Applied Mechanics and Materials Vol. 758

Abstract: This study explored the feasibility of flexural performance of composite sandwich material composed of various low density polyurethane foam core thickness sandwiched between GFRP skins. The mechanical behaviour of this material was assessed by carrying out a flexural testing. Each spesimen had a nominal dimensions of 110 mm x 30 mm x (c + 4 mm). These spesimens with various core thickness (c) of 2 mm. 5 mm. and 8 mm were then tested in three point bending according to ASTM C 393-00. This study revealed that. by incorporating the thickest core ( 8 mm ) . the bending strength decreases by 42.3 % compared to 5 mm core and it further decreases by 72.6 % compared to 2 mm core. The material stiffness showed positive trend for the thickest core (8 mm). it increases by 53.1 % and 78.1 % compared to 5 mm core and 2 mm core respectively. Low shear modulus of polyurethane foam core contributed to the low bending strength of composite sandwich material with 8 mm core. This was further confirmed by failure analysis under optical microscope which revealed that core shear failure was the dominant failure mechanism for 8 mm core. Meanwhile the dominant failure mechanism for 2 mm core and 5 mm core was microbuckling which confirm the high modulus of GFRP skin. The material stiffness was affected by the high modulus of GFRP skin and the core thickness.

Abstract: An investigation on the liquid holdup, wave velocity, and wave frequency in horizontal annular flow has been experimentally conducted through the measurement of liquid holdup using constant electric current method (CECM) sensors. To investigate the effect of viscosity, water and glycerin were used as working liquid, using superficial liquid velocity and superficial gas velocity of 0.05 to 0.2 m/s and 12 to 40 m/s, respectively. Liquids with higher viscosity give the higher liquid holdup, lower wave velocity, and lower wave frequency. Correlations for liquid holdup and mean film thickness, wave velocity, and wave frequency have been developed with mean average errors (MAE) of 13.5%, 9.2%, and 8.6%, respectively.

Abstract: Use of NACA 0012 at the Sultan Wind Turbine prototype provide value coefficient power turbine at wind speed 5.5 m / s by 0017 , wind speed 6.1 m / s at 0.015 , wind speed 7.7 m / s at 0.016 , wind speed 6.5 m / s for 0018 and wind speed 6.2 m / s by 0017 . Where the value of the highest efficiency obtained at a speed of 6.5 m / s at 0.018 . This result is not as expected to generate sufficient energy.The next development carried out investigations on some kind of airfoil, from investigations obtained by using Qblade software that NACA 6612 has a value of 1.78 CL at 15 degrees angle of attack is the largest of all the airfoil .In this research, NACA 6612 will be simulated with a variable chord length, angle of attack, and wind speed, of these three variables will be created which will map graphics 3d sliding value of the ratio of the 3 variables, this graph will give recommendations most optimum combination of variables to types are mapped wind speed throughout the year, to produce optimum power.Optimum combination of NACA 6612 with wind speed varied from 2-7 m/s is chord length 30 cm and angle of attack 7 degree.

Abstract: This paper presents the optimization of a wire electrical discharge machining (WEDM) process of SKD61 tool steel (AISI H13). The use of the Taguchi method coupled with weighted principal component analysis (WPCA) has been applied. The WEDM machining parameters (arc on time, on time, open voltage, off time and servo voltage) were optimized with considerations of multiple performance characteristics, i.e., recast layer thickness (RL) and surface roughness (SR). The quality characteristics of both RL and SR were smaller-is-better. WPCA was applied to eliminate response correlation and to convert correlated responses into equal or less number of uncorrelated quality indices called principal components. Experimental results have shown that machining performance of the WEDM process can be improved effectively through the combination of Taguchi method and WPCA.

Abstract: Friction Stir Welding is a relatively new technique for joining metal. In some cases on aluminum joining, FSW gives better results compared with the arc welding processes, including the quality of welds and produces less distortion. The purpose of this study is to analyze the effect of high speed tool rotation on micro Friction Stir Spot Welding (μFSSW) to the shear fracture load of the welds. Response Surface Methods was used to analyze μFSSW parameters with the response. The welding material was Aluminum A1100, with thickness of 0.4 mm. The tool was made of HSS material which was shaped by micro grinding process. Tool shoulder diameter is 4 mm, and the pin diameter 1.5 mm with length of pin is 0.6 mm. The spindle speed is fixed at 33,000 rpm. The parameters that varied were the plunge speed (2 mm/min, 3 mm/min, 4 mm/min), and dwell time-1 (0 s, 2 s, 4 s) and variable of dwell time-2 (0 s, 2 s, 4 s). From the results of experiment and analysis, it is shown that the important welding parameter in high speed μFSSW process is dwell time-2.

