Measuring and testing – Specimen stress or strain – or testing by stress or strain... – Specified electrical sensor or system
Patent
1998-01-26
1999-11-30
Noori, Max
Measuring and testing
Specimen stress or strain, or testing by stress or strain...
Specified electrical sensor or system
324209, G01B 724
Patent
active
059922419
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a method and equipment for determining the longitudinal loading acting on a beam, such as on a rail of a railway track subjected to longitudinal loading and for determining more particularly the neutral temperature of railway tracks, by energizing the beam longitudinally in the audio-frequency range and measuring the level of Barkhausen noise at the surface of the energized region. Further subject of the invention is an equipment serving for implementing the proposed method.
In the elements used in the construction of track structures lower or higher residual stresses are present due to processes of manufacturing. Further mechanical stresses are added to these residual stresses by dead weight and installation. From the points of view of loadability and fatigue of structural parts, the overall resultant of all these stresses are to be taken into account. However, to find the balance of forces acting on a structure, the force arising in each individual element has to be determined.
The task of determining the forces acting in the various beams of a lattice truss or in a rail of a continuously welded railway track is not a simple technical problem. Application of destructive test methods is not expedient, because, for instance, in the case of a railway track such a test would require setting of scotch blocks.
In a welded track the sleepers prevent displacement of rails through the track fastening elements. After the rails have been clamped, any temperature change causes a thermal stress in the rails due to restriction of dilatation. The temperature at which the thermal stress in the tested cross-section of a rail is zero is termed neutral temperature. It is important that the neutral temperature be in the vicinity of the average of expectable highest and lowest rail temperatures. Should the discrepancy from that average be large, at low temperatures rail ruptures, at high temperatures rail buckling may occur.
In a given cross-section of a rail, stresses may be present even at neutral temperature, resulting from production technology (e.g. due to uneven quenching rate) or installation activities (bending of rails). Characteristic of these stresses is that their resultant referred to the entire cross-sectional area is zero.
For a given cross-sectional area the neutral temperature can be determined from the resultant of stresses arising in the given cross-section.
Non-destructive methods are based on the measurement of a physical characteristic correlated with the stress state of the section of material investigated. A common feature of all such methods is that the correlation is always associated with the actual stress state, and is dependent on the structure of the material concerned (chemical composition, texture, etc.)
The texture of metal and its residual stress depend on the applied manufacturing technology, while the distribution of residual stress may be subject to considerable changes in the course of service--especially during the early years of operation--in a way depending on the location of rails within the track and on the duty imposed on them.
One of the known non-destructive methods is based on the stress-dependence of the level of magnetic Barkhausen noise (Pashley, R. L.: Barkhausen effect--an indication of stress, Materials Evaluation, Vol. 28, No. 7, pp. 157 to 161, 1970).
Magnetic reversals taking place in ferromagnetic materials generate high-frequency electromagnetic and acoustic response signals termed Magnetic Barkhausen Noise. The level of noise depends on the structure of material and its stress state. The stress test performed by measuring the Barkhausen noise is based on the correlation existing between the level of Barkhausen noise and the stress state of the material. Application of Barkhausen noise to stress-state measurements is described in Patent Specification U.S. Pat. No. 4,634,976 and in an international patent application No. PCT/US89/01539. Common feature of the two proposed methods is that the correlation existing betw
REFERENCES:
patent: 5161891 (1992-11-01), Austill
patent: 5166613 (1992-11-01), Perry
patent: 5195377 (1993-03-01), Garshelis
patent: 5280725 (1994-01-01), Stengel
Beli Janos
Molnar Peter
Posgay Gyorgy
Szamos Alfonz
Varga Ferenc
Magyar Allamvasutak Reszvenytarsasag
Noori Max
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