An analysis of the mechanical behavior of Al-Al 3 Ni composites
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PREVIOUSwork on d i r e c t i o n a l l y solidified c o m p o s ites has shown that in many c a s e s the s i m p l e rule of m i x t u r e s f a i l e d to a c c u r a t e l y p r e d i c t t h e i r m e c h a n i c a l behavior. I-4 The main drawback of the r u l e of m i x t u r e s was found to be that it does not take into account the t r a n s v e r s e s t r e s s e s r e s u l t i n g f r o m the difference of P o i s s o n ' s r a t i o of the composite p h a s e s , s'6 Also, the i n t e r f i b e r spacing and the f i b e r i m p e r f e c t i o n s a r e not accounted for. %8 S e v e r a l investigations have been made to a s s e s s the s e p a r a t e effects of the above f a c t o r s on the strength, 9-1~ but no single model is found where all the f a c t o r s a r e c o n s i d e r e d . Also none of the e x i s t i n g m o d e l s d e a l s with both the t e n s i l e and c o m p r e s s i v e p r o p e r t i e s of fiber reinforced composites. In the p r e s e n t work a model is p r o p o s e d to p r e d i c t the m e c h a n i c a l p r o p e r t i e s of fiber r e i n f o r c e d c o m p o s i t e s in tension and c o m p r e s s i o n . The model takes into c o n s i d e r a t i o n the difference in P o i s s o n ' s r a t i o of the p h a s e s , i n t e r f i b e r spacing, and discontinuity and p r e m a t u r e f r a c t u r e of f i b e r s . The v a l i d i t y of the model is checked a g a i n s t the e x p e r i m e n t a l r e s u l t s obtained for A1-A13Ni eutectic c o m p o s i t e s of widely d i f f e r e n t structures. EXPERIMENTAL PROCEDURE Unidirectional Solidification All-AlsNi eutectic alloy ingots w e r e p r e p a r e d f r o m aluminum 99.78 pct p u r i t y and Al-18 pct Ni m a s t e r alloy. Melting was c a r r i e d out in an alumina c r u c i b l e under argon. The homogenized alloy had a c o m p o s i tion 6.19 pct Ni, 0.2 pct Fe, 0.15 Si, 0.02 Mn, 0.01 Cu, balance Al. Rods 8.5 mm in diam and 160 mm long were p r e p a r e d from the c a s t ingots by hot extrusion. These r o d s w e r e then d i r e c t i o n a l l y solidified in v e r t i cal graphite c r u c i b l e s in an argon a t m o s p h e r e . D i r e c t i o n a l s o l i d i f i c a t i o n was a c c o m p l i s h e d by withdrawing the e l e c t r i c a l r e s i s t a n c e heating furnace which MAHMOUDM. FARAG is AssociateProfessor of MaterialsEngineering, The AmericanUniversityin Cairo, Egypt. MOHAMEDH. ABD EL LATIF is Lecturer of MechanicalEngineering,Ain Shams University, Cairo, Egypt. Manuscript submitted June 25, 1974. METALLURGICALTRANSACTIONSA
had an attached water s p r a y c o l l a r to i n c r e a s e the t e m p e r a t u r e g r a d i e n t and to e n s u r e that the solidification speed was the s a m e as that of the furnace withdrawal speed. The growth r a t e s w e r e v a r i e d in the range 9.63 • 10 -z to 1.0 m m / s and the t e m p e r a t u r e gradient was kept a l m o s t constant at 18 K / m m . Mechanical Testing Standard Hounsfield t e n s i l e s p e c i m e n s , 3.
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