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In this study, the impact-damage tolerance of a graphite-fiber/epoxy composite laminate is studied by examining the correlation between the impact force and the resulting delamination area in the laminate. The cross-ply [0 2 /90 2 /0 2 ] s composite laminate was made of thermosetting P7051S-20Q-1000 prepregs (Toray Composites America). A Hopkinson pressure bar (HPB) was employed to create the impulsive loading with varying magnitude. Transient impact force, displacement, impact power, and transmitted impact energy were calculated using the transient signals recorded from the strain gage mounted on the HPB. Impulsive loads with controllable magnitude were used to induce delamination damage with varying size in the composite samples. Nondestructive evaluation based on a novel ultrasonic pulse-echo reflector technique was used successfully for characterizing the delamination areas in the thin composite samples with thickness ~2 mm. The present experimental results indicate that there exists a very good linear correlation between the impact force (e.g. the peak force, impact impulse, peak impact power, and the transmitted impact energy of the first impact force pulse exerted by the HPB) and the delamination area of the composite samples. This correlation can be used to determine the threshold of the impact force that initiates the delamination damage in the composite laminate. In contrast to the weight-drop test, the present experimental method successfully examined the impact damage tolerance of polymer matrix composites (PMCs) subjected to impulsive loading with very high force magnitude and ultra short duration such as the typical ballistic impact. The present method and results can be used for the study of impact damage tolerance of PMCs with varying lay-ups and interface modifications.

The main goal of this study is to examine the size effects including both in-plane dimensional and thickness effects for laminated woven E-glass–epoxy composite subjected to low velocity heavy mass impact. The studies have been carried out with plate dimensions of 150 × 150 mm, 150 × 100 mm and 150 × 50 mm for in-plane dimensional effect. Two nominal thicknesses with averages of 1.4 and2.8 mm are used for studying the thickness effect. The impact testings are conducted with a vertical drop-weight testing machine developed in the department laboratory. Affixed to the drop-weight device, a piezoelectric force transducer, localized in the hemispherical impactor nose, yields the complete force versus time history of impact event. Impact tests are performed at increasing impact velocities 1, 2 and 3m/s and impactor mass of 2.6 kg on clamped plates. A numerical evaluation of these specimens is also carried out by using 3DIMPACT transient dynamic finite element analysis code. The contact forces between the impactor and the composite plate as functions of time, transient stresses during impact and the predicted delamination sizes of composites are found numerically.