Applied Mechanics and Materials Vol. 842

Abstract: Longitudinally welded steel pipe piles are not as commonly used as seamless steel pipe piles in offshore platform. Although longitudinally welded steel pipe piles are considerably cheaper than seamless steel pipe piles, yet many feared that longitudinally welded steel pipe piles are prone to fail because of non-uniformity in the heat affected zone (HAZ), especially when receiving impact loads during the installation process. In this paper, a finite element model is developed to study the deformation and failure of the longitudinal welded piles. Two modelling cases are performed: single and double piles, with two different failure parameters: maximum stress and maximum plastic displacement.

Abstract: Machined product quality depends on its dimension and surface quality. The dimension quality depends on machine tool accuracy while the surface quality depends on machining system stiffness. A low machining system stiffness will shift spindle shaft-tool resonance frequencies to low frequencies. When one of these frequencies coincides with spindle rotational speed or its harmonics, chatter will be generated which in turn worsen the workpiece surface roughness. In addition to increasing machining system stiffness, chatter can be eliminated by decreasing the axial depth of cut as well. Maximum axial depth at certain spindle rotational speed which will not generate chatter is called as chatter threshold. A diagram describing chatter thresholds for certain range of spindle rotational speed is called as a SLD (stability lobe diagram). The diagram is very useful for selecting a maximum depth of cut at certain rotational speed in order to obtain chatter-free machining process. The SLD can be generated theoretically or experimentally. The theoretical one is fast and cheap but it is not guaranteed to be correct. On the other hand, although the experimental one will produce exact values but it is long, cumbersome and expensive, because for certain rotational speed many machining with different axial depth of cut must be conducted until chatter threshold is reached. The same process is then repeated for other rotational speeds. This paper deals with a new method in determining the chatter threshold or SLD experimentally, by using inclined workpiece, by which it only needs one time machining-test for each rotational speed. In this method, during machining process, chatter occurrence is detected by using accelerometer and validated by its surface roughness afterwards. It is shown in this paper that the new method works well for machining aluminium workpiece in vertical machining center.

Abstract: Welding is one of the joining processes and it has been widely used, especially for steel welded structure in off-shore, pipeline or ship construction. Advantages of the welding joint are inexpensive, process joining can be done quickly and can produce light structure compared to other joining processes. One of welding techniques mostly used for joining steel construction is flux cored arc welding (FCAW). The commonly problems arise in this welding technique are distortion and low resistance of crack propagation. The aim of this study is to minimize distortion and to increase fatigue crack growth resistance of weld joint.In this research, FCAW welding was conducted without preheat and the other was preheated around welding area with temperature of 200 °C. Each of temperature welding process was measured using data acquisition. After completing the welding process, a sequence of experiment was conducted including chemical compositions, distortion and fatigue test. Result of this research shows that preheat temperature of 200 °C can decrease distortion and improve fatigue performance.

Abstract: Corrosion at the bilge due to direct contact with the seawater is an issue which is necessary to be taken into account. The problem can be solved by giving combined protection such as coating and cathodic protection impressed current cathodic protection (ICCP). For broader range, there is occasionally a possibility of over-protection at certain area especially that is close to anodes. It can trigger cathodic disbondment to occur. Cathodic disbondment is a situation when the coating loses its adhesion to the steel due to the voltage originated from cathodic protection. This trial was conducted by using several samples of LR Grade A plate coated by primer coat epoxy and top coat polyurethane. The plate was then given artificial defect with the size of R2, R3 and R4 accoring to ISO 4628-3 or is equal to 0,5% ; 1% and 8% of the plate surface width. Futhermore, impressed current cathodic protection was conducted with the steel anode, Ag/AgCl reference electrode and over-protection voltage were-1,5 ; -2,0 ; -2,5 ; -3,0 ; -3,5 and-4,0 volt. Electrolyte media employed was seawater. Furthermore, the disbondment taken place was measured after 6 hours and analyzed the corrosion product produced. In the research, it could be seen that the broader the defect was, the smaller the disbondment area was. The width of disbondment area was depending on current density. The smaller the voltage (volt) was, the broader the disbondment in accordance with the increase of disbondment width taking place on the plate surface. The corrosion product produced was Fe₃O₄ (Magnetite).

