Numerical simulation of self-alignment of chip resistor components for different silver content during reflow soldering

Three-dimensional simulation and experimental investigation of self-alignment phenomena during the reflow soldering process were presented. The multiphase flow model was developed using ANSYS Fluent to investigate the self-alignment effect of laminar melted lead-free solder during the reflow phase on board. User-defined function with c-code was integrated into the model, Volume of Fluid (VOF) method was applied to the melt front tracking, and solidification model was used for the phase change solder material. The material used in the study was SAC 105, SAC 305 and SAC 405. The specific heat, latent heat, solidus temperature, liquidus temperature of the lead-free solder and geometrical data for model input was determined experimentally. The model was validated experimentally. The self-alignment capability of different lead-free solder was presented. It has been observed that higher silver content solder (SAC 405) have higher self-alignment capability during reflow soldering compare to SAC 305 and SAC 105. Moreover, all cases show self-alignment in perpendicular to the longer sides of chip resistor travelled more towards the central position. The experimental and simulation results are in good conformity and can be extended for different cases.     

Fuzzy lagged variable selection in fuzzy time series with genetic algorithms

Fuzzy time series forecasting models can be divided into two subclasses which are first order and high order. In high order models, all lagged variables exist in the model according to the model order. Thus, some of these can exist in the model although these lagged variables are not significant in explaining fuzzy relationships. If such lagged variables can be removed from the model, fuzzy relationships will be defined better and it will cause more accurate forecasting results. In this study, a new fuzzy time series forecasting model has been proposed by defining a partial high order fuzzy time series forecasting model in which the selection of fuzzy lagged variables is done by using genetic algorithms. The proposed method is applied to some real life time series and obtained results are compared with those obtained from other methods available in the literature. It is shown that the proposed method has high forecasting accuracy.     

The effects of cross-linked starch on the properties of thermoplastic starch

In order to improve the poor tensile properties and high water absorption of thermoplastic starch (TPS), cross-linked starch was added into the TPS matrix. The cross-linked starch contents ranged from 0 wt% to 20 wt%. The TPS/cross-linked starch composites were analyzed for the morphology of their fractured surfaces, the thermal decomposition temperatures, ability to absorb water and mechanical properties. The results showed that the incorporation of cross-linked starch into the TPS matrix caused considerable improvement to tensile strength. The maximum tensile strength was obtained with addition of 20 wt% cross-linked starch. Moreover, water absorption of the TPS samples was clearly reduced by the inclusion of cross-linked starch. The thermal degradation temperatures of the composites were also higher than those of the TPS matrix.     

Effect of operating parameters and chemical treatment on the tribological performance of natural fiber composites: A review

The demand for high-performance engineering products made from natural resources is increasing because of the low-cost, low-density, biodegradability, renewable nature and lighter than synthetic fibers. With these characteristics, the tribological performance of natural fiber composite has become an important element to be considered in most industrial and manufacturing functions. This paper presents an overview of the factors that influence the tribological performance of natural fiber composites, which include applied load, sliding distance, sliding velocity and fiber orientation. Influences of chemical treatment is also reviewed and illustrated through scanning electron microscope (SEM) observations. This review will focus on kenaf fibers (KFs) and oil palm fibers (OPFs) which have been widely exploited over the past few years among the available natural resources. The results show that the operating parameter, fiber orientation and chemical treatment has significant effects on the tribological performance of natural composite. A clear understanding of the factors that affect the tribological performance is very essential in performance improvement on natural fibers reinforced polymer composite for potential applications.     

