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Nanofluids have emerged as potential prospect coolant in heat transfer applications. Hybrid nanofluid is the is the recently developed class of nanofluids having two different types of nanoparticles suspended in the base fluid. In this research, a novel hybrid nanofluid containing Fe2O3-TiO2 (50:50) nanoparticles suspended in water basefluid has been used to improve the convective heat transfer in aluminum tube automotive radiator. Three hybrid nanoparticle concentrations (0.005 vol.%, 0.007 vol.% and 0.009 vol.%) were tested. Effect of inlet temperature and fluid velocity on heat transfer rate was examined by varying the inlet temperature from 48 °C to 56 °C and flowrate from 11 LPM to 15 LPM. Heat transfer rate increased by a maximum of 26.7% at 56 °C inlet temperature, 15 LPM flowrate and 0.009 vol.% nanoparticle concentration. At aforementioned operating conditions, Nusselt number increased by 20.03%. Increase in inlet temperature from 48 °C to 56 °C increased the heat transfer rate by 8%. Past 0.009 vol.% concentration, nanoparticle clogging diminished the stability of hybrid nanofluid which results in overall performance deterioration.

The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link. Digital manufacturing was employed to 3D print continuous Carbon, Glass and Kevlar fibre reinforced composites in Unidirectional (UD) [0°], Off-axis ±45° and Cross-ply [0°/90°] layup sequence. These 3D printed composites were subjected to quasi-static, in-plane tension and out-of-plane (compression and shear) loading. The tensile strength of 3D printed Carbon, Glass and Kevlar UD laminates was significantly lower than that of 3D printing filaments used to manufacture them. The type of fibre (brittle/ductile) reinforcement was found to be governing the shear yield strength of 3D printed composites despite having the same Nylon matrix in all the composites. Out-of-plane compressive strength of the 3D printed Carbon and Glass fibre reinforced composites was independent of specimen size. Contrary to that, Kevlar fibre composites showed a pronounced size effect upon their out-of-plane compressive strength. A combination of X-ray tomography and pressure film measurements revealed that the fibres in 3D printed composites failed by ‘indirect tension’ mechanism which governed their out-of-plane compressive strength. To gain further insights on the experimental observations, Finite Element (FE) simulations were carried out using a pressure-dependent crystal plasticity framework, in conjunction with an analytical model based on shear-lag approach. Both FE and analytical model accurately predicted the out-of-plane compressive strength of all (Carbon, Glass and Kevlar fibre reinforced) 3D printed composites.

The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link. A multilayer graphene (MLG) coating was grown on a nickel substrate by atmospheric chemical vapor deposition (CVD). The macroscale dry sliding friction behavior of the coated specimens against a stainless steel counterface was investigated under various contact loads ranging from 1 N to 5 N and at various rotational speeds from 30 rpm to 240 rpm. After the tests, the sliding surfaces were characterized by optical and scanning electron microscopes and Raman spectroscopy. The results show that contact load and sliding speed had significant effects on the lubricity of the MLG coatings under dry sliding conditions. At relatively low contact loads (1-3 N) and sliding speeds (30-120 rpm), the MLG coating exhibited good lubricity with coefficient of friction (COF) below 0.06 and lasted a long period of sliding time for more than 3600 cycles. With increasing contact loads and speeds, the COF of the MLG coating was gradually increased and the coating suffered from sudden breakdown after limited sliding cycles, losing its lubricity. Detailed examination and analysis revealed that material transfer occurred at the early stage of the sliding process, where MLG was transferred from the coating surface to the counterface. This graphene transfer was responsible for the lubricity of the sliding pair and the sustainability of the transferred material on the counterface determined the lifetime of the lubricity regime. High contact loads and high speeds favored severe plastic deformation and mechanical damages of the substrate, which limited the lifetime of the transferred material and thus the lifetime of the lubricity regime. Sliding induced defects in the MLG both on the coating and on the counterface were confirmed by Raman spectroscopy.

