Predicting the effect of lightning strike damage on the structural response of CFRP wind blade sparcap laminates

The structural responses of carbon fibre reinforced polymer (CFRP) panels damaged by lightning strikes are evaluated using a multi-scale model. Material condition maps (damage/undamaged) obtained from a meso-scale lightning damage model are introduced into a structural scale finite element model. The multi-scale model uses buckling/post-buckling Riks’ simulations to predict stresses and displacements. The LaRC failure criteria is used to predict when a failure occurs in the panel. The predictions of the numerical modelling framework are validated experimentally against load-displacement data obtained from ten CFRP test panels manufactured at a scale representative of actual wind turbine blades. Varying degrees of damage were introduced into the panels using lightning strike intensities of 50, 75, 100, and 125 kA with 10/350µs waveforms. The representative panels were tested using a specifically designed test procedure named “Compression After Lightning Strike (CALS)”, which included a novel test fixture and the application of digital image correlation (DIC) to assess the load response of damaged and undamaged composite panels. The CALS test fixture allows the full extent of lightning damage in a large CFRP panel to be included. Stereo DIC was used on both sides of the CFRP panel to obtain the strain and displacement fields that developed during the CALS test. Thus, for the first time, the effect of a lightning strike on the load response and buckling/failure behaviour is determined experimentally at a representative scale. The results from the CALS procedure permitted a validation of the multi-scale model. The model predictions showed excellent agreement with the experimental panel shortening, out of plane displacement and predicted the panel failure loads to within 7.3% for all test cases.