Mixed Mode Partitioning in Beam Like Geometries: A Semi Analytical Cohesive Analysis

摘要

The importance of mixed mode fracture testing of composite laminates and adhesive joints is outlined in section 1 of this paper. It is seen that there is currently no general consensus as to how mixed mode loadings should be partitioned in the case of asymmetric geometries, and experimental evidence exists supporting both local and global partitioning techniques. It has been noted from previous numerical work by the authors, that the mode partition is not just dependent on loading and geometry, but also, in the case of asymmetric fractures, strongly dependent on the nature of the fracture process zone which develops during fracture, and that the upper and lower bounds of partitioning are given by the original analytical local and global partitioning. Building on numerical work that has been presented previously, it is observed that a unique dependency exists between the cohesive zone length scale (l_(nd)) and the mixed mode parameter, f, where f is introduced to linearly average between the lower and upper bounds of local and global partitioning according to eq. 1. Based on this observed unique dependency, a new partitioning scheme (SACA) is proposed, where the mode partition is calculated based on the predicted cohesive zone length scale. This new partitioning scheme, which requires the input of cohesive properties, substrate elastic properties and an assumed failure locus, provides a quick and efficient method of estimating accurate mixed mode partitions. The SACA method is used to predict the mode partition of numerical cases carried out in, and good agreement is obtained between the measured and predicted values.