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Toughness - an unutilized material property

If you throw a rubber bone to a dog, it will try its best to rip it apart. But no matter how much energy the dog consumes, the bone survives the treatment. This is because it is made of tough material. In physical terms, toughness is the ability of the material to absorb energy before rupturing.

 

Among other material properties, stress-strain curve is a great tool for estimating material-specific toughness as well. Toughness equals the area between the curve and the X-axis:

The width of the area depends on weather you want to estimate the energy needed for yield or rupture. How does this help As it was explained in the Stress-strain article the shape of the curve depends on the material. When it comes to toughness…

 

The graph explains very clearly why the strongest material is not necessarily the most durable. Toughness for material B is much higher than for material A despite their difference in strength. Toughness is a benefit on products that are subjected to dynamic loads, to impacts in particular (although the impact resistance of the material is not dependent on toughness only). Looking at the graph you can also see that tough and stiff do not come together; you have to choose one or the other, depending on your needs. Broken plastic containers, buckets and handles are typical examples of products that could have been made, in many cases, more durable using a material with slightly smaller modulus but higher toughness.

Comments

Rajjan Syan
I think total area under stress-strain curve is Toughness. Area upto elastic limit is called Resilience.
Doug Broad
Great points and presentation. Hadn't thought to consider the yield point in addition to the rupture point.

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