Advances in Science and Technology Vol. 141

Abstract: Armour steel products developed in various forms, function and materials. The usage of steel as bulletproof material has many advantages i.e. easy to transport, easy to be formed and has competitive price compared to other material. The mechanical properties of steel which can be used as bulletproof material must meet certain criteria which can be improved through heat treatment process. The aim of this research is to determine the most suitable heat treatment parameter of SKD 11 modified steel material to improve its hardness and the effect of thickness SKD 11 modified as requirement for bulletproof material. This research processed the SKD 11 modified steel material using heat treatment with 1030°C quenching parameter with 3 hours holding time followed by tempering temperature parameter which vary of 400°C, 500°C, 530°C and 600°C with 4 hours holding time for each tempering. The tempering process is done twice for each sample. Result showed that the highest hardness properties was achieved at 1030°C quenching parameter with 3 hours holding time followed by tempering temperature parameter of 530°C with 4 hours holding time. From the best parameter resulted in highest hardness then SKD 11 modified material for ballistic test varied into 5, 7.5 and 10 mm thickness. TheBallistic performance test level III and level IV showed that hardened SKD 11 modified steel material with 10 mm thickness has the lowest BFS value of 3.32 mm and 7.54 mm with a shattered phenomenon present on the experiment. The experiment result confirm that the SKD 11 modified material meet the BFS allowed limit which 46 mm based on NIJ0101.06 standard.

Abstract: This study investigated forming beads of an AlCrFeCoNi high entropy alloy (HEA) using the multi-beam laser directed energy deposition (L-DED). The X-ray diffraction (XRD) and electron backscatter diffraction (EBSD) analyses confirmed the formation of a single phase composed of the AlCrFeCoNi HEA with the body-centered cubic (BCC) structure. Various laser powers (80W, 100W, and 120W) were examined to understand their effects on bead formation and bonding between the formed bead and substrate. At 80W, weak bonding was observed with a gap between the bead and substrate as the laser melted only the AlCrFeCoNi HEA powder. Increased laser power strengthened the bonding, but altered the HEA composition, deviating from the equiatomic compositions. Furthermore, the study revealed a correlation between laser power and grain size. With increasing laser power, microstructures with coarser grains were obtained.

Abstract: Welding plays an important role in the component joining process. This study aimed to determine the effect of shielded metal arc welding on the microstructure, hardness and tensile strength of nodular cast iron. Shielded metal arc welding was performed using AWS A5.15 Eni-CL electrodes. Scanning Electron Microscope is used for metallographic observation. Hardness testing was carried out on base metal, heat-affected zone, and weld metal. This hardness test uses the Vickers technique. Tensile testing was carried out to determine the effect of welding on tensile strength. The results of the metallographic investigation showed the disappearance of the ferrite phase and the appearance of the ledeburite phase in the heat-affected zone and weld metal. The area with the highest hardness occurs in the heat-affected zone while the lowest hardness occurs in the weld metal. There is a decrease in the tensile strength of nodular cast iron due to the welding process.

Abstract: This study aims to determine how the effect of inoculation of manganese (FeMn) on the hardness value, the results of microstructure photos, and the results of the Scanning Electron Microscopy Energy Dispersive X-ray Spectroscopy, test on gray cast iron material with the addition of 3% FeMn. In this casting process using an induction smelting furnace with a temperature of 1300 – 1400 C the material used for smelting is iron (Fe), melted and then mixed with 3%. FeMn after mixed poured into metal molds and prepared sand. The results of the hardness test showed that the hardness values vary in the upper, lower, and intermediate metal molds. The results of microstructure testing of metal molds, transitional molds, and sand molds at the bottom are the hardest because the graphite is neatly arranged and clearly visible. The results of the Scanning Electron Microscopy Energy Dispersive X-ray Spectroscopy test of the Mn element in the metal mold was detected at 3.45% and in the sand mold at 0.00%, the Mn sand mold was actually detected on the graph but did not appear in the data table because it was covered by Fe, C, and Si elements.

Abstract: One type of technical rubber that is currently imported is a pneumatic fender, which mostly only uses synthetic rubber as raw material. Whereas natural rubber has superior mechanical properties that are better than synthetic rubber. This research will combine natural rubber (RSS) with EPDM synthetic rubber by varying the RSS/EPDM mass ratio. This study aims to determine the effect of the mass ratio of RSS/EPDM on the quality of the mechanical properties of pneumatic fender compounds. The rubber compound is made with a ratio of RSS/EPDM: 100/0, 90/10, 80/20, 70/30, and 0/100. The mechanical testing was carried out under normal and aging conditions. The test results showed that the mass ratio of RSS/EPDM rubber affected the mechanical properties of the resulting rubber compound. The rubber compound formula containing EPDM 10 to 30 phr is suitable for pneumatic fender applications due to better properties and resistance after aging, particularly compression set.

