A method was presented to predict impact forces and dynamic strains when a structure is impacted from airborne state. It was found that impact caused dynamic strains and acting forces can be estimated as a function of impact velocity, structure modal parameters and contact stiffness.
The modal parameters were derived by Finite Element Method at the condition of free-free boundary, and the contact stiffness can be measured. The impact velocity can be assumed or can be given as a design parameter. First, the impact forces and responses of the structure were analyzed theoretically in the LAPLACE domain and the actual impact force and dynamic displacements of the structure were calculated by inversing the LAPLACE domain outputs. Then the dynamic stresses were determined utilizing strain-displacement relationships.
The suggested technique was verified by experiments with a simple beam. The expected and measured impact forces and dynamic strains were in good agreements with the assumptions that the structure is linear and the structure remains contact at the contacting point after airborne collision.
A method to calculate equivalent static loads to give identical dynamic strains were also studied.
