A stress correction method and system based on size deviation of ultrasonic fatigue specimen

Abstract

The application discloses a stress correction method and system based on size deviation of an ultrasonic fatigue sample, and comprises the following steps: installing a sample to be detected on an ultrasonic fatigue testing machine; determining whether the sample can vibrate according to the vibration frequency range of the testing machine; if not, reprocessing the sample; otherwise, calculating a corresponding theoretical value of a harmonic frequency by using a preset analytical formula or a harmonic response analysis model according to actual size parameters of the sample, selecting a corresponding stress amplitude calculation method according to the range where the theoretical value of the harmonic frequency is located, and calculating an actual stress amplitude; taking the ratio of the actual stress amplitude of the sample to the theoretical value as a correction coefficient, and correcting a preset stress amplitude of the sample according to the correction coefficient. The application can avoid reprocessing samples in batches due to size deviation of the samples. Moreover, more accurate and safer ultrahigh-cycle S / N curves can be obtained, and dangerous results caused by overestimation of fatigue life due to inaccurate stress can be avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ultrasonic fatigue performance testing of metal materials, and particularly relates to a stress correction method and system based on size deviation of an ultrasonic fatigue sample. BACKGROUND

[0002] With the development of modern industry, some high-strength steels applied to key parts, or structure steels subjected to high-frequency low-load, such as bridge cable steels, high-speed rail steels, aviation and aerospace blade steels, etc., have a high actual service life requirement of up to 10 8 ~ 10 10 million cycles. A large number of test results and engineering cases have confirmed that many engineering steel and alloy material structures will still have fatigue fracture after 10 7 million stress cycles, and the existing fatigue strength evaluation method with 10 7 million cycles as the limit is no longer applicable.

[0003] Ultrasonic fatigue testing is a new technology for testing the fatigue performance of materials, and the working frequency can reach 2.0 x 10 4 Hz. Testing a sample with a service life of 10 9 million cycles can be completed in about one day. Ultrasonic fatigue testing technology is an effective means to study the ultrahigh cycle fatigue performance of metal materials. The principle of ultrasonic fatigue testing is mainly to generate an electric signal of 2.0 x 10 4 Hz by using an ultrasonic generator, to convert the electric signal into mechanical vibration of the same frequency by using a piezoelectric ceramic transducer, to amplify the mechanical vibration by using a displacement amplifier, and to transmit the amplified mechanical vibration to a sample, so that the sample generates a harmonic wave, and the sample obtains an axial displacement and stress which varies in a sinusoidal wave with a frequency of 2.0 x 10 4 Hz, as shown in FIG. 1. In the figure, a represents the axial stress distribution of the sample, and b represents the axial displacement distribution of the sample. Figure 2

[0004] ​The theoretical value of the stress of a smooth sample in the prior art is directly calculated according to quasi-static tension in the process of conventional fatigue test, that is, the external load is divided by the minimum cross-sectional area of the sample. Unlike conventional fatigue test, the stress amplitude theoretical value of an ultrasonic fatigue sample is obtained by derivation of a displacement amplitude function in ultrasonic fatigue test because the frequency is extremely high and the test system adopts a displacement control mode. The displacement amplitude function is obtained by solving a longitudinal wave equation when the sample resonates. Therefore, the stress amplitude of the ultrasonic fatigue sample is related to the sample size, elastic modulus, density, vibration frequency, free end displacement and other parameters. Before the ultrasonic fatigue test is performed, the sample size that meets the test resonant frequency is designed according to a theoretical formula of the sample geometric size, and then the sample is processed according to the designed size. In the processing process, the actual size of the sample may deviate greatly from the designed size due to processing errors and other reasons. The great deviation of the size will cause the actual resonant frequency value of the sample to deviate from the target value 2.0x10 4 Hz, and the actual stress amplitude of the sample will also deviate from the set target value, thereby causing the ultrahigh cycle fatigue test result to be inaccurate. In particular, if the actual stress amplitude of the sample is lower than the set value, the fatigue life will be overestimated, and the test result used for engineering design will bring dangerous consequences.

[0005] In addition, for some relatively light metal materials such as aluminum alloy, when the sample size deviation is large, the resonant frequency of the sample itself may not be within the range of 1.95x10 4 Hz~2.05x10 4 Hz (vibration frequency range of the ultrasonic fatigue testing machine), but because the sample mass is relatively small, the overall resonant frequency of the test system is not sensitive to the sample size deviation. After the sample is installed on the displacement amplifier, it can still vibrate near the frequency of 2.00x10 4 Hz, at which time the vibration of the sample is strictly speaking not a resonant vibration, but a forced vibration driven by the vibration of the displacement amplifier. At this time, the actual stress amplitude of the sample will also deviate from the set value. Therefore, a stress correction method and system based on the size deviation of the ultrasonic fatigue sample are needed for correction. SUMMARY

[0006] The embodiments of the present application provide a stress correction method and system based on the size deviation of an ultrasonic fatigue sample, at least partially solve the technical problem that the fatigue life will be overestimated due to the size and material deviation of the sample in the prior art, and achieve the technical effect of correcting the stress amplitude of the ultrasonic fatigue sample that has been processed without reprocessing the sample in batches due to the size deviation of the sample.

