Thermal barrier coating top layer crack characterization method and device based on laser-induced ultrasound

Abstract

The invention discloses a thermal barrier coating top layer crack characterization method and device based on laser-induced ultrasound, and the method comprises the following steps: building a thermal barrier coating two-dimensional finite element model, and carrying out simulation to obtain a full-time-domain oscillogram under different top layer crack defect widths; the peak wave amplitude value when the crack defect width is zero is used as the reference (the transmission efficiency is 100%), the wave amplitude value of the first peak signal under each crack width is extracted, the proportion of the wave amplitude value to the reference value is calculated, the transmission efficiency is obtained, and then a curve of the crack width and the transmission efficiency is fitted. Then, acquiring a top acoustic surface wave signal of the thermal barrier coating sample, extracting a first peak wave amplitude value of a full-time-domain oscillogram of the top acoustic surface wave signal, and calculating experimental transmission efficiency; finally, the experimental transmission efficiency is substituted into the fitted curve, and the theoretical crack width of the top layer of the thermal barrier coating is obtained through inversion. According to the method, the crack finite element simulation model is constructed, the signal characteristics of the surface acoustic wave at the crack are extracted, and quantitative evaluation of the crack width is achieved.

Description

Technical Field

[0001] The present invention relates to the field of nondestructive testing technology, and specifically to a method and device for characterizing cracks in the top layer of a thermal barrier coating based on laser-induced ultrasound, which is suitable for multi-layer heterogeneous coating systems in high-temperature environments. Background Art

[0002] Thermal barrier coating (TBC) is a core protection technology for high-temperature components. Its multi-layer structure design aims to achieve performance optimization under thermal-mechanical-chemical multi-field coupling through material functional gradient distribution. The top ceramic layer uses yttrium-stabilized zirconia (YSZ) as a thermal barrier. Its cubic phase crystal structure remains stable at high temperatures of 1200°C, and its thermal conductivity is about 80% lower than that of nickel-based alloys. It can effectively reduce the substrate temperature by 150°C to 300°C, significantly delaying high-temperature creep and thermal fatigue damage. The bonding layer forms a dense α-Al2O3 protective film through the high-temperature oxidation of the aluminum element in the NiCoCrAlY alloy, constructing a transition interface between the ceramic layer and the substrate that combines mechanical anchoring and chemical protection. Its thickness is usually controlled in the range of 50μm to 150μm to balance bonding strength and thermal stress. However, under high temperatures exceeding 1100°C and alternating thermal loads in gas turbines, thermal barrier coatings face three major failure risks: First, the YSZ ceramic layer, due to the mismatch in thermal expansion coefficients (23% lower than that of nickel-based alloys), generates transverse tensile stress, leading to vertical crack propagation along columnar grain boundaries. Second, when the thickness of the bondline oxidation product (TGO layer) exceeds 8μm, its increased brittleness easily triggers interfacial delamination. Third, water vapor in the combustion gas undergoes a phase transformation reaction (t→m phase transformation) with the YSZ, resulting in a volume expansion rate of up to 4.5%, further exacerbating crack initiation. These failure modes ultimately lead to ceramic layer delamination, bondline cracking, and even catastrophic oxidation of the base alloy, threatening the safe operation of the equipment.

[0003] The complexity of crack detection in the top layer of thermal barrier coating ceramics stems from the triple contradiction between its material properties and structural characteristics: First, the Vickers hardness of YSZ ceramics reaches 12GPa to 14GPa, and cracks are often distributed in a three-dimensional network at the micron level (10μm to 100μm) and are deeply buried in the coating with a thickness of 100μm to 300μm. Traditional ultrasonic testing is limited by the probe frequency (usually <10MHz) and cannot penetrate the high-hardness ceramic layer; second, the multi-layer heterogeneous structure leads to a complex sound wave propagation path, and the reflection and scattering caused by the cracks are very complex. Signals such as acoustic emission and mode conversion overlap with substrate reflections and interface echoes, forming a "signal maze." Existing signal processing algorithms have an accuracy rate of less than 70% for extracting crack characteristic frequencies (0.5MHz to 2MHz). Finally, there is a significant conflict between dynamic detection requirements and static signal analysis. For example, while acoustic emission technology can monitor crack growth in real time, the overlap between gas turbine operating noise (100dB to 150dB) and the signal frequency band (100kHz to 300kHz) results in detection failure when the signal-to-noise ratio falls below 3dB. These technical bottlenecks have led to the current reliance on periodic disassembly inspections for thermal barrier coating crack detection in engineering practice, which is costly and lacks real-time early warning.

