CN110220622A - A kind of long distance laser stress mornitoring method and detector - Google Patents

Abstract

The present invention is applicable to the field of non-destructive testing, and provides a long-distance laser stress detection method and detector. The present invention uses the respective polarization rotation angles of two perpendicular S-polarized lights and P-polarized lights to determine the incident angle. After the incident angle is determined, The magnetization intensity of the object to be detected can be obtained by using the Kerr deflection angle, and then the stress and fatigue of the object to be detected can be calculated according to the principle of magnetic memory. The invention discloses a technology and implementation method for detecting metal stress and fatigue damage by using the surface magneto-optical Kerr effect. The non-contact property of laser, the magneto-optic Kerr effect and the Villari effect are used to realize the non-contact and detection of stress. Quick scan detection.

Description

A long-distance laser stress detection method and detector

technical field

The invention belongs to the technical field of non-destructive testing, and in particular relates to a long-distance laser stress testing method and a testing instrument.

Background technique

Stress detection is very important as stress is ubiquitous in metals. In some cases, the presence of stress concentrations leads to accelerated corrosion of components, also known as stress corrosion. In addition, in terms of structure, the presence of stress leads to fatigue damage. The structure may suddenly fail without warning, leading to major safety accidents. Regular testing of stress can prevent these accidents, so a convenient and fast on-site stress testing technology and products are needed.

The existing on-site stress detection methods are basically divided into two categories: stress detection based on deformation and stress detection based on a certain physical quantity. The first scheme currently mainly includes the strain gauge method and the fiber grating method. These two methods use the passive deformation of the sensor to calculate the deformation of the object to be detected in reverse, and thus calculate its stress. The second scheme mainly includes acoustic and electromagnetic methods. The acoustic method mainly uses the propagation characteristics of ultrasonic waves, and the electromagnetic method mainly uses the change of its electromagnetic properties. One of the new methods is the magnetic memory stress detection method.

Magnetic memory detection is a rapid on-site stress detection method initiated by Russian scientist Professor Dubov, and is currently widely used in many fields. However, in most cases, it is necessary to perform contact detection on the object to be detected. For large steel structures, this kind of contact detection is more difficult. Therefore, there is a need for a rapid detection method and product suitable for long-distance non-contact stress on site.

Contents of the invention

In view of the above problems, the purpose of the present invention is to provide a long-distance laser stress detection method and detector, so as to be able to realize the non-contact rapid detection of stress by laser.

In one aspect, the remote laser stress detection method comprises the following steps:

On the same optical path, two beams of incident laser light are emitted to the object to be detected;

Detect the polarization rotation angle and light intensity of the two reflected laser beams reflected from the object to be detected respectively;

Determine the incident angle between the incident laser and the object to be detected according to the respective polarization rotation angles of the two reflected lasers and the change and proportional relationship of the light intensity;

According to the incident angle of the incident laser and the polarization rotation angle of the reflected laser, the magnetization of the object to be detected is obtained;

After the magnetization of the object to be detected is detected by the laser, the stress state of the object to be detected is calculated according to the magnetomechanical effect by using the Villari effect.

Further, the two incident laser beams are laser beams with different polarization directions or two laser beams with different wavelengths, and the polarization rotation angles of the two incident laser beams corresponding to the reflected laser beams are different from the incident angles of the incident laser beams.

Further, the two incident laser beams are two vertically polarized S-polarized light and P-polarized light.

Further, before the step of emitting two beams of incident laser light on the same optical path to irradiate the object to be detected, it also includes:

When detecting the object to be detected with surface paint, or when detecting the object to be detected with low reflectivity, paste the reflective sheet at the detection point of the object to be detected.

Further, the reflective sheet is made of soft magnetic material with high reflectivity and anti-rust ability on the surface.

On the other hand, the remote laser stress detector includes a semiconductor laser, a wavelength division multiplexer, a beam splitter, a collimator, a polarizer and a photoelectric probe, and the semiconductor laser emits laser light to the wavelength division multiplexer, Then, two beams of incident laser beams are formed by the beam splitter. After being straightened by the collimator, the two beams of incident laser beams are irradiated to the object to be detected. A corresponding irradiation to two photoelectric probes.

On the other hand, the long-distance laser stress detector also includes a housing with a handle on the back of the housing, a liquid crystal display screen and left, right, up movement and determination buttons on the handle, the semiconductor laser, A wavelength division multiplexer, a beam splitter, a collimator, a polarizer and a photoelectric probe are located in the housing.

