JP4159013B2 - Material property evaluation method and apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for evaluating characteristics such as residual stress level, fatigue damage degree, irradiation damage degree, thermal embrittlement degree, etc. of a material by a nondestructive inspection method, and in particular, the magnetoresistive effect of a test material. The present invention relates to an evaluation method and apparatus used.
[0002]
[Prior art]
Conventionally known methods for nondestructive measurement of material properties, particularly residual stress levels during processing of materials, are X-ray residual stress measurement methods and Barkhausen methods as magnetic methods.
[0003]
The X-ray residual stress measurement method is a method of calculating the residual stress by measuring the displacement of the lattice point of the crystal by transmitting the X-ray through the test material because the stress of the material is based on a slight deformation of the crystal grain. It is.
[0004]
In the Barkhausen method, when magnetization is applied to a ferromagnet, it is magnetized by the discontinuous movement of the domain wall, so that a phenomenon in which noise (Barkhausen noise) occurs in the secondary coil occurs. This is a method of diagnosing the stress field of the test material and its state using this.
[0005]
[Problems to be solved by the invention]
The X-ray residual stress measurement method is excellent in that the measurement result has high reliability, and a transportable measurement device using the X-ray residual stress measurement method is generally known. However, since the X-ray residual stress measurement method and X-ray emission are performed, the size of the apparatus becomes excessive and the weight is large. For this reason, a measuring apparatus cannot be installed in a place where space is limited, such as a narrow measurement place. Moreover, since the weight is large, excessive labor is required to transport and install even in a large place. Furthermore, such an X-ray residual stress measuring device cannot be used in water.
[0006]
On the other hand, in the case of a measuring apparatus using the Barkhausen method, it is possible to measure even in a relatively small installation place, but since the material of measurement is generally a ferromagnetic material, aluminum, copper, austenitic stainless steel, etc. There is a problem that the residual stress of the non-magnetic material cannot be measured.
[0007]
The present invention has been made in view of such problems, and a material characteristic evaluation method and apparatus capable of evaluating the characteristics of a material regardless of a non-magnetic material or a magnetic material with a compact configuration regardless of a measurement place. The main purpose is to provide.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to claim 1 is different in strength from the first measurement step of measuring the electrical resistance value of the test material without generating a magnetic field in the test material. From the second measurement step of measuring the electrical resistance value of the test material, the electrical resistance value measured in the first measurement step, and the electrical resistance value measured in the second measurement step A calculation step of calculating a change in electrical resistance value that changes by applying a magnetic field to the test material, a relationship between the calculated change in electrical resistance value and the strength of the magnetic field, and a change in the electrical resistance value And an evaluation step for evaluating the material property of the test material based on the property data obtained by previously correlating the change in the electrical resistance value due to the magnetic field and the material property. It relates to the evaluation method.
[0009]
The invention according to claim 1 is a method for evaluating the material characteristics of a test material using the magnetoresistive effect. The magnetoresistive effect is a phenomenon in which an electric resistance value changes by applying a magnetic field to a substance having a specific electric resistance at a constant temperature. The change in the electric resistance value, that is, a conductor in which a current flows is applied to the magnetic field. The electrical resistance that appears when placed inside is called magnetoresistance. The magnetoresistive effect includes a longitudinal magnetic effect that occurs when a magnetic field is applied in a direction parallel to the direction of current flow, and a transverse magnetic effect that occurs when a magnetic field is applied perpendicular to the direction of current flow.
[0010]
The change in the electric resistance value due to the magnetic field is correlated with the characteristics of the material. As an example, FIG. 4 shows an explanatory diagram showing the relationship between the magnetic resistance and the strength of the magnetic field when tensile stress is applied to the test material (680 MPa) and when it is not applied (0 MPa). The horizontal axis indicates the strength of the magnetic field applied to the test material, and the vertical axis indicates Δρ / ρ ₁ . Here, Δρ is a magnetic resistance, and ρ ₁ is an electric resistance value in a state where no magnetic field is generated. FIG. 4 shows both the longitudinal magnetic effect and the transverse magnetic effect. As can be seen from FIG. 4, the magnetic resistance is generated in the material (▲, ●) to which tensile stress is applied compared to the material (□, Δ) to which tensile stress is not applied.
[0011]
Therefore, if the characteristic data for which the correlation between the change in the electrical resistance value due to the magnetic field and the material property is prepared in advance, the change in the electrical resistance value due to the magnetic field of the test material is obtained, thereby obtaining the test material. It becomes possible to evaluate the material characteristics of For example, if the residual stress level is measured as a material characteristic, the absolute value and orientation of the residual stress when the predetermined tensile stress is applied to the material to be tested and the change in the electrical resistance value due to the magnetic field . A curve indicating the correlation is obtained as characteristic data. What is necessary is just to obtain | require the change part of the electrical resistance value by the magnetic field used by characteristic data by the 1st measurement process of this invention, a 2nd measurement process, and a calculation process. The material properties in the present invention include the residual stress level, fatigue damage, irradiation damage, thermal embrittlement, impurity content, zircaloy hydrogen absorption, and the like.
