Applied Mechanics and Materials Vol. 315

Abstract: The formation of alumina (Al₂O₃) inclusions was experimentally investigated with the capillary-reservoir method. The inclusions were observed with a SEM (scanning electron microscope). The compositions of iron matrix and inclusion were measured with an EDX (energy dispersive X-ray analysis). The content profile of aluminum was discussed by the counter-diffusion model of aluminum and oxygen with an instantaneous irreversible reaction for alumina formation. The inclusions of spherical and polygonal alumina and spherical hercynite (FeOAl₂O₃) were observed in the vicinity of the diffusion front of aluminum. The hercynite was detected when the initial oxygen content was 0.075 mass% and higher. When the initial oxygen content was more than 0.045 mass% and higher, dendritic alumina formed at the position that was nearer to the interface than the position of spherical and polygonal inclusions. No inclusion was observed around the interface because of the re-dissolution of the inclusions. The initiating position of the inclusion formation was approximated by the reaction position, Z_r, obtained from the model on the assumption that aluminum and oxygen contents at the reaction position were zero. Empirically, 0.9×Z_r and 0.17×Z_r expressed the initiating positions of formation and re-dissolution of inclusions respectively. The critical supersaturation ratio was estimated to be from 1 to 7.4×10⁵, depending on the initial aluminum and oxygen contents.

Abstract: The present work focuses on the development of computer code which allow the engine designer investigate the flow behavior through a divergent nozzle. The flow is assumed as quasi one dimensional and steady inviscid compressible flow. In other word the flow is governed by compressible Euler equation depending on the local Mach number. Solving such a mixed type of equation is difficult. The boundary between hyperbolic and elliptic region is not clear. To avoid such difficulty can be done through treating a steady flow problem as unsteady flow problems with the boundary condition is fixed with respect to time. As unsteady flow problem, the Euler equation becomes hyperbolic type of partial differential equation with respect to time. This approach allows one to solve the unsteady flow problem goes to a steady state solution. There are various methods can used for solving hyperbolic type of equation, such as MacCormacks scheme, Steger Warmings scheme, Beam Warmings Scheme and TVD Scheme. The present work used MacCormacks scheme and Steger Warming scheme will be used to investigate the flow behavior through a divergent nozzle. Comparison with analytic solution shows that Steger Warmings scheme gives a better result than MacCormacks scheme.

Abstract: The large commercial passengers airplanes are mostly designed to have symmetrical body with respect to the longitudinal axis. However for small passengers airplanes or for the airplane designed as UAV plat form is normally having an unsymmetrical fuselage. The aerodynamics characteristics fuselage may give a strong influence to the overall aerodynamics characteristics of the airplane. The present work investigates the aerodynamics characteristics of the unsymmetrical fuselage with respect to the longitudinal axis. The fuselage assumed to have circular cross section and the coordinate of the fuselage are created by using the same equation which had been used in defining the coordinate of cambered airfoil NACA series four digits. The fuselage had been set to have the same maximum thickness 15 % of the fuselage length and different fuselage models are obtained through varying the position as well as the value of the maximum camber line. The semi empirical aerodynamic method for estimating the fuselage lift coefficient C_L, drag coefficient C_D and the fuselage pitching moment coefficient C_M such as given by DATCOM are well established. However when it came to the unsymmetrical fuselage, this approach can not be adopted easily. The required of angle attack at zero lift of the corresponding unsymmetrical fuselage is difficult to define. The result for particular cambered fuselage indicates that the aerodynamics characteristics strongly influenced by how the fuselages camber lines look likes.

Abstract: To realize the STEP-NC based machining system, it is necessary to perform machining feature extraction, generating machine-specific information, and creating a relationship between STEP-NC entities. A process planning system of a STEP-NC information flow that starts with constructing a machining feature from a CAD model will be developed. In this paper, a further in-depth study of the implementation and adaptation of STEP-NC in manufacturing is studied. This study will help to understand how the data from CAD/CAM can be converted into STEP-NC codes and the machining process will be based on the STEP-NC codes generated.

Abstract: Minimizing supplier base allows better supplier relationship management, but any supplier failure will interrupt the supplies chain. Earth quake in Fukushima, Japan and flood in Bangkok, Thailand, caused supply chain breakdown and affect the global production. Decision tree method is recommended to determine optimal number of supplier in supplier base with the risk of supplier failure. This paper presented an approach to integrate fuzzy logic in decision tree approach by rating the supplier risk in linguistic terms for imperfect environment. Numerical example and sensitivity are carried out and presented, and optimal supplier base was identified.

