Newly proposed yield criterion for residual stress and steady state creep in an anisotropic composite rotating disc

Abstract

Processing of composites containing whiskers and short fibers often result in anisotropy due to preferential alignment of reinforcing element during flow as in extrusion. Residual stress originates in these materials during cooling from high temperatures, often involved during processing, resulting in different yield stresses in tension and compression. In absence of any accepted yield criterion to describe plasticity of such materials, the present study proposes a new yield criterion, which, at appropriate limits, reduces to Hill anisotropic and Hoffman isotropic yield criterion. Analysis of steady state creep in a rotating disc made of composites containing silicon carbide whiskers has been carried out using newly proposed yield criterion and compared with the results obtained using Hill anisotropic yield criterion ignoring difference in yield stresses. The material parameters characterizing anisotropy and difference in yield stresses have been used from experimental results of other studies. Stress and strain rate distributions developing due to rotation have been calculated and compared for both the criteria. It is observed that the new yield criterion results in significant changes in the tangential stress distribution but similar radial stress distributions in discs with residual stress compared to those obtained following Hill’s criterion in discs without residual stress. The tangential residual stress in the disc increases the creep rate compared to that in the anisotropic disc without residual stress. This increase is more near the inner and outer radii. The presence of residual stress makes the radial strain rate tensile in the middle region while it remains compressive in the regions near the inner and outer radii. It is concluded that a study of anisotropy and the presence of residual stress in an anisotropic rotating disc have important engineering consequences to draw further attention to this problem.