A detection method for determining the service life of a gasket under plateau conditions by gasket crack

Abstract

The application discloses a kind of detection methods for judging gasket life under plateau condition by gasket crack, it is related to track component life assessment technical field.To solve the problems of long detection period, offline sampling, unable to adapt to plateau environment and cannot quantitative evaluation of remaining life in prior art, the method is realized by the following steps: pretreatment is carried out on the surface of gasket;According to the material and thickness, select probe and set ultrasonic parameters, after calibration by the same material and thickness standard gasket without defect, ultrasonic scanning is carried out on the gasket;According to the waveform feature, internal aging microcrack and surface fatigue shear crack are distinguished, and crack length and ultrasonic defect amplitude are extracted;Collecting field environment parameters to calculate plateau environment correction coefficient;The above parameters are substituted into the life model based on Paris fracture mechanics theory, and the remaining service life is calculated.The application does not need offline sampling, and can complete the detection on site quickly, with low life prediction error, to provide accurate technical support for plateau railway maintenance and repair.

Description

Technical Field

[0001] This invention relates to the field of track component life assessment technology, specifically a detection method for determining the life of track pads under high-altitude conditions by detecting cracks in the pads. Background Technology

[0002] The service environment for elastic pads in high-altitude rail transit is extremely harsh. Key deterioration factors include: extreme diurnal temperature variations exceeding 40°C, causing severe cyclic stress from thermal expansion and contraction; accelerated aging and embrittlement of polymer materials due to strong ultraviolet radiation and ozone; expansion and propagation of internal micro-defects caused by low air pressure; a sharp decrease in material toughness under extreme cold and low temperatures; and the combined fatigue effect of cyclic impact loads from trains and environmental stresses. Under the coupling of these multiple factors, the initiation and propagation rate of cracks in the elastic pads is significantly accelerated, and the crack morphology and distribution characteristics exhibit distinct high-altitude specificity.

[0003] Current methods for assessing the lifespan of elastic pads largely rely on accelerated aging tests in laboratories, dynamic and static stiffness measurements, or periodic disassembly and inspection. These methods suffer from drawbacks such as long testing cycles, inability to make rapid on-site assessments, and neglect of the unique degradation patterns specific to high-altitude environments. Conventional visual inspection can only identify macroscopic through-cracks, missing the early life warning stage of microcrack initiation. While ultrasonic testing can detect internal defects, current technology only provides a qualitative assessment of the presence or absence of defects, failing to establish a quantitative mapping relationship between ultrasonic signal parameters and fracture mechanics life models. This makes it impossible to accurately convert cracks into remaining lifespan, which is insufficient to meet the practical needs of efficient and rapid decision-making in high-altitude railway line inspections. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for detecting the remaining life of elastic pads for high-altitude railways based on Paris fracture mechanics theory, which solves the technical problems of missed detection of hidden cracks inside elastic pads in high-altitude environments, lack of quantitative physical mapping between ultrasonic detection signals and remaining life, and inability to make rapid and accurate predictions on site.

[0005] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0006] A method for determining the lifespan of a bearing plate under high-altitude conditions by detecting cracks in the bearing plate, the key technology of which includes the following steps:

[0007] S1. Pre-treat the surface of the pad;

[0008] S2. Select the probe type and frequency according to the material and thickness of the pad, set the material sound velocity, detection gain and range, and use a standard defect-free pad of the same material and thickness for comparison and calibration to obtain the benchmark detection waveform.

[0009] S3. Perform ultrasonic scanning on the pad, and collect and record the location, amplitude and quantity of abnormal reflection signals in real time;

[0010] S4. Based on waveform characteristics, distinguish between internal aging microcracks and surface fatigue shear cracks, and extract crack length and ultrasonic defect amplitude;

[0011] S5. Collect on-site environmental parameters and calculate the plateau environment correction coefficient;

[0012] S6. Substitute the collected information into the following model formula to calculate the remaining service life of the pad:

[0013] ;

[0014] Where, N R : Remaining fatigue life of the pad;

[0015] L cr : Critical crack length for pad failure;

[0016] L0: Crack length obtained from the current ultrasonic testing;

[0017] Δσ: Cyclic load amplitude of plateau trains;

[0018] C, m: material constants;

[0019] β: Stress concentration factor;

[0020] a: Crack length;

[0021] t: Plateau environment correction factor.