[0007] In the first aspect, to solve the above technical problem, the embodiments of the present application provide the following technical solutions:

[0008] A stress correction method based on size deviation of ultrasonic fatigue specimen, comprising:

[0009] installing a specimen to be tested on an ultrasonic fatigue testing machine;

[0010] According to the vibration frequency range of the above-mentioned testing machine, it is detected whether the above-mentioned specimen can vibrate;

[0011] If not, rework the above-mentioned specimen; otherwise, according to the actual size parameters of the above-mentioned specimen, use a preset analytical formula or a harmonic response analysis model to calculate the corresponding theoretical value of the resonant frequency, and based on the range where the above-mentioned theoretical value of the resonant frequency is located, select the corresponding stress amplitude calculation method to calculate the actual stress amplitude;

[0012] The ratio of the actual stress amplitude of the specimen to the theoretical value is used as a correction coefficient, and the preset stress amplitude of the above-mentioned specimen is corrected according to the above-mentioned correction coefficient.

[0013] Optionally, the step of calculating the corresponding theoretical value of the resonant frequency using a preset analytical formula further comprises:

[0014] When the above-mentioned specimen is symmetrical at both ends and in the shape of a sandglass, the theoretical value of the resonant frequency is calculated according to the formula

[0015] ,

[0016] ,

[0017] ,

[0018]

[0019] , , , , is half of the length of the end of the sandglass-shaped specimen; is half of the length of the variable cross-section section of the specimen; is the diameter of the end of the specimen; is the minimum diameter of the specimen; c is the propagation speed of the resonant wave in the specimen; is the dynamic elastic modulus of the specimen; p is the density of the specimen; f is the resonant frequency of the specimen, and w is the angular frequency.

[0020] Optionally, the step of calculating the actual stress amplitude further comprises:

[0021] When the above-mentioned theoretical value of the resonant frequency and the actual vibration frequency value are both within a preset frequency range, the actual stress amplitude is calculated according to the formula

[0022] , ​

[0023] ,

[0024] calculating the actual stress amplitude;

[0025] wherein, is the amplitude of the vibration displacement of the end of the sample; is the amplitude of the vibration displacement of the end of the sample corresponding to the theoretical stress amplitude at the middle section of the sample;

[0026] When the above theoretical resonance frequency value is not within the above preset frequency range, the sample in vibration is photographed and analyzed by using a high-speed camera, and the actual strain amplitude and stress amplitude of the sample are calculated based on a digital image correlation method.

[0027] Optionally, the step of calculating the corresponding theoretical resonance frequency value by using the preset analytical formula further comprises:

[0028] When the above sample is symmetrical at both ends and has a dog bone shape, the formula

[0029] ,

[0030] ,

[0031] ,

[0032] calculating the theoretical resonance frequency value;

[0033] wherein, , , , is half of the length of the end of the dog bone-shaped sample; is half of the length of the variable cross-section section of the sample; is the diameter of the end of the sample; is the minimum diameter of the sample; c is the propagation speed of the resonance wave in the sample; is the dynamic elastic modulus of the sample; ρ is the density of the sample; f is the resonance frequency of the sample, and ω is the angular frequency.

[0034] Optionally, the step of calculating the actual stress amplitude further comprises:

[0035] When the above theoretical resonance frequency value and the actual vibration frequency value are both within the preset frequency range, the formula

[0036] ,

[0037] ,

[0038] calculating the actual stress amplitude;

[0039] wherein, is the amplitude of the vibration displacement of the end of the sample; is the theoretical stress amplitude value of the middle section of the sample corresponding to the amplitude of the end vibration displacement U0;

[0040] When the above theoretical resonance frequency value is not in the above preset frequency range, the sample in vibration is photographed and analyzed by using a super high-speed camera, and the actual strain amplitude and stress amplitude of the sample are calculated based on a digital image correlation method.

[0041] Optionally, the step of calculating the corresponding theoretical resonance frequency value by using the preset analytical formula further comprises:

[0042] When the sample is symmetrical at both ends and is in a plate shape, the theoretical resonance frequency value is calculated according to the formula

[0043] ,

[0044] ,

[0045] ,

[0046] calculating a theoretical resonance frequency value;

[0047] wherein, , , , is half of the length of the end of the plate-shaped sample; is half of the length of the variable cross-section section of the sample; is half of the length of the parallel section of the sample; is the width of the end of the plate-shaped sample; is the minimum width of the plate-shaped sample; c is the propagation speed of the resonance wave in the sample; is the dynamic elastic modulus of the sample; is the density of the material of the sample; f is the resonance frequency of the sample, and ω is the angular frequency.

