Composite material II type crack growth rate measuring method capable of acquiring crack growth S-N curve

A composite material II type crack growth rate measuring method capable of acquiring a crack growth S-N curve comprises five steps: 1, a single end-notched flexure (ENF) composite material sample is selected and formed through molding fiber cloth and resin; 2, the sample is tested through a three-point bending manner; 3, a triaxial movable high power digital measurement system is adopted to observe and measure the crack growth length, and the test load, the cycle index and the corresponding crack growth length are recorded; 4, the constant interface shear stress of a neutral surface of the composite material is worked out according to the engineering beam theory, and a three-parameter power function is adopted to fit the crack growth interface shear stress and the corresponding cycle index so as to obtain the crack growth S-N curve; 5, a dual-growth exponent function is utilized to fit the test load cycle index and the a-N curve of a corresponding crack growth length, and the crack growth rate is obtained after derivation; a Paris model and an energy release rate formula are adopted, and a crack growth rate curve is obtained through least-squares approximation.