What is toughness, and how is it measured?

• A. The total energy absorbed before fracture; measured by impact tests such as Charpy or Izod.
• B. The amount of energy required to initiate plastic deformation.
• C. The maximum stress before fracture.
• D. The slope of the elastic region.

Answer: (A)

Toughness is the material’s ability to absorb energy as it deforms and resists crack propagation until it finally fractures. In practical terms, it’s the energy a material can take on, per unit volume, up to the point of fracture. That energy is what you capture in tests that measure how much energy the specimen can absorb before breaking.

In many engineering contexts toughness is quantified with impact tests like Charpy or Izod. A notched specimen is struck with a pendulum, and the energy absorbed to cause fracture is measured. This energy reflects how well the material can dissipate energy through plastic deformation and micro-cracking, so ductile materials with substantial deformation show higher toughness, while brittle materials show lower toughness.

The other ideas describe different properties: energy to initiate plastic deformation isn’t a standard toughness measure, maximum stress before fracture is strength, and the slope of the elastic region is the modulus.