The Experts below are selected from a list of 5706 Experts worldwide ranked by ideXlab platform
Graham C Smith - One of the best experts on this subject based on the ideXlab platform.
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a preliminary study to enhance the tribological performance of cocrmo alloy by Fibre Laser remelting for articular joint implant applications
Lubricants, 2018Co-Authors: Chi Wai Chan, Graham C SmithAbstract:CoCrMo alloy has long been used as a pairing femoral head material for articular joint implant applications because of its biocompatibility and reliable tribological performance. However, friction and wear issues are still present for CoCrMo (metal)/CoCrMo (metal) or CoCrMo (metal)/ultrahigh molecular weight polyethylene (UHMWPE) (plastic) pairs in clinical observations. The particulate wear debris generated from the worn surfaces of CoCrMo or UHMWPE can pose a severe threat to human tissues, eventually resulting in the failure of implants and the need for revision surgeries. As a result, a further improvement in tribological properties of this alloy is still needed, and it is of great interest to both the implant manufacturers and clinical surgeons. In this study, the surface of CoCrMo alloy was Laser-treated by a Fibre Laser System in an open-air condition (i.e., no gas chamber required). The CoCrMo surfaces before and after Laser remelting were analysed and characterised by a range of mechanical tests (i.e., surface roughness measurement and Vickers micro-hardness test) and microstructural analysis (i.e., XRD phase detection). The tribological properties were assessed by pin-on-disk tribometry and dynamic light scattering (DLS). Our results indicate that the Laser-treated surfaces demonstrated a friction-reducing effect for all the tribopairs (i.e., CoCrMo against CoCrMo and CoCrMo against UHHMWPE) and enhanced wear resistance for the CoCrMo/CoCrMo pair. Such beneficial effects are chiefly attributable to the presence of the Laser-formed hard coating on the surface. Laser remelting possesses several competitive advantages of being a clean, non-contact, fast, highly accurate and automated process compared to other surface coating methods. The promising results of this study point to the possibility that Laser remelting can be a practical and effective surface modification technique to further improve the tribological performance of CoCr-based orthopaedic implants.
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Fibre Laser joining of highly dissimilar materials: Commercially pure Ti and PET hybrid joint for medical device applications
Materials & Design, 2016Co-Authors: Chi Wai Chan, Graham C SmithAbstract:Abstract Laser transmission joining (LTJ) is growing in importance, and has the potential to become a niche technique for the fabrication of hybrid plastic-metal joints for medical device applications. The possibility of directly joining plastics to metals by LTJ has been demonstrated by a number of recent studies. However, a reliable and quantitative method for defining the contact area between the plastic and metal, facilitating calculation of the mechanical shear stress of the hybrid joints, is still lacking. A new method, based on image analysis using ImageJ, is proposed here to quantify the contact area at the joint interface. The effect of discolouration on the mechanical performance of the hybrid joints is also reported for the first time. Biocompatible polyethylene terephthalate (PET) and commercially pure titanium (Ti) were selected as materials for Laser joining using a 200 W CW Fibre Laser System. The effect of Laser power, scanning speed and stand-off distance between the nozzle tip and top surface of the plastic were studied and analysed by Taguchi L9 orthogonal array and ANOVA respectively. The surface morphology, structure and elemental composition on the PET and Ti surfaces after shearing/peeling apart were characterized by SEM, EDX, XRD and XPS.
Terence A. King - One of the best experts on this subject based on the ideXlab platform.
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Nanosecond Q-switched operation of coupled Yb and Tm Fibre Lasers
Journal of Physics D: Applied Physics, 2005Co-Authors: Yuen Hong Tsang, Terence A. King, Fadi Z. Qamar, Jongmin LeeAbstract:A small scale coupled Yb–silica and Tm–silica Fibre Laser System is described with output at 1.9 µm and with Q-switching using an acousto-optic modulator and also by mechanical optical modulation. The Yb-Fibre Laser pump source exhibited strong self-pulsation with high-intensity pulses due to stimulated Brillouin scattering. But regular Q-switched pulses were generated from the Tm-Fibre Laser with an energy of ~2.4 µJ and duration (FWHM) of ~280 ns for modulation frequencies of 1–20 kHz when using acousto-optic modulation. The main effects that limit the Q-switched pulse peak power are the onset of gain-switched pulsing during the low-Q state and strong pump excited state absorption.
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Theoretical Modelling of Thulium-sensitized Holmium Continuous-wave Fibre Lasers
Journal of Modern Optics, 1994Co-Authors: Jiaxin Wang, Mohammad Ahmad, Terence A. KingAbstract:Abstract Theoretical modelling is described which estimates the performance of thulium-sensitized holmium-doped c.w. fluoride Fibre Lasers at 2020 nm. This model takes into account the mechanisms of cross-relaxation and energy transfer to describe the Laser operation. The model uses an iteration technique together with our own measured transition data and shows good agreement with experimental results. This model also provides data for the optimum parameters of the Fibre for the configuration of an efficient Fibre Laser System.
Chi Wai Chan - One of the best experts on this subject based on the ideXlab platform.
