Response Surface Approximations for Fatigue Life Prediction

Response surface methodology is used to construct response surface approximations for the fatigue life of structures with complex geometry and/or loading conditions. The smooth nature of the response surface approximations eliminates numerical noise, which is inherent to the numerical analysis procedures used to estimate the fatigue life. Procedures for constructing the required response surface approximations, as well as for implementing the resulting approximations in the design process, are discussed. The durability of a structure is introduced into the design process by including the minimum fatigue life as a constraint in a minimum weight optimization of the structure. The smoothness of the response surface approximations allows the use of a derivative based optimization in the design process. Two example problems, typical of the automotive industry, are evaluated to illustrate the proposed methodology. Both example problems have structures modeled by plate elements and the objective of the optimization problem is to find the optimum thickness distribution for a minimum specified fatigue life. It is shown that the thickness