Evaluation of Aircraft Structures Crashworthiness Behavior using Finite Element Analysis

Despite ongoing worldwide research and discussion regarding broad aspects of airplane crashworthiness, no specific dynamic regulatory requirement currently exists. However, the Federal Aviation Administration (FAA) requires an assessment of each new aircraft model to ensure that the airplane crash performance will not significantly deviate or otherwise degrade from typical dynamic characteristics found in previous designs [8]. The increased use of composite airframe structural components warrants a new assessment to ascertain whether the crashworthiness of the associated dynamic structural response provides an equivalent or improved level of safety compared to conventional metallic structures. Generally, this assessment includes the evaluation of the survivable volume, the retention of items of significant mass, deceleration loads experienced by the occupants, and occupant emergency egress paths. Keeping these requirements in mind in order to design, evaluate, and optimize the crashworthiness behavior of composite structures necessitates development of analytical methods and predictive computational tools. With that objective, NIAR used LS-DYNA® to develop a numerical model of the Boeing 737 10-ft section, as drop tested by the FAA. The 10-ft fuselage section geometry and material properties were reverse-engineered using repair manuals, design books, and documentation provided by the FAA. The FE model followed NIAR methodologies and mesh quality criteria. The occupants and seats were represented using mass elements. Items of mass such as lifting fixtures, camera mounts, reinforcing beams, and overhead bins were represented using finite elements. Additionally, the luggage was also incorporated into the FE model, and several studies were performed in order to accurately represent its aggregate mechanical properties. During the validation process, it was found that some geometry simplifications did not provide an adequate level of correlation. Thus, the sensitivity of increased accuracy in the geometric representation was also studied in order to provide guidance on the minimum geometric features necessary to capture the event. The final 10-ft fuselage section model was validated by comparing floor accelerations and velocities, as well as fuselage permanent deformations. A good level of correlation was obtained from this analysis, which shows that numerical methods can be used to support the design and certification of future aircraft structures for crashworthiness evaluation.