Ferromagnetic component residual stress detection method

Abstract

The invention discloses a ferromagnetic component residual stress detection method, and relates to the technical field of residual stress magnetic measurement, and the method comprises the following steps: arranging magnetic conductive boots between a plurality of magnetic poles of a stress detection probe and a to-be-detected ferromagnetic component, and starting magnetic measurement to obtain the residual stress of the to-be-detected ferromagnetic component. When stress detection is carried out, the elastic magnetic conductive boot is additionally padded at the tail end of the magnetic pole of the probe, so that magnetic leakage of an air gap section is reduced, magnetic flux entering the ferromagnetic component to be detected is increased, and detection signals can be effectively obtained and stress detection can be carried out under different lift-off distances. Meanwhile, the abrasion of the detection probe is transferred to the magnetic shoe, so that the service life of the detection probe is effectively prolonged, and the detection cost is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of residual stress magnetic measurement, and in particular to a method for detecting residual stress of a ferromagnetic component. Background Art

[0002] Ferromagnetic components are widely used in large engineering environments such as bridge engineering and pressure vessels. Ferromagnetic components in service are subject to both load stress and residual stress during the production process. When the stress level exceeds the strength limit of the ferromagnetic component, it will cause cracks or failure. It is of great engineering significance to evaluate the service life and safety of ferromagnetic components through stress detection. Magnetic measurement is a new type of non-destructive stress measurement method. It uses the magnetostrictive effect of ferromagnetic materials to convert stress changes into voltage to measure stress. It has the advantages of non-contact measurement, fast measurement speed, strong adaptability, simple operation and light instrumentation.

[0003] Residual stress magnetic measurement system Figure 1 As shown, the oscillator generates alternating current of a certain frequency, which is amplified and passed into the excitation coil. The excitation coil generates an alternating magnetic field to magnetize the point to be tested. Since ferromagnetic materials are positive magnetostrictive materials, the magnetic permeability will increase and decrease in the direction of tensile and compressive stress, respectively, thereby generating an induced electromotive force in the detection coil, and then generating a voltage signal on the detection probe that is proportional to the stress. After amplification and rectification, the signal is converted into stress or principal stress difference according to the calibration curve. For specific reference Figure 2 , the excitation coil and the detection coil constitute the stress detection probe. For the four-pole detection probe, the excitation coil and the detection coil are respectively wound on the two opposite poles and connected. When an alternating current of a certain frequency is passed through the excitation coil, an alternating magnetic field will be generated in the excitation core, and a magnetic flux will flow inside it, thereby forming an alternating magnetic field of a certain intensity on the surface of the test piece. If the test piece is an isotropic ferromagnetic material and the test piece is not subjected to force, the magnetic field intensity at the two poles of the detection coil is equal, and the changes are also the same. Therefore, the magnetic flux passing through the detection core is equal to zero, and no induced electromotive force is generated in the detection coil, so the output voltage signal of the detection probe is equal to zero.

[0004] When the tested piece is subjected to external force or residual stress exists inside, since the ferromagnetic material is a positive magnetostrictive material, the magnetic permeability will increase and decrease in the direction of tensile and compressive stress respectively, thereby distorting the magnetic field generated by the excitation coil. In this way, the two magnetic poles of the detection coil are no longer located on the equal-intensity magnetic potential lines of the magnetic field, and some of the changing magnetic flux will flow through the detection core, which will generate an induced electromotive force in the detection coil, thereby generating a voltage signal on the detection probe that is proportional to the stress.

[0005] When an alternating current is passed through the excitation coil, an alternating magnetic flux Φ is generated in the excitation core. m If the probe is in close contact with the test piece, this alternating magnetic flux Φ m Almost all of them reach the contact point and then pass through the surface of the specimen to form a closed magnetic circuit. Figure 3 As shown. The changing magnetic flux generated by its excitation coil can be written as:

[0006]

[0007] Where: N e is the number of turns of the excitation coil, I e is the excitation current, μ is the magnetic permeability of the excitation pole core, l is the magnetic path length of the excitation pole, and S is the cross-sectional area of ​​the magnetic path.