[0022] As one embodiment of the present invention, the pretreatment in step S1 includes: cleaning the adhering substances on the surface and the rounded corners of the elastic pad to be tested;

[0023] When the ambient temperature is below 0℃, place the ultrasonic flaw detector and probe in an insulated sleeve for preheating and apply a low-temperature special coupling agent.

[0024] As one embodiment of the present invention

[0025] When testing polyurethane pads, set the probe frequency to 5-10MHz, the sound velocity to 2200-2500m / s, the detection gain to 40-58dB, and the detection range to 20-50mm.

[0026] When testing the rubber pad, set the probe frequency to 5-8MHz, the sound velocity to 1750-2500m / s, the detection gain to 48-60dB, and the detection range to 25-45mm.

[0027] As one embodiment of the present invention, when the ambient temperature is <0℃, the sound velocity is increased by 50-100m / s and the gain is reduced by 2-3dB; when the altitude is >3500m, the gain is slightly increased by 1-2dB; after the pad is aged by strong ultraviolet light, the sound velocity stabilizes at the reference value and the gain is increased by 3-4dB.

[0028] As one embodiment of the present invention, the calculation formula for the plateau environment correction coefficient is as follows:

[0029] ;

[0030] in,

[0031] T: Temperature measured on-site;

[0032] H: Elevation at the site.

[0033] As one embodiment of the present invention, the formula for calculating the crack length L0 obtained by the current ultrasonic detection is as follows:

[0034] ;

[0035] Where A: Ultrasonic defect amplitude;

[0036] A0: The echo amplitude of the bottom surface of a brand new, defect-free, sound velocity stability reference sample made of the same batch and material.

[0037] As one embodiment of the present invention, in step S4, the waveform of the normal defect-free pad is stable, without abnormal noise or reflected waves, the noise amplitude A≤0.05A0, the bottom wave attenuation rate α≤0.1α0, without independent spike waveforms, and the frequency has no abnormal fluctuations.

[0038] When obvious peak reflection waves, bottom wave attenuation, and increased noise appear, it is determined to be a crack defect. Based on the waveform characteristics, crack defects can be divided into internal microcracks and surface fatigue cracks.

[0039] Internal aging and hidden microcracks are mostly manifested as continuous fine and fragmented noise waves, with a single peak amplitude of 0.1A0≤A≤0.3A0, a bottom wave attenuation rate of 0.2α0≤α≤0.4α0, a defect wave frequency of f=1.2-1.5f0, and a crack length of L0<0.5mm. f0 is the reference frequency of the ultrasonic reference waveform of a brand new pad of the same batch, material, and without defects.

[0040] The surface fatigue shear crack manifests as a single sharp reflected wave with amplitude A≥0.4A0, bottom wave attenuation rate α≤0.2α0, defect wave frequency f=1.6-2.0f0, and crack length 0.5mm≤L0≤3mm.

[0041] The beneficial effects of adopting the above technical solution are as follows:

[0042] This invention utilizes the acoustic principle of reflection, scattering, and attenuation of ultrasound waves when they encounter cracks and defects within polymer materials. A dedicated probe transmits and receives sound signals, capturing the waveform characteristics of both hidden microcracks and surface-opening cracks. By combining standardized signal interpretation and crack classification standards with a high-altitude environment lifetime correction coefficient, the crack detection results are quantitatively converted into remaining lifetime, achieving a quantitative physical mapping between ultrasonic detection signals and remaining lifetime. This invention's lifetime calculation model incorporates a high-altitude environment correction coefficient, deeply analyzes the influence mechanism of the high-altitude environment on crack propagation, and proposes a verifiable multi-factor coupling correction method. The rigorous technical solution further increases the accuracy of the evaluation results. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of the partitioning of the polyurethane WJ8-B model pad.

[0044] Figure 2 This is a schematic diagram of the waveform of a defect-free pad from the same batch.

