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The effect of impact energy division over repeated low-velocity impact on fiber metal laminates

In this study, a comprehensive comparison was drawn between a single impact with certain amount of energy and two impacts with various amounts of energy, the sum of which is the same as the amount of energy in the single impact. A rational plan for repeated impact tests on fiber metal laminates (FMLs) has been designed so as to assess the effect of impact energy division and its sequence, by varying the energy amount in each of the two impacts, on FMLs under repeated low-velocity impact. The total impact energy is estimated by a quasi-static punch test to use a reasonable amount of energy in the repeated impact tests. The impacts are conducted by a drop hammer machine at the same point. Impact parameters and failure modes for all the repeated impact tests are discussed. The results show that the FML specimen responds stiffer in second impact; to understand the reason of this behavior, impact tests on composite specimens were conducted, and comparison of the results of FML and composite specimens showed that the stiffer behavior is due to the elastic–plastic behavior of aluminum sheets which causes strain hardening and creates a dent. Additionally, the effect of impact energy division and its sequence are so influential that failure modes and impact parameters of each arrangement are considerably different from one another.