Impact resistance mechanisms of polyurea layer in composite structures on ductile/brittle substrates under low-velocity impact
Polyurea shows high promise as an elastomer in impact protection. However, significant challenges persist in the impact resistance mechanisms of the polyurea layer (PUAL) on ductile/brittle substrates under low-velocity impact. This study synthesized a high-strength, highly elastic polyurea and applied it to polyurea-6061Al/polyurea-epoxy resin composite structures. Low-velocity impact tests were conducted to obtain data on impact energy, impact strength, and residual deformation. Based on these results, a numerical model was established and validated. By combining experimental and simulation approaches, the impact resistance mechanism of polyurea was investigated. Results show that: (i) PUAL enhances the performance of the ductile 6061Al substrate more effectively than on the brittle epoxy resin; (ii) on the ductile substrate, PUAL exhibits a synergistic effect with the substrate, enhancing peak force and strain, while on the brittle substrate, enhancement relies on PUAL's deformation resistance; (iii) increased PUAL thickness significantly improves impact strength, but requires a balance with specific energy absorption, with solid PUAL outperforming discrete form; (iv) the optimal PUAL position varies with thickness, form, and substrate type. Overall, the impact resistance mechanisms of composite structures involve PUAL's recoverable multidirectional deformation, stress dispersion and energy transfer on the ductile substrate, structural maintenance for the brittle substrate, and interlayer interfacial dispersion. Therefore, it highlights polyurea's potential to improve low-velocity impact resistance.
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