Brittle failure of specimens of SiCr.s. in individual areas as for SiCsu b specimens be- comes possible due to the tensile stress component with expansion of the zone of thermal activity as a result of a reduction in the level of compressive stress component. Com- pared with reaction-sintered silicon carbide sublimated silicon carbide withstands higher thermal loading (Table 2).

Research performed on silicon carbide once more confirms that failure of brittle materials in complex and nonuniform thermal stress fields is a kinetic process requiring consideration of loading history and the nature of crack development and interaction. De- pending on the ratio of material strength characteristics this process may develop both in the region of the tensile and compressive components of thermal stresses.

LITERATURE CITED

i. F. Porz, G. Grathwohl, and F. Th{immler, "SIC as a structural material in the plasma chamber of nuclear fusion reactors," Mater. Sci. Eng., 71, 273-282 (1985).

2. A.G. Lanin, V. V. Borunov, V. S. Egorov, and V. P. Popov, "Failure of bodies of cy- lindrical shape made of brittle materials with thermal loadng," Probl. Prochn., No. 3, 56-6O (1973).

3. G.G. Gnesin, Silicon Carbide Materials [in Russian], Metallurgiya, Moscow (1977). 4. A.G. Lanin, V. P. Popov, V. S. Kolesov, and N. A. Bochkov, "Failure of ceramic _

materials with local thermal loading," Probl. Prochn., No. 9, 35-38 (1986); 5. V.P. Popov, A. G. Lanin, and N. A. Bochkov, "Method for testing the thermal resis-

tance of specimens of brittle electrical conducting materials using electron beamheat- ing,".Probl. Prochn., No. 9, 77-81 (1984).

6. L.A. Kozdoba, Methods for Solving Linear Thermoelasticity Problems [in Russian], Nauka, Moscow (1975).

7. A. G. Lanin, N. A. Bochkov, V. S. Egorov, and V. A. Sokolov, "Failure of materials in a brittle condition in compression, " Probl. Prochn., No. 9, 75-80 (1985).

STRENGTH OF MODIFIED POLYVINYL CHLORIDE FILMS TAKING ACCOUNT

OF OPERATING CONDITIONS

E. S. Umanskii, N. S. Shidlovskii, L. L. Stezhko, V. V. Kryuchkov, and V. L. Nikityuk

UDC 678.743.22

Experimental data are given for the strength and deformability of a wide range of polyvinyl chloride films obtained by combining different grades of poly- vinyl chlorides and modifiers. The effect is considered of temperature and long- term climatic factors on the strength of these materials. The possibility is demonstrated of predicting the change in deformability of polyvinyl chloride films under conditions of naturalsolar radiation on the basis of results of rapid tests under the action of ultraviolet light.

One of the polymer materials used in the national economy is polyvinvyl chloride (PVC) which is among a number of the cheaper production materials and it exhibits quite good operating characteristics.

Recently in view of the increased requirement for the physicomechanical indices of structural polymers considerable work has been carried out directed towards improving the operating characteristics of this material. A number of additivies have been developed which increases elasticity and promote stabilization of strength and deformation character- istics of PVC with the long term effect of climatic factors. Results obtained in studying stabilized PVC have been described in [1-3]. At the same time there is clearly insufficient study of thequestion of the effect of the original PVC components, stabilizing additions,

Kiev Polytechnic Institute. Translated from Problemy Prochnosti, No. 8, pp. 71-76, August, 1990. Original article submitted March 20, 1990.

