High-temperature mechanical properties of aluminium alloys reinforced with titanium diboride (TiB2) particles

The physical and mechanical properties of metal matrix composites were improved by the addition of reinforcements. The mechanical properties of particulate-reinforced metal-matrix composites based on aluminium alloys (6061 and 7015) at high temperatures were studied. Titanium diboride (TiB2) particles were used as the reinforcement. All the composites were produced by hot extrusion. The tensile properties and fracture characteristics of these materials were investigated at room temperature and at high temperatures to determine their ultimate strength and strain to failure. The fracture surface was analysed by scanning electron microscopy. TiB2 particles provide high stability of the aluminium alloys (6061 and 7015) in the fabrication process. An improvement in the mechanical behaviour was achieved by adding TiB2 particles as reinforcement in both the aluminium alloys. Adding TiB2 particles reduces the ductility of the aluminium alloys but does not change the microscopic mode of failure, and the fracture surface exhibits a ductile appearance with dimples formed by coalescence.

Production of nanoTiC–graphite composites using Ti-doped self-sintering carbon mesophase powder

This work reports the synthesis of nanoTiC–graphite composites using mesophase pitch containing titanium as TiC or TiO2 nanoparticles. NanoTiC–graphite composites have been prepared using Ti-doped self-sintering mesophase powders as starting materials without using any binders or a metal carbide-carbon mixing stage. The effect of manufacture variables on the graphite compacts properties was studied. Graphites were characterised using XRD and Raman spectroscopy, SEM and TEM, as well as by their mechanical, electrical and thermal properties. The presence of TiC promotes graphitisation producing materials with larger crystal sizes. The kind of titanium source and mesophase content of the starting pitch affects to the final properties. Mesophase pitch with higher amount of mesophase content produces graphites with higher degree of graphitisation. The incorporation of TiC nanoparticles to the graphites composites improved thermal conductivity more than four times, and mechanical properties are not significantly modified by the presence of TiC.

Elemental data for composites from DSDP Sites 417A, 417D, and 418A

While the input of river-alkalinity into seawater is relatively well known, the complementary acidity production is poorly understood. Using the major-element budget of seafloor alteration of the upper 500 m of 120-Ma-old oceanic crust at DSDP/ODP Sites 417A, 417D and 418A in the central western Atlantic, we estimate the acidity flux associated with the low-temperature weathering of the upper oceanic crust. The acidity flux is calculated based on major-element fluxes and charge-balance considerations. The relevant chemical fluxes from seawater to the upper crust are 4.1+-0.1; 1.4+-1.4; 2.2+-0.6 and -12+-2 10**11 mol/yr for K, Mg, Na and silicate-Ca, respectively. The associated acidity flux is (3.5+-3)10**11 eq/y. Relative to continental weathering, these fluxes are significant for K and silicate-Ca, but are minor for Na, Mg and acidity. Thus, riverine fluxes of alkalinity are not significantly balanced by acidity fluxes from low-temperature upper ocean crust alteration.

