Abstract: 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. An experimental system for measuring interlaminar crack strain field of CFRP cross-ply laminate samples based on sampling moiré method is established. The system consists of a three-point bending test loading device, a microscope, an industrial camera and a CFRP sample with a nanoim-print grating. In this paper, the system is used to measure the strain field in the loading process of the specimen, and the strain con-centration degree before the specimen begins to bend to crack initiation is 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 the crack initiation, and with the increase of bending load, the strain concentration in the central region increases significantly, while the strain concentra-tion in the surrounding region does not change significantly. The experimental method developed in this paper can accurately meas-ure the strain field of CFRP laminates before crack initiation and predict the location of crack initiation effectively.

Key words: Sampling Moiré method, Carbon Fiber Reinforced Polymer, strain field measurement, crack initiation, Experimental mechanics