CN112964583A - Method for detecting and representing crack evolution based on electric signal induction fatigue system - Google Patents
Method for detecting and representing crack evolution based on electric signal induction fatigue system Download PDFInfo
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Abstract
The invention discloses a method for detecting and representing crack evolution based on an electric signal induction fatigue system, which is applied to the technical field of methods for representing crack propagation and strain evolution and comprises the following steps: s1, preparing a sample required by a fatigue test; s2, a fatigue test starting preparation step; s3, collecting sample fatigue data in a fatigue test; and S4, analyzing the data acquired in the step S3 to acquire the sample characterization crack evolution trend. The crack initiation time can be dynamically monitored by a digital microscope; under the condition of not stopping the fatigue test, the whole process of the crack expansion is recorded by utilizing a high-speed camera accurately and instantly without delay based on the electric signal induction principle, the accurate characterization of the high-frequency fatigue crack expansion is realized, the fatigue crack expansion and the strain evolution dynamic process are reduced to the maximum extent, the accurate strain-displacement cloud chart at the wave crest and the wave trough of the fatigue test is obtained by the DIC technology, and the whole test process is high in precision and efficiency.
Description
Technical Field
The invention relates to the technical field of methods for characterizing crack propagation and strain evolution of crack propagation, in particular to a method for detecting and characterizing crack evolution based on an electric signal induction fatigue system.
Background
The deep horizontal platform structure has some high-stress local complex structures, which are fatigue dangerous parts, and higher requirements are provided for fatigue design and verification, and crack initiation and propagation are the main reasons for equipment failure. In engineering application, the micro-crack has small opening angle and length and is difficult to detect, and meanwhile, the problems of uneven load of a pile leg, severe vibration under the action of severe environment load and the like caused by the large size of the ocean platform are difficult to clearly capture the micro-crack. In the high-frequency fatigue experiment process, crack initiation and propagation are difficult to observe due to too fast vibration, and clear images required by Digital Image Correlation (DIC) cannot be obtained by common industrial cameras due to parameters such as exposure time, shutter speed and shooting frequency. Although the high-speed camera can meet the parameters, the magnification of the high-speed camera is not enough to directly observe the crack initiation, and a long working distance microscope with high price needs to be introduced to observe and judge the crack initiation, so that the cost is increased; because the crack initiation time process is long, the shooting time of the high-speed camera is extremely limited due to the limited storage space of the high-speed camera, the crack initiation and the crack propagation can not be observed and recorded in the whole process, and the workpiece image at the fatigue wave crest and the wave trough can not be captured quantitatively.
At present, the main method for the microcrack propagation and the strain calculation of the microcrack propagation of the material is a finite element analysis method, the method needs to be based on long-time operation and needs appropriate models and material parameters, and in practical application, a structural part usually has holes, notches or other sudden changes of geometric shapes, so that an original uniform stress mode is damaged, and a finite element has certain errors with practical application. In addition, in recent years, the research of obtaining resonance frequency through a frequency sweep experiment and setting the CCD shutter trigger frequency of a stroboscopic light source to obtain a strain field at the tip of a crack appears in China, but the strain field of the crack can be obtained only by carrying out secondary acquisition after numerical fitting, the steps are complex, the speckle surface is not specially prepared, the paint spraying speckles are easy to drop in the high-frequency fatigue process, the obtained result of the DIC technology is seriously influenced, and the DIC technology is not easy to popularize and use.
Therefore, the method for detecting and characterizing the crack evolution based on the electric signal induction fatigue system is provided, the crack propagation at the wave crest and the wave trough of the fatigue sample and the strain cloud chart thereof are accurately and quantitatively obtained, an important theoretical basis and an industrial value are provided for detecting the ocean platform structural member, and the method is a problem that needs to be solved by technical personnel in the field.
Disclosure of Invention
In view of the above, the present invention provides a method for detecting and characterizing crack evolution based on an electrical signal induced fatigue system.
In order to achieve the purpose, the invention adopts the following technical scheme:
the method for detecting and representing crack evolution based on the electric signal induction fatigue system comprises the following steps:
s1, preparing a sample required by a fatigue test;
s2, a fatigue test starting preparation step;
s3, collecting sample fatigue data in a fatigue test;
and S4, analyzing the data acquired in the step S3 to acquire the sample characterization crack evolution trend.
Preferably, the specific content of step S1 is: preparing a sample required by an experiment by a wire cutting technology, polishing the front surface and the rear surface of the sample by using sand paper, removing residual stains on the surface of the sample by using ultrasonic cleaning, wherein the cleaning time is 5-10 minutes, preparing a polished gold phase surface on the front surface of the sample, and preparing a high-viscosity high-contrast speckle surface on the rear surface of the sample.
