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F r i c t i o n a n d W e a r o f A d v a n c e d C o m p o s i t e M a t e r i a l s
T . T s u k i z o e an d N . O h m a e
Osaka Univers i ty , Department o f Prec i s ion Eng ineer ing ,
Facu l ty o f Eng ineer ing , Ya m ada-K am i , Su i ta , Osaka (Japan)
S U M M A R Y
Fric t ion an d wear pro pert ies between u nidirect ional ly oriented f ibre-
re inforced plast ics an d carbon stee l have been investigated. A wide varie ty
o f f b re - re i n f o rc e d p l a s ti c s we re p re p a re d f o r e x p e r im e n t s ; t h e f ib re -
re in forcement s used were h igh- tens i le - s trength carbon fb re , h igh-
mod ulus carbon f ibre , E-g lass f ibre , s ta in le ss s tee l f i bre and ara mid ibre
( Kev lar-49) , whi le epox y res in , po lyes t e r res in a nd P T F E were employed
as mat r i x mater ia l .
The law of mix tu res in the calculat ion o f the f r ic t io n coef ficient o f
com posi te materials i s deduced, and the val idity o f this law is discussed by
a compar i son o f computed values wi th exper imenta l da ta .
The wear per form ances o f seven d i ff e ren t k inds o f f i bre -re in forced
plas t ic s are summari sed . Sur faces o f compo s i t e mater ia l s a f t e r wear are
s tud ied us ing scanning e lec t ron microscopy , and a m ode l i s prop osed
s ta t ing tha t the wear o f compos i t e m ater ia l sproceeds by wear- th inn ing o f
the . fi bre-re in forcement s , subsequent breakdo wn o f the f ibres and by
p e e l i n g - o f f o f t h e f i b re s f ro m t h e m a t r i x . T h e e q ua ti on o f we a r o fcompos i t e m ater ia ls is a lso prop osed s ta t ing tha t the Young ' s modulus
and in te r laminar shear s trength o f fbre -re in forc ed p las t i c s are the
in[tuential fa ct or s on their specif ic wea r rates.
1 . I N T R O D U C T I O N
A d v a n c e d c o m p o s i t e m a t e r ia l s , su c h as f i b r e - r e i n f o r c e d p l a s t i c s ( F R P ) o r
f i b r e - r e in f o r c e d m e t a l s ( F R M ) , h a v e r e c e iv e d h i g h l y t e c h n o l o g i c a l a n d
i n d u s t r i a l a t t e n t i o n in r e c e n t y ea r s . A m o n g t h e s e c o m p o s i t e m a t e r i a ls ,
F R P h a s b e e n p o t e n t ia l ly u s e f u l in m a n y f ie ld s o f i n d u s t r y b e c a u s e o f i ts
g o o d m e c h a n i c a l p r o p e r t i e s , e s p e c i a ll y i ts h ig h - s p ec i fi c s t r e n g th . F r i c t i o n
a n d w e a r p ro p e r t ie s o f F R P h a v e n o t b e e n fu l l y u n d e r s t o o d , a l th o u g hp i o n e e r in g r e s e a r c h b y L a n c a s t e r a n d G i l t r o w h a s s h o w n a n u m b e r o f
s i g n if i ca n t f a c t o r s a f f e ct in g t h e f r i c ti o n a n d w e a r o f F R P . 1 - 7 T h e p r e s e n t
a u t h o r s h a v e s t u d i e d t h e fr i c ti o n a n d w e a r o f u n i d i r e c t i o n a l l y o r i e n t e d
F R P in c o n t a c t w i t h c a r b o n s te e l, a n d d i s c u s s e d t h e i n fl u e n ce s o f t h e
v o l u m e f r a c t i o n o f t h e f ib r e s , a n d t h e k i n d s o f fi b re , a s w e l l a s t r i b o l o g i c a l
a n i s o t r o p y w i t h r e s p e c t t o s l id i n g d i r e c t i o n . 8 - iv
T h i s a r t ic l e r ev i e w s o u r r e c e n t w o r k o n t h e t r i b o l o g y o f F R P ; th e l a w o f
m i x t u r e s i n t h e c a l c u l a t io n o f th e f r i ct io n c o e f fi c ie n t o f F R P , w e a r
p e r f o r m a n c e s o f F R P , t h e w e a r r a te e s t im a t i o n b y a w e a r e q u a t i o n f o rF R P a n d a sy s te m s a p p r o a c h t o t he w e a r o f F R P .
