ELECTRON-BEAM MOIRE STUDY OF FRACTURE OF A GLASS-FIBER-REINFORCED PLASTIC COMPOSITE

Using the method of electron beam moire, a small region at an interfac e of a [O2/90]s glass fiber reinforced plastic composite has been exam ined during tensile testing. The tensile test was conducted inside a s canning electron microscope, with a high spatial frequency line gratin g (10,000 lines/mm) at the interface between a longitudinal ply and a transverse ply. During the test, this region was observed at a magnifi cation of 1900 x . Local strain measurements were made by interpreting the moire fringe patterns over gage lengths that varied from 10 to 30 mum. The magnitude and distribution of the local strains depended on the damage that occurred with monotonically increasing load. Load shed ding by the transverse ply was evident from the fringe patterns. Extre mely high local strains were observed: longitudinal fiber strains up t o three percent, normal strains up to three percent, and shear strains up to 40 percent in the epoxy matrix.