JP3160711B2 - Method for determining plasticity of steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for judging the plasticity of steel using a magnetic sensor.

[0002]

2. Description of the Related Art When a steel material such as a steel frame used as a structure in a structure is overloaded so as to exceed a yield point, plastic deformation occurs.
In a structure that has been loaded by a large earthquake, etc., it is necessary to determine whether the structural material has deformed within the range of elastic deformation or has undergone plastic deformation due to overload exceeding the yield point. This is important when considering measures to determine whether continuous use or reinforcement is necessary. When the plastic deformation is large, the plasticization of the steel material can be determined by visual observation or dimensional measurement. However, when the plastic deformation is small, it is difficult to know the presence or absence of the plastic deformation because the amount of deformation as a structure is small and the steel is covered by an interior material or a fire-resistant coating material covering the steel material. Therefore, the only conventional method for determining plasticity is to indirectly determine the structure by observing the deformation state of the structure or damage to the interior and exterior materials covering the steel material. There was no effective and appropriate engineering method that could directly measure activation.

On the other hand, as a metallurgical method for discriminating the plasticity of a steel material, there is a method of observing the structure of the steel material and observing dislocations and slip lines caused by the plasticization, and oxidizing the surface of the steel material. There is a method of performing processing (etching) and visually observing the strain hardened region. However, in order to observe the structure, it is necessary to collect a sample for observation from the steel material and polish the surface. In the case of observation by etching, the steel material is heated to 250 to 300 ° C. Need to be etched. Therefore, any method can be observed and measured when a small test piece is used in a laboratory, but it is difficult to apply it to an actual structure. Further, as proposed in, for example, Japanese Patent Application Laid-Open No. 6-109412, a method of determining plasticity of a sample by arranging the sample in a detection coil, applying an AC current, and detecting an AC magnetization characteristic is also proposed. However, in this case, it is still difficult to apply the method to an actual structure as in the case of the metallurgical method described above.

The present invention has been made in view of the above circumstances, and provides a method for determining the plasticity of a steel material which enables non-destructive and direct determination of the plasticity of a steel material used in an actual structure. Aim.

[0005]

According to the method of determining plasticity of a steel material according to the present invention, a strong spontaneous magnetic field that can be measured externally is generated by magnetizing a steel material with a magnet (external magnetic field) in advance. The initial spontaneous magnetic field is measured by scanning the magnetic sensor along the surface of the steel, and the spontaneous magnetic field generated from the initial state of the spontaneous magnetic field caused by the magnetic anisotropy induced by the plastic deformation of the steel material is measured. The change is detected by scanning with the magnetic sensor, and the plasticization of the steel material is determined.

[0006] The present invention is based on the principle described below.
Plastic deformation of steel occurs when dislocations and slip lines occur inside the crystal. Since dislocations and slip lines are lattice defects, non-uniform stress is generated around them, and magnetic anisotropy induced by the stress occurs. The present invention focuses on magnetic anisotropy caused by plastic deformation, and seeks to determine the presence or absence and degree of plastic deformation by detecting a change in a magnetic field caused by magnetic anisotropy. That is, as shown in FIG. 19, a ferromagnetic material such as a steel material 1 has a magnetic structure called a magnetic domain structure partitioned by many magnetic domains. Magnetic spins exist. In the stress-strain curve of the steel material shown in FIG. 20, since the magnetization direction of each magnetic domain is random in the elastic region A, the steel material 1 shows isotropic magnetization characteristics as a whole and has little distortion.

