Enhanced Tribological Properties of Vulcanized Natural Rubber Composites by Applications of Carbon Nanotube: A Molecular Dynamics Study

Tribological properties of tread rubber is a key problem for the safety and durability of large aircraft tires. So, new molecular models of carbon nanotube (CNT) reinforced vulcanized natural rubber (VNR) composites have been developed to study the enhanced tribological properties and reveal the reinforced mechanism. Firstly, the dynamic process of the CNT agglomeration is discussed from the perspectives of fractional free volume (FFV) and binding energy. Then, a combined explanation of mechanical and interfacial properties is given to reveal the CNT-reinforced mechanism of the coefficient of friction (COF). Results indicate that the bulk, shear and Young’s modulus increase with the increasement of CNT, which are increasement of 19.13%, 21.11% and 26.89% in 15 wt.% CNT/VNR composite compared to VNR; the predicted results are consistent with the existing experimental conclusions, which can be used to reveal the CNT-reinforced mechanism of the rubber materials at atomic scale. It can also guide the design of rubber material prescription for aircraft tire. The molecular dynamics study provides a theoretical basis for the design and preparation of high wear resistance of tread rubber materials.

Investigation on Reinforced Mechanism of Fiber Reinforced Asphalt Concrete Based on Micromechanical Modeling

Short fibers have been widely used to prepare the fiber reinforced asphalt concrete (FRAC). However, internal interactions between fiber and other phases of asphalt concrete are unclear although experimental methods have been used to design the FRAC successfully. In this paper, numerical method was used to investigate the reinforced mechanism of FRAC from microperspective. 2D micromechanical model of FRAC was established based on Monte Carlo theory. Effects of fiber length and content on stress state of asphalt mortar, effective modulus, and viscoelastic deformation of asphalt concrete were investigated. Indirect tensile stiffness modulus (ITSM) test and uniaxial creep test were carried out to verify the numerical results. Results show that maximum stress of asphalt mortar is lower compared to the control concrete when the fiber length is longer than 12 mm. Fiber reduces the stress level of asphalt mortar significantly. Fiber length has no significant influence on the effective modulus of asphalt concrete. Fiber length and content both have notable impacts on the viscoelastic performance of FRAC. Fiber length should be given more attention in the future design of FRAC except the content.

An Experimental Analysis of Reinforced Mechanism of Polypropylene Fiber Reinforced EPS Concrete

The reinforced mechanism with polypropylene fiber reinforced EPS concrete was researched, based on mechanical experiments and photograph analysis of the Scanning Electron Microscopy with HITACHIS-3400N. Polypropylene fiber with 15-mm length and six volume fractions of 0%, 0.10%, 0.14%, 0.18%, 0.2% and 0.25% were used, and consequently, the resultant effects on the mechanical behavior of these concretes were analysed. The results demonstrate that compressive strength of EPS concretes increase with the rise of the percentage of the fiber volume. It is shown that using 0.15~0.2% polypropylene fiber in cement mixture greatly increases compressive strength. Scanning electron microscope images show that the reason for this improvement is that polypropylene fiber can increase bonding strength at the matrix–inclusion interface.

Ethylenediamine-Functionalized Carbon Nanotubes and Nylon-6 Composites

Carbon Nanotubes (CNTs) are functionalized with ethylenediamine by chemical cut and grafting process. CNTs/nylon-6 (PA6) composite is prepared by solution-evaporation method. The dispersivity of CNTs and mechanical properties of CNTs/PA6 composites are tested. Reinforced mechanism is also investigated. The results show that the ethylenediamine-functioned CNTs (s-CNTs) are well dispersed in the formic acid and the weight content of grafted ethylenediamine is about 30%. With only 2wt% addition of s-CNTs, the modulus, strength and strain of PA6 are dramatically improved by about 46%, 85%, and 200% respectively. The tensile course of s-CNTs/ PA6 composites shows that the increase of modulus were provided by both the increase of matrix crystallinity induced by s-CNTs and the recruitment of s-CNTs, and the improvements of strength and strain were attributed to the malleable integration between the s-CNTs and matrix, which was formed with s-CNTs, crystal matrix based on the tubes and the partial entanglements of tubes.