Development and validation of an algorithm for the numerical implementation of the Virtual Crack Closure Technique

An algorithm for the implementation of the Virtual Crack Closure Technique (VCCT) has been developed to study the crack growth and to make available an accurate tool to predict failures. Griffith’s criterion is employed to evaluate the crack propagation by means of the computation of Strain Energy Release Rate (SERR) values, directly connected to the Stress Intensity Factors (SIFs) for isotropic materials. The VCCT is a powerful tool to efficiently estimate the actual SERR values at the crack tip by means of the implementation of the Irwin energy balance. The ANSYS Parametric Design Language (APDL) has been employed to generate a local mesh and to simulate the crack growth along an user defined path by means of the automatic release of paired nodes. The SERR for all fracture modes are calculated during the process. In order to validate the tool and to optimize the element dimensions, the numerical results have been compared with few well - known closed form solutions: • the single - edge notched (SEN) tensile specimen; • the central cracked (CCT) tensile specimen; • the double - edge notched (DEN) tensile specimen. The definition of the optimum ratio of crack size to element size has allowed to reduce the free - edge effect by mean of an accurate refinement of the local mesh. An application study of the tool has been the evaluation of the critical fracture points in a single - lap joint by mean of the comparison of the SERR versus crack length curves. Several different locations of crack initiation and growth are considered.