3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item A carbon fibre wheel for a lightweight production sports car(2019) Czypionka, Stefan NikolausThe wheel of a passenger vehicle must be designed to be safe and light. Despite the potential of carbon fibre as an automotive material due to high strength and low weight, the prevalence of carbon fibre reinforced plastics (CFRPs) in vehicle wheels is limited. This study develops a method to design a CFRP wheel for a high-performance roadster. The designed CFRP wheel used as a case study to illustrate the method is offered by an automotive manufacturer as a high-performance option instead of aluminium wheels. Finite element (FE) simulations were performed on the geometry of the wheel. These helped remove problematic geometric profiles prior to the manufacture of a mould. FE simulations were conducted to reduce the mass of the aluminium hubs required for mounting the CFRP wheel to a vehicle. The CFRP wheel mass is 6.4 kg as compared to the original aluminium wheel which weighs 8.1 kg. This initial design passed the dynamic cornering fatigue test (the most stringent strength test for wheels). Thereafter a prototype wheel was instrumented with strain gauges and a bending moment was applied to the hub using a custom-built test rig. The test rig produced a static load equivalent to the dynamic cornering fatigue test (in which the applied bending moment varies sinusoidally). The test rig allowed for the deflection of the load arm to be measured. The comparison of the experimentally measured strains and an FE model which includes the CFRP laminate properties showed good agreement. This study shows that an aluminium wheel for a high-performance roadster can be redesigned using CFRP to be 21 % lighter. A bending stiffness test was conducted on another similar CFRP wheel at elevated temperatures. An 18 % reduction in bending stiffness was calculated when the wheel was heated to 140 oC, this reduction reduced to 13 % once the wheel cooled to ambient temperature. Further study of the effect of temperature on CFRP wheels is required. This study has illustrated a successful method to design CFRP wheels for passenger vehicles to affect a reduction in mass.Item Experimental and Numerical Characterization of Interlaminar Properties of SWCNTs Doped PAN Nano-mats Strenthened Multiscale Hybrid Composites(2019) Arif, MuhammadPolymer composite reinforced with conventional macro size bres have taken a major role in various modern engineering applications and their demand is ever increasing due to their light weight and design exibility. Various im-provements in manufacturing methods, fabrication techniques and composite constituents have been made over the years to produce better polymer com- posites. However, the major challenge of the conventional polymer composites is that failure at the matrix rich interlaminar region still remains and limits their performance resulting in unreliable usage of these composites. A number of research attempts had little success due to various limiting factors have been carried out to rectify this problem. One of the potential methods expected to improve the strength of the interlaminar region is the incorporation of nano-size llers, such as electrospun Polyacrylonitrile (PAN) nano bres mat as an interalia into the matrix rich interlaminar region of the conventional polymercomposite. However, controlling the alignment and distribution of the PAN nano bres during the chaotic electrospinning process is a major hurdle for im-proving the interlaminor regions. The random orientation of electrospun PAN nano bres mat reduces their strengthening e ect and also the required material properties.Hence, the current study has focused on the design of electrospinning process for improving the orientation and distribution of the PAN nano bre mats. The developed electrospinning process was used to produce random and aligned PAN nano bres mat and also used for producing both pristine and function-alized single walled carbon nanotubes (SWCNTs) doped PAN nano bres mat. These nanomats were then sandwiched with the glass bre-epoxy matrix to produce nano strengthened multiscale hybrid composites. As part of the electrospinning procedure, electric elds of general electrospin- ning technique were manipulated using two position adjustable auxiliary ver- tical electrodes (AVEs) to produce aligned nano bres mat along with reduced diameter. So as to optimise the electrospinning parameters, the e ect of AVEs on the PAN nano bres mat orientation, distribution and diameter were ex- perimentally matrixed and analysed. The fractographic study showed that auxiliary vertical electrodes (AVEs) added to the electrospinning process re- duced the diameter, enhanced the alignment of the nano bres and improved molecular orientation. Among four di erent volume fractions