Elastic deformation is a reversible strain, unlike the plastic deformation which is irreversible. The tensile stress application results in material becoming slightly longer. Removal of the applied force permits the return of the material to its original position. Similarly, when the applied force is compressive, the material becomes slightly shorter. The dimensions of the unit cells changes as materials undergo elastic strain.
UNDERSTANDING THE ELASTIC MODULI
The Elastic moduli popular known as the modulus of elasticity is the ratio of stress to strain during elastic deformation. When elastic deformation exists, that is provided elastic limit is not exceeded, the strain is directly proportional to the applied stress.
The greater the force of attraction binding the atoms together, the greater the modulus of elasticity. Any lengthening or shortening of the crystal structure in one direction due to a uniaxial force produces an adjustment in the dimensions at right angles to the force. For example, when a small contraction is indicated at right angles to the tensile force. The negative ratio between the lateral strain and the direct tensile strain is called poison’s ratio. But engineering materials can load in tension, compression as well as shear. In shear, the two forces are parallel but are not aligned.
For the above reason, the shear stress is the shear force divided by the sheared area:
Shear stress = shear force/shear area
The shear stress will produce an angular displacement, while shear strain will be a tangent of that angle.
ELASTIC MODULI VERSES TEMPERATURE IN PROCESSING OF METALS
Elastic modulus decreases as the temperature decreases for four common metals which iron is among them.