Probabilistic three-dimensional fracture mechanics and its applications using fcpas

Abstract

Cracks can be seen in many engineering structures. It is important to determine the mechanical strength and life of the cracked structure or design a mechanical part with a damage tolerance approach. It is hard to determine the remaining life of machine parts exactly, since they include some uncertainties and variations in governing parameters of the problem, such as geometric dimensions and the variability of material properties and loading conditions. Therefore, for such problems, crack growth lives must be estimated by means of probabilistic approaches considering the variables that affect lives.

In this study, for three-dimensional fatigue crack growth problems, a probabilistic crack growth life estimation procedure, which also involves Monte Carlo Simulations, was developed and validated by controlled laboratory experiments. The uncertainty in material properties affecting fatigue crack propagation life was determined using standard Compact Tension (CT) specimens machined from 7075-T6 aluminium alloy. Fatigue crack growth models for constant or variable amplitude loading in the literature were investigated and an improved model has been proposed. The data obtained from two-dimensional crack propagation tests were used in three-dimensional crack propagation simulations. A non-standard specimen made from Aluminium 7075-T6 has been designed for three-dimensional mode-I fatigue surface crack growth tests. Surface crack growth experiments under constant and variable amplitude loads were conducted using this specimen. Fatigue crack growth simulations were also carried out by considering the geometric tolerances of the specimen, the scatter of the fatigue crack growth-related material properties and the variability in loading. Experimental results were compared with simulations for different crack growth models, allowing validation of the proposed probabilistic fatigue crack growth methodology.