[0004] Current detection technologies for cracks in thermal barrier coatings have significant limitations: infrared thermal imaging technology identifies defects by detecting thermal conductivity anomalies in the crack area, but when the crack depth exceeds 50μm, the thermal response signal intensity decays by more than 60%, resulting in a 45% missed detection rate for shallow cracks (<30μm); although acoustic emission technology can capture the strain energy release signal at the moment of crack expansion, the operating noise of the gas turbine (100-150dB) overlaps with the signal frequency band (100-300kHz), and detection fails when the signal-to-noise ratio is lower than 3dB; impedance spectroscopy technology evaluates the overall performance of the coating by measuring changes in electrochemical impedance, but the spatial resolution of local defects such as cracks is less than 500μm, which cannot meet the detection needs of microcracks (<100μm).

[0005] Laser ultrasonic testing (LATI) is an emerging technology that uses pulsed lasers to excite surface waves (Rayleigh waves) or body waves (Lamb waves) and can penetrate coatings up to 300μm thick. However, existing technologies still suffer from three major drawbacks: First, the accuracy of signal processing algorithms in extracting the characteristic crack frequency (0.5-2MHz) is less than 70%. Second, under complex operating conditions (such as surface roughness Ra > 3.2μm), acoustic wave scattering causes a 15dB drop in signal-to-noise ratio. Third, the lack of a quantitative relationship model between crack size and signal amplitude makes it difficult to accurately quantify defects. These limitations mean that current crack detection in thermal barrier coatings still relies on manual experience, with an error rate as high as 20%-30%, severely restricting the predictive maintenance capabilities of high-temperature components. Summary of the Invention

[0006] In order to solve the problems of insufficient crack detection accuracy and low non-contact detection sensitivity in the existing technology, the present invention provides a method and device for characterizing cracks in the top layer of thermal barrier coatings based on laser-induced ultrasound. By constructing a finite element simulation model of the crack, the signal characteristics of the surface acoustic wave at the crack are extracted to achieve quantitative evaluation of the crack width.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for characterizing cracks in the top layer of a thermal barrier coating based on laser-induced ultrasound, the specific steps of which are as follows:

[0008] A two-dimensional finite element model of the thermal barrier coating was established, and full-time domain waveforms were obtained by simulation under different top crack defect widths.

[0009] Taking the peak amplitude when the crack defect width is zero as the benchmark, its transmission efficiency is 100%, extract the amplitude of the first peak signal under each crack width, calculate its ratio to the benchmark value, and obtain the transmission efficiency, and then fit the curve of crack width and transmission efficiency;

[0010] Obtain the surface acoustic wave signal of the top layer of the thermal barrier coating sample, extract the first peak amplitude of its full time domain waveform, and obtain the corresponding experimental transmission efficiency based on the ratio to the peak amplitude when the crack defect width is zero;

[0011] The experimental transmission efficiency is substituted into the fitting curve of crack width and transmission efficiency, and the theoretical crack width of the top layer of the thermal barrier coating is obtained by inversion.

[0012] Furthermore, in the step of obtaining the full time domain waveform diagram under different crack defect widths of the top layer of the thermal barrier coating:

[0013] A two-dimensional finite element model was established based on the actual structure of the multilayer thermal barrier coating;

[0014] Set simulation parameters: the distance between the surface crack center and the laser excitation point, the signal transmission and reception distance; set the crack defect depth data, set different crack widths, and set a defect-free group as a control;

[0015] The full time domain waveform diagram obtained by simulation calculation under different crack defect widths of the top layer of thermal barrier coating.

[0016] Furthermore, a Q-switched Nd:YAG pulse laser is used to excite surface acoustic waves. The laser irradiation point is set on the surface of the top ceramic layer, and the acoustic wave propagation direction covers the entire detection area. A dual-wave hybrid interferometer is used to receive the surface acoustic wave signal.

[0017] Furthermore, the wavelength of the laser is 1064 nm; the pulse width is 8 ns, the spot diameter is 1 mm, the single pulse energy is 30 mJ to 50 mJ, and the repetition frequency is 20 Hz.

[0018] Further, the surface acoustic wave of the top layer of the thermal barrier coating sample is excited to obtain a full time domain waveform of the top layer of the thermal barrier coating sample, the peak wave amplitude at the first peak signal in the full time domain waveform is extracted, and the corresponding experimental transmission efficiency is obtained according to the ratio to the peak wave amplitude when the crack defect width is zero:

[0019] The acquired surface acoustic wave was denoised using a wavelet denoising algorithm, and then a time domain window was added from 0 to 4.5 μs to obtain the full time domain waveform of the top layer of the thermal barrier coating sample after windowing.