Synthesis and evaluation of nanoparticle-polymer composites

This thesis describes the synthesis of functionalised polymeric material by variety of free-radical mediated polymerisation techniques including dispersion emulsion, seeded emulsion, suspension and bulk polymerisation reactions. Organic fluorophores and nanoparticles such as quantum dots were incorporated within polymeric materials, in particular, thiol-functionalised polymer microspheres, which were fluorescently labelled either during synthesis or by covalent attachment post synthesis. The resultant fluorescent polymeric conjugates were then assessed for their utility in biological systems as an analytical tool for cells or biological structures. Quantum dot labelled, thiol-functionalised microspheres were assessed for their utility in the visualisation and tracking of red blood cells. Determination of the possible internalisation of fluorescent microspheres into red blood cells was required before successful tracking of red blood cells could take place. Initial work appeared to indicate the presence of fluorescent microspheres inside red blood cells by the process of beadfection. A range of parameters were also investigated in order to optimise beadfection. Thiol-functionalised microspheres labelled successfully with organic fluorophores were used to image the tear film of the eye. A description of problems encountered with the covalent attachment of hydrophilic, thiol-reactive fluorescent dyes to a variety of modified polymer microspheres is also included in this section. Results indicated large microspheres were particularly useful when tracking the movement of fluid along the tear meniscus. Functional bulk polymers were synthesised for assessment of their interaction with titanium dioxide nanoparticles. Thiol-functionalised polymethyl methacrylate and spincoated thiouronium-functionalised polystyrene appeared to facilitate the attachment of titanium dioxide nanoparticles. Interaction assays included the use of XPS analysis and processes such as centrifugation. Attempts to synthesise 4-vinyl catechol, a compound containing hydroxyl moieties with potential for coordination with titanium dioxide nanoparticles, were also carried out using 3,4-dihydroxybenzaldehyde as the starting material.

Hydroxyapatite-nanotube composites and coatings for orthopedic applications

Hydroxyapatite (HA) has received wide attention in orthopedics, due to its biocompatibility and osseointegration ability. Despite these advantages, the brittle nature and low fracture toughness of HA often results in rapid wear and premature fracture of implant. Hence, there is a need to improve the fracture toughness and wear resistance of HA without compromising its biocompatibility. ^ The aim of the current research is to explore the potential of nanotubes as reinforcement to HA for orthopedic implants. HA- 4 wt.% carbon nanotube (CNT) composites and coatings are synthesized by spark plasma sintering and plasma spraying respectively, and investigated for their mechanical, tribological and biological behavior. CNT reinforcement improves the fracture toughness (>90%) and wear resistance (>66%) of HA for coating and free standing composites. CNTs have demonstrated a positive influence on the proliferation, differentiation and matrix mineralization activities of osteoblasts, during in-vitro biocompatibility studies. In-vivo exposure of HA-CNT coated titanium implant in animal model (rat) shows excellent histocompatibility and neobone integration on the implant surface. The improved osseointegration due to presence of CNTs in HA is quantified by the adhesion strength measurement of single osteoblast using nano-scratch technique. ^ Considering the ongoing debate about cytotoxicity of CNTs in the literature, the present study also suggests boron nitride nanotube (BNNT) as an alternative reinforcement. BNNT with the similar elastic modulus and strength as CNT, were added to HA. The resulting composite having 4 wt.% BNNTs improved the fracture toughness (∼85%) and wear resistance (∼75%) of HA in the similar range as HA-CNT composites. BNNTs were found to be non-cytotoxic for osteoblasts and macrophages. In-vitro evaluation shows positive role of BNNT in osteoblast proliferation and viability. Apatite formability of BNNT surface in ∼4 days establishes its osseointegration ability.^

Review of strengthening techniques using externally bonded fiber reinforced polymer composites

This report reviews the selection, design, and installation of fiber reinforced polymer systems for strengthening of reinforced concrete or pre-stressed concrete bridges and other structures. The report is prepared based on the knowledge gained from worldwide experimental research, analytical work, and field applications of FRP systems used to strengthen concrete structures. Information on material properties, design and installation methods of FRP systems used as external reinforcement are presented. This information can be used to select an FRP system for increasing the strength and stiffness of reinforced concrete beams or the ductility of columns, and other applications. Based on the available research, the design considerations and concepts are covered in this report. In the next stage of the project, these will be further developed as design tools. It is important to note, however, that the design concepts proposed in literature have not in many cases been thoroughly developed and proven. Therefore, a considerable amount of research work will be required prior to development of the design concepts into practical design tools, which is a major goal of the current research project. The durability and long-term performance of FRP materials has been the subject of much research, which still are on going. Long-term field data are not currently available, and it is still difficult to accurately predict the life of FRP strengthening systems. The report briefly addresses environmental degradation and long-term durability issues as well. A general overview of using FRP bars as primary reinforcement of concrete structures is presented in Chapter 8. In Chapter 9, a summary of strengthening techniques identified as part of this initial stage of the research project and the issues which require careful consideration prior to practical implementation of these identified techniques are presented.

