Fatigue life prediction of critical metallic components based on strain energy density

The realistic loading condition in most of the mechanical applications is cyclic where fatigue failure is the most possible failure mode. Fatigue failure can occur under the stress levels well below the static strength of the material. Total fatigue toughness is a new energy-based approach for fatigue modeling that has shown promising correlation with fatigue life of engineering metals, shape memory alloys and polymeric materials. In total fatigue toughness method, fatigue damage parameter is defined as the sum of dissipated strain energy density (Wd), which is calculated as the area encompassed by the loading and unloading paths in a stress-strain graph, and tensile elastic strain energy density (W_e^+), which is defined as the maximum linear-elastic strain energy density that is stored in the material per each cycle. In this study, we have investigated applicability of the total fatigue toughness method on fatigue life prediction of popular engineering metals, i.e. steel, aluminum and titanium. To this end, strain-controlled fatigue tests with different strain ratios and maximum strains were conducted on specimens designed according to ASTM standards. For each of the experiments the total fatigue toughness damage parameter was calculated and the correlation with experimentally observed fatigue lives were evaluated. The results showed that the total fatigue toughness damage parameter can closely correlate the experimental fatigue data obtained for three types of materials under different mean strain conditions.