2. E X P E R I M E N T A L P R O C E D U R E S
T h e u n i d i r e c t i o n a l l y o r i e n t e d f i b r e - r e i n f o r c e d p l a s ti c s w e r e p r e p a r e d b y
t h e l e a k y - m o u l d m e t h o d 14 t o o b t a i n a w i d e v a r i e ty o f f ib r e v o l u m e
f r a c t i o n s a n d a u n i f o r m d i s p e r s i o n o f t h e fi b re s in th e m a t r i x .
T a b l e 1 s h o w s t h e e ig h t k i n d s o f F R P u s e d i n t h e e x p e ri m e n t s . T y p i c a l
T A B L E 1Constitution of Composites Tested
N o . S y m b o l o f F R P F i b r e - re i n fo r c e m e n t s R e s i n - m a t r ic e s
1 H S - C F R P H i g h - s t r e n g t harbon fibre Epoxy resin or polyesterresin
Friction and wear of advanced composite materials 273
F i g . 4.
4,30
!8 ~29 FR P
, I l l L , i J
¢48( a ) ( b ) - -
Shapes o f spec imens for wear tes ts , a , Carb on s tee l; b , FR P.
i n F i g . 2 . F r i c t i o n e x p e r i m e n t s w e r e c o n d u c t e d u n l u b r i c a t e d i n a i r
( t e m p e r a t u r e 2 5 + 1 ° C , r e l at i v e h u m i d i t y 5 5 - 6 0 % ).
F i g u r e 3 s h o w s t h e w e a r - t e s t i n g a p p a r a t u s , ~4 a n d F i g . 4 t h e s h a p e s o f
t h e s p e c im e n s . W e a r t e s ts w e r e p e r f o r m e d a t a t e m p e r a t u r e o f 2 0 - 2 5 ° C
a n d a r e la t iv e h u m i d i t y o f 5 5 - 6 0 % .
T h r e e d i f f e r e n t sl i d in g d i r e c t i o n s a r e t o b e i d e n t i fi e d in o r d e r t o c l a r i fyt h e t r ib o l o g i ca l a n i s o t r o p y o f u n i d i r e c t io n a l l y o r i e n t e d F R P w i t h r e s p e c t
t o s l i d i n g d i r e c t i o n s . F i g u r e 5 i l l u s t r a t e s a n F R P b l o c k i n d i c a t i n g t h r e e
s l id i n g d i r e c t i o n s , i .e . , p a r a l l e l, a n t i - p a r a ll e l a n d n o r m a l d i r e c t i o n s .
:fix
Fig. 5. FR P block indic at ing sl iding directions.
Friction and wear of adranced composite materials 277
3 . 3 . W ea r pro per t ie s o f F R P
T h e r e s u lt s o f o u r w e a r t e s ts 9 - 1 4 h a v e s h o w n t h a t w e a r v o l u m e i n c r e a se s
l in e a r ly w i t h s li d in g d i s ta n c e ; n o r u n n i n g - i n p e r i o d o f w e a r h a s b e e na p p a r e n t . T h u s i t is p o s s i b l e to c h a r a c t e r i s e t h e w e a r i n te r m s o f a s p e c if ic
w e a r r a t e w , w h i c h h a s a u n i t o f m m 3 / N m . F i g u r e s 10 , 11 a n d 12
s u m m a r i s e w e a r p e r f o r m a n c e s o f s e ve n k i n d s o f u n i d ir e c t io n a l l y o r i e n t e d
F R P , t h e v o l u m e f r a c t io n o f w h i c h i s a p p r o x i m a t e l y 7 0 % ( se e T a b le s 4
a n d 6 ) . T h e s e t h r e e f i g u r e s s h o w t h e r e l a t i o n s h i p s b e t w e e n t h e s p e c i f i c
w e a r r a t e a n d t h e f r ic t io n c o ef f ic i e n t, t h e Y o u n g ' s m o d u l u s a n d t h e
i n t e r l a m i n a r s h e a r s t r e n g t h , r e s p e c t iv e l y . A s f o r t h e t r i b o l o g i c a l a n i s o t-
r o p y , i t se e m s t h a t e v e r y F R P h a s g o o d w e a r - re s is ta n c e i n n o r m a l a n d
p a r a l l e l s l id i n g b u t p o o r w e a r r e s i s t a n c e i n a n t i - p a r a l l e l s l id i n g . I n n o r m a ls l id i n g , e v e ry F R P e x c e p t A F R P s u f f e r e d 's e i z u r e ' a f t e r s e v e ra l k i l o m e t r e s
s l i d i n g d i s t a n c e , s o t h e s e d a t a a r e n o t g i v e n i n t h e t h r e e f i g u r e s .
