Ultra-high Strain Rate

Ultra high strain rate covering 8 orders of magnitude.

The Alemnis Standard Assembly (ASA) can be configured in several ways to achieve ultra high strain rates up to 10’000 s^-1, thus covering 8 orders of magnitude.

Such high strain rates are possible because the dimensions of a typical micropillar are so small relative to the actuation velocity, the lower magnitude of inertial contributions and faster stress wave equilibration times.

In dynamic micromechanical testing, the elastic and plastic constitutive material properties of microscale samples can be obtained at very high strain rates without interference from the elastic waves in the material. Exploring the high strain rate mechanical properties at the microscale is very advantageous compared to the macroscale.

• Understanding the wave propagation phenomena is vital and only possible with the Alemnis Standard Assembly unique ultra high strain rate capabiltities.

• The four possible configurations for high strain rate testing are summarized in the table, where SmarTip actuators can be mounted either on the displacement head side (all four configurations) or also on the sample side. The resonance frequency of the ASA is of the order of > 10 kHz, depending on the actual configuration. Different SmarTips are available, either in single or 3-axis configuration. For example:
  • VHS-1-1 configuration: the displacement is made by the piezostack actuator and the resultant load is measured by the SmarTip (note that the SmarTip could also be mounted under the sample in this configuration), allowing very high strain rates up to 1000 s^-1. Typical application is high strain rate testing, fatigue, impact, dynamic, etc.
  • UHS-1-1 configuration: two SmarTips are mounted either side of the sample, where one is the actuator and the other the sensor. This allows even higher strain rates up to 10’000 s^-1. Typical application is ultra high strain rate testing, fatigue, impact, dynamic, etc.
  • UHS-1-3 and UHS-3-3 configurations: these are the same as for UHS-1-1, except that either one or both SmarTips are capable of actuation/sensing in 3 axes (normal Z axis and two lateral XY axes). Typical application is ultra high strain rate testing, fatigue, impact, dynamic, as well as scratch testing, tribology, fretting, lateral oscillation, etc.

The SmarTip actuator is powered by a state-of-the-art high voltage, high speed amplifier capable of inputting high voltages across a variety of time scales with very high slew rates. The embedded strain gauges are capable of capturing these high speed displacements with a resolution of   ̴15 nm. The displacement voltage signals are acquired using a data acquisition board capable of high speed sampling up to 50’000 samples per second.

• Senses changes in load at high frequencies up to 10 kHz with a resolution of 30 µN.
• Ultra high sampling rates of up to 2.5 giga samples per second.
• Combined machine compliance reduced to 10^-7 m/N.

Main Components:

• Displacement head: piezo actuated displacement head with integrated displacement sensor for closed loop operation. Maximum displacement 40 µm, displacement resolution < 1 nm;
• Load sensor: max. force: 0.5 N, typically 4 µN RMS noise;
• Sample versus indentation tip positioning: Piezoelectric XY+Z micro-positioning system for sample positioning and tip approach (26 mm range in X and Y, 26 mm range in Z), with integrated position sensors for closed loop operation (< 2 nm resolution);
• 5 standard stubs;
• all cables and connectors for in air operation.

For integration in SEM, additional modifications may be required, such as custom flanges, cabling, mounts and connectors. This is typically quoted on a case-by-case basis.