Applied Mechanics and Materials Vol. 758

Abstract: Boundary layer flow structure developing on an airfoil surfaces strongly affects drag and lift forces acting on the body. Many studies have been done to reduce drag, such as introducing surface roughness on the airfoil surface, gas injection, attachment of vortex generators, or moving surface on the airfoil. Previous results showed that the attachment of vortex generators has potentially been able to control boundary layer separation compared to other controlling devices. This study is focused on the evaluation of the effect of vortex generator attachment on the NASA LS-0417 airfoil profile as this profile is commonly used in wind turbine blade application. The models of this experimental study are NASA LS-0417 profiles, with and without vortex generator. The chord length of the profile is 110 mm, while the span is 210 mm. Profile of the vortex generator is a symmetrical profile of NACA 0012 configured in counter rotating and attached on the upper surface of the main profile. The chord length of the vortex generator is 7 mm with two different values of the height (h): 1 mm and 2 mm. The experiment was conducted in an open loop wind tunnel with maximum attainable freestream velocity of approximately 19 m/s and the turbulence intensity at the tunnel centerline is approximately 0.8%. The wind tunnel cross section is octagonal of 30 cm x 30 cm and of 45 cm to 60 cm adjustable length. The study was performed at two different freestream velocities of 12 m/s and 17 m/s corresponding with Reynolds numbers (Re) of 0.83 x 10⁵ and 1.18 x 10⁵ based on the airfoil chord length and the freestream velocity. Angle of attact (α) was varied from 0^o to 24^o. Drag and lift were measured using a force balance with measurement uncertainty of approximately 0.77% and 2.47% at measured drag of 0.65N and at measured lift of 0.202N, respectively. A flow visualization study using oil flow method was conducted to obtain qualitaive picture of flow structure on the airfoil surface. Results of this study showed that attachment of the vortex generator on the NASA LS-0417 profile has not been able to improve the profile performance compared to that of unmodified profile. There, however, seems Reynolds number effect on the airfoil performance flow conditions performed in this study. At lager Re, there is an increase in C_L/C_D of approximately 36% at angle of attack (α) 6^o. Next, based on the flow visualization results, attachment of the 2mm vortex generator on the airfoil NASA LS-0417 surface results in an advancement of boundary layer separation at the two Re’s conducted in this study. Finally, the 2mm vortex generator accelerates airfoil stall at approximately 16^o, while the 1mm vortex generator is relatively no effect on the airfoil stall angle.

Abstract: In this paper was observed performances of developed three degrees of freedom (dof) parallel mechanism named 3-URU spherical parallel mechanism. The mechanism is composed of three identical limbs mounted symmetrically to base (fixed link) and platform (output link). The limb is constructed by universal-revolute and universal joints. The kinematic constants of mechanism consisting of link lengths, radius of platform, radius of base, mounting angle of limb and platform to base and platform were determined with consideration of velocity transmission and force constraint indices. To evaluate performance of mechanism, it was manufactured a prototype of mechanism designed base on these two mentioned indices. There are three steps proposed to realize the mechanism, (i) kinematic synthesis to determine of kinematic constants, (ii) design of mechanical components to define shape and dimension of links and joints by considering collision in wokingspace and static analysis, (iii) evaluation of mechanism performances consisting of workingspace, controllability of platform motion and static payload. Based on obtained results, it can be clarified that, the mechanism can produce spherical motion of platform which rotates on steady point recognized as center of platform rotation. The platform can achieve maximum inclination angle, 80 degree and at this posture occurs translational error, 0.0102 mm. On the other hand, the mechanism can support payload ten times of weight of moving parts.

Abstract: This study investigates the influences of driven rotary tool (DRT) on temperatures and forces when turning AISI 1045 steel. A set of cutting conditions was used in FE simulations to predict cutting force, stresses and temperatures developed at around the edge of tool. The material cutting speed ranges were set between 20 and 250 m min^-1. The rotary tool speed were 0 and 100 rpm.^. The feed rate and the depth of cut were set constant. Simulation results provided the predicted cutting distribution of temperatures and stresses at the chip and work piece.

Abstract: The objective of this work is to investigate the impact behavior of bamboo fiber/epoxy composites. The test was carried out in accordance with the ASTM D5941 Izod impact test standard. Whilst the fiber was obtained from local bamboo the matrix being used is Eposchon general purpose Bisphenol A-epichlorohydrin epoxy resin mixed with Eposchon general purpose Polyaminoamide epoxy hardener. The specimens were cut from nine bamboo fiber/epoxy composite panels. Each panel contains either random or unidirectional fiber orientation of four different volume fraction, i.e. 10, 20, 30 and 40%, of fiber, along with a pure epoxy, without fiber, panel board as reference. According to the adopted standard, the specimens are of prismatic bars of 85 [mm] long × 10 [mm] wide × 5 [mm] thick. Photo macrographs of selected samples were analyzed to describe their failure modes. It was revealed that both the impact strength and energy absorption capacity of the samples increase with the increase of fiber content up to 40%, for both unidirectional and randomly oriented fiber arrangement. In addition, unidirectional fiber composite samples show higher values in both impact strength and energy absorption capacity (0.162 [J.mm^-2] and 8.5 [J], respectively) in comparison with those of randomly oriented fiber composite samples (0.144 [J.mm^-2] and 7.6 [J], respectively).

