Toughness is mostly related to mechanical vocabulary. Yes, As you might know, the term toughness mainly associated with mechanical components and machines. But actually, it is not. The actual meaning of the toughness relates to the properties of a particular material. And it mostly belongs to the category of mechanical properties of the material.

Common definition

Toughness is the ability to absorb energy when a piece of material meets with an impact. And this ability measures before a fracture happens.

So accordingly, here the scientific definition…

The ability of a metal to deform plastically and absorb energy in the process before the fracture is called toughness. 

Wallah! Now we are with the real scientific definition. But it seems more familiar. It is more similar to the definition of the Ductility of a material. Ductility is another mechanical property of materials, and it describes the measure of how much something deforms plastically before fracture. This is quite different Because, just because of being ductile, it does not make the material tough. 

What properties that material should achieve to be tougher

Critical qualifications to being tougher are the correct and perfect combination of material strength and ductility. So we can say that the material with high strength and high ductility can achieve more toughness than a material with low strength and high ductility.

How to measure toughness?

To measure this property, you need to draw the stress-strain curve from a tensile test and calculate the area under the curve. This is only one way of getting theoretical measurement. And it has the units of energy per volume.

Stress strain curve for Carbon steels | Area under each curve is toughness

Several variables have a strong influence on the toughness of a material. These variables are:

Strain rate

As the above illustration shows, toughness decrease as the rate of loading increases. And it shows the proper combinations of strength and ductility makes the material tougher.

However, these things never say that tough material can survive in every impact. When considering metals, they behave as a satisfactory toughness under static loads but may fail under dynamic loads or impacts.

Temperature

Temperature is the second influence factor. They directly correspond. That means as the temperature is reducing, the ductility and toughness also decrease.

Notch Effect

The third variable is the notch effect. Notch effect is also a limitation, and it relates to impact direction. With distributed stress, metal can withstand for the uniaxial stresses. It will be survived. Nevertheless, if it meets with multiaxial stress, fractures can be grown on the metal piece because of the notch’s presence. So then the material may not resist the simultaneous elastic and plastic deformation in the multi directions.

Toughness is one of the most significant property to consider when generating data for specific loading conditions and mechanical component design strategies.

And for the more next articles will be discussed about the 3 toughness categories.

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