Competition between Arbitrarily Oriented Tunnel Cracks and Delamination

We propose a method for quantifying the competition between tunnel and delamination cracking in laminates. Based on the analytical relation between the compliance derivative and the energy release rate, which we refer to as the compliance method, the competition between the two damage mechanisms is investigated based on compliance maps that may be precomputed, thus providing an efficient tool for predicting damage development in laminates without ad hoc fracture simulations. Tunnel and delamination cracking in an off-axis layer, much thinner than the load-carrying layers of a laminate, are used as an example to illustrate the proposed methodology. However, the compliance method is generalizable to any parameterizable cracking mechanism. The cracks are simulated in a specialized two-dimensional off-axis finite element framework, which fully captures the three-dimensional solution. The method is validated against the energy balance method for tunneling cracks and the virtual crack closure technique for delamination cracks. The method has great potential in the context of nondestructive testing, where future damage states can be predicted from precomputed or experimentally determined compliance maps, thus reducing computational and experimental costs.