Hardness, strength, and toughness are some of the major and important properties expected in metals and other materials. One or more of these properties will determine their suitability on a specific application. Today in out daily, people tend to use the words strong, tough, and hard in their conversations not knowing how important the word could in metallurgy.
Today we’ll get to know about hardness, strength, and toughness in metals. We’ll also get to know their difference and how important they are in different applications. You’ll also get familiar with stress and strain.
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Stress and Strain
Stress is the measure of the force that is acting on an object. Stresses are distinguished by the direction in which forces act relative to the material, which could either be compressive, tensile, or shear. Compressive stress is a stress that acts at the longitudinal directions to compress the object. While tensile stress is the exact opposite, acting to expand the object. Torsional stress is different as it’s the result of forces acting in opposite directions that serve to twist or provide torsional loading.
On the other hand, the strain of a material is a measure of the degree to which it has deformed relative to its original dimensions. For instance, when a material undergoing stress from any direction is bound to respond to the stress by either deforming or outright failing.
Engineers and scientists were able to predict the reaction of materials when subjected to forces at different levels. This has also allowed the classification of materials based on their material properties, which may include brittle, ductile, elasticity, hardness, toughness, and strength.
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What is hardness?
In general terms, hardness is the ability of a material to withstand friction. It’s well known and uses abrasion resistance. The hardness of a material is a measure or ability of its resistance to localized deformation. This deformation in most cases is brought about by abrasion (friction forces) or indentation (constant lateral mechanical forces).
A diamond has a unique characteristic of hardness and it’s known as the hardest substance on earth and incredibly difficult to scratch. In an industrial world or infrastructure, it is rare to use in important applications that require hardness. However, diamond-tipped drill bits are incredibly common and available in various sizes including the ones for handheld drills used for drilling in metals and solid rock.
On a subatomic level, hardness is determined by the strength of intermolecular bonds. Although there are also a couple of things that come into play. However, the hardness of a material is not responsible for resisting the application of a large amount of force. Let take for instance, despite the hardness of a diamond, it can easily be shattered with a sledgehammer. This is where we can differentiate hardness from toughness.
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What is toughness?
Toughness is the ability to measure the amount of force a material can absorb without fractioning. A material like metal, plastic, or wood can undergo a certain amount of force before it fractures, which means when the material will completely fail.
With this, the material can undergo elastic deformation or deformation that allows it to return to its original form without fractioning. in a situation where a material deforms before fractioning means, it’s ductile. This is to say a ductile material can also be considered as tough.
In addition, the toughness of a material can be determined by its ductility and strength. A good example of toughness is metals and foams being equal in terms of toughness. The materials are extremely different in behavior in terms of stress and strain but they have similar yield points.
Metals can only withstand a very small amount of deformation before they fracture, and might require a huge amount of force before they deform. On the other hand, foams will deform with a normal amount of compression force but will only fail at the amount the same amount of force as metals. Rubbers are unique in terms of toughness as it has enough strength to withstand a good amount of force before it deforms and it does not suddenly fail upon deformation. Rubbers have both strength and ductility which makes them a unique tough material. Now, let get to understand the term strength.
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What is strength?
Strength is the amount of force a material can contain to resist deformation. This is to say, the higher the force required to change the shape of a material, the stronger the material. Among the above-listed properties of materials like metals, woods, rubbers, etc. strength is probably the most complex. It’s can also be said to be the measure of the amount of force an object can withstand before it undergoes plastic deformation. It can also undergo a deformation that is non-reversible, which is also known as unrecoverable strain. That is, a material that has undergone plastic deformation will no longer return to its original form even after the stress is removed.
For instance, steel is difficult to pull apart, which means it has high strength. But it’s not strong at all as it can quickly deform into all sorts of shapes will very little force.
The difference between strength and toughness is that toughness measures the force needed for a material to completely fail. Whereas strength is only the amount of force a material requires to reach plastic deformation. In some situations, like a very brittle material such as ceramic, strength and toughness play an important role as they practically overlap.
However, there are different types of material strength, which brought about the types of stress a material can experience. So, a material can have a unique value of compressive strength and tensile strength. This depends on the material’s ability to withstand compressive stress or tensile stress. Furthermore, all materials have their own shear strength, which measures the ability to withstand shear stress before undergoing a sliding failure.
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So, the big question today “The difference between Hardness, Toughness, and Strength.”
The difference between hardness, toughness, and strength is above explained, but in brief, we can quickly say; hardness is the ability of a material to resist friction, while Toughness is the ability to measure the amount of force a material can absorb without fractioning. finally, strength is the amount of force a material can contain to resist deformation.
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Hardness, toughness, and strength are extremely different properties that can be seen in different materials. In this article, we’ve looked into stress and strain and how they brought the various properties in materials like metals, woods, rubbers, etc. finally, we also looked at the difference between hardness, toughness, and strength.
I hope you enjoyed the reading, if so, kindly comment on your favorite section in this article. And please don’t forget to share with other technical students, it might be helpful. Thanks!