Papers by Keyword: Plasticity Theory

Abstract: Comparative analysis of the use of the defining equations of plasticity theories obtained at the loading step in three ways is performed. In the first method, the relations between strains increments and stresses increments are obtained by differentiating the governing equations of the small elastic-plastic deformations theory between full stresses and strains. In the second method, the authors based on the proportionality hypothesis between the component deviators of strains increments and the component deviators of stresses increments without separating the incremental strain into elastic and plastic parts obtain the determining equations at the loading step. In the third method, the relations between the incremental strain and the stresses increment of the plastic flow theory are used on the basis of the hypothesis about the proportionality of the plastic deformations increments to the components of the stress deviator. Based on the analysis of algorithms for obtaining the constitutive relations and the analysis of the numerical results of the calculation example, preference is given to the second method of obtaining expressions between stress increments and strain increments without separating the latter into elastic and plastic parts.

Abstract: The article represents the theoretical basis for the generation of virtual material models with the given crystallographic orientation (CGO) of the structure in metals and alloys with the cubic crystal lattice. The obtained functional interrelations allow to take into consideration a metal sheet CGO in technological calculations of metal forming processes and, most significantly, a priori by means of calculations to determine the structure CGO meeting the requirements of increasing the materials formability and the product performance. It is given an example of the implementation of the calculated CGO of the structure while rolling can sheet from aluminum alloy 3104.

Abstract: Anisotropy of properties is known to be a fundamental material characteristic, which stems from its crystal structure and texturing under plastic deformation. The influence of an anisotropy on the processing and service characteristics of products can be not only negative, but also positive. In this article in order to efficiently use anisotropy of properties in metal forming processes it is described a variation of anisotropic medium plasticity theory with reference to material deformation characteristic and it is analyzed the effect, produced by anisotropy on material behavior in different technological operations (drawing, bending, stretch-forming, etc.). As a result, intensification of deformation processes, increase of production efficiency and improvement of product quality and serviceability become possible.

Abstract: Constitutive plasticity theory is commonly applied to the numerical analysis of welds in one of three ways: using an isotropic hardening model, a kinematic hardening model, or a mixed isotropic-kinematic hardening model. The choice of model is not entirely dependent on its numerical accuracy, however, as a lack of empirical data will often necessitate the use of a specific approach. The present paper seeks to identify the accuracy of each formalism through direct comparison of the predicted and actual post-weld residual stress field developed in a three-pass 316LN stainless steel slot weldment. From these comparisons, it is clear that while the isotropic hardening model tends to noticeably over-predict and the kinematic hardening model slightly under-predict the residual post-weld stress field, the results using a mixed hardening model are quantitatively accurate. Even though the kinematic hardening model generally provides more accurate results when compared to an isotropic hardening formalism, the latter might be a more appealing choice to engineers requiring a conservative design regarding weld residual stress.

Abstract: The computer modeling results for direct extrusion of porous powder billets on a basis of the plasticity theory relations are presented. Distributions of stress-strain state parameters and density during direct extrusion of hollow detail from copper powder billet have obtained. The optimal value of backpressure, that ensures a uniform stress-strain state and given density of detail have found. The dependences of backpressure value from relative depth of cavity and extrusion pressure from backpressure are recommended.