F r o m t h e r e su l ts in F ig . 10, i t is e v i d e n t t h a t H S - C F R P a n d H M -
C F R P h a v e a s m a ll sp ec if ic w e a r r a t e o f t h e o r d e r o f 1 0 - 7 m m 3 / N m a n d a
l o w f r ic t i o n c o e ff ic i en t o f 0 .2 . I n c o n t r a s t , G F R P a n d S F R P s h o w a l a rg e
s pe cif ic w e a r r a te o f th e o r d e r o f 1 0 - 4 m m 3 / N m a n d a h ig h fr ic t io n
c o e f f ic i e n t o f 0 . 4. T h e l o w e s t f r i c t i o n c o e f f i c ie n t o f 0 .1 is o b t a i n e d f o r
C F R T P . T h e g o o d t r i b o lo g i c a l p r o p e r t i e s o f t h e c a r b o n - f ib r e - r ei n f o rc e d
p la st ic s g r o up ( C F R T P , N T - C F R P , H S - C F R P a n d H M - C F R P ) m a y b ec a u s e d b y t h e g o o d m e c h a n i c a l p r o p e r ti e s o f F R P , f o r in s ta n c e , h ig h
Y o u n g ' s m o d u l u s a n d h i g h i n t e r la m i n a r s h e a r s t r e n g th , a s w el l a s b y t h e
g o o d t r i b o l o g i c a l p r o p e r t i e s o f t h e f i b re s , e .g . , s e l f -l u b r i c a t i n g a b i l i ty a n d
h i g h s t r e n g t h .
F r o m t h e r e s u l t s i n F i g . 1 1 , i t i s n o t i c e d t h a t t h e F R P w i t h h i g h e r
Y o u n g ' s m o d u l u s a l w a y s sh o w s a b e t te r w e a r - r e s i st a n c e , a n d t h e
c o e f fi c ie n t o f c o r r e l a t i o n b e t w e e n t h e m is c a l c u l a t e d a s h i g h a s - 0 . 7 4 .
W h e n w e l o o k a t t h e r e s u lt s o f th e C F R P g r o u p i n F i g . 1 2, i t w i ll b e
n o t i c e d t h a t t h e i n t e r l a m i n a r s h e a r s t r e n g t h a l s o h a s a c l o s e r e l a t i o n w i t ht h e s p e c if ic w e a r r a t e ; t h e c o e f f i c ie n t o f c o r r e l a t i o n b e i n g e s t i m a t e d a t
- 0 . 8 8 .
3 . 4 . The w ea r equa t io n f o r F R P
F r o m t h e e x p e r i m e n t a l r e s u l t s a n d d i s c u s s i o n s i n t h e p r e v i o u s s e c t i o n s ,
a n d t h e sc a n n i n g e l e c t ro n m i c r o s c o p e o b s e r v a ti o n s o f w o r n F R P
F r i c t i o n a n d w e a r o f a d v a n ce d c o m p o s i t e m a t e r i a l s 279
s u rf a ce s ,S . 9A 1A,* t h e f o l l o w i n g m o d e l o f w e a r p r o c e s s e s c a n b e p r o p o s e d :
T h e w e a r o f F R P p r o c e e d s b y :
( a) w e a r - t h i n n i n g o f t h e f i b r e - r e i n f o r c e m e n t s ;( b) s u b s e q u e n t b r e a k d o w n o f t h e f ib r e s;
( c) p e e l i n g - o f f o f t h e f ib r e s f r o m t h e m a t r i x .