Abstract: Inverse-turbulent Prandtl number (α) is one of important parameters on RNG k-ε turbulence model which represent the cascade energy of the flow, which occur in cylindrical curved-pipe. Although many research has been done, turbulent flow in curved pipe is still a challanging problem. The range of α of the basic RNG k-ε turbulence model described by Yakhot and Orszag (1986) with range 1-1.3929 has to be more specific on Reynolds number (Re) and geometry. However, since the viscosity is sensitive to velocity and temperature, the reference of α is needed on specific range of Reynolds number. This paper is aimed to gain optimum inverse-turbulent Prandtl number of the flow in curved pipe with upper and lower Re which simulated numerically with CFD. The Re at the inlet side were; Re = 13000 and Re = 63800 on cylindrical curved-pipe with r/D of 1.607.The inverse-turbulent Prandtl number (α) were varied to 1, 1.1, 1.2, 1.3. The curved pipe was an cylindrical air pipe with 43mm inlet diameter. The computational grid that is used for CFD numerical simulation with CFDSOF^®, hexagonal-surface fitted consist of 139440 cells. CFD simulation done with inverse-turbulent Prandtl number α varies by 1, 1.1, 1.2, dan 1.3. The wall is assumed to zero-roughness. The CFD simulation generated several results; at Re 13000, the value of α did not affect the turbulent parameter which also confirmed the basic therory of RNG k-ε turbulence model that the minimum Re of α is 2.5 x 10⁴. At Re = 63800, the use of α of 1.1 shows more turbulent flow domination on molecular flow. Lower eddy dissipation by 1.67%, increasing turbulent kinetic energy by 2.2%, and Effective viscosity increase by 4.7% compared to α = 1. Therefore, the use of α 1.1 is the most suitable value to be used to represent turbulent flow in curved pipe with RNG k-ε turbulence model with Re 63800 and r/D 1.607 among others value that have discussed in this paper.

Abstract: This paper presents a comparative study of the damping force and energy absorbtion capacity of a typical conventional-viscous and a regenerative shock absorber for vehicle suspension. Regenerative shock absorber (RSA) is a shock absorber which can regenerate the dissipated vibration energy from vehicle suspension into electricity. In this research, a prototype of regenerative shock absorber was developed, its damping force and energy absorbtion capacity were tested, and the results were analized and compared with those of a typical conventional-viscous shock absorber. The regenerative and viscous shock absorber were compressed and extended in various excitation frequency using damping force testing equipment to obtain force-velocity and the force-displacement curves. The force-velocity and force-displacement curves indicate the damping force and energy absorbtion capacity of the shock absorber. The results show that the damping force of the typical-viscous shock absorber closed to linear at all exciation frequencies. For regenerative shock absorber, nonlinearity and large hysteresis area of the damping force occur at all excitation frequencies. Further, the energy absorbtion capacity of the typical-viscous shock absorber shows an elliptical area with the compression part bigger than the extension one, while those of the regenerative shock absorber shows an asymmetric square area, which indicates a smaller energy absorbtion capacity. These phenomena indicate the significant effect of implementing dry friction damper and elctrical damper to the characteristics of regenerative shock absorber.

Abstract: The development of innovative micro components depends on the manufacturing system and process that reliable to produce the component in micro scale with good quality. In this case, using CO₂ Laser is one of microfabrication techniques to fabricate material to get micro component. In this research, experiment was performed to fabricate micropattern using engraving method by Laser CO₂ machine with several independent variables such as focus distance of nozzle Laser to workpiece (F), power of Laser (P), and velocity of nozzle Laser movement (V). The workpiece in this research was acrylic. Result of fabrication process will be identified and measured using digital microscope and surface roughness tester to get the value of workpiece quality such as surface roughness and geometrical properties as the dependent variables. The relationship of both variables will be expressed in 3D curves characteristic and mathematical models were analyzed by response surface methodology (RSM). The result of the analysis shows that the power of Laser (P) and velocity of Laser nozzle movement (V) effect is the significant variables affecting the quality of micropattern and micromold fabrications. Micromold can be fabricated using Laser CO₂ with roughness value (Ra_x) is 17,55μm, width of grove (W) is 135 μm, depth (D) is 341 μm.

Abstract: This paper discusses the occurrence and non occurrence of low-frequency stick-slip motion on a simple caliper-slider experimental model. The analysis focused on the relationship between stiffness, i.e. contact stiffness and structure’s stiffness, and the generation of stick-slip motion. The occurrence of stick-slip motion is determined by analyzing the frequency characteristic of resulted vibration acceleration at the beginning of sliding which is resulted from a simultaneous application of force in tangential direction and slow release of force in normal direction. The results show that the occurrence and non occurrence of stick-slip motion can be classified into three regions according to the parameter of stiffness ratio, i.e. non occurrence region, mixed region, and occurrence region. The stiffness ratio S_r, the ratio of contact stiffness K_c to structure’s stiffness K_s, of 40 is found to be critical for the low-frequency stick-slip generation in this experimental model.