Estimations of mechanical properties and fatigue life in pre-strained conditions

In this paper, the effects of tensile pre-deformation on material properties and fatigue life are investigated. For this purpose, a series of tensile fracture tests and fully reversed cyclic mode load-controlled tests have been performed on the tested 430 Stainless Steel in as-received condition and for the same tested material pre-strained at room temperature. Tensile pre-strain, eTP; conditions were induced at three levels: 5%, 8%, and 12%. Experimental observations on tensile properties, fatigue strength coefficient, and exponent were done and are represented in this study. Empirical formulas were developed in polynomial form to estimate the tensile properties in pre-strained condition. Meanwhile, in this study, two empirical relationships for estimating fatigue strength coefficient and exponent using ultimate strength have been proposed and the corresponding approximation of S-N curves based on the Basquin equation form have been developed. The approximation of the S-N curve has provided good predictions with most predicted lives within the factor 4 bound, but 73% of the predicted lives were still within the factor 2 bound. In consideration of the pre-strain effect on material behavior, a modified energy parameter (DWP)(T) was chosen and provided a more accurate prediction of reversals to failure for all pre-strained samples.