Damage quantification in composite laminates based on sparsity-difference estimation of the normal time–frequency representation

•The time–frequency diagrams are obtained based on the Normal Time-Frequency Transform, and the characterization effect on Lamb waves is discussed.•A method to characterize signal differences by Singular Value Decomposition and Dynamic Time Warping is presented.•A new damage index is developed to quantify the damage in composite structures, and the matching performance of damage trends is investigated using experimental tests.