Anyone can notice that a rock is harder than a plastic toy. But when you work in engineering or metallurgy, measuring hardness becomes much more complex. There are several ways to measure the hardness of a material. In the engineering and metallurgy fields, workers most often measure the indentation hardness.
Indentation hardness measures how resistant a material is to changing when it is compressed. To measure indentation hardness, workers use equipment to compress the material. They then measure the level of indentation left behind on the material. Generally speaking, a smaller indentation indicates a harder material.
The way to measure indentation hardness differs depending on the scale you use.
Comparing Hardness Scales
When measuring indentation harness, there are four possible scales to choose from. The type of scale you use affects which type of equipment you use.
Invented in 1900 by Johan August Brinell, the Brinell scale was the first hardness scale used by engineers and metal workers. To perform a Brinell test, an indenter penetrates the desired material.
People prefer the Brinell scale if they also need to determine the ultimate tensile strength (UTS) of steel. That's because when you divide the Brinell scale hardness value in half, you get the UTS in pounds per square inch.
The Rockwell scale was invented in the early 1900s by Hugh and Stanley Rockwell. This scale compares the indentation caused by a large load with the indentation caused by a smaller load.
The Rockwell test preserves a material's integrity better than the Brinell test does. The Brinell test leaves a large impression that can actually damage the material being tested.
The Vickers scale was invented in 1921 by Robert L. Smith and George E. Sandland at Vickers Ltd.
The hardness measurements on the Vickers test are often easier to determine than measurements with other scales. Unlike with other tests, the size of the Vickers indenter doesn't affect the hardness calculations.
Invented by Albert Ferdinand Shore in the 1920s, the shore hardness scale uses a device called a durometer. Like other hardness equipment, the durometer applies force to the material and measures the depth of the indentation.
Unlike the other hardness scales, which focus on metals, the shore scale measures the hardness of elastomers, rubbers, and polymers.
Comparing Tester Equipment
Each type of hardness scale requires different types of equipment. Rockwell and Brinell testing rely on two main kinds of equipment: bench and portable.
Bench equipment sits on top of a work bench. It displays the test results either on a dial (analog models) or on a digital screen (digital models). Portable equipment differs because, along with being portable, it can test larger metal than bench equipment can.
A Vickers hardness tester is unique because it uses a diamond as the indenter. Diamonds create the same shaped impressions, regardless of the material they are measuring. Plus, since diamonds create relatively small indentations, Vickers equipment is ideal for testing thin materials like foil.
As mentioned, a durometer is the instrument used for shore scale testing. A durometer is a test stand that resembles a kitchen scale.
There are several different durometer styles, including classic style, pencil style, and ergo style. Each is built to meet certain specifications. For example, pencil-style durometers have a tiny base, which enables them to measure areas that are difficult to reach.
When it comes to measuring indentation hardness, you have many options to choose from.
If you're looking for the right equipment to test the hardness of your materials, count on us at WESTport Corporation. We offer a variety of hardness testing equipment to meet your project requirements.