Microscale strain distribution measurement before and after crack and delamination occurrence in CFRP laminates by multiplication sampling moiré method

The multiplication sampling moiré (MSM) method achieves a strong noise-immunity deformation measurement by performing phase analysis of the second harmonic of grating patterns, which surpasses the limitation of the conventional sampling moiré method that produces phase errors when the first harmonic is submerged by the background noise. In this study, the multiplication sampling moiré method was utilized to investigate the fracture behavior of a [±15°]2s carbon fiber reinforced plastic (CFRP) laminate specimen under different tensile loads. The full-field microscopic strain distribution maps, including the normal, shear, and principal strains, were successfully measured on the cross-section of the CFRP laminates with fiber discontinuities. The results show strain distribution characteristics before and after transverse crack occurrence in the matrix resin region of the CFPR laminates, and the changes in shear strain at the interlayer interfaces before and after the emergence of delamination. The MSM method holds promise for evaluating mechanical properties, fracture behavior, characterizing strain distributions, and residual stresses in deformation measurements of various structural and composite materials.