Improved Probabilistic Modeling of Multi-Site Fatigue Cracking

The purpose of this paper is to investigate the effect of fatigue, in the presence of neighboring cracks, and to integrate that into a model that could be used to predict crack growth. A total of 20 fatigue experiments were performed at different loading conditions using dog-bone samples of API-5L grade B carbon steel containing neighboring cracks. The impact of the neighboring cracks dimensions and the loading conditions on the interaction, coalescence and growth of cracks were investigated. A design of experiment approach to study neighboring cracks interactions and growth in carbon steel materials is also presented. Simulation efforts were performed to assess the Stress Intensity Factor (SIF) around neighboring cracks. Models discussing how the SIF of single semi-elliptical crack could be corrected to account for the neighboring cracks interaction were discussed in order to better understand the fatigue behavior. A combination of these models was integrated to find the SIF values necessary for the probabilistic life prediction modeling purposes. Finally, a multi-site fatigue crack growth rate model was developed and its parameters including their uncertainties were estimated. A Bayesian approach was adopted to perform uncertainty characterization and model validation.

Cracks Interaction in a Pre-Stressed and Pre-Polarized Piezoelectric Material

ABSTRACTWe formulate and solve the mathematical problem for antiplane cracks in a pre-stressed and pre-polarized piezoelectric material with static initial fields, assuming the initially deformed configuration of the body is locally stable. Using the boundary conditions of antiplane cracks, we get the Riemann-Hilbert problems. Nonhomogeneous linear complex differential equations having the unknown complex potential are obtained. For constant value of the applied incremental forces can be obtained the complex potentials, incremental displacement and stress fields corresponding to the third mode of the classical fracture. The problem of interaction of two collinear, unequal cracks in a pre-stressed and pre-polarized piezoelectric material, is also studied.

Evolution Mechanisms of Thermal Shock Cracks in Ceramic Sheet

Knowledge of crack initiation, propagation, and corresponding thermal shock failure evolution is prerequisite for effective maintenance of civil engineering so as to avoid disaster. Experimental analysis of the cracking in the ceramic sheets subsequent to water quenching has been conducted. Based on statistical mesoscopic damage mechanics, it was revealed that there are four stages in the process of thermal shock evolution of ceramics subjected to water quenching. The multiple cracks interaction mechanism has been analyzed from the viewpoint of the evolution of the elastic strain energy and stress intensity factor.

Benchmark for the Calculation of Quasi-Laminar Elliptical Cracks Interaction Under Bi-Axial Loading

In the frame of the Structural Integrity demonstration of the Doel 3 and Tihange 2 RPVs flawed with quasi-laminar cracks, alternative proximity rules based on 3D eXtended Finite Element Method (X-FEM) calculations have been developed by Tractebel Engineering. The calculations have been performed with the X-FEM software Morfeo Crack. This software uses the Level-Sets method allowing a very straightforward cracks modelling. A large part of the development of these proximity rules for quasi-laminar flaws has been dedicated to the validation of the models and the calculations. This validation has been done through a benchmark with Engineering Mechanics Corporation of Columbus (Emc2). This company uses: • The Finite Element Alternating Method (FEAM) for calculating stress intensity factors through the FRAC@ALT program. The FEAM is a state-of-the-art method for obtaining stress intensity factors for three-dimensional surface and embedded crack problems. • The X-FEM functionality as implemented in Abaqus software. The benchmark consists of the Stress Intensity Factor calculation of interacting quasi-laminar flaws and of the interaction factor assessment as well.