A method and system for detecting fatigue crack growth rate

Abstract

This invention discloses a method and system for detecting fatigue crack propagation rate, relating to the field of material fatigue performance testing technology. The method provided by this invention determines the displacement amplitude of the sample in real time during the experiment. After crack initiation, the fatigue testing machine emits pulses at the sampling frequency, triggering the imaging device to capture an XPCI image. This method has advantages such as extremely relaxed requirements on the experimental environment, high-speed imaging, full-field measurement, high precision, non-contact operation, and high automation, meeting the needs of high-speed, high-resolution, ultrafast measurement. Furthermore, the XDIC method is used to process the XPCI image, analyzing the microscopic strain field and revealing the evolution process and mechanism of fatigue crack initiation, propagation, and fracture from a global perspective of material microscopic and macroscopic deformation.

Description

Technical Field

[0001] This invention relates to the field of material fatigue performance testing technology, and in particular to a method and system for detecting fatigue crack propagation rate. Background Technology

[0002] Fatigue failure is the most common failure mode of mechanical components and structures widely used in engineering during their service life. According to incomplete statistics, fatigue failure accounts for 60%–80% of failure modes in aerospace engineering and 85% of fractures in automotive components. Based on fatigue and fracture theory, fatigue crack propagation rate is a crucial parameter for material damage assessment and remaining fatigue life prediction. However, since the initiation, propagation, and fracture mechanisms of fatigue cracks cannot yet be fully studied using effective theoretical methods, finding an effective and practical detection method is of great significance for the research on fatigue crack propagation rate.

[0003] Currently, commonly used methods for measuring fatigue crack propagation rate in laboratories and engineering practice include the potentiometric method, the replica method, and infrared thermography. The potentiometric method measures crack length by passing a constant current through the sample and utilizing the change in the current field caused by changes in the conductor's cross-sectional dimensions. However, because it measures a voltage signal at the microvolt level, it requires very high insulation of the fixtures; poor insulation can cause a parallel resistance effect between the frame and the sample, significantly affecting the measurement results. Furthermore, the potentiometric method can only measure a limited number of points, not the entire field, and cannot fully reveal the evolution process and mechanism of fatigue crack initiation and propagation. While the replica method offers better measurement accuracy, it requires several stops during the test to measure crack length, increasing the test cycle, especially under high-temperature fatigue testing conditions. Infrared thermography is a non-contact measurement method. It uses infrared thermal imaging technology to acquire a thermal image of the sample surface at a specific moment. Then, using a two-dimensional heat conduction model, it calculates the heat source field from the temperature field, determines the fatigue crack tip position at each moment, and calculates the crack length by comparing the initial position of the crack tip. However, complex pretreatment of the samples is required, and the external ambient temperature has a significant impact on the test results. Furthermore, when the temperature difference of the sample is small, the contrast of the thermal image is low, and the ability to resolve details is poor, the measurement results obtained have large errors. At the same time, existing technologies cannot observe and record the crack initiation process in a timely manner. Summary of the Invention

[0004] To address the aforementioned problems in the existing technology, this invention provides a method and system for detecting fatigue crack propagation rate.

[0005] To achieve the above objectives, the present invention provides the following solution:

[0006] A method for detecting fatigue crack propagation rate, comprising:

[0007] Prepare samples;

[0008] The sample is mounted on a fatigue testing machine, and an imaging device is set up to perform light-tracking operations.

[0009] The experimental parameters of the fatigue testing machine and the imaging parameters of the imaging device are set; the experimental parameters include: alternating load range, test frequency, experimental waveform, and data result storage location; the imaging parameters include: sampling frequency and exposure time.

[0010] The specimen was subjected to fatigue testing based on the experimental parameters.

[0011] The displacement amplitude of the sample is determined in real time during the experiment. After fission initiation, the fatigue testing machine emits pulses according to the sampling frequency to trigger the imaging device to capture an XPCI image.

[0012] The displacement and strain field at the tip of the specimen were obtained by analyzing and calculating the XPCI image using the XDIC method.

