An experimental study into impact wave propagation in cross ply composite plates.

To gain insight into the problem of impact on to composite materials this work has examined experimentally the characteristics of stress waves propagating through a multi layered plate due to a surface impact. Theoretical and numerical techniques have been developed for an impulsive line load acting on the upper surface of a four layer cross ply plate. These resolve the surface and inter lamina disturbances caused by the passing stress waves due to a normal line impulse onto a plate. The objective of this work was to examine the wave propagation in a cross ply plate with experimental techniques and compare the wave characteristics with the analytical predictions. To detect the passing of the stress waves on the surfaces and at the ply interfaces a piezo electric sensor was developed using polarized homopolymer of vinylidene fluoride (PVDF) film. The responses collected from surfaces and mid plane of the impacted plate were dominated by the low frequency contribution of the impact, so the high frequency shear wave responses were extracted with digital filters. The experimental results presented show that when the limiting wave velocity in the plate was that of a Rayleigh type surface wave the largest disturbance in the plate occurred on the upper surface of the plate, and that when the limiting wave velocity in the plate was that in an internal shear wave and the largest disturbance occurred at the mid plane of the plate. These results demonstrated that the presence or absence of shear waves could be resolved experimentally at the surfaces and ply interfaces of a multi layered material. A good correlation was seen between the experimental results and the analytical results which provided some verification for the analysis method