Correction to: Fuzzy rule-based environment-aware autonomous mobile robots for actuated touring

Intelligent Service Robotics -     

Effects of Cu and Mg on thixoformability and mechanical properties of aluminium alloy 2014

Thixoforming is a processing method that deforms metal in a semisolid state. The advantages of this process include the production of parts with good surface finish, fine microstructures and superior mechanical properties. However, the process mostly produces parts from aluminium cast grades, thereby not fully utilising the true potential of this method. Hence, thermodynamic modelling can be used to formulate alloy compositions that favour this processing method. Here, the effects of reducing copper content and increasing silicon and magnesium contents on the thixoformability of aluminium alloy 2014 were presented. The work consists of both the modelling and experimental validation. Results showed that by increasing Si and decreasing Cu content in the alloy, the solidification interval temperature was decreased and the temperature working window between the stipulated liquid fractions was widened, two of the characteristics favouring the process. A high solid-solution temperature employed resulted in the dissolution of unfavourable Mg₂Si compound. An increase in Mg content used also resulted in the formation of the compact π-Al₈FeMg₃Si₆ phase and the decrease in the amount of the sharp and plate-like structure of the β-Al₅FeSi phase, improving the strength of the modified alloy. Subsequent T6 heat treatment successfully further increased the strength of the modified alloy.     

Evaluation of equivalent structural properties of NREL phase VI wind turbine blade

This paper presents the structural model development and verification process for the National Renewable Energy Laboratory (NREL) Phase VI wind which consists of the blades, rotor, nacelle, and tower. The mass and stiffness properties of all parts had to be clearly defined to develop the structural model for the entire turbine. However, it was difficult to define the geometries and material properties of the blade structure and power generating machinery because of their complexity. To perform a FSI analysis, fluid and structural models that shared the associated interface topology had to be provided. With the help of an eigen-value analysis, the structural stiffness and mass properties were verified in comparison with the values reported by NREL. A finite element (FE) model that included the blade, nacelle, and tower was developed based on the NREL's reported data. The commercial FE software ANSYS was used to develop the geometry and mesh, and to perform the eigen-value analysis. The various material properties and configurations of the entire turbine system were tested to obtain the proper material properties to determine this value. Overall, the proposed geometry, material, and mass properties were in good agreement with the measurements, but need to be discussed further.     

Transient simulation and parametric study of solar-assisted heating and cooling absorption systems: An energetic,economic and environmental (3E) assessment

This paper presents energetic, economic, and environmental (3E) analyses of four configurations of solar heating and cooling (SHC) systems based on coupling evacuated tube collectors with a single-effect LiBr–H₂O absorption chiller. In the first configuration (SHC1), a gas-fired heater is used as the back-up system, while a mechanical compression chiller is employed as the auxiliary cooling system in the second configuration (SHC2). The capacity of the absorption chiller is designed based on the maximum building cooling load in these configurations. The third and fourth configurations (SHC3 and SHC4) are similar to SHC2, but the absorption chiller size is reduced to 50% and 20%, respectively. The results show that the highest primary energy saving is achieved by SHC2, leading to a solar fraction of 71.8% and saving 54.51% primary energy as compared to a reference conventional HVAC system. The economic performance of all configurations is still unsatisfactory (without subsidies) due to their high capital costs. However, if a government subsidy of 50% is considered, the results suggest that SHC4 can be economically feasible, achieving a payback period of 4.1 years, net present value of 568,700 AUD and solar fraction of 43%, contributing to 27.16% decrease in the plant primary energy consumption.     

Carbon nanofiber assisted micro electro discharge machining of reaction-bonded silicon carbide

Carbon nanofiber assisted micro electro discharge machining was proposed and experiments were performed on reaction-bonded silicon carbide. The changes in electro discharging behavior, material removal rate, electrode wear ratio, electrode geometry, spark gap, surface finish, surface topography and surface damage with carbon nanofiber concentration were examined. It has been found that the addition of carbon nanofiber not only improves the electro discharge frequency, material removal rate, discharge gap, but also reduces the electrode wear and electrode tip concavity. Bidirectional material migrations between the electrode and the workpiece surface were detected, and the migration behavior was strongly suppressed by carbon nanofiber addition. Adhesion of carbon nanofibers to the workpiece surface occurs, which contributes to the improvement of electro discharge machinability. These findings provide possibility for high-efficiency precision manufacturing of microstructures on ultra-hard ceramic materials.