[0013] The crack length is determined based on the displacement and the strain field;

[0014] The crack propagation rate at each moment is determined using a numerical method based on the crack length.

[0015] Preferably, the preparation of the sample includes:

[0016] Preparation of initial samples;

[0017] The sample is obtained by covering the surface of the initial sample with a speckle field; the speckle field carries grayscale information.

[0018] Preferably, the imaging device performs X-ray phase-contrast imaging on the sample to obtain the XPCI image.

[0019] Preferably, the step of using the XDIC method to analyze and calculate the displacement and strain field at the tip of the specimen from the XPCI image specifically includes:

[0020] Select the computation region on the XPCI image;

[0021] Set DIC parameters;

[0022] Based on the DIC parameters, DIC analysis is performed on the calculation region to obtain the displacement and strain field at the tip of the specimen.

[0023] Preferably, the formula for determining the crack propagation rate is:

[0024]

[0025] In the formula, a j It is the crack length at time j, a j-1 Let a be the crack length at time j-1. j -a j-1 For crack increment, N j N represents the loop count at time j. j-1 N represents the loop count at time j-1. j -N j-1 Indicates the increment of the loop count. For crack increment from a j To a j-1 The average crack propagation rate corresponding to the time.

[0026] Preferably, the average crack length a(j) avg :

[0027]

[0028] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0029] The fatigue crack propagation rate detection method provided by this invention determines the displacement amplitude of the sample in real time during the experiment. After crack initiation, the fatigue testing machine emits pulses according to the sampling frequency, triggering the imaging device to capture an XPCI image. This method has advantages such as extremely relaxed requirements on the experimental environment, high-speed imaging, full-field measurement, high precision, non-contact operation, and high automation, meeting the needs of high-speed, high-resolution, ultrafast measurement. Furthermore, by processing the XPCI image using the XDIC method, the microscopic strain field is analyzed, revealing the evolution process and mechanism of fatigue crack initiation, propagation, and fracture from a global perspective of material microscopic and macroscopic deformation.

[0030] Corresponding to the fatigue crack propagation rate detection method provided above, the present invention also provides the following implementation system:

[0031] A fatigue crack propagation rate detection system, comprising:

[0032] Sample preparation module, used for preparing samples;

[0033] The light-adjusting module is used to mount the sample on the fatigue testing machine and set up the imaging device to complete the light-adjusting operation;

[0034] The parameter setting module is used to set the experimental parameters of the fatigue testing machine and the imaging parameters of the imaging device; the experimental parameters include: alternating load range, test frequency, experimental waveform, and data result storage location; the imaging parameters include: sampling frequency and exposure time.

[0035] A fatigue testing module is used to conduct fatigue tests on the specimen based on the experimental parameters.

[0036] The image acquisition module is used to determine the displacement amplitude of the sample in real time during the experiment. After fission initiation, the fatigue testing machine emits pulses according to the sampling frequency to trigger the imaging device to capture an XPCI image.

[0037] The displacement-strain determination module is used to analyze and calculate the displacement and strain field at the tip of the specimen using the XDIC method on the XPCI image;

[0038] A crack length determination module is used to determine the crack length based on the displacement and the strain field;

[0039] The propagation rate determination module is used to determine the crack propagation rate at each moment based on the crack length using a numerical method.

[0040] Another fatigue crack propagation rate detection system includes: a fatigue testing machine and an imaging device; the fatigue testing machine and the imaging device are connected.

[0041] The fatigue testing machine is used to perform fatigue tests on the specimens.

[0042] The imaging device is used to capture XPCI images of the specimen according to set shooting parameters during the fatigue test based on the control signal of the fatigue testing machine; the fatigue testing machine is internally equipped with a fatigue testing program, which is used to determine the crack propagation rate of the specimen at each moment based on the XPCI image; the fatigue testing program is used to implement the fatigue crack propagation rate detection method provided above.

