Deformation and strength properties prediction of metals with uniformly distributed closed pores under single and cyclic loading

The paper deals with predicting deformation and strength properties of metallic materials with defects uniformly distributed over the product volume in the form of gas bubbles under single and cyclic loadings. The proposed approach is based on the use of the corresponding characteristics of a defect-free material (stress-strain diagram, plasticity resource, curve of deformation in a cycle and cyclic deformation curve, and fatigue curve) and the results of numerical experiments on samples models with different volume fractions of defects (degree of porosity of the medium). We analyze the stress-strain state of the virtual samples using the finite element method in ANSYS. The moment of reaching the limiting state-discontinuities - was recorded with a monotonous loading using the deformation criterion of V.L. Kolmogorov. Under single loading, the elastic constants and stress-strain curves are determined up to the moment of destruction of the model medium simulating a material with different porosity (a possible change in the deformation mechanism due to distortion of the gas bubbles wall shape accompanied by plastic flow of the matrix material was not taken into account). The property of the central similarity of the stress-strain curves is noted. Under cyclic loading conditions, both deformation curves in a cycle representing the trajectory of the state point in “the stress ~ strain” space during the cycle and the cyclic deformation curve, i.e. the stress amplitude versus the strain amplitude, reflecting the hardening (weakening) of the material of various porosity degrees are obtained. The description of the fatigue curves characterizing the strength properties under these conditions was carried out using the local Manson-Langer type criterion. The results can be used to normalize the allowable defect size and density and to assign the reasonable safety factor for stress, strain and durability of a real porous medium.