How is the term "strain hardening" best defined?

Strain hardening, also known as work hardening, is best defined as the increase in strength of a material due to prior deformation. This phenomenon occurs in materials, particularly metals, when they are subjected to plastic deformation beyond their yield strength. As the material is deformed, dislocations within the material's crystal structure multiply and become entangled, leading to an increase in the material's hardness and strength. This process is critical for many engineering applications, as it allows materials to be shaped and manipulated while simultaneously improving their mechanical properties.

The other choices do not accurately capture the essence of strain hardening. While temperature does influence material properties, and microstructure changes can occur with temperature, these factors are not what characterize strain hardening. Strain hardening specifically emphasizes the relationship between deformation and the resultant increase in strength and hardness, making option B the correct choice.