0039-2316/90/2208-1199512.50 �9 1991 Plenum Publishing Corporation 1199

TABLE I. Strength and Deformability of Modified PVC Films

u~

Resin content (%)in PVC grade I!~ ~

�9 ~.~ �9 ,~ ~ O~

o~'~ I~ ~'~o O I A O ~

t~4

~ O ~

80 -- ~ 20 -- -- -- 57,2 49 ,9 . . .64 ,4 15,4 151,0 94,7 . . .207,3 45,3 70 30 . . . . . 58,3 46, I . . . 70 ,5 21,9 125,6 36,1. . .215, I 74,8 70 20 . . . . lO 51,4 44 ,9 . . .57 ,9 13,3 139,2 I09,9 . . .174,5 26,6 50 50 . . . . . 54,0 52 ,2 . . .55 ,9 4 ,7 196,0 186,7. . .205,3 6,6 50 30 ~ 20 - - - - - - 53,8 46 ,9 . . .60 ,6 13,3 168,2 109,1. . .227,3 86,9 50 - - -- 50 -- -- -- 51,0 45 ,5 , . .56 ,6 11,4 118,8 55,9 . . .181,7 55 ,6 50 - - 50 - - - - - - - - 59,0 55 ,3 . . .62 ,8 6,6 198,0 188,5. . .207,5 5,1 20 50 - - 30 . . . . 49,4 39,7. . .59,1 20,5 97,0 16,4. . .177,6 87,1

- - 50 - - - - - - 50 - - 44,1 38 ,1 . . .50 ,0 14,2 89,6 38 ,9 . . .140 ,3 59,3 - - - - 50 50 - - - - - - 64,9 61,4.__68,4 5,7 207,2 196,1.__218,3 5,6 - - - - - - 50 - - 50 - - 53,3 49 ,1 . . .57 ,5 8 ,2 193,6 182,3.. .204,9 6,1 - - - - 50 - - 50 - - - - 51,6 42 ,2 . . .60 ,9 15,4 102,0 43,4. . .160,6 48,8

and modifiers on the strength and deformability of materials in the working temperas range~ There has been little study of the features of the change in properties of modified PVC films with the long term effect of natural climatic factors (temperature, solar radia ~ tion, moisture).

Given in the present communication are experimental data for the strength and deform- ability of a broad range of PVC films created by combination of various grades of PVC and modifiers. The effect of temperature and long-term climatic conditions on the strength pro- perties of these materials is considered. Some of the modified PVC films studied were ob- tained by developing a rational formulation for preparing protective components for flexible magnetic disks used in computers.

Test Materials. PVC films were tested by the method of calendering on drums [3, 4]. The composition of PVC grades in these formulations (Table i) was selected so that in order to provide high technological efficiency for film manufacture with relative material economy. The main component was a suspension of PVC grade S-5868 PZh (GOST 14332-78). In combination with this resin the additions were PVC emulsion grade E-6250Zh (GOST 14089-78), PVC grade MS.6602, PVC emulsion grade EP-6602S (GOST 14039-78), bulk (lump) PVC grade M-64 (TU 6-01- 678-76), vinyl acetate VA-10 (TU 6-01-774-79), and PVC suspension grade S-5078 (GOST 14332- 7 8 ) .

As stabilizers which increase resistance to the action of destructive factors (tempera- ture, oxygen, light) with processing, storage, or operation [3, 5] use was made of calcium stearate, lead acetate, organotin stabilizer (OTS-15), and tribasic lead sulfate (TOSS).

In order to control the main mechanical and production characteristics the following modifiers were introduced: active copolymer Lakris-95 (increases the productivity of equip- ment for producing PVC and it extends the temperature range for processing), and also modi- fiers based on methyl methacrylate, butadiene, and styrene BTA-32! and Inkar-27 (regulate strength and viscoelastic characteristics, homogenize the melt).

A mixture of Lubrikant K-II oil and polyethylene wax PV-200 was used in order to obtain an overall lubricating effect for the whole system.

Accumulation of static electricity charges during PVC processing or film operation was avoided by means of a mixture of alkyi sulfonate E-30 and polymethylene urea PMM.

Given in Table 2 are the additives present in the test PVC formulations and their per- centage content. In total, PVC films of more than forty formulations were strength tested. After the first tests and adjustment of the formulations exhibiting minimum strength PVC films of twenty two formulations remained for further testing.

