Nondestructive evaluation of thermal barrier coating thickness degradation using pulsed IR thermography and THz-TDS measurements: A comparative study

Unnikrishnakurup, Sreedhar; Dash, Jyotirmayee; Ray, Shaumik; Pesala, Bala; Balasubramaniam, Krishnan

doi:10.1016/j.ndteint.2020.102367

Cited by 43 publications

(15 citation statements)

References 34 publications

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“…The modified error function ∆ 𝑚𝑜𝑑𝑖𝑓𝑖𝑒𝑑 as in equation (9), is smooth, monotonous, and parabolic, which results in faster convergence to the minimum. The above-mentioned approach has been used for the material parameter extraction of standalone samples of the PU top layer and FE-PU layers.…”

Section: Figure 2 Schematic Diagram Of the Thz Pulse Transmission In ...mentioning

confidence: 99%

“…Terahertz (THz) waves ranging from 0.1 THz to 10 THz can penetrate through most non-metallic materials, thereby making identification/detection of internal details, within a non-metallic object, possible [5] - [6]. This property has enabled THz waves to be successfully employed in various non-metallic nondestructive testing (NDT) applications, such as ceramic matrix composite materials (CMC) [7], GFRP [8], and thermal barrier coating [9]. Since THz-based NDT doesn't demand a coupling medium and proximity as required by ultrasonic NDT, this technique is non-contact and non-invasive.…”

Section: Introductionmentioning

confidence: 99%

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Material Characterization and Thickness Measurement of Iron Particle Reinforced Polyurethane Multi-layer Coating for Aircraft Stealth Applications Using THz-Time Domain Spectroscopy

Latha

Unnikrishnakurup

Jain

et al. 2022

J Infrared Milli Terahz Waves

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Particle reinforced polymer matrix composites (PMC) are widely used in the military aviation industry as a stealth coating for incident radar attenuation. These coatings are made up of many layers of different materials with varying thicknesses. In this study, we used terahertz (THz) spectral range by means of time-domain spectroscopy (TDS) to examine the thickness of iron particle reinforced polyurethane Radar Absorbing Paint (FE-PU-RAP) composite coatings non-destructively. For accurate estimation of the individual layer thickness in multi-layer coatings, precise knowledge of the material properties of the individual layers is a prerequisite. Hence, standalone samples of the individual layers have been initially employed to extract the material properties, such as the refractive index, absorption coefficient, etc. Then, the accurate thickness estimation by the time-of-flight measurement principle has been carried out using the reflected THz pulses. Further, since the individual reflected pulses from the multi-layered sample are overlapping in nature due to the optically thin coating thickness, a sparse deconvolution technique has been utilized for extracting each individual reflected time instant. The scattering from the iron particles also provides a challenge to the identification of the interface signals. This was addressed by optimizing the regularization parameter in the sparse deconvolution algorithm. With this technique, accurate estimation of each of the individual layers in the multi-layer sample has been accomplished, otherwise difficult non-destructively.

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Section: Figure 2 Schematic Diagram Of the Thz Pulse Transmission In ...mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Material Characterization and Thickness Measurement of Iron Particle Reinforced Polyurethane Multi-layer Coating for Aircraft Stealth Applications Using THz-Time Domain Spectroscopy

Latha

Unnikrishnakurup

Jain

et al. 2022

J Infrared Milli Terahz Waves

Self Cite

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“…Therefore, in practice, inspecting TBCs for delamination represents a significant challenge. On the other hand, THz technology is based on electromagnetic interactions between the TBC layer and signals in the THz frequency range (usually 0.1 − 10 THz) [16], [17]. THz inspection is conducted by transmitting a short pulse into the sample and inspect its reflections from the various discontinuities inside the material.…”

Section: Introductionmentioning

confidence: 99%

“…By doing so, the reflections from various discontinuities inside the dielectric were detected by tracking the reflected pulses to the OERW probe [21], [23]. Such methods are similar to the well-established Time Domain Reflectometry (TDR) method used to estimate the defects' locations in faulty cables [26], and also the previously mentioned THz technology [16], [17]. However, the main drawback of time domain microwave NDT techniques is that, contrary to the TDR and THz technologies, they use bandwidth-limited OERW as a probe.…”

Section: Introductionmentioning

confidence: 99%

“…The variation in the reflection amplitude is then normalized and compensated for the nonlinearity using a predefined sinc function to reveal an accurate estimation of the distance to the source of reflection (in this case, the location of the delaminnation). Relying on the amplitude variations of IFFT results to obtain the delamination depth information represents a significant advantage over tracking the shift of the reflected peaks, as in the THz technology [16], [17] and previously-reported microwave NDT techniques [23]. This is due to the simplicity, narrow bandwidth, and low cost of the NDT setup when compared to the one used in the THz technology.…”

Section: Introductionmentioning

confidence: 99%

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IFFT-Based Microwave Non-Destructive Testing for Delamination Detection and Thickness Estimation

Jawad

Akbar

2021

IEEE Access

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Microwave Non-Destructive Testing (NDT) techniques for dielectric coatings are vital processes in many industrial applications due to their superior defect detection capabilities over traditional NDT methods. However, the limited bandwidth and post-processing complexities of these techniques cause them to fall short of accurately estimating the delamination thickness in such structures. In this paper, a novel low-complexity signal processing method is proposed to estimate the delamination thickness in metalbacked dielectric coatings using bandwidth-limited Open-Ended Rectangular Waveguide (OERW) probes. Here, Inverse Fast Fourier Transform (IFFT) process is used to convert the measured complex reflection coefficients at the surface of the coating to the time domain. Next, the amplitude of a specific time step is used to accurately estimate the delamination thickness without extra time-consuming processing. Using a 3 mm-thick macor samples with machined defects, the proposed technique is validated by correctly estimating delamination thickness down to 0.4 mm using an OERW probe with 13.5 GHz bandwidth. Hence, this technique overcomes the challenge of the OERW's limited bandwidth, which highly affects the possibility of tracking shifting in the peak reflection in the time domain. Moreover, the proposed method does not add to the complexity of the NDT process, which makes it suitable for in-situ real time applications. Hence, following this approach would be of great importance to numerous industries, where accurate thickness estimation of minute delamination in coatings is essential to avoid system failure.

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Overview of Techniques for Zero-Value Detection of Insulators

Liu,

Yang,

Zhang

et al. 2023

2023 the 7th International Conference on Energy and Environmental Science

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Nondestructive evaluation of thermal barrier coating thickness degradation using pulsed IR thermography and THz-TDS measurements: A comparative study

Cited by 43 publications

References 34 publications

Material Characterization and Thickness Measurement of Iron Particle Reinforced Polyurethane Multi-layer Coating for Aircraft Stealth Applications Using THz-Time Domain Spectroscopy

Material Characterization and Thickness Measurement of Iron Particle Reinforced Polyurethane Multi-layer Coating for Aircraft Stealth Applications Using THz-Time Domain Spectroscopy

IFFT-Based Microwave Non-Destructive Testing for Delamination Detection and Thickness Estimation

Overview of Techniques for Zero-Value Detection of Insulators

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