$3(10$ scores$).$ Given a one$-$way process of loading stress path $01\mathrm{.}5{}_{s}0-1\mathrm{.}5{}_s-2{}_{s}0,$ material meets the linear isotropic hardening law, strengthening modulus $E^{\text{'}}=\frac{E}{50},$ where $,{}_s$ and $E$ are the yield limit and the modulus of elasticity respectively. try to work out the corresponding strain path.

$4(10$ scores$).$ Please describe main points of Prandtl$-$Reuss incremental theory and list the equations of Prandtl$-$Reuss.

scores$).$ How do you think about the importance of the theory of elastic and plasticity?