[0043] Since the technical effects achieved by the two fatigue crack propagation rate detection systems provided by this invention are the same as those achieved by the fatigue crack propagation rate detection methods provided above, they will not be described again here. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0045] Figure 1 A flowchart of the fatigue crack propagation rate detection method provided by the present invention;

[0046] Figure 2 This is a schematic diagram of the initial sample structure provided in an embodiment of the present invention;

[0047] Figure 3 This is a schematic diagram of the optical path provided in an embodiment of the present invention;

[0048] Figure 4 A flowchart for determining the displacement and strain field at the crack tip location provided in an embodiment of the present invention;

[0049] Figure 5 This is a schematic diagram of the structure of a fatigue crack propagation rate detection system provided by the present invention. Detailed Implementation

[0050] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0051] The purpose of this invention is to provide a method and system for detecting fatigue crack propagation rate that has advantages such as extremely relaxed requirements for experimental environment, high-speed imaging, full-field measurement, high precision, non-contact, and high degree of automation. It can improve the accuracy of detection and measurement, and at the same time solve the problem of existing technologies that cannot observe and record the crack initiation process in a timely manner.

[0052] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0053] like Figure 1 As shown, the fatigue crack propagation rate detection method provided by the present invention includes:

[0054] Step 100: Sample Preparation. Specifically, the initial sample dimensions and surface roughness are designed according to the national standard "Methods for Fatigue Crack Propagation in Fatigue Testing of Metallic Materials". Then, a random speckle field carrying grayscale information is applied to the surface of the initial sample to obtain the prepared sample. The initial sample is as follows: Figure 2 As shown, its length is L, its width is W, its thickness is B, its notch depth is ap, and its notch width is h.

[0055] Step 101: Mount the specimen on the fatigue testing machine and set up the imaging device to complete the light adjustment operation. The imaging device used in this invention can be a high-speed imaging camera. Based on this, the specific implementation process of this step is as follows: First, connect the three-axis motion displacement stage below the fatigue testing machine, mount the specimen on the fatigue testing machine, and set up the high-speed imaging camera in a suitable position. Then, use the three-axis motion displacement stage to adjust the position of the testing machine in the X, Y, and Z axes until the high-speed imaging camera can clearly observe the crack profile. Its optical path is as follows: Figure 3 As shown, X-ray 1 penetrates the sample 2 and is incident on the imaging scintillator 3. The scintillator 3 converts the X-ray 1 into visible light and then enters the high-speed imaging camera 4 to realize the acquisition of imaging signals.

[0056] Step 102: Set the experimental parameters of the fatigue testing machine and the imaging parameters of the imaging device. Experimental parameters include: alternating load range, test frequency, experimental waveform, and data result storage location. Imaging parameters include: sampling frequency and exposure time.

[0057] Step 103: Conduct fatigue tests on the specimens based on experimental parameters.

[0058] Step 104: During the experiment, the displacement amplitude of the specimen is determined in real time. After fission initiation, the fatigue testing machine emits pulses according to the sampling frequency, triggering the imaging device to capture an XPCI image. Specifically, during the fatigue test, the displacement of any point at the notch when no plastic deformation occurs is related to the sinusoidal vibration of the applied load at the same frequency. When the current maximum displacement exceeds 5% of the amplitude of the sinusoidal wave of the previous cycle (i.e., fission initiation is determined), the fatigue testing machine controls the programmed automatic triggering of the high-speed imaging camera to perform X-ray phase-contrast imaging and acquire the XPCI image of the specimen.

[0059] Step 105: The displacement and strain field at the crack tip are obtained by analyzing the XPCI image using the XDIC method. Specifically, after receiving the trigger pulse, the high-speed imaging camera performs X-ray phase-contrast imaging (XPCI). Then, X-ray digital image correlation (XDIC) is used to analyze the XPCI image. The XPCI reference image and target image are imported into an XDIC processing program written in Matlab. The area to be calculated is selected, and DIC parameters such as the strain radius are set. Digital image correlation (DIC) analysis is then performed to calculate the displacement and strain field at the crack tip. The process is as follows: Figure 4As shown. The image correlation algorithm is similar to the traditional optical DIC method. Specifically, it involves selecting two adjacent frames from the same image sequence, using one frame as the reference image and the other as the target image. The image is then divided into several circular sub-regions. A cross-correlation function is constructed using the pixels within each sub-region, and a nonlinear least squares solution is performed. By tracking the displacement of the sub-region before and after deformation, the displacement fields (u and v) are obtained. The Green-Lagrange normal strain (E) can then be calculated using the displacement gradient. xx and E yy ) and shear strain (E) xy ):

[0060]

[0061]

[0062]

[0063] Where u and v represent displacement, and x and y represent coordinates.

