S T U D Y ON T H E S T R E N G T H AND D E F O R M A B I L I T Y OF

T H I N C O . M P O S I T E M A T E R I A L S OF T H E M A G N E T I C

C A R R I E R T Y P E

COMMUNICATION 1. STRENGTH AND DEFORMABILITY AT

HIGH TEMPERATURES

l~. S. U m a n s k i i , I . E . D e b r i v n y i , a n d V. V. K r y u c h k o v

UDC 539.3/5:678

1. Among the film mater ia ls now extensively used as a basis for magnetic c a r r i e r s , Lavsan (poly- ethylene terphthalate) occupies a prominent place. A modern magnetic c a r r i e r based on Lavsan is a com- plex composite material whose main components constitute the basis and the operating layer . The basis imparts the required strength proper t ies to the magnetic c a r r i e r . Its thickness equals about 2/3 of the total thickness of the magnetic c a r r i e r . Depending on the type and the destination of the magnetic ca r r i e r , the lat ter thickness ranges f rom 0.008 to 0.07 mm.

Fig. 1. Electromechanical scheme of the equipment used for studying the shor t - time strength and deformabil i ty of film materials .

The operating layer consis ts of a mixture of soft mag- netic powders (mainly 7-Fe203) which are dispersed in the binder. The magnetic and electroacoust ic proper t ies of the c a r r i e r depend on the degree of d ispers ion of the magnetic part icles , on their volume concentrat ion and on the unifor- mity of their dispers ion in the operating layer. The opera t - ing layer is deposited by letting a solution penetrate via a f i l ler onto the surface of the basis . The magnetic c a r r i e r may fur ther contain in termediary (adhesive) and surface (screening) l ayers whose thickness is small and va r ies f rom 0.001 to 0.003 mm.

Magnetic c a r r i e r s should possess a sufficient mechan- ical strength, besides the appropriate magnetic and e lec t ro - acoustic propert ies , which are now studied fa i r ly closely and are descr ibed in the l i te ra ture [1-4].

Papers [5-7] dealing with the problems regarding the procedures for determining the physicomechanical p rope r - ties of magnetic c a r r i e r s 9nly recent ly star ted appearing in the Soviet and foreign l i terature .

Analysis of the papers cited reveals that there is no unanimity of opinion, and that standard procedures for de- termining the mechanical charac te r i s t i c s of these mater ia ls over a broad temperature range are not available. On the other hand, magnetic c a r r i e r s , in the fo rm of polymer films, deform noticeably under relat ively small loads and, there- fore, it ls not possible to examine their mechanical p rope r - ties in equipment by methods suited for testing plast ics and other rigid mater ia ls .

Kiev Polytechnical Institute. Translated f rom Problemy Prochnosti , No. 5, pp. 40-45, May, 1972. Original ar t icle submitted November 1, 1971.

�9 1973 Consultants Bureau, a division o[ Plenum Publishing Corporation, 227 West 17th Street, New York, N. Y. 10011. All rights reserved. This article cannot be reproduced [or any purpose whatsoever without permission o[ the publisher. A copy o[ this article is available [rom the publisher [or $15.00.

546

T A B L E 1

Carrier type

G-I Carrier-V PE-41u PE-41 PE-31 Pyral

4

6.25 6.25 6.25 25.4 25.4 25.4

0.034

O. 024

O. 024

O. 024

0.03

0.034

Sizes

o

0.01 0.0: 0.0: 0.0: 0.01 0.01

_ m

o

0.212 0.15 0.15 0.61 0.762 0.8~

o

2%

0.15 0.1 0.1 0.407 0. 508 0.61

,

/8

/

V

IT 20~ %

PE-41u

18

12

8

4

~/mm2

pE-41

I

/ I

]" ZO ~

0 20 40 60 0 20 40 BO 80 ~t,,a~,~

Fig. 2. Stress d iagrams of the magnetic c a r r i e r s examined.

For example, the design of the usual tearing machines does not allow a sufficiently high f r ic t ion force to be produced in the clamp, and "folding" of the samples takes place under strong compression; de forma- tion diagrams, especial ly the initial parts , which are of pract ical importance for the operation regimes of the films, cannot be recorded with sufficient accuracy on the r eco rde r s of the machines. The adjusting devices of the standard machines do not guarantee a sufficiently stable displacement rate of the clamps, and do not permit this rate to be varied over a broad range.

