Re: What is the specific heat capacity of carbon fibres?

Jonathan;
Carbon fibers are commonly used in military and large commercial aircraft 
brakes.  They have been  used in some racing car brakes as well.  For these 
usages, both the rotor and stator (or brake pad) are made from carbon fibers 
that are bonded by amorphous carbon.  Such brakes can operate to 2500C, far 
hotter than brakes that use metallic rotors.  

Aircraft and racing cars need to keep weight to a minimum.  For this reason they 
use brake friction materials that can be used at high operating temperatures, 
that have high specific heat capacities, and which have high thermal 
conductivities.  Carbon fibers are particularly useful for such brakes.  
However, they are too expensive and their friction is too sensitive to 
contamination (water and organic vapors) for most automotive applications.  

You indicated that you want to calculate temperature increases due to braking.  
You should be aware that, during hard braking, about 85% of the braking work 
goes into heating the brake assembly (the remaining 15% mostly goes into heating 
the tires and pavement).  On a panic brake stop, where the wheels lock and the 
tires skid, about 5% goes into heating the brakes and 95% into the tires and 
pavement.    

How hot a brake gets is determined by several factors, one of which is the 
specific heat capacity of the brake materials.  Most materials have specific 
heats that vary with temperature.  Typically, they rise with increasing 
temperatures.  

Carbon has a large variation in its specific heat capacity.  It is very low at 
cryogenic temperatures, but rises rapidly in the brake temperature ranges.  
Variation above 600C is relatively small.  The specific of carbon seems to vary 
somewhat with its structure, be it diamond, graphite, or amorphous carbon.  A 
carbon-carbon (carbon fiber based) friction material should have a specific heat 
that varies with temperature much like graphite.  You can estimate the specific 
heat using the following values from the Handbook of Chemistry and Physics:

Temperature, ºC	        Specific Heat
	20		     0.17
	85		     0.177
        138		     0.254
        642		     0.445
        896		     0.454

You can plot these values to generate a curve for the specific heat versus 
temperature.  Then you might wish to use an approximation technique to estimate 
the temperature increase due to braking.

I, too, did not find any data on the specific heat of carbon--using the 
Internet.  You might try a technical library, and look for a monograph on 
carbon.