User friendly guide for rehabilitation or strengthening of bridge structures using fiber reinforced polymer composites

A worldwide interest is being generated in the use of fibre reinforced polymer composites (FRP) in rehabilitation of reinforced concrete structures. As a replacement for the traditional steel plates or external post-tensioning in strengthening applications, various types of FRP plates, with their high strength to weight ratio and good resistance to corrosion, represent a class of ideal material in external retrofitting. Within the last ten years, many design guidelines have been published to provide guidance for the selection, design and installation of FRP systems for external strengthening of concrete structures. Use of these guidelines requires understanding of a number of issues pertaining to different properties and structural failure modes specific to these materials. A research initiative funded by the CRC for Construction Innovation was undertaken (primarily at RMIT) to develop a decision support tool and a user friendly guide for use of fibre reinforced polymer composites in rehabilitation of concrete structures. The user guidelines presented in this report were developed after industry consultation and a comprehensive review of the state of the art technology. The scope of the guide was mainly developed based on outcomes of two workshops with Queensland Department of Main Roads (QDMR). The document covers material properties, recommended construction requirements, design philosophy, flexural, shear and torsional strengthening of beams and strengthening of columns. In developing this document, the guidelines published on FIB Bulletin 14 (2002), Task group 9.3, International Federation of Structural Concrete (FIB) and American Concrete Institute Committee 440 report (2002) were consulted in conjunction with provisions of the Austroads Bridge design code (1992) and Australian Concrete Structures code AS3600 (2002). In conclusion, the user guide presents design examples covering typical strengthening scenarios.

Decision support tools for concrete infrastructure rehabilitation (using FRP composites)

This report presents a summary of the research conducted by the research team of the CRC project 2002-005-C, “Decision support tools for concrete infrastructure rehabilitation”. The project scope, objectives, significance and innovation and the research methodology is outlined in the introduction, which is followed by five chapters covering different aspects of the research completed. Major findings of a review of literature conducted covering both use of fibre reinforced polymer composites in rehabilitation of concrete bridge structures and decision support frameworks in civil infrastructure asset management is presented in chapter two. Case study of development of a strengthening scheme for the “Tenthill Creek bridge” is covered in the third chapter, which summarises the capacity assessment, traditional strengthening solution and the innovative solution using FRP composites. The fourth chapter presents the methodology for development of a user guide covering selection of materials, design and application of FRP in strengthening of concrete structures, which were demonstrated using design examples. Fifth chapter presents the methodology developed for evaluating whole of life cycle costing of treatment options for concrete bridge structures. The decision support software tool developed to compare different treatment options based on reliability based whole of life cycle costing will be briefly described in this chapter as well. The report concludes with a summary of findings and recommendations for future research.

Decision support in using fibre reinforced polymer (FRP) composites in rehabilitation of concrete bridge structures

This paper compares and reviews the recommendations and contents of the guide for the design and construction of externally bonded FRP systems for strengthening concrete structures reported by ACI committee 440 and technical report of Externally bonded FRP reinforcement for RC structures (FIB 14) in application of carbon fiber reinforced polymer (CFRP) composites in strengthening of an aging reinforced concrete headstock. The paper also discusses the background, limitations, strengthening for flexure and shear, and other related issues in use of FRP for strengthening of a typical reinforced concrete headstock structure such as durability, de-bonding, strengthening limits, fire and environmental conditions. A case study of strengthening of a bridge headstock using FRP composites is presented as a worked example in order to illustrate and compare the differences between these two design guidelines when used in conjunction with the philosophy of the Austroads (1992) bridge design code.