[0020] Furthermore, the transmission efficiency corresponding to the peak amplitude of zero crack defect width is set to 100%, the peak amplitude at the first peak signal in the full time domain waveform of each crack defect width is extracted, and the corresponding transmission efficiency is obtained according to the ratio to the peak amplitude of zero crack defect width, and the step of obtaining the fitting curve of crack width and transmission efficiency:

[0021] Perform a linear fit on the crack width and transmission efficiency.

[0022] The present invention also provides a system for characterizing cracks in the top layer of a thermal barrier coating based on laser-induced ultrasound. When the system is running, the steps of the above-mentioned method for characterizing cracks in the top layer of a thermal barrier coating based on laser-induced ultrasound are implemented. The system includes:

[0023] The simulation module is used to establish a two-dimensional finite element model of the thermal barrier coating and simulate and obtain full-time domain waveforms under different top crack defect widths;

[0024] The curve fitting module is used to extract the amplitude of the first peak signal under each crack width, calculate its ratio to the reference value, and obtain the transmission efficiency, taking the peak amplitude when the crack defect width is zero as the reference and the transmission efficiency as 100% as the transmission efficiency, and then fit the curve of crack width and transmission efficiency;

[0025] The data acquisition module is used to obtain the surface acoustic wave signal of the top layer of the thermal barrier coating sample, extract the first peak wave amplitude of its full time domain waveform, and obtain the corresponding experimental transmission efficiency based on the ratio to the peak wave amplitude when the crack defect width is zero;

[0026] The crack width characterization module is used to incorporate the experimental transmission efficiency into the fitting curve of crack width and transmission efficiency, and inversely obtain the theoretical crack width of the top layer of the thermal barrier coating.

[0027] The present invention also provides a terminal device, comprising a memory, a processor, and a computer program stored in the memory and runnable on the processor. When the processor executes the computer program, the steps of the above-mentioned method for characterizing cracks in the top layer of a thermal barrier coating based on laser-induced ultrasound are implemented.

[0028] The present invention also provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the steps of the above-mentioned method for characterizing cracks in the top layer of a thermal barrier coating based on laser-induced ultrasound.

[0029] The present invention also provides a computer program product, comprising a computer program, which, when executed by a processor, implements the steps of the above-mentioned method for characterizing cracks in the top layer of a thermal barrier coating based on laser-induced ultrasound.

[0030] Compared with the prior art, the present invention has at least the following beneficial effects:

[0031] The present invention provides a method for characterizing cracks in the top layer of thermal barrier coatings based on laser-induced ultrasound. By constructing a two-dimensional finite element model of the thermal barrier coating and simulating the interaction between surface acoustic waves and cracks, the time-domain waveforms of the transmitted wave are obtained for different crack widths. The corresponding transmission efficiency is calculated by extracting the peak amplitude at the first peak signal in the full time-domain waveform and combining it with the peak amplitude at a crack defect width of zero. Furthermore, a theoretical model for crack width characterization is established based on a linear fit relationship between crack width and transmission efficiency. This method effectively characterizes the effect of crack defects on the surface acoustic wave transmission amplitude and enables accurate quantification of crack width. Compared with existing technologies, the present invention eliminates the need for curve fitting for multiple defects of known sizes and can directly perform quantitative detection, significantly improving detection efficiency and accuracy. Furthermore, a relatively low relative error (average error rate of 7.76%) is achieved by comparing the results with theoretical calculations using a laser confocal microscope, demonstrating that the present method can accurately and reliably characterize crack widths in the top layer of thermal barrier coating ceramics.

[0032] Furthermore, the present invention employs laser-induced ultrasound technology, using a Q-switched Nd:YAG pulsed laser to excite surface acoustic waves (SAWs), and a dual-wave hybrid interferometer to receive the signals. This method eliminates the need for a piezoelectric probe to contact the sample surface, thus avoiding the contact detection limitations of traditional ultrasonic testing methods. The laser irradiation point is set on the top surface of the ceramic, and the direction of sound wave propagation covers the entire detection area, making the detection process more convenient and efficient. Furthermore, it reduces manual adjustment factors, improves the repeatability and stability of the detection, and is suitable for online testing on large-scale production lines.

