Equivalent Stiffness as Measure of Low Velocity Impact Damage of Complex Composite Structures

This paper presents an analysis of the application potentials implied in the equivalent stiffness changes of complex mechanical structures as a measure of damage caused by low-velocity impacts. In a series of drop-weight tests of a commercial composite component, the impact force time variation is measured, and by calculating the respective displacement of the impacted structure, the stiffness of the structure in impacted points before and after the impacts is calculated. The determined stiffness change serves as the basis for defining a measure of damage extent that is compared to the damage extent measures based on characteristic values of the measured force. It is shown that the measure of damage based on change of stiffness has correlation with the measure of damage based on reduction of loading capacity of the structure, but it does not have correlation to the measure of damage based on ratio of maximal impact force and force needed for initial material failure.