Tunneling cracks in arbitrary oriented off-axis lamina

The steady-state energy release rate for tunneling cracks under mixed-mode loading is determined using finite element analyses. The balanced and symmetric laminate layup [0/θ/0/-θ]s is investigated, where the tunneling crack is located parallel to the fiber direction of the central off-axis oriented layer. It is found that for the steady-state situation, a simple energy balance calculation of the released energy of the separated crack surfaces for a fully developed crack gives the same value as the average value of a detailed J-integral analysis of the crack front. Furthermore, the crack front mode-mixity, obtained by the same energy balance calculation, was found to give a good prediction of the average mode-mixity found from a detailed stress intensity calculation along the crack-tip. Based on this simplified energy balance approach, the energy release rate is determined for all angles θ ∈ ]0;90]∘for orthotropic elastic properties ranging from typical low modulus glass fiber reinforced polymers to high modulus carbon fiber reinforced polymers. The predicted results can be used to investigate the influence of the layup angles on static and fatigue tunnel crack evolution in composite materials used within, e.g. automotive, aerospace, and wind energy applications.