Plastic Deformation: Mechanisms, Crystal Plasticity, and Yield Criteria

All flashcards

What is plasticity?

The ability of a solid to undergo permanent, non-reversible deformation in response to applied forces.

What is yielding?

The transition from elastic behavior to plastic behavior; the stress at the onset is called the yield strength.

How does elasto-plastic deformation behave on unloading?

Its elastic portion recovers, but its plastic portion remains as a permanent change.

What is work hardening?

The increase in resistance to further plastic deformation after a material has already been plastically deformed.

How do ductility and malleability differ?

Ductility is plastic deformability in tension; malleability is plastic deformability under compression, such as hammering or rolling.

Quiz questions

1. For a single crystal under tensile stress $\sigma$, how does Schmid's law calculate resolved shear stress on a slip system?Answer: $\tau_R=\sigma\cos\phi\cos\lambda$
2. How do dislocations enable plastic deformation in crystalline metals?Answer: Their motion lets parts of the lattice shift progressively.
3. What occurs during crazing in an amorphous material under tension?Answer: Free-volume regions open and fibrils form in highly stressed areas.
4. According to the Tresca criterion, when does yielding begin?Answer: When the difference between maximum and minimum principal stresses reaches the yield threshold.
5. How does decreasing grain size generally affect flow stress in polycrystalline metals?Answer: It generally increases flow stress by providing more grain-boundary obstacles.