Coupled thermal-electrical analysis of carbon nanotube/epoxy composites

Influence of Manufacturing Process in Structural Health Monitoring and Mechanical Behaviour of CNT Reinforced CFRP and Ti6Al4V Multi-Material Joints

Co-cured multi-material metal–polymer composites joints are recent interesting structural materials for locally reinforcing a structure in specific areas of high structural requirements, in fibre metal laminates and lightweight high-performance structures. The influence of manufacturing processes on the morphological quality and their mechanical behaviour has been analysed on joints constituted by sol-gel treated Ti6Al4V and carbon fibre reinforced composites (CFRP). In addition, carbon nanotubes (CNT) have been added to an epoxy matrix to develop multiscale CNT reinforced CFRP, increasing their electrical conductivity and allowing their structural health monitoring (SHM). Mechanical behaviour of manufactured multi-material joints is analysed by the measurement of lap shear strength (LSS) and Mode I adhesive fracture energy (GIC) using double cantilever beam specimens (DCB). It has been proven that the addition of MWCNT improves the conductivity of the multi-material joints, even including surface treatment with sol-gel, allowing structural health monitoring (SHM). Moreover, it has been proven that the manufacturing process affects the polymer interface thickness and the porosity, which strongly influence the mechanical and SHM behaviour. On the one hand, the increase in the adhesive layer thickness leads to a great improvement in mode I fracture energy. On the other hand, a lower interface thickness enhances the SHM sensibility due to the proximity between MWCNT and layers of conductive substrates, carbon woven and titanium alloy.

Matching Rheology, Conductivity and Joule Effect in PU/CNT Nanocomposites

We investigated polyurethane (PU)–carbon nanotube (CNT) nanocomposites (PU/CNT) in a range of concentrations from 1 to 8 wt% CNT as hot melt adhesives. We studied the thermal properties of the nanocomposites, which is relevant from an applied point of view. The phase angle plots versus complex modulus results revealed the existence of a maximum above a given CNT concentration. The intensity of the peak and associated relaxation time was analyzed with percolation theory, leading to a new method to determine the rheological percolation threshold. A lower threshold value was obtained from the electrical conductivity data, which was justified recalling that the hopping/tunnelling effect takes place in the nanocomposite, as stated by previous studies in the literature. Joule effect studies indicated that the heating effect was very significant, reaching temperature increases, ΔT, of 60 °C for low voltages. For the first time, the percolation equation was applied to the ΔT to obtain the corresponding threshold. Stimulus-responsive systems were conceived considering the correlation between the ΔT and the conductivity. The case of PU/CNT nanocomposites acting as hot melt adhesives that are welded/unglued by applying/removing an electrical voltage is presented.

Simulation of self-heating process on the nanoscale: a multiscale approach for molecular models of nanocomposite materials

A theoretical-computational protocol to model the Joule heating process in nanocomposite materials is presented. The proposed modeling strategy is based on post processing of trajectories obtained from large scale molecular simulations. This protocol, based on molecular models, is the first one to be applied to organic nanocomposites based on carbon nanotubes (CNT). This strategy allows to keep a microscopic explicit picture of the systems, to directly catch the molecular structure underlying the process under study and, at the same time, to include macroscopic boundary conditions fixed in the experiments. As validation and first application of the proposed strategy, a detailed investigation on CNT based organic composites is reported. The effect of CNT morphologies, concentration and working conditions on Joule heating has been modelled and compared with available experiments. Further experiments are performed also in this work to increase the number of comparisons especially in specific voltage ranges where available references from literature were missing. Simulations are in both qualitative and quantitative agreement with several experiments and trends reported in the recent literature, as well as with experiments performed in this work. The proposed approach combined with large scale hybrid particle-field molecular simulations can give insights and opens to way to a rational design of self-heating nanocomposites.