For the purpose of comparison similar experiments were carried out on imported PVC film produced in Great Britain, FRG, and Japan (designated I-l, I-2, and I-3 respectively) used extensively in the production of protective components of flexible magnetic disks for computers.

Study Procedure. The strength and deformability of PVC films was studied with short- term uniaxial extension of specimens cut at different angles in relation to the longitudinal

1200

TABLE 2. Content of Additives in Test PVC Films

I Classification number_of PVC film con- Additive raining a given additive and the per-

centage content of additive .

Stabilizers

Calcium s t aaxa te HDF.36, 37, 39 (I %); HDF'-71, 72, 73, 75, 76 (0,5 %)

Lead a c e t a t e MDF-36, 37, 39 (I %); MBF :71, 72, 73, 75, 76 (1,5 %)

OTS-155 MDFV'-74, 95, 97 (2 %); MDF*I06, 107, 108, I09, l l 0 ,11 l , I13, I15, 134, OP-13 (1,5 %); MDF~-II2

TOSS -36, 37 39 (I ,5 %); MDF-71., 72, 73, 75, 76 (1,5 %)

Modifiers

Lakris-95 MDF%71, 72, 73, 74, 76 (I %); MDF~-36, 37, 39, 95, 97 (20 o~1) ~ MDFr'-I06, I13, 115, 134, P (3 %)

BTA-3N MDF:'-I08, 109 (5 %); MDF~..106, 107, l l 0 L l l 3 , I15 (8 %); MDF'-I34, OP'i-13 (I0 %)

Inkar-27 l~F;: 36 (5 %); MDF-,~-37, 39 (10 % )

Antistatic : PMME-30 t,'ff)F!~-71, 7:2, 73, 74, 95, 109, 110

(3 %) Lubricants

Lubrikant K-II MDF:'-II2 (0,8 %); HDF~-36, 37, 39, 71--76, 106--111, l l3, 115, 134, OP[-!3 (1%); MDF~-95,97 (2 %)

Wax PV-200 MPF~-71, 72, 73, 74, 76, 95, 97, 106, 108--112, 134 (0,2 %) F i l l e r s

Ti~O (futile) MDF~ -I06, 107, 108, 109, II0, 111,I12, 113, 115 (0,5 %)

,Carbon b lack MDF:,-106, 107, 108, 109, II0, I II , I12, I13, I15 (0,5 %)

TABLE 3. Inverse Order for Physicomechanical Properties of Modified PVC Films

I Values of' I PVC film formulation Properties proper- classification number

K1es

Ultimate strength 44...50 Oult~ MPa

51...54

56...60 61...65

Maximum relative 15...60 elongation 61...II0 emax, % III...160

161...210

Anisotrop~ of 0,6_.2,0 maximum e,onga- tion 2,1...4,0

smax(0 ~ 4, I...6,0 K =e----T~ ~ 6,1... 15,0

r

Anisotropy of ul- 1,0...I,2 timate s treng:~h

quit(O) 1,21...1,4

K= ault(90~ 1,41...I,55

75, 76, I09, I l l , l l2, 134 37, 71, 72, 74, 95, 97, II0, llS, Op-13 39, I08, I07, 108, If3 36, 73 75, I l l , l l2 72, 76, I09, 134 73, 95, I06, 107, I08, II0 36, 37, 39, 74, 97, I13, 115, OP-13 36, 37, 39, 74, 97_, I08, I I I , I15, 134, OP-13 71, 75, 78, 112, I13 I06, I07, 109, II0 72, 73, 95

95, I07, 109, I l l , I12, 134 71, 72, 73, 74, 75, 76, I06, 108, ll0, 115, OPt-f3 36, 37, 39, 97, ll3

1201

TABLE 4. Maximum Relative Elongation of Modified PVC Films After 24 h Action of UV-Radiation (Inverse Table)

PVC film formulation classifi- 8max" % cation number

5...10 74 76, 95, 97, I06--I15, OP~-I3 II...50 36, 71, 73 >50 37, 39, 72, 134

axis of the prepared sheet of-films. Specimens Were tested in a rupture machine [6] with a standard rate for mobile grip movement of 50 mm/min at 23 • 2~ and a relative moisture content for the air in the room of 65 • 5%.

