ENERGY-BASED VERY LOW CYCLE FATIGUE CRACK GROWTH SIMULATION FOR SEISMIC APPLICATION

In the previous studies, the energy-based damage model was developed by simulating cracked pipe fracture behaviour under seismic loading. The multi-axial fracture strain energy density, the parameter of energy-based damage model, was determined by standard tensile test data and monotonic cracked pipe test data. Very low cycle fatigue crack growth was simulated by applying the multi-axial fracture strain energy density under monotonic loading. When the previous energy-based damage model was applied to simulate cracked pipe fracture test under seismic loading, the simulated results were good agreement with experimental data under high load amplitude reverse cyclic loading and displacement controlled large scale cyclic loading. However, the conservative predicted results are shown in pipe test with low load amplitude and different load ratio. In this paper, the energy-based damage model was improved by incorporating the effect of load amplitude and load ratio on multi-axial fracture strain energy density. The cyclic multi-axial fracture strain energy density increased by depending on the load amplitude and load ratios. The improved damage model was applied by pipe fracture test under seismic loading with various load amplitudes and load ratios. The pipe tests were subjected by using circumferential through-wall crack (TWC) and surface crack (SC) pipe specimen. The seismic loading consisted of two load amplitudes and two load ratios. The simulated results were compared with experimental data and validated.