16.26 Problem Set #7	4/28/97
	Due 5/5/97

1. Consider the following results from Bushby and Scott, "Evaluation of Aluminum-Copper Alloy Reinforced with Pitch Based Carbon Fibres", Composites Science and Technology 57 (1997) 119-128. A composite is made and heat treated such that the matrix is in either the "Cast" condition or the "Peak-aged" condition. The modulus of the matrix in these conditions is identical, but the modulus of the composite, when cooled from manufacturing temperatures and then immediately tensile tested, is not.

   The manufacturing temperatures are above 500°C for the cast composite; the final processing of the aged composite is at around 170°C. The fiber volume fraction in both cases is 50%.

   Analyze these results. What is the expected (elastic) modulus of the composite? How do you explain the low modulus of the cast composite? It looks to me like the in-situ yield stress of the matrix in the aged composite is even higher than that of the alloy (this is not noted in the paper, by the way...); why do I think this? (it is possible that I am confused...).

   		Modulus (GPa)	CTE (microstrain/C)	Yield Stress (MPa)
   Alloy	Cast	70	24	20
   	Peak aged	70	24	210
   P55 Fiber		380	-0.9
   Composite	Cast	200
   	Peak aged	240

    A link to a few extra things.
   
   

2. Using P100 graphite fiber, a boron fiber with properties below, and epoxy matrix, design a three-part composite with zero CTE in the longitudinal direction. The volume fraction of Boron cannot exceed 50%, and the total volume fraction of fibers should be 60%.  

   	Modulus (GPa)	CTE (microstrain/C)
   P100 Fiber	706	-1.6
   Boron Fiber	410	+5.0
   Epoxy	4	65