Study on post-buckling crack propagation in thin-walled cylinders under dynamic cyclic load

Abstract

Buckling is a critical failure mode of the Fast Reactor Main Vessel (FRMV) subjected to seismic load. Post-buckling stability of FRMV is a crucial safety issue during excessive earthquakes. Our prior study revealed that global response becomes stable after buckling by phase-inverse mechanism. However, local fatigue cracks can initiate, penetrate and propagate under cyclic load. In the present study, shaking table experiments using cylindrical models are carried out. The post-buckling crack propagation process is experimentally observed and its mechanism is analyzed. It is shown that dominant cracks always propagate in circumference direction along the diagonal of the diamond-shape buckling dimple. Rapid collapse due to unstable crack propagation never occurs. Instead, a stable propagation mode is observed, where crack growth rate declines with crack circumferential angle. This stability is owing to the displacement-controlled characteristic of dynamic load, which results from the increasing frequency ratio due to crack propagation. Furthermore, a simplified evaluation method based on the estimation of J-integral under displacement-controlled condition is applied to predict the crack growth rate. The comparison with experimental data shows a satisfactory agreement. As a complementary study on global stability of FRMV, the present study confirms a local stability mechanism after buckling, contributing to a more comprehensive understanding on the post-buckling behavior of FRMV.

Keywords

• fatigue crack propagation
• thin-walled cylinder
• post-buckling
• fast reactor
• beyond design basis events