Local and non-local behavior and coordinated buckling of CNT turfs

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

“…[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.…”

Morphology and processing of aligned carbon nanotube carbon matrix nanocomposites

“…Also, for the ψ = 90% case, in order to get φ m,i < 20%, a value of i > 25 is necessary, meaning that such a low value of φ m is likely both physically and practically unattainable for A-CMNCs produced using wet infusion with a diluted (F dilut 60% by mass) phenolic resin. A possible way to achieve φ m,i < 20% at a reasonable value of i (i 10) is to apply pressure during the pyrolysis stage 28 , which will make ∆V p,1 ≡ ∆V p (the simplification in Eq 3 is no longer true), but the compressive stress will probably alter the morphology of the CNTs in the matrix 47,48 , thereby impacting the physical properties of the CNT A-CMNCs. Therefore, in order to synthesize A-CMNCs with very low porosities (φ m 20%) without changing the A-CMNC morphology, a gas phase infusion method, such as carbon vapor infiltration (CVI) 27,49-51 , would most likely be necessary.…”

Compressive response of vertically aligned carbon nanotube films gleaned from in situ flat-punch indentations

“…5,9,11 Unlike foams, however, the compressive strain in VACNTs is accommodated entirely via the formation of localized folds or buckles forming progressively along their lengths. 5,11,16,22,24,25 During compression of our particular APCVD VACNT system, such localized buckles fully recovered upon load release even from relatively large strains of 60-80% (i.e., the onset of densification) under fast displacement rates of 1000 nm/s. In addition, repeated cycling also revealed a distinctive hysteresis behavior for the VACNT bundle in compression, suggesting energy dissipation in every cycle.…”

“…[10][11][12] A wide range of mechanical behavior has been reported in VACNTs as a result of such variations in their microstructure. These include modulus and buckling strengths ranging from sub-MPa 13,14 to tens of MPa [15][16][17] to GPa, as well as a complete gamut of recoverability-from nearly 100% recovery even after large deformations 5,9,13,19,20 to permanent distortion even at modest strains. 2,11,17,21,22 Such drastic differences in properties make it impractical to compare VACNTs synthesized by nonidentical growth techniques.…”