concluding, the current potential and weak points in the simulation of plastics/metal-hybrid structures using FEA is presented and discussed.     

Untersuchungen über das Kleben von Blei

Investigations into adhesive lead joints Lead plate thoroughly prepared for adhesive joining can be connected with other materials with the aid of resin-based adhesives. Picked surface yield higher strengths in the adhesive joint than do surface roughened by mechanical action. Hot-curing epoxy-based adhesive on picked surface yield adhesive strengths superior to the cohesive strength of lead as established in the tensile test. Adhesives requiring high compressive loads for curing, or adhesives based on vinyl resins are not suitable for use with lead. Overlapping joints may neutralize just small fractions of the tensile shearing forces. In such cases lead will become detached from the adhesive layer because of its high degree of deformation. At elevated temperatures, however, the adhesive strength of the adhesive on lead is often superior to the shearing strength of the joint; as a consequence thereof, the lead itself will fail. Adhesive joints with lead can bear temperatures up to 70°C for a long time without any loss of strength. Glass fibre roving embedded in the adhesive layer may increase the tensile strength and yield advantages as far as processing technology is concerned. Lead-coated parts may be deformed even after adhesive joining.     

Corrosion behaviour of reactor coolant system materials in nuclear power plants

The materials used for the pressure‐retaining parts of reactor coolant system components in light water reactor nuclear power plants have to meet special requirements in terms of their mechanical properties, workability and in‐service performance. Corrosion issues play an important role in connection with plant operating conditions. While giving consideration to the specific service environment of the reactor whether a pressurized or boiling water reactor – the materials used for the individual components and the water chemistries employed in the various systems are selected such that metal loss due to general corrosion will remain very low. Thus the materials used in light water reactor plants exhibit a high general resistance to corrosion for their specified service conditions, material conditions and mechanical loads. However, under certain operating conditions other corrosion mechanisms may be found to induce damage. This paper uses data from the literature, published results of national and international research programs, information on damage which has actually occurred world‐wide and experience gained by Framatome ANP GmbH (former Siemens/KWU) in this field as a basis for discussing these mostly localised corrosion phenomena in terms of “classical” corrosion systems. Aspects associated with irradiation and its effects are not considered. Suitable remedial actions are, however, addressed wherever these are of relevance. The materials considered comprise unalloyed and low‐alloy steels, austenitic chromium‐nickel steels as well as high‐nickel steels and nickel‐base alloys which are exposed to the reactor coolant environment of boiling water reactor or pressurized water reactor plants, including materials investigated in corresponding water environments simulated in the laboratory.     

Fundamental principles for choosing steels on the basis of results of wear tests

The development of scientific foundations for the creation of new high-strength steels with high wear resistance and their application is a very important problem of modern engineering. The difficulties of its solution are connected with the absence of methodological foundations for a reliable estimation of the wear resistance. The fundamental scientific principles for control over this characteristic with allowance for the structural changes and the corresponding changes in the mechanical properties of steels have not been developed. The place of this characteristic and its relationship with the structure in the theory of fracture of materials under various loads has not been determined yet. At the same time, the wear resistance is a parameter that can characterize the operational reliability of steels under various conditions. However, the methods for determining the wear resistance should be substantiated experimentally and theoretically. The aim of the present work consisted in choosing steels for parts operating under the conditions of composite loads and abrasive wear. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 2, pp. 28–30, February, 1998.     

陶瓷模具材料的使用性能研究

介绍了当前在拉拔、挤压、冲裁、等温锻造等各类模具中应用的陶瓷材料如金属陶瓷、ZTA，TZP,TZP／Al2O3，TZP／TiC／Al2O3，Al2O3／TiC，PSZ，Si3N4，Sialon等使用性能方面的研究现状，探讨了陶瓷模具材料研究与应用中存在的问题，展望了陶瓷模具材料的应用前景。提出陶瓷模具材料的增韧补强、模具结构优化设计和表面陶瓷化改性技术等将是提高陶瓷模具使用性能的有效措施，而且随着模具技术的迅猛发展，其应用前景也将日益广阔。     

Rauschmessungen zur Früherkennung der Korrosionsneigung mechanisch gefügter Bleche

Application of noise measurement for the early detection of corrosion property of mechanical joined metal sheets In the area of mechanical joining an active development is to be registered. The use of new materials, new rivet forms, new protective layers, changed production technologies, use of mixed materials, changed medial loads, demanded long‐term guarantees etc. let arise various old and new questions regarding the corrosion resistance. Conventional corrosion testing methods often give only insufficient answers to these questions. With the use of the electrochemical noise it is possible to receive meaningful results over material and construction characteristics within a short time since a metal surface constantly sends signals over its condition, even if one does not measure. Apart from the possibility of determining the probability of corrosion also certain processing errors and surface defects can be proven with noise measurements. Thus the application of this method offers possibilities for the process optimization and quality assurance of mechanically joined construction units, or also for the estimation of existing joining connections.