Production of phenol-formaldehyde resin composites

The main objective of this work was to examlne the various stages of the production of industrial laminates based on phenol-formaldehyde resins, with a view of suggesting ways of improving the process economics and/or the physical properties of the final product. Aspects of impregnation, drying, and lamination were investigated. The resins used in all experiments were ammonia-catalysed. Work was concentrated on the lamination stage since this is a labour intensive activity. Paper-phenolic lay-ups were characterised in terms of the temperatures experienced during cure, and a shorter cure-cycle is proposed, utilising the exothermic heat produced during pressing of 25.5 mm thick lay-ups. Significant savings in production costs and improvements in some of the physical properties have been achieved. In particular, water absorption has been reduced by 43-61%. Work on the drying stage has shown that rapid heating of the wet impregnated substrate results in resin solids losses. Drying at lower temperatures by reducing the driving force leads to more resin (up to 6.5%) being retained by the prepregs and therefore more effective use of an expensive raw material. The impregnation work has indicated that residence times above 6 seconds in the varnish bath enhance the insulation resistance of the final product, possibly due to improved resin distribution and reduction in water absorption. In addition, a novel process which involves production of laminates by in situ polymerisation of the phenolic resin on the substrate has been examined. Such a process would eliminate the solvent recovery plant - a necessary stage in current industrial processes. In situ polymerisation has been shown to be chemically feasible.

The influence of tool geometry on the performance of drilling tools

The main objective of the work presented in this thesis is to investigate the two sides of the flute, the face and the heel of a twist drill. The flute face was designed to yield straight diametral lips which could be extended to eliminate the chisel edge, and consequently a single cutting edge will be obtained. Since drill rigidity and space for chip conveyance have to be a compromise a theoretical expression is deduced which enables optimum chip disposal capacity to be described in terms of drill parameters. This expression is used to describe the flute heel side. Another main objective is to study the effect on drill performance of changing the conventional drill flute. Drills were manufactured according to the new flute design. Tests were run in order to compare the performance of a conventional flute drill and non conventional design put forward. The results showed that 50% reduction in thrust force and approximately 18% reduction in torque were attained for the new design. The flank wear was measured at the outer corner and found to be less for the new design drill than for the conventional one in the majority of cases. Hole quality, roundness, size and roughness were also considered as a further aspect of drill performance. Improvement in hole quality is shown to arise under certain cutting conditions. Accordingly it might be possible to use a hole which is produced in one pass of the new drill which previously would have required a drilled and reamed hole. A subsidiary objective is to design the form milling cutter that should be employed for milling the foregoing special flute from drill blank allowing for the interference effect. A mathematical analysis in conjunction with computing technique and computers is used. To control the grinding parameter, a prototype drill grinder was designed and built upon the framework of an existing cincinnati cutter grinder. The design and build of the new grinder is based on a computer aided drill point geometry analysis. In addition to the conical grinding concept, the new grinder is also used to produce spherical point utilizing a computer aided drill point geometry analysis.

Deep hole drilling with twist drills: aspects of the CNC process and its real time monitoring and adaptive control

Deep hole drilling is one of the most complicated metal cutting processes and one of the most difficult to perform on CNC machine-tools or machining centres under conditions of limited manpower or unmanned operation. This research work investigates aspects of the deep hole drilling process with small diameter twist drills and presents a prototype system for real time process monitoring and adaptive control; two main research objectives are fulfilled in particular : First objective is the experimental investigation of the mechanics of the deep hole drilling process, using twist drills without internal coolant supply, in the range of diarneters Ø 2.4 to Ø4.5 mm and working length up to 40 diameters. The definition of the problems associated with the low strength of these tools and the study of mechanisms of catastrophic failure which manifest themselves well before and along with the classic mechanism of tool wear. The relationships between drilling thrust and torque with the depth of penetration and the various machining conditions are also investigated and the experimental evidence suggests that the process is inherently unstable at depths beyond a few diameters. Second objective is the design and implementation of a system for intelligent CNC deep hole drilling, the main task of which is to ensure integrity of the process and the safety of the tool and the workpiece. This task is achieved by means of interfacing the CNC system of the machine tool to an external computer which performs the following functions: On-line monitoring of the drilling thrust and torque, adaptive control of feed rate, spindle speed and tool penetration (Z-axis), indirect monitoring of tool wear by pattern recognition of variations of the drilling thrust with cumulative cutting time and drilled depth, operation as a data base for tools and workpieces and finally issuing of alarms and diagnostic messages.

