Measurement of strain distribution in CFRP cross-ply laminate material based on sampling Moiré method

In recent years, the development of Carbon Fiber Reinforced Polymer (CFRP) in the aviation industry has attracted much attention. Quantitative evaluation of its fracture process and damage prediction has become the key of the research. This paper established an experimental system based on the sampling Moiré method to study the evolution of interlayer strain field of a CFRP cross-ply laminate sample. The system consists of a three-point bending device, a microscope, an industrial camera and a CFRP sample with a nanoimprint grating. Using this system, a full-field measurement of the microscale strain field in the loading process of the sample, and the strain concentration level before crack occurrence was quantitatively evaluated. The results show that the initiation of interlayer cracks in CFRP is directly related to strain concentration, and obvious strain concentration occurs before crack initiation. Compared with the region around the crack, the strain concentration in the crack center is more obvious before crack initiation. With the increase of bending load, the strain concentration in the central region increases significantly, while the strain concentration in the surrounding region does not change distinctly. In the experimental method used, when the set strain of CFRP surface image is 0.1%, the root mean square error of strain measurement is less than 5×10⁻⁵. This allows for accurate analysis of the strain field evolution of CFRP laminates before crack initiation and effectively predicts the location of crack initiation.