[0048] Optionally, the step of calculating the actual stress amplitude value further comprises:

[0049] When the above theoretical resonance frequency value and the actual vibration frequency value are both in the preset frequency range, the actual stress amplitude value is calculated according to the formula

[0050]

[0051] calculating an actual stress amplitude value;

[0052] wherein, is the amplitude of the vibration displacement of the end of the sample; is the amplitude of the vibration displacement of the end of the sample The theoretical stress amplitude value of the corresponding sample intermediate section;

[0053] When the theoretical resonance frequency value is not in the preset frequency range, the vibrating sample is photographed and analyzed by using a super high-speed camera, and the actual strain amplitude and stress amplitude of the sample are calculated based on a digital image correlation method.

[0054] Optionally, the step of calculating the corresponding theoretical resonance frequency value by using the harmonic response analysis model further comprises:

[0055] When the sample is not symmetrical at both ends, a finite element mesh model is established according to the geometric shape and actual size of the sample, harmonic response calculation is performed, and the resonance frequency of the sample is obtained;

[0056] If the resonance frequency is in the preset frequency range, the ratio of the corresponding stress amplitude value and displacement amplitude value is obtained by using harmonic response simulation, and the stress amplitude of the sample is obtained in combination with the end displacement amplitude of the sample;

[0057] If the resonance frequency is not in the preset frequency range, the vibrating sample is photographed and analyzed by using a super high-speed camera, and the strain amplitude and stress amplitude of the sample are calculated based on a digital image correlation method.

[0058] Optionally, the step of reprocessing the sample further comprises:

[0059] When the starting frequency is greater than the maximum value of the preset frequency range, the sample is scrapped;

[0060] When the starting frequency is less than the minimum value of the preset frequency range, the size of the sample is corrected by cutting the sample until the sample can vibrate.

[0061] In a second aspect, a stress correction system based on size deviation of an ultrasonic fatigue sample is provided, and the system comprises:

[0062] The installation module is configured to install the sample to be detected on an ultrasonic fatigue testing machine;

[0063] The initialization module is configured to detect whether the sample can vibrate according to the vibration frequency range of the testing machine;

[0064] The calculation module is configured to detect the starting state, and if not, reprocess the sample; otherwise, calculate the corresponding theoretical resonance frequency value by using a preset analytical formula or a harmonic response analysis model according to the actual size parameters of the sample, and select a corresponding stress amplitude calculation method based on the range in which the theoretical resonance frequency value is located, to calculate the actual stress amplitude value;

[0065] The correction module is used to correct the preset stress amplitude of the sample according to a correction coefficient which is a ratio of the actual stress amplitude of the sample to a theoretical value.

[0066] The one or more technical solutions provided in the embodiments of the present application have at least the following technical effects or advantages:

[0067] Different resonance frequency calculation methods or calculation formulas are given according to the size deviation of different sample structures, and whether the sample is resonating or forced vibration is judged according to the size of the resonance frequency value. If it is resonance, the stress amplitude of the sample is calculated by using a theoretical formula or finite element harmonic response analysis. If it is forced vibration, the stress amplitude of the sample is calculated by using a high-speed DIC system. Thus, the fatigue performance test is more comprehensive, complete, efficient and economical. At the same time, the stress amplitude of the ultrasonic fatigue sample that has been processed can be corrected. As long as the sample can vibrate, it is not necessary to reprocess the sample in batches due to the size deviation of the sample. And the stress amplitude of the sample is corrected according to the ratio of the actual stress amplitude to the preset theoretical value, so that more accurate and safer ultrahigh cycle S / N curves can be obtained, and the dangerous results caused by overestimation of fatigue life due to inaccurate stress can be avoided. BRIEF DESCRIPTION OF DRAWINGS

[0068] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0069] Figure 1 A flowchart of a stress correction method based on size deviation of an ultrasonic fatigue sample is provided in the present application.

[0070] Figure 2 A structural schematic diagram of an ultrasonic fatigue test in the present application is provided.

[0071] Figure 3 A structural schematic diagram of an hourglass-shaped sample in the present application is provided.

[0072] Figure 4 A structural schematic diagram of a dog bone-shaped sample in the present application is provided.

[0073] Figure 5 A structural schematic diagram of a plate-shaped sample in the present application is provided.

[0074] Figure 6 A frequency back-calculation schematic diagram combined with the formula in the embodiment of the present application is provided.

[0075] Figure 7A schematic diagram for calculating the resonance frequency of a sample by harmonic response analysis in the present application;

[0076] Figure 8 A structural schematic diagram of a stress correction system based on size deviation of an ultrasonic fatigue sample provided in the present application;

[0077] Figure 9 A schematic diagram of the designed size of a sample 2 aluminum alloy sample in the present application;

[0078] Figure 10 A schematic diagram of the actual processing size of a sample 2 aluminum alloy sample in the present application.

[0079] The reference signs: 1, industrial computer; 2, ultrasonic generator; 3, piezoelectric transducer; 4, displacement amplifier; 5, sample. DETAILED DESCRIPTION

[0080] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. The components of the embodiments of the present application described and shown in the drawings can be arranged and designed in various different configurations.

[0081] Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without making creative efforts are within the scope of protection of the present application.

