Features of elastoplastic deformation and fracture of hardened isotropic metals in a complex stress state (review)

Kaminskii, A. A.; Bastun, V. N.

doi:10.1007/bf00846994

Cited by 3 publications

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“…Denoting the loading path in the plane σ σ 11 22 − by σ σ 11 22 = n , we determine the direction cosines l 1 and l 2 appearing in (5.18) from (5.1) with l l [17,37,38]. According to the hypothesis from [96], the loading surface ( Fig.…”

Section: Stress-strain Analysismentioning

confidence: 99%

“…This method is based on a statistical analysis of a large body of initial experimental data obtained by experts of the Institute of Mechanics and other scientists and systematized and generalized in the monograph [37]. It was established in [8,9,17,37,38] that during loading along rectilinear and slightly curved paths, the loading surface extends (isotropic hardening) and displaces (kinematic hardening), preserving its shape, in the direction of the vector connecting its center with a representative point on the loading path. The displacement and extension are functions of the intensity of cumulative plastic strains invariant to the stress mode and the form of the loading path.…”

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Applied Problems in the Mechanics of Strain Hardening of Structural Metallic Materials

Bastun

Kaminskii

2005

Int Appl Mech

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Some applied problems of the mechanics of strain-hardening processes in metallic materials are considered. To solve these problems, the concept of loading surface, which separates the elastic and elastoplastic domains in the stress space, is used. Strain-hardening models are analyzed. For a wide range of steels and alloys, the most commonly used hypothesis of isotropic-and-kinematic hardening is experimentally justified Keywords: applied problems, strain hardening, metallic materials, loading surface Introduction. While manufactured, many metal members experience elastoplastic deformation. Examples of processes that induce such deformation are plastic working, hydraulic shaping of pressurized shells, expansion of welded large-diameter pipes, and autofrettage [7, 33, 37, 52, 54, 86, etc.]. Elastoplastic strains may also occur in members of space-rocket and aviation structures, which are characterized by a small margin of safety, during operation and in off-normal situations, under overloads.The elastoplastic deformation of polycrystallic materials, which include structural metals, is accompanied by structural transformations such as shattering and rotation of grains, formation of shear planes when parts of a crystal slide over each other, and preferred orientations (texture). The random orientation of crystals results in residual microstresses [36,51].Dislocation theory regards elastoplastic deformation as displacement of dislocations and increase in their density. The resistance of crystalline materials to deformation is determined by the mobility and density of dislocations. The stress fields of dislocations have a significant blocking effect on the hardening of materials [52].Some of the above-mentioned effects (shattering of grains, change of density and mobility of dislocations) lead to isotropic hardening, i.e., to approximately equal increase in resistance to deformation in different directions, while rotation of grains, preferred orientations and fibration, and residual microstresses make the hardening process directional. This results in anisotropy of mechanical properties. Its degree is determined by the contribution of one mechanism or another. In the case of unstable states, elastoplastic deformation is additionally accompanied by a change in the phase composition of the material. The physical fundamentals of strain hardening of metals are outlined in [7, 52, 57, 58, 64, etc.].Thus, elastoplastic deformation leads to unequal (in different directions) change in strength characteristics (yield points and ultimate strength). The change of the yield point was investigated most adequately in the case of a uniaxial stress state. Decrease in resistance to deformation due to reversal of the sign of the load is known as the Bauschinger effect, which is the simplest manifestation of strain hardening. The degree of strain hardening is determined by the ratio of yield points in two opposite directions, which is a measure of the Bauschinger effect.In the case of a complex stress state, strain hardening is judged fr...

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Section: Stress-strain Analysismentioning

confidence: 99%

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confidence: 99%