Abstract
Low velocity impact is a frequently observed event during the operation of an aircraft composite structure. This type of damage is aptly called as “blind-side impact damage” as it is barely visible as a dent on the impacted surface, but may produce extended delaminations closer to the rear surface. One-sided thermal nondestructive testing is considered as a promising technique for detecting impact damage but because of diffusive nature of optical thermal signals there is drop in detectability of deeper subsurface defects. Ultrasonic Infrared thermography is a potentially attractive nondestructive evaluation technique used to detect the defects through observation of vibration-induced heat generation. Evaluation of the energy released by such defects is a challenging task. In this study, the thin delaminations caused by impact damage in composites and which are subjected to ultrasonic excitation are considered as local heat sources. The actual impact damage in a carbon epoxy composite which was detected by applying a magnetostrictive ultrasonic device is then modeled as a pyramid-like defect with a set of delaminations acting as an air-filled heat sources. The temperature rise expected on the surface of the specimen was achieved by varying energy contribution from each delamination through trial and error. Finally, by comparing the experimental temperature elevations in defective area with the results of temperature simulations, we estimated the energy generated by each defect and defect power of impact damage as a whole. The results show good correlation between simulations and measurements, thus validating the simulation approach.
Highlights
Current research on ultrasonic infrared (IR) thermography is being conducted in two main directions: 1) powerful stimulation by using piezoelectric [1,2,3,4] and magnetostrictive [5] units, 2) low-power stimulation based on the resonant interaction between ultrasonic waves and defects due to local defect resonance [6]
The power of heat generation in each of the 9 defects was varied by performing repeated calculations to match the experimental temperature evolutions on both the sample surfaces through trial and error
In this work, we demonstrated an approach for the evaluation of equivalent thermal power of subsurface defects which operate as heat sources under ultrasonic stimulation
Summary
Current research on ultrasonic infrared (IR) thermography ( called “sonic IR thermography” and “thermosonics”) is being conducted in two main directions: 1) powerful stimulation by using piezoelectric [1,2,3,4] and magnetostrictive [5] units, 2) low-power stimulation based on the resonant interaction between ultrasonic waves and defects due to local defect resonance [6]. There is lack of complete understanding of the physics governing the heat generation process, it is generally accepted that external ultrasonic stimulation of structural defects causes friction at the defect edges. The generated heat diffuses away from these defects and the corresponding temperature distributions are monitored by using an infrared (IR) camera. Thin delaminations which are caused by impact damage in composites subjected to ultrasonic excitation can be considered as local heat sources.
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