Once assessment of material failure characteristics is captured precisely in a unified way, it can be directly incorporated into the structural failure assessment under various loading environments, based on the theoretical backgrounds so called Local Approach to Fracture. The aim of this study is the development of an expert system applicable for the assessment of structural integrity throughout crack initiation and structural failure based on the Local Approach to Fracture. The generalized elasto-visco-plastic constitutive equation, which can consider the internal damage evolution behavior, is developed and employed in the 3-D FEA code in order to numerically evaluate the material and/or structural responses. Explicit information of the relationships between the mechanical properties and material constants, which are required for the mechanical constitutive and damage evolution equations for each material, are implemented in an automatic system using genetic algorithm based on an inference system. The material constants selected from genetic search and constitutive equations are used directly in the failure assessment of material and/or structures. The performance of the developed system has been evaluated for the S-N relationship assessment of several materials as well as the crack initiation assessment of various weldments in steel structures.
In general, latent damage such as micro cracks and/or voids in welding joints may degrade the structural performance, increase maintenance costs, and reduce structural integrity. In this context, a number of studies have been carried out in terms of predicting crack initiation and/or propagation in weldments. In conjunction with finite element analyses, linear elastic fracture mechanics approach is well known as one of attractive methodologies regarding crack propagation problem among others. On the other hand, in terms of crack initiation, it is recognized that only limited number of methods are currently applicable.