Development of an Improved High Cycle Fatigue Criterion

Abstract

An integrated computational-experimental approach for prediction of total fatigue life applied to a uniaxial stress state is developed. The approach consists of the following elements: (1) development of a vibration based fatigue testing procedure to achieve low cost bending fatigue experiments and (2) development of a life prediction and estimation implementation scheme for calculating effective fatigue cycles. A series of fully reversed bending fatigue tests were carried out using a vibration-based testing procedure to investigate the effects of bending stress on fatigue limit. The results indicate that the fatigue limit for 6061-T6 aluminum is approximately 20% higher than the respective limit in fully reversed tension-compression (axial). To validate the experimental observations and further evaluate the possibility of prediction of fatigue life, an improved high cycle fatigue criterion has been developed, which allows one to systematically determine the fatigue life based on the amount of energy loss per fatigue cycle. A comparison between the prediction and the experimental results was conducted and shows that the criterion is capable of providing accurate fatigue life prediction.

An Energy Based Fatigue Life Prediction Framework for In-Service Structural Components

“…the minimum fully reversed point is observed as the origin), E is the modulus of elasticity, and the variables σ 0 , σ c , ε 0 and C are curve fit parameters described in [5]. These curve fit parameters for the cyclic and monotonic representations equations (1-3) are acquired by comparison between low cycle experimental results and experimental monotonic results, respectively.…”

“…The previously developed energy based fatigue models [4][5][6][7] assumed constant energy dissipation per cycle during the entire fatigue life. The assumption is adequate for most of the fatigue life but is questionable when internal microcracks are initiated during the final stage of the life.…”

“…This method consists of the following capabilities: uniaxial fatigue life at various stress ratios [4], tension/compression fatigue life prediction [5], bending fatigue life prediction [6], and shear fatigue life prediction [7]. The previously developed energy based fatigue model [4][5][6][7] assumed constant energy dissipation per cycle during the entire fatigue life. This assumption was adequate for most of the high cycle fatigue life but becomes questionable when internal micro-cracks are initiated during the final stage of the life.…”

“…It is shown that anelastic components become dominant at higher operating frequencies and convergence would be achieved at very low frequencies. In addition, the previous fatigue life prediction capabilities [4][5][6][7] are addressed more extensively to determine the changes of the hysteresis plastic energy dissipation during the life time/ cycles, especially, the final stage of the fatigue life. Transition of microstructure caused by cyclic loading was investigated.…”

“…It is now understood that the strain energy required to fracture a material, monotonically, is the same as the strain energy during a cyclic fatigue procedure, thus iterating that the critical energy value for each material is the monotonic strain energy. Based on this theory, an improved energy-based criterion has been developed to systematically determine fatigue life based on the amount of energy loss per fatigue cycle [4,5].…”