CN110220622B - A kind of long-distance laser stress detection method and detector - Google Patents
A kind of long-distance laser stress detection method and detector Download PDFInfo
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- G01L1/00—Measuring force or stress, in general
- G01L1/24—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet
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Abstract
本发明适用于无损检测领域，提供一种远距离激光应力检测方法及检测仪，本发明利用两个垂直的S偏振光和P偏振光各自的偏振旋转角来确定入射角，入射角度确定之后，就可以利用克尔偏转角度，来得出待检测对象的磁化强度，然后根据磁记忆原理，计算出待检测对象的应力和疲劳情况。本发明公开一种利用表面磁光克尔效应进行金属应力和疲劳损伤检测的技术和实现方式，利用激光的非接触性以及磁光克尔效应、以及维拉里效应，实现应力的非接触、快速扫描检测。
The invention is suitable for the field of non-destructive testing, and provides a long-distance laser stress detection method and a detector. The invention utilizes the respective polarization rotation angles of two perpendicular S-polarized light and P-polarized light to determine the incident angle, and after the incident angle is determined, The Kerr deflection angle can be used to obtain the magnetization of the object to be detected, 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 an implementation method for detecting metal stress and fatigue damage by using surface magneto-optical Kerr effect. Quick scan detection.
Description
Technical Field
The invention belongs to the technical field of nondestructive testing, and particularly relates to a remote laser stress testing method and a remote laser stress testing instrument.
Background
Stress detection is very important and stress in metals is ubiquitous. In some cases, the presence of stress concentrations results in accelerated corrosion, i.e., stress corrosion, of the component. In addition, in terms of structure, the presence of stress leads to fatigue damage. Sudden failures of the structure without warning may occur, resulting in major safety accidents. The periodic testing of stress prevents these accidents and thus a convenient and quick in-situ stress testing technique and product is needed.
Existing field stress detection methods are basically divided into two main categories: stress detection based on deformation and stress detection based on a certain physical quantity. The first scheme mainly comprises a strain gauge method and a fiber grating method at present, and the two methods calculate the deformation of an object to be detected in turn through the passive deformation of a sensor, so that the stress of the object to be detected is calculated. The second scheme mainly comprises methods in aspects of acoustics, electromagnetism and the like, wherein the acoustics method mainly utilizes the propagation characteristics of ultrasonic waves, and the electromagnetism method mainly utilizes the change of the electromagnetic performance of the acoustics method, and a new method is a magnetic memory stress detection method.
Magnetic memory detection is a field stress rapid detection method advocated by professor du bov of russian scientists, and is widely used in a plurality of fields at present. However, in most cases, contact detection of an object to be detected is required. For large steel structures, such contact detection is difficult. Therefore, a non-contact stress rapid detection method and product suitable for remote field is needed.
Disclosure of Invention
In view of the above problems, an object of the present invention is to provide a remote laser stress detection method and a remote laser stress detector, which can realize non-contact rapid detection of stress by laser.
In one aspect, the remote laser stress detection method comprises the steps of:
emitting two beams of incident laser on the same light path to irradiate the object to be detected;
respectively detecting the polarization rotation angle and the light intensity of two beams of reflected laser reflected from an object to be detected;
determining an incident angle between incident laser and an object to be detected according to respective polarization rotation angles of the two beams of reflected laser, and the change and the proportional relation of light intensity;
obtaining the magnetization intensity of the object to be detected according to the incident angle of the incident laser and the polarization rotation angle of the reflected laser;
after the magnetization intensity of the object to be detected is detected through laser, the stress state of the object to be detected is calculated according to the magneto-mechanical effect by utilizing the Villari effect.
Further, the two beams of incident laser are lasers with different polarization directions or two beams of lasers with different wavelengths, and the polarization rotation angles of the two beams of incident laser corresponding to the reflected laser are different from the change rule of the incident angle of the incident laser.
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 and irradiating the two beams of incident laser light on the object to be detected, the method further includes:
when an object to be detected with surface paint is detected or the object to be detected with lower reflectivity is detected, a reflector plate is adhered at the position of a detection point of the object to be detected.