[0082] It should be noted that: similar reference signs and letters represent similar items in the following drawings, therefore, once an item is defined in one drawing, it does not need to be further defined and explained in the subsequent drawings.

[0083] It should be understood that the embodiments of the present application and the specific features in the embodiments are detailed descriptions of the technical solutions of the present application, but not limitations of the technical solutions of the present application, and the technical features in the embodiments of the present application and the embodiments can be combined with each other without conflict.

[0084] In the embodiments of the present application, a stress correction method based on size deviation of an ultrasonic fatigue sample is provided as shown in Figure 1 The method includes steps S101-S104:

[0085] Step S101, installing a sample to be detected on an ultrasonic fatigue testing machine;

[0086] Step S102, according to the vibration frequency range of the testing machine, it is judged whether the sample can vibrate or not;

[0087] It should be noted that before setting the preset frequency range, a smaller displacement amplitude is given to the testing machine to judge whether the sample can vibrate or not. The preset frequency range is 1.95×10 4 Hz~2.05×10 4 Hz. Wherein the vibration refers to the sample starting in the vibration state.

[0088] Step S103, if not, the sample is reprocessed; otherwise, according to the actual size parameters of the sample, the corresponding theoretical value of the resonant frequency is calculated by using the preset analytical formula or the harmonic response analysis model, and based on the range where the theoretical value of the resonant frequency is located, the corresponding stress amplitude calculation method is selected to calculate the actual stress amplitude;

[0089] It should be noted that if the sample cannot vibrate, it means that the size deviation of the sample is too large and needs to be reprocessed. If the sample can vibrate, it means that the size of the sample has deviation, but the sample can still vibrate in the frequency range of 1.95×10 4 Hz~2.05×10 4 Hz, and the test can continue, but the actual stress amplitude of the sample may deviate from the preset value, and the stress amplitude needs to be corrected. Therefore, the corresponding theoretical value of the resonant frequency is calculated first, and then the selected stress amplitude calculation method is judged according to the theoretical value of the resonant frequency to calculate the actual stress amplitude. The size parameters include: is half of the length of the variable cross-section section of the sample; is the diameter of the end of the sample; is the minimum diameter of the sample; c is the propagation speed of the resonant wave in the sample; is the dynamic elastic modulus of the sample; ρ is the density of the sample; is the width of the end of the plate-shaped sample; is the minimum width of the plate-shaped sample, etc.

[0090] Step S104, the ratio of the actual stress amplitude of the sample to the theoretical value is taken as a correction coefficient, and the preset stress amplitude of the sample is corrected according to the correction coefficient.

[0091] It should be noted that by taking the ratio of the stress amplitude of the sample to the theoretical value, the stress amplitude correction coefficient can be obtained. According to the correction coefficient, the stress amplitude of the tested sample is checked, that is, the stress amplitude is multiplied by the correction coefficient to obtain the corrected stress amplitude.

[0092] Further, since the sample may cause the two ends to be asymmetric after processing (i.e. slight processing error), the calculation needs to be distinguished according to whether the sample is symmetric or not. In addition, different types of samples also need to be calculated differently. This embodiment is for the case where the sample is symmetric at both ends and the shape is hourglass-shaped, and the structure is as shown in Figure 3 The theoretical value of the resonant frequency and the actual stress amplitude calculation process are as follows:

[0093] When the sample is symmetric at both ends and the shape is hourglass-shaped, the theoretical value of the resonant frequency is calculated according to the formula

[0094] ,

[0095] ,

[0096] ,

[0097]

[0098] , , , , is half of the length of the end of the hourglass-shaped sample; is half of the length of the variable cross-section section of the sample; is the diameter of the end of the sample; is the minimum diameter of the sample; c is the propagation speed of the resonant wave in the sample; is the dynamic elastic modulus of the sample; p is the density of the sample; f is the resonant frequency of the sample, and w is the angular frequency.

[0099] When the theoretical value of the resonant frequency and the actual vibration frequency value are within the preset frequency range, the actual stress amplitude of the sample is calculated according to the formula

[0100] ,

[0101] ,

[0102] , is the amplitude of the vibration displacement of the end of the sample; is the amplitude of the vibration displacement of the end corresponds to the theoretical value of the stress amplitude at the middle cross section of the sample;

[0103] When the theoretical value of the resonant frequency is not within the preset frequency range, the vibrating sample is photographed and analyzed by using a high-speed camera, and the actual strain amplitude and stress amplitude of the sample are calculated based on the digital image correlation method.