Preparation and electrical properties of graphene nanosheet/Al2O3 composites

Fully dense graphene nanosheet(GNS)/Al2O3 composites with homogeneously distributed GNSs of thicknesses ranging from 2.5 to 20 nm have been fabricated from ball milled expanded graphite and Al2O3 by spark plasma sintering. The percolation threshold of electrical conductivity of the as-prepared GNS/Al2O3 composites is around 3 vol.%, and this new composite outperforms most of carbon nanotube/Al2O3 composites in electrical conductivity. The temperature dependence of electrical conductivity indicated that the as-prepared composites behaved as a semimetal in a temperature range from 2 to 300 K.

An investigation of the relationship between temperature, forces and tool wear in turning and drilling

Developing a means of predicting tool life has been and continues to be a focus of much research effort. A common experience in attempting to replicate such efforts is an inability to achieve the levels of agreement between theory and practice of the original researcher or to extrapolate the work to different materials or cutting conditions to those originally used. This thesis sets out to examine why most equations or models when replicated do not give good agreements. One reason which was found is that researchers in wear prediction, their predictions are limited because they generally fail to properly identify the nature of wear mechanisms operative in their study. Also they fail to identify or recognise factors having a significant influence on wear such as bar diameter. Also in this research the similarities and differences between the two processes of single point turning and drilling are examined through a series of tests. A literature survey was undertaken in wear and wear prediction. As a result it was found that there was a paucity in information and research in the work of drilling as compared to the turning operation. This was extended to the lack of standards that exist for the drilling operation. One reason for this scarcity in information on drilling is due to the complexity of the drilling and the tool geometry of the drill. In the comparative drilling and turning tests performed in this work, the same tool material; HSS, and similar work material was used in order to eliminate the differences which may occur due to this factor. Results of the tests were evaluated and compared for the two operations and SEM photographs were taken for the chips produced. Specific test results were obtained for the cutting temperatures and forces of the tool. It was found that cutting temperature is influenced by various factors like tool geometry and cutting speed, and the temperature itself influenced the tool wear and wear mechanisms that act on the tool. It was found and proven that bar diameter influences the temperature, a factor not considered previously.

Development and deployment of an autonomous micro-drilling system for cochleostomy

This thesis describes the design and development of an autonomous micro-drilling system capable of accurately controlling the penetration of complaint tissues and its application to the drilling of the cochleostomy; a key stage in the cochlea implant procedure. The drilling of the cochleostomy is a precision micro-surgical task in which the control of the burr penetration through the outer bone tissue of the cochlea is vital to prevent damage to the structures within and requires a high degree of skill to perform successfully. The micro-drilling system demonstrates that the penetration of the cochlea can be achieved consistently and accurately. Breakthrough can be detected and controlled to within 20µm of the distal surface and the hole completed without perforation of the underlying endosteal membrane, leaving the membranous cochlea intact. This device is the first autonomous surgical tool successfully deployed in the operating theatre. The system is unique due to the way in which it uses real-time data from the cutting tool to derive the state of the tool-tissue interaction. Being a smart tool it uses this state information to actively control the way in which the drilling process progresses. This sensor guided strategy enables the tool to self-reference to the deforming tissue and navigate without the need for pre-operative scan data. It is this capability that enables the system to operate in circumstances where the tissue properties and boundary conditions are unknown, without the need to restrain the patient.

Carbon nanotube-polycarbonate composites for ultrafast lasers

Carbon nanotube polycarbonate composites with controlled nanotube-bundle size are prepared by dispersion with conjugated polymers followed by blending with polycarbonate. The composite has uniform sub-micrometer nanotube bundles in high concentration, shows strong nonlinear optical absorption, and generates 193 fs pulses when used as passive mode-locker in a fiber laser.

Nanotube-polymer composites for ultrafast photonics

Polymer composites are one of the most attractive near-term means to exploit the unique properties of carbon nanotubes and graphene. This is particularly true for composites aimed at electronics and photonics, where a number of promising applications have already been demonstrated. One such example is nanotube-based saturable absorbers. These can be used as all-optical switches, optical amplifier noise suppressors, or mode-lockers to generate ultrashort laser pulses. Here, we review various aspects of fabrication, characterization, device implementation and operation of nanotube-polymer composites to be used in photonic applications. We also summarize recent results on graphene-based saturable absorbers for ultrafast lasers.

