Displacement pattern matching and boundary-element methods for elastic-plastic stress analysis

A two-dimensional hybrid experimental-numerical technique for elastic-plastic stress analysis is presented. This technique results from merging two relatively new technologies in engineering mechanics: boundary-element methods and image processing. A syntactic pattern recognition scheme, termed displacement pattern matching (DPM), determines the displacement boundary conditions which are used in an elasticplastic boundary-element method (EPBEM) code. The result is an automated stress-analysis tool.Displacement pattern matching is a process where displacements are measured by tracking an arbitrary array of black spots on a white specimen. The digitized images of the specimen are compared in a double-exposure format to determine displacements. Displacement pattern matching is a full-field technique, with spatial resolution on the order of. 1 pixels.Displacement pattern matching supplies the actual specimen displacement increments to the EPBEM code which is based on a von Mises, isotropic work-hardening constitutive model. Given these displacements and free surface conditions, EPBEM is able to incrementally calculate the internal state of stress at selected locations. Results obtained for a variety of geometries and loading conditions compared well with ANSYS finite-element solutions and selected published experimental solutions and therefore are encouraging.