[0064] Step 106: Determine the crack length based on the displacement and strain field. Wherein, the average crack length is a(j). avg :

[0065]

[0066] Step 107: Determine the crack propagation rate at each moment based on the crack length using a numerical method. For example, the numerical method used is the secant method. The principle of the secant method is to plot the fatigue crack length versus life curve, i.e., the aN curve, for a given fatigue crack length. By calculating the slope of the infinitesimal segment corresponding to the crack length on the aN curve, the crack propagation rate at that crack length is obtained, expressed by the following formula:

[0067]

[0068] In the formula, a j It is the crack length at time j, a j-1 Let a be the crack length at time j-1. j -a j-1 For crack increment, N j N represents the loop count at time j. j-1 N represents the loop count at time j-1. j -N j-1 Indicates the increment of the loop count. For crack increment from a j To a j-1 The average crack propagation rate corresponding to the time.

[0069] Based on the above description, this invention mainly focuses on detecting fatigue crack propagation rates using synchrotron radiation sources. Synchrotron radiation sources are a novel and irreplaceable light source, possessing characteristics such as high intensity, high brightness, high polarization, good collimation, small focal spot, and high stability, making them an important means of characterizing the microstructure of materials. XDIC (X-ray Digital Image Correlation) is a method that combines DIC (Digital Image Correlation) with synchrotron X-ray phase-contrast imaging (XPCI). XPCI uses an algorithm that compares image correlation points, with a calculation method similar to DIC. This method can calculate the surface displacement and strain distribution of an object, meeting the requirements of high-speed, high-resolution, ultrafast measurements. XPCI utilizes the phase change of X-rays as they pass through the sample to create contrast differences, thereby achieving imaging.

[0070] In this invention, during fatigue testing, the displacement of any point at the notch before plastic deformation occurs vibrates sinusoidally at the same frequency as the applied load. When a crack initiates, the maximum displacement under the same load increases compared to when no crack has formed. The fatigue testing machine control program compares the displacement amplitude in the current cycle with that in the previous cycle in real time. When the current displacement amplitude exceeds the sinusoidal amplitude of the previous cycle by 5%, the fatigue testing machine control program sends a pulse to the high-speed imaging camera, triggering the camera to run and perform X-ray phase-contrast imaging to acquire speckle images of the sample. The XDIC method is used to calculate the displacement and strain field at the crack tip in each image, thereby calculating the crack propagation rate. Simultaneously, the fatigue crack initiation life can be recorded based on the camera triggering time, and the crack initiation process can be observed. This invention has advantages such as extremely relaxed requirements for the experimental environment, full-field measurement, high speed, high precision, non-contact, and high degree of automation, overcoming the shortcomings of existing technologies and improving measurement accuracy. Meanwhile, the micro-strain field calculated by XDIC compensates for the deficiencies in the material mechanical properties shown by the macro-stress-strain curves, revealing the evolution process and mechanism of fatigue crack initiation, propagation, and fracture from the global perspective of material micro- and macro-deformation.

[0071] Based on the above description, the present invention has the following advantages over the prior art:

[0072] 1) This invention applies synchrotron radiation X-rays to fatigue crack propagation tests and uses X-ray phase contrast imaging (XPCI) method, which has the advantages of high speed and accuracy, and can meet the requirements of high-resolution ultrafast measurement at high speed. The XDIC method is used to process the XPCI images and analyze the microscopic strain field, revealing the evolution process and mechanism of fatigue crack initiation, propagation and fracture from the global perspective of material micro and macro deformation.