Abstract: Lean combustion of CNG has the advantage of high thermal efficiency and fewer pollutants than other fossil fuels. However, problems such as ignitability, cyclic variation and high THC emission were common at combustion leaner than equivalence ratio φ=0.7. The application of gas-jet ignition method to lean combustion was able to address such problems. This paper introduces the concept of gas-jet ignition method, which ensures ignitability at lean bulk equivalence ratio. Moreover, this method is applied to a real CNG engine. Results of engine performance experiment shows that two-stage injection method combined with gas-jet ignition has successfully widen the operating range of a CNG engine from low to high load at corresponding φ=0.17 to 1.1.

Abstract: Mixture formation plays as a key element on burning process that strongly affects the exhaust emissions such as nitrogen oxide (NOx) and Particulate Matter (PM). The reductions of emissions can be achieved with improvement throughout the mixing of fuel and air behavior. Measurements were made in an optically-accessible rapid compression machine (RCM) with intended to simulate the actual diesel combustion related phenomena. The diesel combustion was simulated with the RCM which is equipped with the Denso single-shot common-rail fuel injection system, capable of a maximum injection pressure up to 160MPa. Diesel engine compression process could be reproduced within the wide range of ambient temperature, ambient density, swirl velocity, equivalence ratio and fuel injection pressure. The mixture formation and combustion images were captured by the high speed camera. Analysis of combustion characteristics and observations of optical visualization of images reveal that the mixture formation exhibit influences to the ignition process and flame development. Therefore, the examination of the first stage of mixture formation is very important consideration due to the fuel-air premixing process linked with the combustion characteristics. Furthermore, the observation of a systematic control of mixture formation with experimental apparatus enables us to achieve considerable improvements of combustion process and would present the information for fundamental understanding in terms of reduced fuel consumption and exhaust emissions.

Abstract: The Electro Discharge Sawing (EDS) process is a modified Electro Discharge Machining (EDM) process to obtain high material removal rates in sawing of large bar stocks and billets of high strength materials. In such a complex system as Electro Discharge Sawing (EDS) with multitude of factors affecting its performance. Taguchi approach of orthogonal arrays (OA) is best suited for the design of experiments . In the present investigation the relative influence of five factors was analyzed on typical four response parameters. An orthogonal array L₈ (2⁵) was selected for the five factors set at two levels and designated as low and high. The results show the Electrode polarity to be the most important factor with electrode positive leading to best results. The process variable parameter with highest effect is pulse current followed by pulse on time, pulse off time and voltage. Effect of work material is random depending on which thermal property is more effective out of thermal conductivity and enthalpy of melting.

Abstract: Being widely used in aircrafts structure and aircraft turbine parts, chemical processing equipment and marine hardware, titanium alloys are well known of their high strength and corrosion resistant even though this material is categorized as hard to machine material and reactive to hydrogen and oxygen in elevated temperature. And joining titanium alloys in fabricating parts used in aerospace and medical application requires excellent temperature distribution control to minimize the heat effect. Due to this, laser welding is one of the best methods for the selective area heat induction capability and high accuracy. However, proper processing parameter need to be determined based on the characteristics of the laser source and processed material. Hence, this study is carried out to clarify the performance of a medium range powered laser by comparing and analyzing the welding beads characteristics changes occurred under different processing parameters. Welding beads were analyzed visually from two directions to obtain overall view of molten zones.

Abstract: Structural optimization was important nowadays in getting the optimum design and usage of the material use, where size optimization is part of it. This research is focusing on the application of size optimization on steel wheel rim. Existing steel wheel rim dimension was measured and Finite Element Analysis (FEA) was done to get actual dimension and mechanical properties (stresses), as baseline data. CAD modelling on steel wheel rim was done using Pro-Engineer/Creo 1.0. One structural element was selected to be optimized. Then optimization program was generated using MAPLE to get optimum value (size). Steel wheel rim will be re-modelled with optimum size to get optimum design. FEA was done again on optimized steel wheel rim to compare with actual steel wheel rim data. Optimized steel wheel rim was showing better in mechanical stress with optimum size (minimize the weight and volume).