Furthermore, the reflector plate is made of soft magnetic materials, and has high reflectivity and surface antirust capacity.
On the other hand, the remote laser stress detector comprises a semiconductor laser, a wavelength division multiplexer, a beam splitter, a collimator, an analyzer and a photoelectric probe, wherein laser emitted by the semiconductor laser is transmitted to the wavelength division multiplexer, then two beams of polarized incident laser are formed through the beam splitter, the two beams of incident laser are collimated by the collimator and then irradiate to an object to be detected, and two paths of reflected laser returned from the object to be detected are irradiated to the two paths of photoelectric probes in a one-to-one correspondence mode after passing through the two paths of analyzers.
On the other hand, remote laser stress detector still includes the casing, there is the handle the casing back, there is a liquid crystal display and left and right, upward movement and definite button on the handle, semiconductor laser, wavelength division multiplexer, beam splitter, collimater, analyzer and photoelectric probe are located in the casing.
The invention has the beneficial effects that: the invention realizes the non-contact stress detection of the stress by combining the magneto-optical Kerr effect and the magnetic memory detection principle, and the advantages of the magnetic memory detection technology are kept, and simultaneously, because the laser is used as the detection probe, the data source (detection area) has more locality, the source of the signal can be more accurately distinguished, and the spatial resolution is improved; in addition, in a preferable mode, for an object to be detected with a surface coating or surface paint, the metal non-deformation fatigue detection can be realized in a grinding-free condition by means of attaching the reflector plate.
Drawings
FIG. 1 is a schematic diagram of the normal incidence and Kerr polarization rotation angles of an incident laser;
FIG. 2 is a schematic illustration of non-normal incidence of incident laser light;
FIG. 3 is a schematic view of a reflector plate;
FIG. 4 is a schematic diagram of a remote laser stress detector;
fig. 5 is a structural diagram of a remote laser stress detector.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Before describing the inventive solution, the surface magneto-optical kerr effect is briefly introduced. In 1845, the magneto-optical effect was first discovered by Michael Faraday. He found that when a magnetic field is applied to a glass sample, the plane of polarization of the transmitted light will rotate. In 1877, John Kerr discovered the magneto-optic Kerr effect (MOKE, magnetic-optical Kerr effect). In 1985, Moog and Bader succeeded in obtaining a hysteresis loop of a magnetic substance one atomic layer thick when performing magneto-optical Kerr effect measurement of a ferromagnetic ultrathin film, and defined the surface magneto-optical Kerr effect (SMOKE). Experiments prove that the method can detect the magnetism of the ferromagnetic ultrathin film with the thickness of one atomic layer, thereby becoming an important research method of magnetism.
The basic principle of the surface magneto-optical kerr effect is magneto-optical interaction, which is described below by taking linearly polarized light as an example. When linearly polarized light is incident on the surface of a sample to be magnetically detected, the reflected light becomes elliptically polarized light, and the polarization direction thereof is rotated by a small angle called a kerr rotation angle, i.e., an included angle between the major axis of the ellipse and the incident linearly polarized light, as shown in fig. 1. Meanwhile, generally, the ellipsometry of the reflected light is also changed due to the different absorption rates of the sample for p-polarized light and s-polarized light, and the magnetization of the sample to be measured causes an additional change in the ellipsometry, which is called the kell ellipsometry, i.e. the ratio of the major axis to the minor axis of the ellipse. In summary, the magnetization of the object to be detected can be detected by using linearly polarized light through the surface magneto-optical kerr effect. The magneto-optical kerr effect is widely used for magnetic research of ultrathin films. Another application of the magneto-optical kerr effect is magneto-optical recording, i.e. recording computer information by the magneto-optical effect.