Preferably, the specific contents of the preparation method of the speckle surface with high viscosity and high contrast are as follows: and placing the surface to be prepared of the sample above the acetone solution for 8-10 seconds, and then removing the sample, and spraying acrylic paint on the surface to prepare the high-viscosity high-contrast speckle surface.
Preferably, the specific contents of the preparation method of the speckle surface with high viscosity and high contrast are as follows: and (3) placing the surface to be prepared of the sample above the acetone solution for 9 seconds, then moving away, and spraying acrylic paint on the surface to prepare the high-viscosity high-contrast speckle surface.
Preferably, the specific content of step S2 is: the fatigue test is carried out by adopting the electric signal induction fatigue system, the digital microscope and the sample are respectively fixed on a high-frequency fatigue machine in the electric signal induction fatigue system, the digital microscope is arranged corresponding to the sample, and after the fixation is finished, the fatigue test parameters of the high-frequency fatigue machine are set.
Preferably, the specific content of step S3 is: monitoring the crack initiation process of the sample by using a crack monitoring system, starting an electric signal acquisition and output accessory to acquire and convert a voltage value when the crack length in the monitoring software is 100-150 mu m, and acquiring an image of the sample high-viscosity high-contrast speckle-scattering surface in the step S1 by using an electric signal induction fatigue system.
Preferably, in step S3, the manner of turning on the electrical signal acquisition output accessory is manual turning on or automatic triggering turning on.
Preferably, the specific content of step S4 is: and utilizing DIC technology to analyze and obtain a strain-displacement field at a peak, a strain-displacement field at a trough and a crack tip strain field when the sample is in critical fracture in a single cycle of the high-frequency fatigue test.
Preferably, a high-speed camera is used for instantly and quantitatively acquiring images of fatigue peaks and troughs of the sample.
According to the technical scheme, compared with the prior art, the method for detecting and representing the crack evolution based on the electric signal induction fatigue system is provided, and the crack initiation time can be dynamically monitored through a digital microscope; under the condition of not stopping a fatigue experiment, the whole process of crack expansion is recorded by a high-speed camera accurately and instantly without delay based on the principle of electric signal induction, the accurate characterization of high-frequency fatigue crack expansion is realized, the dynamic process of fatigue crack expansion and strain evolution thereof is reduced to the maximum extent, an accurate strain-displacement cloud chart at the wave crest and the wave trough of the fatigue experiment is obtained by a DIC technology, the whole testing process is high in precision and efficiency, wide in application range, wide in application prospect and economic benefit, and the performance evaluation of marine engineering materials provides important theoretical basis and practical basis.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
FIG. 1 is a flow chart of a method for detecting and characterizing crack evolution based on an electrical signal induced fatigue system in accordance with the present invention;
FIG. 2 is a schematic diagram of an electrical signal induced fatigue system according to the present invention;
FIG. 3 is a schematic diagram showing the structure of the SENT sample in example 2;
FIG. 4 is a schematic view of a polished gold phase surface in the example;
FIG. 5 is a schematic diagram of a high contrast speckle surface in an embodiment;
FIG. 6 shows the crack lengths monitored in the examples
FIG. 7 is a strain-displacement cloud plot at the sample peak in a single cycle, wherein FIG. 7.1 is a strain cloud plot at the sample peak in a single cycle, and FIG. 7.2 is a displacement cloud plot at the sample peak in a single cycle;
FIG. 8 is a strain-displacement cloud image of the SENT sample at the wave trough in a single cycle, wherein FIG. 8.1 is a strain cloud image of the SENT sample at the wave trough in a single cycle, and FIG. 8.2 is a displacement cloud image of the SENT sample at the wave trough in a single cycle;
FIG. 9 is a strain field at the crack tip for fracture protection of SENT specimens in the examples;
the system comprises 1-an electric signal acquisition and output accessory, 2-a synchronous line, 3-a high-frequency fatigue machine, 4-a cable, 5-a signal acquisition controller, 6-a BNC connector, 7-a phototron high-speed camera, 8-a digital microscope, 9-a sample, 10-a USB data line and 11-a computer workstation.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
Referring to the attached drawing 1, the embodiment discloses a method for detecting and characterizing crack evolution based on an electric signal induction fatigue system, which comprises the following steps:
s1, preparing a sample required by a fatigue test;
s2, a fatigue test starting preparation step;
s3, collecting sample fatigue data in a fatigue test;
and S4, analyzing the data acquired in the step S3 to acquire the sample characterization crack evolution trend.
