Development of Surface Crack Analysis Program and its Application to Some Practical Problems

Abstract

The authors have developed a software system called “SCANP™” by which users can analyze residual lives of surface-cracked structural components such as pressure vessels and their piping systems due to fatigue or SCC. The basic concept is based upon an influence function method by which the stress intensity factor “K” of a surface crack can be calculated for arbitrarily distributed surface stresses on the cracked surface. The authors and his group have developed a great number of database of “Kij”, the influence coefficient of the stress intensity factor, for many different types of surface-cracked structural components. The database is installed into the SCANP and the K-values for one of these cracks against an arbitrarily distributed surface stress can be calculated easily through the algorithm of superposition of the surface stress and the corresponding Kij data. The fatigue crack propagation can be simulated by integrating the Paris’ law, and it is easy to estimate the residual fatigue lives up to the leakage. Further, residual lives due to SCC, stress corrosion cracking, can be simulated by following the algorithm described in the JSME Standard. In this paper it is demonstrated how the SCANP works by applying it to some practical industrial problems such as fatigue crack and SCC crack propagations into welded residual stress field, and fatigue crack propagation initiated from double-surface cracks. In the latter case the simulation was compared with the experimental results in order to evaluate the validity of the developed system. It was found that the scatter of the material data describing the Paris’ law is far larger than the errors in estimating K-values, and therefore, the choice of these material data is very important when a user wants to use this program effectively. In order to use the developed program correctly, the authors have organized “SCANP User Meeting” where only the members can use the program. In the User Meeting the users give presentations about how they applied SCANP to analyze practical problems, and discuss about the validity of the modeling, and the computed results. In this paper some of these activities will be described, and the problem of verification, validation and uncertainty quantification is discussed.