JPS6126831A - Measuring method of impact strain - Google Patents

Abstract

PURPOSE:To eliminate the need for an exciting coil by winding a coil around an anode-cathod type probe formed by winding a coil around a ferromagnetic body and a test body or jig, test-piece, etc., and measuring strain at the time of an impact. CONSTITUTION:When an impact 2 is applied to the ferromagnetic body, the longitudinal wave of an elastic body propagate as a compressional wave while accompanies by variation in volume due to expansion and contraction. At this time, the ferromagenetic body is magnetized in the propagation direction of the elastic wave by the reverse effect of magneto-striction to produce magnetic flux in a round bar 1 made of the ferromagnetic body. This magenetic flux is proportional to the intensity of the impact force. Then, a voltage having a speed proportional to variation of magenetic flux penetrating the coil 3 is induced according to the Faraday rule. Thus, variation of the compressional wave of the elastic wave itself is detected to eleminate the problem of follow-up property, eliminating the need for the exciting coil.

Description

[Detailed Description of the Invention] Conventional magnetic sensors and measurements have used a method in which a primary coil (excitation coil) is used to excite the magnet and changes in magnetic resistance, etc. are detected using a secondary coil (search coil). The measurement method is characterized in that it does not require an excitation coil.

Commonly used strain gauges measure the strain on the surface of an object and cannot track it in the case of high-speed impact. In the present invention, when an elastic wave passes through a ferromagnetic body, the average strain inside the cross section of the probe or coil wound is measured, and the change in the compression wave of the elastic wave itself is detected. no problem.

Figure 1 shows that when a shock is applied to a ferromagnetic material, longitudinal elastic waves propagate as compressional waves accompanied by volumetric changes such as expansion and contraction*. At this time, due to the reverse effect of magnetostriction, the rod is magnetized in the direction of propagation of the elastic wave, and magnetic flux is generated within the ferromagnetic round rod. This magnetic flux is proportional to the strength of the impact force. Faraday's law induces a voltage at a rate proportional to the change in magnetic flux passing through the coil. Figure 2 shows that the magnitude of the induced voltage is proportional to the number of turns of the coil. Fig. 3 shows that even if the magnetic flux generated in a round bar is induced by a magnetic circuit to a probe wound with a pole-to-pole coil, the induced voltage can be determined in the same way as when the coil is wound directly.

The magnetic properties of a magnetic material are shown by a BH curve. In the range of initial magnetic permeability, the relationship between B (magnetic flux density) and H (magnetic field strength) is reversible. This measurement method cannot be applied to static load measurements.

Figure 1 shows a comparison of the waveform measured by wrapping a fill around a ferromagnetic round bar and the waveform of a commonly used strain gauge, and the comparison of the waveform measured by a pole-to-pole probe and a strain gauge, respectively. .

FIG. 5 shows seven examples of how to measure by winding a coil around the testing machine body, jig, or test piece, and by attaching a simple probe between poles.

*Magnetostriction is a phenomenon in which the external shape of a ferromagnetic material changes when it is magnetized.

[Brief explanation of the drawing]

Figure 1 Compression wave propagation situation of elastic waves propagating in ferromagnetic material
■Impact, ■Dense, ■Loose, Fig. 2 When a coil is wound around a ferromagnetic material ■Round bar, ■Impact, ■Coil, Fig. 3 When a pole-to-pole probe is attached ■Round bar, ■Impact, ■ Measurement examples ■Round bar, ■Rubber plate, ■Steel ball, ■Strain gauge, ■Waveform measured with a gap type probe, ■Waveform measured with a strain gauge, ■When fixed with round rod, ■screw, O steel ball, O coil 1. G) Strain gauge, waveform measured with @coil, waveform measured with Q strain gauge. Figure 5 Examples of application to impact testers ■Impact testers, ■High-pressure cylinders, ■Test specimens, ■When a coil is wound around a tester, ■When an interpole type probe is attached to a tester, ■When a jig is used When a coil is wound, ■ When a pole-to-pole probe is attached to a jig, ■ When a coil is wound around a test piece, Figure 1 ■ Figure 3

Claims (1)

[Claims] A method of measuring strain upon impact using a pole-to-pole (U-shaped) probe with a coil wound around a ferromagnetic material such as steel, and a coil wound around the testing machine body, jig, test piece, etc.