The variant of a continuum model describing joint deformation and accumulation of microdamages in elastic-brittle materials is presented. The microdamageability is considered as the process of origin of a system of flat elliptic or circular microcracks randomly dispersed over volume, the concentration of which increases with a load. The damageable material is simulated by the continuous medium, for which the elastic symmetry and nonlinear law of deformation are attributed to the pattern of the microstrength distribution, microfracture mechanism, and the mode of the stress state induced in the body. The model provided is used to describe the possible mechanism of non-linear deformation for practically all materials within the range of small strains.
Purpose The purpose of this paper is to consider an approximate model of accumulation of microdefects in a material under repeated loading which makes it possible to define theoretical parameters of the fatigue failure (durability, fatigue limit, etc.). The model is involving the relevant law of distribution of ultimate (yield) stresses in the material of these members in combination with the basic characteristics of main mechanical properties of a material (ultimate and yield stresses and associated standard deviations). Design/methodology/approach The model of fatigue failure of brittle and elastoplastic materials based on the use of the structural-probabilistic approach and up-to-date ideas on the mechanism of material fracture is proposed. The model combines statistical fracture criteria, which are expressed in terms of damage concentrations, with the approximate model of microcrack accumulation under repeating loading of the same level. According to these criteria, the fatigue failure begins with the accumulation of separation- or shear-type microdefects up to the level of critical values of their density. Findings The failure mechanism is associated with the accumulation of dispersed microdamages under repeated loading. The critical value of the density of the microdamages, which are identified with those formed either by separation or shear under static loading in consequence of simple tension, compression or shear, is accepted as the criterion of the onset of fatigue failure. The fatigue being low-cycle or high-cycle is attributed to accumulation of shear microdamages in the region of plastic deformation in the former case and microdamages produced by separation under elastic deformation in the latter one. Originality/value The originality of the paper consists in the following. The authors theoretically define parameters of the fatigue failure (durability, fatigue limit, etc.) using the model in combination with the statistical failure (yield) criteria appearing in the damage measures. The constructed fatigue diagram has discontinuities on the conditional boundary dividing domains with the shear-type and separation-type fractures of structural elements. Such results are supported by the experimental results.
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...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.