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Low velocity impact characterization of monolithic and laminated AA 2024 plates by drop weight test

Kalay, Yunus Eren
The objective of this study was to investigate the low velocity impact behavior of both monolithic and laminated aluminum alloy plates. For this purpose, a drop-weight test unit was used. The test unit included the free fall and impact of an 8 kg hammer with an 8 mm punching rod from 0.5 m to 4 m. The relationship between the change in static mechanical properties (hardness, ultimate tensile strength, yield strength, strain hardening rate) and low velocity impact behavior of monolithic aluminum plates were investigated. Tested material was AA 2024, heat treatable aluminum alloy, which was artificially aged to obtain a wide range of mechanical properties. In the second stage of the study, the relationship between the low velocity impact behavior of laminated plates was compared with that of monolithic aluminum plates at identical areal densities. For this purpose, a series of AA 2024 thin plates were combined with different types of adhesives (epoxy, polyurethane or tape). Finally, fracture surface of the samples and microstructure at the deformation zone were examined with both scanning electron microscope and optical microscope. It is found that the ballistic limit velocities of AA 2024 plates increase with increase in hardness, yield strength and ultimate tensile strength. It is also found that a linear relation exists between the ballistic limit velocity and strain hardening rate or hardness. When the low velocity impact behaviors of laminated and monolithic targets were compared, it was seen that monolithic targets have a higher ballistic limit velocity values for from the 2.5 to 10 mm thick targets. It was also observed that adhesives are not so effective to strengthen the low velocity impact performance. On the other hand, with increasing Charpy impact energy, penetration and perforation behaviors are getting worse in 10 to 30 joules energy range. Different