Research Of Fatigue Damage Analysis Method Based On Loading Sequences

Fatigue damage is one of the most popular damage types which come out in mechanical engineering area. When analyze problems about fatigue damage propagation of metallic material or structures, loading sequences effect must be considered. Although those models about fatigue which can resolve the problem of loading sequences effect on fatigue damage to some extent, there are still a lot of problems about loading sequences effect on fatigue problems need to be solved.In fact, fatigue damage is a phase-developing process, mainly contains four stages: cyclic hardening/softening; crack nucleation; crack propagation and structures or components’failure. And crack propagation can be divided into micro-crack and macro-short-crack propagation stage and macro-long-crack propagation stage. In the stage of micro-crack and macro-short-crack propagation, loading sequences effect on crack growth definitely. In order to analyze fatigue problems conveniently, combining with loading sequences effect on fatigue damage, the paper divides the fatigue damage propagation into three stages, which are cyclic hardening/softening stage; crack nucleation and short crack propagation stage and macro long crack’s subcritical propagation and fracture stage. Then the paper constructs a three-stage model of fatigue damage, describes loading sequences effect on fatigue damage by Kramer model, crack opening model and Miner rule respectively.In three-stage model of fatigue damage, each stage of the model occupies differently length of time, which depends on material, machining methods, heat treatments, loading styles and so on. In order to validate the stage model, the paper assumes D1=0.3, D2=0.5, accomplishes simulated experiments and actual experiments by Aluminum2024-T4,45steel,16Mn steel and AISI4130steel, respectively.Validated experiments demonstrate that the stage model can reflect mechanism of metallic material or structures reasonably, and accumulative damage calculated by stage model is better than Miner damage and Kramer damage. Results testified that although the model can be used to analyze fatigue problems, there are still a lot of problems about three-stage-model need to be solved, such as instability and inaccuracy of the model. In the meantime, the model needs to be compared with other nonlinear fatigue damage models.