Static and dynamic properties of a motorcycle frame: experimental and numerical approach

It is well known how the main frame of a motorcycle plays an important rule in vehicle dynamics. In order to understand the main influences of this component, a dedicated test rig was design and realized. Numerical and experimental experiences were done with the aim to identify static stiffness, natural frequencies and vibration modes of a motorcycle frame. A dedicated test rig was designed and realized in order to load the chassis in torsional and flexural configuration, both within and without the engine. By the use of a hydraulic actuator, displacement controlled, a load ramp was applied to stress the frame in elastic yield, as in real conditions, and the structure flexure was measured with laser transducers. The test rig components were monitored by the use of laser transducers in order to include constraints compliances into the identification step. In this phase, the flexural and torsional static stiffness of the main frame were identified, paying attention to distinguish the engine’s contribute. A modal analysis, processing experimental data, was performed using the frequency response function measured in six different points of the frame. Natural frequencies, deflection modes and damping were identified. At the same time, a detailed numerical model of the main frame was developed. It was processed by the use of the finite element method in order to reproduce the experimental experiences. Numerical and experimental results were compared to validate the model of the chassis. All the obtained parameters are mainly being used in a dynamic study of motorcycle behaviour. Firstly, identified stiffness will be implemented as concentred springs, obtaining a significant model of the vehicle. Following this a multi-body model of the vehicle will be defined, including deformability of structures, using modal coordinates, and just introducing the most interesting modes.