These and other disadvantages were borne in mind in developing a procedure and a test equipment suited for studying the shor t - t ime strength and deformabil i ty of magnetic c a r r i e r s and other fi lm mater ia ls in a broad tempera ture range.

The test equipment (Fig. 1) consis ts of the device which deforms the sample (the driving gear and the t r a n s m i s s i o n - t r a n s f o r m a t i o n nodes a re based on the FM-20 tearing machine), thermostated cells, sys tems suitable for automatical ly controll ing and maintaining a given temperature , a device guaranteeing control of the displacement rate of the lower clamp over a broad range, and a multichannel sys tem for measur ing and recording the forces and deformations.

Sample 1 is fixed in the upper 2 and lower 3 clamps. The construct ion of the c lamps permi ts ve ry thin polymer samples (0.003-0.005 mm thick and up to 50 mm wide) to be rel iably fixed and the squeezing force to be adjusted. The clamp jaws are semicyl indrical a symmet r i ca l ly mounted corrugat ions with cham- my lea ther glued onto them. As the load acting on the sample is increased, the upper jaw provided with a spring ra ises the degree of compression. The upper clamp 2 is connected to the annular dynamometer 5 by means of the thin metal s tr ip 4. The dynamometer is rigidly fixed in the holder 6 mounted on the p r i sm 7. The metal s tr ip is perpendicular to the plane of the sample.

547

7

6

5

4

2

r=2ooc 40 60 80

/ - I .~ I 'I, It I t1

'so �9 ,, ~f ~/ 1t;I k'/ I t / ,11t i t l HI

z~ i / ' f / / I ' ! ~_y_ , t , ,,

/ I / / I I I I l l

"~ 7"--/--" I I I I , , , , I / I!

m I I / / / I1 / I I ~ ~ ~ z~ z,z ~,o q ~ , ~ , %;: ,

Fig . 3.

T=20~ 40 60 80

1,// / J

/

/ s ' / i t l " ,~ I" /#.2 Ij / i / / / i / /

;,'~ " /t/ / t /: ~ / z ,I/i 41 I

/ / / I l l~ I / i / '~r I l /

I , I I / I .

&

/ t / / J ;/I' / / ' / / i ~o 5o 60 70 oo 6o 7o ao go ~oo.

b

Integral d i s t r ibu t ion curves of the l imi t ing s t r e s s e s (a) and deformat ions (b) of the mag- netic PE-41u c a r r i e r at va r ious t e m p e r a t u r e s .

pc' :g/mm2

5 1

2 20

Fig. 4.

PE-# I

epc, %

2,0

45

4o

P E - # l J ~

@ o l

Carrier-V

40 60 T, ~ 20 ~0 6O 7:, ~ a b

T e m p e r a t u r e dependence of the p ropor t iona l i ty l imi t (a) and the co r re spond ing r e l a t ive elongation (b) of the m a t e r i a l s ex- amined.

This const ruct ion gxlarantees r e l i a b l e r e l i e f of the s ide loads f rom the dynamomete r and makes it poss ib le to apply s t r i c t l y axial forces; the metal s t r ip s e r v e s a lso as a t r a n s m i s s i o n e l emen t between the dynamomete r and the c lamp mounted in the the rmos ta t ed cel l 8. Covar, which has a negl ig ib ly smal l and s table coeff ic ient of l i n e a r expansion over a broad t e m p e r a t u r e range, was chosen as the m a t e r i a l of s t r ip 4.

The cons t ruc t ion for the c lamp and i ts fixation to the dynamomete r were so des igned that the i n s t r u - mental e r r o r s could be reduced to a minimum.

By means of the sc rew and nut pa i r 9, the lower movable c lamp 3 can be d i sp laced v e r t i c a l l y at con- stant speed. The sc rew 9 is ro ta ted by means of the c o n s t a n t - c u r r e n t e l e c t r o m o t o r 10, whose motion is t r ansmi t t ed via the V-shaped t r a n s m i t t e r 11, the toothed wheels 12, 13, and the clutch coupling 14. The device, which cons i s t s of revolut ion counter 15, r e c t i f i e r s 16 and 17, and v o l t m e t e r 18, ensures a quite accu ra t e ly constant deformat ion ra te and enables this to be smoothly va r i ed in the range f rom 10 to 500 mm /min.

The d i sp lacement of the lower c lamp is r e c o r d e d by the c lock- type ICh-50 ind ica tor (50 mm total sca le , 0.01 mm divis ions) . The indica tor jaw mounted on the bea r ing is g radua l ly d i sp laced by one of the a r m s of c rank 19, the other bea r ing 20 provided with a sp r ing and connected to the lower movable c lamp being d isp laced by another a r m of the crank.

