The finite element method (FEM) is generally utilized to investigate the chassis strength of a motorcycle. However, it is difficult to determine the load conditions for FEM analysis of a drop test. Therefore, a method of drop test strength prediction at the basic design stage has been developed by combining stress analysis with vehicle dynamics analysis.
A mathematical model and computer simulation system have been developed to predict the load conditions obtained by accelerations at several chassis locations. The model is constructed using flexible bodies (e.g., front fork and rear arm) as well as rigid bodies. The flexible front fork model was made by combining beam theory with substructural methods. Also, the model includes a front fork friction model which describes Coulomb's friction in slide bushings.
If dynamic analysis is replaced by an equivalent static analysis, the force can be predicted from the acceleration data and the mass distribution. The stress analysis for the frame is performed with a static FEM. Therefore, the time for calculation is very short.
The calculated results of this model correspond with actual measurements very closely. The model is necessary and sufficient from the points of view of simplicity and accuracy.