M-13MMitutoyo operates a policy of continuous improvement that aims to provide the customer with the benet of the latest technological advances.Therefore the company reserves the right to change any or all aspects of any product specication without notice.Hardness Testing MachinesQuick Guide to Precision Measuring Instruments■Methods of Hardness Measurement(1) VickersVickers hardness is a test method that has the widest application range, allowing hardness inspection with an arbitrary test force. This test has an extremely large number of application elds particularly for hardness tests conducted with a test force less than 9.807N (1kgf). As shown in the following formula, Vickers hardness is a value determined by dividing test force F (N) by contact area S (mm2) between a specimen and an indenter, which is calculated from diagonal length d (mm, mean of two directional lengths) of an indentation formed by the indenter (a square pyramidal diamond , opposing face angle θ=136˚) in the specimen using a test force F (N). k is a constant (1/g=1/9.80665).HV=kFS=0.102FS=0.1022Fsin d2q2=0.1891Fd2F:Nd:mmThe error in the calculated Vickers hardness is given by the following formula. Here, Dd1, Dd2, and ‘a’ represent the measurement error that is due to the microscope, an error in reading an indentation, and the length of an edge line generated by opposing faces of an indenter tip, respectively. The unit of Dq is degrees.DFF- 2-a2d2DHVHVDd1d- 2Dd2d3.5x10-3Dq(2) KnoopAs shown in the following formula, Knoop hardness is a value obtained by dividing test force by the projected area A (mm2) of an indentation, which is calculated from the longer diagonal length d (mm) of the indentation formed by pressing a rhomboidal diamond indenter (opposing edge angles of 172˚30' and 130˚) into a specimen with test force F applied. Knoop hardness can also be measured by replacing the Vickers indenter of a microhardness testing machine with a Knoop indenter.HK=kFA=0.102FA=0.102Fcd2=1.451Fd2F:Nd:mmc:Constant(3) Rockwell and Rockwell SupercialTo measure Rockwell or Rockwell Supercial hardness, rst apply a preload force and then the test force to a specimen and return to the preload force using a diamond indenter (tip cone angle: 120˚, tip radius: 0.2mm) or a sphere indenter (steel ball or carbide ball). This hardness value is obtained from the hardness formula expressed by the difference in indentation depth h (µm) between the preload and test forces. Rockwell uses a preload force of 98.07N, and Rockwell Supercial 29.42N. A specic symbol provided in combination with a type of indenter, test force, and hardness formula is known as a scale. Japanese Industrial Standards (JIS) dene various scales of related hardness.■Relationship between Vickers Hardness and the Minimum Allowable Thickness of a SpecimenHV=0.1891t>1.5dh≒d/7t: Thickness of specimen (mm)d: Diagonal length (mm)h: Depth of indentation (mm)[Example]Specimen thickness t: 0.15mmSpecimen hardness: 185HV1Test force F: 9.807N (1kgf)Diagonal length d: 0.1mmFd2Vickers hardnessHV200010005003002001005030200.0010.0020.0030.0050. d:mm0.0010.0020.0030.0050. forceHardness symbolF:NHV0.0005Minimum thickness of specimenDiagonal length of indentation9.807x10-319.61x10-329.42x10-349.03x10-398.07x10-30.19610.29420.49030.98071.9612.9424.9039.80719.6129.4249.0398.07196.1294.2490.3dth


page 632