Composite materials with enhanced conductivities

The authors have analyzed the isotropic thermal/electrical conductivities of two types of specially structured composite materials. Closed-form results have been obtained for predicting the conductivities of the composites, and the accuracy has been verified by FE simulations. The obtained results in this paper are compared to the relevant theoretical predictions and experimental measurements. It has been demonstrated that the type-I composites have achieved a conductivity that is almost the same as the highest possible theoretical upper limit, and the type-II composites have a conductivity significantly greater than the experimental results of conventional isotropic composite materials

Nano-structured interpenetrating composites with enhanced Young's modulus and desired Poisson's ratio

This paper has demonstrated that interpenetrating composites could be designed to not only have an significantly enhanced Young�s modulus, but also have a Poisson�s ratio at a desired value (e.g. positive, or negative, or zero). It is found that when the effect of the Poisson�s ratio is absent, the Young�s modulus of interpenetrating composites is closer to the Hashin and Shtrikman�s upper limit than to their lower limit, and much larger than the simulation and experimentally measured results of the conventional isotropic particle or fibre composites. It is also illustrated that at the nanoscale, the interphase can either strengthen or weaken the stiffness, and the elastic properties of interpenetrating composites are size-dependent

Simultaneously improving the mechanical and electrical properties of poly(vinyl alcohol) composites by high-quality graphitic nanoribbons

Although carbon nanotubes (CNTs) have shown great potential for enhancing the performance of polymer matrices, their reinforcement role still needs to be further improved. Here we implement a structural modification of multi-walled CNTs (MWCNTs) to fully utilize their fascinating mechanical and electrical properties via longitudinal splitting of MWCNTs into graphitic nanoribbons (GNRs). This nanofiller design strategy is advantageous for surface functionalization, strong interface adhesion as well as boosting the interfacial contact area without losing the intrinsic graphitic structure. The obtained GNRs have planar geometry, quasi-1D structure and high-quality crystallinity, which outperforms their tubular counterparts, delivering a superior load-bearing efficiency and conductive network for realizing a synchronous improvement of the mechanical and electrical properties of a PVA-based composite. Compared to PVA/CNTs, the tensile strength, Young’s modulus and electrical conductivity of the PVA/GNR composite at a filling concentration of 3.6 vol.% approach 119.1 MPa, 5.3 GPa and 2.4 × 10−4 S m−1, with increases of 17%, 32.5% and 5.9 folds, respectively. The correlated mechanics is further rationalized by finite element analysis, the generalized shear-lag theory and the fracture mechanisms

Leaf-like carbon nanotube-graphene nanoribbon hybrid reinforcements for enhanced load transfer in copper matrix composites

A leaf-inspired nanoengineering is employed for the structural design of carbon nanofillers. We fabricate leaf-like carbon nanotube (CNT)-graphene nanoribbon (GNR) hybrids as novel reinforcements for a copper matrix composite. The straight and stiff CNT ‘midribs’ are conducive to individual dispersion whilst the two-dimensional GNR ‘margins’ provide more sufficient interface contact area and deformation gradient zone, giving rise to significantly improved interfacial load transfer and mechanical strength as compared to the unmodified nanotubes. The mechanics and strengthening mechanisms are further rationalized by finite element analysis and the generalized shear-lag theory

Simultaneously enhancing the strength, ductility and conductivity of copper matrix composites with graphene nanoribbons

The incorporation of low-dimensional nanomaterials into 3D metal matrices are promising to translate their intriguing properties from nanoscale to the macroscopic world. However, the design of robust nanofillers and effective fabrication of such bulk composites remain challenging. Here we report a configuration design of nanocarbon for reinforcing metals via unzipping carbon nanotubes (CNTs) into graphene nanoribbons (GNRs), which are novel quasi-1D carboneous nanomaterials combining elegantly the properties of graphene nanosheets and CNTs, to provide insight into the viability to retrieve good plasticity and conductivity that defy the boundaries of classical composites. We realize an optimal balance between elevated yield strength and impressively larger plastic deformation coupled with a simultaneous improving of electrical conductivity (216 MPa, 8.0% and 54.89 MS m−1, i.e., 1.55 folds, 130.4% and 105% of the matrix, respectively), by highlighting that the excellent intrinsic properties, strong interfacial bonding, optimized orientation control and especially the unique geometric factors of GNRs are conducive to transmitting stress from Cu matrix without sacrificing the ductility and electrical conductance. This work provides a new vista on the integration and interaction of novel low-dimensional nanofillers with bulk 3D metal matrices

