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Vickers hardness of the standard error analysis of the accuracy factor 0 replies,756 views

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First, the accuracy of Vickers hardness of the factors that theoretical analysis and experimental results show that the Vickers hardness with the following factors: 1, test power: the size and hardness test force size, the direction of test force, test speed of force applied to keep the time very related. 2, the pressure head: the hardness and the two opposite sides of the diamond indenter angle, chisel edge and a rectangular cone surface roughness Dengjun related. When the pressure head to the top is not a point but a line, called the horizontal line as the pressure head edge. 3, the specimen: the hardness and the sample material, shape and surface roughness, indentation and the indentation between the distance between the edge of the sample and the sample temperature Dengjun related. Second, the Vickers hardness test error of 2.1-indentation diagonal length measurement inaccuracies caused by measurement errors ----- hardness indentation diagonal length measurement when a big, hardness measured value lower than the true value of the hardness ; the other hand, when the small indentation diagonal length measurement, the measured hardness values higher than the true value of hardness. The longer indentation diagonal, then the hardness measurement relative error is smaller. So when the test conditions allow, should try to use a larger test force in order to get a larger indentation hardness measurements to reduce the relative error. Deviation from the standard 2.2-test force values caused by measurement errors ----- test the hardness of force larger than the standard value, the hardness values measured lower than the true value of hardness; the other hand, test force smaller than the standard value, the hardness values measured higher than the true value of hardness JJG151-1991 "Vickers hardness test procedures," states: Vickers hardness test force tolerance of 1.0%. JJG260-1991 "microhardness testing procedures," states: The test force for 0.9807N tolerance is 2.0%, 0.9807N test force tolerance is 1.5%, 1.961N force tolerance test was 1.0%. 2.3-test force is not perpendicular to the sample surface hardness of measurement error caused by the pressure head ----- factors excluded, as long as the two diagonal measurement of the indentation and the average value to calculate the hardness value, such factors The hardness measurement error is very small. 2.4 The test force dwell time deviation from the standard value of the hardness measurement errors caused by test force ----- As time increases, the hardness value decreased; when the test force for a period of time, the hardness change is slowing down. Verification rules of order: Test force dwell time is 10 ~ 15s. Speed of 2.5-test force is applied due to the hardness measurement errors ----- test force is applied as the speed increases, the hardness decreases. JJG151-1991 "Vickers hardness test procedures," states: Vickers hardness test force applied rate should be 0.15 ~ 0.25mm / s or pressed into time that should be 2 ~ 5s. JJG260-1991 "microhardness testing procedures," states: microhardness test force applied rate should be 0.02 ~ 0.07mm / s. 2.6-diamond indenter angle between the two opposite sides of the hardness caused by deviations from the standard value of the angle measurement error is too large, the hardness measured value lower than the true value of hardness. ----- JJG334-1993 "diamond indenter test procedures," states: two diamond pyramid facet relative angle between the Vickers indenter should be 1360.5,; small load and the Vickers indenter should be 1360.25. 2.7-pressure head chisel hardness measurement errors caused by the pressure head ----- have chisel edge, creasing into a rectangle, so that the measured length of indentation diagonal, hardness values decrease, bringing negative hardness measurement error. In the range of hardness testing, pressure head of a very large chisel edge. JJG334-1993 "diamond indenter test procedures," states: diamond pyramid indenter top of the chisel edge length of the Vickers indenter should be less than 2um; small load and the Vickers indenter should be less than 1um. 2.8-diamond indenter does not meet the requirements of surface roughness caused by measurement errors ----- hardness of the surface roughness increases the pressure head, pressure head pressed into the resistance increases, the hardness value increased. JJG334-1993 "diamond indenter test procedures," states: diamond indenter surface roughness, RZ0.1um. 2.9-sample material hardness measurement errors caused by different ----- The results show that the indentation of different materials have different shapes, on the tip of the indentation diagonal to determine the real cause difficulties, so bring the hardness measurement error. 2.10-surface roughness does not meet the required hardness measurement errors caused by the smaller surface roughness, the more clear the edge of the indentation, the indentation diagonal measurement of the length of the more stable, which can be more accurate, stable hardness value. 2.11-specimen shape the hardness of non-compliance caused by measurement error ----- sample thickness is reduced to a certain extent, will reduce the hardness value. Sample surface is not flat, the hardness of the sample surface with the diameter changes. GB/T4340.1-1999 "Vickers hardness test Part 1: Test methods" provision: the thickness of the sample or test should be at least 1.5 times the indentation diagonal, the back should not appear after the test sample can be seen deformation traces; For test results on the sample surface should be corrected using the correction factor table; for small or irregular shape of the specimen cross-section can be mounted or sample test using a dedicated support units. 2.12-indentation and the indentation between the distance between the edge of the sample does not meet the requirements of the hardness measurement errors caused by the distance between the indentation ----- too close, will increase the hardness; indentation to the distance between the edge of the sample is too Recently, the hardness will decrease. GB/T4340.1-1999 "Vickers hardness test Part 1: Test methods" provision: any specimen edge distance from the indentation center for steel, copper and copper alloys should be at least the length of the indentation diagonal 2.5 times, for the light metal, lead, tin and alloys should be at least 3 times the length of the indentation diagonal; the distance between the centers of two adjacent indentations, for steel, copper and copper alloys should be at least the length of indentation diagonal 3 times, for the light metal, lead, tin and alloys should be at least 6 times the indentation diagonal, if two adjacent indentations of different sizes should be determined to a larger indentation indentation spacing.
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