What is Toughness?
Toughness is the ability of a material to absorb energy before ultimate failure.
Material which can absorb more energy before failure is considered more tough than another material which can absorb less energy.
Unit of toughness is Joules per cubic meter.
Tests for measuring toughness
There are mainly two tests which are generally used to measure toughness.
- Charpy impact test or Charpy V-notch test
- Izod impact strength test
Image attributions: By Chris Allen, CC BY-SA 2.0, https://commons.wikimedia.org/w/index.php?curid=62153008
Toughness of a material can be measured using a small specimen of that material. A typical testing machine uses a pendulum to strike a notched specimen of defined cross-section and deform it. The height from which the pendulum fell, minus the height to which it rose after deforming the specimen, multiplied by the weight of the pendulum is a measure of the energy absorbed by the specimen as it was deformed during the impact with the pendulum.
Impact of temperature on toughness
At low temperatures the material is more brittle and impact toughness is low. At high temperatures the material is more ductile and impact toughness is higher.
Difference between resilience and toughness
The only difference lies in the limiting point. Toughness is energy absorbed till rupture and resilience is energy absorbed till elastic limit.
Difference between toughness and strength
Strength is a measure of the maximum stress that a material can bear before starting to fracture. Toughness is a measure of the energy required to fracture a material.
Difference between toughness and brittleness
Brittleness is a property of material which breaks without significant plastic deformation when an external stress is applied. While toughness is all about energy absorbed by a material before failure.
Featured image attributions: CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=1698529
Toughness test: https://en.wikipedia.org/wiki/Toughness
Temperature toughness relation: https://www.nde-ed.org/EducationResources/CommunityCollege/Materials/Mechanical/ImpactToughness.htm
Toughness and strength: https://www.imetllc.com/training-article/strength-toughness/