In the non-magnetized steel material 1, the magnetization directions of the magnetic domains are random, and the magnetic field acting externally by the magnetic domains (called a spontaneous magnetic field) is weak. The magnetic domain structure will be oriented in a certain direction, and will generate a strong spontaneous magnetic field acting outside. On the other hand, when a load exceeding the yield point is applied to the steel material, dislocations and a slip which is an aggregate thereof occur in the structure. A microscopic stress field is generated around dislocations and slips. In a ferromagnetic material such as steel material 1, magnetic anisotropy induced by stress occurs near the stress field. When the steel material 1 undergoes plastic deformation, dislocations and slips increase, and the portion where magnetic anisotropy occurs also increases. Since the dislocation and slip occur in a direction in which the crystal of the steel material 1 easily slips (easy slip direction), in a polycrystalline material such as steel, the magnetic anisotropy induced by the dislocation and slip does not match the magnetization direction of the magnetic domain. . Therefore, the strong spontaneous magnetic field that is magnetized by the external magnetic field generated by the magnet and acts to the outside is reduced and gradually weakened by the magnetic anisotropy induced by dislocations and slips as the plastic deformation of the steel proceeds. Present.

When the spontaneous magnetic field generated from the steel material to the outside is measured on the surface of the steel material by scanning the magnetic sensor, the following characteristics are exhibited. (1) Immediately after the steel is magnetized by the magnet, the contact point of the magnet is strongly magnetized.
A strong spontaneous magnetic field due to the magnetization by the magnet is measured. The magnetic field in this part is stronger than the magnetic field in other parts. (2) In the range of elastic deformation of the steel material, dislocation and slip do not occur much, and the spontaneous change in the magnetic field is small. Therefore, a strong spontaneous magnetic field similar to (1) is measured just above the contact point of the magnet. (3) However, if the steel material is plastically deformed due to a load or the like, dislocation or slip occurs, and magnetic anisotropy is induced.
Therefore, the spontaneous magnetic field at the contact point of the magnet is reduced,
The difference from the spontaneous magnetic field strength in other parts is reduced. (4) As the plastic deformation of the steel material increases or increases, the spontaneous magnetic field at the contact point of the magnet is further reduced, and the difference in strength from the spontaneous magnetic field at other portions is further increased. Decrease.

When a steel material is magnetized by a magnet, a strong spontaneous magnetic field is formed outside the steel material. However, since a normal steel material is a ferromagnetic material, a magnetic field (spontaneous magnetism) inherent to the steel material is generated. Have. Therefore, a magnetic field inherent to the steel material and a magnetic field in the natural world (for example, geomagnetism) and a spontaneous magnetic field caused by magnetization by a magnet are superimposed on the outside of the steel material. In order to measure the spontaneous magnetic field generated by the magnet, it is necessary to compensate for the magnetic field inherent in steel and the magnetic field in the natural world, and extract only the magnetic field caused by the magnetism of the magnet. In this case, if the steel is not magnetized in a particular direction, the spatial distribution of the magnetic field around the steel is slow. On the other hand, the spatial distribution of the spontaneous magnetic field created outside the steel material by the magnetization of the magnet varies greatly. Therefore, by using a magnetic sensor such as a magnetic sensor having a differential detection coil or a magnetic sensor having an offset function, it is possible to compensate for a magnetic field inherent to a steel material or a magnetic field in the natural world. In addition, by using a magnetic sensor having a small detection area and excellent in spatial resolution, a spontaneous magnetic field due to magnetization of a magnet can be measured with high accuracy. For example, since a magnetic sensor using a superconducting quantum interference device has high sensitivity, the area of a magnetic flux detection portion can be reduced, and spatial resolution can be increased.