[0012]
In the present invention, first, the electrical resistance value of the test material is measured in a state where no magnetic field is generated in the test material in the first measurement step, and the test is performed in the state where the magnetic field is generated in the test material in the second measurement step. Measure the electrical resistance of the material. Here, as a method of measuring the electric resistance value, a known method is used in which a current is passed through the test material, and the passed current and voltage are measured to obtain the electrical resistance value.
[0013]
In the calculation step, the change in the electric resistance value due to the magnetic field is calculated from the two electric resistance values measured in the two measurement steps. In the evaluation step, the material properties of the test material are evaluated based on the change in the electrical resistance value and the previously obtained property data.
[0014]
As described above, in the present invention, the material characteristics of the test material are evaluated using the magnetoresistive effect. Therefore, when the test material is a ferromagnetic material, the material characteristics can be evaluated even if it is a non-magnetic material. Can be performed. Further, in the present invention, since the material characteristics can be evaluated by a magnet or the like for generating a magnetic field in the test material and a simple circuit for measuring the electrical resistance, X-rays or the like that require excessive equipment Compared with the material property evaluation method using radiation, it is possible to evaluate the material property with a small and light facility.
[0015]
In the present invention, both the longitudinal magnetic effect and the transverse magnetic effect, or both the longitudinal magnetic effect and the transverse magnetic effect can be calculated and used for evaluation of material properties. Therefore, when using the longitudinal magnetic effect, the electrical resistance value is measured after generating a magnetic field in a direction parallel to the direction of current flow in the second measurement step, and when using the transverse magnetic effect, In the second measurement step, it is optional to measure the electric resistance value after generating a magnetic field in a direction perpendicular to the direction of current flow.
[0016]
In the present invention, since the amount of change in the electrical resistance value due to the magnetic field may be obtained from the difference in electrical resistance due to the presence or absence of the magnetic field, either the first measurement process or the second measurement process may be performed first.
[0017]
The invention according to claim 2 is measured by removing a pair of detachable magnets for generating a magnetic field on the test material, measuring means for measuring the electrical resistance value of the test material, and removing the magnet from the test material. A calculation means for calculating a change amount of an electric resistance value that is changed by applying a magnetic field to the test material from an electric resistance value and an electric resistance value measured by attaching the magnet to the test material; and Evaluating the material property of the test material based on the calculated change in electrical resistance value and the characteristic data obtained in advance by correlating the change in electrical resistance value due to the magnetic field and the material property This relates to a material property evaluation apparatus.
[0018]
The invention according to claim 2 is an apparatus for carrying out the material property evaluation method according to claim 1, and the function and effect of the present invention are the same as those of the invention according to claim 1.
[0019]
In addition, the pair of magnets can measure the electrical resistance in a state where a magnetic field is generated with respect to the specimen, and can be detachable so that the electrical resistance can be measured in a state where no magnetic field is generated. Alternatively, both magnets may be configured to be detachable, or only one magnet may be configured to be detachable.
[0020]
The measuring means of the present invention may be any means as long as it can measure the electrical resistance value of the test material. Two current terminals, two voltage terminals, a power source for passing a current from the current terminal to the test material, and between the voltage terminals A simple configuration such as a voltmeter for measuring the voltage can be adopted.
[0021]
In the present invention, if a pair of magnets, a measuring unit, and a calculating unit are provided in this way, the material characteristics can be evaluated. Therefore, the evaluation can be performed with a simple configuration, and radiation such as X-rays can be performed. Compared to a conventional material property evaluation apparatus using the material, it is possible to evaluate material properties regardless of whether it is a non-magnetic material or a magnetic material while reducing the size and weight of the device.
[0022]
In the present invention, either the longitudinal magnetic effect or the transverse magnetic effect can be used. When using the longitudinal magnetic effect, arrange a pair of magnets so that a magnetic field is generated in a direction parallel to the direction of current flow, and when using the transverse magnetic effect, set the pair of magnets in the direction of current flow. It may be arranged so as to generate a magnetic field in a direction perpendicular to the direction.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
A preferred embodiment of the present invention will be described below together with illustrated examples. In the present embodiment, the material property evaluation apparatus of the present invention is applied to a residual stress evaluation apparatus that performs nondestructive evaluation of the residual stress of a material, and FIG. 1 is a schematic diagram showing a schematic configuration thereof.