[0033] Furthermore, the present invention employs a wavelet noise reduction algorithm to reduce the noise of the acquired surface acoustic waves, further improving the signal-to-noise ratio and detection accuracy. Using time-domain windowing technology, a window of 0 to 4.5 μs is applied to the time domain, resulting in a clearer full-time windowed waveform, providing more reliable data support for subsequent signal feature extraction and crack width inversion.

[0034] The thermal barrier coating top layer crack characterization system provided by the present invention adopts a modular design, including a simulation module, a curve fitting module, a data acquisition module, and a crack width characterization module. Each module has a clear division of labor and works collaboratively, achieving full automation from finite element simulation to crack width characterization. The simulation module is responsible for establishing a two-dimensional finite element model of the thermal barrier coating and performing simulation calculations; the curve fitting module is responsible for obtaining a fitting curve of crack width and transmission efficiency based on the simulation results; the data acquisition module is responsible for acquiring the surface acoustic wave signal of the top layer of the thermal barrier coating sample and extracting the peak wave amplitude in the full time domain waveform; and the crack width characterization module is responsible for incorporating the experimental transmission efficiency into the fitting curve to obtain the theoretical crack width of the top layer of the thermal barrier coating. This modular design improves the system's data processing efficiency and accuracy.

[0035] The thermal barrier coating top crack characterization system provided by the present invention integrates various functional modules into a complete detection system. Users can complete the entire process, from sample preparation to crack width characterization, through a simple user interface. During system operation, the functions of each module are automatically implemented, eliminating the need for complex parameter settings and data processing. Furthermore, the system features data storage and export capabilities, facilitating subsequent analysis and processing of test results. This integrated system and user-friendly design make the thermal barrier coating top crack characterization system provided by the present invention more suitable for practical applications in industrial production and scientific research experiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Schematic diagram of crack defect model at different signal collection points;

[0037] Figure 2 Laser ultrasonic displacement curves of top crack defect models with different widths at a transmitting and receiving distance of 3 mm; (a) full time domain waveform; (b) local magnified waveform at 2 μs;

[0038] Figure 3 The influence curve of crack defect width on transmission efficiency

[0039] Figure 4 Alloy substrate before spraying and specimen after spraying; (a) Thermal barrier coating specimen; (b) Thermal barrier coating specimen with surface crack defects;

[0040] Figure 5 The full time domain waveform of the crack defect width experiment of different ceramic top layers

[0041] Figure 6 The time domain waveform curve of the crack defect width experiment of different ceramic top layers at a receiving and transmitting distance of 3mm

[0042] Figure 7The confocal scanning thermograms and crack profile morphologies of each defect specimen; (a) confocal scanning thermogram of the crack width 200 μm group; (b) confocal scanning profile of the crack width 200 μm; (c) confocal scanning thermogram of the crack width 250 μm group; (d) confocal scanning profile of the crack width 250 μm; (e) confocal scanning thermogram of the crack width 300 μm group; (f) confocal scanning profile of the crack width 300 μm. DETAILED DESCRIPTION

[0043] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0044] The present invention provides a method for characterizing cracks in the top layer of a thermal barrier coating based on laser-induced ultrasound, the specific steps of which are as follows:

[0045] 1) Finite element simulation: Based on the actual structure of the multilayer thermal barrier coating, a two-dimensional finite element model is established to simulate the interaction between surface acoustic waves and cracks, and analyze the effect of cracks on the amplitude of the transmitted surface acoustic waves.

[0046] 2) Laser-induced surface acoustic wave detection: Surface acoustic waves (SAWs) are excited in the top layer of the ceramic using a pulsed laser. Signals are collected using a dual-wave hybrid interferometer to record changes in the signal characteristics of the transmitted waves from specimens with cracks of different widths.

[0047] 3) Extraction of the influence curve of the characteristic value of the signal of the crack defect width of the top ceramic layer: The transmission wave signal is integrated and extracted using time domain windowing, and the transmission efficiency of the transmission wave caused by cracks of different widths is extracted and calculated.

[0048] 4) Quantitative evaluation of cracks: The transmission efficiency of the transmitted wave obtained from the experiment is matched with the simulation model, and the crack width is obtained by inversion.

[0049] The present invention proposes a comprehensive detection method that combines finite element simulation and laser-induced ultrasound, which makes up for the defect of insufficient crack signal resolution capability of traditional methods. Wavelet analysis technology is used to extract the nonlinear changes of the signal at the crack with high precision. Quantitative characterization of crack parameters is achieved, providing a reliable basis for the evaluation and prediction of crack severity. High sensitivity: The resolution capability of crack signals is improved through wavelet analysis, and the detection accuracy is better than traditional methods. Non-contact: Detection is achieved using laser-induced surface acoustic waves, without contacting the sample to be tested, and it is adaptable to high-temperature and complex environments. Strong versatility: It is applicable to a variety of thermal barrier coating systems and complex crack types, and is widely used in aerospace, energy, transportation and other fields.