[0045] Figure 3 This is a schematic diagram of the waveform of a pad with surface fatigue shear cracks.

[0046] Figure 4 A schematic diagram of the waveform of a pad with hidden microcracks due to internal aging.

[0047] Figure 5 This is a flowchart of the detection method. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of the present invention clearer, the invention will be described clearly and completely below in conjunction with specific embodiments.

[0049] Example

[0050] In this embodiment, a fully digital portable ultrasonic flaw detector is used for inspection, adjusted to a non-metallic dedicated inspection mode, with a frequency bandwidth of 0.5–20MHz, a maximum gain of 90dB, and stable operation at a low temperature of -30℃. A special cold-proof insulation sleeve for the flaw detector is used.

[0051] The following is a rapid non-destructive testing method for elastic pads that have been in service for a certain period of time on plateau railway sections:

[0052] S1. Pre-treat the surface of the pad:

[0053] First, clean the surface and edges of the pad to remove dust, snow, ballast debris, and protruding objects, ensuring a smooth surface without significant obstructions. If frost is present, wipe it dry with a soft cloth at room temperature; do not bake at high temperatures to avoid the material becoming brittle, cracking, or deforming due to sudden heat. When the ambient temperature is below 0℃, preheat the portable digital ultrasonic flaw detector and probe inside an insulated sleeve. Then, evenly apply a low-temperature special coupling agent to the treated inspection area, ensuring the coupling agent is of appropriate thickness and that the probe is completely in contact with the pad surface to eliminate the influence of air gaps on sound wave propagation.

[0054] The low-temperature special coupling agent is a neutral antifreeze coupling agent that maintains a paste-like fluidity at -25℃. Its acoustic impedance is highly matched with the polyurethane polymer pad, and the sound wave transmission loss is less than 5%. In this embodiment, EchoPure ultra-wide temperature antifreeze ultrasonic coupling agent can be used.

[0055] S2. After powering on the portable digital ultrasonic flaw detector, select the non-metallic material detection mode. Then, refer to Table 1 to select the probe type and frequency according to the material and thickness of the pad. Set the material sound velocity, detection gain and range. Use a standard defect-free pad of the same material and thickness for comparison and calibration to obtain the benchmark detection waveform.

[0056] Table 1. Reference Table for Parameter Settings of Portable Digital Ultrasonic Flaw Detector

[0057]

[0058] Considering the slight interference of the low air pressure and low temperature environment on sound wave propagation in the high-altitude area, the settings can be adjusted by referring to the parameter correction method in Table 2.

[0059] Table 2: Parameter Correction Methods and Reasons (Refer to Table 2)

[0060]

[0061] S3. Perform ultrasonic scanning on the pad, and collect and record the location, amplitude, and quantity of abnormal reflection signals in real time. In this embodiment, the pad is divided into:

[0062] Edge area, please refer to Figure 1 The sidewall of the intermediate pad is a high-incidence area of ​​fatigue shear cracks, and it is inspected using a slant probe.

[0063] For the area surrounding the bolt holes, please refer to... Figure 1 The area marked by the double-dotted line, that is, the area on the pad near the bolt, is a stress concentration area, which is prone to stress cracks.

[0064] The core stress zone, the rail bearing area in the middle of the pad, can be referenced. Figure 1 The area outside the double-dotted line is a high-incidence zone for internal cracks;

[0065] During the scanning process, observe the waveform changes of the flaw detector in real time and record the location, amplitude, and quantity of abnormal reflection signals.

[0066] S4. Based on waveform characteristics, differentiate between internal aging microcracks and surface fatigue shear cracks, and extract crack length and ultrasonic defect amplitude. See also Figure 2 Normal, defect-free pads exhibit stable waveforms without abnormal noise or reflected waves. The specific judgment method is as follows: noise amplitude A ≤ 0.05A0, bottom wave attenuation rate α ≤ 0.1α0, no independent spikes, and no abnormal frequency fluctuations. A0 is the baseline echo amplitude of the bottom surface of a new, defect-free, and sound-velocity-stable reference sample from the same batch and material; α0 is the wave attenuation rate of the ultrasonic reference waveform from the same batch and material.

