Measuring and testing – Specimen stress or strain – or testing by stress or strain... – Specified electrical sensor or system
Patent
1995-11-30
1997-08-05
Chilcot, Richard
Measuring and testing
Specimen stress or strain, or testing by stress or strain...
Specified electrical sensor or system
73786, 324209, G01B 700
Patent
active
056545118
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a rail axial-force measuring method by which an axial force acting on a laid rail can be nondestructively measured in the field using magnetic techniques, and also relates to an axial-force measurable rail.
BACKGROUND ART
It has been traditionally practiced to nondestructively test structural members for material qualities, stresses, etc. by utilizing the dependence of the magnetic properties of materials on strain, structures such as crystal grain size and precipitates, etc. Such traditional methods include, for example, a method for estimating the tensile strength of steel by measuring its magnetic permeability and a method for estimating quenched hardness by measuring coercive force. In recent years, methods utilizing Barkhausen noise resulting from discontinuities in magnetization have been attracting attention, and there have been proposed a variety of methods utilizing this phenomenon; among them are a method of estimating the fatigue strength of soft steel (proposed, for example, by L. P. Karjalainen et al., IEEE Trans. Mag. MAG 16,514 (1980)) and a method of estimating the toughness of tool steel (proposed, for example, by Nakai et al., Iron and Steel, 75,833 (1989)).
To measure the magnetic permeability, coercive force, or Barkhausen noise of a body, an apparatus is used that comprises a power supply, a magnetization system consisting of a magnetizing head, etc., and a detection system consisting of a detection head, a signal processing system, etc. An advantage of the head system is that a body to be measured can be magnetized simply by touching the head to the surface of the body, for the detection of a signal from the body.
Using such magnetic techniques, attempts have been made to measure the stresses (axial forces) acting on a laid rail. Rails are constantly subjected to expansion and contraction due to changes in ambient temperatures, but usually the expansion and contraction of the rails are restrained except at portions near joints, since the rails are held rigidly to the crossties with fasteners. As a result, a compressive stress or a tensile stress acts locally on the rail. Since buckling may be caused in the rail when the compressive stress exceeds a certain critical value, it is particularly important in track maintenance to diagnose these axial forces. For this purpose, various techniques have been proposed for nondestructively detecting the axial forces acting on laid rails. For example, Japanese Unexamined Patent Publication No. 60-17330 discloses a rail axial-stress measuring apparatus which ensures reproducibility by demagnetizing the portions of a rail to be measured by a demagnetizer before measuring axial stresses using a magnetically anisotropic sensor. In this apparatus, the head and foot of a rail are taken as the portions to be measured. Further, Japanese Unexamined Patent Publication No. 60-243526 discloses a rail axial-stress measuring apparatus in which a pair of magnetically anisotropic sensors are arranged with their magnetically anisotropic detection coils differentially connected to eliminate the effects of external magnetic field disturbances. However, rails usually have residual stresses of varying magnitude locked into them before they were laid, and the magnitude of such stresses may be greater than the value of the axial forces, depending on the site within the rail. Using the apparatus disclosed in Japanese Unexamined Patent Publication No. 60-17330 or 60-243526, therefore, the absolute magnitude of the axial forces acting on the rail once it has been laid cannot be measured correctly unless the magnitude of residual stresses in the portion to be measured is obtained in advance.
The two prior art methods described above measure the change of permeability caused by stresses. Methods or apparatus for measuring stresses using other magnetic parameters are also disclosed, which include an apparatus for measuring stresses from the rate of change of coercive force (Japanese Unexamined Patent Publication No. 50-1597
REFERENCES:
patent: 3427872 (1969-02-01), Leep et al.
patent: 4596150 (1986-06-01), Kuhr
patent: 4599563 (1986-07-01), Tiitto et al.
Patent Abstracts of Japan, vol. 16, No. 537 (C-1003), Nov. 6, 1992 & JP-A-04 202626 (Nippon Steel Corp.), Jul. 23, 1992.
Database Inspec Institute of Electrical Engineers, Stevenage, GB, Inspec No. 1477797, Aug. 1979, XP002020339 & Archiv Fur Das Eisenhuttenwesen, Aug. 1979, West Germany, vol. 50, No. 8, pp. 347-350, V. Hauk, et al., "X-ray elasticity constants of ferritic, austenitic and hardened steels" ISSN 0003-8962.
Inaguma Toru
Sakamoto Hiroaki
Sugino Kazuo
Biegel Ronald
Chilcot Richard
Nippon Steel Corporation
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