Quantitative stress/strain mapping during micropillar compression

Abstract

Micropillar compression is increasingly used as a method to examine small length-scale mechanical properties since it minimises the strain gradients that are unavoidable during nanoindentation into a flat surface. It also simplifies the data analysis since it is assumed that the compression is uniaxial. But how valid is this assumption when misalignments in the microscale setup are generally unavoidable? In order to investigate this, the stress and strain tensors of the micropillar should be measured during the compression. To accomplish this, electron backscatter diffraction (EBSD) mappings were obtained before, during and after consecutive compressions of a GaAs micropillar inside of a high-resolution scanning electron microscope. Elastic strain and the corresponding stress tensors were determined from the EBSD measurements using a cross-correlation technique. The results show that the von Mises stress compares well to the engineering stress determined from the nanoindenter load-displacement data. Even with rotations of almost 3 at maximum load, the negligible shear components in the strain tensor within the pillar indicates that the assumption of uniaxial compression can be made. Due to its high spatial resolution and strain sensitivity, in situ strain-stress mapping during micromechanical testing is a very promising route for the investigation of deformation phenomena on the sub-micron scale.

Nanoscale deformation mechanisms and yield properties of hydrated bone extracellular matrix

“…Micron sized pillars are produced by erosion of material using a focussed ion beam (FIB) and compressed with a flat punch diamond indenter. Due to the mostly uniaxial loading conditions [29], the interpretation of the resulting force-displacement curves in terms of stress-strain behaviour is relatively straightforward. This is a clear advantage when assessing yield properties compared to microindentation, which results in a heterogeneous and multiaxial stress state under the indenter [23].…”

Elevated temperature, nano-mechanical testing in situ in the scanning electron microscope

“…The advantages of in situ testing in the SEM and the various systems available have been detailed in several recent reviews. [1][2][3] Development of in situ systems has typically focused on increasing force/displacement resolution, generating different loading cases or incorporating additional analytical techniques such as scanning topography, 4,5 EBSD, 6,7 Raman, 8 or electrical measurements. [9][10][11] Very few in situ systems 12 have been developed for varying the environmental conditions, such as temperature.…”

A self-aligning microtensile setup: Application to single-crystal GaAs microscale tension–compression asymmetry

“…The mechanical properties of micro-and nanoscale components can differ significantly from bulk material, as they are affected by factors like fabrication process [1], material architecture [2], crystal size [3], dimensional constraints [4], and surface characteristics [5]. Micromechanical testing allows for improvements in miniaturized components design and may be used to better understand dimensional size effects, deformation mechanisms, as well as crack growth and propagation at small-length scales [6,7,8,9,10,11,12]. In the last decades, micropillar compression and nanoindentation have gained importance due to their relatively straightforward execution on a wide variety of materials.…”