Efficient network-matrix architecture for general flow transport inspired by natural pinnate leaves

Networks embedded in three dimensional matrices are beneficial to deliver physical flows to the matrices. Leaf architectures, pervasive natural network-matrix architectures, endow leaves with high transpiration rates and low water pressure drops, providing inspiration for efficient network-matrix architectures. In this study, the network-matrix model for general flow transport inspired by natural pinnate leaves is investigated analytically. The results indicate that the optimal network structure inspired by natural pinnate leaves can greatly reduce the maximum potential drop and the total potential drop caused by the flow through the network while maximizing the total flow rate through the matrix. These results can be used to design efficient networks in network-matrix architectures for a variety of practical applications, such as tissue engineering, cell culture, photovoltaic devices and heat transfer

Influences of interfaces on dynamic recrystallization and texture evolution during hot rolling of graphene nanoribbon/Cu composites

The influences of rigid heterointerfaces on the dynamic recrystallization (DRX) process and texture evolution during hot rolling of a graphene nanoribbon (GNR)-reinforced Cu-matrix composite system are investigated. The Cu/GNR interfaces contribute to the atypical recrystallization-type and brass-type textures developed in composites within 0.5 and 3 vol pct GNRs, respectively, deviating from the normal Cu-type texture found in their pure Cu counterpart. The heterointerfaces may change the texture evolution of the Cu matrix in four ways, namely, retard the dislocation cross slip, activate partial slip, generate geometrically necessary dislocations, and promote the DRX process. These are corroborated through viscoplastic self-consistent simulations, which well reproduce the texture development in all samples by considering the interface–dislocation interactions, the activation of non-normal slip, and the interface-driven DRX nucleation. This study suggests the possibility of manipulating the microstructure, texture, and mechanical properties of traditional metallic materials through the design of heterophase interfaces

Auxetic interpenetrating composites: A new approach to non-porous materials with a negative or zero Poisson's ratio

In this research, the Poisson’s ratio of three different types of almost isotropic interpenetrating composites are designed to be either positive, or negative, or zero. As they are strengthened by a self-connected fibre-network and do not contain any pore in their structure, they all are stiffer than the conventional particle composites. In addition, structural hierarchy is also demonstrated to be able to significantly enhance the auxetic behaviour for the three types of interpenetrating composites. Thus, these composites could be used not only as functional materials, but also as structural materials in engineering applications

The near-isotropic elastic properties of interpenetrating composites reinforced by regular fibre-networks

It is highly demanding and challenging to maximise the stiffness of the interpenetrating phase composites (IPCs) while still keeping their isotropy. In this paper, the elastic properties of IPCs reinforced by three different types of regular lattice fibre networks are investigated by computer simulation and analytical methods. The numerical results indicate that the larger the difference between the Poisson’s ratios and the smaller the difference between the Young’s moduli of the constituent materials, the larger the Young’s moduli of these IPCs are. It is also found that structural hierarchy can enhance the stiffness of these IPCs by 30%. In addition, the three types of IPCs have Zener anisotropy factors in the range of in most cases, could have an almost isotropic Young’s modulus two times larger than the Voigt limit, and a Poisson’s ratio with a positive or negative or zero value. Moreover, they are easy to manufacture, their Young’s moduli are in general 1.0–3.0 times those of the conventional particle or short fibre reinforced composites and other types of IPCs including those reinforced by the triply periodic minimal surface (TPMS) shells, and the type of IPCs with the largest Young’s modulus has been identified