JP5990808B2 - Surface stress measurement system using Kerr effect - Google Patents

Description

  The present invention relates to a surface stress measuring apparatus.

  Various metal processed products are subjected to various processes such as machining, casting, welding, and heat treatment in the manufacturing process. At that time, residual stress such as tension or compression is generated with the processing, which often adversely affects the strength and shape accuracy of the processed product. For this reason, it is necessary to measure the magnitude of the residual stress and take measures so as not to cause a defect in a place where a large force seems to act or a place where it is difficult to cause deformation.

  In addition, in the process of developing products such as tools and power transmission parts, it is very important to investigate in detail what kind of stress is generated during use of the product when developing new products with improved performance. Useful. Similarly, it is possible to evaluate the strength, durability, and the like of the prototype by measuring changes in the surface stress of the product with respect to external forces in trial production at the development stage of various products.

  Thus, the stress measurement of a product can be said to be an indispensable process for product management, new product development, and the like.

  At present, as a method for measuring the stress, a method using a strain gauge is most widely adopted. A strain gauge is affixed to the surface of the object to be measured, stress can be calculated from the amount of strain measured by the strain gauge and the Young's modulus value of the object to be measured, and the stress change at the affixed portion can be read. Patent Document 1 discloses an example of a stress measurement method using this strain gauge. However, in this method, it is necessary to attach strain gauges to all the parts to be measured, and there is a problem that a great effort is required for the measurement. In addition, there is a problem that the adhesive used for pasting or the stress of the strain gauge itself is applied as a bias. Further, there is a problem that the residual stress cannot be measured because the stress is measured from the change in strain.

  In addition, as another stress measurement method, Patent Document 2 discloses an example of a stress measurement method using infrared rays. This method is a method of measuring stress by measuring a temperature change of the surface of the object to be measured based on a thermoelastic effect when an external force is repeatedly applied to the object to be measured. Although this method can easily measure the stress distribution, it is a measurement method that presupposes deformation of the object to be measured, and has a problem that it cannot be used in applications requiring nondestructive inspection. Also, residual stress cannot be measured in principle.

  In addition, as another stress measurement method, Patent Document 3 discloses an example of a stress measurement method based on X-ray analysis. This method uses the fact that the interstitial distance of the internal crystal changes due to stress in the polycrystalline material, and reads the change in the intercrystalline lattice distance of the X-ray irradiated surface on the member to be measured by X-ray analysis, This is a method of measuring the magnitude of the surface stress on the X-ray irradiated surface from the change. Although this method can measure a nondestructive and minute region, there is a problem that measurement is difficult unless an appropriate crystal plane that diffracts at a high angle exists on the surface. Also, amorphous measurement cannot be performed. In addition, since it is a device that uses X-rays, there are some legal restrictions on its use, and there is a problem that the price of the apparatus becomes expensive.

Patent Publication 2002-22579 Patent Publication 2001-91371 Patent Publication 2012-13423

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a surface stress measurement device capable of measuring the stress on the surface of the object to be measured in a non-contact and safe manner.

The invention according to claim 1 for solving the above-mentioned problem is a stress measuring device for measuring stress on the surface of an object to be measured,
Magnetic field applying means for applying a varying magnetic field to the object to be measured;
A light irradiation means for irradiating light on the surface of the object to be measured;
A polarization plane angle detecting means for detecting the polarization plane angle of the reflected light from the surface of the object to be measured;
Surface stress calculation means for calculating the stress of the surface of the object to be measured from the polarization plane angle detected by the polarization plane angle detection means;
And the surface stress calculation means calculates the stress on the surface of the object to be measured by calculating based on the mathematical formula 1.

The invention according to claim 2 is the embodiment according to claim 1 , further comprising light irradiation position moving means for moving the light irradiation position on the surface of the object to be measured, wherein the object to be measured is moved while moving the light irradiation position. A surface stress measurement apparatus that maps stress distribution on the surface of a measurement object by measuring stress on the surface of the measurement object.

  According to the present invention, the stress on the surface of the object to be measured can be measured safely and simply by non-contact and non-destructive means. In addition, it is possible to perform stress measurement of a minute region on the surface of the object to be measured, and it is also possible to perform mapping of the stress distribution of the measured member table by performing stress measurement while moving the measurement region.

First embodiment of the present invention Second embodiment of the present invention Changes in anisotropic magnetic field due to stress

  A first embodiment for carrying out the present invention will be described with reference to FIG. The present invention is a stress measuring device for measuring the stress on the surface of the object to be measured, the magnetic field applying means 2 for applying a variable magnetic field to the object 1 to be measured, and the light for irradiating the surface of the object 1 to be measured. The measurement is performed from the irradiation means 3, the polarization plane angle detection means 4 for detecting the polarization plane angle of the reflected light 9 from the surface of the object 1 to be measured, and the polarization plane angle detected by the polarization plane angle detection means 4. It is comprised from the surface stress calculating means 5 which calculates the stress of the target object 1 surface. If necessary, data storage means 6 storing magnetostriction constants and stress-free anisotropic magnetic field values of a plurality of known materials is added as a constituent element. In many cases, a polarizing filter 10 for polarizing the incident light 8 is installed on the path of the incident light 8 irradiated from the light irradiation means 3.

