Analysis and modeling of the strain distribution and evolution during a fatigue test in ULCF and LCF on a friction stir welded specimen from steel and aluminum

Under cyclic loading in ULCF and LCF regimes the strain plays a fundamental role in the analysis of the fatigue resistance and in the estimation of the fatigue life. The DIC method, which allows to acquire strain and deformation in large areas is applied in order to obtain the maximum reached strain, strain range, mean strain and SWT parameter during a fatigue test on a friction stir welded specimen. Since the distribution of these variables in the region of interest shows a geometry given by a symmetric bell, a Gaussian model is considered to model it. The evolution of these variables during the fatigue test up to failure is fitted by applying a third grade polynomial. The obtained results, show the plausibility of the proposed method to model the strain distribution and evolution under cyclic loading.