This paper reviews the main strategies used to simulate the mechanical behaviour of nonwoven materials that is defined by a structure of their fibrous networks and a mechanical behaviour of constituent fibres or filaments. The main parameters influencing the network structure of nonwoven materials are discussed in the first part. The second part deals with two main strategies employed in the analysis of mechanical behaviour of nonwoven materials using finite-element models based on continuous and discontinuous techniques. Both strategies have further subtypes, which are critically reviewed, and future trends in this area of research are discussed.

Open Access article Fibrous networks are ubiquitous structures for many natural materials, such as bones and bacterial cellulose, and artificial ones (e.g. polymer-based nonwovens). Mechanical behaviour of these networks are of interest to researchers since it deviates significantly from that of traditional materials treated usually within the framework of continuum mechanics. The main reason for this difference is a discontinuous character of networks with randomly distributed fibres (that can be also curved) resulting in complex scenarios of fibre-to-fibre interactions in the process of their deformation. This also affects a character of load transfer, characterised by spatial non-uniformity and localisation. A discontinuous nature of fibrous networks results in their non-trivial failure character and, more specifically, evolution of failure caused by notches. In order to investigate these mechanisms, various notches are introduced both into real-life specimens used in experimentation and discontinuous finite-element (FE) models specially developed (Farukh et al., 2014a; Hou et al., 2009, 2011a; Sabuncuoglu et al, 2013) to mimic the microstructure of fibrous networks. The specimens were tested under tensile loading in one of the principal directions, with FE-based simulations emulating this regime. The effect of notch shape on damage mechanisms, effective material toughness and damage patterns was investigated using the obtained experimental and numerical methods. The developed discontinuous model with direct introduction of microstructural features of fibrous networks allowed assessment of strain distribution over selected paths in them in order to obtain strain profiles in the vicinity of notch tips. Additionally, evolution of damage calculated in advanced numerical simulations demonstrated a good agreement with images from experiments.

open access article Oxidation-promoted crack growth, one of the major concerns for nickel-based superalloys, is closely linked to the diffusion of oxygen into the crack tip. The phenomenon is still not well understood yet, especially the full interaction between oxygen diffusion and severe near-tip mechanical deformation. This work aimed at the development of a robust numerical strategy to model the full coupling of crystal plasticity and oxygen diffusion in a single crystal nickel-based superalloy. In order to accomplish this, finite element package ABAQUS is used as a platform to develop a series of user-defined subroutines to model the fully coupled process of deformation and diffusion. The formulation allowed easy incorporation of nonlinear material behaviour, various loading conditions and arbitrary model geometries. Using this method, finite element analyses of oxygen diffusion, coupled with crystal plastic deformation, were carried out to simulate oxygen penetration at a crack tip and associated change of near-tip stress field, which has significance in understanding crack growth acceleration in oxidation environment. Based on fully coupled diffusion-deformation analyses, a case study was carried out to predict crack growth rate in oxidation environment and under dwell-fatigue loading conditions, for which a two-parameter failure criterion, in terms of accumulated inelastic strain and oxygen concentration at the crack tip, has been utilized.

The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link. Fibrous networks are encountered in various natural and synthetic materials. Typically, they have random microstructures with complex patterns of fibre distribution. This microstructure, together with significant (in many cases) stretchability of such networks, results in a non-trivial load-transfer mechanism, different from that of continuous media. The aim of this study is to investigate evolution of local deformation, damage and fracture processes in fibrous networks. In order to do this, together with extensive experiments, discontinuous finite-element (FE) models with direct incorporation of microstructural features were developed using a parametric approach for specimens with various dimensions and different types of notches. These models, mimicking a microstructure of the selected fibrous network, were loaded by stretching along a principal direction. Discontinuous FE models provided data not only on a global response of the specimens but also on levels of stresses and strains in each fibre, forming the network. An effect of a notch shape on evolution of fibre strains as well as mechanisms and patterns of damage was investigated using experimental data and simulation results, assessing also toughness of specimens. Strain distribution over selected paths were tracked in notched specimens to quantify strain distributions in the vicinity of notch tips. The growth and patterns of local damage due to axial stretching obtained in advanced numerical simulations with the developed FE models demonstrated a good agreement with experimental observations.