Crack Growth in Three-Point Bend Specimens Made of Polymeric Foams

摘要

The problem of crack growth in a three-point bend specimen made of polymeric foams is investigated. Polymeric foams are anisotropic materials and cracks, generally, propagate under mixed-mode loading. The axes of material anisotropy are inclined with respect to the crack plane. Due to the anisotropy of the material crack kinking occurs even though the applied load is symmetrical with respect to the crack plane. The study will take place within the frame of linear elastic fracture mechanics of anisotropic media. The strain energy density criterion will be used for the determination of the critical load of crack initiation and crack growth path under mixed-mode loading. The opening-mode and sliding-mode stress intensity factors are determined by a finite element program. A special circular core element surrounding the crack tip with 19 nodes is used. The core element is joined to the conventional 12-node quadrilateral element by requiring that the displacement at the nodes on the circumference of the core element match the corresponding singular solution. Results are obtained for the critical load of crack initiation and crack growth trajectories as a function of the orientation of the axes of material symmetry and the anisotropy of the material.