Now showing 1 - 10 of 10
  • Publication
    A comparative study on different BFRP rebar design methodologies
    This study compares the physical properties and tensile behaviour of two different basalt fibre reinforced polymer (BFRP) rebar designs. Both types are developed using basalt fibres and epoxy resin as reinforcement and matrix respectively; composites with a constant cross section of 8 mm diameter are manufactured using a vacuum assisted resin infusion technique. The first configuration consists of eight braided layers at various angles, while the second one combines a unidirectional core with four outer braided layers. The latter hybrid design is introduced to improve the elastic modulus of braided BFRP reinforcement used in concrete structures. Tensile performance of all BFRP rebars produced in UCD laboratory is numerically and experimentally evaluated, and results for both approaches are compared. The effective longitudinal in-plane modulus and the fibre volume fractions (φf) of each sample is calculated using the classical laminate theory and then, tensile tests are performed in accordance to the B2_ACI 440.3R-04 standard to experimentally validate the numerical results. Initial findings indicate that the elastic modulus of BFRP rebar can be enhanced by combining braiding with a unidirectional fibre core while a sufficient tensile strength is obtained, but additional research towards an optimal hybrid design is required.
  • Publication
    The performance of coated tungsten carbide drills when machining carbon fibre-reinforced epoxy composite materials
    (Sage Publications, 2005-12-09) ; ;
    This paper is concerned with the effect of coatings on the performance of tungsten carbide (WC) drills in the drilling of carbon fibre-reinforced epoxy. Although composites are becoming increasing popular, there is a deficit in the existing knowledge of drilling composites, and in particular carbon fibre-reinforced epoxy resins. Two coated drills, namely titanium nitride (TiN)-coated and diamond-like carbon (DLC)-coated drills, were investigated and for comparative purposes an uncoated drill. The testing involved drilling a series of consecutive holes. During these tests the thrust forces and torques were monitored, following which the tool was inspected for flank wear and the workpiece inspected for damage in terms of hole tolerance, delamination and spalling. For all three tool types (uncoated, TiN coated and DLC coated), only a small number of drilled holes were found to satisfy an H8 tolerance criterion. An investigation of the hole diameter through the thickness of the composite revealed that it was the outermost plies that caused the hole to fail this tolerance criterion. The effect of tool wear caused the measured thrust forces and torques to increase over the life of the tool. While the degree of measured tool wear was small by comparison with that associated with drilling conventional materials, the effects were found to result in unacceptable damage to the composite. The damage was apparent in the form of spalling, chip-out and matrix cracking. The coatings were not found to reduce either tool wear or damage to the composite.
    Scopus© Citations 97  671
  • Publication
    Comparison between shot peening and abrasive blasting processes as deposition methods for hydroxyapatite coatings onto a titanium alloy
    Recent studies have shown that combining a compressed air jet with entrained hydroxyapatite (HA) particles with a jet of abrasive particles can be used to deposit a well adhered crystalline HA coatings onto titanium substrates. A similar particle bombardment process utilising a flow of shot peen particles and a flow of suitable powder particles has been used to deposit a range of coatings, though the deposition of bioceramic powders have not yet been reported by this method. In this study a direct comparison between the shot peen and abrasive bombardment processes has been undertaken to determine which technique yields coatings exhibiting higher levels of adhesion on titanium alloy substrates. Both processes were shown to effectively deposit a layer of crystalline apatite onto the titanium substrates over a range of pressures and jet to substrate heights. It was observed that for both processes that an increase in particle kinetic energy producing corresponding enhancements in both deposition rate and surface roughness. The shot peen process however produced a smooth layer of laminar apatite, which was readily removed from the surface using a scratch adhesion test technique. In contrast the combination of a jet of HA and abrasive powders resulted in an increase in surface abrasion and increased mechanical interlocking of the HA into the metal surface was observed. The mechano-chemical affect achieved resulted in a better adhered HA layer. The surface morphology obtained using the two treatments was significantly different with an increase in the average roughness (Ra) of ≈ 70 and 80 % for samples treated with abrasive particles over shot peen. This difference in surface treatment is further highlighted by the removal of the HA using an acid etch. The roughness (Ra) of the underlying titanium layer after this removal is, on average, >175 % higher for the surface treated with the abrasive particles during HA deposition.