The beneficial effects of the present invention are: the present invention realizes the non-contact stress detection of stress by combining the magneto-optic Kerr effect and the magnetic memory detection principle, while the advantages of the magnetic memory detection technology are preserved, because the laser is used as the Detection probe, the data source (detection area) is more localized, so it can more accurately distinguish the source of the signal and improve its spatial resolution; in addition, in the preferred mode, for the object to be detected with surface coating or surface paint For the object, the detection of metal non-deformation fatigue can be realized without grinding by using the method of pasting reflective sheets.

Description of drawings

Figure 1 is a schematic diagram of the normal incidence of the incident laser and the Kerr polarization rotation angle;

Fig. 2 is the schematic diagram of incident laser non-perpendicular incidence;

Fig. 3 is a schematic diagram of detection of a reflective sheet attached;

Fig. 4 is a schematic diagram of a long-distance laser stress detector;

Fig. 5 is a structural diagram of a long-distance laser stress detector.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

Before describing the solution of the present invention, the surface magneto-optical Kerr effect is briefly introduced. In 1845, Michael Faraday first discovered the magneto-optic effect. He discovered that when a magnetic field is applied to a glass sample, the plane of polarization of the transmitted light is rotated. In 1877, John Kerr discovered the magneto-optic Kerr effect (MOKE, magneto-optic Kerr effect). In 1985, Moog and Bader successfully obtained the hysteresis loop of a magnetic substance with an atomic layer thickness when they measured the magneto-optical Kerr effect of ferromagnetic ultrathin films, and defined the surface magneto-optic Kerr effect (SMOKE, surface magneto-optic Kerreffect). Experiments have confirmed that this method can detect the magnetism of a ferromagnetic ultra-thin film with a thickness of one atomic layer, so it has become an important research method for magnetism.

The basic principle of the surface magneto-optical Kerr effect is the magneto-optic interaction. The linearly polarized light is taken as an example to illustrate. When linearly polarized light is incident on the surface of the magnetic sample to be tested, the reflected light will become elliptically polarized light, and its polarization direction will rotate. This small angle is called the Kerr rotation angle, which is the distance between the long axis of the ellipse and the incident linearly polarized light. The angle between them is shown in Figure 1. At the same time, generally speaking, due to the difference in the absorption rate of the sample for p-polarized light and s-polarized light, the ellipticity of the reflected light will also change, and the magnetization of the sample to be tested will cause an additional change in this ellipticity. The change is called the Kerr ellipticity, which is the ratio of the major and minor axes of the ellipse. All in all, through the surface magneto-optic Kerr effect, linearly polarized light can be used to detect the magnetization of the object to be detected. The above-mentioned magneto-optical Kerr effect has been widely used in the magnetic research of ultra-thin films. Another application of the magneto-optical Kerr effect is magneto-optic recording, which is to record computer information through the magneto-optic effect.

More than 30 years of research and application development have confirmed the four advantages of the surface magneto-optical Kerr effect: first, its detection sensitivity to magnetism is extremely high, and advanced devices of this type can detect the magnetism of sub-monatomic layer materials. Secondly, the surface magneto-optic Kerr effect is a non-destructive testing technology, which uses laser as a "probe", which will not cause any damage to the object to be tested, and can be detected in situ and non-contact. Again, the information comes from the illuminated area of the object to be detected. Basically, the signal of the surface area outside the illuminated area can be excluded, and the obtained signal is very local, which can study the gradual change of materials or magnetism. Finally, its structure is simple and easy to integrate.

On the other hand, the magnetic memory stress detection technology has been gradually accepted after more than 20 years of development. Metal magnetic memory testing technology is a rapid non-destructive testing method that utilizes metal magnetic memory effect to detect stress concentration and fatigue damage of parts to be tested. During the processing and operation of ferromagnetic metal parts, due to the periodic action of load, the reorientation of magnetic domain organization will occur in the stress concentration area. This irreversible change of the magnetic state will not only remain after the working load is removed, but also related to the maximum applied stress it has endured. This magnetic state on the surface of metal components "memorizes" the location of microscopic defects or stress concentrations, which is the so-called magnetic memory effect. It overcomes the shortcomings of traditional nondestructive testing and provides a way to detect stress concentration inside ferromagnetic metal components.

The detection instrument based on the basic principle of metal magnetic memory effect can evaluate the stress concentration of the component and whether there are microscopic defects by recording the distribution of the magnetic field intensity component perpendicular to the surface of the metal component along a certain direction, and detect early failure. It is a new detection technology in the field of non-destructive testing to diagnose and evaluate damage and prevent sudden failure.

