Static and dynamic evaluation of a multifunctional crashworthy pi-joint/sandwich energy absorbing structure

Experimental evaluation of a multifunctional crashworthy pi-joint/sandwich structure is described herein. The energy absorbing sandwich webs were bonded into a representative pi-joint, thereby, producing a load carrying joint that also functions as a constraint during crushing. Ply-drop triggers were incorporated into both face sheets of the sandwich web to initiate a controlled failure leading to a progressive crushing failure mode. The energy absorbing structure was evaluated under quasi-static and dynamic loading rates. Stable progressive crushing was observed for all specimens, demonstrating the robustness of the developed configuration. The steady state crushing load recorded during dynamic testing was 11.5% lower than the same configuration evaluated quasi-statically. The reduction in steady state crushing load was attributed to a change in the failure mode (brittle fracture) compared to the lamina bending (splaying) failure mode observed during quasi-static testing. The consistency of the results demonstrate that an energy absorbing pi-joint/sandwich structure, such as the configuration described in this paper, has the potential to be integrated into the crashworthy subfloor of future helicopters and aircraft.