Use of Body Mount Stiffness and Damping In CAE Crash Modeling

This paper reports a study of the dynamic characteristics of body mounts in body on frame vehicles and their effects on structural and occupant CAE results. The body mount stiffness and damping are computed from spring-damper models and component test results. The model parameters are converted to those used in the full vehicle structural model to simulate the vehicle crash performance.

An effective body mount in a CAE crash model requires a set of coordinated damping and stiffness to transfer the frame pulse to the body. The ability of the pulse transfer, defined as transient transmissibility[1]¹, is crucial in the early part of the crash pulse prediction using a structural model such as Radioss[2]. Traditionally, CAE users input into the model the force-deflection data of the body mount obtained from the component and/or full vehicle tests. In this practice, the body mount in the CAE model is essentially represented by a spring with the prescribed force-deflection data. The effect of damping (strain-rate effect) which contributes to part of the body mount force-deflection is therefore not simulated in the traditional CAE crash model. An occupant (a crash test dummy) in a correlated Madymo[3] model is responsive to the shape and magnitude of vehicle body pulse. Meanwhile, a body pulse is affected by body mount design and its material parameters such as stiffness and damping. The ultimate effects of the body mount stiffness and damping on the occupant responses are examined by Madymo models. In a crash test with a 3-point belt and air bag restraint system, the occupant responds favorably to a body pulse with a front-loaded impulse. The inclusion of body mount damping in the CAE models is necessary in transmitting the early frame impulse to the body as in the test. The inclusion of damping results in improved structural and occupant simulations in the low to high speed crashes.

Part one of the paper describes the function and properties of both body mount and its mathematical model. Part two describes how current CAE methods are used to model the body mounts and the limitations of such methods. Madymo simulations are executed to show the effects of different body pulses with and without damping on the occupant responses.