[0073] 2) This invention utilizes a fatigue testing machine control program to judge changes in displacement amplitude in real time, which can be used as a trigger switch for a high-speed imaging camera. During fatigue testing, when no plastic deformation occurs, the displacement of any point at the notch vibrates sinusoidally at the same frequency as the applied load. When a crack initiates, the maximum displacement under the same load will be greater than when no crack has occurred. The fatigue testing machine control program compares the displacement amplitude in the current cycle with the displacement amplitude in the previous cycle in real time. When the current displacement amplitude exceeds the sinusoidal amplitude of the previous cycle by 5%, the fatigue testing machine control program triggers the high-speed imaging camera to run.

[0074] In addition, corresponding to the fatigue crack propagation rate detection method provided above, the present invention also provides the following implementation system:

[0075] A fatigue crack propagation rate detection system, such as Figure 5 As shown, it includes: a sample preparation module 500, a light operation module 501, a parameter setting module 502, a fatigue test module 503, an image capturing module 504, a displacement strain determination module 505, a crack length determination module 506, and a propagation rate determination module 507.

[0076] The sample preparation module 500 is used to prepare samples.

[0077] The light-adjusting module 501 is used to mount the sample on the fatigue testing machine and set up the imaging device to complete the light-adjusting operation.

[0078] The parameter setting module 502 is used to set the experimental parameters of the fatigue testing machine and the imaging parameters of the imaging device. Experimental parameters include: alternating load range, test frequency, experimental waveform, and data result storage location. Imaging parameters include: sampling frequency and exposure time.

[0079] The fatigue testing module 503 is used to conduct fatigue tests on specimens based on experimental parameters.

[0080] The image acquisition module 504 is used to determine the displacement amplitude of the sample in real time during the experiment. After fission initiation, the fatigue testing machine emits pulses according to the sampling frequency to trigger the imaging device to capture XPCI images.

[0081] The displacement-strain determination module 505 is used to analyze and calculate the displacement and strain field at the tip of the specimen using the XDIC method on the XPCI image.

[0082] The crack length determination module 506 is used to determine the crack length based on the displacement and strain field.

[0083] The propagation rate determination module 507 is used to determine the crack propagation rate at each moment based on the crack length using a numerical method.

[0084] Another fatigue crack propagation rate detection system includes a fatigue testing machine and an imaging device. The fatigue testing machine and the imaging device are connected.

[0085] Fatigue testing machines are used to perform fatigue tests on specimens.

[0086] The imaging device, based on the control signals of the fatigue testing machine, captures XPCI images of the specimen according to set imaging parameters during the fatigue test. The fatigue testing machine has an embedded fatigue testing program used to determine the crack propagation rate of the specimen at various times based on the XPCI images. The fatigue testing program is used to implement the fatigue crack propagation rate detection method described above.

[0087] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the systems disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple; relevant parts can be referred to the method section.

[0088] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method of detecting fatigue crack growth rate, characterized by, The method comprises the following steps: preparing a sample; mounting the sample on a fatigue testing machine and setting up an imaging device to complete light operation; setting experimental parameters of the fatigue testing machine and shooting parameters of the imaging device; the experimental parameters include alternating load range, test frequency, experimental waveform and data result saving position; the shooting parameters include sampling frequency and exposure time; performing a fatigue experiment on the sample based on the experimental parameters; determining the displacement amplitude of the sample in real time during the experiment, and after crack initiation, the fatigue testing machine emits a pulse according to the sampling frequency to trigger the imaging device to shoot an XPCI image; wherein the fatigue testing machine control program compares the displacement amplitude in the current period with the displacement amplitude in the last period in real time, and when the current displacement amplitude exceeds the sine wave amplitude of the last period by 5%, the fatigue testing machine control program emits a pulse to the imaging device to trigger the imaging device to run and perform X-ray phase contrast imaging to obtain an XPCI image; using the XDIC method to analyze and calculate the displacement and strain field at the tip position of the sample based on the XPCI image; wherein two adjacent images in the same image sequence are selected, one of which is used as a reference image and the other is used as a target image, then the images are equally divided into a plurality of circular sub-regions, a certain cross-correlation function is constructed through the pixel points in the sub-regions, nonlinear least squares are solved, the displacement field is obtained by tracking the displacement of the sub-regions before and after deformation, and the Green-Lagrange normal strain and shear strain are calculated through the displacement gradient; determining the crack length based on the displacement and the strain field; determining the crack propagation rate at each time point based on the crack length by using a numerical method.

