Effect of the laminate thickness on the composite strength to repeated low energy impacts

The influence of laminate thickness on the resistance to repeated low energy impacts of glass, carbon and aramid fabrics reinforced composites, was evaluated for two levels of energy of impact. The results obtained show that below a certain energy level the cross section of the laminate is the most relevant variable that determines the impact resistance. Under these conditions the experimental points of all tested laminates fall on a single curve, irrespective of the reinforcing fiber used. When the energy level of the impactor is increased, fiber characteristics became relevant. The glass fabric reinforced composite showed the steepest increase on the impact resistance with increasing laminate thickness. This behavior was attributed primarily to the higher areal coverage of the glass fabric used. The isotropic behavior of glass fibers in relation to the anisotropic character of aramid and carbon fibers was also of relevance. A quadratic equation was shown to provide a best fit to the experimental points, and the coefficient of the quadratic term was shown to reflect the increase of the impact resistance with laminate thickness.