PREDICTION OF CRACK PROPAGATION DIRECTION USING PHOTOELASTIC TECHNIQUE

Abstract

The majority of service failures of structural parts are of the mixed mode type. That is because of the lack of -geometric and load symmetry, the direction of crack propagation is not necessarily known as priori. Hence to utilize the potential of fracture mechanics technology to predict the direction of the crack propagation angle, photoelastic technique is used in this dissertation work. Two types of specimens namely, Centrally Cracked Specimens (CCS) and Side Edge Notch (SEN) specimens were considered. 10 Centrally Cracked Specimens were used with crack inclination angle from 00 to 900 with increment of 10° and 9 SEN specimens were used with crack inclination angle from 100 to 900 with increment of 10°. Both types of specimens were fabricated from photoelastic material. Mode I and Mode II mixed mode load condition was obtained by considering the inclined cracks and applying uniaxial tension for both type of specimens. To predict mixed mode crack propagation direction (K1/K11) ratio was obtained by using photoelastic methods of Smith [27] and Dally and Sanford [26]. Four Criteria, namely M-(Maximum stress triaxiality ratio), MTS-(Maximum Tangential Stress), S-(Minimum Strain energy density for plane stress and plane strain condition) and T-(Maximum dilatational strain energy density) were applied. Analysis procedure adopted involves the determination of mixed mode stress intensity factor K1, K11 and far field non-singular stress 6 oX , using K-N relation developed by Dally and Sanford [26]. The method of solution involves an iterative numerical procedure based on the Newton-Raphson technique. For the over deterministic approach arbitrarily located 4 points from each of 4 fringe loops were selected from the fringe field and then the method of least square was employed to fit the K-N relation to the field data in order to determine K1, K11 and a ox .