[0104] ​Further, since the sample is symmetrical at both ends, the calculation process of different types of samples is the same, and this embodiment takes the dog bone shape as an example for detailed description. The specific program structure diagram is as shown in Figure 8 as follows:

[0105] For a batch of processed dog bone-shaped samples, there is a deviation between the size designed according to the theoretical formula and the actual processing size. After the sample is installed on the ultrasonic fatigue testing machine, a smaller displacement amplitude is given to judge whether the sample can vibrate. If the sample cannot vibrate, it means that the size deviation of the batch of samples is too large and needs to be reprocessed. If the sample can vibrate, it means that although the size of the batch of samples has a deviation, the sample can still vibrate in the frequency range of 1.95×10 4 Hz~2.05×10 4 Hz, and the test can continue, but the actual stress amplitude of the sample may deviate from the preset value, and the stress amplitude needs to be corrected. At this time, there are two cases: 1. The sample size is symmetrical at both ends; 2. The sample size is not symmetrical at both ends. Here, the symmetrical case is explained, that is, symmetrical along the Y axis as shown in Figure 4

[0106] When the sample vibrates, the control software of the testing machine will display the actual vibration frequency value of the sample, denoted as , ∈(19.5kHz, 20.5kHz); at this time, the theoretical value of the resonant frequency can be calculated from the actual size parameters of the preset parameters (i.e. the , in the text) as shown in Figure 6

[0107] (1)

[0108] (2)

[0109] (3)

[0110] Combined with formulas (1), (2) and (3), the theoretical value of the resonant frequency is obtained;

[0111] wherein , , , is half of the length of the end of the dog bone-shaped sample; is half of the length of the variable cross-section section of the sample; is the diameter of the end of the sample; is the minimum diameter of the sample; c is the propagation speed of the resonant wave in the sample; is the dynamic elastic modulus of the sample; ρ is the density of the sample; f is the resonant frequency of the sample, and ω is the angular frequency.​​

[0112] After the resonance frequency theoretical value is calculated, the stress amplitude is calculated as follows:

[0113] When the resonance frequency theoretical value and the actual vibration frequency value are both within the preset frequency range (i.e. 1.95x10 4 Hz~2.05x10 4 Hz), it indicates that the size of the sample is deviated, but the size deviation is small, and the sample is still in the resonance state. The actual stress amplitude of the sample is calculated according to formula

[0114] (4)

[0115] (5)

[0116] The actual stress amplitude is calculated;

[0117] wherein, is the vibration displacement amplitude of the end of the sample; is the vibration displacement amplitude of the end of the sample corresponding to the stress amplitude theoretical value of the middle section of the sample;

[0118] When the resonance frequency theoretical value is not within the preset frequency range, i.e. the resonance frequency theoretical value < 19.5 kHz or the resonance frequency theoretical value > 20.5 kHz. It indicates that the resonance frequency theoretical value and the actual vibration frequency value are deviated greatly, and further indicates that the size of the sample is deviated greatly. However, since the mass of the sample is small relative to the displacement amplifier, the overall resonance frequency of the test system is not sensitive to the size deviation of the sample. After the sample is installed on the displacement amplifier, it can still be excited. At this time, the vibration of the sample cannot be strictly called resonance, but forced vibration driven by the resonance of the displacement amplifier. Therefore, formula (4) and (5) cannot be used to calculate the actual stress amplitude of the sample. The high-speed DIC (Digital Image Correlation) system is selected to calculate the actual strain amplitude and stress amplitude of the sample by using a super-speed camera to take pictures of the vibrating sample.

[0119] Similarly, for a plate-shaped sample, as shown in FIG. 1, the resonance frequency theoretical value and the actual stress amplitude calculation process are as follows: Figure 5

[0120] That is, the step of calculating the corresponding resonance frequency theoretical value by using the preset analytical formula further includes:

[0121] When the sample is symmetrical at both ends and in the shape of a plate, the corresponding resonance frequency theoretical value is calculated according to formula

[0122] (6)

[0123] ​a theoretical value of a resonant frequency is calculated;

[0124] wherein, , , , is half of the length of the end of the plate-shaped sample; is half of the length of the variable cross-section section of the sample; is half of the length of the parallel section of the sample; is the width of the end of the plate-shaped sample; is the minimum width of the plate-shaped sample; c is the propagation speed of the resonant wave in the sample; is the dynamic elastic modulus of the sample; is the density of the material of the sample; f is the resonant frequency of the sample, and ω is the angular frequency.

[0125] Then, the step of calculating the actual stress amplitude further comprises:

[0126] When the theoretical value of the resonant frequency and the actual vibration frequency value are both within the preset frequency range, the actual stress amplitude of the sample is calculated according to the formula

[0127]

[0128] (7)

[0129] wherein, is the vibration displacement amplitude of the end of the sample; is the vibration displacement amplitude of the end of the sample corresponding to the theoretical value of the stress amplitude at the middle cross-section of the sample;

[0130] When the theoretical value of the resonant frequency is not within the preset frequency range, the vibrating sample is photographed and analyzed by using a high-speed camera, and the actual strain amplitude and the stress amplitude of the sample are calculated based on the digital image correlation method.

[0131] Further, the step of calculating the corresponding theoretical value of the resonant frequency by using the harmonic response analysis model further comprises:

[0132] When the two ends of the sample are asymmetric, a finite element grid model is established according to the geometric shape and actual size of the sample, harmonic response calculation is performed, and the resonant frequency of the sample is obtained; if the resonant frequency is within the preset frequency range, the ratio of the stress amplitude to the displacement amplitude is obtained by using the harmonic response simulation, and the stress amplitude of the sample is obtained in combination with the displacement amplitude of the end of the sample; if the resonant frequency is not within the preset frequency range, the vibrating sample is photographed and analyzed by using a high-speed camera, and the strain amplitude and the stress amplitude of the sample are calculated based on the digital image correlation method.