A s e q u e n t i a l o c c u r r e n c e o f t h e s e p r o c e s s e s g o v e r n s th e w e a r o f F R P . T h e
e s s e n t i a l f a c t o r s a f f e c t i n g t h e s e t h r e e p r o c e s s e s m a y b e a s f o l l o w s :
( a) i n t h e w e a r - t h i n n i n g o f t h e f i b r e s - - l o a d W a n d s l id i n g d i s t a n c e D ;
( b) in t h e b r e a k d o w n o f t h e f i b r e s - - s t r a i n lap/Eo f th e F R P c a u s e d b y
f r i c ti o n f o r c e , l o a d W a n d s l i d i n g d i s t a n c e D ;
(c ) in t h e p e e l i n g - o f f o f t h e f ib r es f r o m t h e m a t r i x - - i n t e r l a m i n a r s h e a rs t r e n g t h I s o f t h e F R P , s t r a i n lap/Eo f t h e F R P , l o a d W a n d s l i d in g
d i s t a n c e D . T h e r e f o r e , w e a r v o l u m e Q c a n b e g iv e n b y
1 D ) ( 1 0 )
A s f o r f i r s t - o rd e r a p p r o x i m a t i o n , w e c a n a s s u m e
# p lQ=k-~ ~ WD ( l l )
w h e r e k is a d i m e n s i o n l e s s c o n s t a n t . T h e n t h e s p e c if ic w e a r r a t e wr c a n b e
w r i t t e n a s
w~ = k / t p 1 ( 1 2 )E / s
o r
w r /s = k ( 13 )
Ew h e r e WrI a n d kpp/E a r e b o t h d i m e n s i o n l e s s q u a n t i ti e s . F i g u r e 13 s h o w s
t h e r e l a t i o n s h i p b e t w e e n wrIs a n d k#p/E u n d e r v a r i ed n o r m a l p r e ss u r e p
o f l , 1 .5 a n d 2 N / m m 2 f o r s e v e n k i n d s o f F R P . T h e s o l i d li n e i n t h i s f i g u r e
s h o w s t h e e x p e r i m e n t a l v a l u e s f o r p = 1 .5 N / m m 2, a n d t h e w e a r e q u a t i o n
a t a c o n s t a n t n o r m a l p r e s s u r e p i s g i v e n b y
Friction and wear of advanced composite materials 281
is a f fe c t e d b y a n u m b e r o f v a r ia b l e s . T h u s i n o r d e r t o i d e n t i fy t h e
p r e d i c t o r v a r i a b l e s o f t h is s y s t e m , th e s t e p w i s e m e t h o d s ( b o t h f o r w a r d
a n d b a c k w a r d ) w e r e e m p l o y e d . T h e w e a r o f F R P w a s t r ea t e d a s a s t a t ic s
m o d e l w h e r e t h e b l a c k - b o x c u t t i n g w a s m a d e t o e s ta b l i sh a h i e r a rc h i c a ls y s t e m s m o d e l .
