New methods of investigation Automatic apparatus for thermomechanical curves

New methods of investigation Automatic apparatus for thermomechanical curves

NEW METHODS OF INVESTIGATION AUTOMATIC APPARATUS FOR THERMOMECHANICAL CURVES* G. S. SEMEI~OV, N. G. RYZHOV and A. I. KRAVTSOV (Received 11 July 1966)...

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NEW METHODS OF INVESTIGATION AUTOMATIC APPARATUS FOR THERMOMECHANICAL CURVES* G. S. SEMEI~OV, N. G. RYZHOV and A. I. KRAVTSOV

(Received 11 July 1966) THE method of using thermomechanical curves for the investigation of physicochemical and mechanical properties of polymers has recently been increasingly used. Several automatic devices are described in the literature for plotting thermomechanical curves of polymers which were designed for tensile testing of bands [1], testing of pellets and plates b y penetration under continuous and intermittent load [2, 3], and simultaneous testing of five specimens by a method of penetration under a constant load [4]. These devices, however, are of complex construction and are designed to solve particular problems. I n the device proposed for plotting thermomechanical curves (Fig. 1) the recording of the deformation curve, specimen temperature and the linear increase or reduction of temperature at a given rate and the maintenance of any unchanged temperature are carried out by the same EPP-09 multi-point contact electronic potentiometer. Howewer, if necessary, the deformation curve can also be recorded by another potentiometer. Thermomechanical stress/strain curves, stress and strain relaxation curves, and creep curves can be plotted by the apparatus and the effect of intermittent load on creep studied over a wide range of temperatures. The limits of temperature measurement depend on the scale of the regulating electronic potentiometer. The apparatus is reliable in operation, simple in construction and compact. I t consists of a loading device, deformation indicator, temperature indicator and two changeable heating units. The loading device consists of rod 1 with screw 2, lever 3 and load 4. When testing compression the specimen is placed in housing 5. The tensile testing device is shown in Fig. lb. The specimen is fastened in clamps 6 and is placed in the reversing device. The loading rod with the screw-on cap presses the movable frame 7 of the reversing device. Cam 8 rotated b y the electric motor with reductor 9 raises and lowers lever 3 from time to time with the load and thus puts on the load and removes it from the specimen. The cam consists of two identical shaped disks, by means of which the times of loading and relieving the specimen can be altered. By its movement rod I through screw 2 bends the thin steel plate 10 with the four wire resistance strain-gauges fastened * Vysokomol. soyed. A 9: No. 1, 235-239. 1967. 258

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to it and connected b y a bridge circuit. The bending force of the plate does not exceed 10 g per m m deformation. The deformation data unit facilitates testing of slightly and strongly-deforming specimens; for testing the first, the upper end of the loading rod is placed in the left position, for the second, in the right, thus altering the point of application of the force on the plate. The device is equipped with two heating units. Temperature in each unit is controlled and measured by two thermocouples 11 2 3

4

8 9

../3

A

O ,FIG. 1

and 12. Thermocouple 11 is placed along the route of the heat transfer agent in the units, and by means of an electronic potentiometer and relay, regulates the temperature of the units; thermocouple 12 measures the temperature of the specimen. One of the units (Fig. 1) is made according to [2] but, in a more simplified form, consists of an aluminium vessel 13 with a shaft and heating coil 14, Dewar flask 15 for liquid nitrogen. The unit is used for rapid non4inear cooling and linear heating carried out at a given rate. The second unit enables any given

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temperature to be maintained and the specimen to be cooled and heated in a strictly linear manner over a wide range of temperatures. The unit consists of an aluminium vessel 16 with longitudinal grooves on the external surface in which the heating spiral 18 is placed and along which the coolant passes entering through an annular tube 17 with six openings. Washing the lateral surface and the base of the vessel, the coolant passes in the space of the casing between the walls and emerges through two openings. Gaseous nitrogen is used as the coolant enters the unit from the Dewar flask containing liquid nitrogen. The entry of the coolant and electric current into the heating coil of the unit is controlled by an electronic potentiometer through a relay. Although the nitrogen feed during cooling and the feed of electric current during heating are intermittent, owing to the considerable mass and adequate thermal conductivity of the vessel material, the specimen temperature varies linearly.

FIG. 2

FIG. 3

Linear temperature variation of the specimen at a given rate is ensured by a simple device built in a multi-point electronic potentiometer. The layout of the device is shown in Fig. 2. The master device of the electronic potentiometer is connected to a paper roll mechanism and is evenly moved by a system of gear wheels and pulleys with a cable. Cog wheel 1 is placed on the drum axis of the paper roll, cog wheels 2, 3, 4--on cam gear 6. The device facilitates even heating and cooling. This is ensured by interchanging the gear pairs 3-4 to 4-5 and back by means of a earn gear and a clamping screw 7, thus imparting forward and

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reverse motion to the master device. The gear ratio in the device varies slightly because changeable wheels are used which are actuated b y the reduetor of the paper roll mechanism. The rate of temperature variation in the heating-units depends on the strip movement speed and the ratio of diameters of the changeable wheels. The device produces constant and intermittent loads. In the latter the loading cycle is 3.3 min. Specimen retention time under load can vary from 10 sec to 2 min. The use of loading cams enables full load to be applied to the specimen during a time less than that requires for the deformation of the specimen under

