Toughness: Refers to the capacity of a material of absorb energy prior to failure. Its value is equal to the entire area under the stress-strain curve. In most cases, the area under the elastic portion of the curve is a very small percentage of the total area and may be ignored in the calculation of the modulus of toughness. To further simplify the calculation, the nonlinear portion of the stress-strain curve is approximated by a series of straight lines as shown to the right.
In the example to the right, the modulus of toughness is determined by summing the areas A1 through A4.