Therefore, when the strength of the spontaneous magnetic field of a steel material magnetized by an external magnetic field is measured by a magnetic sensor, when the steel material is plastically deformed, the contact portion of the magnet (magnetized by the magnetic anisotropy) is caused by magnetic anisotropy. The spontaneous magnetic field of the steel part is reduced, so that the presence or absence of plastic deformation of the steel material can be determined, and the degree of plastic deformation and the like can be detected from the amplitude of the measured spontaneous magnetic field.
Therefore, the plastic deformation of the steel material can be directly measured without destruction, and the discrimination measurement of the plastic deformation of the steel material applied to the actual structure is possible.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIGS. FIG.
Is a perspective view showing a state where an electromagnet is brought into contact with a steel material, FIG. 2 is a plan view showing a magnetized portion of the steel material and a scanning direction of a magnetic sensor, FIG. 3 is a plan view of a magnetic sensor, and FIG. FIG. 5 is a perspective view showing a state in which the magnetic sensor is scanned on the steel material, FIG. 5 is a diagram showing the strength of the magnetic field measured by the magnetic sensor for the steel material in the initial state, and FIG. FIG. 7 is a diagram showing the strength of a magnetic field measured by a magnetic sensor, and FIG. 7 is a diagram showing the relationship between the amplitude of a spontaneous magnetic field and the ratio of plastic strain of a steel material. FIG. 1 shows a magnet, for example, two electromagnets 5 (which may be permanent magnets) for contacting and magnetizing a plate-like steel material 1. The electromagnet 5 is formed, for example, by winding a coil 7 around an iron core 6 having a U-shaped cross section, and one of both end surfaces of the iron core 6 in contact with the steel material 1 has an N pole.
The other is an S pole. The power supply current of the coil 7 is desirably DC, but may be AC. Therefore, the portion of the steel material 1 magnetized by the electromagnet 5 is a portion 8 (S pole) magnetized by the N pole.
And the portion 9 (N pole) magnetized by the S pole are alternately formed in a stripe shape (see FIG. 2). The magnetized portions 8 and 9 are preferably provided at a plurality of locations, but may be provided at only one location.

Next, a magnetic sensor 10 for measuring a spontaneous magnetic field is, for example, the one shown in FIG. 3, and this magnetic sensor 10 is of a differential type comprising double detection coils 10a and 10b. is there. Each detection coil (detection unit) 1
Reference numerals 0a and 10b are small enough to detect a locally changing magnetic field above the surface of the steel material 1 with high accuracy, and have a minute cross-sectional area of, for example, about 1 mmφ, and are arranged concentrically and on the same plane. The number of windings is adjusted so that their areas are the same, and the winding directions are opposite to each other. In the present embodiment, assuming that the sectional areas of the detection coils 10a and 10b are S1 and S2 and the number of turns is N1 and N2, S1
N1 is set to be S2N2. By using the differential type magnetic sensor 10 including the detection coils 10a and 10b having such a small cross-sectional area, a locally changing magnetic flux can be detected with high accuracy, and a magnetic flux from a distant magnetic field source (natural world) can be detected. As well as slowly changing magnetic flux.

Next, a method of determining plasticity of a steel material according to an embodiment will be described. First, as shown in FIG. 1, both poles of the electromagnet 5 are brought into contact with the surface of the steel material 1 to be magnetized, and as shown in FIG. 2, one or a plurality of stripe-shaped magnetized portions 8, 9 are formed. A spontaneous magnetic field is generated in the magnetized portions 8 and 9 from the surface of the steel material to the outside.
When the magnetic sensor 10 is caused to scan along the surface of the steel material 1 in a non-contact manner in a direction intersecting (see FIG. 4), the spontaneous change in the magnetic field from the steel material 1 is detected by the detection coils 10a and 10b of the magnetic sensor 10. Can be measured. The magnetic field on the steel surface detected by the magnetic sensor 10 changes according to the scanning position of the magnetic sensor 10. Immediately above the magnetized portions 8 and 9, the polarity of the electromagnet 5 differs depending on whether the polarity is positive or negative, but the strength of the magnetic field is maximized, and the strength of the magnetic field greatly changes as compared with other portions. That is, the amplitude of the spontaneous magnetic field in the magnetized portions 8 and 9 is large in the initial state (see FIG. 5) before a load is applied to the steel material 1 (unloaded) (see FIG. 5), but decreases as the plastic deformation proceeds ( See FIG. 6). Therefore,
As shown in FIG. 7, the plastic strain can be detected by measuring the maximum value (minimum value) of the spontaneous magnetic field amplitude at the upper part (or lower part) of the magnetized portions 8 and 9, and the presence or absence of plastic deformation can be determined. The degree can be estimated.

