Abstract
MEMS-based tensile testing platforms are very powerful tools for the mechanical characterization of nanoscale materials, as they allow for testing of micro/nano-sized components in situ electron microscopes. In a typical configuration, they consist of an actuator, to deliver force/displacement, and a load sensor, which is connected to the sample like springs in series. Such configuration, while providing a high resolution force measurement, can cause the onset of instability phenomena, which can later compromise the test validity. In the present paper such phenomena are quantitatively discussed through the development of an analytical model, which allows to find a relationship between the rise of instability and the sensor stiffness, which is the key parameter to be optimized.
Highlights
Mechanical characterization of materials at the micro/nanoscale has gained increasing attention during the last two decades, as acknowledged by the dramatic increase in number of correlated studies (Pantano et al, 2012)
When the sample characteristic becomes negative and its slope overcomes the load sensor spring constant, the system comprising both the sample and load sensor springs shows a snap-back instability with a positive slope, which cannot be followed during a conventional tensile test, where the end of the sample connected to the actuator is not allowed to come back to decreasing values
Our result about the occurrence of instability in the case of sample softening with a slope bigger than the sensor stiffness agrees well with similar conclusions drawn in the past, through an energetic approach, from macroscopic compression tests on rocks (Salamon, 1970), as well as with previous hypotheses adduced to explain divergences of the experimental behavior of ZnO nanowires from numerical simulations (Agrawal et al, 2009)
Summary
Mechanical characterization of materials at the micro/nanoscale has gained increasing attention during the last two decades, as acknowledged by the dramatic increase in number of correlated studies (Pantano et al, 2012). Either of the following cases may occur (Figure 1B): (a) Overall system hardening as a consequence of sample hardening, i.e., if ∂(xS-xLS)/∂F>0; (b) Overall softening with negative slope, if the sample exhibits softening (i.e., ∂F/∂(xS-xLS)
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