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The SI unit, pascal, is sometimes used instead: 1 kg f ⋅mm −2 = 9.80665 MPa. The test was developed by Frederick Knoop [ 2 ] and colleagues at the National Bureau of Standards (now NIST ) of the United States in 1939, and is defined by the ASTM E384 standard.
ISO 18265: "Metallic materials — Conversion of hardness values" (2013) ASTM E140-12B(2019)e1: "Standard Hardness Conversion Tables for Metals Relationship Among Brinell Hardness, Vickers Hardness, Rockwell Hardness, Superficial Hardness, Knoop Hardness, Scleroscope Hardness, and Leeb Hardness" (2019)
{{convert|100|Mm|mm}} → 100 megametres (1.0 × 10 11 mm) The output of {{convert}} can display multiple converted units, if further unit-codes are specified after the second unnamed parameter (without the pipe separator). Typical combination output units are listed below in column 7. {{convert|55|nmi|km mi}} → 55 nautical miles (102 km; 63 mi)
In the above equation, F could be in N and d in mm, giving HV in the SI unit of MPa. To calculate Vickers hardness number (VHN) using SI units one needs to convert the force applied from newtons to kilogram-force by dividing by 9.806 65 (standard gravity). This leads to the following equation: [4]
The conversion in SI units is 1 ksi = 6.895 MPa, or 1 MPa = 0.145 ksi. The megapound per square inch (Mpsi) is another multiple equal to a million psi. It is used in mechanics for the elastic modulus of materials, especially for metals. [5] The conversion in SI units is 1 Mpsi = 6.895 GPa, or 1 GPa = 0.145 Mpsi.
The ultimate tensile strength of a material is an intensive property; therefore its value does not depend on the size of the test specimen.However, depending on the material, it may be dependent on other factors, such as the preparation of the specimen, the presence or otherwise of surface defects, and the temperature of the test environment and material.
EN8 bright has a tensile strength of 800 MPa and mild steel, for comparison, has a tensile strength of 400 MPa. To calculate the force to shear a 25 mm diameter bar of EN8 bright steel; area of the bar in mm 2 = (12.5 2)(π) ≈ 490.8 mm 2 0.8 kN/mm 2 × 490.8 mm 2 = 392.64 kN ≈ 40 tonne-force
For example, to achieve a factor of safety of 4, the allowable stress in an AISI 1018 steel component can be calculated to be = / = 440/4 = 110 MPa, or = 110×10 6 N/m 2. Such allowable stresses are also known as "design stresses" or "working stresses".