Multiscale modeling of stress transfer in continuous microscale fiber reinforced composites with nano-engineered interphase

Here, we report highly strain-tolerant and sensitive strain sensors based on carbon nanostructures (CNS)-polydimethylsiloxane (PDMS) nanocomposites. CNS consist of clusters of aligned multiwall carbon-nanotubes (MWCNT) with high degree of entanglement and wall sharing between nanotubes. The unique features of CNS result in nanocomposites with very low electrical percolation threshold (0.05 wt% CNS), strong linear-piezoresistive-response up to 110% strain, and high sensitivity with gauge factor ranging from 8 to 47. We also present a simple analytical model for predicting resistivity evolution as a function of stretch considering incompressible hyperelastic behavior of CNS/PDMS nanocomposites. CNS/PDMS nanocomposites also show good hysteresis performance and stability up to 100 repetitive stretch/release cycles for 30% maximum strain. Tunable sensitivity and linear piezoresistivity coupled with high stretchability of CNS/PDMS nanocomposites demonstrated here suggest their potential for applications in wearable health and fitness monitoring devices.

Strong linear-piezoresistive-response of carbon nanostructures reinforced hyperelastic polymer nanocomposites

Strain and damage-sensing performance of biocompatible smart CNT/UHMWPE nanocomposites

Ultra-high molecular weight polyethylene (UHMWPE)-based conductive nanocomposites with reduced percolation and tunable piezoresistive behavior were prepared via solution mixing followed by compression molding using carbon nanotubes (CNT) and graphene nanoplatelets (GNP). The effect of varying wt% of GNP with fixed CNT content (0.1 wt%) on the mechanical, electrical, thermal and piezoresistive properties of UHMWPE nanocomposites was evaluated. The combination of CNT and GNP enhanced the dispersion in UHMWPE matrix and lowered the probability of CNT aggregation as GNP acted as a spacer to separate the entanglement of CNT with each other. This has allowed the formation of an effective conductive path between GNP and CNT in UHMWPE matrix. The thermal conductivity, degree of crystallinity and degradation temperature of the nanocomposites increased with increasing GNP content. The elastic modulus and yield strength of the nanocomposites were improved by 37% and 33%, respectively, for 0.1/0.3 wt% of CNT/GNP compared to neat UHMWPE. The electrical conductivity was measured using four-probe method, and the lowest electrical percolation threshold was achieved at 0.1/0.1 wt% of CNT/GNP forming a nearly two-dimensional conductive network (critical value, t = 1.20). Such improvements in mechanical and electrical properties are attributed to the synergistic effect of the two-dimensional GNP and one-dimensional CNT which limits aggregation of CNTs enabling a more efficient conductive network at low wt% of fillers. These hybrid nanocomposites exhibited strong piezoresistive response with sensitivity factor of 6.2, 15.93 and 557.44 in the linear elastic, inelastic I and inelastic II regimes, respectively, for 0.1/0.5 wt% of CNT/GNP. This study demonstrates the fabrication method and the self-sensing performance of CNT/GNP/UHMWPE nanocomposites with improved properties useful for orthopedic implants.

Self-sensing and mechanical performance of CNT/GNP/UHMWPE biocompatible nanocomposites

The properties of nanoscale interphase significantly influence the mechanics of load transfer and hence the macroscopic behavior of fiber-reinforced composites. Herein, we present a theoretical framework to study the mechanics of stress transfer through both homogeneous and inhomogeneous interphases in a curved-fiber pull-out test and analyse the stress field in the three-phase composite system based on the shear-lag theory. Explicit expressions are derived to estimate the normal and shear stresses in the fiber, interphase and matrix. The results from the analytical model are validated with those obtained from a finite element analysis. Furthermore, influence of radially modulus graded interphase, according to linear and power laws, on the pull-out performance is also investigated. Graded interphases are observed to reduce the interfacial shear stresses by up to 40% as compared to the homogeneous interphases. The stress transfer in three-phase curved-fiber pullout test considering interfacial debonding and sliding has also been studied. Finally, models are simplified for straight-fiber pullout case considering both homogeneous and graded interphases. The study can serve as a framework to investigate the pull-out characteristics of a curved fiber in nanocomposites.

Stress transfer through the interphase in curved-fiber pullout tests of nanocomposites

30 Design of high-performance power lines with advanced materials is indispensable to effectively eliminate losses in electrical power transmission and distribution (T&D) lines. In this study, aluminum conductor composite core with carbon nanostructure (ACCC–CNS) coating in a multilayered architecture is considered as a novel design alternative to conventional aluminum conductor steel-reinforced (ACSR) transmission line. In the multiphysics approach presented herein, first, electrothermal finite element (FE) analysis of the ACSR line is performed to obtain its steady-state temperature for a given current. Subsequently, the sag distance of the ACSR line due to self-weight and thermal expansion is determined by performing thermostructural analysis employing an analytical model. The results are then verified with those obtained from the FE analysis of the ACSR line. The electrothermal FE model and the thermostructural analytical model are then extended to the ACCC–CNS line. The results indicate that the ACCC–CNS line has higher current-carrying capacity (CCC) and lower sag compared to those of the ACSR line. Motivated by the improved performance of the ACCC–CNS line, a systematic parametric study is conducted in order to determine the optimum ampacity, core diameter, and span length. The findings of this study would provide insights into the optimal design of high-performance overhead power lines. [DOI: 10.1115/1.4034095]

V. S. N. Ranjith Kumar

Papers

High-Ampacity Overhead Power Lines With Carbon Nanostructure–Epoxy Composites