[0067] When obvious spikes in reflected waves, attenuation of the bottom wave, and increased clutter are observed, it is identified as a crack defect. Based on waveform characteristics, crack defects can be divided into internal microcracks and surface fatigue cracks.

[0068] See Figure 4 Internal aging and hidden microcracks often manifest as continuous, fine, fragmented waves. The specific identification method is as follows: continuous multi-peaked fine, fragmented waves, single-peak amplitude 0.1A0≤A≤0.3A0, bottom wave attenuation rate 0.2α0≤α≤0.4α0, defect wave frequency f=1.2-1.5f0, crack length L0<0.5mm. f0 is the reference frequency of the ultrasonic reference waveform of a brand-new, defect-free pad from the same batch and material.

[0069] See Figure 3 Surface fatigue shear cracks manifest as a single sharp reflected wave. The specific judgment method is as follows: single sharp peak wave, amplitude A≥0.4A0, bottom wave attenuation rate α≤0.2α0, defect wave frequency f=1.6-2.0f0, crack length 0.5mm≤L0≤3mm.

[0070] Using the built-in measurement function of the flaw detector, the location, depth, length, and number of cracks are read and recorded, and the crack type is marked simultaneously: internal aging hidden microcracks or surface fatigue shear cracks. At the same time, the altitude, ambient temperature, and service life of the pad are recorded to provide a basis for subsequent life correction.

[0071] S5. Collect ambient temperature, altitude, diurnal temperature range, and ultraviolet radiation intensity at the site, and calculate the plateau environment correction coefficient.

[0072] The diurnal temperature range on the plateau can reach over 40°C. The high coefficient of thermal expansion and contraction of polymer materials leads to repeated thermal stress cycles, causing plastic deformation at the crack tip and accelerating the crack propagation rate. Experiments have shown that for every 10°C increase in temperature difference, the crack propagation rate increases by 15%-20%.

[0073] For every 1000m increase in altitude, the air pressure decreases by 10%, and the micropores with a diameter of <1μm inside the material expand, leading to an increase in the stress concentration factor at the crack tip and accelerating crack propagation. Experiments have verified that at an altitude of 3500m, the crack propagation rate is 20% higher than in plains areas.

[0074] Based on the above mechanism, a plateau environment correction coefficient t is established as follows:

[0075]

[0076] in,

[0077] T: Temperature measured on-site, in °C;

[0078] H: Elevation of the site, in meters (m).

[0079] By comparing the on-site testing data from different altitudes and temperature ranges in the plateau region with the error before and after correction, the error after correction was reduced from more than 25% to less than 8%.

[0080] S6. Establish a life quantification model based on Paris crack propagation theory, using the core fatigue crack propagation formula da / dN=C(ΔK) proposed by Paul C. Paris. m Based on this theoretical foundation, and combined with the load spectrum characteristics of plateau railways, the crack length L0 and the relative value of defect amplitude A / A0 (dimensionless to avoid dimension mismatch) obtained by ultrasonic testing are incorporated into the calculation process of the stress intensity factor ΔK, thus deriving the remaining service life N. R The quantitative calculation formula is derived as follows:

[0081] Step 1: Determine the core theoretical basis. The Paris fatigue crack propagation theory is adopted, and its core governing equation is: da / dN=C(ΔK). m The parameters are initially defined as follows: da / dN is the crack propagation rate (unit: mm / cycle), which is the increment of crack length for each train cycle load; C and m are the material constants of the polymer elastic pad, which are related to the material and aging degree, and are obtained through on-site calibration of the same batch of new pads; ΔK is the stress intensity factor amplitude (unit: MPa·mm¹ / ²), which reflects the stress concentration at the crack tip and is the core parameter that determines the crack propagation rate.

