SU1747996A1 - Method of creep strength testing of materials - Google Patents

Abstract

Uses1 prediction of the durability of collectors of traction engines. Inventive, two identical specimens are tested under identical loads and different temperatures. The creep deformations over time are measured. The parameter characterizing the creep flow rate on temperature with each strain measurement is determined. The countdown of the measurement time is started from the moment the steady state temperature of the sample is reached when tested at elevated temperature. The tests are completed when the parameter B is equal between the strain measurements.

Description

The invention relates to methods for studying the strength properties of materials, and specifically to methods for studying the creep of solid materials, and can be used in the manufacture of collectors for electric locomotive traction engines to predict their durability as well as to assess the degree of completeness of technological formations of collectors in the process of their manufacture.

A known method for studying the creep of materials consists in applying to the sample under test a constant tensile load for a long time under conditions of a constant temperature and humidity from detecting the deformation of the sample at specified points in time.

The disadvantage of this method is that the determination of the survivability is regulated only for stretching and does not allow to estimate the acceleration of the creep process due to the temperature increment T °

A known method for studying the shrinkage of materials at different temperatures consists in the fact that the sample is made up of sheets of the test material and ground metal gaskets, and a constant load and temperature are applied to the sample, registering the deformation of the sample.

The disadvantage of this method is that it regulates only the method for determining the yield shrinkage of YI at normal temperatures and YZ at elevated temperatures. This method does not provide for the determination of the component

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ABOUT

ABOUT

shrinkage of the creep of the material and its acceleration from temperature increments.

A known method for investigating the creep of materials is that the material samples are kept at a constant load and temperature for a predetermined time, then the load and the temperature of the material are changed to record the deformation and the creep deformation rate and the results of testing two samples about material creep

The disadvantage of this method is the large unaccounted time spent for pre-setting and processing a series of experiments to determine the physical constants n and Q of the test material, as well as a decrease in accuracy due to the fact that the moments of stabilization of creep for a number of materials ds experimentally with large errors due to the random dispersion of the experiments and the asymptotic sloping creep and relaxation curves

The closest to the invention according to its genomic essence and the achieved result is the method of studying the creep of materials, including the choice of the type of approximating dependence of the creep of the material. creep curves.

The disadvantages of this method are time consuming, since the condition of its fairness and accuracy must be carefully checked in direct experiments with a sufficiently large range of changes in the true time. When applying the method, there can be not unambiguous results due to the fact that the processes of heating the test material and the installation, as well as the loading and commencement modes of timing in experiments are not regulated.

The purpose of the invention is to reduce the experiment time to determine the creep parameter while increasing the reproducibility and accuracy of the results.

This goal is achieved by testing two samples. The first sample, which, together with the test setup, has the temperature Tx °, is loaded to the full load F and, maintaining it at a constant level, the deformation Yx (g) of the sample is recorded at specified intervals The second sample is placed in the preheated to the specified temperature Tg ° the installation is loaded with a full compressive load F and the time of the start of the sample heating process is recorded. While maintaining the load at a constant level, the duration of the heating ∆tr is recorded until the sample reaches and sets the stationary At this time point, which is the beginning of the global calculated time axis, and deeper, at specified intervals, shrinkage deformations of georosity of Yr (t) are found. The heating efficiency Dgr of the second sample shifts the beginning of the time reference of the creep process of the first sample, combining the heme with the very beginning of time counts in both experiments with the global calculated time axis

For the detected deformations in the global computational time axis, for each sample, the angular coefficients Kx and Kg and the free terms ax and ar of experimental regressions are determined.

Yx (g) ah -f Kx In t Yr (g) - ar + Cg In t

As new experimental values of shrinkage (Yxft) and Yr (t) accumulate in the scheduled time points when processing them on a PC, all new values of ax, Kx and ay, Kg are obtained. Experiments end when the desired indicator B of time and time scale, relationship relation times gx and mr

/one

(at

/ 1 T °

 I x

Tg °

))

and calculated in each i-th experiment step using the formula

(Yr (r2) -Yr (n)) (-)

mi / x g.

() (Uh (g)) (In r2 -TrlrTJ;

will differ from neighboring steps no more than a predetermined permissible relative value Ј, which is an assessment of the degree of completeness of the convergent empirical and mathematical processes for determining the desired indicator B

(((tg)

at

(W) M

at

where Y (n), Y (r) are the creep shrinkage calculated for time points n and yy;

-, - - inverse absolute temperature ° t2

I x I g

battles of experiments on the Kelvin scale;

ah, ag - free members of regressions; Rm, t2 any fixed time points on one of the regression lines.

