171 research outputs found

    Tensile Behavior of Low Density Thermally Bonded Nonwoven Material

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    A discontinuous and non-uniform microstructure of alow-density thermally bonded nonwoven materialdisplays in a complicated and unstable tensilebehavior. This paper reports uniaxial tensile tests of alow density thermally bonded nonwoven toinvestigate the effect of the specimen size and shapefactor, as well as the cyclic tensile loading conditionsemployed to investigate the deformational behaviorand performance of the nonwoven at differentloading stages. The experimental data are comparedwith results of microscopic image analysis and FEmodels

    Finite Element Modelling of Conventional and Hybrid Oblique Turning Processes of Titanium Alloy

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    AbstractThis study is a part of the on-going research at Loughborough University, UK, on finite element (FE) simulations of ultrasonically assisted turning (UAT) coupled with hot machining processes. In UAT, vibration is superimposed on the cutting tool movement, resulting in several advantages of the process, especially in machining of high-strength engineering materials. Direct experimental studies of machining processes are expensive and time consuming, especially when a wide range of machining parameters affects, complex thermo-mechanical high-deformation processes in machined materials. In recent years, a use of mathematical simulations and, in particular, FE techniques has gained prominence in the research community. These techniques provide an accurate and efficient modelling paradigm for machining processes. In the present work, thermo-mechanically coupled three-dimensional FE models of conventional, ultrasonically assisted turning and a new hybrid turning technique called hot ultrasonically assisted oblique turning for a case of titanium alloy are presented. A nonlinear temperature-sensitive material behaviour is incorporated in our numerical simulations based on the results of the split-Hopkinson pressure bar tests. The simulation results obtained at different cutting conditions are compared to elucidate main deformation mechanisms responsible for the observed changes in the material's responses to various cutting techniques

    Numerical assessment of residual formability in sheet metal products : towards design for sustainability

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    A new computational scheme is presented to addresses cold recyclability of sheet- metal products. Cold recycling or re-manufacturing is an emerging area studied mostly empirically; in its current form, it lacks theoretical foundation especially in the area of sheet metals. In this study, a re-formability index was introduced based on post-manufacture residual formability in sheet metal products. This index accounts for possible levels of deformation along different strain paths based on Polar Effective Plastic Strain (PEPS) technique. PEPS is strain-path independent, hence provides a foundation for residual formability analysis. A user- friendly code was developed to implement this assessment in conjunction with advanced finite- element (FE) analysis. The significance of this approach is the advancement towards recycling of sheet metal products without melting them

    Experimental and Numerical Investigations in Conventional and Ultrasonically Assisted Drilling of CFRP Laminate

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    AbstractCarbon fiber-reinforced plastic (CFRP) composites are attractive for many industrial applications due to their superior properties. The parts made from CFRP are usually manufactured to a near-net shape; however, various machining processes, such as drilling, are often required to facilitate component assemblies. Conventional Drilling (CD) of CFRP induces high stresses in the vicinity of the drilled hole; along with high thrust forces on a drilling tool. An advanced drilling technique known as Ultrasonically Assisted Drilling (UAD) has been used to demonstrate its several advantages over CD including a reduced thrust force. A 3D finite element (FE) models simulating CD and UAD techniques for drilling in CFRP laminates were developed using the general-purpose FE software ABAQUS/Explicit. The numerical results obtained with the FE model were found to be in a good agreement with the experimental data

    Damage assessment in CFRP laminates exposed to impact fatigue loading

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    Demand for advanced engineering composites in the aerospace industry is increasing continuously. Lately, carbon fibre reinforced polymers (CFRPs) became one of the most important structural materials in the industry due to a combination of characteristics such as: excellent stiffness, high strength-to-weight ratio, and ease of manufacture according to application. In service, aerospace composite components and structures are exposed to various transient loads, some of which can propagate in them as cyclic impacts. A typical example is an effect of the wind gusts during flight. This type of loading is known as impact fatigue (IF); it is a repetition of low-energy impacts. Such loads can cause various types of damage in composites: fibre breaking, transverse matrix cracking, de-bonding between fibres and matrix and delamination resulting in reduction of residual stiffness and loss of functionality. Furthermore, this damage is often sub-surface, which reinforces the need for more regular inspection. The effects of IF are of major importance due its detrimental effect on the structural integrity of components that can be generated after relatively few impacts at low force levels compared to those in a standard fatigue regime. This study utilises an innovative testing system with the capability of subjecting specimens to a series of repetitive impacts. The primary subject of this paper is to assess the damaging effect of IF on the behaviour of drilled CFRP specimens, exposed to such loading. A detailed damage analysis is implemented utilising an X-ray micro computed tomography system. The main findings suggested that at early stages of life damage is governed by o degree splits along the length of the specimens resulting in a 20% reduction of stiffness. The final failure damage scenario indicated that transverse crasks in the 90 degree plies are the main reason for complete delamination which can be translated to a 50% stiffness reduction

    Thermo-mechanical damage accumulation during power cycling of lead-free surface mount solder joints

