Investigation on the Dynamic Behaviors of Aluminum Foam Sandwich Beams Subjected to Repeated Low-Velocity Impacts

Abstract

Marine structures are frequently subjected to repeated-impact loadings during navigation and operation. The structural damage accumulates, resulting in structural failures and even serious accidents. Experiments were performed using an INSTRON drop tower to investigate the dynamic behaviors of aluminum foam sandwich beams (AFSBs) subjected to repeated impacts; moreover, the mechanism of plastic deformation and damage and the energy absorption characteristics were analyzed. The results showed that as the number of impacts increased, the AFSB experienced progressive failure. The peak impact force, the deflection of the face sheets, and the rebound velocity gradually increased with increasing numbers of impacts, while their increments declined. However, when cracks occurred on the aluminum foam core and face sheets, as the number of impacts increased, the peak force and the rebound velocity decreased, while the amount of deflection in the front and back faces progressively increased. Before the foam core cracked, as the number of impacts increased, the elastic energy increased, while the plastic energy decreased. Once the foam core cracked, the plastic energy increased suddenly. During repeated impacts, the energy absorbed via local indentation in each impact initially increased with the number of impacts, and then decreased before finally becoming constant.

Theoretical Analysis of Plastic Behavior of Sandwich Beam with Metal Foam under Repeated Impacts

“…As for a fully clamped MFSB, based on the results of the repeated-impact tests conducted by Guo [30], it can be assumed that the displacement of the sandwich beam is almost linearly distributed, as displayed in Figure 5. From the geometrical compatibility equation, we obtain…”

“…It can be observed in reference [30] that, when MFSBs are subjected to repeated impacts, there is no delamination between the face sheets and the metal foam core. Thus, it is assumed that the face sheets are perfectly bonded to the core, and the face sheets and metal foam core obey the perfectly rigid plastic law.…”

“…In order to verify the accuracy of the theoretical model, the permanent deflections predicted by the theoretical method are compared with those of repeated-impact tests [30] and numerical simulations [31].…”

“…The relationship between absorbed energy and the impact number (N) can be obtained from repeated-impact tests [30], as presented in Table 1. Meanwhile, the expression The rebound effect of the MFSB is considered to be a form of the energy-absorption coefficient obtained from impact tests.…”

“…Recently, some studies have been performed on MFSBs subjected to repeated-impact loadings. Guo et al [30,31] applied experimental and numerical methods to MFSBs subjected to repeated impact loadings, and the deformation modes and failure modes of the MFSBs were discussed. Meanwhile, the effects of the impact location and face thickness distribution on permanent deflections were evaluated.…”