A Fatigue Life Estimation Technique for Body Mount Joints

A body mount joint is a typical clamped joint that is under severe loading conditions, due to its structural function services as a gateway of load path between body and frame of an automotive vehicle. Stresses/strains on durability concerned components at the joint cannot be captured accurately by using the pseudo stress analysis approach because of the complexity of stress state generated by the pre-stress from clamp load, contacts between the components and nonlinear material properties. In this paper, development of a technique for fatigue life estimation of the joint is described in detail. The technique includes: 1) a finite element analysis (FEA) of local joint model with contacts, clamp load setup and mesh of continuum elements, 2) modeling of nonlinear material properties under cyclic loading, 3) generation of equivalent constant reversed cyclic load along a dominant vector calculated from tri-axial load time histories, and 4) special considerations in stress/strain analyses and fatigue life estimations. A whole cab model which is used to assist processes of the local joint model and bench tests with same configuration and setup as that of the FEA local joint model also are introduced. It is concluded that this technique can estimate fatigue crack mode so that the parameter study to improve design of the joint can be carried out with appropriate accuracy and high efficiency in terms of analysis time.