Effect of incident angle on crack propagation at interfaces

• When the process zone is small, applying a mode I displacement results in a K-field.
• Small incident angles promote deflection.
• At small angles, penetration versus deflection depends primarily on strengths.
• Changes in the magnitude of normalized toughness has little effect on transition.

The effect of incident angle on crack deflection versus penetration has not been widely studied using a combined stress-and-energy criterion. This work does so by using a cohesive-zone method and dimensionless parameters. Results show deflection becomes more likely as angle decreases with greatest sensitivity to angular change at large angles. Deflection becomes increasingly strength-ratio dependent at small angles due to a shared crack-tip stress field. As fracture length scale decreases, deflection becomes more likely. Normalized toughness is shown to have a small effect on results. Significant is the insight provided on propagation behavior and the simplification in the use of a stress-and-energy criterion.