Early fatigue damage evaluation based on nonlinear Lamb wave third-harmonic phase velocity matching

•Third-harmonic phase velocity matching nonlinear Lamb waves are used for the early fatigue damage detection of aluminum alloys.•The third harmonic first increases and then decreases with the accumulation of fatigue life. When the fatigue life reaches about 80%, the amplitude of the third harmonic declines sharply.•The third-order nonlinear parameters increase continuously with the accumulation of fatigue life. When the fatigue life reaches about 80–90%, the third-order nonlinear parameters increase gradually and shows a downward trend.•The third harmonic and third-order nonlinear parameters are used as indicators of fatigue accumulation to realize detection of early fatigue damage.