Abstract: A Rail-Conveyor can be used as one of solutions for transportation of coal production. This system was rated to have either a competitive capital investment, and operational & maintenance cost, when compared with conventional transportation system.This paper studies a stability analysis of the wagon of the Rail-Conveyor in order to prevent derailment in longitudinal and lateral directions. The main aims of this study are to determine the maximum acceleration, deceleration, operational velocity for all possible conditions such as incline slope, decline slope, and turning with a specific radius. Case study was conducted for the wagon diameter of 0.76 m. The loading conditions were classified into two cases: empty wagon and fully-loaded wagon. It was assumed that the maximum allowable slope was 20%. The result of this analysis will be used as a basic design for rail-conveyor operation, route selection, and power station location & its capacity.

Abstract: Hot tearing is one of metal casting defects and often found in the casting products such as cracks on the surface. Solidifaction metal causes a thermal contraction and shrinkage, when the contraction and shrinkage occurs if a metal alloy is restrained by mold design, it will effect hot tearing. Hot tearing is influenced by several factors, including the chemical composition of the alloy, the casting temperature, mold temperature, mold constraint, fast or slow solidifaction, non uniform solidifaction, and so on. This study aimed to obtain a certain temperature that cause the maximum of hot tearing defects, so it can be recommended to the metal casting industry in aluminum-silicon material to avoid the casting temperature. Three variations of the casting temperature used in this study including 710 oC, 760 oC and 810 oC. The material used in this study is an alloy of Al-1.19% Si (percent by weight). The method used is a visual method using mold CRCM (Constrain Casting Rod Modified) Horizontal used for the index analysis of HTS (Hot tearing Susceptibility). The results gotten include the hot tearing increases with the increasing of casting temperature, and it decreases with the decreasing the casting pouring. The maximum of hot tearing index is 45 HTS at 760 oC for casting temperature. Tear formed on products from smooth categories (hairline cracks) to the complete categories (broken specimen).

Abstract: Safety is one of important factors which has to be considered in designing automobile in the automotive industry. One of the components related to the automobile safety is bumper. Bumpers are attached on front and rear of vehicle’s body in order to protect the body from damage due to low speed crash. In this research, hollow glass microsphere (HGM) reinforced epoxy is used as the material for the bumper since this material has not been applied to this application yet. This research is conducted in order to find the ability of this composite material in absorbing impact energy from low speed crash by using finite element method. Thickness of the bumper varied from 4 mm to 8 mm with 1 mm increment. Low speed collision is simulated by following Economic Commission for Europe Regulation 42. The bumper energy absorption is analyzed and indicated by the internal energy, deformation, and equivalent stress from each bumper’s thickness.

Abstract: The used of palm-biodiesel fuel in automotive industry is increasing rapidly nowadays. Among the reasons are high efficiency modern fuel injection system of diesel engines and the shortage of petroleum diesel fuel from fossil resources. Among the parts affected by the fuel switch are fuel pumps components, including the fuel injection needle. Those components, working under the lubrication environment of the fuel, have to be prevented from excessive wear to maintain their high performances. This paper discussed the wear characteristics of stainless steel 304 sliding against cast iron under the lubrication environment of palm-biodiesel fuel with the concentration of 7.5% palm methyl ester in the petroleum diesel fuel. The material pair is chosen because of their widely used as mechanical components. The tests were conducted using a ball on disk tribometer. The results show that wear of the stainless steel ball is smaller in the environment with the presence of palm methyl ester content in the diesel fuel compared to that in the environment without the presence of the palm methyl ester content. The results suggested that palm-biodiesel fuel is favorable in decreasing the wear of the material.

Abstract: . Research on sea current energy uses as a sea current electrical power plant (PLTAL) in the region of Lembongan-Nusa Penida-Ceningan carried out since 2013, aiming to meet the demand for electricity in the coastal areas and remote islands. This study aims to design a marine current turbine which is planned to generate electricity of about 50 kW, with a construction system made ​​fixed and the turbine set inside that can spin revolving without interruption. Simulation model of the flow is done by using Computational Fluid Dynamics analysis, CFD. Simulations conducted in private with a variety of flow velocity and pressure of the sea water and various forms of channels. Based on the results obtained by simulation, the best flow of sea currents is with a slope angle of 30⁰ with a channel length of 15 m where the flow speed of the turbine of about 39 m/s with a flow pressure of 201,426 Pa, which predicted to be capable of producing 1,500 kW turbine power.

Abstract: The current work deals with the tensile and flexural properties of bamboo fiber/epoxy composites. Tensile and flexural property evaluations were carried out in accordance with the ASTM D638 and ASTM D790 standards, respectively. Bamboo fiber was obtained from local bamboo by means of degumming process. The matrix being used is Eposchon general purpose Bisphenol A-epichlorohydrin epoxy resin mixed with Eposchon general purpose Polyaminoamide epoxy hardener supplied by P.T. Justus Kimiaraya. The specimens were cut from five bamboo fiber/epoxy composite panels. Five different fiber volume fractions, V_f, i.e. 0, 10, 20, 30 and 40 vol%, have been considered. All mechanical and physical characterization were carried out at the Mechanical Engineering laboratory, Universitas Muhammaiyah Yogyakarta. Photo macrographs of selected samples were analyzed to describe their failure modes. Physical property evaluation revealed that a slight fiber content deviation from their expected results was observed. Whilst tensile strength, modulus and strain to failure, as well as flexural strength and modulus were found to increase with the increase of fiber content up to 29.8%, maximum flexural strain to failure was being at V_f = 21.1%. Tensile specimens were mostly failed by debonding followed by fiber breakage, while flexural specimens were mostly failed by debonding followed by fiber breakage and fiber pull-out at tension sides.