1 5 pts How and why do grain boundaries affect the strength

1, (5 pts) How and why do grain boundaries affect the strength of a material? 2\" (10 pts) Discuss the bonding and structure of plastics. How do these differ from metals?

Solution

1.

Grain is a virtual single crystal. For the material to be stronger, it is necessary to make it harder for dislocation movements. Dislocations cannot simply slide from one grain to the next because the slip planes do not line up. The grain boundary acts as a barrier to dislocation motion as the grains are of different orientations ans the atomic disorder within the grain boundary region will result in a discontinuity of slip planes from one grain in to the other.