Behavior of laminated composite structures subjected to low velocity impact

ABSTRACT The purpose of this thesis is the evaluation of the dynamic behavior of fiber- reinforced laminated composites under low velocity impact. An experimental and numerical investigation has been carried out to study the transient response of E- glass/epoxy composite. The numerically computed contact force history is compared with the same experimental results. The importance of the impact velocity, the impactor mass, the dimensions and the thickness of the composite plate are determined for laminated composites subjected to low velocity impact. A vertical drop- weight testing machine is developed in the Mechanical Laboratory for the low velocity impact test. Affixed to the drop-weight device, a piezoelectric force transducer, localized in the hemispherical impactor nose, yields the complete force versus time history of the impact event. Impact tests are performed at increasing impact velocities 1 m/sec, 2 m/sec and 3 m/sec, and impactor masses of 135 g and 2600 g. The studies have been carried out with plate dimensions of 150 mm by 150 mm, 150 mm by 100 mm and 150 mm by 50 mm with two opposite sides clamped and the other two free and the impact load is applied at the center of each plate. Unidirectional and woven fiber form is selected for laminated composite materials with different stacking sequence. A numerical evaluation of these specimens is also carried out by using 3DIMPACT transient dynamic finite element analysis code. The contact force between the impactor and the composite plate, maximum transverse deflection at the center of the plate, stresses and strains during impact are plotted, as functions of time and the predicted delamination sizes of composites are determined numerically. Finally, results are obtained by numerical simulation and experimental testing of the dynamic behavior of composite material and an approach to the problem of optimum design of composite plates subjected to low velocity impact is presented.