Analysis of Strain Energy Behavior throughout a Fatigue Process

The dissipation of strain energy density per cycle was analyzed to understand its trend through a fatigue process. The motivation behind this analysis is to improve a fatigue life prediction method, which is based on a strain energy and failure correlation. The correlation states that the same amount of strain energy is dissipated during both monotonic fracture and cyclic fatigue. This means the summation of strain energy density per cycle is equal to the total strain energy density dissipated monotonically. In order to validate this understanding, the strain energy density per cycle was analyzed at several alternating stress levels with fatigue life between 10

3

and 10

5

cycles. The analysis includes the following: Alternating between high and low operating frequencies (50x difference), interruption of cyclic load during testing, and idle/zero-loading for intervals of 20-40 minutes between cyclic loading sequences. All experimental results show a consistent trend of cyclic softening as the loading cycles approach failure, which further validates the theories used in developing the energy-based fatigue life prediction method.