Experimental investigation of trans-scale displacement responses of wrinkle defects in fiber-reinforced composite laminates

Wrinkle defects were found widely existing in the field of industrial products, that is, wind turbine blades and filament-wound composite pressure vessels. The magnitude of wrinkle wavelength varies from several millimeters to over one hundred millimeters. The detection and quantificationally evaluation of these defects are critical for structural integrity assessments. This study introduces a meso-mechanical model using the homogenization method, which calculates the effective stiffness of graded wrinkle defects. Finite element analysis (FEA) predicts a trans-scale out-of-plane displacement response in wrinkled laminates, with the maximum displacement ranges from nanoscale to millimeter scale. To address this, we utilized shearography (Speckle Pattern Shearing Interferometry) for nanoscale displacements and fringe projection profilometry (FPP) method for larger displacements. In FPP method, a displacement extraction algorithm was presented to obtain the out-of-plane displacement. Comparative analysis indicates that shearography possesses higher sensitivity, capable of detecting load responses as low as 10 N, whereas FPP requires a load range from 200 N to 1000 N. The FEA-validated measurement errors for shearography and FPP are within 3.3%–7.1% and 2.8%–10.5%. The comparison of measurement sensitivity and accuracy between shearography and FPP provides a quantitative reference for industrial non-destructive tests.