[0024]
As shown in FIG. 1, the residual stress evaluation apparatus 1 according to this embodiment measures a voltage between a pair of magnets 2 a and 2 b, two current terminals 3, two voltage terminals 4, and a voltage terminal 4. A voltmeter V, a battery 5 that supplies a current between the current terminals 3, and a calculation unit 6 that calculates a change in electrical resistance value due to a magnetic field are provided.
[0025]
The pair of magnets 2 a and 2 b are for generating a magnetic field in the test material 7. Of the pair of magnets, the magnet 2a is detachably attached to the test material 7, and generates a magnetic field on the test material 7 in a state of being attached to the test material 7 as shown in FIG. . The magnetic field direction at this time is the A direction in FIG. On the other hand, FIG. 2 shows a state in which the magnet 2a is removed from the test material 7. In such a state, naturally, no magnetic field is generated in the test material 7.
[0026]
The two current terminals 3 are attached to the test material 7 at a predetermined interval, and current is supplied to the test material 7 by supplying current from the battery 5. The current direction is the B direction in FIG. 1 and is parallel to the magnetic field direction A, so that a longitudinal magnetic effect is generated. The interval between the current terminals 3 can be arbitrarily determined according to the size of the test material 7 or the like.
[0027]
Two voltage terminals 4 are also attached to the specimen 7 at a predetermined interval, and a voltage is measured between the voltage terminals 4 with a voltmeter V. The interval between the voltage terminals 4 is configured such that each voltage terminal 4 is attached in the vicinity of the current terminal 3.
[0028]
The two current terminals 3, the two voltage terminals 4, the voltmeter V and the battery 5 constitute the measuring means of the present invention, and the voltage value measured by the voltmeter V (between the two voltage terminals 4). Is divided by the current value supplied to the two current terminals 3 to obtain the electric resistance value.
[0029]
The calculation unit 6 calculates the amount of change in the electrical resistance value due to the magnetic field from the electrical resistance value measured by removing the magnet 2a from the test material 7 and the electrical resistance value measured by attaching the magnet 2a to the test material 7. Further, the ratio between the change in the electric resistance value and the electric resistance value in a state where no magnetic field is generated is calculated, and constitutes the calculating means of the present invention. The calculation unit 6 can be configured by a simple electronic desk calculator or the like.
[0030]
Here, assuming that the electrical resistance value measured by removing the magnet 2a from the test material 7 is ρ ₁ , and the electrical resistance value measured by attaching the magnet 2a to the test material 7 is ρ ₂ , the change in the electrical resistance value due to the magnetic field. The minute Δρ is expressed by Equation 1. In the present embodiment, an evaluation value Δρ / ρ ₁ obtained by dividing the change Δρ of the electric resistance value by ρ ₁ is used for evaluation of the residual stress level of the material.
[0031]
[Expression 1]
Δρ = ρ ₂ −ρ ₁
Evaluation value Δρ / ρ ₁
[0032]
In the present embodiment, the residual stress is evaluated using the longitudinal magnetic effect of the test material 7, but the pair of magnets 2a is shown in FIG. 3 so that the magnetic field direction A is orthogonal to the current direction B. Even if it arrange | positions in this way and evaluation of a residual stress is performed using a transverse magnetic effect, the effect of this invention is achieved.
[0033]
A method for evaluating the residual stress (residual strain) of the SUS304 material 7 as the test material using the residual stress evaluation apparatus 1 configured as described above will be described. In this embodiment, the residual stress is evaluated when a tensile stress of 680 MPa is applied to the SUS304 material 7 that is a non-magnetic material that has undergone solution heat treatment at 1100 ° C. FIG. 5 is a flowchart of the residual stress evaluation method of this embodiment.
[0034]
First, as shown in FIG. 2, the magnet 2a is removed from the SUS304 material 7 (step 501), and a magnetic field is not generated by the current value passed through the current terminal 3 in this state and the voltage value measured by the voltmeter V. measuring the electrical resistance value [rho ₁ of (step 502).
[0035]
Next, the magnet 2a is attached to the SUS304 material 7 as shown in FIG. 1 (step 503), and a magnetic field is generated by the current value passed through the current terminal 3 in this state and the voltage value measured by the voltmeter V. the electric resistance [rho ₂ in measuring (step 504).
[0036]
Next, a change Δρ in the electric resistance value due to the magnetic field is obtained from the difference between the electric resistance values ρ ₂ and ρ ₁ (step 505), and the ratio between the change Δρ in the electric resistance value due to the magnetic field and the electric resistance value ρ ₁ is evaluated. (Step 506).