Depending on the maximum deformat ion of the m a t e r i a l examined, the r e c o r d sca le of the d i s p l a c e - ment of the movable c lamp can be va r i ed over a broad range by means of an app rop r i a t e a l t e ra t ion of the c rank a r m s .

548

,mm 2 ~x,% .

1 6 .

7z

Zo

PE-41

oo

PE-llu �9

00 20 O0 SO T, ~ 20 ~0 ~0 T, ~

a b

Fig. 5. Tempera ture dependences of the l imiting strength (a), and the maximum elongation at rupture (b) of the magnetic c a r - r i e r s .

I00

G-1 C a r r i ~

Ps

20, 20 ~,o 60 r, oc

Fig. 6. The residual elonga- tion measured di rec t ly after rupture as a function of the temperature .

Moreover, the displacement of the movable clamp is recorded also by the following Selsyn system. By means of the toothed gear 22, the rotation of shaft 23 is t ransmit ted to the Selsyn senser 21. The

I

Selsyu pickup 24 mounted in an EPP-09M3 potentiometer is rotated synchronously and displaces the ruled paper s tr ip of the equipment.

Thanks to this system, the record scale of the deformation dia- g ram on the potent iometer can be easi ly adjusted and varied. To r e - cord the forces acting on the sample, four identical semieonducting t enso res i s to r s forming an e lectr ic bridge were glued on the annular dynamometer 5.

The high tensosensi t ivi ty coefficient of the sensing elements pe r - mits recording the variat ion of the load di rec t ly on the r eco rde r s , with- out any in termediary amplif ier being needed, thereby enhancing the ac - cu racy and the rel iabil i ty of the measurements . The bridge sys tem is fed by the stabilized BSP-24/1 voltage source.

The voltage divider 25 is used for varying the range of the mea- sured forces (from 0.5 to 25 kg) and, consequently, for al tering the total scale and the scale divisions of the record . The deformation d iagram is recorded by means of two independent channels in the following way.

The initial (Gukov) part of the d iagram is recorded on the N-700 oscil lograph. The signal of the load variat ion f rom the annular dynamom-

eter 5 is fed to the inlet of one of the osci l la tor loops, and the deformation signal f rom the elastic element 26 to the inlet of the other loop. One end of the elastic element 26 is fixed, and the other end is deformed by the knob of the ICh-50 indicator. The time mark establishes the correspondence between the load and deformation at a given moment. The sensit ivity of the osci l la tor loops was so chosen that the initial region of the diagram, which is an important charac te r i s t ic of the mater ia l examined, is recorded with great ac - curacy on the required scale.

The complete l o a d - e l o n g a t i o n d iagram is recorded simultaneously on the one-point ~.PP-09M3 poten- t iometer . The signal of the load variat ion comes f rom the annular dynamometer mentioned above, and the deformation was recorded by means of the Selsyn tracing sys tem 21, 24. This permit ted the ~.I:>P device to be used as a two-coordinate ins t rument in which the deformation of the sample was recorded along the coordinate axis, and the force along the axis of absc issas .

5 4 9

TABLE 2

u ~J

Strength and deformability Standard de- Reliability Intervals Reliability intervals for the standard de- Indices vtations viations for the averages

16,5" [57,5"

14,7"J65,9"

13,0"/68,8"

11,8'180"

E

13,4 35

12,5 44 40 ~

11,2 47 60 ~ gg

53 8o ~ N

Note: 1. The numerator gives the by an asterisk.

2,8

1,6

1.2

0,9

12,5

8,7

6,9

6,0

E

, f ,2,1--3,~

1,4--2,7

1,0--1,8

0,8--I ,4

Variation coefficients

2

Accuracy parameters

e~. i |

I0,1--13,3115,9--17, 2154,2--60 17,1 21,3 3,~ 3,9 I t " 7, ~--10, ~[ ]3,8-- 15,3163,9--68 ,,,3 ]3,2 ~,1 2,45 I I

6,3--8,4112,5--13,6165,9--71 9,2 l O,O 1,7 1,8 l !

5,8-- 7,611!,4--12,6[ 78--85 7,6 8,4 1,3 1,5 / /

and the denominator the maximum values. 2. Averages are indicated minimum,

The cor respondence of the deformat ion measu red by means of the p r o c e d u r e s mentioned was checked by means of a K-7 ca the tome te r (1 p sca le divis ions) with r e f e r ence to data points on the sample examined.

