oa Behavior of porous materials under asymmetric dynamic loading

Background and Objectives: Stress concentration around cavities and cracks strongly influence the fracture and fatigue properties of porous materials. Microcracks that form around discontinuities in the material such as cavities link up to form macrocracks leading to substantial degradation of material mechanical properties. The dominant factor aiding the formation of microcracks is the stress concentration. The study investigates the dynamic stress concentration around different size oblate spheroidal cavities due to shear waves in an infinite elastic medium. Methods: As the available analytical methods are only applicable to simple shape cavities, hybrid methods have been presented to study the stress concentration around different shape cavities embedded in an elastic medium. The method used combines the finite element method with analytical procedure for elastic wave propagation in an elastic medium. The accuracy of the method was verified by analyzing a spherical cavity. Results: Different shape oblate cavities are investigated under varying frequencies of shear waves and different matrix material properties. The stress concentrations within the matrix are found to be dependent on the frequency of incident shear wave, aspect ratio of the cavity and the Poisson's ratio of the matrix. Conclusions: The study reveals that the dynamic stress concentration can reach much higher values than the static case. Dynamic stress concentration factors as high as 6 result for low aspect ratio cavities of 0.2 and even values of 6.6 with a materials Poisson's ratio of 0.45.