WSTRESS: Numerical Computation of Probabilistic Fracture Parameters. This document describes the theoretical aspects and commands necessary to use WSTRESS, a research code for computation of crack-tip fracture parameters based upon probabilistic fracture mechanics. WSTRESS calculates the Weibull stress, aw , and provides estimates for the Weibull parameters from fracture mechanics test data. Recent developments have focused on its application for analyzing the effects of constraint loss and ductile tearing on macroscopic measures of cleavage fracture toughness (Je , de). In particular, it now accommodates modeling of ductile crack extension offered by the finite element code WARP3D. WSTRESS implements a multiaxial form of the weakest link model applicable for a three-dimensional cracked solid; the Weibull stress, aw , then emerges as a fracture parameter reflecting the local damage of material near the crack tip. The formulation currently implemented in WSTRESS conveniently handles the inhomogeneous character of the near-tip stress fields and the spatial (random) location of microcracks. Computation of the Weibull stress is accomplished by integration of the local tensile stresses using a numerical scheme at the element level. Statistical inference of the parameters that describe the Weibull distribution of aw centers on the maximum likelihood method to yield efficient estimates for the Weibull parameters. Tabulated functions implemented into the code automatically provide the confidence intervals for these estimates. WSTRESS also supports statistical inference of Wei bull parameters for censored observations based upon a Type I censoring model for the Weibull distribution. This provides an additional facility needed when different populations of experimental data are present in the analyses. Specific features of the code also include a convenient free-form command language and a seamless interface with finite element results files stored in Patran binary or ASCII format

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  1. Ruggieri, Claudio; Dodds, Robert H. jun.: Numerical evaluation of probabilistic fracture parameters using WSTRESS (1998)