Issue 8

K. G. Kodancha et alii, Frattura ed Integrità Strutturale, 8 (2009) 45-51; DOI: 10.3221/IGF-ESIS.08.04 50 Fernandez et al . [19]. The effect of variation of K I for specimens with a/W=0.4, 0.5 and 0.6 are also studied. A typical plot of effect of a/W ratio on variation of K I for specimen thickness 10 mm is shown in Fig.10. This figure illustrates that the nature of variation of K I along the crack-front is almost similar for various a/W ratios. But, the magnitude of difference in K I ( δ K I ) estimated by 2D and 3D analyses measured at the centre of the specimen thickness is found to vary with respect to specimen thickness. For the similar applied load it is observed that ( δ K I ) is higher for a/W=0.6, which indicates that the specimen experience high crack-tip constraint at the centre than other specimens with a/W < 0.6. The T-stress results obtained in the present analysis together with corresponding K I values can be used for analysis of constraint effects in a fracture specimen. The 3D results indicate that the magnitude of T-stress and K I are lesser on the surface than the centre of the specimen. Compared to 2D results one can infer from these results that the crack-tip constraint is very high at the centre of the specimen than at the surface. The constraint effect on the surface is referred as in-plane constraint and at the centre is referred as out of plane constraint [20]. Due to higher out of plane constraint the material at the centre of the specimen thickness fails earlier than on the surface. The constraint also depends on the specimen a/W ratio. The present results infer that the specimen with higher a/W ratio experiences highest crack-tip constraint. The 3D results obtained in this study can also be used to formulate/correct two parameter characterization of crack-tip fields proposed by Betegon and Hancock [5]. Figure 9 : Variation of K I along the crack-front for various specimen thicknesses. Figure 10 : Variation of K I along the crack-front for various a/W ratio and specimen thickness 10 mm. C ONCLUSIONS ollowing conclusions are made from the present study: - The magnitude of T-stress and K I varies along the crack-front; the variation depends on the specimen thickness and a/W ratio of the specimen. - Crack-tip constraint is very high at the centre of the specimen than at the surface because of higher magnitude of T-stress and K I at the centre of the specimen. - Due to higher out of plane constraint the material at the centre of the specimen thickness fails earlier than that on the surface. A CKNOWLEDGEMENT uthors gratefully acknowledge the computational facilities provided by Research Center, B. V. B. College of Engineering & Technology, Hubli, and ProSim, Bangalore. F A