Experimental and Numerical Determination of Mixed Mode Crack Extension Angle

Crack initiation angles for mixed mode fracture are measured and predicted using photoelastic and finite element techniques. Different crack inclination angles (0 degrees, 10 degrees, 20 degrees, 30 degrees, and 40 degrees) are considered. The Schroedl and Smith method is used for estimating pure opening mode I stress intensity factor. On the other hand, the Sanford and Daily method is used to estimate stress intensity factors in mixed mode (I and II). The Smith and Smith method for estimating mixed mode SIF is also examined. In addition, the ANSYS finite element code is employed to estimate the pure and mixed mode SIF numerically. The estimated values of the SIF from both finite element analysis and photoelasticity are incorporated into six criteria for crack initiation angle prediction. The applicability of the crack initiation criteria such as maximum tangential stress (NITS), minimum strain energy density (S), maximum dilatational strain (T), maximum triaxial stress (M), modified NITS (MMTS), (R) criterion, and fringe symmetry axis method (FSAM) are investigated. An experimental setup is used to measure the initiation angles at different crack inclinations. The measured crack initiation angles are used to validate the predicted values. The results showed that the initiation angles estimated by different criteria using SIFs determined experimentally and numerically compared well with the measured ones, especially at higher inclination angles.