In situ Mechanical Testing Reveals Periodic Buckle Nucleation and Propagation in Carbon Nanotube Bundles

Abstract

Typical TEM images of CNTs extracted from an undeformed pillar. In situ videos: (included)PillarCompression_25xspeed.mpg PillarCompression_25xspeed.avi A pillar compression performed at a strain rate of 0.001 s -1 , then sped up to 25× the original rate for easier viewing.PillarCompression_25xspeed_data.mpg PillarCompression_25xspeed_data.aviStress-strain data gathered simultaneously with the pillar compression shown in 'PillarCompression_25xspeed.mpg'. Both videos may be played side-by-side to correlate the buckling events and stress-strain humps.

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.…”

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

“…VACNT micro-pillar 6 and (d) 50 µm × 60 µm (diameter × height) VACNT micro-pillar. 7 All of these VACNT systems show 3 distinct regimes in their stress-strain responseelastic, plateau and densification -similar to open-cell foams. Unlike foams, the plateau region in the VACNTs generally has a strong positive slope.…”

“…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).…”

“…Here the first buckle generally nucleates close to the substrate, and each subsequent lateral collapse event initiates only after the preceding one was completed, thus sequentially collapsing the entire structure. 3,[5][6][7] We are unaware of any literature report that suggests a different buckling sequence (such as top-to-bottom or otherwise) for VACNT pillars under compression. VACNT micro-pillar 6 and (d) 50 µm × 60 µm (diameter × height) VACNT micro-pillar.…”

“…2 in the manuscript), where the first buckle is nucleated close to the substrate and each subsequent buckle initiates above the previous one. 5,7 If the sample is unloaded from a maximum compression of ~70% strain, the top third of the pillar remains virtually unscathed (Fig. S9b, left panel), and the buckle closest to the pillar-top is always the last one to form (Fig.…”