The influence of preloading on the ballistic properties of GFRP

Tensile tests were performed to obtain the quasi-static mechanical properties of glass-fiber reinforced plastics (GFRP) at the testing machine INSTRON 5942. Extensive ballistic tests have been carried out on GFRP panels using 6.35 mm steel ball. Special powder gun stand for acceleration of projectiles with terminal velocity up to 900 m/s was developed. The tests were carried out for plates without preload, and also for five preloading levels. For the experiments the ballistic stand was placed in an INSTRON 5882 testing machine. The sample was placed in the grips and the required tensile force was given, after then the sample was fired. The ballistic performance was assessed in terms V50 threshold as well as post V50 limit. After the tests, the material performance was compared at different preload levels. Ballistic curves for each preload level were plotted by experimental data. Also the dependence of ballistic limit versus preload level was obtained. Preloading reduces the ballistic limit of GFRP plates. Ballistic limit can be decreased by 15 % in comparison with 50 % preload of the tensile strength. Also, the dependence of the fiberglass delamination area versus initial velocity for each preload level was found. The fact that the response time to the rupture of the specimen after penetration depends on preload was noted as unusual phenomenon. The maximum rupture delay after penetration was about 8 seconds for the specimen loaded at 180 MPa. This delay occurs due to the creep of material and time dependence of strength.