An experimental/analytical comparison of three-dimensional deformations atthe tip of a crack in a plastically deforming plate - I: Optical interferometry and experimental preliminaries

A critical examination of measured and computed three-dimensional deformati ons in the vicinity of a crack in an elastic/plastic plate subjected to thr ee-point-bending are presented in a series of three papers. The aim is to a pply interferometric measurement methods to the large plastic deformation a t the tip of a crack in a ductile steel, and to assess the current ability to model that deformation numerically Comparison between the precise interf erometric measurements and the finite element model, which has been closely matched to the physical specimen, including internal tunneling of the crac k, indicates good agreement up to 75 percent of the ultimate failure load; above that level, discrepancies increase to levels on the order of 25 perce nt. It also develops that out-of-plane measurements are less than optimal f or deducing in-plane stress and deformation states. This finding implies co nsequences for working with caustics and similar methods when applied to cr acks in plastically deforming solids. This first paper presents a description and assessment of the experimental methods and outlines the fracture experiment itself. The second paper descr ibes the material characterization to closely match the finite element mode l to the physical fracture specimen, as well as a description of the finite element model itself. The third paper presents the results of the comparis on between experiment and model, as well as some additional results from th e numerical model alone.