Analysing Residual Stresses in Wind Turbine Blade Repair: A Hole Drill Method and Digital Image Correlation Approach

The primary reason for residual stresses in the wind turbine blade during the repair process is mismatch between the chemical shrinkage and thermal expansion coefficients of the base composite (blade) and the patch. These residual stresses have the potential to compromise structural integrity and require thorough investigation and quantification. Among the techniques used for measuring residual stresses, the hole drill technique is used. Digital image correlation (DIC) is employed to measure the strains around the hole both before and after drilling. Calibration coefficients which relate the relaxed strains and residual stresses are derived by finite element method. Subsequently, residual stresses are measured at various points on the patch and base composite near the patch/base composite interface and are compared with those predicted by the computational model from prior studies.