I I

2

-70

-3O

0

3O

7O 7",°C

FIG. 4

the effect of the load applied. At the same time impact on the specimen is excluded as the lever with the load is lowered on the rod from a height not exceeding 1 ram. During compression work a specimen 4 mm in diameter, 3 mm in height is used as a vessel for the specimen 3 mm in depth and 5 mm in diameter. The specimens used for tensile testing are shaped as bilateral blades with a working length of 6 mm and a section of 3 × 3 ram. To determine stress relaxation, a device with a dynamometric plate with strain gauges I (Fig. 3) and helical deformation indicator 2 are connected to the apparatus. The variation of specimen deformation and the consequent error in the stress value due to the camber of the plate are negligible. With intermittent load a curve is obtained shown in Fig. 4. The curve was recorded with a single-point potentiometer for a commercial rubber specimen. Joining the outer upper and outer lower points, two deformation curves can be obtained according to temperature. The upper curve is a graph of overall deformation under load, the lower, a graph showing irreversible deformation during the time elapsing before the application of the next load. The distance between the curves along the deformation axis determines elastic deformation. From these curves a graph is plotted in the coordinates showing temperaturerelative deformation. The glass temperature is determined from the inflexion of

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the curve which shows overall deformation or, in the case of an indistinct inflexion, from the appearance of high elastic deformation, to which a point on the graph where the curves separate corresponds. The point of divergence is normally 'on the inflexion of the curve showing general deformation. The curve is recorded on a large scale and is sensitive to all the variations in the specimen thus facilitating physical and chemical processes in the material to be studied. With a lengthened loading cycle and a low rate of temperature variation the thermomechanical curve consists of separate creep curves which correspond to different temperatures. Figure 5 shows a section of the thermomechanical curve of ~,%

~J

i

k. a

~

b

FIG. 5 commercial rubber which consists of two loading cycles and is recorded at a high rate of strip motion of the potentiometer. Section a is the creep curve, section b the strain relaxation curve. These curves of creep and strain relaxation, which were plotted over a wide range of temperatures and for small relative deformations, can be used for plotting generalized creep and strain relaxation curves according to the principle of temperature-time equivalence [5]. The use of the thermomechanieal curve for plotting generalized curves is particularly useful because for plotting similar curves a few hours are required in all. CONCLUSIONS

(1) A small universal device is proposed for plotting thermomechanieal curves over a wide range of temperatures with strictly linear variation of temperature. (2) The device is used for compression and tensile testing of specimens under constant and intermittent load. (3) Thermomechanical curves, stress and strain relaxation, and creep curves can be plotted b y the device and physical and chemical processes in the material followed. (4) The device makes it possible, in principle, to use thermomechanical curves for plotting generalized creep and stress relaxation curves b y the prinpicle of temperature-time equivalence. Translated by E. SEMERE

Application of the emanation technique

263

REFERENCES

1. A. V. SIDOROVICH and E. V. KUVSHINSKII, Zavodsk. lab. 26: 100, 1960 2. B. Ya. TEITEL'BAUM and M. P. DIANOV, Vysokomol. soyed. 3: 594, 1961 (Not translated in Polymer Science U.S.S.R.) 3. B. Ya. TEITEL'BAUM, Vysokomol. soyed. 4: 1552, 1962 (Not translated in Polymer Science U.S.S.R.) 4. S. K. ZAgHAROV and E. V. KUVSHINSKII, Zavodsk. lab. 30: 1399, 1964 5. Dzh. FERRI, Vyazkouprugiye svoistva polimerov. (Visco-elastic Properties of Pol)wners.) Lzd. inostr, lit., 1963

APPLICATION OF THE EMANATION TECHNIQUE TO STUDY THE PHYSICO-CHEMICAL BEHAVIOUR OF HIGH MOLECULAR WEIGHT COMPOUNDS * K. B.

ZABOREI~'KO,I).

I~ITTSOL'D and N. F. BAKEYEV

M. V. Lomonosov State University, Moscow

(Received 2 September 1966) THE emanation technique is based on the use of radioactive inert gases (emanations) as radioactive indicators. I f a material contains micro-quantities of a parent isotope, emanations will be given off at a constant rate inside the substance. P a r t of the atoms formed up to the m o m e n t of decay can be separated, whereby the ratio of the num ber of atoms leaving the substance to the overall n u m b e r of emanation atoms formed inside th e substance, is called the emanating power (E) of a substance or the emanation coefficient. According to the Fliigge and Zimens [1] t h e o r y the emanating power, in the simplest case of a spheroidal grain, is expressed by the formula 3 R

3/-D

E=ERq-E~=7~o +~o f

'

(1)

where R is the emission range of emanation atoms; r o is the grain radius; ~ is the decay factor of emanation; D - - t h e diffusion coefficient of emanation through the substance. 3R The first component of formula (1) E R - - is due to emission and is a func4r o tion of the grain surface. The second component * Vysokomol. soyed. Ag: No. 1, 240-244, 1967.

ED=

~ is due to exterior