[0050] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with examples. The illustrative embodiments of the present invention and their descriptions are only used to explain the present invention and are not intended to limit the present invention.

[0051] The present invention provides a method for characterizing cracks in the top layer of a thermal barrier coating based on laser-induced ultrasound, the specific steps of which are as follows:

[0052] Step 1: Finite element numerical simulation

[0053] Build as Figure 1 In the two-dimensional finite element model of the thermal barrier coating shown, the center of the surface crack is set 2 mm away from the laser excitation point. To better reflect the effect of the crack width on the surface acoustic wave signal, the signal receiving point is set 1 mm away from the defect center on the other side of the defect, that is, the receiving and transmitting distance is 3 mm.

[0054] The crack defect depth is controlled to be 200μm, and the crack width is set to 50μm, 100μm, 150μm, and 200μm, totaling four groups. A non-defective group is set as a control. The full time domain waveform diagram under different crack defect widths obtained by simulation calculation is as follows: Figure 2 shown.

[0055] Step 2: Finite element simulation results analysis

[0056] Comparing the ultrasonic time-domain waveforms for different crack widths in the figure reveals a distinct spike wave that first appears early in the signal (approximately 2 μs). This waveform feature is present in all five data sets, but its amplitude decreases significantly as the crack transitions from absence to presence. As the crack width increases, the amplitude decreases evenly and more steadily. This phenomenon demonstrates that this spike wave is highly structurally sensitive and can well reflect the width of the crack defect.

[0057] Analysis of the propagation time shows that the spike arrives earlier than the main wave packet (approximately 3 to 6 μs). This suggests that it originates from the initial energy response of the laser-generated surface acoustic wave after encountering the crack, undergoing partial transmission, diffraction, or modal coupling. Considering the approximately 1 mm distance between the receiving point and the crack, the corresponding surface wave propagation time is approximately 2 to 2.5 μs. This spike corresponds precisely to this propagation path and can therefore be considered a transmitted surface wave after penetrating the crack.

[0058] Further analysis of the relationship between peak amplitude and crack width revealed that as the crack widens from 50μm to 200μm, the peak wave amplitude gradually decays, exhibiting strong monotonicity and a gradient response. This change reflects the crack's blocking effect on surface acoustic wave energy: the wider the crack, the less energy penetrates, and the weaker the transmitted wave amplitude at the receiving point. This mechanism is consistent with classical acoustic wave scattering theory, which states that when the width of an obstacle approaches or exceeds a certain fraction of the acoustic wavelength, the penetration path is suppressed, reflection and scattering are enhanced, and the transmitted component is weakened.

[0059] Step 3: Eigenvalue extraction and fitting function calculation

[0060] Therefore, the first spike signal in this model can be considered an approximate measure of crack transmission efficiency. The signal amplitude at this location is further extracted for each defect width model, and the peak amplitude at 2μs for the crack-free defect group is considered to be 100% transmission efficiency. The corresponding transmission efficiency percentages for the remaining defect width models are calculated, as shown in Table 1:

[0061] Table 1 Peak wave amplitude and corresponding transmission efficiency at 2μs for different defect width models

[0062] Crack width (μm) Peak amplitude at 2μs Transmission efficiency 0 (no defects) 2.311E-4 100％ 50 1.754E-4 75.89％ 100 1.662E-4 71.90％ 150 1.562E-4 67.60％ 200 1.451E-4 62.78％

[0063] Based on the data in Table 1, the curve of the effect of crack defect width on transmission efficiency is drawn as follows: Figure 3 As shown in the figure, it can be seen that without considering the control group without crack defects, the transmission efficiency and crack width change approximately linearly. Therefore, based on the simulation data of crack defect width (50μm~200μm) and transmission efficiency (peak wave amplitude at 2μs), the linear fitting expression is obtained as follows:

[0064] η(w)=-0.0783×w+80.45

[0065] Where w is the defect width (unit: μm); η(w) represents the transmission efficiency (%)

[0066] Therefore, the influence of crack width on penetration efficiency can be approximately estimated according to the above formula. Then, in actual detection, the propagation time is estimated by the distance between the laser excitation point and the signal receiving point and the sound speed of the material, the amplitude of the peak is accurately extracted, and the transmission efficiency is calculated, thereby realizing the crack width characterization based on the energy transfer efficiency of the transmitted wave.

