The effect of subsurface crack opening on the stress intensity factor under cyclic thermal loads

This study considers surface crack behaviour under periodic thermal loads using weight functions and finite element calculations. A surface and subsurface crack opening mode during the load cycle was observed. The subsurface mode where the crack mouth is closed while the crack tip remains open can be more critical for deeper cracks. Crack face contact is required to obtain the subsurface mode both with finite elements and weight functions. A combination of surface and subsurface weight functions can capture the crack behaviour throughout the load cycle. This behaviour is demonstrated using numerous simulations with periodic thermal loads with different extent and frequency.