Why are Different Hardness Tests and Scales Required

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Different types of hardness tests and scales are used today. So, let's dive deep into this point and understand why different hardness tests/scales are used.

The hardness of a material is its ability to resist deformation, scratching, cutting, or bending. Hardness testing is a commonly used mechanical test applied to a wide range of materials using specialized hardness testing machines. Today, there are various standardized hardness tests, each with its own hardness scale and area of applicability for different types of materials, such as metals, rubbers, ceramics, etc. This raises the question of why there is a need for different hardness tests and scales instead of one standard test. Let's talk about this point in detail and uncover all the information you need to know.

Types of Hardness Tests – A Quick Overview

Before we dive deep into the necessity of different hardness tests, it is important that we clear our concepts around hardness tests. There are many hardness tests with their particular hardness scales, so let's cover a few of the popular hardness tests:

1. Rockwell Hardness Test

The Rockwell hardness test is the most widely used, fastest, and most accurate hardness test. In this test, the load is applied three times. The first time, a minor load is applied on the material for a short time period using a ball or diamond indenter. Afterward, the major load is applied, which causes a deeper penetration. Next, the major load is removed, and a minor load is applied again. After these three stages, the difference in depth is used to measure the material hardness.

This test is mainly used for metallic samples but can also measure hardness for alloys and plastics. It applies around 15 kgf to 3000 kgf load. The combination of test load and indenter determines the hardness scale of the Rockwell hardness test. It is represented by alphanumeric code with a scale letter and alphabet combination, such as HRA, HRB, HRC, etc. There are 30+ different scales used with the Rockwell hardness test because of the wide range of choices between loads and indenters.

2. Brinell Hardness Test

The Brinell hardness test is the oldest and first standardized hardness scale. It helps to measure the hardness of metals and alloys. In this test, a hardened steel ball indenter is pressed on the material surface with a constant force for a specific time through a hardness testing machine. Afterward, the indentation is measured to get the hardness value.

This test mostly applies the force of up to 3000 kgf for steel and 500 kgf for non-ferrous metals. The Brinell hardness scale value is presented as HB (Hardness Brinell). The bigger the HB value, the harder the material.

3. Vickers Hardness Test

The Vickers hardness test was designed as a Brinell test alternative. It is mostly used to measure the hardness of thin or small materials, such as metals, ceramics, etc. It is also often called a microhardness test.

In this test, a pyramidal diamond indenter with a light force is applied to the material, and the corresponding depth is measured optically. The applied force usually ranges between 10 g to 1 kgf. The Vickers hardness scale value is presented as HV (Hardness Vickers) and formatted as xxxHVyy/zz, where "xxx" represents the hardness number, "yy" represents the force load, and "zz" represents the load duration.

4. Shore Hardness Test

The Shore hardness test is commonly used for measuring the hardness of soft/hard polymers and elastomers. In this test, a durometer (spring-loaded indenter) is pressed on the material, and the penetration depth is measured to get the hardness value.

The applied force usually ranges between 0.1 kgf to 4.5 kgf. There are two Shore hardness scales: Shore A for softer materials and Shore D for harder materials. The scale ranges from 0 to 100, meaning that a Shore hardness of 100 reflects zero penetration.

Why Do We Need Different Hardness Tests and Scales

Now that we know the basics of a few of the popular hardness tests and scales, let's head to our main question: why are there so many different hardness tests and scales?

The hardness test is an empirical test instead of a material property. Since different materials have different hardness levels, they are not able to be measured with one standard hardness test and scale. Let's better understand it with the help of an example.

Consider that we have to measure the hardness of steel and rubber. Using the Rockwell Hardness Test for both materials will provide accurate results for steel, but it will break rubber instantly due to massive load force. The Shore Hardness Test is a better option for measuring rubber's hardness.

Below are the key reasons that reflect the need for different hardness tests:

· Material Strength: Different materials have different strengths. Some don't show any impact with one load press, while others can easily deform in one press. So, the hardness tests are customized according to the material strength.

· Different Testing Purpose: A hardness test is used for many different purposes, such as researching the material properties, creating the product hardness specification, testing the reliability of the prototype, etc.

· Standards: There are different standardized hardness tests in different industries to ensure consistency. For instance, the aerospace industry uses Rockwell and Brinell hardness testing machines, while the electronics industry may use Vickers hardness testing machines.

All the above reasons reflect how hard it is to create a standardized hardness test that can incorporate all materials. However, you might be wondering why we cannot standardize the hardness scale even with different hardness tests.

Since different hardness tests are required to measure the hardness of different materials, each test has specific hardness scales. Creating a standardized hardness scale for all hardness tests will be hard. For instance, the Shore hardness scale ranges between 0-100, while the Vickers hardness scale ranges between 1 to 3000 HV. So, it is challenging to create a universal hardness scale.

Wrapping Up

Hardness testing has been around for decades and is an essential specification for quality control and material selection. However, the varying hardness of different materials forces the need for different hardness tests and scales. Owing to that, there are now different hardness testing machines for different purposes.

Sinowon provides a wide variety of high-quality hardness testing machines for accurate and precise hardness tests of different types. So, we will wrap up the discussion by recommending you check the extensive product line of Sinowon and pick the hardness testing machine that aligns with your hardness testing requirements.