2. The method of claim 1, wherein The method for preparing a sample comprises: preparing an initial sample; covering a speckle field on the surface of the initial sample to obtain the sample; the speckle field carries gray scale information.

3. The method of claim 1, wherein the fatigue crack growth rate is determined by the following equation: ###0001### wherein K is the stress intensity factor, Kth is the threshold stress intensity factor, and n is the Paris law exponent. The method for analyzing and calculating the displacement and strain field at the tip position of the sample based on the XPCI image by using the XDIC method comprises: selecting a calculation region on the XPCI image; setting DIC parameters; performing DIC analysis on the calculation region based on the DIC parameters to obtain the displacement and strain field at the tip position of the sample.

4. The method of claim 1, wherein The formula for determining the crack propagation rate is: ； wherein a j is j the crack length at time t, a j-1 is j the crack length at time t-1, a j - a j-1 is the crack increment, N j denotes j the number of cycles at time t, N j-1 denotes the number of cycles at time t-1, N j - N j-1 denotes the increment of the number of cycles, is the average crack growth rate corresponding to the crack increment from a j to a j-1 time t-1.

5. The method of claim 4, wherein Average crack length : 。 6. A system for detecting fatigue crack growth rate, characterized by, The method comprises the following steps: a sample preparation module for preparing a sample; a light operation module for mounting the sample on a fatigue testing machine and setting up an imaging device to complete light operation; a parameter setting module for setting experimental parameters of the fatigue testing machine and shooting parameters of the imaging device; the experimental parameters include alternating load range, test frequency, experimental waveform and data result saving position; the shooting parameters include sampling frequency and exposure time; a fatigue experiment module for performing a fatigue experiment on the sample based on the experimental parameters; a fatigue experiment module for performing a fatigue experiment on the sample based on the experimental parameters; An image shooting module is configured to determine the displacement amplitude of the sample in real time during the experiment. After the initiation of the crack, the fatigue testing machine emits a pulse according to the sampling frequency to trigger the imaging device to shoot an XPCI image. The fatigue testing machine control program is used to compare the displacement amplitude in the current period with the displacement amplitude in the previous period in real time. When the current displacement amplitude exceeds the sine wave amplitude in the previous period by 5%, the fatigue testing machine control program emits a pulse to trigger the imaging device to run and perform X-ray phase contrast imaging to obtain an XPCI image. A displacement and strain determination module is configured to analyze and calculate the XPCI image by using the XDIC method to obtain the displacement and strain field at the tip of the sample. Two adjacent images in the same image sequence are selected, one of which is used as a reference image and the other as a target image. Then, the images are equally divided into several circular sub-regions. A certain cross-correlation function is constructed by using the pixel points in the sub-regions, and a nonlinear least squares solution is performed. The displacement field is obtained by tracking the displacement of the sub-regions before and after deformation. The Green-Lagrange normal strain and shear strain are calculated by the displacement gradient. A crack length determination module is configured to determine the crack length based on the displacement and strain field. An expansion rate determination module is configured to determine the crack expansion rate at each time point based on the crack length by using a numerical method.

7. A system for detecting fatigue crack growth rate, characterized by, The fatigue testing machine and the imaging device are connected. The fatigue testing machine is configured to perform a fatigue experiment on the sample. The imaging device is configured to shoot an XPCI image of the sample according to the set shooting parameters during the fatigue experiment based on the control signal of the fatigue testing machine. The fatigue testing machine has a fatigue experiment program implanted therein, which is configured to determine the crack expansion rate of the sample at each time point based on the XPCI image by using the fatigue experiment program. The fatigue experiment program is configured to implement the fatigue crack expansion rate detection method according to any one of claims 1-5. ​ ​

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