It is poss ib le thus to r eco rd the Gukov par t and the comple te s t r e s s - s t r a i n d i a g r a m with the requ i red a c c u r a c y for the m a t e r i a l s examined under exact ly the same expe r imen ta l condi t ions. Applicat ion of the scheme worked out for measu r ing the fo rces makes it poss ib le to achieve a highly l i nea r ca l ib ra t ion c h a r a c - t e r i s t i c of the forces , and to compensate the t e m p e r a t u r e d i f fe rences not only by including the sens ing e l e - ments in a b r idge , but a l so by u t i l iz ing a vol tage d iv ider , which i n c r e a s e s the in t e rna l r e s i s t a n c e of the vol tage supply. The main shor tcomings of semiconduct ing t e n s o r e s i s t o r s - the dependence of the t enso- sens i t iv i ty coeff ic ient on the deformat ion and t e m p e r a t u r e - a re thus e l imina ted .

At posi t ive t e m p e r a t u r e s the samples were tested in the the rmos ta t ed cel l 8 f i l led with a hea t -p roof insula t ing ma te r i a l . The heat ing e lement 27 cons is ted of he l i ces mounted in po rce la in insu la to r s . Fan 28 mixed the heated a i r in the cel l . The t e m p e r a t u r e was kept constant throughout the ce l l by means of con- tact t h e r m o m e t e r 29, and the automat ic t e m p e r a t u r e control block 30. Section 31 was used for keeping the s amples at the given t empera tu re .

2. The s t rength and de fo rmab i l i t y of va r ious magnetic c a r r i e r types under uniaxial s t r e t ch in a b road t e m p e r a t u r e range was studied in the equipment de sc r ibed . The p a r a m e t e r s of the c a r r i e r s a r e g iven in Table 1.

In choosing the app rop r i a t e magnetic c a r r i e r s , a l lowance was made for the d e s i r e to study the p r o p - e r t i e s of m a t e r i a l s which a re of the highest p rac t i ca l i n t e r e s t .

Since magnet ic c a r r i e r s were d i r e c t l y used as the s a m p l e s to be tes ted, the r e s u l t s furnish a d i r ec t c h a r a c t e r i s t i c of the p r o p e r t i e s of the m a t e r i a l s examined. The magnet ic c a r r i e r s mentioned in Table 1 were tested at 20, 40, 60, and 80~ i . e . , in the range of pos i t ive t e m p e r a t u r e s most often encountered under actual opera t ion conditions.

At the t e m p e r a t u r e given, eve ry magnet ic c a r r i e r type was r e p r e s e n t e d by 30 samples , the length of the opera t ing par t equall ing 100 mm. The tes t s were c a r r i e d out at a s tandard deformat ion ra te of 100 mm/min. Magnetic c a r r i e r samples of 25.4 mm width were the rmos ta t ed in the ce l l s fo r 30 min, and those of 6.25 mm width for 15 rain. P r e l i m i n a r y expe r imen t s showed that in these t ime in te rva l s the s a m p l e s were comple te ly heated to the t e m p e r a t u r e given.

An i l l u s t r a t i ve p resen ta t ion of the c h a r a c t e r of the de fo rmab i l i t y of magnet ic c a r r i e r s under uniaxial s t r e s s at t e m p e r a t u r e s f rom +20 to +80~ can be der ived f rom the de format ion d i a g r a m s in Fig . 2. The deformat ion curves of all magnetic c a r r i e r types examined at room t e m p e r a t u r e a r e a l so shown in this f igure. As can be seen f rom the f igures , the deformat ion d i a g r a m s a re monotonously r i s i n g cu rves whose ini t ia l s t r a igh t pa r t changes smoothly into a convex curve . This c h a r a c t e r of the cu rves ind ica tes that the m a t e r i a l examined was a l r e a d y cons ide rab ly o r ien ted during the manufac ture .

550

The s t r e s s f igures for all magnetic c a r r i e r types examined indicate that the mechanical p rope r t i e s a re cons iderably sca t tered , as is usual ly observed in tes t s on such po lymer ma te r i a l s .

