fibre orientation distribution in short fibre reinforced plastics

8/3/2019 Fibre Orientation Distribution in Short Fibre Reinforced Plastics

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J O U R N A L O F M A T E R I A L S S C I E N C E 1 0 ( 19 7 5) 9 L E T T E R S

~ 0

7O

6 O

50

~40

2 O

0 lO 0 30 40 50 ~ 7

T I M E ( m i n u t e s )

Figure 2 Wetting of borosilicate glass on evaporated thin

film of chromium in wet and dry N2 at 900~

in dry and wet N~ indicate that introducing a wetatmosphere is an effective way of lowering and

maintaining the wetting angle. Dry nitrogen-containing atmospheres, on the other hand, seemto raise the wetting angle with prolonged time.The mechanism contributing to this increase inwetting angle is not known for certain, but it

coincides with the deveiopment of mostlynitrides and a small amount of oxides in thesurface of the film [5]. Whereas a continuouslayer of Cr~O3 is always present in the surface ofthe film in wet atmospheres, both oxides (oxideshaving been formed from 3 to 5 ppm O3impurity in N2) and nitrides are present in dryatmospheres. This implies that chromium oxidescontribute to better wetting than nitrides.Unfortunately, no data are available to prove or

disprove the effect of chromium nitrides.It appears that water vapour lowers the

wetting angles in both glass-ceramic and glass-metal systems. The mechanism by which thisoccurs is not known for certain, but it appears to

be largely due to lowering surface energy of glassby water vapour.

R e f e r e n c e s

1. J . A . ]" A s K a nd R . M . F U L R A T H , J. A me r. Ce ra m. So c.

4 5 ( 1 9 6 2 ) 5 9 2 .

2. B. W. KIN G~ I-I . P. TRI PP and w . H . D U C K WO R T H ,

i b i d 4 2 ( 1 9 5 9 ) 5 0 4 .

3 . M . L . V O L P E , R . M . F U L R A T H a n d J . A . P A S K , i b i d

4 2 ( 1 9 5 9 ) 1 0 2 .

4 . N . M . P A R I K H , ib id 4 1 ( 1 9 5 8 ) 1 8 .

5. v. BROSlC and E. I. A L L E S A N D R I N I , J . Vae . Sc i .

Tech. 9 (1972) 83.

Rece ived 5 Augus t

and accep ted 20 Novemb er 1974R . R . T U M M A L A

B . J . F O S T E R

Glass Development Department ,

IB M E a s t F i sh k il l, N e w Y o rk , U S A

F i b re o r i e n t a ti o n d i s t r ib u t i o n i n s h o r t f i b r er e i n fo r c e d p l a s t i c s

A knowledge of the fibre orientation distribution

is an essential pre-requisite in seeking to predictthe deformation behaviour of a short-fibrereinforced plastic. For asbestos fibres, wide-angle X-ray diffraction techniques have beenapplied with some success to the determinationof the variation of fibre orientation distributionwith position in an injection moulding [1 ]. Thispowerful technique cannot be applied in theimportant area of short glass-fibre reinforcedthermoplastics and alternative techniques mustbe sought.

The texture that is often visible in mouldingswhen examined in transmitted light or by

906

(macro) radiography is not necessarily related tothe orientation of the well-dispersed fibres thatare primarily responsible for the enhancement of

the mechanical properties. Such texture or flow

markings have been found to be misleading whenpredicting mechanical response [2].

Examination of individual fibre orientationhas been widely performed using microtomedsections or surfaces prepared by the metallo-graphic polishing technique. The latter tech-nique is far more widely used since it is notrestricted to translucent mouldings and causesless damage to the fibres and less disruption oftheir orientation. It is, however, a time con-suming and laborious task with the resultssometimes disappointing due to lack of contrastbetween the fibre and matrix.

9 1 9 7 5 C h a p m a n a n d H a l l L t d .



J O U R N A L O F M A T E R I A L S S C I E N C E 1 0 ( 1 9 7 5 ) 9 LETTERS

These d i f f icu lt ies a re remo ved by the use of the

t echn i que o f con t ac t m i c ro - r ad i og raphy (C M R )

[3] which has been ex tens ive ly appl i ed to b io-

log ica l mater i a l s for 20 years . CM R i s a modi f i ed

rad iographic t echnique in which the spec imen

t h ickness i s r educed i n o rde r t ha t t he num ber o f

images cas t does not c onfuse the to t a l p i c ture . Af ine gra in f i lm and developer a re used to enable

enlarged images of the nomina l 10 gm diameter

f ibres to be ma de w i thout pro blems of gra in s i ze .

F i na ll y , t he geom e t ry o f t he sy s tem fo r C M R is

chos en so th at th e f ibre sha dow is sufficiently wel l

reso lved to be c l ear on the f inal en largement s .