The joints of the structure have a complicated shape and the stress distribution is not uniform. The stress can be measured using a strain gauge, a displacement gauge, or the like before the load is applied, but it is difficult to know the stress concentration location in the actual structure after the construction. In this regard, according to the method according to the present embodiment, when reinforcing the structure, it is possible to specify the presence or absence and the location of the location where plasticization occurred early in the stress concentration location without contact.

As described above, according to the present embodiment, the presence or absence and degree of plastic deformation of the steel material 1 can be easily measured in a non-contact manner, and even if the steel material is used for an actual structure, it is non-destructive. Plastic deformation can be determined directly.

Next, a method of determining plasticity of a steel material according to a second embodiment will be described. In FIG. 8, the magnetized portions 8, 9 of the magnetic sensor 10 are arranged in a state where the portions 8, 9 magnetized in a striped pattern like the steel material 1 shown in FIG.
Is scanned in the form of a rectangular wave along the line, and a plane distribution diagram of the strength of the spontaneous magnetic field of the steel material 1 is obtained. That is, as shown in FIG. 8, the magnetic sensor 10 is scanned in a rectangular waveform over the entire surface of the steel material 1 to obtain a spontaneous planar intensity distribution of the magnetic field. And
A scanning point is set on each scanning line according to a sampling frequency, a magnetic field strength in each scanning line is converted into a digital value via an A / D converter, and points where the magnetic field strengths in each scanning line are equal are connected. In this case, an isomagnetic map can be obtained. The plane distribution diagrams shown in FIGS. 9 to 12 are isomagnetic diagrams connecting points at which the measured magnetic field strengths are equal. In the steel material 1 in the initial state (unloaded) shown in FIG. Immediately above the portions 8 and 9, the intervals between the isomagnetic lines are dense (indicated by reference numerals 8 'and 9'), and sparse in other portions. When plastic deformation is applied to the steel material 1, as shown in FIG. 10, FIG. 11, and FIG. 12, the distance between the isomagnetic lines gradually increases in each state of the elastic region, the residual strain of 0.2%, and the residual strain of 1.0%. It becomes sparse. FIG. 13 shows the relationship between the density of isomagnetic lines and the plastic strain of a steel material. As described above, the presence and degree of plastic deformation can be measured by measuring the density of isomagnetic lines on each plane distribution map.

The shape of the portions 8 and 9 of the steel material 1 to be magnetized by the magnets such as the electromagnet 5 does not need to be striped, and may be concentric circles as shown in FIG.
Alternatively, small circles may be provided in a checkered pattern as shown in FIG. Further, the electromagnet 5 is magnetized by bringing both poles into contact with the steel material 1, but instead of this, like the electromagnet 12 in FIG.
Only one pole may be brought into contact with the steel material to be magnetized. Further, as the detection coils 10a and 10b of the differential type magnetic sensor 10, instead of the concentric circular coils shown in FIG. 3, the detection coils 10a and 10b are arranged at intervals above and below as shown in FIG. It may be configured, or may be arranged in a rectangular or polygonal shape as shown in FIG. Further, in the above-described embodiment, the magnetic field in the direction perpendicular to the surface of the steel 1 is measured by the magnetic sensor 10, but the magnetic field in the direction parallel to the surface of the steel 1 may be measured. Alternatively, instead of the direction component of the magnetic field, the combined magnetic field strength may be measured.

As described above, according to the method for judging plasticity of a steel material according to the present invention, a strong spontaneous magnetic field that can be measured externally is generated by magnetizing the steel material in advance with a magnet. When the initial spontaneous magnetic field is measured and plasticity determination is performed, the magnetic sensor is scanned along the surface of the steel material, resulting from magnetic anisotropy induced by plastic deformation. The spontaneous magnetic field from the steel used for the actual structure was measured in a non-contact manner by detecting changes in the spontaneous magnetic field from the initial stage and thereby determining the plasticity of the steel. The presence or absence of plasticization of the steel material can be determined directly in a non-destructive state.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a state in which an electromagnet is brought into contact with a steel material in a method for determining plasticity according to an embodiment of the present invention.

