This paper describes a practical approach to extract the global static stiffness
of a body in white (BIW) from dynamic measurements in free-free conditions.
Based on a limited set of measured frequency response functions (FRF), the
torsional and bending stiffness values are calculated using an FRF based
substructuring approach in combination with inverse force identification.
A second approach consists of a modal approach whereby the static car body
stiffness is deduced from a full free-free modal identification including
residual stiffness estimation at the clamping and load positions. As an extra
important result this approach allows for evaluating the modal contribution of
the flexible car body modes to the global static stiffness values.
The methods have been extensively investigated using finite element modeling data
and verified on a series of body in white measurements. The results are compared
with the conventional static test bench measurements and have shown to deliver
robust results, with similar accuracy, in a more efficient way in terms of
testing time and costs.