[0008] When the detection coil picks up the detection voltage, according to Faraday's law of electromagnetic induction, the changing magnetic field will generate an induced electric field, thereby generating an electromotive force and an induced current in the closed loop.

[0009]

[0010] Therefore, when the detection probe and the test piece are in close contact, the magnetic leakage at the contact point is minimal. At this time, the magnetic field generated by the excitation coil almost completely enters the test piece, the electromotive force induced in the detection coil is the largest, and the detection signal is also the strongest. As the lifting distance increases, the air gap between the detection probe and the test piece causes magnetic leakage, causing a large amount of attenuation of the magnetic flux in the detection coil, and the detection signal also drops significantly. The experiment found that when the lifting distance is 1mm, the detection signal is 70% of the zero-distance signal, attenuated by 30%, and when the lifting distance is 3.3mm, the detection signal is 30% of the zero-distance signal, attenuated by 70%. At this time, the detection signal is very weak, the signal-to-noise ratio is very low, and it is no longer suitable for stress measurement. Therefore, in actual measurement, the lifting distance is generally not more than 3mm. When the stress of ferromagnetic components (steel plates) is detected in situ on the assembly line, if the stress detection probe is close to the steel plate to be tested, the probe will be severely worn, and if the probe is far away from the steel plate, the detection signal will be severely attenuated. Summary of the invention

[0011] The present invention provides a residual stress detection method for ferromagnetic components, specifically a residual stress detection method for ferromagnetic components at a large lifting distance, which solves the problem that when performing residual stress magnetic measurement on existing ferromagnetic components, if the stress detection probe is close to the steel plate to be tested, the probe will be severely worn, and if the probe is far away from the steel plate, the detection signal will be severely attenuated.

[0012] The present invention provides a method for detecting residual stress of a ferromagnetic component, comprising the following steps:

[0013] Magnetic conductive shoes are arranged between the multiple magnetic poles of the stress detection probe and the ferromagnetic component to be tested, and magnetic measurement is started to obtain the residual stress of the ferromagnetic component to be tested;

[0014] The shape of the magnetic shoe is the same as that of the magnetic pole, and the size is determined by the area of ​​the magnetic pole end and the vertical distance between the magnetic pole end and the ferromagnetic component to be measured.

[0015] Preferably, the dimensions of the magnetic conductive shoe include area and thickness, wherein the area is 1.1 to 1.3 times the area of ​​the magnetic pole end, and the thickness is the vertical distance from the surface of the ferromagnetic component to be tested to the magnetic pole end during detection.

[0016] Preferably, a mold is made according to the shape and size of the magnetic conductive shoe, and relevant materials for preparing the magnetic conductive shoe are poured into the mold and solidified to obtain the magnetic conductive shoe.

[0017] Preferably, iron powder is used as the magnetic conductive filler, epoxy resin is used as the adhesive, and the magnetic conductive filler and the adhesive are configured into the magnetic conductive shoe in a mass percentage ratio of 8: (0.5-1).

[0018] Preferably, curing is performed by standing for 24 hours or heating at 60° C. for 4 hours.

[0019] Preferably, the mold material includes metal, paper and plastic.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] When performing stress detection, the present invention adds an elastic magnetic conductive shoe at the end of the probe magnetic pole to reduce magnetic leakage in the air gap section and increase the magnetic flux entering the ferromagnetic component to be detected, so that the detection signal can be effectively obtained and stress detection can be performed at different lifting distances. At the same time, the wear of the detection probe is transferred to the magnetic conductive shoe, which effectively prolongs the use time of the detection probe and reduces the detection cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0023] Figure 1 This is the principle diagram of the existing residual stress magnetic measurement;

[0024] Figure 2 It is a schematic diagram of an existing four-pole detection probe;

[0025] Figure 3 A schematic diagram of the magnetic circuit formed by the stress test piece to be tested and the probe;

[0026] Figure 4 A schematic diagram of the use of magnetic conductive shoes in stress nondestructive testing of the present invention;

[0027] Figure 5 It is a schematic diagram of the magnetic shoe mold of the present invention;

[0028] Figure 6 This is the specimen verification curve diagram.

