Researchers in the field of nanotechnology and nanoscale material research are constantly looking for new ways of improving the strength of nanomaterials, trying to understand the fundamental interactions between atoms, making the materials. How do forces interact to produce elasticity properties of various materials and how will understanding these atomic and structural forces help scientists and engineers create more stable and stronger nanostructured materials?
A phenomenon known as nano-buckling is one that has been the focus of attention from international research teams, having implications for the strength and viability of nanostructured materials. However, this phenomenon is still poorly understood. This article will provide an overview of this subject.
Buckling is defined as an instability leading to structural failure and is categorized by a sudden sideways deflection of one of the structural members. This can occur below the threshold that is required for structural failure and further unpredictable deformations can arise as stress increases, eventually leading to the complete loss of the substance’s load-bearing capabilities.
Nano-buckling is essentially buckling which occurs at the nanoscale in nanostructured materials. Both nanolayers and nanotubes exhibit buckling effects due to various stress factors.
What Causes Nano-Buckling?
Buckling loads of nanomaterials can be predicted by principles such as modified strain gradient theory (MSGT), modified couple stress theory (MCST), strain gradient theory (SGT) and classical theory (CT.) These are simple forms of strain gradient elasticity theory. Strain gradient elasticity theory governs the calculation of elastic strain energy function.
Recent research has demonstrated that nano-buckling arises due to a variety of factors. The most important of the factors responsible is a thermal mismatch. As substances tend to change their volume, shape, and area in response to temperature, this can have ramifications for the structural integrity of substances when they are exposed to fluctuations in temperature, and nanomaterials are no different in this respect.
Another factor that governs buckling in nanomaterials is the absence of cross-links between individual atomic layers. A team including research scientists from the Max Planck Institute and the University of Vienna demonstrated this in 2005 by using a hundred nanometer-side X-ray beam to observe the effect in carbon nanofibers, in which stress was applied to them, by being bent.
Whilst the tensile strength of carbon fiber is stronger than other known materials (carbon fibers are only a few micrometers thick and are used to mechanically reinforce other materials including polymers) when compression is applied parallel to their axis, buckling of the layers occurs. This is comparable to the buckling of a rod under a compressive load. It was found that some carbon fibers exhibit very good shear properties, however. In these types of fibers nano-buckling very rarely occurs, which suggests the presence of a large number of cross-links between the carbon layers.
In a study of layered copolymer materials, buckling was observed in the material at the nanoscale at a wavelength-dependent on the strain rate. Contrary to popular assumptions, the undulation was found not to be linked to physical defects in the microstructure, but rather, due to kinetic effects. There was a correlation between the strain rate and instability growth rate.
Research on nanoscale materials is still in its infancy. Understanding the factors that lead to buckling at the nanoscale and discovering materials that can resist these stress factors will help scientists develop even stronger and more versatile nanostructured materials that can be used in a myriad of applications.
Makke, A et al. (2012) Nanoscale buckling deformation in layered copolymer materials PNAS Vo. 109 Issue 3, Pgs. 680-685
Why nanolayers buckle when microbeams bend – Max Planck Institute
Shaat, M et al. (2018) Buckling characteristics of nanocrystalline nano-beams International Journal of Mechanics and Materials in Design Vol. 14 Issue 1 pp 71-89