RU2515351C1 - Plant for mechanical and thermal tests of sample from current-conducting material during pulse heating - Google Patents

Abstract

FIELD: testing equipment.

SUBSTANCE: plant is proposed for mechanical and thermal tests of a sample from a current-conducting material during pulse heating, comprising a working vacuum chamber with current leads, collet clamps for fixation of the sample, recording equipment, a loading element, a dynamometer. Recording equipment comprises thermocouples, welded directly on the working part of the sample, an inductive coaxial motion sensor fixed on the middle part of the sample, and a dynamometer. The loading element is made in the form of a thin-walled pipe, in which the traction rod is installed, rigidly connected via the collet clamp with a sample. The other end of the sample also via the collet clamp is connected with the dynamometer installed hingedly on the available frame. Current leads are installed with the possibility of heating of the sample and the loading element. Recording equipment is connected with control and measurement equipment, which is connected to a PC.

EFFECT: increased information value of these tests.

4 cl, 1 dwg

Description

The invention relates to mechanical and thermophysical tests, and specifically to testing conductive materials (TM) in order to obtain a set of mechanical properties and characteristics (strain diagrams under uniaxial tension, conditional yield strength, tensile strength) and thermophysical properties (thermal expansion, specific heat, relative resistivity, enthalpy, heat conductivity, thermal) at strain rate of ~ 10 ^-2 sec ^-1 and pulsed heating (at a rate of 100-1000 K / s) d Temperature ~ 800 ° C in vacuo.

Known dilatometers for studying the kinetics of phase transformations in steels and alloys during rapid heating, for example, a capacitive dilatometer, where the sample is heated by an electric current passing through it current [S.I. Novikova. Thermal expansion of solids. M .: Nauka, 1974, p. 79-80].

The disadvantage of these devices is the impossibility of determining the complex of thermophysical properties of various TM, it is possible to determine only thermal expansion, as well as the absence of a working chamber for testing samples of high toxicity, pyrophoricity, chemical and radiation activity.

A known installation for mechanical testing of materials in various environments at high temperatures and pressures (patent RU 2240531 with priority from 02.26.03, publ. 11/20/2004, G01N 3/18), which contains a working chamber with grippers for the sample, a loading mechanism, a heater , means of supplying a gaseous medium and instrumentation, while the walls and flanges of the working chamber are equipped with a cooling jacket, the sample gripper rods and the heater current leads have cooling ducts, and heat insulation is located on the inside of the cooling jacket In addition, at the inlet to the working chamber of the gas medium, a rechargeable expansion tank with a piston and a control gas supply regulator is additionally introduced, and the heater is made in the form of a spiral and is located in the working chamber so that the sample is inside the spiral.

A disadvantage of the known installation is the impossibility of pulsed heating during mechanical testing of TM samples, as well as the inability to determine, in addition to the mechanical and thermophysical properties of TM samples.

Installation for mechanical testing of materials in various environments at high temperatures and pressures (patent RU 2240531) is selected as a prototype.

The challenge facing the authors of the present invention is to develop an installation for mechanical and thermophysical testing of TM samples under pulsed heating with the possibility of measuring thermal expansion on the working part of the sample, with a constant increase in temperature, determining specific heat, relative electrical resistance, enthalpy, thermal conductivity, thermal diffusivity and obtaining uniaxial tensile strain diagrams in one experiment with protecting personnel and the environment from exposure TM test, which may be environmentally hazardous.

The technical result of the proposed solution is the ability to determine thermal expansion on the working part of the sample, specific heat, relative electrical resistance, enthalpy, thermal conductivity, thermal diffusivity and obtaining a deformation diagram under uniaxial tension and pulsed heating in one experiment with the protection of personnel and the environment from the effects of the TM which can be environmentally hazardous.

The technical result is achieved by the fact that in the installation for mechanical and thermophysical testing of a sample of conductive material during pulsed heating, containing a working vacuum chamber with current leads, collet clamps for fastening the sample, recording equipment, loading element, dynamometer, according to the invention, recording equipment consists of thermocouples, welded directly to the working part of the sample, a displacement sensor inductive coaxial, mounted on the middle part of the sample, and dynamo Meter, the loading element is made in the form of a thin-walled tube in which a rod is placed rigidly connected through a collet to the sample, the other end of the sample is also connected through a collet to a dynamometer mounted pivotally on the existing frame, current leads are installed to heat the sample and the loading element, the recording equipment is connected with the control and measuring equipment, which, in turn, is connected with the PC.