In a specific embodiment, the specific content of step S1 is: preparing a sample required by an experiment by a wire cutting technology, polishing the front surface and the rear surface of the sample by using sand paper, removing residual stains on the surface of the sample by using ultrasonic cleaning, wherein the cleaning time is 5-10 minutes, preparing a polished gold phase surface on the front surface of the sample, and preparing a high-viscosity high-contrast speckle surface on the rear surface of the sample.
In a specific embodiment, the method for preparing the high-viscosity high-contrast speckle surface comprises the following specific contents: and placing the surface to be prepared of the sample above the acetone solution for 8-10 seconds, and then removing the sample, and spraying acrylic paint on the surface to prepare the high-viscosity high-contrast speckle surface.
In a specific embodiment, the method for preparing the high-viscosity high-contrast speckle surface comprises the following specific contents: and (3) placing the surface to be prepared of the sample above the acetone solution for 9 seconds, then moving away, and spraying acrylic paint on the surface to prepare the high-viscosity high-contrast speckle surface.
In a specific embodiment, the specific content of step S2 is: the fatigue test is carried out by adopting the electric signal induction fatigue system, the digital microscope and the sample are respectively fixed on a high-frequency fatigue machine in the electric signal induction fatigue system, the digital microscope is arranged corresponding to the sample, and after the fixation is finished, the fatigue test parameters of the high-frequency fatigue machine are set.
In a specific embodiment, the specific content of step S3 is: monitoring the crack initiation process of the sample by using a crack monitoring system, starting an electric signal acquisition and output accessory to acquire and convert a voltage value when the crack length in the monitoring software is 100-150 mu m, and acquiring an image of the sample high-viscosity high-contrast speckle-scattering surface in the step S1 by using an electric signal induction fatigue system.
In one embodiment, in step S3, the electrical signal collection output assembly is turned on by manual or automatic triggering.
In a specific embodiment, the specific content of step S4 is: and utilizing DIC technology to analyze and obtain a strain-displacement field at a peak, a strain-displacement field at a trough and a crack tip strain field when the sample is in critical fracture in a single cycle of the high-frequency fatigue test.
In another embodiment, a high-speed camera is used to obtain images of fatigue peaks and valleys of the sample instantaneously and quantitatively.
Example 2
Referring to fig. 2, the embodiment discloses an electrical signal induction based fatigue system, which comprises an electrical signal induction system and a crack monitoring system.
The electric signal induction system comprises an electric signal acquisition output accessory 1, a synchronous line 2, a high-frequency fatigue machine 3, a cable 4, a signal acquisition controller 5, a BNC connector 6 and a phototron high-speed camera 7; the electric signal acquisition and output accessory 1 comprises a DoLi controller acquisition card and an output module.
The crack monitoring system comprises a digital microscope 8, a USB data line 10 and a computer workstation 11.
The electric signal induction system connection and transmission principle is as follows:
one end of an electric signal control output accessory 1 is connected with a high-frequency fatigue machine 3 through a synchronous line 2, a DoLi controller acquisition card acquires load signals at wave crests and wave troughs of a sine wave in the fatigue machine, and the load signals are converted into corresponding voltage signals through an output module; the other end of the electric signal control output accessory 1 is connected with one end of a signal acquisition controller 5 through a cable 4, and voltage signals are synchronously transmitted to the signal acquisition controller through the cable 4; the other end of the signal acquisition controller 5 is connected with a phototron high-speed camera 7 through a BNC connector 6, and the voltage signal is induced by utilizing the phase synchronization technology; when the signal acquisition controller 5 induces a voltage signal, the high-speed camera 7 automatically induces and shoots through the BNC joint, and instantly and quantitatively obtains images of the wave crests and the wave troughs of the fatigue test sample.
The crack monitoring system connection and observation principle is as follows: the digital microscope 8 is connected with a computer workstation 11 through a USB data line 10, and the crack length of the sample 9 is monitored through the computer workstation 11.
In one embodiment, the method comprises the following steps:
(1) the SENT sample 9 with the size shown in figure 3 is prepared by adopting EH36 marine steel as a material through a wire cutting technology, the front surface and the rear surface of the sample 9 are polished by sand paper, residual stains of the sample wire cutting are removed by ultrasonic cleaning, the cleaning time is 5-10 minutes, and a polished gold phase surface is prepared on the front surface of the sample 9, as shown in figure 4; preparing a high-viscosity high-contrast speckle pattern on the rear surface of the sample 9, as shown in fig. 5;
(2) carrying out a fatigue test by adopting an electric signal induction fatigue system, fixing a sample 9 on a high-frequency fatigue machine 3 in the electric signal induction fatigue system, setting a fatigue application load of 16kN, a fatigue frequency of 125Hz, and a waveform of sine wave;
(3) monitoring the crack initiation process through a crack monitoring system, fixing a digital microscope 8 on the surface of a sample 9 shot by a high-frequency fatigue machine 3, and connecting the digital microscope 8 with a computer workstation 11 through a USB data line 10 to monitor the length of the crack; as shown in fig. 6, when the crack length is monitored to be 133 μm, manually starting or automatically starting an electric signal acquisition output accessory by setting a trigger condition, acquiring and converting the electric signal acquisition output accessory into a voltage value in an electric signal induction fatigue system, and obtaining an image of the high-viscosity high-contrast speckle pattern of the sample 9 in the step (1);
(4) obtaining a strain-displacement field at a peak in a single cycle of the high-frequency fatigue test after DIC analysis, as shown in FIG. 7; FIG. 8 is a graph of strain-displacement field at the trough in a single cycle of a high frequency fatigue test by DIC; FIG. 9 is a crack tip strain field at critical fracture for sample 9.
