21.13: Questions

Quick questions

You should be able to answer these questions without too much difficulty after studying this TLP. If not, then you should go through it again!

What is the main cause of lattice resistance?

 a Change in the dislocation width as the dislocation moves b Changes in misfit energy as the dislocation moves c Change in the Peierls stress as the dislocation moves d Dislocations interacting and causing work hardening

B

What is the main problem with the Peierls continuum elasticity model?

 a It only includes the nearest-neighbour misalignment energy and does not include the next-nearest-neighbour term. b It assumes the in-plane energy is negligible and can be ignored c It assumes the total energy remains constant as the dislocation moves d It assumes that in-plane energy is constant and does not vary as the dislocation moves

D

How do the misalignment and in-plane energies change with w/b?

 a As w/b increases, both misalignment and in-plane energies increase b As w/b increase, both misalignment and in-plane energies decreases c As w/b increases, misalignment energy increases; in-plane energy decreases d As w/b increases, misalignment energy decreases; in-plane energy increases

C

What is the relationship between dislocation width and Peierls stress?

 a Peierls stress increases linearly as the dislocation width increases. b Peierls stress decreases exponentially as the dislocation width increases. c Peierls stress increases exponentially as the dislocation width increases. d Peierls stress decreases linearly as the dislocation width increases.

B

What is the Peierls stress?

 a The minimum stress for which fracture occurs b The tensile stress at which slip starts to occur c The minimum shear stress required to move a dislocation across the slip plane d The minimum stress at which plastic deformation begins

C

Deeper questions

The following questions require some thought and reaching the answer may require you to think beyond the contents of this TLP.

1. For what value(s) of alpha (fraction the dislocation has moved across the unit cell) is the misfit energy maximum?
 Yes No a Alpha = 0 Yes No b Alpha = 0.25 Yes No c Alpha = 0.5 Yes No d Alpha = 0.75