A laser shock peening black tape damage monitoring method based on acoustic signals

Abstract

The present application relates to the field of laser shock peening, and specifically discloses a laser shock peening black tape damage monitoring method based on acoustic signals, which comprises the following steps: collecting laser shock discrete acoustic signals, obtaining a discrete acoustic signal sequence, and performing Hilbert envelope extraction on the discrete acoustic signal sequence to obtain an envelope signal; performing weighted processing on the extracted envelope signal to obtain a weighted envelope, and constructing a loudness index based on the weighted envelope; using short-time window frequency analysis to extract a main frequency sequence with time-varying main frequency, and using the main frequency sequence to calculate a main frequency stability offset; constructing a loudness-frequency coupling damage score criterion, and calculating a damage score. The present application significantly improves damage identification sensitivity, realizes real-time online monitoring of the laser shock process, has strong environmental adaptability and simple engineering deployment, significantly improves the consistency of laser shock peening quality, and has good scalability and universality.

Description

Technical Field

[0001] This invention relates to a monitoring method, specifically a method for monitoring damage to laser-shock-strengthened black tape based on acoustic signals, belonging to the field of laser shock strengthening. Background Technology

[0002] Laser shock peening is an advanced surface strengthening technique that uses high-energy short-pulse lasers to generate plasma shock waves on the material surface, thereby introducing high-amplitude residual compressive stress into the surface layer of the part to improve fatigue life and damage resistance. During the strengthening process, a layer of black adhesive tape is often applied to the metal surface as a sacrificial and absorbing layer to stabilize plasma formation and protect the substrate. However, this black adhesive tape is highly susceptible to cracking, bulging, delamination, and localized detachment under repeated high-energy laser impacts. These damages directly lead to attenuation of the impact pressure, instability of the peak waveform, or insufficient plasma coupling, thus affecting the distribution of residual stress and the consistency of the strengthening effect.

[0003] Current methods for monitoring the condition of black tape mainly rely on visual inspection, high-speed camera imaging, or laser spectral response. However, these methods have limitations such as insufficient real-time performance, high equipment costs, and sensitivity to environmental conditions. Especially in engineering-scale batch processing scenarios, if damage to the black tape is not identified in a timely manner, it will cause fluctuations in processing quality or even irreversible surface damage. Therefore, there is an urgent need for a method that can identify the damage state of black tape in real time, stably, and at low cost during laser shock peening to ensure the stability of the laser shock peening process window, controllable strengthening effect, and consistency of structural component processing quality. Summary of the Invention

[0004] Existing methods for monitoring the condition of black tape mainly rely on techniques such as visual inspection, high-speed photography, and plasma spectroscopy. However, these methods generally suffer from drawbacks such as poor real-time performance, reliance on expensive optical equipment, sensitivity to environmental conditions (dust, humidity, and light), and difficulty in large-scale engineering deployment. Furthermore, they cannot provide rapid and reliable damage feedback at each laser impact point level, leading to the neglect of early damage such as cracking, bulging, or detachment of the black tape. This results in problems such as unstable impact waveform, uneven residual stress, and uncontrollable strengthening quality. To address these issues, this invention provides a laser shock-strengthened black tape damage monitoring method based on acoustic signals.

[0005] The objective of this invention can be achieved through the following technical solutions: A method for monitoring damage to laser-shock-reinforced black tape based on acoustic signals, the method comprising the following steps: Step 1: Acquire discrete acoustic signals from laser shock to obtain discrete acoustic signal sequences. The envelope signal is obtained by Hilbert envelope extraction. ; Step 2: Extract the envelope signal The weighted envelope is obtained by weighting. And based on weighted envelope Construct a loudness index N; Step 3: Use short-time window frequency analysis to extract the dominant frequency sequence that varies with time. And use this to calculate the main frequency stability offset FSS; Step 4: Construct a loudness-frequency coupled damage scoring criterion and calculate the damage score D.

[0006] Optionally, the envelope signal in step one The extraction process is as follows: While the black tape is in good condition, multiple laser shocks are applied sequentially to the same location, and the corresponding discrete acoustic signals from the laser shocks are collected to obtain a discrete acoustic signal sequence. For each collected discrete acoustic signal sequence Bandpass filtering is performed to obtain the preprocessed signal. Then the preprocessed signal Perform a discrete Hilbert transform to obtain the analytic signal, and calculate its envelope signal. .