[0067] Step 4: Set up the experimental setup

[0068] 1. Laser excitation device

[0069] A Q-switched Nd:YAG pulse laser was used, with the following parameters: wavelength: 1064 nm; pulse width: 8 ns; spot diameter: 1 mm; single pulse energy: 30 mJ to 50 mJ; and repetition rate: 20 Hz.

[0070] The laser is focused by a lens and irradiated on the top surface of the ceramic to excite surface acoustic waves.

[0071] 2. Signal receiving device

[0072] A dual-wave hybrid interferometer (wavelength 1550nm) is used to receive surface acoustic wave signals: spot diameter: 0.5mm; maximum receiving power: 2W; detection sensitivity can reach micron level.

[0073] The dual-wave hybrid interferometer can receive signals contactlessly and eliminate the influence of environmental noise.

[0074] 3. Data acquisition and control system

[0075] Equipped with a high-speed data collector (32x averaging mode) for real-time acquisition of ultrasonic signals and noise reduction.

[0076] Robotic arm and optical motion platform: Accuracy: 0.05mm; used to precisely adjust the positions of laser emission and receiving points to achieve two-dimensional scanning detection.

[0077] Step 5: Sample preparation

[0078] Prepare multiple groups of thermal barrier coating specimens with different thickness of ceramic top layer. Figure 4 Its material components and property parameters are shown in Table 2 and Table 3:

[0079] Ceramic top layer (8YSZ): 400μm thick; bonding layer (NiCoCrAlY): 100μm thick; base material (nickel-based superalloy): 5mm thick. The defect depth is 200μm, and the defect widths are 200μm, 250μm, and 300μm, respectively.

[0080] Ensure that the surface of the test piece is smooth and free of pollution to reduce the interference of the environment on the test.

[0081] Table 2 Material composition

[0082]

[0083] Table 3 Material property parameters of thermal barrier coating system

[0084]

[0085] Step 6: Laser-induced surface acoustic wave excitation

[0086] Excitation settings: Adjust the laser's spot diameter and pulse energy to optimize the quality of the excitation signal and ensure non-destructive testing; excite surface acoustic waves to propagate along the top layer of the ceramic, and their propagation characteristics directly reflect coating crack defects.

[0087] Excitation area: The laser irradiation point is set on the surface of the top ceramic layer, and the sound wave propagation direction covers the entire detection area.

[0088] Step 7: Signal Acquisition and Noise Reduction

[0089] 1. Signal reception

[0090] The dual-wave hybrid interferometer receives the surface acoustic wave signal in real time. By adjusting the distance between the laser receiving point and the excitation point, the signal intensity is optimized, and the full time domain waveform of the crack defect width experiment of different ceramic top layers is obtained. Figure 5 .

[0091] 2. Data Noise Reduction

[0092] Use wavelet denoising algorithm to process the signal, remove high-frequency noise and environmental interference, and improve the signal-to-noise ratio.

[0093] 3. Time Domain Windowing

[0094] In order to avoid the interference of air shock waves, the time domain window of 0 to 4.5 μs is added, and the experimental time domain waveform curves of different ceramic top crack defect widths after windowing are obtained as shown in the figure. Figure 6 .

[0095] Step 8: Experimental signal feature value extraction and crack width inversion calculation

[0096] Considering that the distance between the signal receiving point and the laser excitation point is about 3mm, the corresponding surface wave propagation time is about 2μs to 2.5μs. The peak signal in the red box in the figure corresponds to this propagation path, so it can be regarded as the surface wave transmission wave after penetrating the crack. It can be seen that the variation law of the acoustic surface wave transmission wave amplitude measured by the specimens with different crack widths is consistent with the simulation conclusion. Next, the transmission wave amplitude measured by the specimens of each defect width is calculated respectively, and the amplitude at 2μs of the crack-free defect group is regarded as 100% transmission efficiency, and the transmission efficiency percentage under the remaining defect width models is calculated accordingly. Finally, the obtained transmission efficiency is substituted into the linear fitting expression to inversely calculate the theoretical crack width, as shown in Table 4:

[0097] Table 4 Transmission wave amplitude and corresponding transmission efficiency of specimens with different defect widths

[0098]

[0099] Step 9: Experimental Characterization

[0100] After obtaining the theoretical crack width, the actual crack size of the test piece was detected by laser confocal measuring instrument. The confocal scanning thermal map and crack profile morphology of each defective specimen are shown in Figure 2. Figure 7 As shown in the figure, the actual depth and width of the crack defects of each specimen are marked.