Thickness of the test specimens was 0.2-0.3 mm, and the width and gauge length were I0 and I00 mm respectively. Deformation diagrams were recorded during testing from which the ultimate strength, maximum relative elongation, yield stress (limit of constrained elasticity), elongation corresponding to the yield stress, and also the nominal elasticity modulus found from the initial part of the diagram were determined. No less than ten speci- mens were tested in each series.

Some modified PVC films were tested for strength at 20, 40, 60, 70, 80, 90 and 100~ Specimens placed in a heating chamber were heated at a rate of 2~ held at the test temperature for 15 min, and deformed.

Statistical treatment of the experimental data was carried out on the basis of the hypothesis of a normal distribution rule. Scatter of the results was evaluated for stan- dard deviation and coefficient of variation. The confidence ranges were calculated with a confidence level of 95%.

Test PVC films were subjected to natural and artifical light radiation. Aging of films under the action of ultraviolet (UV) radiation was carried out in a mercury-quartz lamp type DRT-1000 whose nominal value of radiant flux in the wave band 240-320 nm was 115 W. Speci- mens were placed at a distance of 300 mm from the lamp so that the light flux fell perpen- dicular to the specimen plane and they were cooled by means of a ventilation system.

Natural aging of specimens was carried out on board scientific research vessels voy- aging in the tropical zone of the Pacific ocean. The exposure procedure and climatic char- acteristics are similar to those described previously [7, 8].

Effect of Formulation on Strength with Normal Climatic Conditions. Results of testing modified PVC films are given-in Tables i and 3 where apart from ultimate strength and maxi- mum elongation the confidence ranges for mathematical expectation and coefficients of variation for a series of tests are indicated. Data are presented in Table 3 in the form of inverse order where formulations are grouped in relation to values of aul t and emax"

Some features are noted of deformation diagrams for the test PVC films typical for amor- phous polymers for which in tensile tests a local reduction in transverse section ("neck") is observed. The initial rectilinear section (o = 40...60 MPa) corresponds formally to Hooke's law with a nominal elasticity modulus 1400...2000 MPa. With a further increase in stress in the range 50-70 MPa constrained elastic strain develops and a neck develops jumpwise which leads to a fall in tensile load. In GOST 14236-81 (Polymer film. Tensile test method) this point of inflection on the deformation diagram is identified with the yield stress. In view of this by the value ay in future we understand the stress corresponding to the maxi- mum of the elastic section on the deformation curve. Strength of the test materials in relation to film formulation varies in the range 44-65 MPa (deformation along the longitu- dinal axis of the sheet) and 33-53 MPa (deformation across the longitudinal axis of the sheet). The effect of formulation is more marked on maximum relative elongation which for different modifications of PVC reaches 15-210%.

It is necessary to note marked scatter of test results which points to marked inhomo- geneity of mechanical properties for practically all of the materials considered (Table 3). Strength and maximum elongation of the majority of PVC films in the longitudinal direc- tion are greater than in the transverse direction, which is connected with production fea- tures of their preparation method by calendering. Strength anisotropy for the majority of the test PVC films is much lower than the anisotropy of maximum elongation.

1202

E__ffect of Temperature on Strength and Deformability. Four modifications of film were tensile tested at elevated temperatures by the procedure indicated previously.

Deformation diagrams for test materials at 20-70~ have a clearly defined platform of constrained elasticity. At temperature above 70~ a material softens markedly, i.e., transition from the glass-like to highly elastic condition is complete. A specimen de- forms uniformly over the whole length up to breakage and the curve acquires a monotonic nature.