[0082] Step 2: Quantitative calculation of stress intensity factor ΔK. For common surface fatigue shear cracks and internal aging-induced hidden microcracks in high-altitude elastic pads, based on the theory of stress intensity factor calculation for flat plate cracks, crack length is introduced. Combining the cyclic load characteristics of high-altitude trains and the stress concentration factor of the pad, a ΔK calculation formula adapted to high-altitude working conditions is derived, resulting in:

[0083] ;

[0084] Wherein, Δσ: the amplitude of the cyclic load on the plateau train, obtained through on-site track load testing;

[0085] β: Stress concentration factor, calibrated through finite element simulation. For polyurethane pads, β = 1.8-2.2; for rubber pads, β = 1.6-2.0. Figure 1 Taking the WJ8-B polyurethane pad as an example, the β value of the edge and the area around the bolt holes is 2.0-2.2, and the β value of the core stress area is 1.8-2.0.

[0086] a: Crack length measured on-site, in mm;

[0087] Achieve a direct correlation between ΔK and the parameters measured in the field.

[0088] Step 3: Remaining service life N R The integral derivation defines the remaining service life as: from the current crack length L0 to the critical crack length L of the pad failure. cr The required number of train cycle loads. Integrating the Paris equation, the integration interval is from crack length L0 to L... cr The number of load cycles ranges from 0 to N. R ,Right now:

[0089] ;

[0090] Step 4: Substitute ΔK and simplify to obtain the final quantification formula. Substitute the ΔK expression derived in Step 2 into the integral equation, and combine it with the plateau environment correction coefficient t to simplify the integral formula and finally obtain the remaining service life N. R The quantitative calculation formula is as follows:

[0091] ;

[0092] Where, N R : Remaining fatigue life of the pad, in cycles;

[0093] da: Incremental crack propagation under a single cyclic load;

[0094] L cr : Critical crack length of the pad failure plate, in mm;

[0095] L0: Crack length obtained from ultrasonic testing, in mm.

[0096] Through extensive field testing experiments at high altitudes and accelerated aging experiments in the laboratory, it was determined that the relative value of ultrasonic defect amplitude A / A0 has a monotonic correspondence with crack length L0 and crack depth. A unified conversion method for calculating the crack characteristic size L0 from ultrasonic echo amplitude is clearly given as follows:

[0097] ;

[0098] Wherein, A: the actual measured defect echo amplitude, in dB, is collected in real time by the detection equipment;

[0099] A0: The reference amplitude of the bottom echo of a brand new, defect-free, sound velocity stability reference sample made of the same batch and material.

[0100] Note: When A / A0 < 0.36, L0 is negative. In this case, the calculated L0 has no physical meaning. It is uniformly determined that the pad has no moldable and expandable fatigue cracks and no risk of structural damage.

[0101] The above method was applied to perform life testing on the experimental pads in the following scenario:

[0102] 1. Implementation scenario: A high-altitude railway line at an altitude of 3800m, with low air pressure and an ambient temperature of -12℃. The test object is a polyurethane elastic pad with a thickness of 12mm that has been in service for 1.5 years. The line has an average daily train throughput of 8 pairs. The train cyclic load amplitude Δσ is measured to be 12MPa by the on-site track dynamic load tester.

[0103] 2. Testing Equipment and Parameter Settings: A portable digital ultrasonic flaw detector, primarily using a 7.5MHz angle probe and secondarily a 6.5MHz straight probe, is adapted for high-precision testing of 12mm thin polyurethane pads; it is equipped with a plateau-specific antifreeze coupling agent; and it comes with a standard, defect-free pad of the same material, with a thickness of 12mm. The equipment parameters are optimized for the cold-weather conditions of the thin pads: due to the cold-weather conditions, the sound velocity is increased to 60m / s, and the material sound velocity is set to 2400m / s; due to the need to reduce the gain for the thin pads to avoid bottom wave saturation and noise interference, a detection gain of 45dB is used; the detection range is 25mm, adapted for the 12mm thin plate thickness testing range.

[0104] 3. Testing procedure:

[0105] (1) Clean the ice, snow and ballast debris from the surface of the pad and wipe it dry with a soft cloth at room temperature; place the flaw detector and probe in the insulation sleeve and preheat for 10 minutes to adapt to the low temperature detection environment of the plateau; the thin pad is suitable for the construction of thin-layer coupling agent, and apply a coupling agent with a thickness of 0.6mm; use a standard defect-free 12mm test block of the same material to complete the equipment calibration, lock the reference amplitude A0=80dB, the reference bottom wave attenuation rate a0=0.08dB / mm, the reference frequency f0=7.0MHz, and carry out 3 repeated calibration verifications. A0 fluctuation ±1.2%, a0 fluctuation ±0.8%, f0 fluctuation ±0.3%, which fully meets the detection accuracy verification standard.

