GB2231160A

GB2231160A - Non-destructive, multi-parametric determination of structural and mechanical conditions of metallic materials

Info

Publication number: GB2231160A
Application number: GB9008783A
Authority: GB
Inventors: Libor Keller; Petr Stanek
Original assignee: Z NA VYROBU LOZISEK KONCERN PO
Current assignee: Z NA VYROBU LOZISEK KONCERN PO
Priority date: 1989-04-20
Filing date: 1990-04-19
Publication date: 1990-11-07
Also published as: GB9008783D0; DE4011588A1; CZ247789A3; CZ278755B6

Description

- 1 I- GE, G29 NON-MSTRUCTIVB, MULTI-PARAMBTRIC DETERMINATION OF

STRUCTURAL AND MECHANICAL CONDITIONS OF METALLIC MATERIALS The invention relates to a method of nondestructive, multi-parametric determination of structural and mechanical conditions of metallic materials and to an equipment for executing this method applicable in the research of properties of metallic materials and the evaluation of their qualities, employing electromagnetic non-destructive methods.

Known methods for non-destructive determination of structural and mechanical conditions of metallic materials employing electromagnetic methods, can be divided into three groups.

The first group is represented by methods employing for the magnetization of the material tested a field with harmonic pattern of such an intensity that the magnetization of the material occurs in the initial permeability zone. Evaluated are amplitude and phase changes of the basic harmonic component of the voltage induced in a pick-up coil in connection with the changes of the properties of the material tested. Higher harmonic components, even in testing ferramagnetic materials, are negligible because of the practically linear magnetization characteristics within the given range of the intensity change of the exciting magnetic field. An example of an equipment employing said method is testing apparatus for non-destructive testing of materials according to DE patent no 32 07 569. The apparatus enables determination of the amplitude and phase changes of the measured induced voltage for one or more exciting field frequencies. The tested material is differentiated on the basis of these two

4000 2 - -features. A disadvantage of this method is that only two features can be used to characterize the condition of the material tested.

The second group is represented by methods employing for the magnetization of the material tested a field with harmonic pattern of such an intensity that the material is magnetized within substantial portion of its magnetization characteristics. Evaluated are amplitude and phase changes of the harmonic voltage components induced in a pick-up coil in connection with the changes of properties of the material tested. In testing ferromagnetic materials, due to non-linear. magnetization characteristics higher harmonic components, appear in the induced voltage spectrum. An example of an equipment employing the second mentioned method is the equipment for the identification of machineability of ferromagnetic materials according to Czechoslovak Inventor's Certificate No 245 114. The equipment magnetizes the ferromagnetic material in a pulsating magnetic field and measures amplitudes and phase of harmonic components of the voltage produced by the distorted magnetic field. The values obtained by the measurement are compared with known values of standard ferromagnetic material. An advantage of said method, compared with the aforementioned one, is that the harmoic spectrum of the signal thus obtained renders several features for the characterization of the condition of the material tested. The signal spectrum, however, is virtually limited to four harmoic components. A disadvantage of said method for characterization of the conditions of the material is that all harmoic comDonents need not be informatively significant and., as practice indicates,

4000 3 - that they are frequently relatively dependent, thus restricting the attainable number of features characterizing the condition of the material tested approximately to a half of the data obtained. A further disadvantage of said second method is its low measuring sensitivity for obtaining features in the region of such frequencies, at which the influence of the field of eddy currents induced in the tested material upon the output voltage of the pick-up coil significantly decreases. These are frequencies usually below 10 Hz. The eddy current field, which at higher frequencies could significantly influence the pick-up coil voltage is determined not only by the conductivity but also by the surface finish and by discontinuities of the material, which may lead to distortion of the features for the characterization of the structural and mechanical condition of the material tested.

The third group is represented by methods employing for the magnetization of the material tested a variable field magnetizing the material almost to the saturation zone. Evaluated are significant arbitrary points and quantities from the hysteresis curve of the material tested. An example of an equipment employing the third mentioned method is the equipment for magnetic assessment of mechanical properties of ferromagnetic material according to US patent NO 3 586 963. This equipment determines the value of coercive force serving for the assessment of mechanical properties of the material tested. A disadvantage of said third method is that virtually only three -features (coercive force, remanent induction, area - limited by the hysteresis curve) characterize the condition of the material tested.

