Multiscale mass-spring models of carbon nanotube foams

This article is concerned with the mechanical properties of dense, vertically aligned CNT foams subject to one-dimensional compressive loading. We develop a discrete model directly inspired by the micromechanical response reported experimentally for CNT foams, where infinitesimal portions of the tubes are represented by collections of uniform bi-stable springs. Under cyclic loading, the given model predicts an initial elastic deformation, a non-homogeneous buckling regime, and a densification response, accompanied by a hysteretic unloading path. We compute the dynamic dissipation of such a model through an analytic approach. The continuum limit of the microscopic spring chain defines a mesoscopic dissipative element (micro–meso transition) which represents a finite portion of the foam thickness. An upper-scale model formed by a chain of non-uniform mesoscopic springs is employed to describe the entire CNT foam. A numerical approximation illustrates the main features of the proposed multiscale approach. Available experimental results on the compressive response of CNT foams are fitted with excellent agreement.

Graphical AbstractAxial strain localization in a mesoscopic chain of five bistable springs. The spring collapse mimics the local kinking of compressed carbon nanotubes. Predicted stress-strain response (solid line) at the macroscopic scale, reproducing the experimental behavior of a real CNT foam (dashed line). Figure optionsDownload full-size imageDownload as PowerPoint slideResearch Highlights► Axial strain localization in microscopic bi-stable spring chains mimics kinking of compressed carbon nanotube arrays. ► Infinitesimal viscous events at the microscale induce time-independent hysteresis at the mesoscale. ► Multiscale mechanical modeling of CNT foams is obtained through an information-passing approach. ► Available experimental results on compressed CNT foams are reproduced with excellent agreement.