The coordinated buckling of carbon nanotube turfs under uniform compression

Abstract

Complex structures consisting of intertwined, nominally vertical carbon nanotubes (CNTs), referred to as turfs, have unique properties that arise from their complex nanogeometry and interactions between individual CNT segments. For applications such as contact switches for electrical or thermal transfer it is necessary to understand the properties that arise from the collective behavior of an assemblage of CNTs rather than the properties of a single tube. In this study, the mechanical response of turfs bonded to substrates under compressive loading is demonstrated experimentally; coordinated alignment and buckling takes place under uniform loads. The mechanical response of turf structures provides some surprising results regarding parameters that control permanent deformation and buckling in assemblages of nanostructures; buckling of the turf structure is controlled by the height and effective modulus of the turf, but not the aspect ratio of the structure. We present and verify a model which describes the coordinated buckling phenomena relevant for applications such as CNT turfs for thermal transfer media.

A microstructurally motivated description of the deformation of vertically aligned carbon nanotube structures

“…We provide a microstructure-based motivation for such a phenomenological constitutive relation and use it to explore changes in structural response with nanotube volume fraction. The collective properties of carbon nanotubes in the form of vertically aligned carbon nanotubes (VACNTs) have been explored for applications ranging from micro-electromechanical system (MEMS) [1][2][3] to low temperature energy dissipating materials. [4][5][6] This has led to growing interest in developing an understanding of VACNT's mechanical response which is key for rational design and life cycle analysis.…”

“…[4][5][6] This has led to growing interest in developing an understanding of VACNT's mechanical response which is key for rational design and life cycle analysis. [1][2][3]5,[7][8][9][10][11][12][13] VACNT materials are complex, hierarchical, and largely disordered assemblies of carbon nanotubes (CNTs) aligned nominally vertically with respect to the growth substrate. Experimental investigations have found that VACNTs have mechanical energy dissipative properties, 4,5,7,10 can exhibit high recoverability after large strains, 8,14,15 and deform via a sequential periodic buckling mechanism under uniaxial compression.…”

“…Experimental investigations have found that VACNTs have mechanical energy dissipative properties, 4,5,7,10 can exhibit high recoverability after large strains, 8,14,15 and deform via a sequential periodic buckling mechanism under uniaxial compression. 1,2,7,8,11 While observations of these behaviors are numerous, the physical mechanisms governing them remain poorly understood. To date, only a few mathematical models have been proposed and those either numerically replicate aspects of the structural response without taking into account underlying mechanisms 16,17 or describe only the linear elastic and viscoelastic response.…”

“…To date, only a few mathematical models have been proposed and those either numerically replicate aspects of the structural response without taking into account underlying mechanisms 16,17 or describe only the linear elastic and viscoelastic response. 2,8,10 What is lacking is a physically motivated hypothesis from which predictions of structural behavior can be made given systematic variation of material properties.…”

Local Relative Density Modulates Failure and Strength in Vertically Aligned Carbon Nanotubes

“…Other differences between these nominally identical VACNT samples are the ability of some of them to recover almost completely after large compressions (Figs. S1a and c) while others deform permanently even at modest strains [7][8][9][10][11] (Figs. S1b and d).…”