Fatigue Crack Bending and Growth from a Precrack under Mixed-Mode Condition. Based on Discontinuous Displacement along Cracks with a Center-Hole Notch.

Abstract

Fatigue crack bending and growth behaviors were studied under mixed-mode conditions, using annealed and fatigue slant precracks with a center-hole notch. The crack growth direction was estimated from the stress intensity factors KI (mode I) and KII (mode II) evaluated from the discontinuous displacements along the precrack, using the maximum tangential stress criterion, and it was in good agreement with the measured ones. The fatigue crack propagation rate during bending was controlled by the effective stress intensity factor range ΔKeff using KI and KII, in which a total critical displacement ahead of the crack tip under the mixed-mode condition is adopted as the fracture criterion based on the BCS crack theory. After the crack was bent, the subsequent fatigue crack propagated under the mode I behavior at the crack tip; therefore KI determined from the discontinuous displacements could be regarded as ΔKeff for the bent crack.