In this article, the quantitative relationship between the static stiffness,
lightweight factor, and modal parameters of an aluminum space frame was
investigated. Modal theory calculation and finite element method were employed
in the analysis. Fifty modal parameters were extracted from the finite element
model of the frame to calculate the bending stiffness, torsional stiffness, and
lightweight factor of the frame. The deviations of the bending stiffness,
torsional stiffness, and lightweight factor obtained from the modal theory and
the finite element theory were found to be 0.91%, 1.72%, and 1.71%,
respectively. It indicates that these two methods have similar accuracy. It was
confirmed that the sum of each order modal compliance could be used to calculate
the static compliance of the aluminum space frame. The first-order bending mode
was found to be the corresponding mode order, which made the largest
contribution to the bending stiffness. This method is also applicable for
identifying the first-order torsional mode. The results also show that such a
modal identification method can avoid effectively the interference of local mode
on the major body mode identification. The results obtained from finite element
analysis and modal theory method were both verified by the experimental testing
results. It proved that both of these two methods were effective in calculating
the bending stiffness, torsional stiffness, and lightweight factor. As a
comparison, the modal theory showed higher accuracy with lower deviation in the
calculated parameters to the experimentally measured ones. The modal theory
results of the bending stiffness, torsional stiffness, and lightweight factor
were closer to the experimental results with deviations of 4.64%, 3.61%, and
3.64%, while they are 5.82%, 5.53%, and 5.29% for the finite element method,
respectively. This article supplies important guidance for the lightweight
design and target setting of aluminum space frames in the concept stage.