[0101] extract Figure 7 The crack width measured by the CCP scanning crack profile is compared with the theoretical crack width. The calculated error is shown in Table 5:

[0102] Table 5 Theoretical and measured crack widths and error rates of specimens with different defect widths

[0103] Crack width Crack width characterization results Crack width measurement results Relative error About 200 μm 216.73μm 197.79μm 9.58％ About 250μm 272.20μm 264.02μm 3.10％ About 300 μm 328.10μm 296.66μm 10.60％

[0104] As can be seen from the above table, the average error rate of this measurement scheme is 7.76%, which can better characterize the crack width within the allowable error range.

[0105] The following are device embodiments of the present invention, which can be used to perform the method embodiments of the present invention. For details not disclosed in the device embodiments, please refer to the method embodiments of the present invention.

[0106] In another embodiment of the present invention, a system for characterizing cracks in the top layer of a thermal barrier coating based on laser-induced ultrasound is provided. When the system is running, the steps of the above-mentioned method for characterizing cracks in the top layer of a thermal barrier coating based on laser-induced ultrasound are implemented. The system includes:

[0107] The simulation module is used to establish a two-dimensional finite element model of the thermal barrier coating and simulate and obtain full-time domain waveforms under different top crack defect widths;

[0108] The curve fitting module is used to extract the amplitude of the first peak signal under each crack width, calculate its ratio to the reference value, and obtain the transmission efficiency, taking the peak amplitude when the crack defect width is zero as the reference and the transmission efficiency as 100% as the transmission efficiency, and then fit the curve of crack width and transmission efficiency;

[0109] The data acquisition module is used to obtain the surface acoustic wave signal of the top layer of the thermal barrier coating sample, extract the first peak wave amplitude of its full time domain waveform, and obtain the corresponding experimental transmission efficiency based on the ratio to the peak wave amplitude when the crack defect width is zero;

[0110] The crack width characterization module is used to incorporate the experimental transmission efficiency into the fitting curve of crack width and transmission efficiency, and inversely obtain the theoretical crack width of the top layer of the thermal barrier coating.

[0111] In another embodiment of the present invention, a terminal device is provided, comprising a processor and a memory, wherein the memory is configured to store a computer program, wherein the computer program includes program instructions, and the processor is configured to execute the program instructions stored in the computer storage medium. The processor may be a central processing unit (CPU), or may be other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc., and is the computing core and control core of the terminal, and is adapted to implement one or more instructions, specifically, to load and execute one or more instructions to implement a corresponding method flow or corresponding function. The processor described in the embodiment of the present invention can implement a method for characterizing cracks in the top layer of a thermal barrier coating based on laser-induced ultrasound.

[0112] In another embodiment of the present invention, the present invention further provides a storage medium, specifically a computer-readable storage medium (Memory), which is a memory device in a terminal device for storing programs and data. It is understandable that the computer-readable storage medium here can include both the built-in storage medium in the terminal device and, of course, the extended storage medium supported by the terminal device. The computer-readable storage medium provides a storage space that stores the terminal's operating system. In addition, the storage space also stores one or more instructions suitable for being loaded and executed by the processor. These instructions can be one or more computer programs (including program codes). It should be noted that the computer-readable storage medium here can be a high-speed RAM memory or a non-volatile memory, such as at least one disk storage. The processor can load and execute one or more instructions stored in the computer-readable storage medium to implement the corresponding steps of the above-mentioned embodiment of a method for characterizing cracks in the top layer of a thermal barrier coating based on laser-induced ultrasound.

[0113] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0114] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the steps in the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0115] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0116] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 The steps for the function specified in one or more boxes.

[0117] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. A method for characterizing cracks in the top layer of a thermal barrier coating based on laser-induced ultrasound, characterized in that: The specific steps are as follows: A two-dimensional finite element model of the thermal barrier coating was established, and full-time domain waveforms were obtained by simulation under different top crack defect widths. Taking the peak amplitude when the crack defect width is zero as the benchmark, its transmission efficiency is 100%, extract the amplitude of the first peak signal under each crack width, calculate its ratio to the benchmark value, and obtain the transmission efficiency, and then fit the curve of crack width and transmission efficiency; Obtain the surface acoustic wave signal of the top layer of the thermal barrier coating sample, extract the first peak amplitude of its full time domain waveform, and obtain the corresponding experimental transmission efficiency based on the ratio to the peak amplitude when the crack defect width is zero; The experimental transmission efficiency is substituted into the fitting curve of crack width and transmission efficiency, and the theoretical crack width of the top layer of the thermal barrier coating is obtained by inversion.

