Elastic modulus cast iron

[sydneyjongleur]

The elastic modulus of grey cast iron is relatively low (approximately half that of steel and almost the same as titanium) and I was wondering why this is, considering that cast iron is particularly brittle. When dealing with titanium in a machining environment the material tends to move/ deflect etc. due to the modulus. I dont see the same with cast iron and I would have thought that given the brittle nature of the material the modulus would be high? Am I confusing strength and stiffness.

 

[swall]

Gray cast iron consists of a ferrite/pearlite matrix (i.e. steel) interspersed with graphite flakes. The graphite forms a semi continuous network, which lowers the mechanical properties. The modulus of graphite is much lower than steel.

 

[prex]

Yes, I guess you are mixing strength and stiffness.
Due to its relatively lower strength and also to its brittle nature, cast iron sections will be comparatively thicker than an equivalent section in steel. So the overall stiffness of a cast iron item may appear higher wrt to the corresponding steel item, however this is because of the higher thickness.
The same happens with concrete wrt steel. A steel structure may be much slenderer than the corresponding one in RC, and this makes it more flexible. However the elastic modulus of concrete (and of RC too) is much lower than with steel only, but the sections are bigger because of the lower strength.

prex
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