Lubricity Assessment, Wear and Friction of CNT-Based Structures in Nanoscale

Abstract

Abstract:In this work, three case studies are reported, namely carbon nanotube/polyvinyl butyral composites, MWCNTs/polydimethylsiloxane-based coatings and vertically aligned CNT forest array, of which the friction and resistance to wear/deformation were assessed through nanoindentation/nanoscratch. Additional deformation parameters and findings are also addressed and discussed; namely, material deformation upwards (pile-up) or downwards (sink-in) with respect to the indented surface plane, hardness to modulus ratio (index of resistance to wear) and coefficient of friction. The enhancement of the scratch resistance due to the incorporation of CNTs in a polymer matrix is investigated. For the case of the forest structure, sliding between neighboring nanotubes is identified, while, through ploughing of the tip, local deformation and the extent of plasticity are also addressed.

Integrity of Carbon-Fibre Epoxy Composites through a Nanomechanical Mapping Protocol towards Quality Assurance

“…Results show that for the case of epoxy-PAACFs, higher plastic deformation is evidenced (together with viscoelasticity and adhesion-discontinuities and fluctuations during measurement), while for the case of epoxy-CFs a load of 40 μΝ of is depicted, together with lower plastic deformation (epoxy-PANCFs and epoxy-PMAACFs with a load range of ~55 μΝ and ~90 μΝ, respectively). As nanoindentation produces relatively high local stresses [17,25], it is often that such generation of obvious time-dependent effects (e.g., progressive indenter penetration when a constant load is maintained) occur. Apparently, there is a need for taking into consideration the possibility of creep affecting the results when experimental nanoindentation data are to be re-used to calculate constitutive relations.…”

“…The hardness (as contact pressure, in the means of resistance to applied load) and the elastic modulus of the material being probed are calculated from the initial part of the unloading curve, on the assumption of elastic behaviour using the theory of contact mechanics [13]. Information on the elastic recovery and plastic deformation [14] is also provided, fracture [15], sensitivity of strain-rate and strain-hardening, residual stresses effect [16], and size effects in plasticity locally [17]. As nanoindentation is being recently utilised for assessing the in situ properties of fibrous composite constituents [18,19], issues such as effects of sample preparation, neighbouring constituents, residual stress, pile-up, time-dependent deformation and hydrostatic stress on the important nanoindentation parameters and properties need to be carefully considered [20].…”