ASTM C730-98(R2021) pdf free download

ASTM C730-98(R2021) pdf free download.Standard Test Method for Knoop Indentation Hardness of Glass
4. Significance and Use
4.1 The Knoop indentation hardness is one of many prop- erties that is used to characterize glasses. Attempts have been made to relate Knoop indentation hardness to tensile strength, grinding speeds, and other hardness scales, but no generally accepted methods are available. Such conversions are limited in scope and should be used with caution, except for special cases where a reliable basis for the conversion has been obtained by comparison tests.
5. Apparatus
5.1 Testing Machines: 5.1.1 There are two general types of machines available for making this test. One type is a self-contained unit built for this purpose, and the other type is an accessory available to existing microscopes. Usually, this second type is fitted on an inverted- stage microscope. Good descriptions of the various machines are available. 3,4 5.1.2 Design of the machine should be such that the loading rate, dwell time, and applied load can be standardized within the limits set forth in 3.1.1.2 – 3.1.1.4. It is an advantage to eliminate the human element whenever possible by appropriate machine design. The machine should be designed so that vibrations induced at the beginning ofa test will be damped out by the time the indenter touches the sample. 5.1.3 The calibration ofthe balance beam should be checked monthly or as needed. Indentations in standard glasses are also used to check calibration when needed. 5.2 Indenter: 5.2.1 The indenter shall meet the specifications for Knoop indenters. 4 See Test Method E384. 5.2.2 Fig. 1 shows the indenter and its maximum usable dimensions. The diagonals have an approximate ratio of 7:1, and the depth of the indentation is about 1 ⁄ 30 the length of the long diagonal. A perfect Knoop indenter has the following angles: 5.2.2.1 Included longitudinal angle 172° 30′ 00″. 5.2.2.2 Included transverse angle 130° 00′ 00″. 5.2.3 The constant C p for a perfect indenter is 0.07028 and the specifications require a variation ofnot more than 1 percent from this value. 5.3 Measuring Microscope—The measurement system shall be so constructed that the length of the diagonals can be determined with errors not exceeding 60.0005 mm. The apparent length of the diagonal should be corrected for the limit of resolution of the objective being used in the micro- scope (see Appendix X1).
6. Test Specimen
6.1 The Knoop indentation hardness test is adaptable to a wide variety of glass specimens, ranging from tubing to television faceplates to polished plate glass. In general, the accuracy of the test will depend on the smoothness of the surface and, whenever possible, ground and polished speci- mens should be used. The back of the specimen shall be fixed so that the specimen cannot rock or shift during the test. 6.1.1 Thickness—As long as the specimen is over ten times as thick as the indentation depth, this will not affect the test. In general, if specimens are at least 0.10 mm thick, the hardness will not be affected by variations in the thickness. 6.1.2 Surface Finish—As pointed out above, the accuracy of the test depends on the surface finish. However, if one is investigating a surface coating or treatment, he cannot grind and polish the sample. Experience has shown that six inden- tations on a ground and polished surface of glass will repro- duce within 61 %. Six indentations on an “as-received” surface may be as bad as 610 %. Ground and polished surfaces should be used. If this is not possible, the number of indenta- tions should be increased. 6.1.3 Radius of Curvature—The KHN obtained will be affected even when the curvature is only in the direction of the short diagonal. Care should be used when relating KHN values obtained on curved surfaces to those obtained on polished flat surfaces. 7. Verification of Apparatus 7.1 Verification of Load—Most of the machines available for Knoop hardness testing use a loaded beam. This beam should be tested for zero load. An indentation should not be visible with zero load, but the indenter should contact the sample. A visible indentation should be obtained with a load of 0.1 gf. Other methods of verifying the load application are given in Practices E4.