[0007] Step one also involves simultaneously acquiring the corresponding transient acoustic signal of the laser shock, and using the transient acoustic signal to construct a reference feature. , N0 and FSS0.

[0008] Optionally, the loudness index construction process in step two is as follows: envelope signal The weighted envelope is obtained after processing by a preset weighted filter. ; The loudness index N of a single laser shock is defined as the weighted envelope. The power integral form within the effective time interval of the impact, i.e. This index can sensitively reflect changes in sound field intensity caused by damage such as cracking and bulging of the black tape, which is something that traditional sound pressure amplitude cannot achieve; where α is a power exponent parameter used to adjust the sensitivity of the loudness index N to the signal amplitude.

[0009] The weighted processing procedure is as follows: envelope signal With the preset weighted sequence Multiplication, where the weighted sequence It is a discrete sequence designed based on the acoustic characteristics of black tape damage, used to enhance the damage-sensitive frequency band or time-domain components and suppress irrelevant noise.

[0010] Optionally, the main frequency sequence in step three that varies with time... The extraction process is as follows: Perform short-time-window frequency analysis on the same acoustic signal, and preprocess the signal. The time window is divided into several overlapping or non-overlapping short-time segments. A Fast Fourier Transform is performed on each segment to extract the dominant frequency with the largest amplitude within that segment, forming a dominant frequency sequence that varies with time. .

[0011] Optionally, the calculation process for the main frequency stability offset FSS is as follows: Based on the time-varying main frequency sequence Construct the formula for calculating the main frequency stability offset: ; Where M is the number of short time windows. The reference frequency is the frequency obtained directly from the data acquisition process, provided the black vinyl tape is in good working order. This represents the dominant frequency sequence within the (k+1)th short time window; the dominant frequency stability offset is used to characterize the propagation path disturbance and frequency instability caused by changes in the structure of the black tape.

[0012] Optionally, the construction process of the loudness-frequency coupled damage scoring criterion in step four is as follows: The relative change in loudness and the relative change in dominant frequency stability shift are weighted and combined to obtain the result. ; Where N0 is the reference loudness of the intact black tape, FSS0 is the reference frequency stability offset, w1 and w2 are weighting coefficients, N / N0 is the relative change in loudness, and FSS / FSS0 is the relative change in main frequency stability offset; this damage scoring criterion provides real-time, quantitative identification of the damage level of the black tape. It avoids reliance on complex optical measurements or ultrasonic imaging details, has a simple monitoring structure, can be directly embedded in existing laser shock equipment, and features good environmental adaptability, high sensitivity, and ease of engineering deployment.

[0013] Optionally, the reference loudness N0 of the intact black tape is obtained by statistically and normally processing the loudness index N obtained from multiple impact tests of the intact black tape, and the relative loudness change N / N0 is obtained accordingly, which is used to characterize the influence of black tape damage on the overall intensity characteristics of impact sound.

[0014] Optionally, the reference frequency stability offset FSS0 is obtained by normalizing the main frequency stability offset FSS obtained from multiple tests under the condition of the black tape being intact, and the relative change of the main frequency stability offset FSS / FSS0 is calculated based on it, which is used to characterize the sound wave propagation path disturbance and transient frequency instability caused by damage to the black tape.

[0015] The beneficial effects of this invention are: 1. Significantly improved damage identification sensitivity: By leveraging the coupling characteristics of loudness and dominant frequency stability shift, this invention can sensitively capture acoustic changes caused by black tape at different stages such as cracking, bulging, delamination, and detachment. The identification accuracy and stability are significantly better than traditional sound pressure amplitude or energy criteria.

[0016] 2. Real-time online monitoring of the laser impact process: This invention relies solely on the acoustic signals naturally generated during the laser impact process, without the need for high-speed cameras, spectrometers, or ultrasonic scanning equipment. It can perform instantaneous, single-point damage assessment on each laser impact point, significantly improving the real-time controllability of the processing process.

[0017] 3. Strong environmental adaptability and simple engineering deployment: Since the monitoring method uses acoustic signals as the carrier, it is not affected by complex processing environments such as light, dust and water mist, and only requires conventional acoustic sensors. The equipment is low in cost, easy to install, and can be operated stably for a long time in actual engineering equipment.

[0018] 4. Significantly improves the consistency of laser shock strengthening quality: This invention can promptly identify early damage to the black tape, avoiding fluctuations in impact pressure or uneven residual compressive stress during continuous impact, thereby improving the stability of laser shock strengthening treatment and the consistency of fatigue performance of metal components.