A sample of TM can be made of environmentally hazardous material.

The frame is made in the form of two racks, rigidly fixed on the existing platform of the loading element, with a cross member fixed on their upper part, in the middle part of which a dynamometer is pivotally mounted.

The working chamber consists of a base and a cap, in which the current leads for heating the sample and the loading element are sealed, as well as an electrically insulated sealed connector.

One current lead is connected to the sample, the second to the loading element, and the third is common to both of them.

The possibility of testing a sample of TM at elevated temperatures is achieved by using a sealed vacuum working chamber, in which a sample of TM is fixed in collet clamps, and passing electric current through it through current leads. The required accuracy of determining thermal expansion is achieved by installing an inductive coaxial displacement sensor directly on the working part of the sample, tensile forces are measured on the sample by a dynamometer installed in series with the sample, digital signals are recorded from the displacement sensor of the inductive coaxial, dynamometer and thermocouples through the control and measurement PC hardware. To ensure loading of the sample with tensile force, the loading element in the form of a steel thin-walled tube is heated by passing an electric current pulse through it through current leads, expands and transfers the force to the sample through the frame, which is made in the form of two racks, rigidly fixed to the existing area of the loading element, with their upper part with a cross-member, in the middle part of which a dynamometer is pivotally mounted, through a collet clamp connected to the sample, which, in turn, also through the collet A new clamp is connected to a rod located inside a thin-walled loading element. Processing signals from a displacement sensor of inductive coaxial, thermocouples and a dynamometer to a PC through the control and measuring equipment increases the reliability of determining the characteristics of the test samples.

Thus, the claimed technical solution provides the ability to conduct mechanical and thermophysical tests of the TM sample under pulsed heating at speeds of ~ 100-1000 deg / s.

Figure 1 shows an example of a specific implementation of the working vacuum chamber of the installation for mechanical and thermophysical testing of samples of TM with pulsed heating, where:

1 - sample;

2 - collet clamp;

3 - base;

4 - a cap;

5 - current leads for heating the loading element;

6 - current leads for heating the sample;

7 - loading element;

8 - rack;

9 - a cross-section;

10 - displacement sensor inductive coaxial;

11 - dynamometer;

12 - hinge;

13 - sealed connector;

14 - thermocouples;

15 - thrust.

The working vacuum chamber consists of a base 3 and a cap 4. On the base 3, a loading element 7 and a rod 15 are fixed. Sample 1 is clamped with the lower end in a collet clamp 2, rigidly connected to the rod 15. The upper end of the sample 1 is fixed in a collet clamp 2, which is attached to the dynamometer 11, which in turn is connected to the cross-member 9 through the hinge 12. The power circuit of the installation is closed through the struts 8, rigidly connected to the cross-member 9 and the loading element 7. Thermocouples 14 are welded to the surface of the sample 1, the sensor is fixed in its middle part Inductive coaxial 10. For outputting signals from thermocouples 14, an inductive coaxial displacement sensor 10 and a dynamometer 11, an electrically isolated sealed connector 13 is installed in the cap 4. Through current leads 6, an electric current is supplied from the battery of batteries (not shown) to heat up sample 1. When by heating the sample 1 to a predetermined temperature, its thermal expansion is recorded by means of a displacement sensor of inductive coaxial 10, and using thermocouples 14, the thermopower and the difference potentials on the working part of sample 1, which allows one to determine the specific heat, relative electrical resistance, enthalpy, thermal conductivity and thermal diffusivity of sample 1. After heating the sample 1 through current leads 5, an electric current is supplied from the battery of batteries (not shown) to heat up the loading element 7, which is made in the form of a thin-walled steel pipe. When heated, the loading element 7 expands in the vertical direction and moves the struts 8 with a cross member 9, rigidly connected to the upper end of the sample 1, thereby transmitting a tensile force to the sample 1. In this case, the dynamometer 11 through the hinge 12 connected to the cross member 9 registers the amount of tensile force applied to the sample 1, and the displacement sensor is inductive coaxial 10 resulting in deformation of the sample 1, which allows one to obtain a deformation diagram of the sample 1 at its known section. The supply of electrical pulses occurs automatically using a switching device (not shown). The heating rate of the sample can vary from 100 to 1000 deg / s.