4 . 1 . S e l e c t i o n o f p r e d i c to r v a r i a b l es
A m u l t i p l e re g r e s s io n a n a l y s i s m o d e l is e x p r e s s e d b y
o r b y
I ! l ] ¸ [ i x x l• n X n l " " " X n p
I ! ° l + [ ! l n( 1 6 )
y = X f l + s ( 1 7 )
T h e n , a r e s id u a l s u m o f s q u a r e s i s w r i t t e n a s
S-~-gT.g
= [y - X /J] r . [y - X/~] (18)
T h e n o r m a l e q u a t i o n d e r iv e d f r o m e q n (1 8) le a d s to
fl = ( X T X ) - 1 X T y ( 19 )
U s i n g t h e l e a st s q u a r e s e s t i m a t e / ~ d e r i v e d f r o m e q n ( 19 ), w e o b t a i n
y = X/~ (20)
A n o r m a l i s a t i o n is m a d e o n e a c h v a r i a b le i n su c h a w a y t h a t t h e a v e r a g e
is z e r o a n d t h e v a r i a n c e i s u n i ty . T h e n o r m a l i s a t i o n e x c l u d e s th e p r o b l e m
o f u n i t s o f v a r ia b l e s . T h e s i g n i fi c a n c e o f m u l t i p l e r e g r e s s i o n i s t e s t e d b y
t h e v a r i a n c e a n a l y s i s .P r e d i c t o r v a r i a b le s a r e s e le c t e d b o t h b y s te p w i s e f o r w a r d a n d b a c k -
w a r d m e t h o d s . T h e f o r m e r i s b a s e d o n t h e c o r re l a t i o n , w h i le t h e la t te r o n
t h e m u l t ip l e c o r r e l a t i o n . I n a n a c t u a l o p e r a t i o n , a s e q u e n t ia l c a l c u l a t io n
o f th e s e a n a l y s e s i s m a d e b y a l a r g e - sc a l e c o m p u t e r ( F i g . 14).
F i v e m e c h a n i c a l p r o p e r t i e s w e r e t a k e n i n t h e s te p w i s e m e t h o d s ; t e n s i le
s t r e n g t h a B, Y o u n g ' s m o d u l u s E , b e n d i n g s t r e n g t h B , B a r c o l h a r d n e s s H
a n d i n t e r l a m i n a r s h e a r s t r e n g t h I~. I t w a s f o u n d t h a t t h e m o s t s i g n if ic a n t
p a r a m e t e r t o th e w e a r o f F R P is E a n d t h e s e c o n d m o s t s i gn i fi c a n t
F r i c t i o n a n d w e a r o f a d v a n c e d c o m p o s i t e m a t e r i a l s 283
para m ete rs a re aB an d I S. Th ere fo re , t he p resen t sy s t ems ana lys i s ag rees
w i t h e q n (1 2) c o n c e rn i n g t h e s i gn i f ic a n c e o f E a n d I So n t h e w e a r o f F R P .
4 . 2 . M o d e l b u i l d in g
Fi g u re 15 is a mo d e l o f t h e FR P w e a r s y s t e m. W e a r o f FR P p ro c e e d s fi rs t
b y w e a r - t h i n n i n g o f t h e f ib r es , t h e n b y b r e a k d o w n o f t h e fi br e s a n d f i n a ll y
by pee l ing -o f f o f t he f ib res , a s p ro po sed in Sec t ion 3.4 . F ro m a heu r i s t i c
o,o
SLI Di HGVELOCITY
TYPE OFFRP
SUB SYSTEIv
1
FRICTION
[ ]
SUB SYSTEM
2
RISE OF
TEMPERATURE
[]
SUB SYSTE]~
3
CHANCE IN
MECHANICAL
"-" PROPERTIES
[]
F i g . 15. Approach by systems methodology-hierarchical modelling.
c r i te r i o n th a t t h e w e a r o f F R P is c a u s e d b y a d e g r a d a t i o n o f m e c h a n i c a l
p ro p e r t i e s , t h e b l a c k -b o x c u t t i n g w a s d o n e ; s u b s y s t e m 1 i d en t if ie s t h e
f r ic t io n , s u b s y s t e m 2 , t h e s u r f ac e t e m p e ra t u r e , a n d s u b s y s t e m 3 , t h ed e g r a d a t i o n o f F R P d u e t o t e m p e r a t u r e r i s e .
