Analysis Of Stress Waves Generated During Normal And Oblique Impacts On Aerospace Panels
Abstract
Foreign object impact on aircraft structures is a critical event that can affect the structural integrity and compromise the safety of the aircraft. The aerospace industry devotes a considerable amount of effort to detect impact damage. The real time impact detection and quantification system can improve safety and reduce operation cost. In order to identify the impact damage, it becomes necessary to study the impact location and force history. There are a number of studies on this topic which focus on obtaining an approximate representation of force history in damage events. However, a number of important aspects of foreign object impact including the angle of oblique impact and stress distribution at the impact site are rarely addressed in these studies. The objective of this thesis is to obtain a closer representation of the impact force history based on the Hertz contact theory and verify it experimentally through acoustic emission technique. Experiments were performed on a large Aluminum plate that was instrumented with piezoelectric acoustic emission sensors capable of detecting the shear component of the acoustic emission waves. This thesis establishes that oblique impacts produce shear horizontal components in addition to other lamb wave components. Detailed finite element analysis that includes the impact dynamics as well as the resulting wave propagation was performed. The results of this finite element analysis are compared with the experimental results.