JPS5950922B2 - Principal stress measurement method for magnetic materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for measuring the principal stress of a magnetic material by measuring the core loss of the magnetic material using one magnetic sensor and determining the direction and magnitude of the principal stress acting on the magnetic material. It is.

For magnetic materials such as steel used in assembled structures, there is generally a relationship between the stress acting on the magnetic material and the iron loss characteristics as shown in Figure 1. The direction and magnitude of the acting stress can be measured using a magnetic sensor.

That is, as shown in FIG. 3, the magnetic sensor 2 is constructed by winding an excitation coil (primary coil) 3 and an output voltage coil (secondary coil) 4 around a magnetic core 5 having a U-shaped cross section. As shown in FIG. 2, if the center of this magnetic sensor 2 is aligned with the measurement point 6 at which the stress on the surface of the magnetic material 1 is to be measured, and the excitation coil 3 is excited with alternating current, the magnetic flux from the magnetic core 5 is As shown in FIG. 3, the magnetic material 1 forms a closed magnetic path that flows in the direction of the arrow in the magnetic material 1 and returns to the magnetic core 5 again. At this time, the primary voltage is controlled to keep the output voltage induced in the secondary coil constant, and the primary coil is connected to the current terminal of the wattmeter (not shown), and the secondary coil is connected to the wattmeter. If you measure the iron loss by connecting it to the voltage terminal of magnetic material 1.
The stress in the center line direction of the magnetic sensor 2 acting on the measurement point 6 can be determined from the relationship shown in FIG. Magnetic sensor 2
The direction of the center line may be in the longitudinal direction of the magnetic sensor 2, as shown in FIG. 2, or may be in the direction perpendicular to the longitudinal direction. Now, in order to measure the stress at the measurement point 6 when the magnetic material 1 is in a certain stress state (tension, compression), it is necessary to find the direction and magnitude of the principal stress acting on the measurement point 6. .

For this purpose, conventionally, the center of one magnetic sensor 2 is aligned with the measurement point 6, and the magnetic sensor 2 is rotated around the measurement point 6 to produce the maximum or minimum iron loss. The direction of the center line was determined, the iron loss in that direction and the direction perpendicular to that direction was determined, and the magnitude of the principal stress was determined from the iron loss. In this case, if the iron loss of the magnetic material 1 when the stress is 0 is Wo, then as can be seen from Figure 1, when compressive stress is acting on the magnetic material 1, the iron loss WM is larger than Wo. , when tensile stress is acting, the iron loss Wm
becomes smaller than WM.

In addition, in order to measure the stress distribution at an arbitrary point in terms of iron loss, when the magnetic sensor 2 is rotated around that point and the iron loss is measured, the iron loss corresponding to the principal stress is measured as shown in Figure 4. Experiments have also confirmed that the loss is distributed symmetrically with respect to the directions of maximum and minimum loss. As you can see from this curve,
Since the curve is gentle near the point where the iron loss is maximum or minimum, it is difficult to directly and accurately measure the direction of the maximum or minimum iron loss and the iron loss in that direction with one magnetic sensor 2. Therefore, there was a drawback that the direction and magnitude of the principal stress could not be determined accurately. In view of the above points, the present invention provides a method for measuring principal stress in a magnetic material that can accurately determine the direction and magnitude of the principal stress in the magnetic material using one magnetic sensor.

An embodiment of the method of the present invention will be described below with reference to the drawings.

As shown in FIG. 5, the magnetic sensor 2 is mounted with its center aligned with the point 8 at which the principal stress of the magnetic material 7 is to be measured.
Excite the primary coil, rotate the magnetic sensor 2 around point 8, and find two adjacent directions B, B'' or B'', B'''' (see Figure 4) with equal iron loss, The angles formed with the initial starting direction BO of the magnetic sensor 2 are α1, α2,
Assuming α3, the direction of the principal stress to be determined is the direction of the perpendicular line passing through the center of WW, or the direction of the bisector of the angle α1-α2 or α2α3.

Next, if the iron loss WO when the stress is 0 is known, find the iron loss WM in the direction of the principal stress and the iron loss Wm in a direction different from this principal stress, for example, in a direction perpendicular to it, and directly use the main stress from Fig. 1. Although the stress may be calculated, the value of WM-WO is WO・,WM・,Wrrl
Since it is a small value compared to , the value read from the curve in Figure 1 is W.

Since the value changes due to temperature, slight changes in input voltage, etc., the obtained value also has a large error. Therefore, in the present invention, WM and Wr are calculated from the following equation without using WO.
It was confirmed that the principal stress can be determined more accurately than rl. That is, it can be more easily determined by setting σ to be the principal stress and α to be a coefficient determined by the quality of the magnetic material.

FIG. 6 illustrates this relationship. As described above, when using the principal stress measurement method for magnetic materials of the present invention, 1
Align the center of the magnetic sensor with a point on the surface where you want to measure the principal stress of the magnetic material, excite the primary coil, and rotate the magnetic sensor around that point until the core loss is equal. The direction of the principal stress can be determined accurately by simply measuring two adjacent directions, and the iron loss in the direction of the principal stress and the iron loss in the direction perpendicular to the principal stress can be determined. ,
Since the magnitude of the principal stress can be determined accurately, magnetic materials can be measured more accurately than conventional methods. It is possible to know the stress state of the material.

[Brief explanation of the drawing]

Figure 1 is a characteristic curve diagram showing the relationship between stress and iron loss of magnetic materials, Figure 2 is an explanatory diagram of the conventional principal stress measurement method using one magnetic sensor, and Figure 3 is A of Figure 2. - An enlarged cross-sectional view of A, FIG. 4 is a characteristic curve diagram showing the stress distribution around the measurement point on the surface of the magnetic material in terms of iron loss, and FIG. 5 is an example of the method for measuring principal stress of the present invention. FIG. 6 is a characteristic curve diagram showing the relationship with principal stress σ. 1, 7... Magnetic material, 2... Magnetic sensor, 3... Excitation coil (primary coil), 4...
...output [ヮ沒d pressure coil (secondary coil), 5...
···core.

Claims (1)

[Claims] 1 Rotate one magnetic sensor that can measure iron loss in any direction around a measurement point of the magnetic material, find two adjacent directions with equal iron loss, and calculate the principal stress at the measurement point. 1. A method for measuring principal stress in a magnetic material, characterized in that the direction is determined, and the magnitude of the principal stress is determined by determining the iron loss in the direction of the principal stress and the iron loss in a direction different from the principal stress.