Metals- Elasticity Review and Concept of Dislocations

Question 1

In the elastic region, what happens when stress is removed?

Answer 1

Material reverts back to its original state

Question 2

Shear stress formula

Answer 2

τ=Gγ

Question 3

Elastic strain energy

Answer 3

Stored energy=1/2 σε=1/2 Eε^2
Or in shear =1/2 Gγ^2
Area of triangle on stress strain graph in elastic region

Question 4

What does plastic deformation require?

Answer 4

Atomic places to slide over each other under the influence of shear stress

Question 5

How does shear stress develop from normal stress?

Answer 5

Shear stress develops from normal stress applied to the material. Magnitude of shear stress depends on angle of plane with stress axis. Max shear is half that of normal stress at 45 degrees to normal stress direction

Question 6

Why is ideal stress for deformation to occur much greater than what is observed?

Answer 6

About 1000x more. Due to action of dislocations. When they are present deformation occurs by their progressive movement. Fewer bonds need to be broken by dislocation slipping than atomic planes shearing past each other