Upper and lower fatigue life limits model using energy-based fatigue properties

Cyclic strain-life data and corresponding Coffin–Manson coefficients for both normal and shear strain-lives were first defined. Energy–fatigue life curves were then generated from strain-fatigue life properties. The upper and lower limits of life are estimated using the proposed life equations. The upper life limit is obtained by assuming that the dominant cracking mechanism is Case A and the lower life limit is obtained by assuming that the dominant cracking mechanism is Case B. The proposed method was developed based on physical evidences of crack initiation and growth as well as the amount of dissipated energy over life cycles. The fatigue life data fall between the upper and the lower limits resulting in a promising life prediction. The proposed method has been used to evaluate the fatigue life of various metallic materials of SAE 1045, AISI 304, Inc 718 and Haynes 188 reported in the literature. Results of fatigue life predictions were found in good agreement with experimental life data.