Multiscale shear-strain gradient for detecting delamination in composite laminates

Delamination is a typical failure mode in composite laminates. For detecting delamination, a new physical concept of a multiscale shear-strain gradient (MSG) is formulated from a vibrational mode shape of a Kirchhoff plate. In a laminate containing a small delamination, the MSG characterizes shear-strain singularities with an explicit physical implication and no need for material properties, in turn manifesting the distribution of the delamination; moreover, multiscale property enables the MSG to identify delaminations at a high noise level. Numerical and experimental results show that the MSG defies the traditional understanding that vibrational features are inappropriate to localize a slight delamination.