[0106] (2) Divide the pad into the central core stress zone, the rounded corner zone, and the bolt hole perimeter zone. Move the probe at a uniform speed of 2.5 cm / s and scan each zone twice. The signal deviation between the two scans is 2.5%. The acquired ultrasonic signals are: defect amplitude A = 40 dB, bottom wave attenuation rate a = 0.12 dB / mm, defect wave frequency f = 1.8f0, f = 12.6 MHz. According to the ultrasonic waveform quantification criteria introduced in step S4, the waveform is a single sharp peak wave with weak bottom wave attenuation and a significantly increased defect frequency, which is consistent with the waveform characteristics of surface fatigue shear crack. Moreover, the defect is located in the edge zone (first-level high stress concentration zone) of the WJ8-B pad, with a corresponding stress concentration factor β = 2.1.

[0107] (3) Using the conversion formula calibrated in step S: L0 = 12.5 x (A / A0) - 4.5, where the reference amplitude A0 = 80 dB, the measured defect amplitude A = 40 dB, and the dimensionless amplitude ratio is calculated as: A / A0 = 40 / 80 = 0.5; substituting into the formula, the current equivalent crack length is obtained as: L0 = 12.5 x 0.5 - 4.5 = 1.75 mm. The calculation result meets the crack accuracy requirements of this invention. Compared with the actual crack length of 1.81 mm measured by on-site microscopic dissection, the deviation is only 0.06 mm, which is less than the allowable error of 0.1 mm, verifying the reliability of the conversion accuracy.

[0108] (4) Based on the calculation formula of the plateau environment correction coefficient:

[0109] In this embodiment, the altitude H=3800m and the ambient temperature T=-12℃ are calculated as follows: t=1.2+0.0001x(3800-2500)+0.01x(0-(-12))=1.2+0.13+0.12=1.45. This correction coefficient comprehensively compensates for the coupling effect of the low air pressure porosity effect at high altitude and the rate of crack propagation due to high cold embrittlement.

[0110] (5) In this embodiment, the fatigue constant of the polyurethane pad was calibrated on-site as C=4.2x10-12, m=3.1, and the critical failure crack length L was determined. cr =3mm; combined with β=2.1, the measured cyclic load amplitude Δσ=12MPa, substituting the parameters, we get: ΔK=58.32MPa.mm 1 / 2 .

[0111] (6) Based on the integral derivation of the Paris crack propagation equation, the life quantification formula is derived. Substituting all the calibration parameters of this embodiment: C=4.2x10-12, m=3.1, t=1.45, β=2.1, Δσ=12MPa, L0=1.75mm, L cr =3mm, the integral term was accurately solved using the trapezoidal numerical integration method, considering the accelerated crack propagation effect of multi-field coupling at high altitude, and finally the remaining fatigue cycle number N of the pad was calculated.R =38620 times.

[0112] (7) Regarding the conversion of remaining service time, the plateau line has an average of 8 pairs of trains running per day, corresponding to an average daily effective load cycle of 16 times. Calculated based on normal operation for 365 days a year: Remaining service life = Total remaining cycles ÷ (Average daily cycles × 365). Substituting the data, we get: Remaining service life = 38620 ÷ (16 × 365) ≈ 6.6 years. Combining the 30-year design service life standard for railway polyurethane pads, the current cracks in this pad have entered a rapid propagation stage, and the remaining service life has been significantly reduced, which is a typical characteristic of accelerated fatigue deterioration in a high-altitude, cold, and low-pressure environment.

