Measuring and testing – Specimen stress or strain – or testing by stress or strain... – Specified electrical sensor or system
Reexamination Certificate
1999-05-18
2001-10-23
Noori, Max (Department: 2855)
Measuring and testing
Specimen stress or strain, or testing by stress or strain...
Specified electrical sensor or system
C324S209000
Reexamination Certificate
active
06305229
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to the technical field of material testing and, more particularly, to detecting stress, strain, and fatigue in various materials.
BACKGROUND ART
In recent years, resistive changes in detector elements due to elongation and compression were detected by strain gauges, but there was no method for measuring fatigue. However, recently methods have been adopted wherein magnetic changes in structural materials were observed by use of detectors. In such cases, the measuring devices were large-scale and it was difficult to use them in actual job sites. As examples, 1988
, J. Appl. Phys
. 63(8) April 15, D. C. Jiles, Iowa State Univ. and
J. Appl. Phys
. 75(10) May 15, 1994, Z. J. Chen, D. C. Jiles, J. Kamedas' “
Estimation of Fatigue Exposure from Magnetic Coercivity
” cover this subject matter.
As summarized in
J. Appl. Phys
. 75(10) May 15, 1994 paper, magnetic structural steel materials were represented by H∞ ln(N), expressing the relationship between stress cycles (N) and coercivity (H), indicating a fixed linearity existing between the stress cycles (N) and coercivity (H). However, this relationship applies only to structural steel materials and not to magnetic steel materials which are exceedingly corrosion prone. Furthermore, when a magnetic measuring device is attached to the material structure itself, it is the same method that is presently being used for measuring magnetic strain.
Generally speaking, magnetic substances are very hard, brittle and difficult to machine. Furthermore, they are very corrosive and unstable. Since they also become brittle under repeated stress cycling and rupture easily, it is vital that noncorrosive and stable materials be selected. Devices for magnetically detecting stress, strain, and fatigue in various materials must be capable of maintaining stability over at least ten years, and they must be small in size so as to permit easy attachment and detachment.
DISCLOSURE OF INVENTION
Solving the preceding problems in magnetically detecting stress, strain, and fatigue in various materials requires detector elements having the following essential characteristics:
1. Being noncorrosive and stable (over ten years).
2. Having a small, vibration-free, low cost, and low power consuming power system that permits easy attachment of the detector onto the fatigue measuring sample.
3. Having a fatigue-resistant (at least 10
8
) magnetic material.
4. Having a magnetic detecting method that has a high signal-to-noise (“S-N”) ratio.
The principal objective of the present invention is to satisfy all of the above requirements simultaneously.
The present invention does not detect changes directly; it attempts to determine such characteristics as material grouping, degree of pressurization, fatigue, etc., of basic materials by magnetically detecting values of coercivity, flux density, magnetic susceptibility, magneto-resistance, impedance, permeability, etc. Furthermore, the earth's magnetic field, temperature, pressure and vibration are maintained as stable as possible. The detector element is made as small as possible so it can be readily attached to the measured specimen. Also, the fatigue element should be structured in its most stable crystalline and amorphous states.
The present invention positions a detector element at a spot where stress is directly encountered and where it can be readily attached and detached from the specimen. As an alternative, a series of detector elements can be distributed across the stress generating body and moved in such a manner as to accurately record on an encoder the positions where the magnetic change causing fatigue are located. At first, the detector elements can be positioned at set spacing and set width so that the magnetic values can be recorded continuously until fatigue occurs. Furthermore, the spacing can be varied to predict changes in fatigue generation.
By utilizing a machinable magnetic substance and form-fitting it into a stress concentrated part of a structural material, it is possible to measure the magnetoresistive effect, Hall effect and impedance of the material. Also, the changes in the resistivity of the structural material from direct strain (frequency) can be detected and its frequency recorded to estimate the fatigue condition of the material. By sealing the entire detector element and detecting means, it is possible to determine the fatigue frequency by measuring the magnetic changes brought about by the direct fatigue cycling in the magnetic specimen. In this manner, it is possible to measure a stable high S-N ratio pertaining to fatigue.
In accordance with the Concentrated Stress Constant, K=∂m/∂n, in certain applications, the S-N ratio can be improved by utilizing certain types of torsional machining. Furthermore, it is possible to form a concentrated stress specimen subjected to distortional concave pressure, with a detector means attached to the specimen in order to improve the S-N ratio. Some specimens formed under stress can be used by controlling the tension from various angles.
In a similar manner, the stress/strain of even nonmagnetic workpieces can be predicted by measuring the magnetic changes in the tool used as a detector. When the workpiece is magnetic, fatigue can be detected directly with the tool used as a detector element. In some cases, the workpiece itself can be used as a detector element. In this way, the fatigue-resisting capabilities of the tool and workpiece can be determined.
In some cases, it is possible to determine machining accuracy. This is accomplished by measuring the changes in magnetic characteristics of the tool wherein undergoing torque (stress-strain) changes during machining, and the tip of the tool is being subjected to high fatigue stresses. In similar manner, bearings are subjected to high stresses and increased distortion caused by tensile and compressive forces leading to fatigue. Similar fatigue predictions can be made for a thermally stressed oiler and turbine blades.
Detector elements must be able to maintain their characteristics throughout a long period of time. This can be accomplished by subjecting the elements to adequate heat treatment, maintaining the reaction until stabilization is reached, by taking advantage of the supinenodal metamorphosis relationship, and by amorphously forming the elements into wire and ribbon shapes. It is possible to readily detect the characteristics of such wire or ribbon detector elements from changes in their stress-strain crystallization. Furthermore, the detector elements must be fixed sturdily to the material to resist fatigue, such as brazing with a noncorrosive noble alloy.
When short detector elements are used, they are machined to introduce cutting, torsional and tensile stresses into elements, making them stable for mounting on the material specimen. Sensitive detection is possible with such short detector elements since all of the stresses are concentrated. Additionally, bellows and inert gases such as Ar and He are used to isolate the elements from the atmosphere. By doing this, the elements can last from ten to twenty years while maintaining their stable, basic characteristics. It is also possible to enclose the elements in a protective non-corrosive, synthetic, elastic resin body.
If stable detector elements are needed, hard magnetic materials are used. These can be of heat-treated martensitic alloys, dispersed hardened steel, rolled magnets, sintered magnets and others selected at one's option. When corrosion is a concern, using Pt—Fe and Pt—Co type elements are advantageous. Amorphous ferromagnetic materials, and hard and semi-hard materials, such as, Co—V—Cr—Fe types, Fe—Cr—Co wire material, Cu—Ni—Fe types, Fe—Co—Mo wire material, 13Cr stainless steel wire material, piano wire materials, ferrites and others can be used.
Heat treatment processes should conform to this invention. This heat treatment includes magnetic field heating and quenching. To improve corrosion resistance, PVC and PVD treatments are used. In some
Noori Max
Schreiber D. E.
Tanaka Systems Incorporated
LandOfFree
Detecting fatigue from magnetic characteristics does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Detecting fatigue from magnetic characteristics, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Detecting fatigue from magnetic characteristics will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2575280