Re: Expecting cooments..

[codrick martis]

There is a strength called cleavage strength of the material which is independent of temperature and without much plastic deformation (brittle fracture) which is very high . ALSO there is flow stress by applying which deformation occurs by dislocation motion which is dependent on temperature . In BCC as the temperature is reduced the flow stress required to move dislocation increases and it reaches cleavage strength of the material and BCC material fails by brittle transition..:) In FCC its flow stress is always less than cleavage stregth for all temperature :) . Its due to the difference in disassociation of dislocation (partial dislocations ) in FCC and BCC material .In BCC  disassociation is complicated and its highly dependent on temperature and hence the flow stress( as disscoiation increases more stress is needed to move the disloc across the barrier due to more no of disloc.) . In FCC it does not very much with temp and its always less than cleavage stregth..:) 

[abhinandan admuthe]

good work codrick... good explanation from u r side.. expecting much
more from you... thanks