Estimating Weight Reduction Effects of Material Substitution on Joints with Constant Stiffness

The concept of a structural index, λ, is developed using the simple example of a hollow beam with a cantilever load case. It is assumed that when performing material substitution, only the thickness, t, is changed. It is shown that the stiffness, K, of the beam can be defined as a function of t^λ, that 1 ≤ λ ≤ 3, and that λ can be used to predict the weight savings from material substitution where stiffness is held constant. It is then demonstrated that λ can be used to predict the weight savings from material substitution in the more complex cases of the joints of a light truck cab.