Heterogeneous plastic deformation in bimodal bulk ultrafine-grained nickel

Heterogeneous plastic deformation behavior of two bimodal ultrafine-grained nickel materials with different ultrafine-grained (UFG) and coarse-grained (CG) components fractions was investigated experimentally at the grain level. The prismatic specimens were deformed quasistatically up to 10% axial plastic strain using compression test at room temperature. The local microstructure of the initial and deformed samples was measured by electron backscattered diffraction pattern analysis in a scanning electron microscope. It was found that the plastic deformation of bimodal materials is highly heterogeneous and the degree of heterogeneity depends strongly on the grain size distribution and the volume fraction of the CG component. The large localized plastic strain within the coarse grains was observed during compression. The strain localization resulted in occurrence of debonding and cracks in the UFG region or in the interface between CG and UFG components.     

铝塑复合包材的开发应用

铝箔不仅质地柔软,延展性好,便于加工,而且轻便美观,回收容易,有利环保,是现代包装中最常用的材料之一.但因铝箔容易在包装、使用过程中形成针孔而降低其阻隔性能,所以铝箔常与高分子塑料聚合物、纸或其他金属薄板等制成复合材料使用.     

Constitutive equation of a non-simple elastic plastic material

Summary The mechanical response predicted by the constitutive equation of a non-simple elastic material is considered in relation to the total strain behaviour of an elastic-plastic solid extensively deformed in the range of plastic strain. Both loading and unloading are considered in relation to the range of total elastic-plastic strain. In the absence of appropriate experimental studies, comparison of the predictions of the proposed constitutive equation of a non-simple elastic material, when applied to the work-hardening behaviour of the material, has been restricted to a study of the characteristic stress-strain behaviour of a strain hardening material. This has centred on the correlation of stress-strain curves characteristic of the mechanical response of a material tested in simple compression, simple torsion and pure shear with the object of obtaining a universal stress-strain curve.With 1 Figure     

塑胶运动场地及其相应的塑胶材料

介绍了塑胶运动场地的种类、铺装技术及相应的塑胶材料.重点讨论了以聚氨酯、乙丙橡胶为主体的运动场地用的塑胶材料的特点和优势,并分析和阐述了运动场地用的塑胶材料的技术进展和发展趋势.     

铝塑复合包材的开发应用

铝箔不仅质地柔软,延展性好,便于加工,而且轻便美观,回收容易,有利环保,是现代包装中最常用的材料之一.但因铝箔在包装使用过程中容易形成针孔而降低其阻隔性能,所以铝箔常与高分子聚合物、纸或其他金属薄板等制成复合材料使用.实践证明,铝塑复合材料可大大提高包装的阻隔性,提高铝箔的强度,尤其适合制做复合软包装及包装衬里,广泛应用于食品、医药、化妆品等商品的包装.     

带缺口塑性材料的声发射特性研究

以带线切割加工缺口的碳钢在拉伸试验时的断裂过程为研究对象,通过对其产生的声发射信号进行检测和分析,研究其开裂时的声发射特性。试验结果表明:带缺口塑性材料在拉伸断裂过程中会产生幅值在47dB￣90dB范围内的声发射信号;信号的振铃累计数在材料的塑性变形段与裂纹稳态扩展段均与应变成线性关系,但后者斜率大于前者;试样缺口深度越大,材料开裂时间越早,振铃计数率越高,且信号能量累计数与应变成线性关系。     

Theory of stable crack growth in an elastic-perfectly plastic material

A theory of stable crack growth, for generalized plane stress conditions, is presented which is based upon a Dugdale model of plasticity and an energy balance approach to fracture. Several forms for the rate of energy dissipation in the plastic zone are considered. It is shown that the J-integral, when used in conjunction with the Dugdale model, may not be of direct relevance to the rate of stable crack growth. By introducing the well known concept of a fracture process zone, and incorporating it into an expression for the rate of energy dissipation in the plastic zone, a simple stable crack growth law is derived which is very similar to an existing relation based upon a final stretch fracture criterion.The energy balance approach is extended to derive the growth law for cracks propagating in test specimens subjected to point loads. The material may be non-linear elastic-plastic provided that the Dugdale model of yield is appropriate. It is shown how load-displacement records might be used to predict the amount of stable crack growth in linear elastic-perfectly plastic sheets having reasonably general geometries which are subjected to point loads.

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Résumé On présente une théorie pour la croissance stable d'une fissure dans le cas de conditions d'état plan de déformation généralisé, qui est basée sur le modèle de Dugdale de plasticité et sur une approche d'équilibre d'énergie jusqu'á la rupture. Diverses formes sont envisagées pour le taux de dissipation d'énergie dans la zône plastique. On montre que l'intégrale J, lorsqu' elle est utilisée en conjonction avec le modèle de Dugdale, peut n'être pas directement pertinente pour déterminer la vitesse de croissance stable d'une fissure. En introduisant le concept bien connu de la zône du processus de fracture et en l'incorporant dans l'expression donnant la vitesse de dispersion d'énergie dans la zône plastique, on dérive une loi de croissance stable et simple de la fissure qui est très similaire à la relation existante basée sur un critère de rupture par étirement final.L'approche de l'équilibre d'énergie est étendue afin de dériver la loi de croissance de fissure se propageant dans des éprouvettes d'essai soumises à des charges ponctuelles. Le matériau peut être non linéaire élastique-plastique pourvu que le modèle de Dugdale de l'écoulement plastique soit approprié. On montre comment les enregistrements charge-déplacement peuvent être utilisés pour prédire le taux de croissance stable d'une fissure dans des tôles minces à caractéristiques linéaires élastiques et parfaitement plastiques, et possédant une géométrie raisonnablement générale, et soumises à des charges ponctuelles.

     

谈食品用塑料包装材料安全性能检测鉴定(上)简

近段时间塑料制品有毒的问题弄的大家人心惶惶,而双酚A、塑料助剂、塑料添加剂等许多的塑料填料就成了人们首先开始怀疑的罪魁祸首了。针对食品塑料包装成“隐形杀手”造成的污染,论述了食品塑料包装的安全关系到消费者的健康和社会的安定和谐,研究了塑料食品包装材料的卫生标准及其危害分析,提出了食品塑料包装安全性能的鉴定和测评,同时指出了食品塑料包装有毒有害物质的预防。     

Wrinkling analysis of membranes with elastic–plastic material behavior

This paper concerns membrane wrinkling in conjunction with inelastic effects. A method will be presented, able to treat wrinkling in membranes with elastic–plastic material behavior. Some effort is spent to obtain a suitable initial guess for the internal wrinkling algorithm iteration, which improves the reliability of the method. The wrinkling algorithm is implemented into a FE–program and applied to structural analysis. Numerical and experimental results are discussed.     

Flow of pressure-dependent plastic material between two rough conical walls

Summary The present paper deals with a general thermodynamic framework for the modelling of temperature and rate dependent deformation behavior of anisotropically damaged elastic-plastic materials subjected to impact loadings. Based on the concepts of continuum damage mechanics, rate-dependent constitutive equations are derived from the first and second law of thermodynamics which are only based on a limited number of material parameters. Identification of the constitutive parameters is discussed and the applicability of the present continuum damage approach is demonstrated by numerical simulations of low and high strain rate tension tests. The evolution of different data is studied and compared with available experimental results.