Numerical analysis of the cold gas dynamic spray surface coating process

Abstract: In Cold Spray, bonding is formed between substrate and the particles and between particles by impact which causes material deformation and temperature rise. During impact process, plastic deformation and frictional interaction of materials generate heat and strains/stresses. In this paper, a numerical study on multiple particles deposition process show that the plastic equivalent strain (von misses stress) and the temperature values, compare to a single particle impact under same conditions, are higher in multiple particles compared to a single particle impact. Based on this observation, there is a possibility of the bonding mechanism for the whole film coating better explained using the multiple particles modeling than is predicted using single particle analysis However the actual impacting mechanism in the multiple particle interaction is not yet fully understood and still requires further investigation

Residual stress characterization from numerical analysis of the multi-particle impact behavior in cold spray

Abstract: In cold spray, bonding is created between a substrate and the particles and between particles through impact deformation at high strain rates. A prominent feature of the cold spray process is the compressive residual stress that arises during the deposition process. Compressive residual stress on the surface can be beneficial for fatigue resistance. As a post processing technique several applications require surface treatment processes that produce this state of stress on component surfaces such as shot peening, laser shock peening, ultrasonic impact treatment, low plasticity burnishing, etc. In all of these methods the compressive stress is produced through plastic deformation of the surface region. In a similar manner, the cold spray process induces compressive stress by high speed impact of the sprayed particles on the surface, causing a peening effect. The effects of these variations in the properties of the coatings are rarely reported. Moreover there are some applications which require minimal residual stresses in the components such as in optics. In this study, we have investigated the residual stress using numerical analysis of the multi-particle impact behavior in cold spray

Film surface characterization in cold spray using advanced numerical modeling and simulation techniques

Abstract: In cold spray, even when the initial properties are within the critical values for deposition, the multi-impact process is much more complex to ensure a 100% deposition. In inelastic impact, part of the initial kinetic energy of the particles at impact is lost through plastic deformation. After impact and subsequent restitution, unbounded particles will be ejected through rebound forces or material jetting at erosion. Observation of the final kinetic energies achieved in the particles after impact was used as criteria for a rough estimate of the coating process. The surface roughness increased with reduced deposition efficiency. The interface roughness was less affected by this process. Qualitative comparison to experimental results shows some closer correlations with some of the surfaces of experimentally obtained surfaces in cold spray. This could provide some of the answers to the underlying mechanisms in which the cold spray surfaces are generated

Open Biomedical Engineering education in Africa

Despite the virtual revolution, the mainstream academic community in most countries remains largely ignorant of the potential of web-based teaching resources and of the expansion of open source software, hardware and rapid prototyping. In the context of Biomedical Engineering (BME), where human safety and wellbeing is paramount, a high level of supervision and quality control is required before open source concepts can be embraced by universities and integrated into the curriculum. In the meantime, students, more than their teachers, have become attuned to continuous streams of digital information, and teaching methods need to adapt rapidly by giving them the skills to filter meaningful information and by supporting collaboration and co-construction of knowledge using open, cloud and crowd based technology. In this paper we present our experience in bringing these concepts to university education in Africa, as a way of enabling rapid development and self-sufficiency in health care. We describe the three summer schools held in sub-Saharan Africa where both students and teachers embraced the philosophy of open BME education with enthusiasm, and discuss the advantages and disadvantages of opening education in this way in the developing and developed world

Techniques to investigate the application of cold spray in fabrication of nanoplasmonic films : parameter identification

Abstract: The decomposition of a complex system allows identification of its interacting variables. In this article the coupling between the Cold Spray (CS) thin film fabrication and functional properties in Surface Plasmon Polaritons (SPP) are investigated with a view to optimise the CS fabrication process in nano thin films. There are many reported advantages of the cold gas spray over other thermal spray technologies. However the fabrication of thin films by cold gas is limited on the capability of the transport system. This study is meant on finding ways to improve the cold gas spray for deposition of nano particles. In particular, the deposition of plasmonics nano particles for functional films in the nano scale regime. Since the requirements for each film application are different, this study is specifically targeted at films used in biosensor technology with a focus on the plasmonics sensor that use gold or silver nano particles. The paper gives the details of the parameter identification process that was used to determine missing links between the cold spray process and the optical functional thin film characteristics. In the preliminary study, intuitively, the systems engineering and pattern recognition techniques were used to explore the most probable driving variables for the cold gas coating process in functional films. This process determines the deposition parameters that characterize the surface roughness, interface roughness and film thickness as would be required for functional thin films. We have since designed a systematic numerical process for the iterations towards this direction. This study opens new avenues for further research and advancement of the cold gas spray method in nano thin film