Therefore, aiming at the above content, the present invention provides a scheme integrating the magneto-optical Kerr effect and magnetic memory stress detection technology, so as to realize the non-contact rapid detection of stress by laser. A specific implementation manner may be a handheld device, which is convenient to carry and operate.

In order to illustrate the technical solutions of the present invention, specific examples are used below to illustrate.

Embodiment one:

The remote laser stress detection method provided in this embodiment includes the following steps:

Step S1, emitting two incident laser beams on the same optical path to irradiate the object to be detected.

Referring to FIG. 1 , the polarized incident laser light is straightened and emitted from the hand-held detector to the surface of the object to be measured. In general, linearly polarized light is incident on the surface of the object to be inspected, and when the incident angle is perpendicular to the incident angle, the reflected light returns from the original path. At this time, the polarization direction of the reflected light is rotated, and when the magnetization of the object to be detected is not very large, the polarization angle of the reflected light is linearly related to the magnitude of the magnetization M. In practice, it is difficult to ensure the detection Normal incidence of the laser. Generally there is an angle of incidence. This angle of incidence will cause a serious impact: the reflected light does not return from the original path, so it is difficult to capture, as shown in Figure 2. The schematic diagram of non-perpendicular incidence. For this case, this scheme utilizes the diffuse reflection caused by the incident light. Diffuse reflection laser light is also polarized, and the rotation angle of this polarization is still related to the magnetization M of the object to be detected. However, because it is diffuse reflection, the light intensity returned to the hand-held detector is relatively weak, and the photoelectric probe behind needs to have relatively high sensitivity and magnification, which can be achieved by the current general photoelectric technology.

Therefore, in this step, two polarized incident lasers are directly emitted from the detector to irradiate the object to be detected. Specifically, for example, two perpendicular linearly polarized lights S and P may be used as incident laser light, that is, S polarized light and P polarized light. There are many ways to realize it, such as using two lasers, or taking out two different linear polarizations after splitting a beam of laser, or other ways. Pulsed incident lasers can also be used to increase incident as well as reflected and diffuse energy.

Step S2, respectively detecting the polarization rotation angle and light intensity of the two reflected laser beams reflected from the object to be detected.

The detection of the polarization state of directly reflected or diffusely reflected laser light can be achieved with an analyzer, such as a polarizer, a polarizing prism, or other optical devices. In the case of normal incidence, only one linearly polarized light is needed to obtain the magnitude of the magnetization M of the object to be detected. In the case of non-normal incidence, the angle of incidence is also an unknown quantity. Therefore, the solution of the present invention adopts two different incident linearly polarized lights: S linearly polarized light and P linearly polarized light. The rotation angles of the two kinds of polarized light and the magnetization M follow different nonlinear relationships. By comparing the two rotation angles, the magnitude of the magnetization M and the laser incident angle can be known at the same time.

Step S3: Determine the incident angle between the incident laser light and the object to be detected according to the respective polarization rotation angles of the two reflected laser beams, the change of the light intensity, and the proportional relationship.

Step S4. Obtain the magnetization of the object to be detected according to the incident angle of the incident laser light and the polarization rotation angle of the reflected laser light;

Step S5 , after the magnetization of the object to be detected is detected by the laser, the stress state of the object to be detected is calculated according to the magnetomechanical effect by using the Villari effect.

Typically, the angle of incidence is a variable that is difficult to control. Especially when using a handheld device on site, it is difficult to achieve vertical incidence due to hand shake and the relative position between the point to be detected and the handheld device. The present invention uses the respective polarization rotation angles of the two perpendicular S-polarized light and P-polarized light to determine the incident angle. After the incident angle is determined, the magnetization of the object to be detected is obtained by using the polarization rotation angle of the reflected laser light. Then, the stress and fatigue of the object to be tested are calculated according to the Villari effect and the magnetomechanical effect.

In addition, in general, there may be a layer of paint on the surface of the object to be detected, and this paint layer is non-magnetic. At the same time, it shields the magnetic signal of the object to be detected itself. For this situation, it can be solved by fixing the reflector. As shown in Figure 3, the reflector is made of soft magnetic materials with good linearity, low remanence and low coercive force, and anti-rust treatment at the same time. The reflective sheet has high reflectivity and surface rust resistance. For the object to be detected, after the detection point is determined, the reflective sheet is fixed to the detection point of the object to be detected by means of adhesive. Because the reflector is made of magnetic metal with good linearity, its magnetization is basically synchronized with the object to be detected. Of course, this method can also be adopted if the object to be detected with low reflectivity is detected.

