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Microhardness
Indentation hardness tests are used in mechanical engineering to determine the hardness of a material to deformation. Several such tests exist, wherein the examined material is indented until an impression is formed; these tests can be performed on a macroscopic or microscopic scale. When testing metals, indentation hardness correlates roughly linearly with tensile strength, but it is an imperfect correlation often limited to small ranges of strength and hardness for each indentation geometry. This relation permits economically important nondestructive testing of bulk metal deliveries with lightweight, even portable equipment, such as hand-held Rockwell hardness testers. Material hardness Different techniques are used to quantify material characteristics at smaller scales. Measuring mechanical properties for materials, for instance, of thin films, cannot be done using conventional uniaxial tensile testing. As a result, techniques testing material "hardness" by indenting a materia ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Knoop Hardness Test
The Knoop hardness test is a microhardness test – a test for mechanical hardness used particularly for very brittle materials or thin sheets, where only a small indentation may be made for testing purposes. A pyramidal diamond point is pressed into the polished surface of the test material with a known (often 100g) load, for a specified dwell time, and the resulting indentation is measured using a microscope. The geometry of this indenter is an extended pyramid with the length to width ratio being 7:1 and respective face angles are 172 degrees for the long edge and 130 degrees for the short edge. The depth of the indentation can be approximated as 1/30 of the long dimension. The Knoop hardness ''HK'' or ''KHN'' is then given by the formula: :HK where: :''L'' = length of indentation along its long axis :''C''p = correction factor related to the shape of the indenter, ideally 0.070279 :''P'' = load HK values are typically in the range from 100 to 1000, when specified in the co ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