FIG. 2 is a plan view showing a magnetized portion of a steel material and a scanning direction of a magnetic sensor.

FIG. 3 is a plan view of a detection coil of the magnetic sensor.

FIG. 4 is a perspective view showing a state in which a magnetic sensor scans a partially magnetized steel material.

FIG. 5 is a waveform diagram showing the amplitude of a magnetic field measured by a magnetic sensor on a steel material in an initial state.

FIG. 6 is a waveform diagram showing the amplitude of a magnetic field measured by a magnetic sensor on a plastically deformed steel material.

FIG. 7 is a diagram showing the relationship between the amplitude of a spontaneous magnetic field and the ratio of plastic strain of steel.

FIG. 8 is a diagram illustrating a scanning direction of a magnetic sensor with respect to a magnetized portion in a plasticization determination method according to a second embodiment of the present invention.

9 is an isomagnetic diagram in an initial state of a magnetic field in a region measured by the magnetic sensor shown in FIG. 8;

10 is an isomagnetic diagram similar to FIG. 9 and is an isomagnetic diagram in an elastic region.

FIG. 11 is a magnetic isomagnetic diagram similar to FIG. 9, and is a magnetic isomagnetic diagram in the case of a residual strain of 0.2%.

FIG. 12 is a magnetic isomagnetic diagram similar to that of FIG. 9, and is a magnetic isomagnetic diagram in the case of a residual strain of 1.0%.

FIG. 13 is a diagram showing a relationship between the density of isomagnetic lines and the plastic strain of a steel material.

FIG. 14 is a diagram showing another example of the shape of a portion magnetized by a steel magnet.

FIG. 15 is a view showing still another example of the shape of a portion magnetized by a steel magnet.

FIG. 16 is a perspective view showing another example of a state where an electromagnet is brought into contact with a steel material.

FIG. 17 is a diagram showing another example of the magnetic sensor.

FIG. 18 is a diagram showing still another example of the magnetic sensor.

FIG. 19 is a diagram schematically showing microscopic magnetic characteristics of a steel material in an elastic region.

FIG. 20 is a view showing a stress-strain curve of a steel material.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steel material 5 Electromagnet 8, 9 Magnetized part 10 Magnetic sensor

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Kazuo Chine 1-8-3 Nakase, Mihama-ku, Chiba-shi, Chiba Seiko Electronics Industries Co., Ltd. (72) Inventor Satoshi Nakayama 1-8-8 Nakase, Mihama-ku, Chiba-shi, Chiba Seiko Inside Electronic Industries Co., Ltd. (72) Inventor Narikei Odahara 1-8 Nakase, Mihama-ku, Chiba-shi, Chiba Seiko Electronic Industries Co., Ltd. (56) References JP-A-6-109412 (JP, A) JP-A-5 -142203 (JP, A) JP-A-2-22626 (JP, A) JP-A-1-245149 (JP, A) Noboru Ishikawa, "Study on stress measurement method using magnetostriction effect (Part 1)" , Shimizu Institute of Construction Research, April 1983, No. 37, p. 71-77 (58) Field surveyed (Int. Cl. ⁷ , DB name) G01N 27/72-27/90 JICST file (JOIS)

Claims (1)

(57) [Claims] 1. A magnetizable steel material is magnetized in advance by a magnet to generate a strong spontaneous magnetic field that can be measured and acts outside .
The initial spontaneous magnetic field is measured by scanning the magnetic sensor along the surface of the steel material, and the initial spontaneous magnetic field caused by magnetic anisotropy induced by plastic deformation of the steel material is measured. A plasticity discrimination method for steel material, wherein a change from is detected by scanning with the magnetic sensor to determine plasticity of the steel material.