Greg Byrne

The performance of coated tungsten carbide drills when machining carbon fibre-reinforced epoxy composite materials

Abstract 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.

Biological responses to hydroxyapatite surfaces deposited via a co-incident microblasting technique

Hydroxyapatite (HA) is routinely used as a coating on a range of press-fit (cementless) orthopaedic implants to enhance their osseointegration. The standard plasma spraying method used to deposit a HA surface layer on such implants often contains unwanted crystal phases that can lead to coating delamination in vivo. Consequently, there has been a continuous drive to develop alternate surface modification technologies that can eliminate the problems caused by a non-optimal coating process. In this study two methods for creating a HA layer on metal alloys that employ micro-blasting have been evaluated to determine if the inclusion of an abrasive agent can enhance the in vitro and in vivo performance of the modified surface. The first method employs direct micro-blasting using HA as the abrasive media, while the second employs a simultaneous blasting with an alumina abrasive and coincident blasting with HA as a dopant. Whereas, both methods were found to produce a surface which was enriched with HA, the respective microstructures created were significantly different. Detailed surface characterisation revealed that the use of the abrasive produced disruption of the metal surface without producing detectable incorporation of alumina particles. Roughening of the metal surface in this way breached the passivating oxide layer and created sites which subsequently provided for impregnation, mechanical interlocking and chemical bonding of HA. The co-incident use of an alumina abrasive and a HA dopant resulted in a stable surface that demonstrated enhanced in vitro osteoblast attachment and viability as compared to the response to the surface produced using HA alone or the metal substrate control. Implantation of the surface produced by co-incident blasting with alumina and HA in a rabbit model confirmed that this surface promoted the in vivo formation of early stage lamellar bone growth.

Measuring knife stab penetration into skin simulant using a novel biaxial tension device

This paper describes the development and use of a biaxial measurement device to analyse the mechanics of knife stabbings. In medicolegal situations it is typical to describe the consequences of a stabbing incident in relative terms that are qualitative and descriptive without being numerically quantitative. Here, the mechanical variables involved in the possible range of knifetissue penetration events are considered so as to determine the necessary parameters that would need to be controlled in a measurement device. These include knife geometry, in-plane mechanical stress state of skin, angle and speed of knife penetration, and underlying fascia such as muscle or cartilage. Four commonly available household knives with different geometries were used: the blade tips in all cases were single-edged, double-sided and without serrations. Appropriate synthetic materials were used to simulate the response of skin, fat and cartilage, namely polyurethane, compliant foam and ballistic soap, respectively. The force and energy applied by the blade of the knife and the out of plane displacement of the skin were all used successfully to identify the occurrence of skin penetration. The skin tension is shown to have a direct effect on both the force and energy for knife penetration and the depth of out of plane displacement of the skin simulant prior to penetration: larger levels of in-plane tension in the skin are associated with lower penetration forces, energies and displacements. Less force and energy are also required to puncture the skin when the plane of the blade is parallel to a direction of greater skin tension than when perpendicular. This is consistent with the observed behaviour when cutting biological skin: less force is required to cut parallel to the Langer lines than perpendicularly and less force is required to cut when the skin is under a greater level of tension. Finally, and perhaps somewhat surprisingly, evidence is shown to suggest that the quality control processes used to manufacture knives fail to produce consistently uniform blade points in knives that are nominally identical. The consequences of this are that the penetration forces associated with nominally identical knives can vary by as much as 100%.

Comparison of pilot and industrial scale atmospheric pressure glow discharge systems including a novel electro-acoustic technique for process monitoring

