# Volume change during tensile test

During tensile test, why does the specimen's(let's say mild steel) volume changes during elastic deformation and does not change during plastic deformation?

• The effect is completely dependent on the Poisson's ratio; a Poisson's ratio of 0.5 implies no volumetric change for tensile stretching or compressive contraction of a bar/rod, for example, in the elastic regime. Try calculating the volumetric strain $\epsilon_x+\epsilon_y+\epsilon_z$ for various loading configurations using generalized Hooke's Law to gain insight. – Chemomechanics Jul 20 '18 at 2:28