Key Engineering Materials Vol. 892

Abstract: The screw press is a type of machine press used for extracting crude palm oil from the oil palm’s mesocarp, where its short driveshaft, a mechanical component for transmitting torque and rotation, is often found to be susceptible to failure. Since the initial damage to the short driveshafts in the shaft keyway area is associated with the frequent incidence of shaft failure, this research aimed to discover the root cause of this failure and how to prevent it using visual inspection and stress analysis methods as well as those of the fractography, metallography, chemical composition, and hardness tests. Using the descriptive method to analyse the collected data, the visual inspection and the fractography results of the research indicated that the fatigue crack failure of the short drive shaft in the palm oil screw press machine was caused by the fatigue crack initiation that was safe from stress concentration in its keyway areas. This crack initiation was followed by crack propagation as indicated in beach mark forms. Finally, the ductile fracture observed on the shaft surface was found to have resulted from the continuous rotational motion and the loading and unloading effect of the central shaft driving system.

Abstract: The rim is one of the main components in a motorized vehicle system, both two and three wheels. Rim loads when used are dynamic and often even shock. This study aims to study the mechanical characteristics, especially the hardness properties of spoke wheel rims and cast wheel rims made of aluminum alloy used in motorcycles and compare the results. Hardness testing is carried out on the spoke wheel and cast wheel specimens, using the Rockwell method with an identifier of 1/16 ball and a spectrometer used for both microstructure observations. The result of the average hardness test for the spoke wheel is HRB 99.3, while for the cast wheel is HRB 76.5. From the hardness test, it can be concluded that the hardness of the spoke wheel type is higher than the cast wheel type due to the difference in the manufacturing process. Cast wheel rims can withstand a load of 3 tons (30000 N) and the value of rim tension that can be accepted until the fracture is 45.84 MPa. Meanwhile, spoke wheel rims have the ability to withstand smaller compressive loads than cast wheel rims, which are 2 tonnes (20000 N) and the rims can accept the stress of 66.04 MPa until they break.

Abstract: A spring is a component which is designed to have relatively low stiffness compared to normal rigid rods, thereby making it possible to accept certain forces that are charged. A leaf spring is an important suspension component for heavy vehicles, as a failure of the leaf spring can cause severe if not fatal accidents. This study aims to investigate the factors that cause leaf spring failure in the form of a 125 PS dump truck vehicle suspension system. The method employed incorporated experimental and finite element analyses. The experimental work included visual observations, observation using a scanning electron microscope (SEM), hardness testing, and microstructure testing. Leaf spring modelling was conducted using Autodesk Inventor 2017 software, and the finite element analysis (FEA) was performed using Siemens ™ FEMAP V12.0.1 application software to calculate the maximum stress and strain that occurred near the crack tip of the leaf spring. The results from the analysis indicated that the cause of the fracture that occurred in leaf spring No. 3 was due to a defect discovered on the surface of the leaf spring. Based on the observations of the fracture surface, it is revealed that the cause of failure was due to the cyclic load experienced by the components during operation which caused crack propagation beginning from micro-cracks until reaching a significant dimension to cause a final fracture. In addition, the overload imposed on the leaf springs also caused maximum stress on the springs to increase, thus accelerating the failure of the leaf springs. Further results also showed that the value of the stress intensity factor, K_I = 29.15 MPa.m^1/2 was greater than the value of fracture toughness, K_IC = 23 MPa.m^1/2 of the spring material.

Abstract: Flexural resistance is the ability of a specimen to withstand force in two pedestals with vertical axis until it is broken. Flexible pavement is a type of pavement which is very dependent with pavement course underneath. The dependency of flexible pavement in both base course and subgrade makes this pavement difficult to apply in unstable soil. Using wire mesh course as reinforcement is considerably able to raise the flexural resistance. This study is aimed to analyze flexural resistance value in hot mix by using wire mesh course as reinforcement. The study is conducted by applying experimental method with designing four types of wire mesh laying models in hot mix using three points flexural test equipment. Based on the study result, it is found that hot mix with wire mesh laying 30 mm from specimen surface is the best model type with 291,85 KN flexural resistance value with 8 mm of deflection depth. In this laying, it can be concluded that wire mesh course can raise up the flexural resistance up to 35,41% compared to the hot mix without wire mesh course.

Abstract: Shaft failures often occur, even in the shafts of centrifugal pumps. This study aims to determine the cause of shaft fracture through experimental and numerical study. The fracture surface was observed using Scanning Electron Microscopy (SEM) to identify the initial crack. The chemical composition test results show that the material used was in accordance with the AISI 420 standard, which is necessary to make Finite Element Analysis (FEA) modelling. Shear stress, strain and stress intensity factors were analysed around the fillet using FEA. The results show that the value of maximum stress intensity factor, K_I, occurs in the multilevel shaft fillets that experienced initial cracks due to torsional loads. The shear stress value, obtained from the FEA, was higher than the shear stress value of the material. The K_I value, also derived from the FEA, was higher than the K_IC value of the material.

