Layer-by-layer failure mechanism of triple-walled carbon nanotubes: From atomic stress partitioning to in-situ bundle-scale

Layer-by-layer load transfer and degradation pathways in nested multi-walled structures remain a central focus in nanomechanics. Here, we present a cross-scale study combining molecular dynamics (MD) simulations with in-situ TEM tensile testing to elucidate the failure mechanisms of triple-walled carbon nanotubes (TWCNTs) from atomic layers to macro-scale bundles. Our findings demonstrate that both scales undergo a non-catastrophic progressive failure path governed by interlayer van der Waals (vdW) shear interactions, culminating in an irreversible pull-out fracture rather than a synchronous brittle rupture. Under concurrent loading boundary conditions, MD simulations reveal a sequential layer-by-layer fracture process from the outer to the inner shell within an individual TWCNT under concurrent loading boundary conditions, wherein the failure sequence arises from the combined effects of direct boundary displacement constraints and interlayer vdW-mediated stress transfer. In-situ TEM tensile testing on macro-scale bundles, quantified through stress-strain analysis, reveals incomplete load sharing and inter-tube sliding, demonstrating that the macroscopic bundle strength is substantially lower than the intrinsic strength of individual CNTs. Two-step cyclic loading sequences demonstrate that following large-scale sliding and a sharp load drop, the bundle avoids immediate avalanche-like structural collapse, maintaining a steady and substantial residual load-bearing capacity driven by the frictional sliding of the pulling-out nanotubes. The weak vdW interfaces serve as efficient energy dissipation hubs, dissipating external work through interfacial sliding and separation processes prior to the final complete separation. This cross-scale mechanism mitigates severe localized stress concentrations, providing a foundational guideline for the defect-tolerant design of advanced carbon nanotube assemblies and high-strength nanocomposites.