Illustrated in Fig. 1 is the change in main mechanical properties of test PVC films with short-term tension in relation to temperature. With an increase in temperature from 20 to 100~ there is amarked reduction in ultimate strength (by a factor of 10-17) and limit of proportionality (up to disappearance of the linear section), but elongation at breaking increases gradually, reaching maximum values in the range 70-90~ and then it decreases. On the whole the value of Smax of the test materials in the temperature range studied is quite high (100-300%).

Nominal elasticity modulus up to the temperature range of phase transition (70-80~ decreases almost linearly, but in this range it decreases by more than two tenths of an order of magnitude.

Effect of UV-Radiation and Sun Light. It is well known that PVC is among structurally unstable materials and it changes its properties to a considerable degree with the pro- longed effect of light in the UV-spectrum [3, 5]. Introduction of various stabilizers markedly reduces the rate of destruction and it hinders the change in physicomechanical properties during aging.

Analysis of the results obtained for a number of PVC films of different modification under the action of UV-radiation (Tables 1 and 2) followed by short-term strength tests for specimens in tension (Table 4) showed that OP-13 film is one of the most stable of the materials studied. The strength of this film is retained almost at the original level with action of intense radiation in the range up to 48 h (Fig. 2a) while the maximum elongation is retained up to 1.5-2.0 h (Fig. 2b).

The greatest rate of change in the value of Cmax is observed in the range 0.5-4 h of radiation and subsequently it is retained at a level of 10%. As is well known, the maximum relative elongation is a more distinct structure-sensitive parameter of polymer film sub ~ jected to aging than ultimate strength~ This is also confirmed by data in Fig. 2.

It is of interest to compare the results of aging PVC materials with intense UV-radia- tion in the laboratory with those obtained with exposure under tropical conditions~

Curves are shown in Fig. 3 for the change in maximum relative elongation of PVC films of formulation OP-13. Solid line I was obtained for unstressed specimens with long-term storage at a location equipped with louvered screens under tropical conditions. Specimens were protected from direct solar beams with retention of the action of the whole tempera- ture and moisture complex [7, 8]. It can be seen that for an exposure time up to 180 days the value of Emax, the same as for strength, changed little.

Storage of specimens for 5 days to 6 months under the direct action of solar beams under tropical conditions (broken line 3) led to a sharp reduction in Sma x as a result of intense material destruction. Given in addition in Fig~ 3 are the results of testing speci- mens subjected to the artificial action of UV-radiation by the procedure indicated above for 24 h (broken line 2). In order to compare experimental results obtained under natural and laboratory conditionsthetime scale tar t was moved in relation to the time scale tnat by the value

In/ha s Infart= 6,7.

Figure 3 illustrates the similarity of processes occurring in a material with exposure under natural conditions and in the selected aging schedule.

Thus prediction of the change in maximum elongation of PVC film specimens subjected to natural solar radiation may be accomplished with accelerated tests under the action of UV-radiation in mercury-quartz lamps. Mechanisms of natural and artificial tests depend markedly on the intensity of radiation in the UV-spectrum and on the composition of sta- bilizers introduced into PVC.

1203

Oult, MPa

Oy,

E~

(lu].t > MPa

30

o I oZ

A3

0

O 8 g 10 tl Zn t, s e c

I I I ] I I I

~0 40 60 80 T,~ 0,5 1,0 f,5 2,0 4,0 12,0 ~,0 t, h

Fig. i Fig. 2

Fig. i. Temperature dependences for physicomechanical properties of modi- fied PVC films of the formulations MDCh-244 (i), MDCh-246 (2), MDCh-254 (3), 1-2 (4) and 1-3 (5).

Fig. 2. Dependence of physicomechanical properties of modified PVC films of the formulations MDF-36 (I), OP-13 (2), and I-i (3) on long-term UV-radia- tion (intensityofUV-radiation in the b~7-spectrum E = I00 W/m2).