[0133] It should be noted that for the asymmetric case of the sample, the embodiment still takes the dog bone-shaped sample as an example for illustration. Along the length direction axis is asymmetric, that is, the values of the two ends of the sample are different. At this time, the theoretical formula is not applicable to calculate the frequency and stress amplitude of the sample. The finite element method can be used to establish a finite element grid model according to the geometric shape and actual size of the sample, and perform harmonic response analysis to calculate the resonant frequency of the sample, as shown in formula (1). If the resonant frequency theoretical value calculated by the finite element harmonic response analysis is ∈ (19.5 kHz, 20.5 kHz), the deviation of the resonant frequency theoretical value and the actual vibration frequency value is small, indicating that the sample size deviation is small. At this time, the stress amplitude value of the sample can be obtained from the ratio of the stress amplitude and displacement amplitude in the harmonic response analysis result shown in formula (2). Figure 7 Figure 7

[0134] If the resonant frequency theoretical value calculated based on the finite element harmonic response analysis is < 19.5 kHz or > 20.5 kHz, the deviation of the resonant frequency theoretical value and the actual vibration frequency value is large, indicating that although the sample size deviation is large, the sample mass is still small relative to the displacement amplifier, and the sample can still be forced to vibrate under the resonance action of the displacement amplifier. In this case, the finite element harmonic response analysis cannot be used to calculate the stress amplitude of the sample. The high-speed DIC system can be used to analyze the sample vibration by using a super-speed camera to calculate the actual strain amplitude and stress amplitude of the sample.

[0135] Further, the step of reprocessing the sample further includes:

[0136] When the vibration frequency is greater than the maximum value of the preset frequency range, the sample is discarded; when the vibration frequency is less than the minimum value of the preset frequency range, the sample size is corrected by cutting the sample until the sample can vibrate.

[0137] It should be noted that in the case where the sample cannot vibrate, it means that the sample size deviation of the batch is too large, and there are two cases: 1. The system displays a frequency greater than 2.05 x 10 4 Hz, indicating that the sample is too short and can only be discarded; 2. The system displays a frequency less than 1.95 x 10 4 Hz, indicating that the sample is too long and can be adjusted in size by cutting until the sample can vibrate.

[0138] Based on the above embodiment, specific implementation data is given for verification and illustration:

[0139] Sample 1, for a low-alloy high-strength weathering steel, dynamic elastic modulus ​​​​​= 206 Gpa; density = 7.85 The structure is a plate-shaped sample, and according to formula (6), the size of the theoretically designed sample is: = 12.5 mm, = 20 mm, = 3 mm, = 10 mm, = 11.13 mm. After actual processing, the actual processing size of the sample is measured as = 12.5 mm, = 20 mm, = 11.00 mm, = 2.86 mm, = 9.90 mm. The sample is installed in the displacement amplifier and connected to vibrate, and the displacement amplitude of the end of the sample is given as = 22.1 μm, and the corresponding stress amplitude theoretical value is obtained from formula (7) = 200 MPa, the sample can normally start to vibrate, and the control software interface of the testing machine displays the actual vibration frequency = 19.95 kHz. And the sample is symmetrical at both ends, and the corresponding resonance frequency theoretical value is calculated from formula (6) as 19.88 kHz. The resonance frequency theoretical value ∈ (19.5 kHz, 20.5 kHz), and the deviation is small, indicating that the sample size has a small deviation, but the sample is still in resonance state, and = 12.5 mm, = 20 mm, = 11.00 mm, = 2.86 mm, = 9.90 mm. The actual stress amplitude is obtained by bringing into formula (7) = 198 MPa. The correction coefficient .

[0140] Sample 2, for a certain aluminum alloy, dynamic elastic modulus = 76.6 Gpa; density = 2.77 The structure is a dog bone-shaped sample,

[0141] The sample size designed according to formula (1) is shown in Figure 9 The actual processing size of the sample is shown in Figure 10 The sample is installed in the displacement amplifier and connected to vibrate, and the displacement amplitude of the end of the sample is given as = 23.8 μm, and the corresponding stress amplitude theoretical value is obtained from formula (4) = 124 MPa, the sample can normally start to vibrate, and the control software interface of the testing machine displays the actual vibration frequency = 20.13 kHz. From Figure 10 it can be seen that the sample is not symmetrical at both ends, and the resonant frequency of the sample cannot be calculated by formula (1). Therefore, a finite element mesh model is established according to the geometric shape and actual size of the sample, and a harmonic response analysis is performed by using the finite element method, and the results are shown in Figure 7 . The theoretical value of the resonant frequency is 21904.4 Hz, that is, the theoretical value of the resonant frequency is greater than 20.5 kHz. The difference between the actual vibration frequency and the theoretical value is relatively large, which indicates that although the deviation between the actual size and the design size is large, the aluminum alloy has a relatively small mass, and the sample can still vibrate with the displacement amplifier, and at this time, the vibration of the sample is forced vibration. Therefore, the stress amplitude of the sample cannot be calculated by using the finite element harmonic response analysis. In this case, the high-speed DIC system is used, the sample in vibration is photographed and analyzed by using the super-speed camera, and the actual stress amplitude of the sample is calculated = 116 MPa. The correction coefficient .

