Cohesive zone modelling of Mode III delamination using the edge crack torsion test

Abstract

In the experimental studies of mode III delamination using the edge crack torsion test, the crack initiation and propagation measurement are always difficult. This information could be obtained through numerical modelling. The objective of this study is to propose a guideline to model mode III delamination behaviour using cohesive elements. Finite element models of an edge crack torsion specimen were developed based on the data from the literature. The delamination behaviour of the specimen along the pre-crack, which was located at the mid-thickness location, was modelled using cohesive elements. Through parametric studies, it was found that for reliable numerical modelling, a mesh size of 0.5 mm was suggested, which provided three elements in the cohesive zone. As for the interface strength, it was recommended to choose 80 MPa. In addition, a viscosity parameter of 110-3 was found to be a good choice for reasonable computational time and converged numerical results. Besides, the interface stiffness was suggested to be 4106 MPa/mm. Furthermore, the fracture process zone contour revealed that the delamination was started at a normalised location of approximately 0.7. Not only that, the fracture energy and strain distribution plots have shown the delamination was mode III dominated within the normalised distance of 0.34-0.86. The results from this study suggested that cohesive zone modelling is a useful method for the detailed analysis of the mode III delamination of an ECT specimen. The numerical modelling approach suggested from this study could be applied to ECT specimens at various different initial crack lengths. It also has the potential to be used to simulate the mode III delamination of other various types of laminated composites.

Keywords

• interlaminar fracture
• mode iii
• edge crack torsion
• cohesive zone modelling