Hardness testing

Hardness test results can be extremely useful when selecting materials, because the reported hardness value indicates how easily the material can be machined and how well it will wear. This preload breaks through the surface to reduce the effects of surface finish.

More than thirty different scales are used between Rockwell and Superficial Rockwell hardness testing due to the various choices and combinations of tests, indenters and major loads.

Micro or Macro hardness testing, also commonly referred to as Knoop or Vickers testing, is also performed by pressing an indenter of specified geometry into the test surface. Vickers is also available on the macro scale to 50 kg.

Hardness testing machine

Unlike Rockwell testing, the Knoop or Vickers test applies only a single test force. After holding the preliminary test force for a specified dwell time, the baseline depth of indentation is measured. The preliminary test force is removed and the indenter is removed from the test specimen. This distance is converted to a hardness number. The entire procedure requires as little as a few seconds up to 15 for plastics. These conditions include test specimens that are below the minimum thickness for the depth of indentation; a test impression that falls too close to the edge of the specimen or another impression; or testing on cylindrical specimens. After the preload, an additional load, call the major load, is added to reach the total required test load. The Knoop Test is performed like Brinell hardness by applying controlled force for a specific amount of time to an indenter in a rhombus-shape. This preload breaks through the surface to reduce the effects of surface finish.

First, a preliminary test force commonly referred to as preload or minor load is applied to a sample using a diamond or ball indenter. The most basic and commonly used definition is the resistance of a material to permanent, plastic deformation.

Unfortunately, since these studies can only be effectively done on test blockstheir value does not necessarily translate into actual testing operations. Each test machine also uses a different force or load application system and records an indentation hardness value in kilograms-force according to their individual hardness scales.

The resultant impression or un-recovered area is then measured using a high powered microscope in combination with filar measuring eyepieces, or more recently, automatically with image analyzing software.

hardness testing methods

Tables or automatic electronic or imaging measurements are a more common and convenient way to generate Knoop and Vickers hardness numbers. Lower forces and smaller diameter balls are sometimes used in specific applications. Learn more about hardness testing basics here.

Microhardness testing by Knoop and Vickers Hardness Test methods measure small samples or small regions in a sample. In this case any Rockwell test result is going to be subject to doubt, there is often a history of testing using a particular scale on a particular material that operators are used to and able to functionally interpret.

Hardness testing
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Hardness testing insight