of 0.1%, 0.2%, 0.5% and 1% randomly oriented PAN nano bre mats, the volume fraction of 0.5% PAN polymer was selected to manufacture aligned PAN nano bres mat strengthened hybrid composite based on the improved experimental randomly oriented PAN nano bre mats strengthened hybrid composites. A series of tests showed that glass bre composites (GFC) reinforced with the volume fraction of 0.5% aligned nano bre mats were better than those of 0.5% randomly distributed nano bre mats. The aligned nano bre mat with reduced diameter increased the tensile, exural, and impact properties of glass bre composite by 68.91%, 95.32% and 45.30% respectively. Aligned nano bres mat was further utilised to align and disperse the pristine and functionalized SWCNTs into the interlaminar region of breglass compos- ite. Alignment and a nano-range diameter of nano bres helped in improved distribution and alignment of pristine SWCNTs (p-SWCNTs), which was re- ected in an increase in tensile, exural and impact resistance by 89.30%, 105.48% and 107.17% respectively. A nondestructive functionalization method (Friedel craft alkylation) was used to improve the interface bonding of SWC- NTs with the host PAN polymer nano bre. PVA chains crafted to the surface of the SWCNTs without damaging the wall was con rmed using FTIR and Ra- man spectroscopy. The e ect of functionalized SWCNTs (f-SWCNTs) doped aligned PAN nano bre mats improved the properties of nano-hybrid multiscale composite up to 111.34%, 117.11% and 180.03% in tensile, exural and impact resistance respectively. A multiscale model was used to determine the properties of the multiscale nanohybrid composite strengthened with random and aligned PAN nano bre mats, PAN doped with p-SWCNTs and f-SWCNTs aligned nano bre mats. Three length scales, such as nano, micro and macro scales were modelled. At rst, a numerical model was developed to determine the elastic properties of di erent carbon nanotubes (CNTs) i.e. Pristine and defective single wall (SWCNTs), double wall (DWCNTs), and multiwall (MWCNTs) for zigzag and armchair con gurations. CNTs atomic geometry was replicated with an equivalent space frame structure (SFS). Co-ordinates de nition of SFS of CNTs was developed in MATLAB code and transferred to the nite element analysis (FEA) software 'ANSYS'. The basic entity of SFS, C-C chemical bond was designed as a circular beam of orthotropic properties. The properties were determined by linking the energy equation of molecular mechanics to structural mechanics along with the parametric study. The van der Waals forces between inter-shell of DWCNTs and MWCNTs were modelled as linear elastic springs in a simpli ed way. The simpli ed model avoided the problems due to the nonlinear behaviour of van der Waals forces and improved the performance of the FEA software by computational resources. The e ect of chirality, vacancy defects, di erent diameters and numbers of walls on elastic properties of CNTs were calculated, tabulated and compared with each other. The result of the proposed SFS model with orthotropic properties was compared with others result. The SFS model is found better than the equivalent shell model as the defects can be placed at the exact location and a more realistic behaviour could be predicted. The SFS models could be developed with any type of defects, a number of walls, van derWaals and agglomerated forms with variable geometries. Using the space frame structures (SFS) of SWCNTs, the nanoscale RVE of PAN nano bre doped with SWCNTs was modelled. Simulated results of nanoscale RVEs were used to determine the equivalent properties of p-SWCNTs and f-SWCNTs doped nano bres, which were further used in microscale RVE models. Four micro scale RVEs were developed to represent the random and aligned PAN nano bres mats, PAN nano bres mat doped with p-SWCNTs and f-SWCNTs aligned PAN nano bres mat in epoxy matrix. Analysed micro scale RVEs provided equivalent properties of interlaminar regions developed with random and aligned PAN nano bres mat, PAN doped with p-SWCNTs and f-SWCNTs aligned nano bres mat. At the macro scale, MNHCs were de- veloped with equivalent interlaminar regions and analysed. The results of the simulated MNHCs were compared with experimentally obtained results. The results of the experimental study suggested that aligned nano bres with reduced diameter improved the properties of interlaminar region noticeably than the random nano bres mat of the same volume fraction. Aligned nano - bres successfully placed the pristine and functionalized SWCNTs within the multiscale hybrid composites which signi cantly improved the properties of the multiscale hybrid composite. Results of the multiscale modelling were in line with the experimental results, which could be useful in extending the small- scale theoretical results to the real-life applications.Item