Deformation measurement of carbon fiber reinforced plastics using phase-shifting scanning electron microscope Moiré method after Fourier transform

Abstract

The deformation distributions of carbon fiber reinforced plastics (CFRP) under a three-point bending load were nondestructively investigated using the phase shifting scanning electron microscope (SEM) moire method. The complex fast Fourier transform (FFT) and the discrete Fourier transform (DFT) were used to filter the useless moire fringes in the case of bidirectional moire fringes. The SEM moire fringes under different magnifications and the deformation results measured by the direct, complex FFT- and the DFT- phase shifting moire methods as well as the moire fringe centering method were compared and analyzed. Experiments demonstrate that the deformation measurement is a bit influenced by the useless moire fringes in the phase shifting moire methods and complex FFT processing works better for nondense moire fringes. The relative strain changes gradually and the specimen grating pitch increases gradually from top to bottom along the loading direction, suggesting that the real compressive strain is greater in the upper side. The micro/nano-scale deformation distribution characteristic is helpful for better understanding of the mechanical properties of the CFRP specimen.