Measuring and testing – Specimen stress or strain – or testing by stress or strain... – Specified electrical sensor or system
Reexamination Certificate
2002-07-22
2004-06-22
Lefkowitz, Edward (Department: 2855)
Measuring and testing
Specimen stress or strain, or testing by stress or strain...
Specified electrical sensor or system
C073S763000, C073S774000
Reexamination Certificate
active
06752023
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and a device for carrying out the nondestructive material characterization and the measurement of stress in the interior of a ferromagnetic part under test by measuring the high-frequency change in its electric potential caused by flowing an excitation current through the part under test or by the deformation of the part under test. Furthermore, a purpose of the method is utilizing ferromagnetic reference materials as temperature sensors and gas sensors.
BACKGROUND OF THE INVENTION
Determining the properties of ferromagnetic materials by means of micromagnetic methods is known in the art. The principle of these methods is based on continually changing the magnetic domain structure within the material by subjecting the to-be-examined ferromagnetic material cyclically to an external change in magnetization. Boundaries between regions of the same magnetization, so-called Bloch walls, are moved through the structure of the material which for their part interact with the microstructure of the material. Such interaction can be received as electromagnetic signals, known as Barkhausen noise in the literature. Evaluation of these signals, representing Barkhausen noise, can provide information about the microstructure of the material and the stress in its interior. The published publications DE 43 43 225 C 1, EP 683393 A1 and DE 196 31 311 C2 describe such methods for nondestructive testing of ferromagnetic substances which permit determining material properties such as grain structure and internal stress.
Such micromagnetic interaction can also be determined by measuring superimposed permeability, analysis of harmonic waves as well as dynamic magnetostriction.
Devices based on these micromagnetic processes have been developed and applied. A cyclic magnetic field is generated in an as such known manner via an electromagnet and the Barkhausen noise is received with the aid of a magnetic inductive sensor on the surface of the to-be-tested part. In addition to this, a Hall probe is required to measure and control the cycle period of the bias magnetic field strength (cf. DE 43 43 225 C2). Only the analysis of harmonic waves does not require using magnetically inductive sensors. A simplification of the device for measuring micromagnetic test parameters is realized in DE 196 31 311 C2. As changes in magnetization processes are excited by current flowing through and a measure of the excitation is the time-dependent course of the current strength, an electromagnet and a Hall probe are no longer required. The device comprises only two electrodes and a magnetically inductive sensor. In this manner, a fixed sensor geometry comprising an electrogmagnet respectively two current electrodes and a sensor element is always given. However, such given fixed geometry greatly restricts the possible utilization of such a measuring device.
All generic methods known in the art have the drawback that at least one magnetically inductive sensor or a Hall probe is required, which for example must be placed at the measuring position on a part under test. However, the hitherto known test methods have failed at inaccessible points, at high temperatures or in difficult environmental conditions.
WO89/10556 deals with a process for determining mechanical stress in the interior of ferromagnetic objects. It is used for detecting Barkhausen noise by means of wire strain gauges which must be attached to the to-be-examined object in a suited manner dependent on its geometry. In particular, the known method cannot be used on object surfaces which are unsuited for such attachment of wire strain gauges, for instance if their surface temperatures are too high.
SUMMARY OF THE INVENTION
The object of the present invention is to further develop a method and a device for the nondestructive material characterization and the measurement of stress in the interior of a ferromagnetic part under test by flowing an excitation current through the part under test or by the deformation of the part under test caused by the high-frequency change in its electric potential in such a manner that the previously mentioned disadvantages of the prior art are avoided. In particular, the object is to expand the possibilities of the method with regard to the versatility of its application. Possibilities are to be created to also be able to apply the method for determining the temperature and/or the gas composition respectively the chemical activity of certain process gas compositions.
The solution to the object of the present invention is given in claim
1
. An invented device for carrying out the invented process is the subject matter of claim
16
. Advantageous further developing features of the inventive idea are the subject matter of the subclaims as well as the description and the accompanying drawings. An element of the present invention is that a generic method according to the introductory part of claim
1
is further developed in such a matter that the electric potential of the part under test is determined by direct or indirect electrical tapping of the part under test, that the high-frequency potential component caused by a change in magnetization is determined from the electric potential of the part under test and is utilized as the high-frequency noise signal for determining the test parameters.
An essential aspect of the invented process is obviation of all magnetically inductive sensors, Hall probes or electromagnets which must be positioned on respectively relative to the part under test, thereby, on the one hand, considerably reducing the technical complexity and, on the other hand, creating significant advantages regarding possible applications of this method. Obviation of positioning sensors in relation to the part under test at the same time also eliminates the significance of the lift-off sensitivity of the sensors during measuring. With the invented method, the measuring results are less subject to disturbing influences and are therefore more accurate, because, as will be described in more detail below, only the potential and the current strength are measured. By this means, determination of the micromagnetic test parameters becomes largely independent of sensors respectively independent of measuring devices. Furthermore, the micromagnetic test parameters can be determined integrally over large regions of the part under test. However, at the same time, the method also permits determining the micromagnetic test parameters with high local resolution and direction dependent. Finally, the invented method permits utilizing ferromagnetic reference materials, in particular in difficult environmental conditions, for example lack of space respectively lack of accessibility, high temperatures and corrosive media.
Measuring the potential on the part under test occurs with the aid of two electrodes which are contacted with the part under test and form with it a closed electric circuit, in which a current source is provided. Depending on the magnetic behavior of the to-be-examined material and its cross section area, a cyclical current strength is selected in such a manner that a ferromagnetic hysteresis occurring in the to-be-examined material can be measured. Preferably the electric current density should be set so high at least locally in the test region of interest that changes in magnetization processes are triggered by means of which the to-be-detected potential noise or Barkhausen noise is generated. In principle, excitation of the ferromagnetic potential noise can also occur by means of mechanical stress or a combination of flowing current through and mechanical stress.
In order to determine the ferromagnetic potential noise, potential tapping is conducted preferably on both sides of the test region. In the case of excitation of the part under test with an alternating current, alternating voltage corresponding to the excitation current frequency, the so-called macropotential which is superimposed on the ferromagnetic potential noise is filtered out with a suited frequency
Meyendorf Norbert
Michel Fritz
Rösner Henrik
Sourkov Alexandre
Burns Doane Swecker & Mathis L.L.P.
Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung
Mack Corey D.
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