CNT Doped PAN Nanofibre strengthened Aramid-pp composites: Improved interlaminar properties(2018) Ncube, MkhuliliThis study focused on the strengthening of aramid polypropylene hybrid composites using both electrospun PAN and CNT doped PAN nanomat. The strengthening of the aramid-polypropylene (PP) composites with both aligned and randomly distributed nano bres resulted in the improvement of the tensile strength, exural strength, impact energy absorption and interlaminar shear strength (ILSS). However, compared to the randomly distributed 0.5% PAN nano bre strengthened aramid-PP composites, the aligned PAN nano bre strengthened aramid-PP composites had higher mechanical properties with improvements in tensile strength by 6%, exural strength by 5%, impact energy absorption by 7% and ILSS by 3%. The doping of PAN nanomat with pristine and functionalized CNTs resulted in an improved mechanical properties of the hybrid composites with those strengthened with functionalized CNTs achieving higher mechanical properties. With the increase in CNT concentration in the CNT doped PAN nanomat strengthened hybrid composite the mechanical properties increased. Compared with PAN reinforced aramid-PP composites, the addition of PAN doped with 0.5% functionalized CNTs resulted in an increase in tensile strength by 15%, exural strength by 35%, impact absorption energy by 26% and ILSS by 32%. It was found that the dominant mechanism of failure for aramid-PP composites without PAN/CNT reinforcement was due to interfacial debonding. This study shows that the use of aligned electrospun nano bres help to improve the imterlaminar properties of the the hybrid composites. Functionalization of CNTs greatly improves the bre-matrix interaction and thus greatly reducing failure by interfacial debonding. Overall, the doping of aligned PAN nano bres with functionalized CNTs resulted in improvement in interlaminar and mechanical properties of the hybrid compositesItem The effect of montmorillonite clay on the mechanical properties of kenaf reinforced polypropylene composite(2017) Govinden, SumilanAn investigation was carried out to determine the effect of the addition of clay on the mechanical properties of a Natural Fibre Composite consisting of a polypropylene matrix with kenaf fibre reinforcement. The kenaf fibres were treated using various chemical treatments to improve the strength of the composites manufactured. Four treatments using different 3-mercaptopropyltrimethoxy silane (MPS) concentrations were investigated to determine which treatment resulted in the best mechanical properties. [Abbreviated Abstract. Open document to view full version]Item Determination of residual stresses in a carbon-fibre reinforced polymer using the incremental hole-drilling technique(2017) Okai, Smart KAn extensive variety of experimental techniques exist to determining residual stresses, but few of these techniques is suitable, however, for finding the residual stresses that exist in orthotropic or anisotropic layered materials, such as carbon-fibre reinforced polymers (CFRP). Among these techniques, particularly among the relaxation techniques, the incremental hole-drilling technique (IHD) has shown to be a suitable technique to be developed for this purpose. This technique was standardized for the case of linear elastic isotropic materials, such as the metallic alloys in general. However, its reliable application to anisotropic and layered materials, such as CFRP materials, needs to be better studied. In particular, accurate calculation methods to determine the residual stresses in these materials based on the measured in-depth strain relaxation curves need to be developed. In this work, existing calculation methods and already proposed theoretical approaches to determine residual stresses in composite laminates by the incremental hole-drilling technique are reviewed. The selected residual stress calculation method is implemented using MATLAB. For these calculations, specific calibration coefficients have to be numerically determined by the finite element method, using the ANSYS software. The developed MATLAB scripts are then validated using an experimental procedure previously developed. This experimental procedure was performed using CFRP specimens, with the stacking sequence [0o, 90o]5s and, therefore, this composite laminate was selected as case study in this work. Some discrepancies between the calculated stresses using the MATLAB scripts and those imposed during the experimental calibration procedure are observed. The errors found could be explained considering the limitations inherent to the incremental hole-drilling technique and the theoretical approach followed. However, the obtained results showed that the incremental hole-drilling can be considered a promising technique for residual stress measurement in composite