4000 The mentioned disadvantages are largely avoided by a method of nondestructive, multiparameteric determination of structrual and mechanical conditions of metallic materials by the measurement of the magnetic induction flux through the material tested located in an exciting magnetic field with a periodically variable intensity according to the invention in which the variable intensity period of the exciting magnetic field is divided into n intervals where n> 1, and where to each interval pertains a predetermined value of the exciting magnetic field intensity, whereby an ndimensional exciting magnetic field intensity value vector is produced, the magnetic induction flux through the material tested being sampled in individual intervals of variable intensity period of the exciting magnetic field, whereby an n-dimensional magnetic induction flux value vector through the material tested is obtained, which, together with the n-dimensional exciting magnetic field intensity value vector, characterizes the structural and mechanical conditions of the material tested.

Further principle of the method according to the invention is in that the n-dimensional vector of the values of the exciting magnetic field intensity constitutes a first column of a matrix and the n-dimensional vector of the values of the magnetic induction flux through the material tested constitutes the second column of the matrix of the type (n x 2), whose rows represent coordinates of points in a plane determined by the intensity of the exciting magnetic field and magnetic induction flux through the material tested, by which is parametrically expressed a closed curve characterizing the structural and mechanical

4000 - 5 conditions of the material tested by n-indications.

Purther principle of the method according to the invention is in that the shape of the closed curve in a plane determined by the intensity of the exciting magnetic field and magnetic induction flux through the material tested is mathematically analyzed and expressed by its pattern characterizing the structrual and mechanical conditions of the material tested by k< n indications.

The invention provides also an equipment for executing the method generating an exciting magnetic field with a periodically variable intensity for the magnetization of the material tested and thus producing magnetic induction flux through the material tested. The principle of the equipment according to the invention is in that it comprises a variable voltage generator connected to a power voltage-to-current converter connected to an exciting coil, and a pick-up coil, whose outlets are connected to a voltage-to-frequency converter connected to a counter. The counter is interconnected, via a databus, with a control computer, which is, via a databus, interconnected with the variable voltage generator. The control computer is interconnected, via a control-bus, with the variable voltage generator, with the power voltage-to-current converter, with the voltage-to-frequency converter and with the counter.

The invention also provides an equipment comprising a variable current generator connected to a power current amplifier attached to an exciting coil and a pick-up coil, whose outlets are connected to a voltage-tofrequency converter connected to a counter. The counter is interconnected, via a databus, with a control computer, this again, via a data- 4000 - 6 bus is interconnected with the variable current generator. The control computer is interconnected, via a control-bus, with the variable current generator, with the power current amplifier, with the voltage-tofrequency converter and with the counter.

The equipment may be provided with an amplifier connected between the pick-up coil and the voltage-to-frequency converter.

As the most effective method of nondestructive identification of structure and mechanical condition of metallic materials using electromagnetic methods appears such a method which proceeds from evaluation of the hysteresis curve shape of the material tested. The hysteresis phenomenon is one of the commonest natural phenomena. Through its study it is possible theoretically to obtain the highest possible amount of significant information on the material tested. Utilization of magnetic hysteresis in ferromagnetic materials enables discernment of the structural and mechanical conditions of the material tested whose parameters are meaningfully correlating with indications obtained from the analysis of the material's hysteresis response. The advantage of the presented method of non-desetructive identification of structural and mechanical conditions of metallic materials consists partly in advantageous sampling of the magnetic induction flux through the material tested in dependence on the changes of the exciting magnetic field variable intensity, partly in a suitably chosen representation of the values measured by a closed curve of the type of a hysteresis curve in a plane, defined by the exciting field intensity and induction flux through the material tested and, last and but not least, in mathematical analysis oil

1 4000 the shape of this closed curve whose pattern's indications characterize the structural and mechanical conditions of the material tested. Numerical experiments which had been conducted, indicate that through analysis of typical hysteresis curve shapes obtained by the invention- based method, it is now possible to realistically attain as many as twenty numerically significant indications. Specific examples show that approximately half of these numerically significant indications is informatively meaningful for the characterization of parameters of the structural and mechanical conditions of the material tested. A higher effect of the presented method of non-destructive, multi-parlametric identification of structural and mechanical conditions of metallic materials consists in obtaining about twice the number of attainable indiciations, compared with known methods.

The invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings illustrating two examples of arrangement of an equipment for carrying out a method according to the invention. In the drawings:

Figure 1 shows an arrangement incorporating a variable voltage generator connected with a power voltage-to-current converter, Figure 2 shows an arrangement incorporating a variable current generator connected with a power current amplifier, and Figure 3 shows a further possible varient of an equipment provided with an amplifier.

The idea of an equipment for executing the method of non-destructive, multi-parametric identification of the structural and mechanical L conditions of metallic materials according to the 4000 - 8 invention is based on the principle that a parametrically expressed function corresponding to the hysteresis curve is obtained from known values of the time behaviour of the induction flux through the material tested 4 assessed in accurately defined points of the time behaviour of the magnetizing current. The main aim is a high reproducibility of the measured data at maximum measurement sensitivity. The equipment serves for the generation of an exciting magnetic field and for the scanning of a magnetic induction flux through the material tested 4.

Periodic time behaviour of the exciting magnetic field and its frequency are determined by the variable voltage generator 1. A part of this variable voltage generator 1 is, among others, a numerical value-tovoltage converter and an electronic store for the storage of n numerical values approximating the variable voltage period pattern. Numerical values of the approximation represent an n-dimensional vector of the exciting magnetic field intensity values multiplied by a constant given by the design of the variable voltage generator 1, power voltage-to- current converter 2 and exciting coil 3. The size of the store used determines the number of numerical values of the approximation of the required time behaviour of the field. Successive and cyclic conduting of approximative values from the store to the numerical value-to-voltag converter is controlled by means of accurate clock pulses whereby the required frequency and amplitude stability of the output voltage of the variable voltage generator 1 is achieved.

In a specimen embodiment of the equipment, the triangular voltage waveform was used, its i Z 4000 frequency was adjustable within the range of 0.2 to 20 Hz. The power voltage-to-current converter 2 serves for obtaining required current values for the feeding of the exciting coil 3, which provides magnetization of the material tested 4. The maximum value of exciting current is selected so as to achieve such a magnetic field intensity for the given ferromagnetic material tested and the used dimension of the exciting coil 3, that the material is magnetized to the beginning of the saturation zone. The material tested 4 was in the shape of a rod and the exciting coil 3 was formed by a system of cylindrical coils arranged so as to generate in the control portion of the material tested 4 an approximately homogeneous magnetic field in which the pick-up coil 5 was located.

The ouput voltage of the Dick-up coil 5 is conducted to the voltage-tofrequency converter 6. The magnetic induction flux through the material tested 4 is determined by the time integral of the pick-up coil 5 voltage. Digital integration is provided by the voltage-to-frequency converter 6 in connection with the counter 7. Numerical values of the time behaviour of the induction flux through the material tested 4 are obtained by synchronous reading of the counter 7 by the control computer 8 by means of a data-bus 9. Synchronized reading is ensured by the interconnection of the variable voltage generator 1 with the control computer 8 by means of the data-bus 9. In the described specimen embodiment, the sampling of the time behaviour of the induction flux through the material tested 4 was selected 250 times within the magnetizing current period. The setting of the frequency and amplitude of the exciting magnetic field is executed by the

4000 control computer 8 by means of a control-bus 10 and a data-bus 9. The control program enables selection of the number of sampled magnetic induction flux periods and adjustment of the initial magnetization mode of the material tested 4.

Another possible equipment for the generation of an exciting magnetic field and for the scanning of the magnetic induction flux through the material tested 4 is shown in Figure 2. It differs from the equipment shown in Figure 1 in that instead of the variable voltage generator 1 a variable current generator 11 is used. In this case, part of the variable current generator 11 is, among others, a numerical value-to-current converter as well as an electronic store. Then, for obtaining the required current for the feeding of the exciting coil 3, the power voltage-to-current converter 2 is used.

In the embodiment shown in Figure 3 the equipment is provided with an amplifier 13 interposed between the pick-up coil 5 and the voltagetofrequency converter 6. By means of the amplifier 13, the output signal level of the pick-up coil 5 is modified relative to the sensitivity of the used voltage-to-frequency converter 6.