Abstract: Piping systems at gathering stations in the oil and gas industries often fail due to corrosion attacks from the brine water solution containing 8% NaCl that flows through the system. This solution is highly corrosive on the API 5L grade B steel pipes, thereby shortening its lifespan, with an increase in the frequency of pipe replacements. However, the corrosion resistance of API 5L grade B pipes can be improved by using chromate and molybdate inhibitors. Therefore, the objective of this research is to improve the corrosion resistance of the steel pipes using sodium chromate (Na₂CrO₄) and sodium molybdate (Na₂MoO₄) inhibitors with concentrations of 0.2, 0.4, 0.6, 0.8 and 1,0%. This research also aim to determine the optimum concentration of inhibitors to produce minimum corrosion rate, by testing the brine water solution containing 8% NaCl through the potentiodynamic polarization method. The results show that generally, the addition of sodium chromate and sodium molybdate inhibitors to the brine solution causes the steel pipes to be more resistant to corrosion. Furthermore, the sodium chromate inhibitor concentration of 0.6% produces the greatest corrosion potential of – 400 mV with the lowest rate of 0.38 mpy, while sodium molybdate concentration of 0.4% produces the highest corrosion potential of – 385 mV with the lowest rate of 0.34 mpy. The results of SEM observations at 0.4% sodium molybdate concentration showed that the corrosion inhibition/passivation effect of the inhibitor made the steel surface smoother, while the sodium chromate inhibitor at similar percentage failed to reach the optimal concentration to inhibit the corrosion process.

Abstract: This study aims to analyze the stress that occurred on the automotive coil spring made of SAE 5160 carbon steel due to various types of road surfaces. The 60-second strain signals measured on a coil spring of a car being driven on a flat, uphill, and downhill road surface were used as the loads in these dynamic analyses. The analysis results showed that the maximum stress occurred on the inside of the spring in the second coil from the top. The results of this dynamic analysis also showed that the three types of road surfaces provided almost the same stress. The downhill road surface gave the highest stress, which was 0.622 GPa, followed by flat road (0.621 GPa) and uphill road (0.62 GPa). The reasons for this are the shifting of the vehicle load to the front wheels together with the braking effect when driving downhill.

Abstract: In this paper, the magnetic properties of Aceh iron sand was studied. The iron sand was collected from the Syiah Kuala coastal area, Banda Aceh and obtained by mechanical alloying method using planetary ball milling. The mineral compositions were investigated by XRD and XRF analysis tests. The XRF test showed that the sand mostly contain magnetite, Fe₃O₄ (85.80%) in association with other impurities of SiO₂, TiO₂, Al₂O₃ and some others minor minerals. Compare to XRD results, the phase compositions were mainly magnetite (Fe₃O₄). So, it is consistent with the XRF data. The electron microscopy observation (SEM) showed the fine crystalline structure and the main morphology was micro-crystalline in agglomerate forms. Furthermore, the magnetic properties after 20 hours milling showed the increasing in the coercivity (Hc) and remanent (Br), while the magnetic saturation (Ms) was decreased. This behavior can be explained that nano-Fe₃O₄ phase after the milling process plays an important role in the magnetic properties of iron sand.

Abstract: The Fiber Metal Laminate (FML) discussed here was made from Fiber Reinforced Polymer (FRP) composite, laminated by aluminum alloy sheet. The FRP composite panel was made from abaca fiber and polyester resin matrix. The objective was to study the bending strength of the FML with different fiber content. Five panels of abaca FRP were prepared using hand-lay-up methods. The weight content of the fiber in the panels were 0%, 3.56%, 5.18%, 8.94% and 12.22% respectively. The aluminum alloy sheet was laminated to the composite panel using epoxy super glue. The density of the FMLs were measured to confirm the fiber content in the panels. The bending specimen were prepared based on ASTM D-7264. The bending strength that represented by flexural stress of the FML panels were 53.15, 56.44, 46.80, 63.53 61.48 and 49.57 MPa, respectively. The result of the experiment showed that the content of abaca fiber significantly affects the bending strength of the FML. The highest bending strength (63.53 MPa) was produced by the FML with 5.18% fiber content. The result of the study showed that the bending strength of abaca FML was 19.5% higher than commercial FML (53.15 MPa). It was an indication that abaca fiber could be used to substitute the glass fiber in commercial FML.

Abstract: The objective of this study is to carry out an atmospheric corrosion analysis on low carbon steel in the form of plates and elbows in the port area of Belawan. The exposure of the test specimen was carried out at five locations for 12 months. The location points are notated as A, B, C, D, and E. The process of specimen exposure and data collection followed the ASTM G-1 and ASTM G-50 standards. The measurement results indicated a slight difference in the corrosion rate at each location. Location C and D have the highest corrosion rate and location A has the lowest corrosion rate. Meanwhile, for locations B and E have a corrosion rate value that is not much different from location A. This difference in value is probably a consequence of the distance from the exposure location to the seaside. Locations C and D are adjacent to the seaside while the other locations are not. The steel plate has an average value of corrosion rate 0.2214 mpy and steel elbow has a rate of 0.2412 mpy. From the measurement results obtained, the two specimens exposed at each location are still in the "outstanding" category.