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

Abstract

Micromechanical experiments, image analysis, and theoretical modeling revealed that local failure events and compressive stresses of vertically aligned carbon nanotubes (VACNTs) were uniquely linked to relative density gradients. Edge detection analysis of systematically obtained scanning electron micrographs was used to quantify a microstructural figure-of-merit related to relative local density along VACNT heights. Sequential bottom-to-top buckling and hardening in stress–strain response were observed in samples with smaller relative density at the bottom. When density gradient was insubstantial or reversed, bottom regions always buckled last, and a flat stress plateau was obtained. These findings were consistent with predictions of a 2D material model based on a viscoplastic solid with plastic non-normality and a hardening–softening–hardening plastic flow relation. The hardening slope in compression generated by the model was directly related to the stiffness gradient along the sample height, and hence to the local relative density. These results demonstrate that a microstructural figure-of-merit, the effective relative density, can be used to quantify and predict the mechanical response.

Effects of Nanostructure and Coating on the Mechanics of Carbon Nanotube Arrays

“…[ 1,2 ] This nanostructured foam-like material has shown a variety of properties ranging from; super mechanics of individual CNTs have also been investigated by discrete modeling approaches such as molecular dynamics. [ 21,22 ] This computational method allows for the detailed study of defects.…”

“…[ 31 ] More recently, a continuum model with a spatially varying property gradient in the elastic-viscoplastic constitutive relationship was used to investigate local failure events. [ 2 ] Multiscale approaches that combine both discrete MD results and continuum models have been used to investigate CNT reinforced concrete fracture, highlighting the importance of microstructure. [ 32 ] Despite the promising applications, a comprehensive investigation of the effects of nanoscale conformal coatings, contacts, and coupling with van der Waals interaction among CNTs, is still missing.…”

“…More so, it has been postulated that there is not yet a quantitative theory that can predict the mechanical behavior of CNT arrays as function of its microstructure. [ 2 ] In this work, we systematically explore the mechanical and kinematic behavior of vertically aligned CNT arrays modifi ed with nanoscale conformal coatings through experiments and simulations. The effects of multiple CNTs contacting and coupling through van der Waals interaction, and the effects of different nanostructure parameters such as the conformal coating thickness, waviness, and friction on the material properties are investigated.…”

Research Paper in Literature of Increasing Thickness by Inclined Target

“…The quickest edges are ordinarily seen on the frontal glacis plate, both as it is the body side well while in transit to be hit and in light of the way that there is more space to incline in the longitudinal heading of a vehicle [22][23][24][25].…”

Data-driven understanding of collective carbon nanotube growth by in situ characterization and nanoscale metrology

“…[9][10][11][12][13][14][15][16] Importantly, the non-uniform morphology of CNT forests influences their properties, such as in mechanical compression for example, which was shown to be affected by density gradients. 17 Hence, revealing the process-structure and structure-property relationships requires a comprehensive understanding of the atomic scale physicochemical processes underlying the bottom-up synthesis and selforganization of aligned CNTs. To that end, a large number of in situ nanoscale metrology and characterization techniques were explored over the past two decades for interrogating a large number of individual CNTs simultaneously as they grow, interact with each other, and self-assemble into the aligned morphology.…”