A multibody/finite element analysis approach for modeling of crash dynamic responses

Occupant models are robust tools for gaining insight into the gross motion of ground vehicle or aircraft occupants and evaluating loads and deformations of their critical parts in the studies of crashworthiness. One of the most important issues in occupant modeling is how the large motion of rigid segments of occupants such as the limbs and the small deformations of flexible bodies such as the spine column are handled. In this dissertation, mathematical models of the occupants with a finite element model of the spine are developed based on the principles of the rigid/flexible multibody dynamics and finite element methods along with numerical techniques. An exhaustive study of the occupant modeling and post-crash dynamic behavior of the vehicle occupants under various crash environments is performed by both experimental and analytical means.;Based on the developed method, two finite element models of the lumbar spine are created: one for a Hybrid II (Part 572) anthropomorphic test dummy and one for a 50th percentile male human. Detailed information of kinematic, geometric, inertial and material properties of the lumbar spine are used for both models. These models are then incorporated into code SOM-LA/TA (Seat Occupant Model-Light Aircraft/Transport Aircraft). The analytical results obtained from the modified code are correlated to the experimental results from the impact sled tests. Comparison of the results showed much closer match of the analyses to the experiments than it has been predicted by the original SOM-LA/TA code.;With the validated occupant model containing the lumbar spine, the gross motion of occupant segments, including displacements, velocities and accelerations are evaluated. The spinal axial loads, bending moments, shear forces, internal forces, nodal forces, and deformation time histories are also determined. In addition, variables such as Head Injury Criteria (HIC), Severity Index (SI) and Dynamic Response Index (SI) are evaluated to determine possibilities of the injuries in particular crash scenario. This detailed information helps assess the level of spinal injury, determine mechanisms of spinal injury, and design and develop better occupant safety devices.;A methodology for the quasi-static analysis of multibody systems with flexible structures undergoing large motion and complicated structural deformations is first developed. Rigid multibody dynamics is used to predict gross motions and displacements at the boundaries at each time step. Finite element analysis is then performed to determine the corresponding loads and deformations on the entire structure. This methodology produces highly efficient numerical solutions for systems containing both rigid and flexible bodies. A general-purpose nonlinear finite element computer program was developed for the quasi-static analysis which would address plane-frame problems with large displacements and mixed force and displacement boundary conditions.