laminates.Item Electrospun nano-mat strengthened aramid fibre hybrid composites : improved mechanical properties by continuous nanofibres(2016) Jinasena, Isuru Indrajith KosalaAramid fibre reinforced epoxy composites were hybridised by the addition of electrospun PAN (polyacrylonitrile) and ECNF (electrospun carbon nanofibre) doped PAN nanomats. One of the major concerns in polymer composites is the effect of the interlaminar properties on the overall mechanical properties of the composite. Electrospun carbon nanofibres were used as doping agents within PAN nanofibres, and coated in between aramid epoxy laminates to improve the interlaminar properties. PAN nanomats and ECNF doped PAN nanomats were created by the use electrospinning on the surface of aramid fibre sheets. Multiscale hybrid aramid reinforced composites were then fabricated. Mechanical characterization was carried out to determine the effect of PAN and CNF doped PAN nanofibre mats on aramid fibre reinforced epoxy. It was found that PAN reinforced nanomats had improved the mechanical properties and more specifically, when doped by ECNFs, the volume fraction of ECNFs played a vital role. An addition of 1% vol. CNF doped 0.1% vol. PAN reinforcement within a 30% vol. aramid fibre composite (control composite), improved the tensile strength and elastic modulus by 17.3% and 730% respectively. The 0.5% vol. PAN reinforced AFC (aramid fibre composite) specimens revealed a major increase in the flexural strength by 9.67% and 12.1%, when doped by both 0.5% vol. ECNFs and 1% vol. ECNFs respectively. The 0.5% vol. CNF doped reinforcement increased the impact energy by over 40%, for both the 0.1% vol. and 0.2 % vol. PAN reinforced aramid hybrid specimens. The 0.5% vol. CNF doped 0.5% vol. PAN had increased by 30% when compared to a non-doped sample. Morphological studies indicated interlaminar shearing between plies was affected by CNF agglomerations. This was discovered when determining the impact properties of the multiscale doped hybrid composites. Electrospun nanofibres however, assisted in improving the interlaminar regions within aramid epoxy by mechanical locking within the epoxy, and creating an adhesive bond using Van der Waals forces and electrostatic charges between nanofibre and macro fibre. Hybridising aramid epoxy with the use of nanofibres assisted in improving various mechanical properties. Impact degradation was one disadvantage of hybridising using CNF doped PAN nanofibre reinforcements.Item Characterisation of the structural properties of ECNF embedded pan nanomat reinforced glass fiber hybrid composites(2016-10-11) Bradley, PhilipIn this study, hybrid multiscale epoxy composites were developed from woven glass fabrics and PAN nanofibers embedded with short ECNFs (diameters of ~200nm) produced via electrospinning. Unlike VGCNFs or CNTs which are prepared through bottom-up methods, ECNFs were produced through a top-down approach; hence, ECNFs are much more cost-effective than VGCNFs or CNTs. Impact absorption energy, tensile strength, and flexural strength of the hybrid multiscale reinforced GFRP composites were investigated. The control sample was the conventional GFRP composite prepared from the neat epoxy resin. With the increase of ECNFs fiber volume fraction up to 1.0%, the impact absorption energy, tensile strength, and flexural strength increased. The incorporation of ECNFs embedded in the PAN nanofibers resulted in improvements on impact absorption energy, tensile strength, and flexural properties (strength and modulus) of the GFPC. Compared to the PAN reinforced GRPC, the incorporation of 1.0% ECNFs resulted in the improvements of impact absorption energy by roughly 9%, tensile strength by 37% and flexural strength by 29%, respectively. Interfacial debonding of matrix from the fiber was shown to be the dominant mechanism for shear failure of composites without ECNFs. PAN/ECNFs networks acted as microcrack arresters enhancing the composites toughness through the bridging mechanism in matrix rich zones. More energy absorption of the laminate specimens subjected to shear failure was attributed to the fracture and fiber pull out of more ECNFs from the epoxy matrix. This study suggests that, the developed hybrid multiscale ECNF/PAN epoxy composite could replace conventional GRPC as low-cost and high-performance structural composites with improved out of plane as well as in plane mechanical properties. The strengthening/ toughening strategy formulated in this study indicates the feasibility of using the nano-scale reinforcements to further improve the mechanical properties of currently structured high-performance composites in the coming years. In addition, the present study will significantly stimulate the long-term development of high-strength high-toughness bulk structural nanocomposites for broad applications.