X-ray stress measurement method for grooves or lines

Abstract

The present invention provides a method for measuring the normal stress in the longitudinal direction of a thin groove or thin wire simply and quickly, without requiring special equipment or long-term irradiation.The present invention relates to a method for measuring the residual stress generated in the longitudinal direction of a groove-shaped or thin wire-shaped member with high accuracy. [Solution] By using the position where the shear stress is closest to zero as the stress measurement point, or by estimating the normal stress at the point where the shear stress is zero by interpolation, it is possible to relax the restrictions on the irradiation diameter while enabling high-precision stress measurement.

Description

[Technical Field]

[0001] The present invention relates to a method for measuring longitudinal normal stress using X-rays of a thin groove or thin wire, utilizing shear stress. [Background technology]

[0002] Conventionally, in stress measurement using X-ray diffraction, in order to measure the longitudinal normal stress of a thin groove or thin wire, it was necessary to narrow the X-ray irradiation diameter to 20% or less of the diameter of the object and to irradiate it accurately onto the center line of the object. However, narrowing the irradiation diameter reduces the X-ray irradiation area, which means it takes time to acquire a diffraction signal of the required intensity. In addition, the small irradiation area reduces the number of crystal grains that contribute to diffraction, which increases the variability of the measurement values. The following non-patent literature is available as references: [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] X-ray residual stress measurement method for springs and spring steel. Research Committee on X-ray residual stress evaluation method for springs. Vol. 2012, No. 57, pp. 59-79 Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention provides a method for measuring the normal stress in the longitudinal direction of a thin groove or thin wire simply and quickly, without requiring special equipment or long-term irradiation.The present invention relates to a method for measuring the residual stress generated in the longitudinal direction of a groove-shaped or thin wire-shaped member with high accuracy. [Means for solving the problem]

[0005] The present invention provides a method for measuring residual stress using X-ray diffraction on a measurement object that is approximately symmetrical about a groove or linear center line, The object to be measured is irradiated with X-rays, and shear stress and normal stress are measured simultaneously using a two-dimensional detection sensor such as the cos α method. Measurements are taken at multiple positions while changing the irradiation position across the width of the object to be measured. The method is characterized by determining the position where the obtained shear stress value is closest to zero as the measurement point of the normal stress, or by estimating the normal stress at the point where the shear stress is zero by interpolation. [Effects of the Invention]

[0006] This invention eliminates the need to narrow the X-ray irradiation diameter (to less than 20%), as was previously required, and enables accurate normal stress estimation even with an irradiation diameter of 20% or more. As a result, the measurement time is reduced in inverse proportion to the square of the irradiation diameter compared to conventional methods, and the increase in irradiation area also reduces the variability in measurement values. [Brief explanation of the drawings]

[0007] [Figure 1] Schematic diagram of measurement showing the first embodiment of the present invention [Figure 2] Schematic diagram of measurement showing the second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0008] (Definition of terms)