The reso lu t ion obta inable i s cont ro l l ed by the

f i lm gra in s i ze and the wid th of the pe nu mb ra [3 ] .

T he K o dak H i gh R eso l u t i on P l at e em p l oyed has

a gra in s i ze of 0 .25 gm w hich i s near the reso lu-

t ion l imi t o f t he opt i ca l microscope , permi t t ing

magn i f i ca t ion of x 500 wi tho ut d i ff i cu l ty . In the

wors t case of a f ib re ly ing on the f ree surface of a

100 gm th ick spec imen in contac t wi th theem ul s ion , t he penu m bra w i d t h o f t he f i bre

image ma y be m ade l ess than the f i lm gra in s i ze

by se t ting the focus- to- f i lm d i s t ance a t 50 cm. I f ,

i ns t ead o f a norm al focus X-ray tube , a f ine

focus tube i s used , t h is ma y be reduc ed to 25 cm.

The cont ras t be tween the image of the f ib re

and t he backg round m a t r i x depends upon t he

( a )

fig 2

f ig 1

( c , e )

Figure 1 Fibre orientation distributionin an injection moulded ASTM tensilebar of glass fibre reinforced nylon 66.(a) Location of section cut from barand areas of section presented in ac-companying figures. (b) and (c) Photo-graphs of two parts of the surface asprepared by metallographic polishing.(d) and (e) Photograph produced fromthe micro-radiograph of the section,corresponding to the parts illustrated in(b) and (c).

907



J O U R N A L O F M A T E R I A L S S C I E N C E 1 0 ( 1 9 7 5 ) - L E T T E R S

Figure 2 Variation o f fibre orientation through the thickness direction for the moulding shown in F ig. 1, determinedusing the CM R technique. (a) View from top to bo ttom surface (the approximate site of th is photograph on themicro-radiograph of the section is shown in Fig. 1a). (b) Part of the central region of Fig. 2a at higher magnification.

th i ckness of the f ib re in the d i rec t ion of the X -ray

beam and t he d i f fe r ence be t w een t he X - ray

absorp t ion coeff i c i en t s of t he f ib re and mat r ix .

Since this di fference increases wi th X -ray

wavelength , t he sof t e r rad ia t ions a re more

des i rab le . In prac t i ce , however , unf i l te red copp er

rad ia t ion i s found to g ive sa t i s fac tory resu l t s

and the shor t es t exposure t imes .

T he op t i m um spec i m en t h i cknes s fo r C M R

var ies wi th f ib re conten t and the or i en ta t ion of

the f ibres in the sect ion. Usual ly i t l ies in the

range o f 50 to 150 gm . The surface condi t ion i s

re l a t ive ly unimpor tan t ; t he only requi rement s

are tha t t he f ibre or i en ta t ion i s no t d i s turbed by

the cu t t ing process and tha t t he cu t t ing debr i s is

removed. Such spec imens a re eas i ly prepared

us ing a low-speed d iamond cu t t ing saw.

A s a com par i son o f t he C M R t echn i que w i t h

the convent iona l sec t ion ing and pol i sh ing

m e t hod , an i n j ec ti on m ou l de d A S T M t ens il e ba r

of g l ass re inforced nylon 66 has been mounted

and pol i shed on the p l ane shown in F ig . l a . T wo

micrograp hs o f the surface a re shown in F ig . l b

908

and c. A 100 gm sl ice was then re mo ved

para l le l t o an d inc luding the pol i shed surface and

exam i ned by t he C M R t echn i que . F ig . l d and e

are th en the ide nt ical f ields of view to tho se o f

Fig. lb and c, excep t tha t the f ibres seen are

not on ly those tha t penet ra t e the pol i shed surface

but a l so a ll t hose under nea th the surface to a

depth of 100 gm. The c l earer representa t ion

of f ib re or i en ta t ion d i s t r ibu t ion by the CMR

technique i s apparent . An unexpected l ack of

symm et ry in the f low pa t t e rns in the two corners

o f t he m ou l d i s show n m uc h m ore c l ea rl y

by the C M R t echn i que .

T he C M R t echn i que i s ex t r em e l y u se fu l fo r

examining the through- th ickness f ib re or i en ta-

t ion d i s t r ibu t ion in mould ings , as i l l us t ra t ed in

Fig. 2. This represents a sect ion near the centre

of the sl ice ident i f ied in Fig. la . Th e relat ively

high degree of f ib re a l ignment a long the ax i s of

the bar , and the t ransverse or i en ta t ion in the

cent ra l zone are read i ly apparent .

A m icro-rad iograp h of a sl ice f rom a com-

merc ia l mou ld ing in p igmented shor t g l ass f ib re



J O U R N A L O F M A T E R I A L S S C I E N C E 1 0 ( 1 9 7 5 ) , L E T T E R S

Figure 3 Part of a micro-radiograph of a slice cut from acommercial injection moulding produced in pigmented,

short glass fibre reinforced thermoplastic polyester.

