WEB Nanoindentation Testing at High Sustained Deformation RatesWednesday (01.01.2020) 00:00 - 00:30 Part of:
Constant strain rate nanoindentation is a popular method for accessing the local strength of complex materials. However, with currently available testing systems using continuous stiffness measurement (CSM), nanoindentation is so far limited to strain rates of ~0.1/s, which precludes it from ballistic applications.
Here, we show that the current limitation derives primarily from a plasticity issue related to the continuous stiffness measurements. In order to access high deformation rates, we took the drastic step of modifying the standard Oliver-Pharr evaluation method, so as to avoid the need for a measurement of the contact stiffness. With this improvement, the experimental upper strain rate limit is mostly determined by the time constants of the hardware components and lies around 100 /s with most current commercial systems. The potential of the new method will be illustrated by the mechanical characterization of a superplastic Zn22Al alloy over 5 orders of magnitude of strain rates, i.e. a wider range than accessible with any other technique.
 B. Merle, V. Maier-Kiener, G.M. Pharr. Influence of modulus-to-hardness ratio and harmonic parameters on continuous stiffness measurement during nanoindentation. (2017) Acta Materialia, 134, pp. 167-176.
 B. Merle, W.H. Higgins, G.M. Pharr. Critical Issues in Conducting Constant Strain Rate Nanoindentation Tests at Higher Strain Rates. (2019) Journal of Materials Research, 34(20), pp. 3495-3503
 B. Merle, W.H. Higgins, G.M. Pharr. Extending the Range of Constant Strain Rate Nanoindentation Testing. (2020) Journal of Materials Research, DOI:10.1557/jmr.2019.408