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    This is a conference paper [© IEEE]. It is also available from: http://ieeexplore.ieee.org/servlet/opac?punumber=4658784. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.It is well known that in surface mount technology (SMT), thermal strains in electronic assemblies are induced in the solder joints by the mismatch between the coefficients of thermal expansion (CTE) of the components, substrate and solder, both during their processing and in service. Therefore, thermo-mechanical damage is likely to occur in the solder and the principle reliability hazard in SMT assemblies is the resulting fatigue cracking of the solder fillet, caused by cyclic thermal stresses. These stresses may be caused by both cyclic variations in power dissipation within equipment and by external environmental temperature changes. Most work reported to date has focused on the effects of environmental temperature changes, although for many types of equipment power cycling may result in significant stresses. The present paper describes the experimental determination of the actual temperature distribution in a chip resistor assembly when it is powered. The paper also discusses the significance of such experimentally determined non-uniform temperature distributions in electronic assemblies to fatigue damage accumulation due to both power cycling and to cyclic variations in the ambient temperature whilst the chip resistor is powered. This fatigue damage accumulation study is carried out using finite element analysis

    Numerical analysis of dynamic out-of-plane loading of nonwovens

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    This paper presents finite element (FE) modelling of deformation behaviour of thermally bonded bicomponent fibre nonwovens under out-of-plane dynamic loading. Nonwoven fabric was treated as an assembly of two regions with distinct mechanical properties. Bond points were treated as composite material having a matrix of the sheath material reinforced with fibres of the core material. Elastic-plastic and viscous properties of the constituent fibres, obtained with tensile and relaxation tests were implemented into the FE model. The mechanical behaviour of the material under out-of-plane dynamic loading was observed with visual techniques. The deformation behaviour of nonwoven under out-of-plane dynamic loading computed with the numerical model was compared with that observed in the tests

    Optical properties of graphene-based materials in transparent polymer matrices

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    This paper was published in the journal, Applied Physics Letters [© American Institute of Physics]. It is also available at: http://dx.doi.org/10.1063/1.4961674Different aspects of graphene-based materials (GBMs) and GBM-nanocomposites have been investigated due to their intriguing features; one of these features is their transparency. Transparency of GBMs has been of an interest to scientists and engineers mainly with regard to electronic devices. In this study, optical transmittance of structural, purpose-made nanocomposites reinforced with GBMs was analyzed to lay a foundation for optical microstructural characterization of nanocomposites in future studies. Two main types of GBM reinforcements were studied, graphene oxide (GO) and graphite nanoplates (GNPs). The nanocomposites investigated are GO/poly(vinyl alcohol), GO/sodium alginate, and GNP/epoxy with different volume fractions of GBMs. Together with UV-visible spectrophotometry, image-processing-assisted micro and macro photography were used to assess the transparency of GBMs embedded in the matrices. The micro and macro photography methods developed were proven to be an alternative way of measuring light transmittance of semi-transparent materials. It was found that there existed a linear relationship between light absorbance and a volume fraction of GBMs embedded in the same type of polymer matrices, provided that the nanocomposites of interest had the same thicknesses. This suggests that the GBM dispersion characteristics in the same type of polymer are similar and any possible change in crystal structure of polymer due to different volumetric contents of GBM does not have an effect on light transmittance of the matrices. The study also showed that the same types of GBMs could display different optical properties in different matrix materials. The results of this study will help to develop practical microstructural characterization techniques for GBM-based nanocomposites

    Strength assessment of PET composite prosthetic sockets

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    open access articleA prosthesis is loaded by forces and torques exerted by its wearer, the amputee, and should withstand instances of peak loads without failure. Traditionally, strong prosthetic sockets were made using a composite with variety of reinforcing fibres such as glass, carbon, and kevlar. Amputees in less- resourced nations can lack access to composite prosthetic sockets due to their unavailability or prohibitive cost. Therefore, this study investigates the feasibility of polyethylene terephthalate (PET) fibre-reinforced composites as a low-cost sustainable composite for producing functional lower-limb prosthetic sockets. Two types of these composites were manufactured using woven and knitted fabric with a vacuum assisted resin transfer moulding (VARTM) process. For direct comparison purposes, traditional prosthetic-socket materials were also manufactured from laminated composite (glass-fibre reinforced (GFRP)) and monolithic thermoplastic (polypropylene (PP) and high-density polyethylene (HDPE)) were also manufactured. Dog-bone-shaped specimens were cut from flat laminates and monolithic thermoplastic to evaluate their mechanical properties following ASTM standards. The mechanical properties of PET-woven and PET-knitted composites were found to be have been demonstrated to be considerably superior to those of traditional socket materials such as PP and HDPE. All the materials were also tested in the socket form using a bespoke test rig reproducing forefoot loading according to the ISO standard 10328. The static structural test of sockets revealed that all met the target load-bearing capacity of 125 kg. Like GFRP, the PETW and PETK sockets demonstrated higher deformation and stiffness resistance than their monolithic counterparts made from PP and HDPE. As a result, it was concluded that the PET-based composite could replace monolithic socket materials in producing durable and affordable prostheses
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