[0142] Based on the same inventive concept, the embodiments of the present application provide a stress correction system based on size deviation of an ultrasonic fatigue sample, as shown in Figure 8 , comprising:

[0143] The installation module 201 is configured to install the sample to be detected on the ultrasonic fatigue testing machine.

[0144] The initialization module 202 is configured to detect whether the sample can vibrate according to the vibration frequency range of the testing machine.

[0145] The calculation module 203 is configured to detect the vibration state, and if not, the sample is reprocessed. Otherwise, the corresponding theoretical value of the resonant frequency is calculated according to the actual size parameters of the sample by using a preset analytical formula or a harmonic response analysis model, and the corresponding stress amplitude calculation method is selected based on the range where the theoretical value of the resonant frequency is located, and the actual stress amplitude is calculated.

[0146] The correction module 204 is configured to take the ratio of the actual stress amplitude of the sample to the theoretical value as a correction coefficient, and correct the preset stress amplitude of the sample according to the correction coefficient.

[0147] Those skilled in the art should understand that the embodiments of the present application can be provided as methods and systems. Therefore, the present application can be in the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can be in the form of a computer program product implemented on one or more computer usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer usable program code.

[0148] The present application is described in reference to the drawings of flowchart and / or block diagrams of the methods and systems according to embodiments of the application. It will be understood that each block of the flowchart and / or block diagrams, and combinations of blocks in the flowchart and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general purpose computer, special purpose computer, embedded processing machine, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart and / or block diagram block or blocks. Figure 1 one or more functions specified in the flowchart and / or block diagram block or blocks. Figure 1 one or more functions specified in the flowchart and / or block diagram block or blocks.

[0149] While the preferred embodiments of the application have been described, additional variations and modifications can be made to the embodiments by those of skill in the art once they have the benefit of the present disclosure. Therefore, the appended claims are intended to encompass within their scope all such variations and modifications as are within the scope of the application. It should be understood that all references back to a same number of elements are based on the recognition of a common element that can satisfy similar, but not necessarily the same, functions and can be configured similarly, but not necessarily identically. Thus, one or more features shared by a plurality of elements are identified by the element number common to those elements.

[0150] It will be apparent to those skilled in the art that various modifications and variations can be made to the present application without departing from the spirit or scope of the application. Thus, it is intended that the present application cover the modifications and variations of this application provided they come within the scope of the appended claims and their equivalents.

Claims

1. A stress correction method based on size deviation of an ultrasonic fatigue specimen, characterized by, The method comprises: installing a test sample to be tested on an ultrasonic fatigue testing machine; detecting whether the test sample can vibrate according to a vibration frequency range of the testing machine; if not, reprocessing the test sample; otherwise, calculating a corresponding theoretical value of a resonant frequency according to actual size parameters of the test sample by using a preset analytical formula or a harmonic response analysis model, and selecting a corresponding stress amplitude calculation method based on a range in which the theoretical value of the resonant frequency is located to calculate an actual stress amplitude; wherein the step of calculating the corresponding theoretical value of the resonant frequency by using the harmonic response analysis model further comprises: when the test sample is asymmetric at both ends, establishing a finite element mesh model according to a geometric shape and actual size of the test sample to perform harmonic response calculation to obtain the resonant frequency of the test sample; if the resonant frequency is within a preset frequency range, obtaining a ratio of a stress amplitude to a displacement amplitude by using harmonic response simulation, and obtaining the stress amplitude of the test sample in combination with an end displacement amplitude of the test sample; if the resonant frequency is not within the preset frequency range, taking a photo of the vibrating test sample by using a high-speed camera to analyze, and calculating a strain amplitude and a stress amplitude of the test sample based on a digital image correlation method; taking a ratio of the actual stress amplitude of the test sample to a theoretical value as a correction coefficient, and correcting a preset stress amplitude of the test sample according to the correction coefficient.

2. The method of claim 1, wherein, The step of calculating the corresponding theoretical value of the resonant frequency by using the preset analytical formula further comprises: when the test sample is symmetric at both ends and has a shape of a sandglass, calculating the theoretical value of the resonant frequency according to a formula ， ， ， The step of calculating the actual stress amplitude further comprises: wherein , , , is half the length of the end of the hourglass-shaped sample; is half the length of the variable cross-section section of the sample; is the diameter of the end of the sample; is the minimum diameter of the sample; c is the speed of propagation of the resonant wave in the sample; is the dynamic modulus of elasticity of the sample; p is the density of the sample; f is the resonant frequency of the sample, and w is the angular frequency.