To determine the complex of thermophysical properties of sample 1, it is necessary to carry out its preliminary and several main heating with subsequent cooling. Preheating is used to determine the thermophysical properties of the test material at normal temperature. The temperature increment does not exceed 25 ° C in order to avoid a noticeable change in the determined properties. Subsequent main heating of sample 1 is carried out to the required test temperature, while the thermophysical properties are determined as a function of temperature and heating rate. The experimental information needed to determine the thermophysical properties is recorded both during heating and when sample 1 is cooled. When heated, the following parameters are recorded as functions of time: signals of an inductive coaxial displacement sensor 10, which measures thermal expansion; potential differences on the working part of sample 1; current flowing through sample 1; thermopower of thermocouples 14. Upon cooling, the temperature distribution is determined along the axis of sample 1.

Thermal expansion is measured by an inductive coaxial displacement sensor 10. To determine the potential difference on the base length of sample 1, fixing needles of the inductive coaxial displacement sensor 10 are used. The current flowing through the sample 1 is determined by measuring the voltage drop across the resistor in series with the sample 1 connected to the power circuit ( not shown). The temperature distribution along the length of sample 1 when it is cooled is measured by four thermocouples 14 with an electrode diameter of 50 μm. One of these thermocouples 14 is used to measure the temperature of sample 1 when it is heated. Thermocouples 14 are welded to the surface of sample 1 by spot electric welding in a separate way at a certain distance from each other. The marking of sample 1 according to the template and welding of thermocouples 14 are made under magnification using a microscope.

Method for calculating thermophysical characteristics

a) Specific heat and enthalpy

The specific heat at normal temperature is determined by the formula

$$c_{p0}=\frac{Q}{m\cdot \Delta t}\left(\mathrm{one}\right)$$

where Q is the amount of heat received by the working part of sample 3, Δt is the temperature increment, m is the mass of the working part of sample 3. To calculate c _{p0, we} use the experimental results of preliminary heating of sample 3, in which the thermoelectric power of thermocouples 5, current I ₀ , are recorded (τ) flowing through sample 3 and the voltage drop U ₀ (τ) based on L ₀ of the inductive coaxial displacement sensor 6. Then

$$Q={\displaystyle \underset{0}{\overset{{\tau }_n}{\int }}{U}_0\left(\tau \right)\cdot I_0\left(\tau \right)\cdot d\tau \left(2\right)}$$

where τ _n is the preheating time. The temperature increment Δt is determined by the thermopower of thermocouples 5 at time τ _n . Taking into account (1) and (2), we obtain an expression for calculating the specific heat capacity, which, taking into account the small value of Δt, in preheating can be considered constant

$$c_{p0}=\frac{{\displaystyle \underset{0}{\overset{{\tau }_n}{\int }}{U}_0\left(\tau \right)\cdot I_0\left(\tau \right)\cdot d\tau }}{m\cdot t}.\left(3\right)$$

The mass of the working part m is determined by calculation, based on the known mass of the entire sample 3, its diameter and the assumption of a uniform distribution of mass along the length of sample 3.

For subsequent main heating of sample 3, the specific heat at an arbitrary test temperature t is determined by the dependence

$$c_p\left(t\right)=\frac{U\left(t\right)\cdot I\left(t\right)\cdot d\tau }{m\cdot dt}\left(\mathrm{four}\right)$$

or

$$c_p\left(t\right)=\frac{U\left(t\right)\cdot I\left(t\right)}{m\cdot \left(dt/d\tau \right)},\left(5\right)$$

where I (t), U (t), t are the instantaneous values of current, voltage, and temperature recorded during subsequent main heating of sample 3. The main error in determining c _p (t) is introduced by the absolute value of the temperature rise rate. To the greatest extent, this error is manifested at temperatures close to normal. The exclusion from the calculations of the absolute value of the velocity V = dt / dτ significantly increases the accuracy of determining c _p (t). This is achieved by calculating the temperature dependence of the relative change c _p (t) / c _p0

$$\frac{c_p\left(t\right)}{c_p{}_0}=\frac{U\left(t\right)\cdot I\left(t\right)}{U\left(t_0\right)\cdot I\left(t_0\right)}\cdot \frac{V\left(t_0\right)}{V\left(t\right)}\left(6\right)$$

The product of the ratio c _p (t) / c _p0 calculated from the results of subsequent main heatings and the value c _p0 obtained for the same sample in preliminary heating gives the specific heat capacity c _p (t) as a function of temperature.