In one specific embodiment, step (1) requires a high viscosity, high contrast speckle surface preparation method: placing the surface to be prepared of the sample above acetone liquid with high volatility for 8-10 seconds, removing the sample, spraying acrylic paint which is easily soluble in acetone on the surface, and preparing a random spray paint spot surface with high viscosity and high contrast to prevent spray paint particles from falling off in a high-frequency fatigue test and influencing DIC analysis results;
in another embodiment, in the step (4), the high-speed camera shooting parameters are: frame number 250fps, captured image resolution 640 x 480, exposure time 1/640 sec.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention in a progressive manner. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (8)
1. The method for detecting and characterizing the crack evolution based on the electric signal induction fatigue system is characterized by comprising the following steps:
s1, preparing a sample required by a fatigue test;
s2, a fatigue test starting preparation step;
s3, collecting sample fatigue data in a fatigue test;
and S4, analyzing the data acquired in the step S3 to acquire the sample characterization crack evolution trend.
2. The method for electrical signal-based induction fatigue system detection and characterization of crack evolution of claim 1,
the specific content of step S1 is: preparing a sample required by an experiment by a wire cutting technology, polishing the front surface and the rear surface of the sample by using sand paper, removing residual stains on the surface of the sample by using ultrasonic cleaning, wherein the cleaning time is 5-10 minutes, preparing a polished gold phase surface on the front surface of the sample, and preparing a high-viscosity high-contrast speckle surface on the rear surface of the sample.
3. The method for electrical signal-based induction fatigue system crack evolution detection and characterization according to claim 2,
the specific contents of the preparation method of the speckle surface with high viscosity and high contrast are as follows: and placing the surface to be prepared of the sample above the acetone solution for 8-10 seconds, and then removing the sample, and spraying acrylic paint on the surface to prepare the high-viscosity high-contrast speckle surface.
4. The method for electrical signal-based induction fatigue system detection and characterization of crack evolution of claim 1,
the specific content of step S2 is: the fatigue test is carried out by adopting the electric signal induction fatigue system, the digital microscope and the sample are respectively fixed on a high-frequency fatigue machine in the electric signal induction fatigue system, the digital microscope is arranged corresponding to the sample, and after the fixation is finished, the fatigue test parameters of the high-frequency fatigue machine are set.
5. The method for electrical signal-based induction fatigue system detection and characterization of crack evolution of claim 1,
the specific content of step S3 is: monitoring the crack initiation process of the sample by using a crack monitoring system, starting an electric signal acquisition and output accessory to acquire and convert a voltage value when the crack length in the monitoring software is 100-150 mu m, and acquiring an image of the sample high-viscosity high-contrast speckle-scattering surface in the step S1 by using an electric signal induction fatigue system.
6. The method for electrical signal-based induction fatigue system detection and characterization of crack evolution of claim 5,
in step S3, the manner of turning on the electrical signal acquisition output accessory is manual turning on or automatic triggering turning on.
7. The method for electrical signal-based induction fatigue system detection and characterization of crack evolution of claim 1,
the specific content of step S4 is: and utilizing DIC technology to analyze and obtain a strain-displacement field at a peak, a strain-displacement field at a trough and a crack tip strain field when the sample is in critical fracture in a single cycle of the high-frequency fatigue test.
8. The method for electrical signal-based induction fatigue system detection and characterization of crack evolution of claim 7,
and (3) instantaneously and quantitatively acquiring images of fatigue wave crests and wave troughs of the sample by using a high-speed camera.
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| CN202110153437.9A CN112964583B (en) | 2021-02-03 | 2021-02-03 | Method for detecting and representing crack evolution based on electric signal induction fatigue system |
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| CN202110153437.9A CN112964583B (en) | 2021-02-03 | 2021-02-03 | Method for detecting and representing crack evolution based on electric signal induction fatigue system |
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