A NOVEL FIXTURE DEVELOPMENT TO CHARACTERIZE COMPRESSION AFTER IMPACT DAMAGE OF UNIDIRECTIONAL THERMOPLASTIC COMPOSITE LAMINATES

Impact testing of unidirectional thermoplastic composite materials is a challenge due to the Mode I shear of the primary tows on the impact side. Thermoplastic composite products manufactured using laminate stacking are bonded together with films of polymer on both sides of oriented fiber in typically a cross-ply or quasi-isotropic stack. The resulting failure from the distortion field imposed by a hemispherical tup is debonding along the interface between layer 1 and layer 2 oriented in the layer 1 direction from impact site to edge of panel. This failure mode results when the sample is too small relative to the weave pattern and fixturing resulting in more damage than will be witnessed on a large panel. The conservative estimate of impact strength would be appropriate for designing near edges of panels. In order to characterize an effective mid-panel impact toughness with standard Compression After Impact (CAI) fixturing, samples were created with additional length of the primary tows while still being able to fit in the CAI fixturing. Impact Energy was obtained using a Drop Tower Testing Machine. Damage zones were measured using backlit photography after the impact event. Specimens were machined post impact to allow for ASTM D7137 CAI testing to be conducted.