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Some critical discussion of the state of the art of uncertainty evaluationin Instrumented Indentation Testing IIT
Nowadays the Instrumented Indentation Testing (IIT), in the nano range often named as nano indention, is one of the most commonly used methods to determine the mechanical properties of materials in the micro and nano range. This method is already extensive standardized in ISO 14577 part 1-4. In the past, the application of this standard in testing praxis shows that the established values have an excellent precision.If an uncertainty is calculated, the range of values within which the true value is asserted to lie with some level of confidencewill be known. In part 1 of ISO 14577 [1] two methods for evaluation of the uncertainty in IIT are mentioned:
Method 1 for determining uncertainty considers only those uncertainties associated with the overall measurement performance of the testing machine with respect to the reference blocks.
Method 2calculates a combined uncertainty from individual contributions. These may be grouped into random and systematic uncertainties.
Both methods will be described in detail using examples from the dailyexperimental praxis. The comparabilityof both methods will be critically discussed. Finally, it will be showedhow the calculated uncertaintiescan be used for performancetests and product specifications.
Acknowledgement
This work was performed under the support of the EMPIR project 17NRM05Advancing measurement uncertainty̶ comprehensiveexamples for key international standards
References
[1] ISO 14577 part 1 (2017)
In der DIN EN ISO 14577 Metallische Werkstoffe – Instrumentierte Eindringprüfung zur Bestimmung der Härte und anderer Werkstoffparameter sind die Durchführung und Auswertung des Verfahrens, sowie die Kalibrierung der zu verwendenden Prüfmaschine genormt. In dieser Norm werden auch grundsätzliche Aussagen zur Bestimmung der Messunsicherheit gemacht.
An Beispielen aus der täglichen Prüfpraxis werden verschiedene Möglichkeiten, aber auch die Grenzen der Bestimmung der Messunsicherheitbei der Instrumentierten Eindringprüfung beschrieben und kritisch diskutiert.
Nowadays the Instrumented Indentation Testing (IIT) is one of the most commonly used methods to determine the mechanical properties of materials in the nano range. This method is already extensive standardized in EN ISO 14577 part 1-4. Because of the great interest of researchers and industries in investigations of time depending material behavior mostly all suppliers of IIT equipment are offering the possibility of dynamic testing. Realizing this development ISO/TC 164/SC3 Hardness Testing has proposed to start the new standardization project “Linear elastic dynamic instrumented indentation testing DIIT”. The development of this standard is accompanied by the first international intercomparing exercise comparing results of dynamic instrumented indentation testing from testing machines using different hardware solutions and different models for data evaluation.
The draft of part 5 of ISO 14577 “Linear elastic dynamic instrumented indentation testing DIIT” specifies verification and calibration of testing machines for carrying out the measurement of the dynamic material response when an oscillatory force or displacement, with amplitudes small in comparison to the prescribed target values, is imparted to the indenter while the indenter is continuously loaded to a prescribed target load or target depth or while the load or displacement is held constant at a prescribed target value. In case of a material showing plastic-elastic behavior, the measured dynamic response is used for continuous evaluation of the dynamic stiffness of the contact as a function of depth and frequency. Using the dynamic stiffness of the contact a reduced dynamic modulus will be calculated. In case of a material showing visco-elastic behavior from the measured dynamic response also the dynamic contact damping coefficient as function of depth and frequency is evaluated continuously. Using dynamic contact stiffness and dynamic contact damping coefficient reduced lost and storage modulus for visco-elastic materials will be calculated.
The main normative requirements of the draft will be presented and discussed in the light of the first results of the intercomparing excise.