Low-velocity impact of functional gradient honeycomb sandwich plate with CFRP face sheets

In recent years, with the increase of vehicle speed, the energy absorption in traffic accidents and collisions keeps increasing. In order to further improve the energy absorption properties of honeycomb structure and realize the goal of lightweight, and to protect the safety of passengers and valuables, energy absorption of all kinds of equipment and vehicles, such as cars, planes, etc.) meet with impact shuold in a more gentle form.This paper proposed a functional gradient honeycomb sandwich structure wtich has a advantage in energy absorption compare with traditional honeycomb.

The density gradient was introduced into the traditional honeycomb structure, and the gradient coefficient was used to characterize the gradient size. CATIA was used to establish multiple groups of ABS gradient honeycomb cores with different gradient coefficient . ABAQUS/Explicit simulation software was used to construct the finite element model of functional gradient honeycomb sandwich plate with CFRP face sheets, and the finite element impact simulation was conducted according to the impact energy used in the experiment. The simulation results were compared with experimental data. The error between simulation results and experimental data is within acceptable range. The verified finite element model is used to simulate the functional gradient honeycomb sandwich plate with CFRP face sheets with multiple gradient coefficient cores at 20J, 50J and 100J impact energies.

According to the damage deformation diagram of functional gradient honeycomb sandwich plate with CFRP face sheets in the paper, the damage morphology of functional gradient honeycomb sandwich plate with CFRP face sheets under 20J, 50J and 100J impact energy was mild damage, moderate damage and complete penetration, respectively. The impact resistance of the gradient coefficient for functional gradient honeycomb sandwich plate with CFRP face sheets is different under three damage modes. (1) For small energy impact, the core with gradient coefficient greater than 1 is better, mainly because the material distribution is concentrated at the impact side, which improved the material utilization rate and reduces the damage depth. When the gradient coefficient is 1.6, the impact resistance was increased by 10.15% compared with the same mass of non-gradient core sandwich plate.(2) For medium energy impact, the deformation and damage gradually expand downward, and the impact energy borned by the core gradually increases. Damage and deformation can reach the middle of the sandwich plate. The impact resistance and energy absorption characteristics of the core with gradient coefficient greater than 1 remain optimal, but the advantage is slower than that of small energy impact. When the gradient coefficient is 1.6, the energy absorption advantage decreases to 6.53%. (3) For large energy impact, the punch will penetrate the sandwich plate, and the core with gradient coefficient less than 1 has an advantage in impact resistance and energy absorption characteristics. The total energy absorption increases first and then decreases with the increase of the gradient coefficient, and reaches the maximum value when the gradient coefficient =0.7, which is 9.87% higher than the non-gradient sandwich plate. (4) The overall law shows that: in the process of the impact energy from small to large, the core structure has an advantage in energy absorption shift from the gradient coefficient >1 gradually to the gradient coefficient <1.Conclusion: Around the functional gradient honeycomb structure impact resistance under low-velocity impact in the finite element simulation, aiming at different impact energy and gradient coefficient, compared functional gradient honeycomb sandwich plate with traditional sandwich plate in energy absorption characteristics, the results show that introduced density gradient into traditional honeycomb sandwich plate can improve the low-velocity impact resistance performance of sandwich structures. Under different impact energy and damage forms, the effect of the gradient value on the impact resistance of sandwich panels is different. Combined with different application backgrounds, a more appropriate protective structure can be proposed. Those laws proposed a reference for the impact resistance optimization design and application of honeycomb sandwich panels.