Measurement of Strain Distribution of Composite Materials by Electron Moiré Method

Abstract

It is very important to measure the local strain and stress distributions for understanding the mechanical properties of structural materials. Therefore, there are many techniques to measure the strain or stress distribution such as the strain gage method, optical elasticity method, optical Moire method, etc. In these methods, the optical Moire method (Weller & Shepard, 1948; Morse et al., 1960; Sciammarela & Durelli, 1961; Durelli & Parks, 1970; Theocaris, 1969; Post et al, 1994; Chiang, 1982; Post, 1988) is one of the convenient methods to measure the deformation of the materials. However, these methods are difficult to apply for deformation measurements from a microscopic aspect. To measure the micro-deformation in a very small area, the authors have developed an electron Moire method (Kishimoto et al., 1991, 1993) , and J.W. Dally, D. T. Read (Read & Dally, 1994; Dally &.Read, 1993) and H. Xie (Xie et al., 2007) advocated it. This method keeps the main advantages of the moire and laser moire interferometry methods, and has the additional ability of measuring deformation in a micro-area with a high sensitivity. Besides, the electron moire method also uses a wide range for measuring the deformation. The range of the measurable deformation is from 25microns to 0.1micron using a model grid with different pitches. To measure the micro-deformation i.e. sliding and slip lines in a smaller area, micro-grid method is very useful. Compare these two methods, electron moire method is easy to understand the strain distribution and the large sliding (Kishimoto et al., 1991, 1993). In this study, In order to pursue the application of the electron moire method, some typical experiments were performed. The strain distribution at the interface of the laminated steel, strain distribution of the fiber and the matrix in the fiber reinforced plastic, the thermal strain in or around the metallic fiber in Al alloy were observed.