Figure 4 Part of a micro-radiograph of a slice cut from acommercial moulding in a dough moulding compound.

re inforced thermoplas t i c polyes ter i s presented

in Fig . 3. The f low around a corne r is shown w i th

the turbulent eddy f low region on the down-

s t r eam s ide of the corner . I t i s apparen t tha t the

observat ion of the f ibre d i s t r ibut ion i s not

h indered b y the presence of the p igment . Fur the r -

more , the r adiograph enables the d i sper s ion of

the p igment par t i c l es to be examined as pre-

vious ly r epor ted for un- re inforced polym ers [4].In ano ther r egion of the same radiograph, the

meet ing of two f low fronts was clear ly vis ible.

F ig. 4 shows an exam ple of a doug h m oulding

com p ound . The h i gh pe r cen tage o f f il le r

mater i a l, and the presence of h igh a tomic num -

ber addi t ives has not in t er fered wi th the obser -

vat ion of the f ibre dis t r ibut ion, which is seen to

be f ar f rom uni form in d i sper s ion or or i enta-

t ion . The t echnique has a l so been appl i ed

success fu l ly to sheet moulding compounds .

In addi t ion to the c l earer r epresenta t ion of

or i enta t ion , the CMR technique i s l es s t ime-consuming s ince the specimen prepara t ion by

diamond saw i s s t r a ight forward and semi -

automat i c . Al th oug h a s igni fi cant volum e of the

sample is imaged, al l f ibres lying through the

thickness o f the s l ice are proje cted in focus , on to

the p lane of the photographic f i lm. Thi s ensures

tha t in subsequent examinat ion of the f i lm by

high magni f i ca t ion opt i ca l microscopy, there are

no d epth of fi e ld problems as are encoun tered in

the examinat ion of micro tom ed sec t ions .

The use of a s l ice (of kno wn th ickness ) whose

thickness is s ignif icant ly less than the mean

f ibre length sugges ts the poss ibi l i ty o f es t imat ing,

f rom the r adiograp h, the or i enta t ion of the

f ibres to the plane of the s l ice ( in addi t ion to the

obvious de term inat ion o f the or i enta t ion in the

projec ted p lane) . The three-dimens ional or i enta-

t ion d i s t r ibut ion th roug h the th ickness of a

moulding could then be as ses sed f rom a r adio-

graph of one s l i ce cut perpendicular to the

moulded sur face . However , unles s the f ibredi s t r ibut ion i s symmet r i ca l about the p lane

of the s l ice, the angle of the f ibre to the plane of

the s l i ce cannot be de termined unambiguous ly

f r om one s uch r ad i og r aph .

The us e o f s t e r eo - CM R [ 3] m ay ove r com e th is

problem. Al ternat ive ly , the examinat ion of

several s l ices cut at a var iety of angles f rom the

mou lding could be under t ak en. In pr inc ip le , bo th

techniques offer the poss ibi l i ty of obtaining

quant i t a t ive informat ion on the three-dimen-

s ional f ibre or i enta t ion d i s t r ibut ion through the

moulding. Thi s speci f i ca t ion would then beequivalent to the X- ray pole f igure s tudy on

an asbes tos r e inforced polym er ment ion edabove .

Acknowledgement

The author s thank the Science Research Counci l

for a grant in su ppor t of th i s work .

References1 . M . W . D A R L I N G T O N a n d P . L . M C G I N L E Y , D e p a r t -

m e n t of Materials Report, March 1974, to bepublished:

9(]9



J O U R N A L O F MA T E R I A L S S C I E N C E 1 0 ( 1 9 7 5) . L E T T E R S

2. M. W. D A R L I N G T O N ~ P . L . MC G I N L E Y a n d G. R.

S M I T H , t o b e p u b l i s h e d .

3 . A . E ~q G ST R O M , i n " P h y s i c a l T e c h n i q u e s i n B i o l o g i c a l

R e s e a r c h " , V o l . 3 , e d i t e d b y G . O s t e r a n d A . W .

P o l l i s t e r (A c a d e m i c P r e s s , N e w Y o r k , 1 9 5 6) p . 4 9 5 .

4 . c . G . W A T E R F I E L D a n d J . P E A C O C K , S.P.E. Tech.

Papers 19 (1973) 393 .

Received 29 Novemberand accepted 11 December 1974

M. W. D A R L I N G T O N

P . L . MC G I N L E Y

Department o f Materials,

Cranfield Institute o f Technology,Cranfield, Bedford, UK

H an d b ook o f M ater ia l s S c ien ce

Edi ted by Char les T . Lynch Ph .D.

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fibre orientation distribution in short fibre reinforced plastics

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