Industrial Engineering

Understanding hardness of a material

The ability of a material to tolerate localized permanent deformation, such as indentation, is characterized by its hardness. Cutting, abrasion, penetrating, and scratching can all cause materials to distort, hence hardness can also be used to define a material’s resistance to deformation.

The resistance of a substance to localized permanent deformation is measured by its hardness. Plastic deformation is another term for permanent distortion. While elastic deformation occurs when a material changes shape solely when force is applied, plastic deformation occurs when a substance does not return to its original shape.

material hardness

In this article, the following questions will be discussed:

  • What is the hardness of a material?
  • What are the types of hardness?

Let’s dive in!

Read more: Understanding compressive strength

What is the hardness of a material?

Hardness is a method used to determine how resistant a material is, to localized plastic deformation caused by mechanical indentation or abrasion. Hardness varies by materials; for example, hard metals like titanium and beryllium are harder than soft metals like sodium and metallic tin, as well as wood and ordinary polymers.

Strong intermolecular connections describe macroscopic hardness, but the behavior of solid materials under force is complex, therefore scratch hardness, indentation hardness, and rebound hardness are all different metrics of hardness. Ductility, elastic stiffness, plasticity, strain, strength, toughness, viscoelasticity, and viscosity are all factors that influence hardness. Ceramics, concrete, certain metals, and ultra-hard materials are examples of hard matter, which can be compared with soft matter.

Some materials have a high natural hardness. Tungsten, for example, is a very hard metal that is used as an alloying element in tool steels. This ensures that this group of steels can withstand wear even when cutting at high temperatures. Tungsten is frequently included in cemented carbide, which is commonly used in milling cutters. These interchangeable cutting tool bits significantly extend the life of cutting tools.

On the other hand, other materials, such as metals, are soft to the point of being unusable in a variety of applications. Because pure gold is so delicate, scratching or bending it requires little effort. To improve its hardness, other metals such as silver, copper, and aluminum must be added.

With some materials, heat treatment can be used to increase surface hardness while preserving the metal’s other properties. This is a common operation for machine shafts to ensure a longer lifespan. When developing a product design concept, an engineer must also consider the hardness ratio. In a bearing and shaft fit, for example, the bearing must be softer since it is easier to replace. With frequent movement, one part must wear, and the engineer has the last say.

Read more: Understanding Hardness, strength, and toughness of materials

What are the types of hardness?

The ability of a material to resist deformation is tested by a standard test that measures the resistance of the surface to indentation. The shape or kind of indent, the size, and the amount of load applied are the most frequent hardness tests.

Scratch, indentation, and rebound are the three basic types of hardness tests. Individual measurement scales exist within each of these measurement classes. Conversion tables are used to convert from one scale to another for practical purposes. The followings are the various types of hardness:

  • Scratch hardness
  • Indentation hardness
  • Rebound hardness


Scratch hardness

Scratch types of hardness refer to a sample’s resistance to fracture or persistent plastic deformation as a result of friction from a sharp item. An object made of a harder substance will scrape an object made of a softer material, according to the principle.

Scratch hardness refers to the force required to cut through the film to the substrate while testing coatings. The Mohs scale, which is employed in mineralogy, is the most prevalent test. The sclerometer is one tool that can be used to accomplish this measurement.

The pocket hardness tester is another tool used to do similar tests. A scale arm with graduated markings is coupled to a four-wheeled carriage in this gadget. A scratch instrument with a sharp rim is attached to the testing surface at a predefined angle. To use it, place known mass weight on the scale arm at one of the graduated markings, then draw the tool across the test surface. Without the use of expensive machinery, a known pressure can be exerted using the weight and marks.

Read more: Understanding the flexibility of a material

Indentation hardness

The resistance of a sample to material deformation caused by a steady compressive load from a sharp item is measured by indentation hardness. Indentation hardness tests are most commonly employed in engineering and metallurgy. The tests are based on the principle of determining the critical dimensions of an indentation created by a specially dimensioned and loaded indenter. Rockwell, Vickers, Shore, and Brinell are some of the most common indentation hardness scales.

Read more:  Understanding fiber reinforced plastic

Rebound hardness

The height of the “bounce” of a diamond-tipped hammer dropped from a fixed height into a material is measured by rebound hardness, also known as dynamic hardness. Elasticity is linked to this type of hardness. A stereoscope is an apparatus used to take this measurement.

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The Leeb rebound hardness test and the Bennett hardness scale are two scales that quantify rebound hardness.

By measuring the frequency of an oscillating rod, the Ultrasonic Contact Impedance (UCI) approach assesses hardness. A metal shaft with a vibrating element and a pyramid-shaped diamond attached to one end makes up the rod.

Read more: Understanding the various types of residual stress

In summary

Material hardness is a very important thing to consider when designing an engineering project. This is what determines the reliability and functionality of the project. In other words, material hardness is a key factor in engineering design. That is all for this brief article on material hardness.

I hope you learn a lot from the reading, if so, kindly share with others. Thanks for reading, see you around!