Damage can occur internally to composite aerospace materials, where it is not visible on the surface. Various nondestructive methods have been developed for detecting internal damage. However, prior to the present invention, there was no method for detecting “shadowed” or hidden damage (e.g., damage disposed below/overlapping damage near the surface) with only single sided access to the specimen (which is the case in many real-world settings, such as access to only the exterior of aircraft or space vehicle). The extent of damage (including any shadowed/hidden damage) correlates to how the damage grows in the material. As more aeronautics and space vehicles use more extensive amounts of composite materials, detecting the full extent of damage is increasingly important for composite vehicles/components.
Damage or other defects can exist both close to an accessible (e.g., outer) surface and towards an inaccessible (e.g., inner) surface of a structure. The damage located near the accessible surface can hide (or shadow) damage that exists directly below it when inspected from the accessible side/surface. “Below” as used herein means further from the accessible side or surface (regardless of the orientation of the accessible side/surface), and “directly below” means further from the accessible side or surface and at least partially overlapping (regardless of the orientation of the accessible side/surface). Current NDE techniques which can be deployed in a real-world non-laboratory setting and can be applied to components/structures larger than a coupon size only detect the near surface damage, and cannot detect the hidden damage. Current NDE techniques (such as ultrasonic scans) cannot detect the type of hidden/shadowed damage described above when only single sided access is available. Current NDE techniques can only detect the near surface non-shadowed damage, and therefore do not yield data that can identify or quantify the full damage extent.
Prior studies published in the scientific literature have investigated the phenomenon of guided wave energy trapping in delaminated plate-like components, such as composites. Prior studies reported in the scientific literature have also investigated cumulative energy due to wave trapping. However, these studies only investigated energy trapping in relation to locating damage, and/or sizing the near surface damage. Specifically, these prior studies focused on identifying damage in cases where only a single layer of damage exists. However, this is not a realistic scenario for composites in which damage typically occurs as multiple damage layers at multiple ply levels through the composite thickness. Prior methods cannot identify the presence of hidden “shadowed” damage. Additionally, prior NDE methods are not capable of detecting hidden “shadowed” damage in situations that are limited to single sided access. Current NDE techniques (such as ultrasonic and thermographic methods) for single sided access scenarios are limited to only detecting the near surface (non-hidden) damage.
Accordingly, there is a need for a novel nondestructive method of detecting internal damage in various structures, including aerospace materials.