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a preliminary study to enhance the tribological performance of cocrmo alloy by Fibre Laser remelting for articular joint implant applications
Lubricants, 2018Co-Authors: Chi Wai Chan, Graham C SmithAbstract:CoCrMo alloy has long been used as a pairing femoral head material for articular joint implant applications because of its biocompatibility and reliable tribological performance. However, friction and wear issues are still present for CoCrMo (metal)/CoCrMo (metal) or CoCrMo (metal)/ultrahigh molecular weight polyethylene (UHMWPE) (plastic) pairs in clinical observations. The particulate wear debris generated from the worn surfaces of CoCrMo or UHMWPE can pose a severe threat to human tissues, eventually resulting in the failure of implants and the need for revision surgeries. As a result, a further improvement in tribological properties of this alloy is still needed, and it is of great interest to both the implant manufacturers and clinical surgeons. In this study, the surface of CoCrMo alloy was Laser-treated by a Fibre Laser System in an open-air condition (i.e., no gas chamber required). The CoCrMo surfaces before and after Laser remelting were analysed and characterised by a range of mechanical tests (i.e., surface roughness measurement and Vickers micro-hardness test) and microstructural analysis (i.e., XRD phase detection). The tribological properties were assessed by pin-on-disk tribometry and dynamic light scattering (DLS). Our results indicate that the Laser-treated surfaces demonstrated a friction-reducing effect for all the tribopairs (i.e., CoCrMo against CoCrMo and CoCrMo against UHHMWPE) and enhanced wear resistance for the CoCrMo/CoCrMo pair. Such beneficial effects are chiefly attributable to the presence of the Laser-formed hard coating on the surface. Laser remelting possesses several competitive advantages of being a clean, non-contact, fast, highly accurate and automated process compared to other surface coating methods. The promising results of this study point to the possibility that Laser remelting can be a practical and effective surface modification technique to further improve the tribological performance of CoCr-based orthopaedic implants.
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Fibre Laser joining of highly dissimilar materials: Commercially pure Ti and PET hybrid joint for medical device applications
Materials & Design, 2016Co-Authors: Chi Wai Chan, Graham C SmithAbstract:Abstract Laser transmission joining (LTJ) is growing in importance, and has the potential to become a niche technique for the fabrication of hybrid plastic-metal joints for medical device applications. The possibility of directly joining plastics to metals by LTJ has been demonstrated by a number of recent studies. However, a reliable and quantitative method for defining the contact area between the plastic and metal, facilitating calculation of the mechanical shear stress of the hybrid joints, is still lacking. A new method, based on image analysis using ImageJ, is proposed here to quantify the contact area at the joint interface. The effect of discolouration on the mechanical performance of the hybrid joints is also reported for the first time. Biocompatible polyethylene terephthalate (PET) and commercially pure titanium (Ti) were selected as materials for Laser joining using a 200 W CW Fibre Laser System. The effect of Laser power, scanning speed and stand-off distance between the nozzle tip and top surface of the plastic were studied and analysed by Taguchi L9 orthogonal array and ANOVA respectively. The surface morphology, structure and elemental composition on the PET and Ti surfaces after shearing/peeling apart were characterized by SEM, EDX, XRD and XPS.
Emmanuel Bruno Jean Paul Brousseau - One of the best experts on this subject based on the ideXlab platform.
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Nanosecond Laser processing of Zr41.2Ti13.8Cu12.5Ni10Be22.5 with single pulses
Journal of Materials Processing Technology, 2016Co-Authors: Eleri Williams, Emmanuel Bruno Jean Paul BrousseauAbstract:In addition to their attractive mechanical properties, the amorphous structure of bulk metallic glasses (BMGs) leads to favourable conditions for their processing using micro machining operations. At the same time, the generally high hardness and strength of such amorphous metals make short or ultra-short pulsed Laser ablation a fabrication technology of interest for generating micro scale features on BMG workpieces in comparison with mechanical material removal means. In spite of this, relatively little research has been reported on the prediction and observation of the thermal phenomena that take place when processing BMGs with pulsed Laser irradiation for a range of delivered fluence values and pulse lengths. Such investigations are important however as they underpin reliable Laser processing operations, which in turn lead to more predicable material removal at micro scale. In this context, this paper reports complementary theoretical and experimental single pulse Laser irradiation analyses conducted in the nanosecond (ns) regime for possibly the most prominent BMG material due to its relatively high glass forming ability, namely Zr41.2Ti13.8Cu12.5Ni10Be22.5, which is also known as Vitreloy 1. To achieve this, different pulse lengths comprised between 15 ns and 140 ns and varied fluence values were considered when delivering single pulses on a Vitreloy 1 substrate using a Yb Fibre Laser System. A simple thermal model of the Laser material interaction process for single pulses was also developed to support the observations and interpretations of the experimental data obtained. One of the main conclusions from this research, with respect to potential micro machining applications, is that shorter pulses, i.e. 25 ns and less, could lead to the formation of relatively clean craters. For higher pulse lengths, the low thermal conductivity and melt temperature of this BMG substrate mean that Laser irradiation easily leads to the formation of a relatively large melt pool and thus to the re-solidification of material ejected outside craters.
Jongmin Lee - One of the best experts on this subject based on the ideXlab platform.
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Nanosecond Q-switched operation of coupled Yb and Tm Fibre Lasers
Journal of Physics D: Applied Physics, 2005Co-Authors: Yuen Hong Tsang, Terence A. King, Fadi Z. Qamar, Jongmin LeeAbstract:A small scale coupled Yb–silica and Tm–silica Fibre Laser System is described with output at 1.9 µm and with Q-switching using an acousto-optic modulator and also by mechanical optical modulation. The Yb-Fibre Laser pump source exhibited strong self-pulsation with high-intensity pulses due to stimulated Brillouin scattering. But regular Q-switched pulses were generated from the Tm-Fibre Laser with an energy of ~2.4 µJ and duration (FWHM) of ~280 ns for modulation frequencies of 1–20 kHz when using acousto-optic modulation. The main effects that limit the Q-switched pulse peak power are the onset of gain-switched pulsing during the low-Q state and strong pump excited state absorption.