Isoparametric Elements as Singular Elements for Crack Problems.

摘要

The quadratic isoparametric elements, which embody the inverse square root singularity, are used for calculating the stress intensity factors at tips of cracks. The elements used are the quadratic quadrilateral (8-node), quadratic triangular (6-node) and three-dimensional quadratic brick (20-node) elements. Singularity elements are obtained in a simple manner by placing the mid-side nodes at quarter points in the vicinity of the crack tip or an edge. These elements are implemented in NASTRAN as dummy (user) elements. The method eliminates the use of special crack tip elements and in addition, these elements satisfy the constant strain and rigid body modes required for convergence. The stability of two-dimensional elements is also investigated. (Author)