II$-$

Given the engineering stress$-$strain diagram for a low$-$carbon steel alloy initially $10mm$ in diameter and $60mm$ in length $($the curve in the middle is a zoom on the stress$-$strain curve up to a strain of $0\mathrm{.}005)$:

$1-$ From the curves above find:

An approximation of the vield stress of this material using the $0\mathrm{.}2\%$ offset method.

$-$Young modulus E using the Hooke's law.

$2-$ Define the hardening and softening of stress? Considering the plastic zone of the curve, does the stress experience a hardening or a softening? Explain

$3-$ Assuming a tensile test of the same low$-$carbon steel alloy, at very low temperature, giving a breaking strain of $0\mathrm{.}015,$ how can you qualify this behavior?