Impact Testing and Simulation of a Crashworthy Composite Fuselage Section with Energy-Absorbing Seats and Dummies

AbstractA 25-ft/s vertical drop test of a composite fuselage section was conducted with two energy-absorbing seats occupied by an-thropomorphic dummies to evaluate the crashworthy features of the fuselage section and to determine its interaction with theseats and dummies. The 5-ft. diameter fuselage section consists of a stiff structural floor and an energy-absorbing subfloorconstructed of Rohacel foam blocks. The experimental data from this test were analyzed and correlated with predictions froma crash simulation developed using the nonlinear, explicit transient dynamic computer code, MSC.Dytran. The anthropo-morphic dummies were simulated using the Articulated Total Body (ATB) code, which is integrated into MSC.Dytran.IntroductionA research program was conducted at NASA Langley Re-search Center to develop an innovative and cost-effectivecrashworthy fuselage concept for light aircraft and rotor-craft [1-3]. The composite fuselage concept was designedto meet structural and flight-load requirements and toprovide improved crash protection. The two primary de-sign goals for crashworthiness are to limit the impactforces transmitted to the occupants, and to maintain thestructural integrity of the fuselage to ensure a minimumsafe occupant volume. To meet these objectives, an air-craft or rotorcraft fuselage must be designed for high stiff-ness and strength to prevent structural collapse during acrash. Yet, the fuselage design must not be so stiff that ittransmits or amplifies high impact loads to the occupants.ldeally, the design should contain some crushable ele-ments to help limit the loads transmitted to the occupantto survivable or non-injurious levels.The fuselage concept, shown in Figure 1, consists of astiff upper fuselage, a structural floor, and an energy-absorbing subfloor. The upper section of the fuselagecabin is fabricated using a composite sandwich construc-tion and is designed to provide a protective shell thatencloses the occupants in the event of a crash. The en-ergy-absorbing subfloor is designed to dissipate kineticenergy through stable crushing. Finally, a key feature ofthe fuselage concept is the stiff structural floor. Thestructural floor is designed to react the loads generated bycrushing of the subfloor, and to provide a stable platformfor seat and restraint attachment.During the first year of the research program, a 12-in.diameter, 1/5-scale model composite fuselage was de-signed, fabricated, and tested to verify structural andflight-load requirements [3]. During the second year ofthe research program, energy-absorbing subfloor configu-rations were evaluated using quasi-static testing and finiteelement simulation to determine the best design for use inthe 1/5-scale model fuselage concept [4, 5]. During thethird year of the program, a full-scale version of the fuse-lage concept was fabricated, and a vertical drop test wasconducted to validate the scaling process [6]. Test, analy-sis, and correlation with finite element models were per-formed for each test in the series. For the 1/5- and earlyfull-scale drop tests, the inertial loading that normallywould be provided by seats and occupants was representedwith lead weights. In April 2001, a full-scale fuselagesection was tested with two energy-absorbing seats, eachwith an anthropomorphic dummy occupant. The objec-tive of the drop test was to demonstrate the crashworthi-ness of the fuselage concept for a more realistic loadingenvironment using seats and dummies. The data from thedrop test and the development of an integrated crashsimulation are the focus of this paper.Since the completion of the initial research, the compositefuselage section has been used as a test bed for conductingother crash-related experiments. In 2000, two drop testsof a composite fuselage section were performed for thespecific goal of examining test and analysis correlationapproaches for detailed finite element crash simulations[7]. One test was performed from a drop height of 1.75inches to excite the linear frequency response, and testdata were correlated with an MSC.Nastran analysis. Thesecond test was performed for an impact velocity of 25ft/s, and the test data were correlated with a nonlinear,transient dynamic crash simulation. For both tests, thefuselage section was loaded symmetrically using leadmasses that were attached to the floor through seat tracks.The total floor mass was approximately 1000 lbs. The 25ft/s impact test described in Ref. 7 is of particular interestbecause it was performed at the same initial vertical veloc-ity as the fuselage test with seats and dummies describedin this paper. In addition, the fuselage section describedin Ref. 7 had nearly the same floor loading; however,only lead masses were attached to the floor in that test.