13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- weight of 6.9025 kg. Tests were performed in the different energies ranging from 5J to 123J. The time history of impact force and impactor displacement was obtained by the test machine. After impact, the residual displacement, indentation depth and the crack length of back surface have been measured. Figure 1. Damage at the non-impacted side of AL and FMLs Figure 2.Force-displacement curves Figure 3.Residual displacement against impact energy Figure 4. Crack length against impact energy In Fig.1, damage after the different impact energy was shown and compared between FMLs and 2024T3 sheets. For monolithic 2024-T3 sheets, the first crack was found at non-impact side at impact energy of 36.5J, and almost completely penetrated at energy of 68.8J. The shape of crack was first in rolling direction and growth into "C" shape with high energies. Whereas, for both types of FMLs A and B, the initial crack at non-impact side were found at energy of 43.5J and crack at impact side appeared at 71.5J. It is differently from others work, the first crack found there were perpendicular to rolling direction of aluminium alloy sheets and the adjacent fibre direction. The shape of crack at non-impact side of FMLs was grown into "H" shape at energies of 71.5J. There are little difference between two types of FMLs for the force-displacement curves, indentation depth ,the crack length and others permanent were almost the same at one energy level (see figure 3 and 4). Force-displacement curves were compared in figure 2. It were shown that the route of them kept the same before crack were appeared during loading stage for FMLs and monolithic 2024-T3 sheets respectively, and the quadratic equation can be used to relate the force with displacement. While the path is not coincident in unloading stage, but their slope were basic paralleled that is the Up 2024-T3 AL/43.2J FMLs-A/62.3J FMLs-B/62.6J Blow 2024-T3 AL/68.8J FMLs-A/91.9J FMLs-B/88.5J A B Rolling diraction
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