A Methodology of Design for Fatigue Using an Accelerated Life Testing Approach with Saddlepoint Approximation 2019-01-0159

We present an Accelerated Life Testing (ALT) methodology along with a design for fatigue approach, using Gaussian or non-Gaussian excitations. The accuracy of fatigue life prediction at nominal loading conditions is affected by model and material uncertainty. This uncertainty is reduced by performing tests at a higher loading level, resulting in a reduction in test duration. Based on the data obtained from experiments, we formulate an optimization problem to calculate the Maximum Likelihood Estimator (MLE) values of the uncertain model parameters. In our proposed ALT method, we lift all the assumptions on the type of life distribution or the stress-life relationship and we use Saddlepoint Approximation (SPA) method to calculate the fatigue life Probability Density Functions (PDFs). Finally, a design for fatigue is performed where a Reliability-Based Design Optimization (RBDO) process is developed to optimize the system’s characteristics (model parameters, fatigue and/or material properties) which are subject to probabilistic constraints. This optimization problem determines optimal values of system parameters to achieve a fatigue reliability target. We will demonstrate all developments using a representative example.