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Abstract: The application of the indentation method to measure the elastic modulus of particles embedded in a composite is theoretically investigated in this paper by finite element simulation. The Oliver–Pharr method, which is widely used in commercial nanoindentation instruments, is used to probe the elastic modulus of the particle from the simulated indentation curve. The predicted elastic modulus is then compared with the inputted value. Two cases are studied, that of a stiff particle embedded in a soft matrix and a soft particle embedded in a stiff matrix. In both of these cases, there exists a particle-dominated depth. If the indentation depth lies within this particle-dominated depth, the Oliver–Pharr method is able to be applied to measure the particle’s elastic modulus with sufficient accuracy if the real contact area is used. This could lead to an experimentally-convenient method of determining the primary properties of individual particle, providing they can be well dispersed in the polymeric matrix. [Copyright &y& Elsevier]

In this study, the effects of cladding direction, preheating and post heat treatment on microstructural and mechanical properties of laser cladded rail repairs are presented. Laser cladding of a premium hypereutectoid rails grade with 410L stainless steel powder were conducted using a fibre laser gun with a powder feeder. Two different cladding directions and different heat treatment regimes were investigated. An excellent microstructural consistency was established across the railhead and its heat affected zone (HAZ) by changing cladding direction and using a heat treatment consisting of pre-heating and post-heating. The microstructure of the cladding layer and HAZ were characterized by optical microscopy and SEM. Phase identification and distribution were investigated by using XRD, EDS, and EBSD. Indications of the mechanical and tribological performance of the cladding layer in wheel-rail contact were obtained via shear punch tests and Vickers indentation, which demonstrated great correlation with the obtained microstructure. [ABSTRACT FROM AUTHOR]

Carbon nanotube (CNT) reinforced polymeric composites provide a promising future in structural engineering. To understand the bridging effect of CNT in the events of the fracture of CNT reinforced composites, the finite element method was applied to simulate a single CNT pullout from a polymeric matrix using cohesive zone modelling. The numerical results indicate that the debonding force during the CNT pullout increases almost linearly with the interfacial crack initiation shear stress. Specific pullout energy increases with the CNT embedded length, while it is independent of the CNT radius. In addition, a saturated debonding force exists corresponding to a critical CNT embedded length. A parametric study shows that a higher saturated debonding force can be achieved if the CNT has a larger radius or if the CNT/matrix has a stronger interfacial bonding. The critical CNT embedded length decreases with the increase of the interfacial crack initiation shear stress. [ABSTRACT FROM AUTHOR]

Abstract Scarf or stepped-lap repairs are desirable for composite structures in aerospace, especially where a flush finish is required. Damage tolerance is a critical issue in the repair design. This paper investigates and compares the damage tolerance of scarf and stepped-lap joints (repairs) under quasi-static loading using finite element analysis (FEA). The damage was represented by a flaw embedded in the bondline between composite adherents. 3D FE models were built for both scarf and stepped-lap joints. Both linear and nonlinear adhesive properties were simulated under room temperature (RT) and hot-wet (HW) conditions. The flaws with varying length and width were imbedded in the bondline, so that the sensitivity of damage tolerance to the flaw size can be analysed and compared between scarf and stepped-lap joints. Other parameters, which may affect the damage tolerance of both joints, include flaw location, number of steps of stepped-lap joint, stacking sequence of laminate adherend, out-of-plane boundary conditions and the presence of an external doubler. The results showed that the stepped-lap joint exhibited better damage tolerance than the scarf joint with linear elastic adhesive. The damage tolerance of both joints became similar when the adhesive became nonlinear under RT or HW conditions. The damage tolerance of both joints can be improved by attaching composite doubler reinforcement or constraining the out-of-plane movement. [ABSTRACT FROM AUTHOR]

A novel one-step flame synthesis method was used to coat carbon nanotubes (CNTs) onto plain weave S-glass fibre (GF) fabrics. Nickel chloride, as a catalyst, was applied on the GF fabrics, and CNTs were formed in an ethanol flame. Results showed that different carbon materials were synthesised, and they were sensitive to the flame synthesis parameters. Short CNTs (shorter than 0.5 μm) were dominant with a low catalyst concentration of 0.2 mol/L, and long CNTs (lengths of ~1.2–2.0 μm) started to appear when the catalyst was increased to 0.4 and 0.6 mol/L. With even higher catalyst concentration at 0.8 and 1.0 mol/L, most of the CNTs were embedded in a thick layer of carbon soot. In addition, the thermal and electrical conductivities of GF/epoxy and multi-scale CNT-GF/epoxy composites were measured. Compared to GF/epoxy composite, a more than 40% increase of thermal conductivity and 10 orders of magnitude decrease of electrical resistance were achieved in these multi-scale CNT-GF/epoxy composites. • CNTs were successfully synthesised in an ethanol flame and coated onto glass fibres. • Catalyst concentration influenced significantly the composition of the synthesised carbon materials. • The multi-scale CNTs-glass fibre composite laminates exhibited enhanced thermal and electrical conductivities. [ABSTRACT FROM AUTHOR]