Thirty years of research and application progress have demonstrated four advantages of the surface magneto-optical kerr effect: firstly, the detection sensitivity to magnetism is extremely high, and advanced devices of the type can detect the magnetism of the material of the sub-monoatomic layer. Secondly, the surface magneto-optical Kerr effect is a nondestructive testing technology, which adopts laser as a probe, does not cause any damage to an object to be tested, and can carry out in-situ and non-contact detection. Again, the information is derived from the illuminated area of the object to be detected, the signal of the surface area substantially outside the illuminated area can be excluded, the resulting signal is very local and gradual changes in material or magnetism can be studied. Finally, it is simple in construction, easy to integrate.
On the other hand, magnetic memory stress detection technology has been gradually accepted after more than twenty years of development. The metal magnetic memory detection technology is a rapid nondestructive detection method for detecting stress concentration and fatigue damage of a part to be detected by using a metal magnetic memory effect. During processing and operation of ferromagnetic metal parts, magnetic domain organization reorientation occurs in stress concentration areas due to the cyclic action of the load. This irreversible change in magnetic state is not only retained after the removal of the operating load, but is also related to the maximum applied stress to which it is subjected. This magnetic state of the surface of the metal component "remembers" the location of the microscopic defect or stress concentration, a so-called magnetic memory effect. The method overcomes the defects of the traditional nondestructive detection and provides a way for detecting the stress concentration inside the ferromagnetic metal component.
The detector based on the basic principle of metal magnetic memory effect can evaluate the stress concentration degree of the member and the existence of micro defects by recording the distribution condition of the magnetic field intensity component perpendicular to the surface of the metal member along a certain direction, diagnose and evaluate early failure, damage and the like, prevent sudden failure and is a new detection technology in the field of nondestructive detection.
Therefore, aiming at the content, the invention provides a scheme for integrating the magneto-optical kerr effect and the magnetic memory stress detection technology, and the non-contact rapid detection of the stress by using laser is realized. The specific implementation mode can be a handheld device, and the handheld device is convenient to carry and operate.
In order to explain the technical means of the present invention, the following description will be given by way of specific examples.
The first embodiment is as follows:
the method for detecting the remote laser stress provided by the embodiment comprises the following steps:
step S1 is to emit two incident laser beams on the same optical path and irradiate the two incident laser beams to the object to be detected.
Referring to fig. 1, the polarized incident laser is straightened and then emitted from the handheld detector to the surface of the object to be measured. In general, linearly polarized light is incident on the surface of an object to be detected, and when the incident angle is vertical, the reflected light returns from the original path. At this time, the polarization direction of the reflected light is rotated, and when the magnetization intensity of the object to be detected is not very large, the polarization angle of the reflected light and the magnitude of the magnetization intensity M thereof are linearly related, and in practical cases, it is difficult to ensure the vertical incidence of the detection laser. There is typically one angle of incidence. This angle of incidence can have a serious impact: the reflected light does not return from the original path and is therefore difficult to capture, as shown schematically in figure 2 for non-normal incidence. For this case, the present solution makes use of diffuse reflection caused by incident light. The diffusely reflected laser light also has a polarization, and the rotation angle of this polarization is again related to the magnetization M of the object to be detected. However, because of the diffuse reflection, the light intensity of the light returning to the handheld detector is weak, so that the subsequent photoelectric probe is required to have higher sensitivity and amplification factor, and the current general photoelectric technology can achieve the purpose.
Therefore, the two paths of polarized incident laser emitted from the detector directly irradiate on the object to be detected. Specifically, for example, two perpendicular linearly polarized lights S and P may be used as the incident laser light, i.e., S-polarized light and P-polarized light. There are many ways to implement this, such as using two lasers, or taking out two different linear polarizations after splitting a beam of laser, or other ways. Pulsed incident laser light may also be used to increase the incident and reflected and diffusely reflected energy.
And step S2, detecting the polarization rotation angle and the light intensity of the two beams of reflected laser light reflected from the object to be detected respectively.
Detection of the polarization state of the directly or diffusely reflected laser light may be accomplished with an analyzer, such as a polarizer, polarizing prism, or other optical device. Under the condition of vertical incidence, the magnitude of the magnetization M of the object to be detected can be obtained only by one linearly polarized light. In the case of non-normal incidence, the angle of incidence is also an unknown quantity. Therefore, the scheme of the invention adopts two different linearly polarized light incidences: s-linearly polarized light and P-linearly polarized light. The rotation angles of the two polarized lights respectively and the magnetization M follow different nonlinear relations. By comparing these two rotation angles, the magnitude of the magnetization M and the laser incidence angle can be known at the same time.