T

O

~GO �9 S

72O i I ~ 8 0 - -

12 l+ 16 In t, s e r ~5 30 90 180 , i i , - , ==~..,,. tna t, days

10 20 120 tar t, h r I I I J I

0,5 t5 #,0 ~,0

Fig. 3. Change in maximum relative elongation of PVC films of formulation OP-13 in a closed location and under the action of solar or artificial radiation.

1204

i,

2.

~

4. 5.

6.

7.

.

LITERATURE CITED

L. D. Strelkova, G. T. Fedoseeva, and K. S. Minsker, "Photochemical aging of rigid PVC," Plast. Massy, No. 7, 72-73 (1976). A. P. Aleksandrov et al., "Spatial distribution of the products of PVC photodestruc- tion under conditions of intense polychromatic radiation," Vysokomol. Soedin., Ser. A, 27, 1060-1065 (1985). K. S. Minsker and G. T. Fedoseeva, Destruction and Stabilization of PVC [in Russian], Khimiya, Moscow (1979). T. Gisaku, Polymer Films [Russian translation], Khimiya, Leningrad (1971). K. S. Minsker, S. V. Kolesov, and T. E. Zaikov, Aging and Stabilization of Polymers Based on Vinyl Chloride [in Russian], Nauka, Moscow (1982). E. S. Umanskii, V. V. Kryuchkov, and N. S. Shidlovskii, "Supporting capacity of wound ~olymer films," Probl. Prochn., No. i0, 104-113 (1980). E. S. Umanskii, N. S. Shidlovskii, V. V. Kryuchkov, et al., "Static strength of poly- ethylene film after prolonged exposure in different climatic zones," Probl. Prochn., No. 5, 82-86 (1984). E. S. Umanskii, N. S. Shidlovskii, L. L. Stezhko, et al., "Static strength of modified polyethylene after prolonged exposure in different climatic zones," Probl. Prochn., No. 2, 47-53 (1985).

MECHANICAL PROPERTIES OF LOW-CARBON STEELS OVER A WIDE RANGE

OF TEMPERATURES AND STRAIN RATES APPLIED TO PROCESSES OF THIN

SHEET ROLLING

A. P. Vashchenko; G. N. Suntsov, G. V. Belalova, E. G. Zinov'ev, A. M. Bragov, A. K. Lomunov, and A. A. Medvedev

UDC 620.172.254:539.4

Results are given for mechanical tests on a number of low-carbon steels in uniaxial tension and compression in the strain rate range 10-3-4"103 sec -I and at tempera- tures of 293-573 K. An increase is confirmed for strength and ductility character- istics with an increase in strain rate. It is shown that the sensitivity of metals to strain rate depends on the specific temperature and rate conditions of load- ing. On the basis of experimental data obtained analytical dependences are sug- gested for the resistance of materials to deformation on the degree and rate of deformation, and also on temperature.

Creation of modern high-productivity mills for continuous and endless rolling and also skin rolling is connected with a considerable increase in the temperature and rate schedules for metal processing. The rate of rolling in these mills reaches several tens of meters a second and the deformation rate for the processed metal is about 103 sec -I or more. With an increase in rolling rate from 20 to 40 m/sec there is sharp increase in the release of heat, strip and roller temperature, and there is change in metal resistance to deformation and contact conditions at the site of deformation. Therefore release of heat and the dynamic properties of the metals and alloys being processed acquire exceptional importance for carrying out the process.

Institute of Strength Problems, Academy of Sciences of the Ukrainian SSR, Kiev. Pro- duction Association 'Uralmash', Scientific-Research Institute of Heavy Machines. Gorky University Scientific-Research Institute of Mechanics. Translated from Problemy Pro- chnosti, No. 8, pp. 76-84, August, 1990. Original article submitted December 20, 1989.

0039-2316/90/2208-1205512.50 �9 1991 Plenum Publishing Corporation 1205