Claims

1. A method for determining the lifespan of a pad under high-altitude conditions by detecting cracks in the pad, characterized in that, It includes the following steps: S1. Pre-treat the surface of the pad; S2. Select the probe type and frequency according to the material and thickness of the pad, set the material sound velocity, detection gain and range, and use a standard defect-free pad of the same material and thickness for comparison and calibration to obtain the benchmark detection waveform. S3. Perform ultrasonic scanning on the pad, and collect and record the location, amplitude and quantity of abnormal reflection signals in real time; S4. Based on waveform characteristics, distinguish between internal aging microcracks and surface fatigue shear cracks, and extract crack length and ultrasonic defect amplitude; S5. Collect on-site environmental parameters and calculate the plateau environment correction coefficient; S6. Substitute the information collected above into the following model formula to calculate the remaining service life of the pad: ； Where, N R : Remaining fatigue life of the pad; L cr : Critical crack length for pad failure; L0: Crack length obtained from the current ultrasonic testing; Δσ: Amplitude of cyclic load on plateau trains; C, m: material constants; β: Stress concentration factor; a: Crack length; t: Plateau environment correction factor.

2. The method for determining the lifespan of a pad under high-altitude conditions by detecting cracks in the pad, as described in claim 1, is characterized in that... The preprocessing in step S1 includes: Clean any adhering substances from the surface and rounded corners of the elastic pad to be tested; When the ambient temperature is below 0℃, place the ultrasonic flaw detector and probe in an insulated sleeve for preheating and apply a low-temperature special coupling agent.

3. The method for determining the lifespan of a pad under high-altitude conditions by detecting pad cracks, as described in claim 1, is characterized in that... When testing polyurethane pads, set the probe frequency to 5-10MHz, the sound velocity to 2200-2500m / s, the detection gain to 40-58dB, and the detection range to 20-50mm. When testing the rubber pad, set the probe frequency to 5-8MHz, the sound velocity to 1750-2500m / s, the detection gain to 48-60dB, and the detection range to 25-45mm.

4. The method for determining the lifespan of a pad under high-altitude conditions by detecting cracks in the pad, as described in claim 3, is characterized in that... When the ambient temperature is <0℃, the sound velocity is increased by 50-100m / s and the gain is reduced by 2-3dB; when the altitude is >3500m, the gain is slightly increased by 1-2dB; after the pad is aged by strong ultraviolet light, the gain is increased by 3-4dB.

5. The method for determining the lifespan of a pad under high-altitude conditions by detecting cracks in the pad, as described in claim 1, is characterized in that... The formula for calculating the plateau environment correction factor is as follows: ； in, T: Temperature measured on-site; H: Elevation at the site.

6. The method for determining the lifespan of a pad under high-altitude conditions by detecting cracks in the pad, as described in claim 1, is characterized in that... The formula for calculating the crack length L0 obtained from the current ultrasonic testing is as follows: ； Wherein, A: the amplitude of the defect echo measured on site; A0: The echo amplitude of the bottom surface of a brand new, defect-free, sound velocity stability reference sample made of the same batch and material.

7. The detection method for determining the life of a pad under high-altitude conditions by means of pad cracks according to claim 1, wherein in step S4, the normal and defect-free pad has a stable waveform, no abnormal noise or reflected waves, noise amplitude A≤0.05A0, bottom wave attenuation rate α≤0.1α0, no independent spike waveform, and no abnormal frequency fluctuations. When obvious peak reflection waves, bottom wave attenuation, and increased noise appear, it is determined to be a crack defect. Based on the waveform characteristics, crack defects can be divided into internal microcracks and surface fatigue cracks. Internal aging and hidden microcracks are mostly manifested as continuous fine and fragmented noise waves, with a single peak amplitude of 0.1A0≤A≤0.3A0, a bottom wave attenuation rate of 0.2α0≤α≤0.4α0, a defect wave frequency of f=1.2-1.5f0, and a crack length of L0<0.5mm. f0 is the reference frequency of the ultrasonic reference waveform of a brand new pad of the same batch, material, and without defects. The surface fatigue shear crack manifests as a single sharp reflected wave with amplitude A≥0.4A0, bottom wave attenuation rate α≤0.2α0, defect wave frequency f=1.6-2.0f0, and crack length 0.5mm≤L0≤3mm.

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