[0037]
Here, FIG. 4 shows the relationship (▲, ●) between the change in the electrical resistance value due to the magnetic field when a tensile stress of 680 MPa is applied to the SUS304 material 7 and the magnetic field, and when the tensile stress is not applied (0 MPa). The relationship between the change in electrical resistance value due to the magnetic field and the magnetic field (□, Δ) is shown. As can be seen from FIG. 4, the material to which the tensile stress is applied has a change in the electric resistance value due to the magnetic field as compared with the material to which the tensile stress is not applied. The reason why such a change in the electric resistance value due to the magnetic field appears is the martensitic transformation and magnetization accompanying the strain caused by the tension of the stainless steel material. For this reason, the correlation between the residual stress and Δρ / ρ ₁ is obtained in advance as residual stress characteristic data. An example of such characteristic data is shown in FIG. FIG. 6 is an explanatory diagram showing a change in magnetoresistive effect accompanying the stress applied to the SUS304 material, with the horizontal axis representing the applied stress (MPa) and the vertical axis representing Δρ / ρ (%). . The strength of the magnetic field is 0.4T.
[0038]
Then, with reference to the residual stress characteristic data (step 507), the absolute value and direction of the evaluation value [Delta] [rho] / [rho ₁ value from the residual stress (residual strain) non-destructively evaluated (step 508).
[0039]
As described above, in the residual stress evaluation apparatus 1 and method of the present embodiment, since the magnetoresistive effect of the test material 7 is used, the residual stress is also evaluated for a nonmagnetic material such as the SUS304 material 7. It becomes possible. Further, the configuration of the apparatus is simplified, and an excessive apparatus is not required, so that the apparatus can be reduced in size and weight.
[0040]
In this embodiment, the non-magnetic SUS304 material 7 is used as the test material, but other non-magnetic materials may be used and can be applied to the evaluation of the characteristics of the magnetic material. Absent.
[0041]
In the present embodiment, the present invention is applied to the evaluation of residual stress. In addition, the present invention is used to evaluate characteristics such as fatigue damage, irradiation damage, thermal embrittlement, impurity content, and hydrogen absorption of zircaloy. Is also applicable.
[0042]
【The invention's effect】
As described above, the present invention measures the electrical resistance value of the test material without generating a magnetic field in the test material, generates the magnetic field in the test material, and measures the electrical resistance value of the test material, calculating a change in the electrical resistance due to a magnetic field and an electric resistance value in the state that caused the electric resistance and the magnetic field in a state not causing magnetic field, and the change amount of the calculated resistance value, advance the magnetic field electrical resistance due to Since the material properties of the test material are evaluated based on the characteristic data obtained by correlating the change in value with the material properties, a simple configuration is possible regardless of whether the test material is ferromagnetic or non-magnetic. In addition, the material properties can be evaluated with a small and light facility. For this reason, it is easy to carry the material property evaluation apparatus to the inspection place, and even in the case of a place where there is a spatial restriction such as a narrow inspection place, the material property evaluation apparatus can be easily installed to remove the non-magnetic material. It has the effect that characteristic evaluation can be performed.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a schematic configuration of a residual stress evaluation apparatus according to an embodiment.
FIG. 2 is an explanatory view showing a state where one magnet is removed in the residual stress evaluation apparatus of the present embodiment.
FIG. 3 is a configuration diagram showing the arrangement of magnets when utilizing the transverse magnetic effect in the residual stress evaluation apparatus of the present embodiment.
FIG. 4 is an explanatory diagram showing the relationship between the change in electrical resistance value due to the magnetic field and the strength of the magnetic field when the tensile stress is applied to the test material and when the tensile stress is not applied to the test material in the residual stress evaluation apparatus of the present embodiment. is there.
FIG. 5 is a flowchart of a residual stress evaluation method according to the present embodiment.
FIG. 6 is an explanatory diagram showing, in a graph, changes in the magnetoresistive effect accompanying stress application of SUS304 material as an example of residual stress characteristic data used in the present embodiment.

Claims (2)

A first measurement step of measuring the electrical resistance value of the test material without generating a magnetic field in the test material;
A second measurement step of measuring the electric resistance value of the test material by generating magnetic fields of different strengths on the test material;
A calculation step of calculating a change amount of the electric resistance value that is changed by applying a magnetic field to the test material from the electric resistance value measured in the first measurement step and the electric resistance value measured in the second measurement step. When,
Based on the relationship between the calculated change in electrical resistance value and the strength of the magnetic field, the change in electrical resistance value, and the characteristic data obtained in advance by correlating the change in electrical resistance value due to the magnetic field and the material properties. An evaluation step for evaluating the material characteristics of the test material,
A material property evaluation method comprising: A pair of detachable magnets that generate a magnetic field on the specimen, and
A measuring means for measuring the electrical resistance value of the test material;
Change in electrical resistance value that changes by applying a magnetic field to the test material from the electrical resistance value measured by removing the magnet from the test material and the electrical resistance value measured by attaching the magnet to the test material Calculating means for calculating
Evaluating the material characteristics of the test material based on the calculated change in electrical resistance value and the characteristic data obtained in advance by correlating the change in electrical resistance value due to the magnetic field and the material characteristics; Material characteristic evaluation device.

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