Numerical analysis for the thermal ageing effect on fracture behaviors of CF8A pipes and piping systems under monotonic and very low cycle fatigue loading conditions

In this research, the effect of thermal ageing for CF8A is studied under displacement-controlled low cycle fatigue. Virtual tests of pipe and pipe system are considered and they have the same shape and loading conditions as the pipe and pipe systems tested in Battelle. Only material was changed from A106 Gr. B to CF8A. The pipe tests are four-point bending tests with three different load ratio (R= -1, 0, 1) having through-wall crack. The pipe system test also has through wall crack with seismic loading condition (PGA=1g). To simulate the cyclic loading and thermal ageing effect, multi-axial fracture strain energy based FE damage model and thermal ageing constant "C" was applied. From the simulation, it can be known from the virtual pipe test that crack growth rates of unaged and aged CF8A become similar when loading type is changed from monotonic to cyclic. Also, it is can be known from the virtual pipe system test that the crack growths of unaged and aged CF8A are almost same when the size of through-wall crack is 43.2 ^o . However, the crack growth of unaged CF8A is almost 25% smaller that aged CF8A when the size of through-wall crack is 90 ^o .