STRESS SINGULAR ELEMENT APPLICATION TO FRACTURE PROBLEMS

Abstract

Stress singularity is developed in standard eight-node isoparametric finite elements, by shifting the mid-side nodes on the edges radiating from the corner node of interest to the quarter-points nearest that node. This feature is invaluable for use in the analysis of structural bodies with crack-like discontinuities; this analysis being particularly important for engineering development in Canada's northern and offshore regions. In these regions, extremely cold temperatures can lead to premature and sudden failure in structures that contain internal cracks, such as those imposed by welding. Consequently, a rational, cost-effective technique is required for the analysis of this type of problem. The modified elements are used to investigate the fracture behaviour of three classical cracked body problems for which a number of results are available: the isotropic rectangular plates with a central crack or with symmetric edge cracks, and the orthotropic square plate with a central crack. The strain energy release-rate approach is used to determine the Mode I stress intensity factor for each specimen, and these are compared to data available in the literature. Good agreement is obtained between the results of this analysis and those of other authors, even with the use of a very coarse finite element mesh. The approach is then applied to the analysis of a standard ASTM E-399 bend bar specimen, and the results compared to values obtained from actual experiments on similar specimens. The objective of this phase is to investigate the possible practical application of the method to actual crack problems. When compared to the results obtained from an E-399 analysis of a high strength steel alloy, the finite element approach again yields good a g r e emen t . The proposed approach is therefore regarded as an appropriate analytical tool for use in the study of cracked body problems, in materials that exhibit plane-strain behaviour.