      1056Scopus© Citations 39
  • Publication
    Development of Braided Basalt FRP Rebar for Reinforcement of Concrete Structures
    (The Hong Kong Polytechnic University, 2016-12-16) ; ;
    In recent years, the development and use of Fibre Reinforced Polymer composite materials in infrastructure have gained increasing attention worldwide. More specifically, natural mineral fibres such as basalt are currently being developed and are showing promising properties. Within an appropriate polymer matrix, their use as reinforcement in concrete structures offers performance benefits related to their environmentally friendly and non-corrodible nature. In particular, BFRPs have the potential to replace conventional internal steel rebar and thus, to be the next generation material in concrete reinforcement applications. A detailed literature review indicates that a careful selection of the appropriate manufacture technique and design methodology are required in order to prevent brittle failure on a concrete structure reinforced with FRP composite material. This paper reports on how to use the additional helical reinforcement and the braid configuration in order to increase strength, structural ductility and long term durability. Moreover, this study outlines the development of an analytical numerical model to predict the longitudinal elastic modulus of braided composites, as well as its validation by comparison of the results with available data from the literature.
  • Publication
    Comparison between microwave and microwave plasma sintering of nickel powders
    There is considerable interest in processing technologies which can lead to more energy efficient sintering of metal powders. The use of microwave sintering in particular leads to reduced energy usage during sintering as the volumetric heating process is considerably more efficient compared with resistance heating. In this study the use of a novel plasma microwave processing technology for the sintering of nickel powder discs is evaluated. The sintering study was carried out on 20 mm diameter by 2 mm thick pressed discs of nickel powder, with mean particle size of 1 μm. The discs were fired in a 5 cm diameter microwave (2.45 GHz) plasma ball under a hydrogen atmosphere at a pressure of 2 kPa. The same discs were also sintered using both non plasma microwave and tube furnace firing. The microwave plasma sintering is very rapid with full disc strength of approx. 1000 N based on 3--point bend tests being achieved within 10 minutes. In contrast the sintering time in the tube furnace involved treatments of up to 6 hours. The non plasma microwave system involved intermediate treatment periods of 1 to 2 hours. Another advantage of the microwave plasma treatment is that the degree of sintering between the individual nickel powder particles can be precisely controlled by the duration of the treatment time in the plasma. There was a broadly linear increase in fired pellet breaking strength with plasma treatment duration. In addition to breaking load, the mechanical properties of the sintered nickel discs were compared based on Rockwell hardness tests and density measurements. The morphology of the sintered discs was compared using microscopy and SEM. This study demonstrated that the plasma microwave sintered discs produced similar or superior performance (depending on processing conditions) to discs fired using the non-plasma microwave and furnace firing conditions. Accurate control of the sample conditions and structure can easily be controlled with the plasma system compared with the conventional systems. The apparent volumetric heating in the microwave systems give a more uniform heating at lower temperatures and allows for greater control and homogeneity.
    Scopus© Citations 5  630
  • Publication
    Mechanical characterisation of braided BFRP rebars for internal concrete reinforcement
    This study investigates the tensile behaviour of basalt fibre reinforced polymer (BFRP) composites that were developed using braiding as a manufacturing technique. Those materials will be introduced in concrete reinforcement applications. Three BFRP rebar sizes with a circular constant cross section and different braided configurations are developed and characterised with respect to their internal architecture. The braid angle on each layer of the rebar, varying from 10◦ to 45◦, is an important parameter that has a direct impact on its performance characteristics. The effective longitudinal in-plane modulus (ExFRP) of each braided sample is calculated numerically using the classical laminate theory (CLT) approach and then, tensile tests are performed according to the relevant standard. Comparisons between analytical and experimental data demonstrate a significant influence of braiding parameters, like braiding angle and number of braiding layers, on the mechanical properties of BFRP rebars. In addition, it is noteworthy that all predicted moduli determined with CLT numerical approach are found to be higher than the test results and overestimate rebar’s stiffness, most probably due to the degree of undulation from braiding process.
  • Publication
    Rapid discharge sintering of nickel-diamond metal matrix composites
    In this study rapid discharge sintering (RDS) and furnace sintering of nickel–diamond metal matrix composites (MMCs) is compared. Nickel–diamond powder composites (80–20% by weight respectively) were uniaxially pressed into 20 mm discs at compaction pressures of 100, 200 and 300 MPa. Discharge sintering was carried out using a microwave plasma formed with hydrogen and hydrogen/nitrogen as the discharge gases and tube furnace sintering carried out in a argon or a hydrogen/nitrogen (3:1) atmosphere. Discs pressed to 300 MPa were treated at both 850 and 1000 °C. The properties of the sintered nickel–diamond composites were characterized using density, approximate flexural strength, hardness, wear resistance, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The RDS samples sintered at 1000 °C achieved the maximum approximate disc flexural strength of 473 MPa within a 20 min treatment time compared with 6 h for furnace sintered samples. Samples sintered using the RDS technique exhibited increased hardness values and a finer nickel matrix over furnace sintered samples. Using the RDS technique it has been possible to process nickel–diamond MMCs without oxidation or graphitisation at temperatures above 900 °C. Minimal diamond destruction was observed during abrasive wear testing of the RDS samples compared with damage and pull-out observed for furnace sintering.