[0019] 5. Excellent scalability and versatility: The loudness-frequency coupling method of the present invention has universality and can be extended to impact state monitoring under different materials, different coatings or different laser parameters, making it easy to integrate into various laser impact systems. Attached Figure Description

[0020] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to the accompanying drawings.

[0021] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0022] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Please see Figure 1 As shown, a method for monitoring damage to laser-shock-reinforced black tape based on acoustic signals is described. This method includes the following steps: Step 1: Acquire discrete acoustic signals from laser shock to obtain discrete acoustic signal sequences. The envelope signal is obtained by Hilbert envelope extraction. ; Step 2: Extract the envelope signal The weighted envelope is obtained by weighting. And based on weighted envelope Construct a loudness index N; Step 3: Use short-time window frequency analysis to extract the dominant frequency sequence that varies with time. And use this to calculate the main frequency stability offset FSS; Step 4: Construct a loudness-frequency coupled damage scoring criterion and calculate the damage score D.

[0024] Preferably, the envelope signal in step one The extraction process is as follows: While the black tape is in good condition, multiple laser shocks are applied sequentially to the same location, and the corresponding discrete acoustic signals from the laser shocks are collected to obtain a discrete acoustic signal sequence. For each collected discrete acoustic signal sequence Bandpass filtering is performed to obtain the preprocessed signal. Then the preprocessed signal Perform a discrete Hilbert transform to obtain the analytic signal, and calculate its envelope signal. .

[0025] Step one also involves simultaneously acquiring the corresponding transient acoustic signal of the laser shock, and using the transient acoustic signal to construct a reference feature. , N0 and FSS0.

[0026] Preferably, the loudness index construction process in step two is as follows: envelope signal The weighted envelope is obtained after processing by a preset weighted filter. ; The loudness index N of a single laser shock is defined as the weighted envelope. The power integral form within the effective time interval of the impact, i.e. This index can sensitively reflect changes in sound field intensity caused by damage such as cracking and bulging of the black tape, which is something that traditional sound pressure amplitude cannot achieve; where α is a power exponent parameter used to adjust the sensitivity of the loudness index N to the signal amplitude.

[0027] The weighted processing procedure is as follows: envelope signal With the preset weighted sequence Multiplication, where the weighted sequence It is a discrete sequence designed based on the acoustic characteristics of black tape damage, used to enhance the damage-sensitive frequency band or time-domain components and suppress irrelevant noise.

[0028] Preferably, the main frequency sequence in step three that varies with time is... The extraction process is as follows: Perform short-time-window frequency analysis on the same acoustic signal, and preprocess the signal. The time window is divided into several overlapping or non-overlapping short-time segments. A Fast Fourier Transform is performed on each segment to extract the dominant frequency with the largest amplitude within that segment, forming a dominant frequency sequence that varies with time. .

[0029] Preferably, the calculation process for the main frequency stability offset (FSS) is as follows: Based on the time-varying main frequency sequence Construct the formula for calculating the main frequency stability offset: ; Where M is the number of short time windows. The reference frequency is the frequency obtained directly from the data acquisition process, provided the black vinyl tape is in good working order. This represents the dominant frequency sequence within the (k+1)th short time window; the dominant frequency stability offset is used to characterize the propagation path disturbance and frequency instability caused by changes in the structure of the black tape.

[0030] Preferably, the construction process of the loudness-frequency coupled damage scoring criterion in step four is as follows: The relative change in loudness and the relative change in dominant frequency stability shift are weighted and combined to obtain the result. ; Where N0 is the reference loudness of the intact black tape, FSS0 is the reference frequency stability offset, w1 and w2 are weighting coefficients, N / N0 is the relative change in loudness, and FSS / FSS0 is the relative change in main frequency stability offset; this damage scoring criterion provides real-time, quantitative identification of the damage level of the black tape. It avoids reliance on complex optical measurements or ultrasonic imaging details, has a simple monitoring structure, can be directly embedded in existing laser shock equipment, and features good environmental adaptability, high sensitivity, and ease of engineering deployment.

[0031] Preferably, the reference loudness N0 of the intact black tape is obtained by statistically and normally processing the loudness index N obtained from multiple impact tests of the intact black tape, and the relative loudness change N / N0 is obtained accordingly, which is used to characterize the influence of black tape damage on the overall intensity characteristics of impact sound.

