Papers by Keyword: Plasticity

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Authors: Xue Ping Zhang, C.H. Wang, Jia Cai Li, Yiu Wing Mai, Lin Ye
Authors: Alexander M. Korsunsky
Abstract: The sin2ψ technique for near-surface and bulk stress evaluation is frequently considered to be the method of reference, largely due to the historical reason of being established early on in the development of experimental study of residual stress, and due to the widespread availability of laboratory X-ray facilities equipped with goniometers allowing ψ-tilting to be carried out. In recent years other diffraction-based techniques of residual strain and residual stress evaluation have been developed, some of them based at large facilities such as synchrotrons, neutron reactors or spallation sources, and others becoming available in the laboratory setting. It is therefore perhaps relevant and timely to review the strengths and shortcomings of the sin2ψ technique in today’s context. In the present study this task is addressed through the use of polycrystal elasto-plastic modelling that allows the determination of equivalent average elastic lattice strains following complex deformation history, and by post-processing of the model results in order to extract the parameters measurable in diffraction experiments. In particular, it is possible to extract the simulated strain values that would be measured at different tilt angles, and to build a family of sin2ψ plots for different reflections. It then becomes possible to assess the degree to which the hypotheses underpinning the principle of this method are enforced or violated; to select the most suitable reflections; and to discuss how the method could be improved or varied to provide more reliable residual stress measurement procedures.
Authors: Jarosław Kaczmarek, Wiesław M. Ostachowicz
Abstract: In this paper we introduce nanoscale description of fracture in a single crystal in order to obtain foundations for modelling damage at more averaged scale. Nanoscale model of fracture is discussed together with nanoscale model of slip plasticity. Fracture systems and slip systems are introduced consistently by means of free energy. They enable us to express critical conditions for initiation of both crack and slip. Evolution equations which describe evo- lution of crack, slip and boundary of slip surface are introduced. Furthermore, we also discuss crack initiation and propagation on active slip surface. With the aid of variables characterizing damage at nanoscale level we discuss the form of damage tensor for more averaged model. One discusses larger context of nanoscale modelling in which the nanoscale models are considered as a segment of multiscale description of behaviour of materials.
Authors: Wen Li Zhang, Jian Guo Jin
Abstract: The forming property of clay is one of the most important processing properties. Mineral composition and plasticity of various kinds of clays were determined, and the relations among yield value, degree of deformation and mineral composition were analyzed. According to the relations between acting force and distance between colloidal particles in clay-water system, the determining method of plasticity index II was set up, and compared with the traditional determining methods. The results show that the determining method of plasticity index II can better reflect the effect of clays on the plasticity of body by the comparison of determined values in different ways with the actual plasticity of body, the plasticity indexes II of different kinds of clays have relations of summation with the plasticity of body. The forming property of clay can be reasonably evaluated by plasticity index II.
Authors: Xiao Yan Guo, Jin Zhi Zhou, Da Peng Feng, Hou Min Li
Abstract: The dynamic property of carbon filled rubber materials is related to pre-load, excitation frequency and amplitude etc. A model by superimposing an elastic model, a viscoelastic model and an elastic-plastic model is presented to model the dynamic property of a rubber isolator. In this paper, this approach is adopted to calculate the dynamic property of a rubber isolator. It is shown that the presented model can predict the amplitude and frequency dependency of a rubber isolator with small relative errors. The validity of this model is verified by experiment. The approach described in this paper can be used in the design and calculation for rubber isolators.
Authors: Yuan Tong Gu, Liang Chi Zhang
Abstract: This paper presents a concurrent multiscale method for the stress analysis of solids using a coupled meshless and molecular dynamic analysis. A new transition algorithm using transition particles was employed to ensure the compatibility of both displacements and their gradients. The equivalent continuum strain energy density was obtained locally based on the atomic potential and Cauchy-Born rule, and hence plasticity can be easily handled in not only the atomic domain but also the continuum domain. Numerical examples demonstrated that the present multiscale technique has a promising potential of application to multiscale systems subjected to deformation.
Authors: Khanh Dien Le, Tan Hung Nguyen, Ngoc Huy Tran, Thanh Son Le, Huy Bich Nguyen, Thanh Nam Nguyen
Abstract: Single Point Incremental Forming (SPIF) is a recent technology of forming sheet in several decades. Nowadays, SPIF technology is still continued to be studied, applied and ameliorated in sheet manufacturing in industry. However one of the difficulties of the technology is the forming angle is still small (smaller than 800 according the properties of metal sheets). This paper recommends a measure of increasing the plasticity of the sheet by heating in time of forming by SPIF technology. Naturally, the plasticity of metal sheet increases by the temperature of the material in forming process with its limitation and constraint. The paper represents the effect of heating metal sheet through the empirical process of SPIF technology directed by the design of experiment (DOE). The analyses of the results of experimental process is applied to show the effect of heating to the precision of Titanium sheet. Finally, some private opinions about the heating in SPIF are also mentioned as a very tiny contribution of the research for the new technology.
Authors: Qiang Hu, Zhi Heng Deng, Zhen Zhong Pang, He Yong Lu
Abstract: A simplified seismic design model on steel truss coupling beam is suggested based on compatible distortion and balance conditions, considering second order effect and perfect plasticity. This model regards web members of the coupling beam as constraints, thus just the chord need be studied instead of the whole truss. End moments and end shears of chords and relations between distortions of components of the truss and displacement of the coupling beam are established. So curve of load-displacement, plasticity formation and development and influences of area of web members on ductility are convenient to obtain. Results show that this model is more convenient and accuracy than finite element method. Finally some valuable conclusions about influences of span-to-depth ratio and area of web member on ductility of the coupling beam are acquired to contribute to design.
Authors: Sergei Alexandrov, Elena Lyamina, Yeau Ren Jeng
Abstract: Gradient theories of plasticity play an important role in the description of inelastic behavior of materials. Usually, these theories involve space derivatives of stress or strain. On the other hand, conventional theories of plasticity can be divided into two groups, flow and deformation theories. Each of these groups has its own area of applications. The main conceptual difference between the theories belonging to the different groups is that the primary kinematics variables in deformation theories are displacements (or strains) whereas in flow theories velocities (or strain rates). Therefore, it is of interest to propose a gradient theory of plasticity involving space derivatives of a measure of strain rate (strain-rate gradient theory of plasticity) and to compare qualitative behavior of solutions for the strain-rate gradient theory of plasticity and an existing strain gradient theory of plasticity. One possible strain-rate gradient theory of plasticity is proposed in the present paper. The equivalent strain rate (second invariant of the strain rate tensor) is used as a measure of strain rate. The Laplacian operator is adopted to introduce the gradient term. An analytic solution for expansion of a hollow sphere is given for two strain-rate gradient theories of plasticity and one strain gradient theory. Comparison of the solutions shows that some qualitative features of the solutions for the strain-rate gradient theories are in better agreement with general physical expectations than those for the strain gradient theory.
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