http://hdl.handle.net/10204/917 Thu, 20 Jun 2013 05:24:26 GMT 2013-06-20T05:24:26Z http://hdl.handle.net/10204/6775 Title: Complete azimuthal decomposition of optical fields Authors: Dudley, A; Litvin, I; Roux, FS; Forbes, A Abstract: By using digital holograms, we present a simple technique for performing a complete azimuthal decomposition of an arbitrary laser mode. The match-filter, used to perform the azimuthal decomposition, is bounded by an annular ring, allowing us to conduct a scale-independent decomposition on our selected mode. This technique therefore requires no prior knowledge of the mode structure, the mode phases, or the amplitude distribution. A basis comprising of the angular harmonics is used to express the spatial distribution of the selected mode in terms of spatially dependant coefficients. We use this to infer directly from the measured weightings of the azimuthally decomposed modes and their phase-delay measurements, the intensity of the selected field, its phase, and its orbital angular momentum (OAM) density. We illustrate the concept by executing a full decomposition of two examples: a superposition of two Bessel beams, with relative phase differences, and an off-axis vortex mode. We show a reconstruction of the amplitude, phase and OAM density of these fields with a high degree of accuracy. Description: Proceedings of SPIE, San Francisco (USA), 3-6 February 2013. Published in SPIE Digital library. Fri, 01 Feb 2013 00:00:00 GMT http://hdl.handle.net/10204/6775 2013-02-01T00:00:00Z http://hdl.handle.net/10204/6749 Title: Revolutionary additive manufacturing: an overview Authors: Mahamood, RM; Akinlabi, ET; Shukla, M; Pityana, RM Abstract: Consumer demands are moving away from standardized to customized products, as such, the evolution of alternative manufacturing technique has become imperative. Additive manufacturing (AM) is a process of building components layer by layer as against the traditional methods which are subtractive in nature. Though AM offers lots of advantages over traditional manufacturing techniques, its wide application is still however at the infancy phase. Despite all the benefits derived from AM technology, there are still a lot of unresolved issues with the technology that has hindered its performances thereby limiting its application to high tolerant jobs. This paper takes a look at some important AM technologies, some problems currently facing AM technology at large and proposes some solutions to these problems. A major known drawback in AM is poor dimensional accuracy and poor surface finish, only the layer height and melt pool temperature are controlled to solve this problem in the literature. The stair-stepping effect in adaptive manufacturing is rooted in a natural phenomenon of surface tension which is the cause of the poor surface finish and in combination with other factors is responsible for the poor dimensional accuracy. An adaptive controller is proposed for removing stair-stepping effect to improve the dimensional accuracy, the surface finish and the mechanical properties of the components. Successful implementation of these proposed controllers will greatly improve the performances of AM technologies and also aids its wide application for end use products. Further research works are also suggested to improve the overall AM performances. Description: Copyright: 2012 Old City Publishing. This is an ABSTRACT ONLY. The definitive version will be published in Lasers in Engineering, pp 1-18 Sun, 01 Jan 2012 00:00:00 GMT http://hdl.handle.net/10204/6749 2012-01-01T00:00:00Z http://hdl.handle.net/10204/6708 Title: Effects of Ti and TiC ceramic powder on laser-cladded Ti-6Al-4V in situ intermetallic composite Authors: Ochonogora, OF; Meacock, C; Abdulwahaba, M; Pityana, S; Popoolaa, API Abstract: Titanium metal matrix composite (MMCs) was developed on titanium alloy (Ti–6Al–4V) substrate with the aim of improving the hardness and wear properties by laser cladding technique using a Rofin Sinar 4 kW Nd: YAG laser. Wear investigations were carried out with the aid of three body abrasion tester. The resultant microstructure show homogeneous distribution of TiC particles free from cracks and pores. Multiple track deposited systems with 50% overlap revealed micro-hardness increase from 357.3 HV0.1for the substrate reaching a peak as high as 922.2 HV0.1 for 60%Ti + 40%TiC and the least 665.3 HV0.1 for 80%Ti + 20%TiC MMCs. The wear resistance of the materials improved significantly, indicating a fifteen-fold wear rate reduction due to the proper distribution of ceramic particles thereby forming interstitial carbides as revealed by the X-ray diffraction spectrum. Description: Copyright: 2012 Elsevier. This is an ABSTRACT ONLY. The definitive version is published in Applied Surface Science, vol. 263, pp 591-596 Sat, 01 Dec 2012 00:00:00 GMT http://hdl.handle.net/10204/6708 2012-12-01T00:00:00Z http://hdl.handle.net/10204/6702 Title: Impact toughness of laser surface alloyed Aluminium Authors: Mabhali, LAB; Sacks, N; Pityana, S Abstract: Laser surface alloying of aluminium AA1200 was performed with a 4kW Nd:YAG laser and the impact resistance of the alloys was investigated. The alloying powders were a mixture of Ni, Ti and SiC in different proportions. Surfaces reinforced with intermetallic phases and metal matrix composites were achieved during laser alloying. Brittle fracture of the SiC particles and transgranular cracking of the intermetallic phases was observed for the laser alloyed samples, while ductile fracture was observed for the bulk aluminium. The aluminium metal absorbed more energy during fracture compared to the laser alloyed samples due to its high ductility. Laser alloyed layers with a high Ti content had high absorbed energies which represent a reduction in brittleness, while alloyed layers with a high Ni content had low absorbed energies which indicate a preference for brittle fracture. Description: Copyright: 2012 Elsevier. This is the Pre/post print version of the work. The definitive version is published in Journal of Materials Science & Technology, pp 1-29 Thu, 01 Mar 2012 00:00:00 GMT http://hdl.handle.net/10204/6702 2012-03-01T00:00:00Z