[0009] The main terms used in this specification are defined as follows: (1) "Fine wire" means a linear object with a diameter of a few millimeters or less. (2) "Groove" means a long, narrow recess formed on the surface of a component. (3) "Longitudinal direction" means the direction of the main axis of the groove or thin wire. (4) "Normal stress" refers to the normal stress component perpendicular to the measurement surface. (5) "Shear stress" refers to the component of stress acting parallel to the measurement surface. When the X-ray irradiation diameter is less than the diameter of the object to be measured, the X-ray is aimed at the center line of the object to be measured, and the change in the obtained shear stress value is used as an indicator to select the measurement point closest to zero, thereby obtaining a normal stress value with high measurement accuracy. Furthermore, when the X-ray irradiation diameter is more than twice the diameter of the object to be measured, by arranging multiple grooves or thin wire members in parallel without gaps within the irradiation range, it becomes possible to perform stable measurements with wide-area irradiation. According to the present invention, when the measurement object is groove-shaped or thin wire-shaped and its shape is axisymmetric with respect to the center line in the longitudinal direction, the principal stress tends to occur along the longitudinal direction due to the shape and processing state. Therefore, when the principal stress direction coincides with the longitudinal direction, the shear stress is theoretically zero. On the other hand, in residual stress measurement using X-rays, the measured shear stress value tends to contain not only the true shear stress component but also a pseudo-shear stress component resulting from the rounded cross-sectional shape of the object being measured (the curvature of grooves or thin wires). However, in the configuration according to the present invention, by focusing on the fact that the measurement object is approximately axisymmetric, the pseudo component can be offset axisymmetrically by adjusting the irradiation position so that the center of the X-ray irradiation range coincides with the center line of the object. As a result, the measured shear stress value approaches zero, and the stress value at that position can be measured as the true principal stress, which is the normal stress. Furthermore, since the present invention employs a configuration in which the measurement position is minutely displaced to search for the position where the shear stress is zero, there is no need to determine the measurement position with high precision in advance. In other words, the optimal position for the measurement object can be identified using the change in shear stress as an index, so the precision of positioning in the measurement process can be relaxed. This eliminates the need for special equipment. Therefore, according to the present invention, it is possible to measure the principal stress with high accuracy even in locations that are difficult to measure in X-ray stress measurement, such as grooves and thin wires, and it is possible to suppress the influence of pseudo components caused by the shape. A first embodiment of the present invention will be described with reference to FIG. Using an X-ray stress measuring device, X-rays are irradiated by visually aiming at the center of the groove. When visually aiming at the center, the X-rays are off by up to 0.3 mm from the actual center, so the measurement is made between -0.3 and +0.3 mm from the visual center. Table 1 shows an example in which a groove with a diameter of 3.6 mm was measured. The top half of Table 1 shows the normal stress and shear stress values ​​measured from -0.3 to +0.2 mm above the center line in an example with an irradiation diameter of approximately 2 mm. The position of zero shear stress is between -0.1 mm and 0 mm, and the normal stress at the position of zero shear stress calculated by proportional interpolation is -679 MPa. The bottom half of Table 1 shows the normal stress and shear stress values ​​measured with an irradiation diameter of 0.6 mm. The zero position of shear stress is between -0.1 mm and 0 mm, and is calculated by proportional interpolation to be -658 MPa. The difference in measurement results between an irradiation diameter of 2 mm and an irradiation diameter of 0.6 mm is approximately 3%, maintaining sufficient accuracy. The required irradiation time was 30 seconds for 2 mm and 270 seconds for 0.6 mm, a difference of approximately 9 times, resulting in an 89% time reduction. [Table 1] [Table 2]

[0010] Next, a second embodiment of the present invention will be described with reference to FIG. Table 2 shows an example where a product with 10 0.5 mm diameter thin wires arranged closely together was measured. As shown in Figure 2, the irradiation diameter is 2 mm, so approximately 4 wires are irradiated. Measurements were taken by moving the 0.5 mm diameter thin wire from -0.3 to +0.3 mm. The zero shear stress position is between 0.1 and 0.2 mm, and proportional interpolation gives a normal stress of -613 MPa. [Industrial Applicability]

[0011] This contributes to reducing the time required for stress measurement of industrial parts with thin grooves and thin wires. [Explanation of symbols]

[0012] 1 X-ray irradiation and detection device main body 2 X-ray beam irradiated onto the measurement object 3. Grooved sample to be measured 4. Mechanism for fine-tuning the sample position 5 Thin wire to be measured

Claims

1. A method for measuring longitudinal residual stress using X-ray diffraction for a grooved or linear measurement object that is approximately symmetrical about a center line, characterized in that the measurement object is irradiated with X-rays, shear stress and normal stress are measured simultaneously using a two-dimensional detection sensor, measurements are made at multiple positions in the width direction of the measurement object, and the position where the obtained shear stress value is closest to zero is determined as the measurement point for normal stress, or the normal stress at the zero shear stress point is estimated by interpolation calculation.

2. The residual stress measuring method according to claim 1, Measurements are taken continuously or discretely at multiple widthwise positions, A residual stress measurement method characterized by identifying the optimal measurement position based on the obtained shear stress value.

3. 3. The residual stress measurement method according to claim 1, wherein the object to be measured has a configuration in which a plurality of thin wires are arranged in parallel, the irradiation diameter is set so as to include the plurality of thin wires at the same time, a position where the shear stress value approaches zero is selected, and the normal stress at that position is measured.

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