GB2027538A

GB2027538A - Evaluating mechanical deformation characteristics

Info

Publication number: GB2027538A
Application number: GB7832947A
Authority: GB
Original assignee: VYZKUMNY USTAV 070
Current assignee: VYZKUMNY USTAV 070
Priority date: 1978-08-10
Filing date: 1978-08-10
Publication date: 1980-02-20
Also published as: GB2027538B

Abstract

Apparatus for evaluating characteristics of the deformation of a specimen of material subjected to mechanical, particularly tensile, stress in an appliance 1 comprises TV-camera 2, which in operation scans the specimen, a control device 3, and an evaluating unit 4. The camera provides input signals to the unit and device, these signals being analysed to detect the onset of deformation in the test specimen and to provide corresponding control signals to the appliance 1 to control the loading programme for the test. <IMAGE>

Description

SPECIFICATION Evaluation of deformation characteristics of a mechanically stressed specimen The invention relates to a device for evaluating the deformation characteristics of mechanically tested metallic and non-metallic materials, in which the course of their deformation depends on their structural conditions and properties. In the course of elongation of a test piece having the shape of a cylindrical rod, a local necking sometimes takes place, which is evaluated after the end of the test by determining the corresponding deformation coefficients.

With the known devices the necked-down portion of a test piece can be evaluated at the point of failure when the loading forces are no longer applied, or the course of deformation can be scanned by onedimensional contact gauges. The shape of the test piece during the testing process can also be recorded by a motion picture camera. The drawback of these known devices and methods is that they do not enable the dynamics of all the effects taking place in the test piece to be perfectly followed, that is particularly and directly to evaluate character of the test pieces in the whole course of their loading.

Moreover, the testing machine cannot be controlled with respect to the progress of changes in the shape of the test piece by a loading program which would correspond to the assumed alternatives in the mode of progressive structural deformation of the material tested, as well as its damaging, which is a very important information for material property analysis.

The mentioned drawbacks have been eliminated by a device for evaluating the deformation characteristics of mechanically tested materials according to the present invention, in which for the purpose of controlling the loading program of a test piece in accordance with the definition of the structuralmechanical plastic-deformation model, and for the purpose of evaluating the corresponding deformation characteristics, the picture of the test piece is scanned by a TV-camera which serves as a scanning member and is connected both with an evaluating unit and with a control block having two outputs, one being connected with the loading device and the other being connected with a second input of the evaluating unit, the output of which is connected with the second input of the control block.By means of the control block the evaluating unit realizes a particular logical operator to transform the scanned picture of the test piece into quantitative signs, such as analytical functions forming the geometric figures observed, which enables the speed of scanning to be controlled and the testing machine to be operated by means of the derived functional criteria (such as centrai moments of symmetrical contour, coefficients of expansion, differential forms), for an optimum testing process as sequential experimenting with reaction of the material upon the conditions of loading. The-device is especially intended for laboratories examining properties of materials and for workshop quality checking of metallurgical semiproducts, which must have specific deformation characteristics.

In simple cases, the picture of the test piece to be scanned by a TV-camera can be produced by suitable illumination or, in some complicated applications, by the use of laser holography. The video signal on the camera output contains in the line scan of the scanned picture pulses corresponding with the contrast boundaries, which are supplied to the evaluating unit, synchronized by the line and picture frequency of the camera, and processed by the respective logical system. This result is stored in the memory system of the evaluating unit and processed by the respective logical system.

The function of an evaluating unit can be realized by a computer completed by electronic blocks for the interconnection of the unit as well as the checking and control of synchronization.

The accompanying drawings show in Figure 1 a general block diagram of a device according to the invention, where 1 is the testing machine with a test piece, 2 is the TV-camera, 3 the control block for synchronization according to synchronizing pulses and for the control of the testing machine, and 4 is the evaluating unit of the video signal.

Figure 2 shows one embodiment of a device according to this invention. From a camera 2, in the viewing field of which is placed the test piece, the video signal is led to the output 2' and the synchrd- nizing signal to the output 2". The video signal is led both to the video-signal amplifier 4b and to the check monitor 4a for the bearing and focusing of the camera. The synchronizing signal from the output 2" is fed to a block 3c defining the time period in which the video signal is evaluated, thus removing the synchronization pulses contained in the video signal.