[0032] Preferably, the reference frequency stability offset FSS0 is obtained by normalizing the main frequency stability offset FSS obtained from multiple tests under the condition of the black tape being intact, and the relative change of the main frequency stability offset FSS / FSS0 is calculated based on this, which is used to characterize the sound wave propagation path disturbance and transient frequency instability caused by damage to the black tape.

[0033] To better demonstrate this monitoring method, the following example will be used for explanation: The laser shock source was a Nd:YAG laser with a pulse width of approximately 8 ns and a single pulse energy of approximately 3 J. The treated sample was a 7075 aluminum alloy sheet, with a 20 mm wide black adhesive tape covering its surface as an absorption layer and a sacrificial layer. Acoustic signal acquisition employed a piezoelectric acoustic sensor, fixed to the sidewall of the sample using a coupling agent, with the sensor center approximately 25 mm from the laser shock point. The data acquisition system's sampling frequency was set to 5 MHz and electrically connected to modules for envelope extraction, weighted processing, short-time-window frequency analysis, and damage scoring. When the black tape is in good condition, laser shocks are applied to the same location multiple times (e.g., 10 times) and the corresponding transient acoustic signals are collected to construct a baseline feature. N0 and FSS0. Collect the corresponding discrete acoustic signals to obtain discrete acoustic signal sequences. For each collected discrete acoustic signal sequence Bandpass filtering is performed to obtain the preprocessed signal. Then the preprocessed signal Perform a discrete Hilbert transform to obtain the analytic signal, and calculate its envelope signal. envelope signal The weighted envelope is obtained after processing by a preset weighted filter. The loudness index N of a single laser shock is defined as the weighted envelope. Power integral form within the effective time interval of the impact By statistically analyzing and normalizing the N obtained from multiple impact tests on the intact state of the black tape, the reference loudness N0 in the intact state can be obtained, and the relative loudness change N / N0 can be obtained accordingly, which is used to characterize the influence of black tape damage on the overall intensity characteristics of impact sound.

[0034] Short-time-window frequency analysis is further performed on the same acoustic signal. Specifically, the preprocessed signal... The time window is divided into several overlapping or non-overlapping short-time segments. A Fast Fourier Transform is performed on each segment to extract the dominant frequency with the largest amplitude within that segment, forming a dominant frequency sequence that varies with time. This invention uses a main frequency stability offset to quantify the degree of time drift of the main frequency, for example, defined as: Where M is the number of short time windows. The reference frequency is defined as the fundamental frequency when the black tape is intact. By normalizing the FSS obtained from multiple tests in the intact state, the reference frequency stability offset FSS0 can be obtained, along with the relative change FSS / FSS0, which is used to characterize the sound wave propagation path disturbance and transient frequency instability caused by damage to the black tape.

[0035] Subsequently, multiple laser shocks were applied to the same area, causing the black tape to gradually develop different damage states, including slight cracking, bulging, local delamination, and even local detachment. The acoustic signals under each damage state were subjected to the same envelope weighting and short-time-window frequency analysis as described above. It was observed that as the degree of damage increased, the loudness index N and its relative change N / N0 showed a gradual increasing trend, while the dominant frequency stability offset FSS and its relative change FSS / FSS0 also increased significantly.

[0036] Based on this, a loudness-frequency coupling damage scoring criterion is constructed, which weights and combines the relative change in loudness with the relative change in dominant frequency stability shift. Where w1 and w2 are weighting coefficients, which can be determined based on calibration tests. Taking w1=w2=0.5, and through statistical analysis of the correspondence between the scores D obtained under different damage states and the actual state of the black tape, the following evaluation thresholds are set: D=1.00~1.10 for intact state; D=1.10~1.30 for minor damage to the black tape (such as minor cracks or small local bulges); D=1.30~1.60 for obvious bulges or local delamination of the black tape; and D≥1.60 for structural damage to the black tape (such as large-scale delamination, tearing, or local detachment). An alarm threshold is set based on the scores, and the system automatically triggers an alarm or stops the laser shock operation.

[0037] This invention protects a real-time identification method and system for black tape damage based on "envelope weighted loudness + dominant frequency stability offset + coupling score".

[0038] A method for constructing loudness indices based on envelope weighting is used to analyze discrete acoustic signal sequences obtained during laser shock. Hilbert envelope extraction is performed to obtain the envelope signal. The envelope is weighted to obtain Its weighting design is used to emphasize the main frequency band of the impact sound, in order to A loudness index is constructed in the form of a method to characterize the change in the overall intensity of the impact sound as the black tape is damaged, and loudness is used as the core acoustic feature for damage identification.

