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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.

This paper reports a study of the impact dynamic characteristics of body mounts in a body-on-frame vehicle. Two methods of dynamic analyses are utilized. One method is direct impact; and the other excitation on the body mount. Using a series of component test data, the direct impact method yields the natural frequency, f, and damping factor, ζ, for a spring-mass-damper model of a body mount. The functional relationship between the g-force versus deflection curve and f, ζ, and v (impact speed) is examined. Given a frame impulse, the excitation method predicts the body response by the convolution integral. The transient transmissibility (TT), the ability of a body mount to transmit shock impulse from the frame to the body in the early part of crash duration, is investigated. The degree of front-loadedness on the body pulse is determined by TT and thus it affects the occupant/vehicle crash response.