In this paper an improved method for calibrating the 3D geometry of Rockwell indenters using a metrological stylus profilometer is reported. The measured geometry of the indenter is not only applied to determine the quality of the indenter, but also used for correcting the hardness values for improved hardness measurement accuracy. A method for such a correction has been proposed. A virtual indentation device simulated using finite element method (FEM) has been developed. By applying both the measured and the theoretically ideal indenter geometries in the virtual device, two different...
The geometric parameters of 28 candidate Standard Reference Material (SRM) Rockwell hardness diamond indenters are calibrated by an automated system recently developed at the National Institute of Standards and Technology (NIST). The calibration results show that the cone flank straightness is a key issue for the calibrated indenters to be qualified for the geometrical specifications of NIST SRM diamond indenters. The effect of selecting different window sizes and locations for the evaluation of cone flank straightness is discussed.
An analytical method of the geometrical parameters of hardness indenters from bitmap data obtained AFM, etc. is introduced. The method is based on the fitting to the analytical geometric shape by the least square method. The results of the analysis are not influenced by human factors which are usually included in the operation of analyzing software's GUI. Examples of analytical results are shown with the estimation of the uncertainty of measurement. The uncertainty is estimated considering the uncertainty of AFM itself and the misfit of plan regression, and the uncertainty of facet angles,...
The international standards for qualification of material testing machines like the ISO standards for hardness testing [1] -[3] use the relative span (range) as a repeatability parameter. Form the view of statistics and uncertainty the determination of the range is not suitable for this purpose. We propose a transition from range to standard deviation for describing the machines quality parameter which allows a direct estimate of the machines uncertainty and of the reliability of test results within the limits fixed by the ISO standards. For the transition from range to standard deviation...
The load and partial unload technique adds partial unload processes to the load curve. The mechanical properties like elastic modulus can be determined for each of these unload curves. This allows for a faster depth dependent measurement of the characteristic quantities. If the elastic modulus of a material is known and not dependent of the depth, an indenter shape correction can be performed using this technique. The results of such a correction are compared with those gained using a correction based on the Martens hardness of the material. The elastic modulus E IT as well as the Martens...
The model function of the torque generated in a static torque standard machine contains a cosine function for the inclination of the lever against the horizontal plane. An inclined lever has a shorter effective lever arm length, and a smaller torque is generated in this case. The uncertainty analysis of this model function gives a zero sensitivity coefficient for the inclination angle when the estimate of the angle is zero – a mathematical correct, but from the uncertainty point of view, obviously improper result. A method for dealing with this problem is proposed in this paper.
In 2008 one ILC, for the calibration of torque wrenches, was organised in Italy by COPA-SIT (Sistema Italiano di Taratura). In the present paper the main results obtained during the ILC are discussed, in particular the differences on the repeatability and accuracy given by the different laboratories are compared and evaluated.
Standard torque measuring machines and their traceability is relatively new in metrology field. The growing car manufacturing and assembly industry in Egypt made it necessary to develop a national standard for torque measurement which can provide traceability to the industry according to world wide standards. A new design of 3 kNm reference torque standard machine was therefore considered. The machine was designed following the component system principle based on the vertical axis measurement method, without intermediate bearing, which reduces about 70% of the cost. Prior to that, the parts...
A 10 N·m dead weight torque standard machine (10-N·m-DWTSM) has been under development at NMIJ/AIST since 2006 to expand the range of the torque standard. Estimation of the sensitivity limit of the fulcrum is one of the most important issues to realize a precise reference torque of small capacity by using a dead weight torque standard machine. In this study, a torque transducer was installed on the 10-N·m-DWTSM in order to keep the moment-arm on the horizontal line (balancing). The sensitivity limit of the fulcrum under real calibration conditions was estimated by reading the change in the...
This paper presents the study of behavior of torque four transducers under pure torque and torque with cross force. This explains how cross force causes the measurement result deviating from pure torque. Output signals at every 45° loading angle around measurement axis of pure torque and torque with cross forces at minimum arm length and middle arm length were compared. The result shows that cross force causes sinusoidal-like relationship between the output signals and loading angles. Moreover, cross force effect shifts the sinusoidal graph from x-axis or average of output signals was...