Effect of the deformation of the supporting structure on the measurement of the inertia properties of vehicles

In the measurement of the inertia properties of rigid bodies (mass, centre of gravity location and inertia tensor) the structures carrying the body under test are usually considered to be rigid. This assumption is less and less satisfied as the dimensions of the body grow. Consequently, the forces exchanged between the body and the structures can be large enough to deform the structure and affect the measurement, especially the location of the centre of gravity. In this paper, with special reference to the InTenso+ Measuring System of the Politecnico di Milano, the effects of the deformation of the test rig structure when measuring large bodies is investigated. A theoretical analysis is performed by using a flexible multibody mathematical model of the test rig. The deformation of the test rig is deeply investigated by a dedicated FEM model. The results of the theoretical analysis are then validated by measuring the inertia properties of a light truck. It turns out that the deformation of the test rig can actually affect the measurement. This deformation can be compensated by a proper mathematical procedure. The method can, consequently, be employed also for very large bodies for which the construction of a sufficiently rigid structure as to neglect its deformation is practically impossible.