Abstract
Delamination is one of the most common defects in carbon fibre reinforced plastic (CFRP) components, such as those used in aircraft and wind turbine blades. To detect delaminations, different NDT methods such as ultrasonic (UT), eddy current (EC) scanning, flash thermography, and recent developed pulsed-eddy-current-(PEC-) simulated thermography are conducted for comparison and evaluation of the new developed PEC thermography system at Nanjing University of Aeronautics and Astronautics (NUAA), China through UK-China collaboration. A PEC-stimulated thermography system is built at NUAA, extended from previous joint work between Newcastle and Bath Universities. Using these NDT systems, man-made, dedicated delaminations with varied diameters and depths are investigated and studied. Through this comparison, PEC-stumilated and flash thermography show relatively good indications of the shape of delaminations. The joint studies also show that PEC-stimulated thermography has unique advantage for fibre orientation evaluation.
Highlights
A composite material can be defined as a combination of two and more materials with very different mechanical, thermal, and electrical properties
Many reflections in the nondefected region, which is caused by the multilayer structure of carbon fibre reinforced plastic (CFRP)
The UT experiment shows the limitations of this approach for composite materials, due to (1) multiple reflections and scattering in composites, (2) inaccurate measurement for thin samples, (3) liquid coupling is required
Summary
A composite material can be defined as a combination of two and more materials with very different mechanical, thermal, and electrical properties. Because carbon fibres are electrically conductive, for the nondestructive evaluation of CFRP, electromagnetic methods such as those based on eddy currents [8, 9] and microwaves [10] can be used. PEC-stimulated thermography, combining PEC and thermography, involves the application of a high current electromagnetic pulse to the conductive material under inspection for a short period. Based on recent development at Newcastle and Bath in collaboration with Rolls Royce and Alstom [19], a new low cost and portable PEC-stimulated thermography system is built at NUAA to evaluate the composites and metallic object used in wind or aerospace industry, delamination in composite in this paper. Delaminations within CFRP composites are investigated using PEC-stimulated thermography in reflection mode (the inductor and infrared camera are on the same side of the sample) aiming to reduce the inspection period significantly.
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