A Technique for Relating Vehicle Structural Modes to Stiffness as Determined in Static Determinate Tests

During the development of a new vehicle, the vehicle is usually tested to determine both its static torsional and bending stiffness, and its dynamic torsional and bending modes. This paper discusses a method for determining both static and dynamic properties from the modal analysis test. Such a connection between static stiffness and dynamic modes would be useful for three reasons: (1) the relative importance of apparent bending and torsion modes could be determined by their contribution to stiffness, (2) the stiffening effect of structural modifications could be determined from experimental modal tests (the modal frequency shift is also affected by any change in mass), (3) the total static compliance could easily be split on a modal basis into compliance due to the overall structure and local compliance due to local structural deflections.