Abstract: Resin is a compounding ingredient that can be used in tire treads to improve (wet) grip resistance. Increasing tan delta in the temperature range between 0°C and 20°C is important to improve (wet) grip resistance. To understand the behavior of resins and determine which resin is best suitable to improve traction in SBR/BR blends, the solubility of polyterpene and α-methyl styrene resin in SBR-BR blends is investigated. The method for measuring the solubility of resin in SBR/BR blends at a 70/30 weight ratio was developed. The solubility parameters (δ) were calculated based on the group contribution method, and the Δδ values between resins and rubbers were correlated with the weight increase of lightly crosslinked SBR/BR blends at different temperatures. A smaller Δδ means higher solubility of the resin in the rubber, which is confirmed by the high level of resin uptake in the rubber. Based on the research, it was found that molecular weight, polarity, and temperature, are factors, which influence the solubility of resins into the rubber. In addition, based on the DMA measurements, SBR/BR (Ni-cat) containing polyterpene shows a higher tan delta at 0 – 20°C compared to SBR/BR (Nd-cat) containing polyterpene. This fact indicates that a correct selection between the type of rubber and resin is important depending on the requirement needed.

Abstract: This work reports on the effect of adding GO on the microstructural properties of fly ash-based geopolymer-GO composites. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier Transform Infrared (FTIR) tests were performed to investigate microstructural properties of fly ash-based geopolymer-GO composites. The XRD data showed that the intensity of the peaks in the fly ash-based geopolymer-GO composites increase with increasing the amount of the GO composition, which indicates the quartz phase (SiO₂) remained in crystal form. Fourier Transform Infrared (FTIR) data showed that the presence of GO absorption bands indicates the successful inclusion of GO into the geopolymer matrix/network, which affected the microstructural development of fly ash-based geopolymer-GO composites. In addition, the SEM images reveal that fly ash's diameter decreased up to the GO content of 1 gram, and the matrix was denser, which will increase the strength of the fly ash-based geopolymer-GO composites. While adding larger than 1 gram (e.g., 2 grams) of GO results in a bigger diameter of fly ash with the coarser matrix, which will decrease the strength of the fly ash-based geopolymer-GO composites.

Abstract: This work deals with the effect of adding GO on the mechanical properties of fly ash-based geopolymer-GO composites. Compressive strength, water absorption, density, and flexural strength tests were carried out to investigate mechanical and physical properties of fly ash-based geopolymer-GO composites. The results showed that the addition of graphene oxide into fly ash-based geopolymer-GO composites up to threshold value (i.e., in this study, 1 gram or 1.1 wt.%) will decrease total porosity as well as a change in the total quantity of pores and their distribution due to densification of bulk matrix of the specimens. Consequently, it reduced water absorption, increased the density of the specimens, and subsequently increased mechanical properties (i.e., compressive strength and flexural strength). Conversely, the addition of graphene oxide into fly ash-based geopolymer-GO composites greater than above the threshold value will increase total porosity due to coarsening of bulk matrix of the specimens and subsequently increased water absorption and reduced density of the material. As a result, it decreased the mechanical properties (i.e., compressive strength and flexural strength) of fly ash-based geopolymer-GO composites. The present research demonstrates how graphene oxide can improve the mechanical properties of fly ash-based geopolymer-GO composites to a certain extent, which may match with industrial applications.

Abstract: This research investigated the Fe doping effects on the Strontium Titanate (SrTiO₃) structure to improve its photocatalytic activity. The so-called Fe-doped STO photocatalysts with a stoichiometry formula of SrTi_1-xFe_xO₃ (x = 0, 0.01, and 0.05) were successfully fabricated using the coprecipitation method. The XRD characterization confirmed the formation of STO, SrTi_0.99Fe_0.01O₃, and SrTi_0.95Fe_0.05O₃ photocatalysts and the shrinkage crystallite size due to increasing Fe content. The FTIR characterization supported the XRD results, where all samples revealed Sr-Ti-O bonds with no observed Fe-O bonds indicating the successful fabrication and doping. The photocatalytic activity was examined by the degradation of Methylene Blue (MB) dye under UV light for 1, 2, 3, 4, and 5 irradiation times, and the absorbance was determined using a Spectrophotometer instrument. All samples have successfully degraded MB dye where the %degradation linearly increased with longer irradiation times. The results further exhibited that the SrTi_0.95Fe_0.05O₃ sample had the highest %degradation at 75.3% while SrTi_0.99Fe_0.01O₃ samples achieved the highest kinetic rate at 0.2557 min^-1. All Fe-doped samples revealed better photocatalytic activity than the undoped STO, proving that Fe doping could improve the photocatalytic activity of SrTiO₃.