GLASS

Glasses present a rich field of study both for academia and industry. Large window glass becomes increasingly functional, while novel microfabrication techniques are pushing the limit of their miniaturization. Many open questions remain though, ranging from fundamental glass physics to ways of reducing brittleness for real-world applications. To achieve a more scientifically driven approach to glass design and processing, the industry must build on the physics of atomic rearrangements, defect initiation, and dynamic fracture in response to mechanical loading. The mechanical behaviour of glasses is fundamentally different from crystalline materials due to the lack of grain boundaries, dislocation activities, and slip systems. In stead, the amorphous arrangement tends to deform via alternative mechanisms such as viscous flow, densification and shear bands. It is crucial to study these mechanisms to predict the mechanical performance of glasses, both for real-world applications and fundamental sciences.

Testing the strength of microscale fused silica. What is the influence of the surface finish on the mechanical properties?

The strength of glasses has been studied for over 100 years. Yet, ever more complex experiments and computational studies continue to refine our description of this class of materials till today. The intricacy of the topic is well illustrated for example by the 6 (six!) definitions of strength of fused silica.¹ Firstly, one has to differentiate extrinsic from intrinsic strength. The extrinsic strength is limited by the extreme sensitivity of glasses to extrinsic microdefects on the surface or in the bulk of glass samples. The intrinsic strength, on the other hand, excludes the presence of such flaws. This is only the case in very small specimens on the micrometer length-scale, such as carefully drawn fibers or micropillars. Secondly, both the extrinsic and the intrinsic strength can be impaired by fatigue, i.e. the delayed failure due to crack nucleation under stress. Fatigue can occur under inert and environmental conditions during slow testing, or it can be absent, as for example during fast testing.

Factors such as the sample size and fabrication method, the testing environment (humidity, temperature), and the testing speed are therefore not only variables of interest to fundamental science , but are highly relevant for real world applications. The Alemnis Standard Assembly (ASA) is a highly versatile test platform featuring true displacement control and the widest range of environmental control available on the market. Some aspects that make the ASA particularly suitable for testing of brittle glasses are:

The ability to precisely control the rate of deformation, irrespective of any yielding, cracking, flow, or other deformation response.
The option for environmental control including relative humidity and temperature from – 150 °C up to 1000 °C
The possibility to perform ultra-high strain rate tests.
The large load capacity of up to 4 N

Micromechanical testing in the glass domain covers a wide variety of topics:

Mapping of hardness and elastic properties
Push-out, tensile, and bending of glassfiber
Strength of µ-additively manufactured or laser-assisted micro-etched structures
Flow and densification during indentation and compression
Rate dependence of strength and plasticity

Automated mapping of mechanical properties of large glass sample arrays

Selected papers where the Alemnis system has been used for investigating glasses:

High strain rate:

Ramachandramoorthy, et al. (2019). Dynamic Plasticity and Failure of Microscale Glass: Rate-Dependent Ductile–Brittle–Ductile Transition. Nano Letters, 19(4), 2350–2359. https://doi.org/10.1021/acs.nanolett.8b05024
Ramachandramoorthy, R., et al. (2021). High strain rate in situ micropillar compression of a Zr-based metallic glass. Journal of Materials Research, 36(11), 2325–2336. https://doi.org/10.1557/s43578-021-00187-5
Widmer, R. N., et al. (2021). Plasticity of Metal-Organic Framework Glasses. Journal of the American Chemical Society, 143(49), 20717–20724. https://doi.org/10.1021/jacs.1c08368
Guillonneau, G., et al. (2022). Plastic Flow Under Shear-Compression at the Micron Scale-Application on Amorphous Silica at High Strain Rate. Jom. https://doi.org/10.1007/s11837-021-05142-7

High temperature:

Widmer, R. N., et al. (2022). Temperature–dependent dynamic plasticity of micro-scale fused silica. Materials & Design, 215, 110503. https://doi.org/10.1016/j.matdes.2022.110503
Wheeler, J. M., et al.. (2011). In situ SEM indentation of a Zr-based bulk metallic glass at elevated temperatures. Materials Science and Engineering A, 528(29–30), 8750–8756. https://doi.org/10.1016/j.msea.2011.08.057

Other:

Martinet, C., et al. (2020). Highlighting the impact of shear strain on the SiO2 glass structure: From experiments to atomistic simulations. Journal of Non-Crystalline Solids, 533(January), 119898. https://doi.org/10.1016/j.jnoncrysol.2020.119898
Kermouche, G., et al. (2016). Perfectly plastic flow in silica glass. Acta Materialia, 114, 146–153. https://doi.org/10.1016/j.actamat.2016.05.027
Tong, X., Wang, G., et al. (2018). Structural evolution in a metallic glass pillar upon compression. Materials Science and Engineering A, 721, 8–13. https://doi.org/10.1016/j.msea.2018.02.050

Temperature-dependent plasticity of fused silica micropillars

The Alemnis Standard Assembly (ASA) can also be coupled to correlative analytical techniques including:

in situ Raman spectroscopy to probe local rearrangement of bonding during mechanical deformation
in situ SEM imaging to correlate the mechanical response with visual observations such as shear bands and crack formation
in situ Synchrotron experiments, such as pair distribution analysis (PDF)

Other hot topics in the field of novel, functional glasses:

Hybride organic-inorganic glasses
Metal-organic glasses
Metallic glasses

References:

1 Kurkjian, C. R., Gupta, P. K., Brow, R. K. and Lower, N., “The intrinsic strength and fatigue of oxide glasses”, J. Non. Cryst. Solids 316, 114–124 (2003).