Abstract: Gear is one of the machine components that is widely used in industrial and automotive fields. In machinery process, gear has a very important function to forward speed, power, or torque from one engine component to other components as a mechanical drive. Today a lot of development to obtain a good quality of gear, due to many gears were damage, worn out, and broken because they were not strong enough to resist friction and pressure. In addition, broken gears due to pressure and friction make them did not last long. To increase the hardness value of gear, then it needs though material that can be used when the gear reach optimum rotation. The material that is widely used for gear application is medium carbon steel. The medium carbon steel is a metal material that has carbon composition ranging from 0.30 to 0.59%. This medium carbon steel has hardness value of 174.501 HVN without treatment. The process of quench tempering and carburizing are conducted to increase hardness and toughness value of the material. The hardness value of gear is 140 HVN. The result of the research showed the hardness value at various temperature 780°C, 810°C, and 840°C. The optimum hardness values ​is 165.355 HVN at the temperature of 840°C. Medium carbon steel is expected to be an alternative to produce steel material with certain mechanical properties. This research also conducted heat treatment in austenite area and then detained with holding time of 20, 40, and 60 minutes. Furthermore, quench tempering was conducted and followed by carburizing to obtain a ferrite phase and coarse pearlite and to increase hardness value after quech tempering. It is expected that after quech tempering and carburizing process, steel with better mechanical properties can be produced. This research obtained the increase of hardness value and the number of pearlite and ferrite.

Abstract: Chlorella zofingiensis Dönz is not only known as feed in aquaculture industry, but also it has been developed as biodiesel source. In order to optimize the microalgae as a biodiesel feedstock, it is necessary to study its environmental factors, such as light and medium salinity. This study was conducted to determine the effect of red-blue light in a wide range of salinity medium. C. zofingiensis Dönz used in this study were cultured for 21 days on a laboratory scale using a medium consisted of ZA, Urea and Farmpion (local agriculture fertilizer) with a ratio of 4: 2: 1. There were three variations of salinity treatments, including culture without the addition of NaCl (its medium salinity was 14 ppm); the addition of NaCl 5 ppm (its medium salinity was 19 ppm) and NaCl 10 ppm (its medium salinity was 24 ppm). Its cell density and dry weight were measured every 7 days. Neutral lipid content was determined with Nile Red staining method and analyzed with Cell Profiler software every 7 days. The highest lipid content was achieved by treatment of blue light and the addition of NaCl 5 ppm, accounted for 344.6 mg L^-1 or 50% of the dry weight.

Abstract: The manufacturing industry is now growing rapidly in the area of non-conventional machining, especially Electrical Chemical Machining (ECM). The ECM can be used for machining of very hard material and very complex shape. This research is performed in order to manufacture mini-channel, which has a complex shape. The ECM machine cutting conditions are as follow; voltage: 7 Volt, feed rate: 1 .0 mm/minute, electrolyte: Natrium Cloride (NaCl), electrolyte concentration: 15 %, electrolyte speed: 3.32 m/s. The result shows that the mini-channel can be manufactured with the average of Material Removal Rate 0.035 g/min with the overcut average is 0.481 mm, and the surface roughness is 5.19 micro meter.

Abstract: Iron ores should be separated from oxygen and impurities which are coming along during the mining process. The separation process is known as reduction. There are two types of reduction process, and the most common is direct reduction process (DRP). There are several parameters in DRP which will determine the quantities of the product known as direct reduction iron (DRI). This worked discussed the effect of reduction temperature and pellet heap to the quantities of DRI using single conveyer belt Hearth furnace. The worked was done in laboratory scale using composite pellets with 14 mm in diameter. The ratio of iron ore to coal in the composite pellet is 1 to 1. The reduction process temperatures are 500^oC, 700^oC and 900^oC. The reduction time is 25 minutes. While the pellets heap are also varied to 1, 3, 5, 7, 8 and 9 layers. The results show that DRI was formed in 700^OC and the quantities of DRI are in line with the reduction temperatures and layers of composite pellets heap.

Abstract: In the dissimilar materials and dissimilar thin thickness sheets joining, welding current and welding time parameters of resistance spot welding (RSW) effect weld ability. RSW used for joining thin plate less than 1000 μm is called micro-resistance spot welding (μRSW). The objective of this article is to study the effect of welding current and welding time to the joining dissimilar thin thickness materials and the microstructure of a weld joint. The thickness of Al 1100 is 400 μm, and KS 5 Spring Steel is 200 μm. Welding parameters are Cycle Time 0.5, 1, 1.5, Welding Current 1kA and 2 kA, and holding time 10 second. Welding current 1kA, Cycle time of 0.5 produce maximum shear load of 227.4 N and fracture area of 6.644 mm². Welding current 2 kA, cycle time of 1.5 affect maximum load of 222.7 N and fracture area of 10.559 mm². Welding parameters lead to the majority fracture on aluminum material. The welding current and cycle time do not significantly affect maximum shear load and fracture area.

Abstract: SPH is a Lagrangian based computational method that can be used for solving fluids and solid mechanics problems. In this work, SPH is utilized to solve the two dimensional Navier’s equation for linear elastodynamics problems. The SPH technique computes the discrete particle properties using a smoothing distribution function, which takes into account the effect of neighboring particles. To investigate the performance of the developed method in solving solid mechanics problems, the problem of plate bending was simulated. The results show good agreement between the simulation and analytical solution. Additionally, the study found an indication that the current method of enforcing boundary conditions produces boundary effects at locations where the plate is attached to the wall and at the end of the plate.