A n i n p u t - o u t p u t r e l a ti o n o f e a c h s y s t e m is w r it te n a s
/a = f l ( W , v , M ) s u b s y s t e m 1 (2 1)
A T = fz ( / a , W , v , M ) s u b s y s t e m 2 (2 2)
A E = f 3 (A T , M ) }
A I S = f 4 ( A T , M ) subsys t em 3 (23 )
A a a = f s ( A T , M )
w h e re f is t h e c r i te r i o n fu n c t i o n , M is a p ro p e r t y o f ma t e r i a l, A T i s
t e mp e ra t u r e r i s e , a n d A E , A IS and A trB a r e t h e c h a n g e s i n Y o u n g ' s
m o d u l u s , i n t e r l a m i n a r s h e a r s t r e n g t h a n d t e n s i l e s t r e n g t h o f F R P ,
r e s p ec t iv e l y . A s s u m i n g a f u n c t i o n o f
Friction and wear of adt,anced composite materials 285
5. C O N C L U S I O N S
F r o m i n v e s t i g a t i o n s o n t h e u n l u b r i c a t e d f r i c t i o n a n d w e a r b e t w e e n
u n i d i r e c t i o n a l l y o r i e n t e d F R P a n d c a r b o n s te e l, th e f o l lo w i n g r es u lt s w e r eo b t a i n e d :
1. T h e l a w o f m i x t u r e s in t h e c a l c u l a t i o n o f t h e fr i c t io n c o e f f ic i e n t o f
F R P w a s d e d u c e d , a n d t h e v a li d i ty o f t h is la w w a s c o n f i r m e d b y
t h e e x p e r i m e n t a l r e s u l t s .
2 . C F R P g a v e a s m a l l s p ec i fi c w e a r r a t e a n d a lo w f r i c ti o n c o e f fi c ie n t .
I n c o n t r a s t , G F R P a n d S F R P p r o v i d e d l a r ge sp e ci fi c w e a r r a te s
a n d h i g h f r i c t i o n c o e f f i c i e n t s . T h e l o w e s t f r i c t i o n c o e f f i c ie n t o f 0 .1
w a s o b t a i n e d w i t h C F R T P .3. A m o d e l w a s p r o p o s e d s t a ti n g t h a t t h e w e a r o f F R P p r o c e e d s b y
t h e w e a r - t h i n n i n g o f t h e f ib re s w i t h s u b s e q u e n t b r e a k d o w n o f t h e
f ib r e s a n d b y p e e l i n g - o f f o f t h e f ib r e s f r o m t h e m a t r i x . U s i n g t h i s
m o d e l , t h e e x p e r im e n t a l e q u a t io n f o r th e w e a r o f F R P w a s
d e d u c e d . I t w a s f o u n d , b y c r i ti c is i ng th i s w e a r e q u a t i o n , t h a t t h e
m o s t s i g n if ic a n t p a r a m e t e r s i n t h e w e a r o f F R P a r e Y o u n g ' s
m o d u l u s a n d i n t e r la m i n a r s h e a r s tr e n g th .
4 . A m e t h o d o f s y s t em s a n a l y s is w a s a p p l i e d t o t h e w e a r o f F R P . T h e
s p ec if ic w e a r r a t e w a s f o u n d t o h a v e a c lo s e c o r r e l a t i o n w i t hY o u n g ' s m o d u l u s , t e n si le s t r e n g t h a n d i n t e r l a m i n a r s h e a r s tr e n g t h .
T h e t o t a l s y s t e m a t i c p r o g r a m m i n g s w e r e p e r f o r m e d ; t h e m o d e l
p r e d i c t e d t h e s p e ci fi c w e a r r a t e .
R E F E R E N C E S
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12. T. Tsukizoe and N. Ohmae, Friction and wear of with parallely oriented
fibre reinforced plastics--tribological assessment for CFRP, GFRP andSFRP, J. Japan Society of Lubrication Engrs, 21(5) (1976) p. 330 (in
Japanese).13. T. Tsukizoe and N. Ohmae, Friction properties of composite materials,
Trans. Japan Society of Mech. Engrs, 43(367) (1977) p. 115 (in Japanese).14. T. Tsukizoe and N. Ohmae, Wear mechanism of unidirectionally oriented
fibre-reinforced plastics, Trans. ASME, 99(4) (1977) p. 401.15. T. Tsukizoe, Friction and wear of fibre reinforced plastics, J. Japan Society
of Lubrication Engrs, 23(1) (1978) p. 11 (in Japanese).16. M. Yukumoto, T. Tsukizoe and N. Ohmae, Systems approach to the wear of
fibre-reinforced plastics, J. Japan Society of Lubrication Engrs, 23(12)
(1978) p. 881 (in Japanese).17. N. Ohmae, M. Yukumoto and T. Tsukizoe, Analysis of System Structure in
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