It is advisable to apply the described procedure for determining the temperature change in specific heat if there are violations of the monotonic dependence of temperature on time and enthalpy on temperature, i.e. if in the studied temperature range in the material of sample 3 there are processes characterized by a certain thermal effect (for example, phase transformations, etc.) With the monotonic character of the indicated dependences, based on the experimental data, there is enthalpy, which is determined as a function of temperature from the expression

$$H\left(t\right)=\frac{\mathrm{one}}{m}{\displaystyle \underset{0}{\overset{{\tau }_n}{\int }}U\left(\tau \right)\cdot I\left(\tau \right)\cdot d\tau .\left(7\right)}$$

After that, the specific heat is determined as the derivative of the enthalpy with respect to temperature c _p (t) = dH (t) / dt.

b) Thermal expansion

To determine the characteristics of thermal expansion, the time and temperature dependences obtained in subsequent main heating are used. Absolute thermal expansion of the working part of sample 3 is defined as the elongation recorded by the inductive coaxial 6 displacement sensor. For the same instants of time, the temperature of the sample 3 and the elongation of its working part, which are used to construct the dilatometric curve, are determined.

c) Relative electrical resistance

When determining the relative electrical resistance, the waveforms of the following main heatings are used: voltage drop U (τ), current I (τ), temperature t (τ). Relative electrical resistance is determined without taking into account changes in geometric dimensions when heating sample 3, which gives an additional error of ~ 1%. With this assumption, the relative electrical resistance is the ratio of the resistance R (t) of the working part of sample 3 at temperature t to its value at the initial test temperature R (t ₀ ), i.e.

$$\frac{r\left(t\right)}{r\left(t_0\right)}=\frac{R\left(t\right)}{R\left(t_0\right)}\mathrm{and}l\mathrm{and}\frac{r\left(t\right)}{r\left(t_0\right)}=\frac{U\left(t\right)}{I\left(t\right)}\cdot \frac{I\left(t_0\right)}{U\left(t_0\right)}.\left(8\right)$$

Thus, determining the voltage and current from the oscillograms of subsequent main heatings for the same instant of time, the relation (8) calculates the relative electrical resistance (temperature change of electrical resistance) at a specific temperature, and ultimately, the dependence of the relative electrical resistance on temperature in the studied range .

The cap 4 and the base 3 form a sealed cavity to create a vacuum that prevents convective heat transfer with the environment, as well as corrosion of TM samples when tested at elevated temperatures.

Thanks to the claimed combination of solution features, it becomes possible to thermophysically and mechanically tensile test the TM samples to produce a set of mechanical and thermophysical properties during pulsed heating (at a speed of ~ 100-1000 deg / s) to a temperature of ~ 800 ° C in vacuum while protecting personnel and the environment environment from exposure to test subjects TM.

A prototype of the installation was manufactured, tested, the results confirmed the operation of the installation and obtaining a new technical result.

Claims (4)

1. Installation for mechanical and thermophysical testing of a sample of conductive material during pulsed heating, containing a working vacuum chamber with current leads, collet clamps for mounting the sample, recording equipment, loading element, dynamometer, characterized in that the recording equipment consists of thermocouples welded directly to the working part of the sample, the displacement sensor inductive coaxial, mounted on the middle part of the sample, and the dynamometer, the loading element is made in the form of t on-walled tube, in which the rod is placed, rigidly connected through the collet clamp to the sample, the other end of the sample is also connected through the collet to a dynamometer mounted pivotally on the existing frame, current leads are installed with the possibility of heating the sample and the loading element, recording equipment is connected with the control and measuring equipment, which, in turn, is connected to a PC. 2. Installation according to claim 1, characterized in that the sample is made of environmentally hazardous material. 3. Installation according to claim 1, characterized in that the frame is made in the form of two racks, rigidly fixed to the existing area of the loading element, with a cross member fixed on their upper part, in the middle part of which a dynamometer is pivotally mounted. 4. Installation according to claim 1, characterized in that the working chamber consists of a base and a cap, in which the current leads for heating the sample and the loading element are sealed, as well as an electrically insulated sealed connector.

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