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Hardness measurement test is one of the simplest material test, it is a kind of material mechanical test to measure the surface hardness of solid material in laboratory. The hardness value can not be directly used in the design of machine parts, but because the hardness test is easy to carry out, it is often used in material quality control and experimental research. There are three main types of hardness measurement: scratch, indentation and rebound. In each of these measurement categories, there are separate measurement scales. For practical reasons, conversion tables are used to convert between one scale and another.

1. Indentation hardness

Indentation hardness measures the resistance of the sample to deformation of the material due to constant compressive loads from sharp objects. Indentation hardness testing is mainly used in engineering and metallurgy. The basic premise of these tests is to measure the critical dimensions of the indentation left by a specific size and loaded indenter. Common indentation hardness scales include Rockwell, Vickers, Shore and Brinell.

2.Rebound hardness

Rebound hardness, also called dynamic hardness, measures the "rebound" height of a diamond hammer falling from a fixed height onto the material. This hardness is related to elasticity. The device used to make this measurement is called a scleroscope. The two scales for measuring rebound hardness are Richter rebound hardness test and Bennett hardness scale.

Ultrasonic contact impedance (UCI) method determines hardness by measuring frequency of vibrators. The rod consists of a metal shaft with a vibrating element and a pyramid-shaped diamond mounted on one end.

3.Scratch hardness

Scratch hardness is a measure of a sample's resistance to fracture or permanent plastic deformation caused by friction with sharp objects. [1] The principle is that objects made of harder materials scratch objects made from softer materials. When testing a coating, scratch hardness refers to the force required to cut the film into the substrate. The most common test is the Morse scale, used in mineralogy. One tool for this measurement is a durometer.

Another tool used to perform these tests is a pocket hardness tester. The tool consists of a scale arm with a scale mark attached to the four-wheel carrier. A scraping tool with sharp edges is mounted to the test surface at a predetermined angle. To use it, add the weight of the known mass to the scale mark on one of the scale arms and then pull the tool across the test surface. The use of weights and marks allows the application of known pressures without the need for complex machinery.

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