Design, Testing, and Simulation of Crashworthy Composite Airframe Structures at NASA Langley Research Center

Abstract

As composite materials gain increased usage in the aviation industry, it is important to address crashworthy design of composite aircraft. This chapter describes the facility used for full-scale aircraft crash testing at National Aeronautics and Space Administration (NASA) Langley, summarizes the research programs conducted to achieve improved crashworthiness, provides a brief definition of crashworthy design goals, documents existing certification requirements for crashworthiness, and provides a brief discussion of crash modeling and simulation. Next, results of a research program are presented in which two different composite energy absorbers were developed and evaluated through multilevel testing and simulation. One of the energy absorbers was a conical-shaped design, designated the conusoid, that consisted of four layers of hybrid graphite-Kevlar plain weave fabric oriented at [+45/−45/−45/+45 degrees] with respect to the vertical direction. A second sinusoidal-shaped energy absorber, designated the sinusoid, was developed that consisted of hybrid graphite-Kevlar plain weave fabric face sheets, two layers for each face sheet oriented at ±45 degree with respect to the vertical direction, and a closed-cell ELFOAM P200 polyisocyanurate (32.0 kg/m3) foam core. The design goal for the energy absorbers was to achieve average floor-level accelerations of between 25 and 40 g during the full-scale crash test of a retrofitted CH-46E helicopter airframe. Variations in both designs were assessed through dynamic crush testing of component specimens. Once the designs were finalized, subfloor beams of each configuration were fabricated and retrofitted into a barrel section of a CH-46E helicopter. A vertical drop test of the barrel section was conducted onto concrete to evaluate the performance of the energy absorbers. Finite element models were developed of all test articles and simulations were performed using LS-DYNA, a commercial nonlinear explicit transient dynamic finite element code. Test-analysis results are presented for both energy absorbers as comparisons of time-history responses, as well as predicted and experimental structural deformations and progressive damage under impact loading.