Seminar Series - Recent innovation in Scanning Electron Microscope (SEM) in-situ extreme mechanics in extreme environments

17. 5. 2022  9:30 - 10:30  

CEITEC BUT S building meeting room C2.11  

Dr. Nicholas Randall  

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.