In-situ SEM compression tests on samples such as cantilevers, particles, or microcapsules are performed to gain an understanding about physical processes and systematic development of new materials.
It is possible to combine and synchronize nanomechanical testing with specialized SEM detectors such as STEM or EBSD.
Quantification of Shear Band Behavior in Micropillars
A quantitative understanding of the effect of irradiation onto the material of the load bearing structures is essential for applications in environments with high radiation fluxes, such as in space and nuclear reactors. In-situ SEM nanomechanical testing enables the high-resolution recording of stress versus strain curves and the compression testing of micropillars.
The depicted image sequence by Prof. Daniel S. Gianola from UC Santa Barbara demonstrates the stress-strain curve of the micropillar and its plastic morphology with high irradiation dose.
Following the linear elastic regime (a), it is possible to observe macroscopic yielding and nucleation of shear localization (b). With an additional increase of the strain, the shear band propagates until it reaches the pillar surface (c), which is indicated by the stress drop. This is followed by the correlation of smaller stress drops with intermediate slip events on parallel planes (d).
Characterization of Lightweight Nanocomposite Materials
The systematic development of new, high-strength, and lightweight materials requires accurate examination of their mechanical properties. Complex composites based on nanoscale structures such as bubbles, particles, and fibers are gaining increasing attention because of their ability to increase the specific stiffness and strength of materials.
The incorporation of stiff, hollow microparticles, also called bubbles, into a polymeric matrix has been demonstrated in the depicted work by Prof. Daniel S. Gianola from UC Santa Barbara. It is essential to customize the mechanical properties of the hollow microparticles for developing such lightweight materials.
Prof Gianola used in-situ SEM nanomechanical testing to demonstrate that thermal treatment of these nanoparticle-shelled bubbles will improve the strength and stiffness by a factor up to 14.
Micro- and Nano-Scale Chevron Notch Fracture Test
The standardized mechanical investigation of materials in the micro- and nano-scale, for example, the depicted chevron notch fracture test (Prof. Mortensen, Laboratory of Mechanical Metallurgy, EPFL, Switzerland) is crucial for determining their mechanical behavior.
The nanoscale mechanical examination, particularly for crystalline materials, provides new opportunities to understand the effect of stress onto the structure-property relationship of the material.
Nanomechanical testing can be integrated with customized SEM detectors such as Electron Backscatter Diffraction (EBSD) detectors. This combination enables investigators to compare the applied mechanical stress with the material’s crystallographic properties, such as grain structure and orientation using Transmission Kikuchi Diffraction.
Thermomechanical Creep Testing of Individual Metallic Glass Nanowires
Metallic glasses are receiving increasing attention because of their unique mechanical properties, such as high fracture toughness and a large elastic limit. Additionally, the large supercooled liquid region allows superplastic forming, making room for new material processing strategies.
Therefore, it is essential to have a quantitative understanding of its thermomechanical behavior. The depicted work from Prof. Daniel S. Gianola at UC Santa Barbara examines the superplastic-like flow of metallic glass. For this purpose, a metallic glass nanowire is fixed between a second substrate by Pt-EBID and the FT-S Microforce Sensing Probe.
A constant tensile load should be applied while measuring the deformation when performing a creep test. An electric current passed through the nanowire increases the temperature stepwise. The creep behavior is analyzed at varied nanowire temperatures with this method.
Uniaxial Compression Testing of CNT Micropillars
Vertically aligned carbon nanotube (CNT) pillars are considered to be a promising material for applications such as 3D super capacitors, compliant thermal interface materials, and flexible batteries. The mechanical properties of CNT arrays rely on the individual nanotubes as well as on their packing density and the interaction forces between the individual tubes.
A compression test is performed to experimentally study the mechanical properties of a CNT pillar. In this method, the CNT pillar is first aligned to the microforce sensing probe of the testing system (a). This is followed by applying a load to the CNT pillar. The deformation is measured and simultaneously visualized by the scanning electron microscope (b). The plastic deformation of the pillar after the load application is depicted in (c). Stress relaxation effects are illustrated in (d).
(Image courtesy: Prof. Daniel S. Gianola from UC Santa Barbara)
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