Abstract
This paper proposes an efficient non-destructive testing technique for composite materials. The proposed vibro-thermal wave radar (VTWR) technique couples the thermal wave radar imaging approach to low-power vibrothermography. The VTWR is implemented by means of a binary phase modulation of the vibrational excitation, using a 5 bit Barker coded waveform, followed by matched filtering of the thermal response. A 1D analytical formulation framework demonstrates the high depth resolvability and increased sensitivity of the VTWR. The obtained results reveal that the proposed VTWR technique outperforms the widely used classical lock-in vibrothermography. Furthermore, the VTWR technique is experimentally demonstrated on a 5.5 mm thick carbon fiber reinforced polymer coupon with barely visible impact damage. A local defect resonance frequency of a backside delamination is selected as the vibrational carrier frequency. This allows for implementing VTWR in the low-power regime (input power < 1 W). It is experimentally shown that the Barker coded amplitude modulation and the resultant pulse compression efficiency lead to an increased probing depth, and can fully resolve the deep backside delamination.
Highlights
Active infrared thermography is a cost-effective non-destructive testing technique which enables fast full-field inspection of relatively large objects using a highly sensitive infrared camera [1,2]
Vibro-thermal wave radar (VTWR) technique was introduced as an efficient lowpower non-destructive methodology for inspecting materials
The Vibro-Thermal Wave Radar (VTWR) technique was benchmarked with the classical lock-in vibrothermography (LVT)
Summary
Active infrared thermography is a cost-effective non-destructive testing technique which enables fast full-field inspection of relatively large objects using a highly sensitive infrared camera [1,2]. The test-piece is generally excited with an external heat source so that a heat flow is stimulated throughout the sample and the defects are detected based on their impact on the thermal response recorded at the inspection surface. The test-piece may be inspected in the transmission mode such that the defects are detected based on the thermal response transmitted to the back surface, which leads to increased detectability of deep defects [7]. In case of testing polymeric materials, this will further lead to efficient self-heating of the test-piece due to viscoelastic damping which reveals defects as areas with distinctive variation of self-heating (so-called self-heating based vibrothermography) [15] Another approach is to tune the excitation frequency band at a local defect resonance (LDR) frequency, which enables low-power vibrothermography using a piezoelectric (PZT). VTWR is applied by binary phase modulation (5 bit Barker code) of the heat flux at the defect’s depth, and its depth resolvability is compared with LVT
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