The essential distinctive features of the proposed method are to bring the origin of time t in both cases to a common global time axis, the beginning of which coincides with the point of onset of the stationary temperature regime in the experiment with elevated temperature; determining the end time of the experiment according to the maximum allowable relative deviation of each other from one another successively found empirically indicators of the time-time scale B |.

The execution of the first feature ensures the elimination of the effect of shrinkage of the material's fluidity on the amount of deformation, since during the time required to establish a stationary temperature regime, the yield shrinkage ends. The execution of the first feature also provides for the elimination of the temperature error, since the sample and the installation are already in a stationary temperature mode,

The fulfillment of the second feature eliminates a significant part of the error from the variance of the experiment and ensures the minimum expenditure of the experiment time, since it meets the theoretically exact condition about the asymptotic behavior of the random variable (B) i; provides an increase in the accuracy of the results, since the desired creep parameter B is found from the theoretically exact differential equation of the kinetics of accumulation of dislocation defects in the material during its formation and corresponds to the natural physical meaning of the indicator B.

The method is carried out as follows.

Test two identical samples from the test material. If the material is a sheet, for example, a collector insulating material for interglass insulation, then a sample packet of ten insulation sheets with steel polished gaskets are assembled. The first completed sample is placed

Into the working space of the screw testing machine and apply to it the calculated compressive load F, include a load stabilizer and a sample deformation regimator of the sample as a function of the ppm. The second sample, assembled in exactly the same way as the first, is placed in the working space of the testing machine equipped with thermostat heater, m

10 are heated to the required temperature Tg °. The same compressive load applied to the sample as for the first sample includes a load stabilizer, a temperature stabilizer, and a sample deformation recorder as a function of time. When the sample and the installation are heated to a stationary temperature regime with the Noah temperature Tg °, a time mark is made in the recorder diagram

0 zogrvea Lrg. When processing the results of the experiments, the marks “.” Of the time of the deformation recorder of the first sample are shifted. Accumulated Creep Strains

5 Yr (g) and Yx (g) are processed on a PC or a programmed calculator using the least squares method according to a standard program for semi-log regression and get two regression equations

0 for the first and second samples:

Yx (t) ax + Kx In r, Yr (r) ar f Kr In r.

As the creeping process accumulates in experiments, it is processed for an extended sample, obtaining all new ag, Kr, ax, Kx, and B. Experiments end when the sequence of B found converges to zero. relative accuracy of эксперимент% for the experimenter.

Example. Two samples of KIPE-A collector electrically insulating material are tested. Each sample is made up of 10 KIPE-A sheets approximately 1.5 mm thick and 11 polished steel gaskets with roughness parameter Ra 1.25 and hardness LDC 50-55.

0 The first sample is tested at T 25 ° C (298 ° K). The second sample is tested at 165 ° C (438 ° K). The working compressive load for both specimens is 10,000 kG (7cf 60MPa). five

The experiment was completed at r 108 h; Kg 4.33 kx 2.46 ar 4.249 mm; ah 1.18 mm.

Find

(YrCt2) -Yr (ri) (- (B) s1 u (g X- (T)) (, n G2H-, PGG1)

(1,9944-10-2) (-) 1 (3,945) (1l 100-In 1) 8492 ° K

1 31.

Deviations (B) s1 from experiment step 29% 2.45%, Deviations B from the exact value A% 1.18% (in the experiment with v = 1000 h).

Therefore, shrinkage creep processes at 1 ° 165 ° C (438 ° K) develop faster than at T ° 25 ° C (298 ° K), in

| 0 9032 times.

1x рК -Ь рв 9гао7 670 3

 9032 times

or shrinkage of creep at T ° 165 ° C, achieved in 108 hours, in the experiment at T ° 25 ° C takes place over time

..

 111 years

Claims (1)

The Invention Method A method for testing creep materials, in which two samples are tested under the same loads and different temperatures and measure creep deformations in time, characterized in that, in order to increase productivity and accuracy of testing, from deformation measurement time for both Samples start from the moment the steady state temperature is reached in the sample volume when tested with increasing temperature, the parameter B, characterizing the flow rate creep versus temperature with each measurement of deformation, and testing is completed when the B parameter values are equal between successive measurements of deformation.