This block comprises two monostable sweep circuits, the first of which is started by a horizontal synchronizing pulse. From the output 2" the synchronizing signal is further fed to a picture-pulse selector circuit 3a, this being an integrator, the output of which supplies picture-synchronizing pulses. These pulses are used for synchronization of the device by means of a block 3b, on the input of which besides the picture-pulse a starting pulse 3' is fed, by means of which the evaluation of the pictures is started. The output signal 3" duration is just equal to that of one picture after the entry of the external starting pulse, and it is cleared by the next picture pulse. In this way the moment can be selected, in which the shape of the test piece shall be evaluated.

The signals coming from the output of the videosignal amplifier4b, and oftheconstant-frequency oscillator 4h and the signal 3" defining the duration of one picture, are fed over to a logical-product gate 4c to the output of which a counter 4e is connected.

the number of pulses having a frequency produced by the oscillator 4h, metered by the counter in each line, is proportional to the width of the test piece in a place corresponding to the arrangement of the lines.

This information is fed through the matching block 4fto the input of the computer 4g, where the numerical values are stored. The counter is then neutralized by a pulse from a reset circuit 4d, controlled from the block for defining the duration of the video signal. The registration of the deformation characteristics is diagramatical ly represented by the output 12. On the output 8 of the computer 4g is connected a block 3d, used to generate the starting pulse 3' and to control the power members of the loading device in the testing machine 1. The possibility of controlling the speed of the rectilinear scanning of the camera 2 is diagrammatically represented by the output 3"' of the control block 3b.

The device described can be used to obtain information about the behaviour of material under loading conditions simulated by a simple testing arrangement (tensile test) and, especially in those cases where special pre-conditions of material strength represented by deformation characteristics may be tested by a controlled loading.

The number of quantatitive parameters of deformation in the test pieces can be extended by placing various marks (e.g. sleeves) on the test piece, or by following other characteristics (e.g. the overall extension) and their parallel transmission on to the input of the evaluating unit

Claims

1. A method of evaluating characteristics of the deformation of a specimen of material subjected to mechanical stress in an appliance, wherein a TVcamera is arranged to scan the specimen, a control device is arranged and connected to control the stress applied to the specimen in response to signals received from the TV-camera, and an evaluating unit is arranged and connected to provide data relating to said deformation under the control of said control device, and wherein, for the purpose of controlling the stress applied to the specimen in accordance with a predetermined program depending on the characteristic of the material during plastic deformation, and for the purpose of evaluating said deformation characteristics, said camera is connected so as to provide input signals to said evaluating unit and to said control device, a first and second output of said control device is connected to, so as to provide inputs respectively to, said appliance and to said evaluating unit, and an output of said evaluating unit is connected to, so as to provide an input to, said control device.

2. A method according to Claim 1 substantially as herein described with reference to the accompanying drawings.

3. A method of evaluating characteristics of the deformation of a specimen of material subjected to tensile stress according to Claim 1 or 2.

4. A device for evaluating characteristics of the deformation of a specimen of material subjected to mechanical stress in an appliance, the device comprising a TV-camera for scanning the specimen, a control device for converting signals representative of the image of the specimen from a first output of the camera into quantitive signals, and an evaluating unit for evaluating signals from a second output of the camera, wherein for the purpose of controlling the loading program of the specimen in accordance with the definition of the structural-mechanical plastic-deformation model, and for the purpose of evaluation of the deformation characteristics, the TV-camera, in the field of vision of which the specimen being tested is situated in operation, is connected so as to provide input signals to said evaluating unit and to said control device, the latter having two outputs, one connected to provide input to said appliance and the other connected to provide input to said evaluating unit, an output of said evaluating unit being connected to provide an input to said control device.

5. A device according to Claim 4 constructed, arranged and adapted to operate substantially as herein described with reference to, and as shown in, the accompanying drawings.

6. An apparatus for carrying outthe method according to Claim 1 or 2 constructed, arranged and adapted to operate substantially as herein described with reference to, and as shown in, the accompany-; ing drawings.