<P> If a material has been subjected to prior deformation (at low temperature) then the yield stress will be increased by a factor depending on the amount of prior plastic strain ε: </P> <Dl> <Dd> σ = σ y + K (ε 0 + ε p) n (\ displaystyle \ sigma = \ sigma _ (y) + K (\ epsilon _ (0) + \ epsilon _ (p)) ^ (n) \, \!) </Dd> </Dl> <Dd> σ = σ y + K (ε 0 + ε p) n (\ displaystyle \ sigma = \ sigma _ (y) + K (\ epsilon _ (0) + \ epsilon _ (p)) ^ (n) \, \!) </Dd> <P> The constant K is structure dependent and is influenced by processing while n is a material property normally lying in the range 0.2--0.5 . The strain hardening index can be described by: </P>

During failure the stress in a material will