What is the primary effect of strain hardening on materials?

Strain hardening, also known as work hardening, primarily increases the strength and hardness of a material through the mechanism of dislocation movement. When a material is deformed plastically, it introduces dislocations within the crystal structure, and these dislocations become tangled and interact with one another. This interaction makes further dislocation movement more difficult, which in turn enhances the material's yield strength and hardness.

As the material undergoes additional deformation, the density of dislocations increases, contributing to the material's overall strength. This is particularly important in applications where the material needs to withstand high stresses without failure. The increase in strength and hardness often comes at the expense of ductility, as the material becomes less able to undergo further plastic deformation without fracturing.

The other choices reflect different effects that do not accurately describe the primary consequence of strain hardening. Thus, the option that highlights the increase in strength and hardness is the most accurate portrayal of strain hardening's primary effect.