How is toughness in a material tested?

Toughness in a material is fundamentally a measure of its capacity to absorb energy and plastic deformation before fracturing. To test toughness effectively, the material is subjected to an impact force, and the ability to withstand this sudden force is assessed. Specifically, option B highlights the importance of evaluating how a material responds to an impact by assessing the rise of a weight, which indicates the energy absorption capability of the material during the test.

In practical terms, toughness is frequently quantified using impact tests, such as the Charpy or Izod tests, where a notched sample is struck by a swinging pendulum. The height to which the pendulum swings after breaking the material directly correlates with the energy absorbed. A material that rises significantly after the impact indicates a high toughness level, showcasing its ability to withstand sudden loads without fracturing.

The other options don't effectively measure toughness. Measuring the time of deformation under load focuses more on creep or viscoelastic behavior rather than toughness. Observing changes in color and texture is related to the aesthetic or surface alterations, which does not quantify toughness. Recording thermal expansion under heat assesses thermal properties, which is not directly tied to how a material behaves under mechanical impact. Thus, option B stands out as the correct answer due to