[0029] In the figure: 1- ferromagnetic component to be tested, 2- stress detection probe, 3- magnetic pole, 4- magnetic conductive shoe. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] A method for detecting residual stress of ferromagnetic components, by adding a magnetic conductive shoe between the end of the detection probe and the test piece, reduces magnetic leakage in the air gap section, increases the magnetic flux entering the test piece, and achieves the purpose of improving signal strength. The method includes the following steps:

[0032] Step 1: Prepare special magnetic adhesive according to the proportion: iron powder is used as magnetic filler, epoxy resin is used as adhesive, and the magnetic filler and adhesive are configured according to the mass percentage of 8: (0.5-1).

[0033] The magnetic conductive adhesive used in the present invention includes but is not limited to the above formula, which should at least contain magnetic conductive filler and adhesive. Curing agent or toughening agent can be added according to the usage. The configuration ratio should be determined based on the following factors.

[0034] Magnetic adhesive does not need very strong bonding ability, but needs the highest possible magnetic permeability. Therefore, under the premise of ensuring the hardness and elasticity of the magnetic shoe, the proportion of magnetic filler should be increased as much as possible.

[0035] The thickness of the magnetic conductive shoe formed by solidification is as similar as possible at each point, and the density is uniform.

[0036] Step 2: Obtain the shape and size of the magnetic shoe according to the shape and size of the magnetic pole of the stress detection probe and the distance between the end of the magnetic pole and the ferromagnetic component to be tested.

[0037] The shape of the magnetic shoe should be as similar as possible to the shape of the probe magnetic pole. For cylindrical magnetic poles, a cylindrical magnetic shoe is selected; for square cylindrical magnetic poles, the magnetic shoe is made into a cuboid.

[0038] The larger the magnetic shoe area, the more likely it is that during stress testing, a magnetic shoe needs to be configured under each magnetic pole of the probe. The magnetic shoe area should cover the magnetic pole, and the magnetic shoes under each magnetic pole cannot touch each other, otherwise a through magnetic circuit will be formed between the conductive magnetic shoe and the magnetic core. Therefore, the area of ​​the magnetic shoe should be at least equal to the area of ​​the magnetic pole, and should not be too large. Generally, it should be 1.1 to 1.3 times the area of ​​the end of the magnetic pole.

[0039] The thickness of the magnetic shoe is equal to the vertical distance from the surface of the ferromagnetic component to be tested to the end of the magnetic pole of the probe during detection.

[0040] Take the use of a four-pole detection probe to detect a steel plate as an example. The magnetic pole shape is a cylinder with a bottom diameter of 10mm at the end. Therefore, the magnetic shoe used is also a cylinder with a bottom diameter of 12mm. When the probe is fixed during detection, if the vertical distance from the steel plate to the end of the probe magnetic pole is 3mm, the thickness of the magnetic shoe is selected to be 3mm. Figure 5 shown.

[0041] Use iron powder as magnetic filler and epoxy resin as adhesive to prepare special magnetic glue in proportion, pour it into the mold and let it stand for 24 hours or heat it at 60℃ for 4 hours to cure. After the magnetic glue is cured, demould it to form a magnetic shoe with a specific shape and thickness.

[0042] The mold materials used include metal but are not limited to metal, and also include paper or plastic.

[0043] Reference Figure 4 The present invention can obtain detection signals at a large lifting distance and perform stress detection by adding an elastic magnetic conductive shoe 4 between the end of each magnetic pole 3 of the stress detection probe 2 and the ferromagnetic component 1 to be detected, while protecting and extending the service life of the probe and reducing the detection cost. Its technical principles are based on three aspects:

[0044] According to the shape and size of the magnetic pole of the detection probe, specially configured magnetic conductive glue and mold are used to solidify it into an elastic magnetic shoe of specific shape and thickness. During stress testing, it is placed between the probe and the ferromagnetic component to be tested. Since the magnetic permeability of the magnetic conductive shoe is much greater than that of the air, magnetic leakage and magnetic resistance are reduced, thereby improving the detection signal strength and realizing stress detection under large lift-off (3mm-7mm).