To de te rmine the number of samples required for obtaining re l iable resu l t s , we tes ted the elongation of 300 samples of the magnetic PE-41u c a r r i e r . The s ta t i s t ica l evaluation of the exper imenta l r e su l t s was based on the assumpt ion that the normal distr ibution law holds, F o r this purpose the exper imenta l points were plotted on no rma l probabi l i ty paper . They were all found to be grouped f a i r l y c lose ly around the the- ore t ica l s t ra ight l ines predic ted by the normal dis tr ibut ion law (Fig. 3a, b).

F o r this r ea son the ave rages and the s tandard deviat ions were taken to be the probabi l i ty c h a r a c t e r - i s t ics of the s t rength and the deformabi l i ty . Since the empi r i ca l ave r ages and standard deviat ions a lso b e a r a s tochas t ic cha rac t e r , the re l iabi l i ty in terva ls we re de te rmined in o rde r to enhance the re l iabi l i ty of the es t imated dis tr ibut ion p a r a m e t e r s . F r o m these data we cons t ruc ted the ranges compr i s ing the ex- pe r imenta l cu rves of the s t rength and deformabi l i ty l imi t s with a probabi l i ty equal to 95%. The sca t t e r ing of the mechanical p r o p e r t i e s was cha rac t e r i zed by the var ia t ion coefficient v and the accuracy index p.

It was es tabl ished that to obtain s table sca t t e r ing c h a r a c t e r i s t i c s , it suff ices to t es t 25-30 samples .

F r o m the tes t s on all m a t e r i a l s examined we de te rmined the minimum, the maximum, and the a v e r - age values of the s t rength and deformabi l i ty p a r a m e t e r s , and also their sca t t e r ing c h a r a c t e r i s t i c s (Table 2).

Judged by the data of Table 2 and Fig. 3, the re la t ive sca t t e r ing of the mechanical p r o p e r t i e s is s o m e - what reduced when the t e m p e r a t u r e r i s e s . The re la t ive sca t t e r ing of the deformabi l i ty p a r a m e t e r s i s l a r g e r than that of the s t rength p a r a m e t e r s , all other tes t conditions being identical.

The t e m p e r a t u r e dependences of the propor t ional i ty l imi t apc and the cor responding re la t ive e longa- tion epc, the l imit ing s t rength r b and the m ax i mum elongation at rup ture emax, and the res idual elongation e 0 measured d i rec t ly a f t e r rupture , a re shown in Figs. 4-6, r e spec t ive ly .

As can be seen in the f igures , the strength c h a r a c t e r i s t i c s d e c r e a s e and the deformabi l i ty c h a r a c t e r - i s t ics inc rease when the t e m p e r a t u r e is ra i sed . It was found that the t ea r s t rength d e c r e a s e s by a fac tor 1.4-1.6, and the re la t ive elongation i nc rea se s by 20-30%, when the t e m p e r a t u r e is va r ied f rom +20 to +80~ in the t e m p e r a t u r e range examined the dependences of the s t rength and deformabi l i ty c h a r a c t e r i s - t ics genera l ly b e a r a l inear c h a r a c t e r . As the t e m p e r a t u r e is ra i sed , the propor t ional i ty l imi t d e c r e a s e s somewhat , but the re la t ive elongation cor responding to the propor t ional i ty l imi t tends to inc rease .

The propor t ional i ty l imit in the t empe ra tu r e range examined ave rages 30-40% of the l imit ing s t rength. The res idual elongation e 0 measured d i rec t ly a f t e r rupture , i nc rea se s not iceably with the t empera tu re . The e 0 value for all magnetic c a r r i e r s examined at +80~ equals about 80% of the max imum elongation ema x at rupture .

1. 2. 3. 4. 5.

6.

7.

L I T E R A T U R E C I T E D

Technique of Magnetic Recording [Russian t ranslat ion] , IL, Moscow (1965). Ch. Mi, Phys ics of Magnetic Recording [in Russian], Energiya, Moscow (1967). Theory and Technique of Magnetic Recording [Russian t rans la t ion ], Mir, Moscow (1968). Ya. A. Mazo, Magnetic Tape [in Russian], Eaergiya , Moscow (1968). M. S. Kalantarova, Phys icomechanica l P rocedu re s of Tes t ing Magnetic Tapes , Trudy VNIIRT, No. 11, 1 (1964). L. E. Amborsk i and D. W. F l ie r l , "Physical p rope r t i e s of polyethylene te rephtha la te f i lms, n Ind. and Eng. Chem. , 45 (1953). A. W. Meeuss, "Das Messen de r Eigenschaften eines Magnetbandes," Funk-Technik, 16 (1961).

551