A NONLINEAR FINITE-ELEMENT APPROACH FOR KINETO-STATIC ANALYSIS OF MULTIBODY SYSTEMS

Methods that treat rigid/flexible multibody systems undergoing large m otion as well as deformations are often accompanied with inefficiencie s and instabilities in the numerical solution due to the large number of state variables, differences in the magnitudes of the rigid and fle xible body coordinates, and the time dependencies of the mass and stif fness matrices. The kineto-static methodology of this paper treats a m ultibody mechanical system to consist of two collections of bulky (rig id) bodies and relatively flexible ones. A mixed boundary condition no nlinear finite element problem is then formulated at each time step wh ose known quantities are the displacements of the nodes at the boundar y of rigid and flexible bodies and its unknowns are the deformed shape of the entire structure and the loads (forces and moments) at the bou ndary. Partitioning techniques are used to solve the systems of equati ons for the unknowns, and the numerical solution of the rigid multibod y system governing equations of motion is carried out. The methodology is very much suitable in modelling and predicting the impact response s of multibody system since both nonlinear and large gross motion as w ell as deformations are encountered. Therefore, it has been adopted fo r the studies of the dynamic responses of ground vehicle or aircraft o ccupants in different crash scenarios. The kineto-static methodology i s used to determine the large motion of the rigid segments of the occu pant such as the limbs and the small deformations of the flexible bodi es such as the spinal column. One of the most dangerous modes of injur y is the amount of compressive load that the spine experiences. Based on the developed method, a mathematical model of the occupant with a n onlinear finite element model of the lumbar spine is developed for a H ybrid II (Part 572) anthropomorphic test dummy. The lumbar spine model is then incorporated into a gross motion occupant model. The analytic al results are correlated with the experimental results from the impac t sled test of the dummy/seat/restraint system. With this extended occ upant model containing the lumbar spine, the gross motion of occupant segments, including displacements, velocities and accelerations as wel l as spinal axial loads, bending moments, shear forces, internal force s, nodal forces, and deformation time histories are evaluated. This de tailed information helps in assessing the level of spinal injury, dete rmining mechanisms of spinal injury, and designing better occupant saf ety devices.