3. The method of claim 2, wherein, when the theoretical value of the resonant frequency and an actual vibration frequency value are both within the preset frequency range, calculating the actual stress amplitude according to a formula When the theoretical value of the resonant frequency is not within the preset frequency range, taking a photo of the vibrating test sample by using a high-speed camera to analyze, and calculating an actual strain amplitude and a stress amplitude of the test sample based on a digital image correlation method. ， ， The step of calculating the corresponding theoretical value of the resonant frequency by using the preset analytical formula further comprises: wherein, is the amplitude of the oscillation of the end of the specimen; is the amplitude of the oscillation of the end of the specimen is the theoretical value of the stress amplitude at the middle section of the corresponding specimen; when the test sample is symmetric at both ends and has a shape of a dog bone, calculating the theoretical value of the resonant frequency according to a formula 4. The method of claim 1, wherein, The step of calculating the actual stress amplitude further comprises: when the theoretical value of the resonant frequency and an actual vibration frequency value are both within the preset frequency range, calculating the actual stress amplitude according to a formula ， ， ， When the theoretical value of the resonant frequency is not within the preset frequency range, taking a photo of the vibrating test sample by using a high-speed camera to analyze, and calculating an actual strain amplitude and a stress amplitude of the test sample based on a digital image correlation method. wherein , , , is half the length of the end of the dog bone shaped sample; is half the length of the variable cross section section of the sample; is the diameter of the end of the sample; is the minimum diameter of the sample; c is the speed of propagation of the resonant wave in the sample; is the dynamic modulus of elasticity of the sample; p is the density of the sample; f is the resonant frequency of the sample, and w is the angular frequency.

5. The method of claim 4, wherein, The step of calculating the corresponding theoretical value of the resonant frequency by using the preset analytical formula further comprises: when the test sample is symmetric at both ends and has a shape of a plate, calculating the theoretical value of the resonant frequency according to a formula ， ， The step of calculating the actual stress amplitude further comprises: wherein, is the amplitude of the oscillation of the end of the specimen; is the theoretical value of the stress amplitude at the middle section of the specimen corresponding to the amplitude of the oscillation of the end U0. when the theoretical value of the resonant frequency and an actual vibration frequency value are both within the preset frequency range, calculating the actual stress amplitude according to a formula 6. The method of claim 1, wherein, ​ ​ ， ， ， ​ wherein , , , is half the length of the end portion of the plate-shaped sample; is half the length of the variable cross-section portion of the sample; is half the length of the parallel portion of the sample; is the width of the end portion of the plate-shaped sample; is the minimum width of the plate-shaped sample; c is the propagation speed of the resonant wave in the sample; is the dynamic elastic modulus of the sample; is the density of the material of the sample; f is the resonant frequency of the sample, and ω is the angular frequency.

7. The method of claim 5, wherein, ​ ​ ​ wherein, is the amplitude of the oscillation of the end of the specimen; is the amplitude of the oscillation of the end of the specimen is the corresponding theoretical value of the stress amplitude at the middle section of the specimen; When the resonance frequency theoretical value is not in the preset frequency range, the specimen in vibration is photographed and analyzed by using a super high-speed camera, and the actual strain amplitude and stress amplitude of the specimen are calculated based on a digital image correlation method.

8. The method of claim 1, wherein, The step of reprocessing the specimen further includes: When the vibration frequency is greater than the maximum value of the preset frequency range, the specimen is scrapped; When the vibration frequency is less than the minimum value of the preset frequency range, the size of the specimen is corrected by cutting the specimen until the specimen can vibrate.

9. An ultrasonic fatigue specimen size bias-based stress correction system, comprising: The system includes: An installation module for installing a specimen to be detected on an ultrasonic fatigue testing machine; An initialization module for detecting whether the specimen can vibrate according to the vibration frequency range of the testing machine; A calculation module for detecting the vibration state, if not, reprocessing the specimen, otherwise, according to the actual size parameters of the specimen, using a preset analytical formula or a harmonic response analysis model to calculate the corresponding resonance frequency theoretical value, and based on the range of the resonance frequency theoretical value, selecting the corresponding stress amplitude calculation method to calculate the actual stress amplitude; Wherein, the step of calculating the corresponding resonance frequency theoretical value by using the harmonic response analysis model further includes: when the specimen is asymmetric at both ends, a finite element grid model is established according to the geometric shape and actual size of the specimen, harmonic response calculation is performed to obtain the resonance frequency of the specimen; if the resonance frequency is in the preset frequency range, the ratio of the corresponding stress amplitude and displacement amplitude is obtained by using harmonic response simulation, and the stress amplitude of the specimen is obtained combined with the end displacement amplitude of the specimen; if the resonance frequency is not in the preset frequency range, the specimen in vibration is photographed and analyzed by using a super high-speed camera, and the strain amplitude and stress amplitude of the specimen are calculated based on a digital image correlation method; A correction module for taking the ratio of the actual stress amplitude of the specimen to the theoretical value as a correction coefficient, and correcting the preset stress amplitude of the specimen according to the correction coefficient.

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