40P

MODEL STUDY OF STRESSES I N GROOVED T A B L E T S UNDER D I A M E T R A L COMPRESSION J , M . Newton*, P , S t a n l e y , * * & C.S, Tan**, Departments of Pharmacy* and Mechanical Engineering**, Nottingham U n i v e r s i t y , Nottingham, NG7 2RD

The t e n s i l e f r a c t u r e stress o f plane-faced c y l i n d r i c a l t a b l e t s can be derived from t h e r e s u l t s of d i a m e t r a l compression t e s t s u s i n g t h e s t a n d a r d stress s o l u t i o n (Den Hartog, 1952), Commercial p h a r m a c e u t i c a l t a b l e t s , however, are seldom of t h e simple p l a n e - f a c e d c y l i n d r i c a l form; t h e e f f e c t s o f d e p a r t u r e s f r o m t h i s form on t h e stress d i s t r i b u t i o n and f r a c t u r e c h a r a c t e r i s t i c s a r e l a r g e l y unknown and f r a c t u r e stress v a l u e s cannot t h e r e f o r e be r e a d i l y derived from t h e r e s u l t s o f d i a m e t r a l compression t e s t s , A ' b r e a k - l i n e ' , i n t h e form of a d i a m e t r a l groove, i s a common f e a t u r e of p h a r m a c e u t i c a l t a b l e t s ; t h e effects of such a groove on t h e stresses i n a s e r i e s of c y l i n d r i c a l ' t a b l e t s ' Subjected to d i a m e t r a l compression have been s t u d i e d u s i n g t h e t h r e e - d i m e n s i o n a l ' f r o z e n stress' p h o t o e l a s t i c t e c h n i q u e ( D u r e l l i & R i l e y , 1 9 6 5 ) . The model m a t e r i a l A r a l d i t e CT200; t h e m a n u f a c t u r i n g , l o a d i n g , s l i c i n g and a n a l y s i s of t h e models ( d i a m e t e r 5.08 cm, t h i c k n e s s 0.635 cm) were a s d e s c r i b e d by S t a n l e y (1968). E~~~ model c o n t a i n e d a d i a m e t r a l groove on one f a c e , w i t h a t i p r a d i u s o f 0 . 0 3 8 cm The models were and a 90° i n c l u d e d a n g l e , The groove d e p t h was v a r i e d . o r i e n t a t e d w i t h t h e groove e i t h e r c o i n c i d e n t w i t h t h e loaded d i a m e t e r (groove v e r t i c a l ) o r p e r p e n d i c u l a r t o i t (groove h o r i z o n t a l ) ; a p l a n e - f a c e d model was also tested, To f a c i l i t a t e comparison, r e s u l t s were e x p r e s s e d i n t h e form of d i m e n s i o n l e s s ' s t r e s s f a c t o r s ' i . e , stress f 2P/ndt ( P , l o a d : d , d i a m e t e r : t , t h i c k n e s s ) ; s u r f a c e v a l u e s a t t h e c e n t r e o f each model ( i o e o a t t h e groove t i p and t h e c e n t r a l p o i n t on t h e p l a n e f a c e ) , i n a d i r e c t i o n p e r p e n d i c u l a r t o t h e a p p l i e d l o a d , a r e t a b u l a t e d below, The c o n s i d e r a b l e e f f e c t of t h e groove on t h e stress a t t h e c e n t r e o f t h e t a b l e t i s e v i d e n t ; t h e o c c u r r e n c e o f compressive stresses ( i n d i c a t e d by t h e minus sign) a l o n g t h e t i p of t h e d e e p e r h o r i z o n t a l grooves and t h e a s s o c i a t e d i n c r e a s e i n t h e t e n s i l e stress on t h e p l a n e f a c e , are o f p a r t i c u l a r i n t e r e s t i n t h e i n t e r p r e t a t i o n of f r a c t u r e t e s t r e s u l t s f o r grooved t a b l e t s . Table.

Maximum stress f a c t o r s , p e r p e n d i c u l a r t o t h e a p p l i e d l o a d , a t c e n t r e o f grooved t a b l e t models s u b j e c t e d t o d i a m e t r a l c o m p r e s s i o n .

Groove depth cm No groove 0.051 0.102 0.153 0,203

Maximum stress f a c t o r Groove v e r t i c a l Groove h o r i z o n t a l A t groove t i p On p l a n e f a c e A t groove t i p On p l a n e f a c e 1.00 1.24 2.51 3,51 4-26

1.00 0.99 0.89 0.77

0.60

1.00 0.63 0.09 -0.31 -0.93

1,oo 1.05 1.17 1.39 1.93

D u r e l l i , A . J . & R i e l y , W.F. (1965). I n t r o d u c t i o n t o Photomechanics. P r e n t i c e H a l l , Inc/Englewood C l i f f s , N , J . S t a n l e y , P. (1968). E x p e r i m e n t e l l e Tech, d e r Phys. XVI, 201-216. Den H a r t o g , J , P . (1952), Advanced S t r e n g t h o f M a t e r i a l s , McGraw-Hill, N e w York.