Computational life prediction methodology for mechanical systems using dynamic simulation, finite element analysis, and fatigue life prediction methods

This study deals with an integrated life prediction methodology using dynamic simulation, finite element analysis, the fatigue life prediction method, and experimental validation for the finite life evaluation of a mechanical system.;As a practical example, a multi-body dynamic model of an existing ground vehicle was developed, using kinematic joints and components. The vehicle model was hypothetically run over a measured road profile at constant speed. From this dynamic analysis, load histories were obtained for each component. A lower control arm, which is a critical suspension component, was selected for the component fatigue life prediction, and a finite element model of this component was developed. Several high stress regions were identified from the finite element stress analysis. Local notch stresses at each high stress region were then obtained at potential fatigue crack "initiation" points, which can be called potential fatigue-critical locations.;Dynamic stress histories at potential fatigue-critical locations were produced by the quasi-static approach. The local strain life method was used to predict fatigue lives of each potential fatigue-critical location. The fatigue life was defined as the typical crack "initiation" life of a crack about 2 mm in length. The fatigue life of the component was defined as the shortest fatigue life among several potential fatigue-critical locations.;To validate this computerized procedure, the lower control arm was experimentally tested for stress and fatigue durability. The brittle coating method was used to identify high stress regions. Experimental stress analysis was carried out, using strain gages. The experimental results and predicted results based upon finite element analysis were very close: every comparison showed a difference of less than 5 percent. Also fatigue durability tests were done for the component by repeatedly applying the same load history that was applied to the finite element model until a 2 mm long fatigue crack formed. The breakthrough in this integration is that dynamic stress and fatigue life can be predicted in early design stages without experimental measurement of either loads or stresses. This methodology can be extended to design optimization, based upon durability.