Embodiment two:

Embodiment 1 provides a long-distance non-contact detection method, which is applied to a detector. The present embodiment discloses the principle structure of the detector, as shown in Figure 4, comprising a semiconductor laser 101, a wavelength division multiplexer 102, a beam splitter 103, a collimator 104, and a polarizer (there are two paths in the figure, Respectively mark 105 and 107) and photoelectric probes (also two-way, mark 106 and 108 respectively), the semiconductor laser 101 emits laser light to the wavelength division multiplexer 102, and then forms two beams of polarized incident laser light through the beam splitter 103 After the two incident laser beams are straightened by the collimator 104, they are irradiated to the object to be detected, and the two reflected laser beams returned from the object to be detected pass through the two analyzers, and are irradiated to the two photoelectric probes correspondingly. The photoelectric probe can detect the polarization rotation angle and light intensity of the reflected laser, and then determine the incident angle between the incident laser and the object to be detected according to the polarization rotation angle and light intensity change and proportional relationship, according to the incident angle and the polarization rotation of the reflected laser Angle, the magnetization of the object to be detected is obtained, and finally the stress state of the object to be detected is calculated according to the magnetization. Here, the two incident laser beams are laser beams with different polarization directions or two laser beams with different wavelengths, and the polarization rotation angles of the two incident laser beams corresponding to the reflected laser beams are different from the incident angles of the incident laser beams.

Embodiment three:

Embodiment 3 discloses the principle structure of the detector. This embodiment discloses the specific results of a long-distance laser stress detector, including a housing 1, a handle 2 on the back of the housing 1, and a piece on the handle 3. The liquid crystal display screen 3 and the left, right, up movement and confirmation buttons are used for simple operation of the detector, and the buttons are uniformly marked as 4, and the semiconductor laser, wavelength division multiplexer, beam splitter, collimator, and polarizer and photoelectric probes are located within the housing. This hand-held design has a compact structure and is easy to carry, and can realize stress non-contact and fast scanning detection.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the protection of the present invention. within range.

Claims (7)

1. a kind of long distance laser stress mornitoring method, it is characterised in that: the method includes the following steps:

Two beam incident laser radiations are emitted in same optical path to object to be detected；

The po-larization rotational angular and light intensity of the reflected two beams reflection laser from object to be detected are detected respectively；

According to the variation and proportionate relationship of the respective po-larization rotational angular of two beam reflection lasers and light intensity, determine incident laser and Incident angle between object to be detected；

According to the po-larization rotational angular of incident angle on incident laser and reflection laser, the intensity of magnetization of object to be detected is obtained；

After the intensity of magnetization by laser detection to object to be detected, using Villari effect, according to magneto-mechanical effect, calculate to The stress state of test object.

2. long distance laser stress mornitoring method as described in claim 1, it is characterised in that: the two beams incident laser is polarization The different laser in direction or the different laser of two beam wavelength, two beam incident lasers correspond to the po-larization rotational angular of reflection laser and enter The changing rule for penetrating the incident angle of laser is different.

3. long distance laser stress mornitoring method as claimed in claim 2, it is characterised in that: two beam incident lasers are two vertical The S polarized light and P-polarized light of polarization.

4. the long distance laser stress mornitoring method as described in claim any one of 1-3, it is characterised in that: described same It is emitted in optical path before two beam incident laser radiations to object step to be detected, further includes:

When detection has the object to be detected of surface paint, or when the detection lower object to be detected of reflectivity, to be checked The test point position of object is surveyed, reflector plate is pasted.

5. long distance laser stress mornitoring method as claimed in claim 4, it is characterised in that: the reflector plate uses soft magnetic materials Production, and its reflectivity is high, there is surface rust protection ability.

6. a kind of long distance laser tension gauge, which is characterized in that including semiconductor laser, wavelength division multiplexer, beam splitter, Then collimator, analyzer and photoelectric probe, the semiconductor laser shoot laser to wavelength division multiplexer pass through beam splitter shape At the incident laser that two beams polarize, two beam incident lasers expose to object to be detected after collimator straightening, to be detected right As the two-way reflection laser of return is after two-way analyzer, one-to-one correspondence exposes to two-way photoelectric probe.

7. long distance laser tension gauge as claimed in claim 6, which is characterized in that the long distance laser tension gauge Further include shell, the back side of shell has handle, have on the handle one piece of liquid crystal display and left and right, upper movement and really Determine button, the semiconductor laser, wavelength division multiplexer, beam splitter, collimator, analyzer and photoelectric probe are located at the shell It is interior.