Strain rate effects in the mechanical response of polymer anchored carbon nanotube foams

TL;DR

This study investigates how strain rate influences the nonlinear viscoelastic mechanical response of polymer-anchored carbon nanotube foams, revealing rate-dependent behaviors such as elastic recovery, buckling, and defect formation.

Contribution

It introduces a method of anchoring carbon nanotube forests on polymer layers to enhance stability and explores their strain rate-dependent mechanical responses under different loading conditions.

Findings

Variable nonlinear response with strain rate

Observation of Bauschinger-like effect at low strain rates

Buckling and permanent defects at high strain rates

Abstract

Super-compressible foam-like carbon nanotube films have been reported to exhibit highly nonlinear viscoelastic behaviour in compression similar to soft tissue. Their unique combination of light weight and exceptional electrical, thermal and mechanical properties have helped identify them as viable building blocks for more complex nanosystems and as stand-alone structures for a variety of different applications. In the as-grown state, their mechanical performance is limited by the weak adhesion between the tubes, controlled by the van der Waals forces, and the substrate allowing the forests to split easily and to have low resistance in shear. Under axial compression loading carbon nanotubes have demonstrated bending, buckling8 and fracture9 (or a combination of the above) depending on the loading conditions and on the number of loading cycles. In this work, we partially anchor dense vertically aligned foam-like forests of carbon nanotubes on a thin, flexible polymer layer to provide structural stability, and report the mechanical response of such systems as a function of the strain rate. We test the sample under quasi-static indentation loading and under impact loading and report a variable nonlinear response and different elastic recovery with varying strain rates. A Bauschinger-like effect is observed at very low strain rates while buckling and the formation of permanent defects in the tube structure is reported at very high strain rates. Using high-resolution transmission microscopy