Materials strength and acoustic nonlinearity: case study of CFRP

Nonlinear acoustic approach is assessed as a nondestructive tool for reconstructing stress-strain curves and quantifying the ultimate tensile strength for various orientations of composite materials. It is shown that a direct use of nonlinear acoustic data requires some adjustments to be applied in the quasi-static tensile conditions. The approach is validated by the calculations using the data for the two in-plane orientations of Carbon Fiber-Reinforced Plastic (CFRP) of totally different strengths. The higher strength arrangement manifests much lower nonlinearity, while the low strength orientation indicates the higher nonlinearity. The quantitative proof-of-concept test is based on the direct measurement of the acoustic nonlinearity for the out-of-plane orientation CFRP. Far higher nonlinearity measured correlates well with the lowest strength for this orientation being a reason of characteristic materials damage in the form of delaminations.