Recent innovation in Scanning Electron Microscope (SEM) in-situ extreme mechanics at the micro and nanoscale
WHERE AND WHEN
Thursday, January 21, 2021
11 am – 12 pm EST
Attendees can join via Zoom.
Meeting ID: 945 8610 0937
Presented by: Nicholas Randall, Vice President Alemnis AG, Thun, Switzerland
Nanomechanical tests are moving beyond the basic measurement of hardness and elastic modulus to encompass a host of different mechanical properties such as strain rate sensitivity, stress relaxation, creep, and fracture toughness by taking advantage of focused ion beam milled geometries. New developments, such as high cycle fatigue, are extending the range of properties which can be studied at the micro and nanoscale. However, such techniques are challenging due to low oscillation frequencies, long duration of tests and large thermal drift when attempted with standard indentation instruments. Novel piezo-based nanoindentation methods are now allowing access to extremely high strain rates (>104 s-1) and high oscillation frequencies (up to 10 kHz).
Until only recently, high strain rate testing of materials at strain rates from ~100/s – 10000/s has only been possible using macroscale techniques, such as split Hopkinson bar, Kolsky bars and plate impact testers. At the microscale, strain rates have typically been limited to ̴ 0.1/s or less, owing to limitations in instrumentation, insufficient data acquisition rates and elastic wave propagation conflicts during testing.
This talk will focus on the most recent developments in instrumentation for in-situ extreme mechanics testing at the micro and nanoscales, with specific focus on a testing platform capable of strain rate testing over the range 0.0001/s up to 10’000/s (8 orders of magnitude) with simultaneous high speed actuation and sensing capabilities, with nanometer and micronewton resolution respectively.
Other recent innovations include cryogenic and high temperature tests covering the temperature envelope from -150 to 1000 °C. The challenges in variable temperature tests and the associated technological and protocol advances will be discussed along with select case studies. The inherent advantages of using small volumes of sample material, e.g., small ion beam milled pillars, will be discussed together with the associated instrumentation, technique development, data analysis methodology and experimental protocols. Some examples of test data will be presented where a wide range of strain rate has been combined with variable temperature in order to investigate rate effects as a function of temperature. Finally, future research directions in this sub-field of micromechanics will be discussed.