      994Scopus© Citations 19
  • Publication
    Wear resistance enhancement of the titanium alloy Ti6AI4V via a novel co-incident microblasting process
    A study was undertaken to investigate the potential of a novel surface modification process to enhance Ti6Al4V wear resistance. The process consists of co-incident particle streams of abrasive and dopant materials which impact a substrate to create a modified surface. Al2O3 was chosen as the abrasive and Teflon, SiC and B4C were investigated as dopants. Al2O3-SiC and Al2O3-B4C modified Ti6Al4V both exhibited increased surface hardness compared to the unmodified metal alloy. However, pin-on-disc tribometer measurements indicated that such hardening modifications exhibited no appreciable benefits in terms of wear resistance. On the other hand, Al2O3-Teflon modified Ti6Al4V demonstrated significantly reduced coefficients of friction and reduced wear rates under the same test conditions. Investigations suggest that although the Al2O3 abrasive is not incorporated into the coating, its presence is essential in order to achieve a wear resistant surface. Combinations of hard material (SiC or B4C) modifications with a further layer of Teflon resulted in further enhancement of wear resistance as increased surface hardness was allied with similar low coefficients of friction. In conclusion, a number of the surface modifications conducted have a beneficial affect on the wear resistance of Ti6Al4V. The process is also likely applicable to other metal/metal alloys such as CoCr, NiTi and stainless steels. Furthermore, the chemical-free nature and ambient temperature conditions concerned afford this process the potential to act as an attractive alternative to some of the more problematic high temperature approaches currently in use.
    Scopus© Citations 17  732
  • Publication
    Comparison of thermal and microwave-assisted plasma sintering of nickel-diamond composites
    There is considerable interest in processing technologies which can lead to more energy efficient sintering of metal powders. Microwave sintering has recently been shown to reduce energy usage as the volumetric heating process is considerably more efficient than resistance heating. RF plasma sintering meanwhile has been shown to deliver heat via uniform excitation of the processing gas resulting in ion bombardment of the workpiece. In this study the use of a rapid, novel microwave-assisted plasma sintering (MaPS) technology for processing of nickel-diamond metal matrix composites is evaluated. Nickel powder and polycrystalline diamond were mixed to prepare 20 mm discs under uniaxial compaction pressures of 100, 200 and 300 MPa. The discs were fired in a low pressure microwave plasma under a hydrogen atmosphere. For comparison, discs were also sintered using conventional tube furnace firing. The MaPS sintering is very rapid with full disc strength of >1000N, based on 3-point bend tests, being achieved within 10 minutes compared with 8 hours for furnace treatment. This study demonstrates that the microwave-assisted plasma sintered discs produced similar or superior performance to discs fired using furnace firing conditions but with sintering cycle time reduced by up to 95%.
    Scopus© Citations 4  349
  • Publication
    Developing braided FRP reinforcement for concrete structures
    (Civil Engineering Research Association of Ireland, 2016-08-30) ; ;
    In recent years, significant research has been conducted, by both industry and academia, into the optimum development and use of Fibre Reinforced Polymer composite materials in infrastructure. In particular, it is widely recognised that FRPs have the potential to replace conventional internal steel rebars in concrete reinforcement and offer performance benefits related to their advanced properties, such as corrosion resistance, high tensile strength etc.A review of the available literature indicates that brittle behaviour of FRP can significantly decrease the expected ultimate load capacity and, thus have a negative effect on structure¿s long term durability. However, selecting braiding as manufacture technique and enhancing flexural capacity and shear strength through additional helical reinforcement, could provide structure with the additional ductility needed to prevent a brittle failure. Furthermore, the impact of deterioration mechanisms, focusing on the interaction between FRP and concrete in a structure, is an aspect for further investigation via laboratory testing and advanced analysis.This study summarises the results of research on structural design and manufacture methods of FRP composite materials by presenting new configuration and types of FRP reinforcement in order to encourage the use of these promising materials in construction industry.