Infrared Imaging for Quantitative Defect Detection in Composite Structures

University Of California-San Diego, La Jolla CA

Investigators

Abstract

Due to their superior mechanical performance, light-weight and resistance to corrosion, composite materials are used in a variety of structural components in the civil and military sectors. Parts made of composite materials are found in modern aircraft (e.g., Boeing 787 and Airbus A380), ships, cars, wind turbines, sporting goods and many other high performance structures. Unfortunately, defects in these materials, caused by either manufacturing or operational conditions, can greatly reduce the ultimate performance of the structure, and even impact human safety in the case of catastrophic failures. In order to guarantee structural performance and safety, engineers need to know the presence, size and position of the flaws (in much the same manner that an oncologist doctor needs to know the extent of a tumor in a patient to best cure it). The technique of Infrared Thermography offers unique advantages for defect detection in composite structures, including broad coverage, speed of inspection and easily-interpretable diagnostic images. This project will advance the state-of-the-art in Infrared Thermography by improving the determination of the size and the position of a flaw in the composite material. This capability will allow maintenance engineers and structures' owners to make informed decisions on remedial steps following a damage detection event, ultimately increasing the reliability and the safety of the structure. The research goal of this project is to advance the known technique of Infrared Thermography for the Non-Destructive Testing (NDT) of composite structures by enabling quantitative defect detection. Current Thermographic capabilities allow for qualitative defect detection, with quantitative predictions only based on simplistic and unrealistic 1-D heat diffusion models. This research will develop realistic 3-D heat diffusion models for composite materials based on a novel concept of "Virtual Heat Source" (VHS) to simulate the excess surface heat produced by an internal defect in the structure following active heating. A Green's function solution to the 3-D heat diffusion problem will be also sought to account for the most general defect cases (e.g. non-planar defects). The models will predict the temperature field in the test object as a function of quantifiable defect features, including (1) defect depth, (2) defect size, and (3) defect orientation. The theoretical models will be validated and iterated by a series of experimental thermographic tests conducted on existing specimens at UCSD, including a unique, 9-m long composite wind turbine blade (CX-100 blade) containing 45 well-documented defects, and several panels representative of composite aircraft construction.