[0039] A damage feature extraction method based on the main frequency stability offset uses short-time window frequency analysis to extract the main frequency sequence of each window. Construct the main frequency stability offset The FSS is used to quantitatively reflect the propagation path disturbance and transient frequency drift caused by cracking, bulging, delamination or detachment of black tape, and the FSS is used as the core feature of structural state change. Loudness-frequency coupled damage criterion and real-time grading method, constructing a unified damage score The state of the black tape is classified in real time and quantitatively according to the scoring range, and the coupling criteria are used for online monitoring, alarm and linkage control in the laser shock process. The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for monitoring damage to laser-shock-reinforced black tape based on acoustic signals, characterized in that, The method includes the following steps: Step 1: Acquire discrete acoustic signals from laser shock to obtain discrete acoustic signal sequences. The envelope signal is obtained by Hilbert envelope extraction. ; Step 2: Extract the envelope signal The weighted envelope is obtained by weighting. And based on weighted envelope Construct a loudness index N; Step 3: Use short-time window frequency analysis to extract the dominant frequency sequence that varies with time. And use this to calculate the main frequency stability offset FSS; Step 4: Construct a loudness-frequency coupled damage scoring criterion and calculate the damage score D; The loudness index construction process in step two is as follows: envelope signal The weighted envelope is obtained after processing by a preset weighted filter. ; The loudness index N of a single laser shock is defined as the weighted envelope. The power integral form within the effective time interval of the impact, i.e. In the formula, α is a power exponent parameter used to adjust the sensitivity of the loudness index N to the signal amplitude. The construction process of the loudness-frequency coupled damage scoring criterion in step four is as follows: The relative change in loudness and the relative change in dominant frequency stability shift are weighted and combined to obtain the result. ； Where N0 is the reference loudness in the intact state of the black tape, FSS0 is the reference frequency stability offset, w1 and w2 are weighting coefficients, N / N0 is the relative change in loudness, and FSS / FSS0 is the relative change in main frequency stability offset. The reference loudness N0 of the black tape in its intact state is obtained by statistically and normally processing the loudness index N obtained from multiple impact tests of the black tape in its intact state, and the relative change in loudness N / N0 is obtained accordingly. The reference frequency stability offset FSS0 is obtained by normalizing the main frequency stability offset FSS obtained from multiple tests under the condition of intact black tape, and the relative change of main frequency stability offset FSS / FSS0 is calculated based on this.

2. The method for monitoring damage to laser-shock-reinforced black tape based on acoustic signals according to claim 1, characterized in that, The envelope signal in step one The extraction process is as follows: While the black tape is in good condition, multiple laser shocks are applied sequentially to the same location, and the corresponding discrete acoustic signals from the laser shocks are collected to obtain a discrete acoustic signal sequence. For each collected discrete acoustic signal sequence Bandpass filtering is performed to obtain the preprocessed signal. Then the preprocessed signal Perform a discrete Hilbert transform to obtain the analytic signal, and calculate its envelope signal. .

3. The method for monitoring damage to laser-shock-reinforced black tape based on acoustic signals according to claim 2, characterized in that, The weighting process in step two is as follows: envelope signal With the preset weighted sequence Multiplication, where the weighted sequence It is a discrete sequence designed based on the acoustic characteristics of black tape damage, used to enhance the damage-sensitive frequency band or time-domain components and suppress irrelevant noise.

4. The method for monitoring damage to laser-shock-reinforced black tape based on acoustic signals according to claim 3, characterized in that, The main frequency sequence in step three that changes with time The extraction process is as follows: Short-time window frequency analysis is performed on the same acoustic signal, and the preprocessed signal is... The time window is divided into several overlapping or non-overlapping short-time segments. A Fast Fourier Transform is performed on each segment to extract the dominant frequency with the largest amplitude within that segment, forming a dominant frequency sequence that varies with time. .

5. The method for monitoring damage to laser-shock-reinforced black tape based on acoustic signals according to claim 4, characterized in that, The calculation process for the main frequency stability offset FSS is as follows: Based on the time-varying main frequency sequence The formula for calculating the frequency stability offset (FSS) is as follows: ； Where M is the number of short time windows. This is the base frequency when the black vinyl tape is in good condition. Indicates the first k +1 short time window of the main frequency sequence.

Images