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 interface of a [O₂/ 90]_s glass fiber reinforced plastic composite has been examined during tensile testing. The tensile test was conducted inside a scanning electron microscope, with a high spatial frequency line grating (10,000 lines/mm) at the interface between a longitudinal ply and a transverse ply. During the test, this region was observed at a magnification of 1900 × . Local strain measurements were made by interpreting the moire´ fringe patterns over gage lengths that varied from 10 to 30 μm. The magnitude and distribution of the local strains depended on the damage that occurred with monotonically increasing load. Load shedding by the transverse ply was evident from the fringe patterns. Extremely high local strains were observed: longitudinal fiber strains up to three percent, normal strains up to three percent, and shear strains up to 40 percent in the epoxy matrix.