[0045] During stress testing, there is relative movement between the moving ferromagnetic component to be tested and the fixed probe, which makes the probe very easy to wear. By adding a magnetic conductive shoe between the probe and the ferromagnetic component to be tested, the wear of the probe during the test is transferred to the low-cost magnetic conductive shoe, thereby protecting the probe and extending the service life of the probe, reducing the detection cost.

[0046] Since the main filling material of the magnetic shoe is iron powder, the magnetic pole of the probe and the ferromagnetic component to be tested are ferromagnetic materials, the material properties of the three are similar, and the magnetic permeability is not much different. The magnetic pole of the probe and the ferromagnetic component to be tested are connected by the magnetic shoe. When the magnetic lines of force enter from one material to another, there is less magnetic field scattering on the interface, and the degree of magnetic line distortion is low, making the magnetic lines of force in the magnetic circuit more uniform, thereby ensuring the detection sensitivity.

[0047] Use iron powder as magnetic filler and epoxy resin as adhesive to prepare special magnetic glue in proportion, pour it into the mold and let it stand for 24 hours or heat it at 60℃ for 4 hours to cure. After the magnetic glue is cured, demould it to form a magnetic shoe with a specific shape and thickness.

[0048] Place the magnetic shoe at the bottom of each magnetic pole of the probe, close to the standard specimen for tensile test, and obtain the relationship curve between the output voltage signal and stress of the probe when using a specific magnetic adhesive, such as Figure 6 As shown, this is the calibration curve when the magnetic shoe exists.

[0049] For stress detection, place the magnetic shoe at the bottom of each magnetic pole of the probe, and perform the test according to the stress magnetic detection process. Use the calibration curve when the magnetic shoe is present to convert the detection voltage signal into stress, and realize stress detection under large lift-off (3mm-7mm) and reduce probe wear.

[0050] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0051] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for detecting residual stress of a ferromagnetic component, characterized in that: The following steps are involved: Magnetic conductive shoes are arranged between the multiple magnetic poles of the stress detection probe and the ferromagnetic component to be tested, and magnetic measurement is started to obtain the residual stress of the ferromagnetic component to be tested; The shape of the magnetic shoe is the same as that of the magnetic pole, and the size is determined by the area of ​​the magnetic pole end and the vertical distance between the magnetic pole end and the ferromagnetic component to be measured.

2. A method for detecting residual stress of a ferromagnetic component according to claim 1, characterized in that: The dimensions of the magnetic shoe include area and thickness. The area is 1.1 to 1.3 times the area of ​​the magnetic pole end, and the thickness is the vertical distance from the surface of the ferromagnetic component to be tested to the magnetic pole end during testing.

3. A method for detecting residual stress of a ferromagnetic component according to claim 1, characterized in that: A mold is made according to the shape and size of the magnetic conductive shoe, and relevant materials for preparing the magnetic conductive shoe are poured into the mold and solidified to obtain the magnetic conductive shoe.

4. A method for detecting residual stress of a ferromagnetic component according to claim 3, characterized in that: Iron powder is used as magnetic conductive filler, epoxy resin is used as adhesive, and the magnetic conductive filler and adhesive are configured according to the mass percentage ratio of 8: (0.5-1) to form a magnetic conductive shoe.

5. A method for detecting residual stress of a ferromagnetic component according to claim 3, characterized in that: Curing was performed by leaving the mixture to stand for 24 hours or heating at 60°C for 4 hours.

6. A method for detecting residual stress of a ferromagnetic component according to claim 3, characterized in that: The mold materials include metal, paper and plastic.

Images