SU1679352A1 - Method of measuring residual stresses in surface layers of materials - Google Patents

Abstract

This invention relates to methods for non-destructive testing. It allows, under production conditions, to control residual stresses with high accuracy and performance. For this, the end time of the machining of the part is recorded and in the period before the stable oxidation of the material of the part. The invention relates to the methods of nondestructive control of the surfaces of metal products under the conditions of production and repair of machines when checking residual stresses arising during machining of parts. The aim of the invention is to improve the accuracy and performance of the control. M and with er and aa, X M e in chol ao and m o h r in th. A series of measurements of the contact potential difference UH is performed with fixing the time intervals Ati between the end of processing and measurements, and with that larger A g i, the UKi is measured later after the treatment, the 1st Komarov criterion E.A. KG1 is calculated and the calibration chart Km x fi (cr) is determined by OOCT. With significant fluctuations in temperature, humidity and atmospheric composition with measurements UK | in order to reduce errors, the 2nd criterion of Komarova E.A. CG2 and according to the tarot schedule 2 ((f) is determined by 0bst. To exclude calculations of Kri and Cg2, the semi-logar grid of coordinates is plotted along the abscissa axis, the values An. And the ordinate axis corresponds to the corresponding UKI. its intersections with the axis of ordinates read the values of КГ1, and with the axis of the abscissa - In Ar0 and take Cr2 Cr1 / 1p Dg i. For the purpose of automatic control of the processing modes (K, i), the sensor measures directly UK and the machine are electrically connected. 2 Cp f-crystals, 1 ill. H The drawing shows a diagram of a device for carrying out the method: The device comprises a test piece 1, a miniature overhead sensor 2 with a stabilized measuring electrode 3 (IE) having a re-const, and a constant voltage preamplifier 4 with 10 t2 Ohm, an electrometric unit 5 with an indicator. (L S ck VI CHO sn N3 WAIR

Description

The device works as follows.

Upon completion of the studied exposure to the part 1 (turning, grinding) with a time latch, a sensor 2 is applied to the monitored section with secured electrical contact of its body with the part 1. The resulting potential potential difference between the measuring electrode 3 and the surface of the part 1 part is perceived preamplifier 4 and measured by an electrometer 5. Then sensor 2 moves away from part 1 and after some (fixed) time is again applied to the same part of the part.

If necessary, contactless PKD (From) measures, sensor 2 is located at a constant distance from part 1, and electrical contact between them is made using wires (possible with the machine on which the part is installed). At the same time, several parts of the part can be controlled with fixing the measurement time for each section

The method is carried out as follows.

The time of completion of the machining (or other impact on the part, for example, surface plastic deformation) is fixed and several measurements of ATC time intervals are held between processing and measurements, and with that at longer intervals than later measured by the formula

CP

() EJInAri) 2 Intel) g In Ar, Uki) n 2 (lnAr, / - (E In An

the first criterion of E.A. Kocharov is calculated and the calibration curve i (cr) is used to determine the value of the residual voltage, where the stress in the calibration samples made of the material of the controlled part,

In the case of significant changes in temperature, humidity and atmospheric composition in the room during the time between the completion of part processing and the PKK measurements using the formula

nS (e ™ C; -UK; HSenAЈ; USUKU

nS

() Ekles:) a

Calculate the 2nd criterion E.A. Komarov and the calibration chart (cr) determine the value of the residual stresses,

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For simplicity, CG1 and Cr2 are determined graphically. On the semi-logarithmic coordinate grid, the value AriCr.e.lnATj is plotted on the abscissa axis), and the corresponding UKI points are plotted on the ordinate axis, their intersections are connected directly to the coordinate axes, the Kri-iko value is read to the intersection, at the intersection with the axis of the abscissa, the value of n is Ar and takes Kr2 UKo / In Ar0.

The time of stable oxidation (the time when the growth of the thickness of the oxide film ceases and the change in U "ceases to change) of metals is not less than 10 sugs for aluminum and not less than 1 hour for copper. According to experimental data, the oxidation of flat polished samples continued for armored metal. iron for at least 1 month, for steel ZOHGSN A - less than 20 days. In this case, the longer the time interval А g between processing and measurement 1) k, the less accurate the time of completion of processing can be recorded.

The application of the method allows to optimize the processing modes of parts in order to ensure their dimensional stability in precise machine building and instrument making, by reducing relaxation deformations, to minimize the harmful effects of residual stresses on the strength and durability of parts, as well as to impose maximum residual stresses for example, when reinforced by surface plastic deformation or in preparation for coating. With contactless methods of measuring the PKK (ionization, condenser) UKO can be measured during the processing of parts, provided feedback with processing modes. In this case, in fact (Kri) j UKi.

Claims (3)

1. A method of monitoring residual stresses in the surface layers of materials, namely, that measurements of a physical parameter are carried out, according to the data obtained, residual stresses are judged, characterized in that, in order to improve the accuracy and performance of the control, samples are selected from material, at different applied voltages (o} in the test range a, remove the oxide layer from the surface of the samples and record the time of completion of the removal of the oxide layer, n samples of the final measurements are performed on each sample tact potential difference (1 / kO with fixation of time intervals (AT i) between the moments of completion of removal of the oxide layer and measurements using the formula Kri . (2 Uk,) E (Anfl-HlnArQglnun-U,.,). nlpnAnf-cDinAn) 2 calculate the first criterion Komarova E.A. and build a calibration graph of Km f 1 (0), then the operations are repeated on the monitored part, Km is calculated and the values of residual stresses Toast are calculated using a calibration chart. 2. The method according to claim 1, characterized in that, in order to reduce the influence of fluctuations in temperature, humidity and the composition of the environment between the time points for the completion of the removal of the oxide layer and the measurements of UKi and during the measurement K itself " 0 five 0 rhenium, the calibration graph is constructed as a dependence. (a) where Kr2 is the second criterion of Komarov E.A. calculated by the formula nS (enuO; 4JK; H enufr.U2Uict) hSien / tfOMsEnbfc;) 4 then, the above operations are repeated on the controlled part, Cr2 is calculated according to the calibration curve to determine the value of oist. 3. A method according to claim 1, characterized in that, in order to automatically control the removal modes of the oxide layer by means of known types of surface treatment of the material Uicr (Kri) i, they are measured non-contact directly during the processing of the part.