NDI Method for Quantification of Weak Bonding Strength of Composite Structures

The development of an intelligent shearography optical inspection system with an innovative and robust excitation technique for detecting weak bonds, delamination, and disbonds in composite materials and structures is proposed. This development will be conducted with the collaboration of Sandia National Laboratories, which manages the Federal Aviation Administration Aging Aircraft NDI Validation Center, and with The Boeing Company and General motors R&D Polymers/Adhesives group. The proposed system will require the development of intelligent software, including finite element analysis and image processing capabilities, a scanning microwave heating source, and a scanning acoustic excitation system for the shearography NDI technique. With this technique, the shearography camera is synchronized with the excitation unit to be able to detect the resonant frequency of weak bonds. Real- time electronic speckle shearing interferometry, or real-time shearography, is a laser interferometry technique capable of measuring components of out-of-plane strain in structures under stress. It is a vision system, so a large area can be analyzed simultaneously. The system will be automated and will use state-of-the-art image processing combined with Sandia's COBRA software (Coherent Optics Based inspection Requirements Analysis code) to provide quantitative strain measurements. These quantitative data will be used for determining the bonding strength of composite structures and also to evaluate the ability of the system to detect disbonds and delamination.