Fatigue crack growth under mixed mode I + III loading

• The maximum tangential stress criterion can be used for mixed-mode I + III fatigue.
• Transition length from mixed to pure mode I increases by increasing inclination angle.
• Fatigue lives increase by increasing crack angle and decreasing the pre-crack length.
• By increasing the thickness, the SIF values decrease for all modes.
• ‘Factory roof’ facets have little effects on path and extension of mixed mode cracks.

Mixed mode I + III fatigue crack growth is studied numerically and experimentally by using modified CT specimen. Some parameters such as initial angle and initial length of crack, thickness and load ratios can affect the fatigue behaviors. The crack growth path and surface, crack front length, variations of stress intensity factors, twisting of crack surface and fatigue lives were determined by using Franc3d and compared with experimental data. By increasing angle and length of initial crack, mode I effects decrease while mode III effects increase. Mode II of the fracture is almost negligible for the modified CT specimen.