  The present invention is based on the premise that the member 1 to be measured is a magnetic material. The magnetic field applying means 2 includes a solenoid coil, a Helmholtz coil or an electromagnet, and an excitation power source for driving them. The shape needs to be designed so that a magnetic field can be applied to the entire measured member or the measured region of the surface of the measured object 1. As the light irradiation means 3, a laser oscillator or a monochromatic lamp can be used. Further, as the polarization plane angle detection means 4, a combination of an optical sensor such as a photodiode or a photomultiplier tube and a rotating polarizer can be used. If more accuracy is required, a lock-in amplifier may be added to this configuration. Further, as the surface stress calculation means 5, a personal computer, a built-in microcomputer, an analog calculator or the like is used. As the data storage means 6, a storage medium such as a hard disk, an optical disk, or a semiconductor memory is used.

  When a varying magnetic field is applied to the object 1 to be measured from the magnetic field applying means 2, the magnetization of the surface of the object 1 to be measured is changed by this varying magnetic field. At this time, the variable magnetic field is preferably sinusoidal or triangular. When the measurement object 1 in this magnetic field is irradiated with light from the light irradiation means 3, the polarization plane of the reflected light 9 rotates in proportion to the magnitude of the magnetization of the measurement object 1. This rotation of the plane of polarization is a phenomenon known as the “Kerr effect”. When the reflected light 9 enters the optical sensor through the rotating polarizer, the amount of incident light to the optical sensor is maximized when the angle of the rotating polarizer and the polarization plane angle of the reflected light match. That is, the angle of the polarization plane of the reflected light 9 can be obtained by obtaining the angle of the rotating polarizer that maximizes the amount of incident light. Since the change in the polarization plane angle is proportional to the change in magnetization, the magnitude of the magnetization on the surface of the measurement object 1 can be calculated by inputting the measured polarization plane angle to the surface stress calculation means 5.

  When stress is generated in the measurement object 1 that is a magnetic body, the magnetic anisotropy energy inside the measurement object 1 changes. The anisotropic energy that changes due to this stress is called magnetostrictive anisotropic energy, and its magnitude is expressed by Equation 3. This energy change can be read as a change in the anisotropic magnetic field Hk, and it is known that there is a relationship of Formula 4. By transforming this, Equation 5 is obtained. That is, if the magnetostriction constant of the object 1 to be measured and the magnitude of the anisotropic magnetic field when no stress is known, the change in stress can be read as the change in the anisotropic magnetic field.

  The magnitude of the anisotropic magnetic field Hk is defined as shown in FIG. Here, considering that the magnitude of the magnetization I is proportional to the change in the polarization plane angle of the reflected light, the value of Hk can be obtained by Equation 6. Substituting Equation 6 into Equation 5 yields Equation 7. That is, by inputting the change of the rotation angle of the polarization plane with respect to the varying magnetic field and the two constants α and β to the surface stress calculation means 5, the stress on the surface of the object to be measured can be calculated by Equation 1. Actually, these two constants α and β are the characteristics (saturation magnetization, no-stress anisotropic magnetic field, magnetostriction constant), magnetic field angle, incident angle of light, and shape of the object 1 to be measured. It varies depending on various factors such as the shape of the magnetic field applying means 2. If the measurement is performed while applying the known stress to the material to be measured in a state where the measurement conditions are combined in advance, the two constants α and β in each measurement condition can be determined.

  A second embodiment for carrying out the present invention will be described with reference to FIG. The basic configuration is the same as in the first embodiment. In the second embodiment, in addition to the constituent elements in the first embodiment, a light irradiation position moving means 7 for moving the light irradiation position on the surface of the measurement object 1 is provided. As the light irradiation position moving means 7, an XY stage, an XYZ stage, an XYθ stage, and an XYZθ stage that can attach an object to be measured are assumed. Alternatively, an irradiation angle adjusting mechanism that changes the irradiation direction of the light irradiation unit 3 may be used as the light irradiation position moving unit 7. These light irradiation position moving means 7 are preferably capable of moving the light irradiation position by automatic control. When moving the light irradiation position by changing the irradiation direction of the light irradiation means 3, it is necessary to track the reflected light 9. Therefore, it is necessary to combine the polarization plane angle detection means 4 with a position controller capable of automatic tracking. is there.

  The stress measurement process in the second embodiment is the same as that in the first embodiment, but the stress distribution on the surface of the object to be measured is measured by measuring the stress on the surface of the object to be measured while moving the light irradiation position. Can be mapped.

  According to the present invention, the surface stress of an industrial product can be measured safely and simply by a non-contact and non-destructive means, which is useful for durability tests and development of new products. In addition, it is considered that by using an on-site type device, it can be used for finding a place where a fatigue test or reinforcement of a structural material or piping of an already constructed building is necessary.

DESCRIPTION OF SYMBOLS 1 Object to be measured 2 Magnetic field application means 3 Light irradiation means 4 Polarization surface angle detection means 5 Surface stress calculation means 6 Data storage means 7 Light irradiation position moving means 8 Incident light 9 Reflected light 10 Polarizer

Claims (2)

A stress measuring device for measuring stress on the surface of an object to be measured,
Magnetic field applying means for applying a varying magnetic field to the object to be measured;
A light irradiation means for irradiating light on the surface of the object to be measured;
A polarization plane angle detecting means for detecting the polarization plane angle of the reflected light from the surface of the object to be measured;
Surface stress calculation means for calculating the stress of the surface of the object to be measured from the polarization plane angle detected by the polarization plane angle detection means;
The surface stress measuring device calculates the stress on the surface of the object to be measured by calculating based on the following formula 1 by the surface stress calculating means.

A light irradiation position moving means for moving the light irradiation position on the surface of the object to be measured, and measuring the stress on the surface of the object to be measured while moving the light irradiation position; The surface stress measuring device according to claim 1, wherein the surface stress measuring device is mapped.

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