The method and the equipment according to the invention can be used in the research of materails and in the development of new structrual materials for the evaluation of changes of structural and mechanical conditions of the tested samples. Especially parallel non-destructive, multi-parametric determination of characteristics of a material during static or dynamic load tests contribite to the obtaining of significant material values which cannot be determined by standard techniques. The method and equipment according to the invention can also be used C Z 4000 - 11 in material quality evaluation of semiproducts and components during the production cycle. Its application enables requirements of standards, acceptance conditions as well as exploitation demands on machines and appliances to be met. Generally, the method and equipment according to the invention can be suitably utilized as an automation element.

4000

Claims

1. Method of non-destructive, multi-parametric determination of structural and mechanical conditions of metallic materials by the measurement of the magnetic induction flux through the material tested located in an exciting magnetic field with a periodically variable intensity, wherein the variable intensity period of the exciting mangetic field is divided into n intervals where n> 1, and where to each interval pertains a predetermined value of the exciting magnetic field intensity, whereby an ndimensional exciting magnetic field intensity value vector is produced, the magnetic induction -flux through the material tested being sampled in individual intervals of variable intensity period of the exciting magnetic field, whereby an n-dimensional magnetic induction flux value vector through the material tested is obtainted, which, together with the n-dimensional exciting magnetic field intensity value vector, characterizes the structural and mechanical conditions of the material tested.

2. Method as claimed in Claim 1, wherein the n-dimensional vector of the values of the exciting magnetic field intensity constitutes the first column of a matrix and the n-dimensional vector of the values of the magnetic induction flux through the material tested constitutes the second column of the matrix of the type (n x 2), whose rows represent coordinates of points in a plane determined by the intensity of the exciting magnetic field and magnetic induction flux through the material tested, by which is parametrically expressed a closed curve characterizing the structural and mechanical conditions of the material tested by n features.

3. Method as claimed in Claim 2, wherein the c 4000 shape of the closed curve is a plane determined by the intensity of the exciting magnetic field and magnetic induction flux through the material tested is mathematically analyzed and expressed by its pattern characterizing the structural and mechanical conditions of the material tested by k n features.

4. Method as claimed in Claim 1 substantially as herein described.

5. Equipment for carrying out the method as claimed in any of of Claims 1 to 4 generating an exciting magnetic field with a periodically variable intensity for the magnetization of the material tested and thus producing a magnetic induction flux through the material tested, comprising a variable voltage generator connected to a power voltage-to current converter connected to an exciting coil and a pick-up coil, whose outlets are connected to a voltage-to-frequency converter connected to a counter, which is interconnected, via a data-bus with a control computer, which is, via the data-bus, interconnected with the variable voltage generator, the control computer being innterconnected, via a control-bus, with the variable voltage generator, with the power voltage-to-current converter, with the voltage-to-frequency converter and with the counter.

6. Equipment for carrying out the method as claimed in any one of Claims 1 to 4 generating an exciting magnetic field with a periodically variable intensity for the magnetization of the material tested and thus producing a magnetic induction flux through the material tested, comprising a variable current generator connected to a power current amplifier attached to an exciting coil, and a pick-up coil, whose outlets are connected to a voltage-to frequency converter connected to a counter which is 4000 inteconnected, via a data-bus, with a control computer, which is, via the data-bus, interconnected with the variable current generator, the control computer being interconnected, via a control-bus, with the variable current generator, with the power current amplifier with the voltage-to-frequency converter and with the counter.

7. Equipment as claimed in Claim 4 or 5 provided with an amplifier connected between the pick-up coil and the voltage-to-frequency converter.

8. Equipment for carrying out the method as claimed in any one of Claims 1 to 4 constructed, arranged and adapted to operate substantially as herein described with reference to, and as shown in the accompanying drawings.

Published 1990 atThePatentoffice. State House. 6671 Higb Holborn, LondonWC1R4TP.Purther copies maybe obtainedfrom The Pa;tentMce my, 1>--A -- tc,.hTnoues ltd. St Mary Cray, Kent. Con, 1187 ---TI--, tc,.hTnoues ltd. St Mary Cray, Kent. Con, 1187