2. The method for characterizing cracks in the top layer of a thermal barrier coating based on laser-induced ultrasound according to claim 1, characterized in that: The steps for obtaining the full time domain waveform diagram of the crack defect width of the top layer of the thermal barrier coating are as follows: A two-dimensional finite element model was established based on the actual structure of the multilayer thermal barrier coating; Set simulation parameters: the distance between the surface crack center and the laser excitation point, the signal transmission and reception distance; set the crack defect depth data, set different crack widths, and set a defect-free group as a control; The full time domain waveform diagram obtained by simulation calculation under different crack defect widths of the top layer of thermal barrier coating.

3. The method for characterizing cracks in the top layer of a thermal barrier coating based on laser-induced ultrasound according to claim 1, characterized in that: A Q-switched Nd:YAG pulse laser is used to excite surface acoustic waves. The laser irradiation point is set on the top surface of the ceramic, and the acoustic wave propagation direction covers the entire detection area. A dual-wave hybrid interferometer is used to receive the surface acoustic wave signal.

4. The method for characterizing cracks in the top layer of a thermal barrier coating based on laser-induced ultrasound according to claim 3, characterized in that: The wavelength of the laser is 1064nm; the pulse width is 8ns, the spot diameter is 1mm, the single pulse energy is 30mJ~50mJ, and the repetition frequency is 20Hz.

5. The method for characterizing cracks in the top layer of a thermal barrier coating based on laser-induced ultrasound according to claim 1, characterized in that: The steps of exciting a surface acoustic wave on the top layer of the thermal barrier coating sample to obtain a full time domain waveform of the top layer of the thermal barrier coating sample, extracting the peak wave amplitude at the first peak signal in the full time domain waveform, and obtaining the corresponding experimental transmission efficiency based on the ratio to the peak wave amplitude when the crack defect width is zero: The acquired surface acoustic wave was denoised using a wavelet denoising algorithm, and then a time domain window was added from 0 to 4.5 μs to obtain the full time domain waveform of the top layer of the thermal barrier coating sample after windowing.

6. The method for characterizing cracks in the top layer of a thermal barrier coating based on laser-induced ultrasound according to claim 1, characterized in that: The transmission efficiency corresponding to the peak amplitude of zero crack defect width is set to 100%, the peak amplitude at the first peak signal in the full time domain waveform of each crack defect width is extracted, and the corresponding transmission efficiency is obtained according to the ratio to the peak amplitude of zero crack defect width, and the fitting curve of crack width and transmission efficiency is obtained in the steps: Perform a linear fit on the crack width and transmission efficiency.

7. A thermal barrier coating top crack characterization system based on laser induced ultrasound, characterized in that: When the system is running, the steps of the method for characterizing cracks in the top layer of a thermal barrier coating based on laser induced ultrasound according to any one of claims 1 to 6 are implemented, and the system comprises: The simulation module is used to establish a two-dimensional finite element model of the thermal barrier coating and simulate and obtain full-time domain waveforms under different top crack defect widths; The curve fitting module is used to extract the amplitude of the first peak signal under each crack width, calculate its ratio to the reference value, and obtain the transmission efficiency, taking the peak amplitude when the crack defect width is zero as the reference and the transmission efficiency as 100% as the transmission efficiency, and then fit the curve of crack width and transmission efficiency; The data acquisition module is used to obtain the surface acoustic wave signal of the top layer of the thermal barrier coating sample, extract the first peak wave amplitude of its full time domain waveform, and obtain the corresponding experimental transmission efficiency based on the ratio to the peak wave amplitude when the crack defect width is zero; The crack width characterization module is used to incorporate the experimental transmission efficiency into the fitting curve of crack width and transmission efficiency, and inversely obtain the theoretical crack width of the top layer of the thermal barrier coating.

8. A terminal device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the computer program, the steps of a method for characterizing cracks in a top layer of a thermal barrier coating based on laser induced ultrasound are implemented as claimed in any one of claims 1 to 6.

9. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the steps of a method for characterizing cracks in a top layer of a thermal barrier coating based on laser induced ultrasound are implemented as claimed in any one of claims 1 to 6.

10. A computer program product comprising a computer program, characterized in that When the computer program is executed by a processor, the steps of a method for characterizing cracks in a top layer of a thermal barrier coating based on laser induced ultrasound are implemented as claimed in any one of claims 1 to 6.

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