Repeated impact response of hand lay-up and vacuum infusion thick glass reinforced laminates

Vacuum infusion (VI) is being considered as a viable alternative to more traditional hand lay-up (HL). Main reason in favor of the more costly technique is the cleaner and friendlier work environment. Moreover, VI potentially offers another important benefit over HL in that prepreg levels of resin may be achieved, resulting in stronger and lighter laminates. The present paper compares the two manufacturing techniques on the basis of the response to repeated impact loading. The laminate is a thick non-symmetric glass fiber reinforced plastics intended for nautical application. Four impact velocities (1.5 m/s, 2.2 m/s, 3.1 m/s and 3.8 m/s) were considered, and a minimum of four specimens for any given velocity were subjected to forty repeated impacts or up to perforation. The impact response was evaluated in terms of damage progression by visual observation of the impacted specimens, evolution of the peak force and of the bending stiffness with the number of impacts and by calculating the Damage Index (DI), a damage variable recently proposed by the authors to monitor the penetration process in thick laminates. Results point out that for impact velocities for which no perforation occurs within test duration, the experimental data essentially overlap. On the contrary, for perforation tests, HL specimens survived more impacts before perforating absorbing more total energy than VI specimens. Plots of the DI variable against the number of impacts were observed to exhibit an initial linear portion, owing to a stable process of damage accumulation within the laminate, and to undergo an unstable growth a few impacts before perforation. When comparing the VI and HL specimens it was observed that, given an impact energy, the level of damage at first impact as well as the rate of stable damage accumulation is alike for the two sets of specimens. On the contrary, it is the number of impacts of the stable damage accumulation region which is lower for VI specimens.