Drilling of glass filled resin bonded materials

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Nanoindentation measurement of surface residual stresses in particle-reinforced metal matrix composites

The surface residual stresses in SiC particle-reinforced Al matrix composites are measured using a recently developed nanoindentation technique. The tensile biaxial residual stress in Al is found to increase with the particle concentration. The stress magnitudes are in reasonable agreement with those from numerical modeling.

Composites take off without a parachute

The review is devoted to the cost effectiveness of composite materials applications as compared with their high performance characteristics. The use of reinforced plastics, ceramic matrix and metal matrix composites reinforced by carbon and graphite fibers in aerospace industry is considered. Until recently, the two major drivers for the application of composites in engines have been weight reduction and performance improvement. As shown, today a major challenge to be met by the industry is cost reduction.

Interfacial effects on fatigue and fracture in discontinuously reinforced metal matrix composites

Interfaces in conventional monolithic alloys exert an important influence on fatigue and fracture behavior. In discontinuously reinforced metal matrix composites (MMCs), the role of interface is even more dominant. The interfacial is higher in MMCs and the interfaces are generally of high energy and chemically unstable. This paper reviews the factors which can affect interfacial strength in discontinuously reinforced MMCs, and the ways in which interfacial strength can be controlled. The effects of interfacial strength on fatigue crack propagation and fracture behavior are then illustrated.

Fatigue in SiC-particulate-reinforced aluminium alloy composites

The fatigue behaviour in SiC-particulate-reinforced aluminium alloy composites has been briefly reviewed. The improved fatigue life reported in stress-controlled test results from the higher stiffness of the composites; therefore it is generally inferior to monolithic alloys at a constant strain level. The role of SiC particulate reinforcement has been examined for fatigue crack initiation, short-crack growth and long-crack growth. Crack initiation is observed to occur at matrix-SiC interface in cast composites and either at or near the matrix-SiC interface or at cracked SiC particles in powder metallurgy processed composites depending on particle size and morphology. The da/dN vs ΔK relationship in the composites is characterized by crack growth rates existing within a narrow range of ΔK and this is because of the lower fracture toughness and relatively high threshold values in composites compared with those in monolithic alloys. An enhanced Paris region slope attributed to the monotonic fracture contribution are reported and the extent of this contribution is found to depend on particle size. The effects of the aging condition on crack growth rates and particle size dependence of threshold values are also treated in this paper. © 1991.

The effect of bioglass addition on mechanical and physical properties of photoactive UDMA-TEGDMA resin composites

Light curable dimethacrylate resin composites undergo free radical photopolymerisation in response to blue light (wavelength 450-500 nm) and may offer superior handling and setting characteristics for novel hard tissue repair materials. The current investigation aims to determine the optimum formulation of bisphenol-A glycidyl methacrylate and triethyleneglycoldimethacrylate (bisGMA/TEGDMA) or urethane dimethacrylate (UDMA)/TEGDMA resin mixtures and the effect of Bioglass incorporation on the rate of polymerisation (RP), degree of conversion (DC) and flexural strength (FS) of light-curable filled resin composites (FRCs). Experimental photoactive resins containing a range of bisGMA, UDMA and TEGDMA ratios and/or filled with non-silanised irregular or spherical 45S5-Bioglass (50 μm; 5-40 wt%) and/or silanised silicate glass filler particulates (0.7 μm; 50-70 wt%) were tested. RP and DC were analysed in real-time using nearinfrared spectroscopy. FS of resins and FRCs were determined using three-point flexural strength tests. UDMA/TEGDMA resins exhibited increased DC compared with bisGMA/TEGDMA resins (p<0.05). The addition of spherical particles of Bioglass had a detrimental effect on the FS (p>0.05), whereas they increased DC of UDMA/TEGDMA resins (p<0.05). Addition of irregular shaped Bioglass particles increased the FS of UDMA/TEGDMA resins up to 20 wt% Bioglass (p<0.05). The flexibility and strength conferred by the urethane group in UDMA may result in enhanced physical and mechanical properties compared with conventional resins containing bulky (bisGMA) molecules. Addition of 45S5-Bioglass with specific filler content, size and morphology resulted in enhanced mechanical and physical properties of UDMA/TEGDMA composites. © (2014) Trans Tech Publications, Switzerland.