And step S3, determining the incident angle between the incident laser and the object to be detected according to the respective polarization rotation angles and the light intensity changes of the two beams of reflected laser and the proportional relationship.
Step S4, obtaining the magnetization intensity of the object to be detected according to the incident angle of the incident laser and the polarization rotation angle of the reflected laser;
and step S5, after the magnetization intensity of the object to be detected is detected through laser, calculating the stress state of the object to be detected according to the magneto-mechanical effect by utilizing the Villary effect.
Typically, the angle of incidence is a variable that is difficult to control. Especially when using the handheld device in the field, it is difficult to achieve vertical incidence due to hand vibration and the relative position between the point to be detected and the handheld device. The invention utilizes the respective polarization rotation angles of two orthogonal S-polarized light and P-polarized light to determine the angle of incidence. And after the incident angle is determined, the magnetization intensity of the object to be detected is obtained by utilizing the polarization rotation angle of the reflected laser. And then calculating the stress and fatigue condition of the object to be detected according to the Villari effect and the magneto-mechanical effect.
In addition, in general, a layer of paint may be present on the surface of the object to be detected, this layer of paint being non-magnetic. At the same time, it shields the magnetic signal of the object to be detected itself. For this situation, a fixed reflector plate can be used, and as shown in fig. 3, the reflector plate is made of a soft magnetic material with good linearity, low remanence and low coercive force, and is subjected to rust prevention treatment. The reflector plate has high reflectivity and surface antirust capability. After the detection point is determined for the object to be detected, the reflector plate is fixed to the detection point of the object to be detected in an adhesive-backed mode. Because the reflector plate is made of magnetic metal with good linearity, the magnetization condition of the reflector plate is basically synchronous with that of an object to be detected. Of course, this may also be used if an object to be detected having a low reflectivity is detected.
Example two:
the embodiment one provides a remote non-contact detection method, which is applied to a detector. The embodiment discloses a principle structure of a detector, as shown in fig. 4, the detector includes a semiconductor laser 101, a wavelength division multiplexer 102, a beam splitter 103, a collimator 104, a polarization analyzer (two paths are shown in the figure, and respectively marked with 105 and 107) and a photoelectric probe (also two paths are shown in the figure, and respectively marked with 106 and 108), the semiconductor laser 101 emits laser to the wavelength division multiplexer 102, then two beams of polarized incident laser are formed through the beam splitter 103, the two beams of incident laser are collimated by the collimator 104 and then irradiate to an object to be detected, and two paths of reflected laser returned from the object to be detected irradiate to the two paths of photoelectric probes one-to-one after passing through the two paths of polarization analyzer. The photoelectric probe can detect the polarization rotation angle and the light intensity of the reflected laser, then determines the incident angle between the incident laser and the object to be detected according to the polarization rotation angle, the change of the light intensity and the proportional relation, obtains the magnetization intensity of the object to be detected according to the incident angle and the polarization rotation angle of the reflected laser, and finally calculates the stress state of the object to be detected according to the magnetization intensity. Here, the two incident laser beams are laser beams having different polarization directions or two laser beams having different wavelengths, and the polarization rotation angle of the reflected laser beam corresponding to the two incident laser beams is different from the change rule of the incident angle of the incident laser beam.
Example three:
the third embodiment discloses the principle structure of detector, and this embodiment discloses a remote laser stress detector's concrete result, including casing 1, there is handle 2 casing 1 back, there are a liquid crystal display 3 and left and right, upward movement and confirm the button on the handle 3 for simple operation detector, button uniform mark is 4, semiconductor laser, wavelength division multiplexer, beam splitter, collimater, analyzer and photoelectric probe are located in the casing. The handheld design has the advantages of compact structure and convenient carrying, and can realize non-contact and rapid scanning detection of stress.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
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