The indentation of plain woven glass cloth and chopped strand mat reinforced plastic materials by wedge indenters was accomplished in order to get the general rules on the indentation of composite materials by wedge indenters. The both phenomena of failure and fracture were obtained by means of optical method as same as used in previous report. And the fracture mode of glass fibers and yarn is strongly affected by that how the fibers are restrained to move in the specimen. The main results obtained are as follows: (1) The failure range which occurs in the wedge indentation appears at the point of intersection of yarn for plain woven glass cloth reinforced plastic materials. The area and shape of this fracture range are strongly affected by the inclination angle of yarn to the side of rectangular specimen. (2) The fracture of yarn is almost partial helical buckling fracture. In the case of wedge angle is 160°, breaking of yarn appears at deeper part than helical buckling fracture. (3) For the chopped strand mat, the fracture range of fibers is very small compared with that of plain woven glass cloth and the fracture mode of helical buckling fracture takes place rarely in this case.
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