split Hopkinson pressure bar method [10] is used. Quantitative loading for the bi-material is possible by a split Hopkinson pressure bar method. A moment when the elastic wave propagates in the bi-material specimen is observed by high-speed camera. Adapting digital image correlation to some images captured by high-speed camera, deformation and strain distribution of the bi-material are investigated. 22.2 Bi-material Figure 22.1 shows the schematic figure used in this study. Figure 22.1a is the bi-material composed of two different materials. Acrylic resin and polyurethane resin are used for the bi-material. An acrylic bonding agent is used for making the bi-material. Single material specimens made from acrylic and polyurethane resin are also prepared to compare the deformation behavior of bi-material and single material. Impact load is applied to the left side of the specimens, then the impact deformation behaviors at the front side of the specimens are observed. 22.3 Impact Test and Observation Figure 22.2 shows the experimental equipment of split Hopkinson pressure bar method for the impact test. This experimental equipment is composed of a striker (1,000 mm length), an input bar (2,500 mm length) and an output bar (1,300 mm length) made from steel having the diameter of 16 mm for each, and specimen is attached in between the input bar and the output bar. The striker is launched by the release of the compressed air, and the striker impacts the input bar. Then, the impact load is imparted to the specimen through the input bar. The particle velocity of the input bar is 5.91 m/s. High-speed digital camera (SHIMADZU corporation, HPV-2) with the resolution of 312 260 pixels and two halogen light sources are set in front of the specimen. A strain gage is put on the input bar at the position of 1,200 mm from the right end. The delayed pulse generator gets signal from the attached strain gage, and generates trigger for the high-speed capturing, when elastic wave reaches the specimen on the input bar. Frame rate of the recording is 1,000,000 frames/s. The number of the capturing images is 100 frames. Figure 22.3 shows the specimen set in between the input and the output bar. The white and black random pattern are painted on the specimen surface. To use digital image correlation, random pattern is prepared. In Fig. 22.3, the area surrounded by the white broken line is the capturing location. Fig. 22.1 Geometry of specimen. (a) Bi-material, (b) single-material (acrylic resin or polyurethane resin) 142 Y. Oishi et al.
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