A comparison of a pilot and industrial scale atmospheric pressure polymer processing plasma system has been carried out using process-monitoring diagnostic tools during treatment of amorphous polyethylene terephthalate. These systems have been compared using optical emission spectroscopy (OES), photodiode (PD) analysis and multi-variate analysis of the applied electrical and emitted electro-acoustic signals to facilitate scale up operations from the pilot to the industrial scale system. The voltage, current, electro-acoustic intensity and frequency of the plasma systems were found to change systematically with an increase in applied plasma power and addition of oxygen (O2) into a helium (He) plasma. The plasma drive frequency was pulled by the plasma reactance from approximately 26 to 16 kHz on the pilot system and from approximately 36 to 32 kHz on the industrial system, for an increase in applied plasma power and addition of O2. The OES analysis revealed a number of peaks associated with nitrogen (N2) species between 250 and 450 nm due to the presence of air within the He plasma. Temporally resolved analysis of the discharge emission carried out using a PD showed an increase in the number of discharge events per power cycle with an increase in power and a decrease in emission intensity for addition of O2 into the He plasma for both the pilot and industrial scale systems. Using these diagnostic tools both plasma stability and run to run variations were assessed. A visual analysis of the 1.2 m wide plasma was also carried out where a more homogeneous plasma was observed at higher powers.

Plasma power can slash small run sintering times

A group of Irish researchers have demonstrated that rapid discharge sintering can dramatically reduce sintering times for processing small numbers of green compacts. But while mainstream sintering technologies have the upper hand for the time being, commercial prospects for plasma are being assessed…

Comparison between microwave and microwave plasma sintering of nickel powders

The objective of this study is to investigate the use of microwave plasma treatments as a processing technology for the sintering of metal powders. The volumetric heating process achieved with microwaves is considerably more efficient compared with resistance heating. The sintering study was carried out on 20 mm diameter by 2 mm thick compacted discs of nickel powder, with mean particle size of 1 µm. The discs were fired in a 5 cm diameter microwave plasma ball, under a hydrogen atmosphere at a pressure of 2 kPa. There was an increase in fired pellet transverse rupture strength (TRS) with plasma treatment duration. The mechanical properties of the sintered nickel discs were compared based on TRS, Rockwell hardness tests and density measurements. The morphology of the sintered discs was compared using microscopy and SEM. Comparison disc sintering studies were carried out using both a non plasma microwave and tube furnace firing. Using the microwave plasma sintering process full sintered disc strength of ≈1000 N (based on 3-point bend tests) was achieved after a 10 minute treatment time. In contrast the sintering time in the tube furnace treatment involved total processing time of up to 6 hours. The non plasma microwave system involved intermediate treatment periods of 2 hours. The degree of sintering between the individual nickel powder particles can be precisely controlled by the duration of the treatment time in the plasma.

Novel rapid discharge sintering technique for damage-free diamond metal matrix composites

Abstract The performance of diamond/nickel metal matrix composites (MMCs) produced using a novel microwave plasma technique, rapid discharge sintering (RDS), and conventional tube furnace sintering in argon is compared. The MMCs were sintered at temperatures between 850 and 1050°C in both cases. The RDS treatments were carried out at 20 mbar in plasmas containing hydrogen or hydrogen–nitrogen gases. The addition of nitrogen gas to the hydrogen plasma facilitated a substantial increase in composite firing temperatures. A significant reduction in sintering times, to 10 min from several hours, was achieved using the RDS technique. A further advantage of the RDS treatments was the absence of any diamond graphitisation (as detected by X-ray diffraction), which was reflected in higher sintered densities and flexural strength for RDS than for furnace sintering.

Comparison of thermal and microwaveassisted 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 been shown to reduce energy usage as volumetric heating is more efficient than resistance heating. Plasma sintering meanwhile delivers heat via uniform excitation of the processing gas. The use of a rapid, novel microwave-assisted plasma sintering (MaPS) technology has been evaluated for processing nickel-diamond composites. Discs fired in a low pressure microwave plasma under a hydrogen atmosphere were compared with discs sintered in a conventional tube furnace. MaPS is very rapid, with full disc strength being achieved within 10 min, compared with 8 h for furnace treatment. MaPS produced similar or superior mechanical properties to furnace sintering but with sintering cycle time reduced by up to 95%.

Rapid Discharge Sintering of Powder Metallurgy Components

A microwave circumferential antenna plasma system has been used to sinter pressed-powder metallurgy components. The rapid heat generated in the discharge once the plasma is fired is sufficient to sinter samples within minutes and to temperatures upward of 1300°C based on gas mixtures and applied powers. Images of the sintering process in hydrogen at various flow rates and applied powers are presented.