Key Engineering Materials Vol. 880

Abstract: Residual stresses generated during high-speed machining of spoiler beams used in aircraft cause product deformation and dimensional mismatch, which increases the defect rate and leads to material waste. To overcome this problem, the processing site uses manual modification techniques that stretch part of the workpiece according to the experience of skilled workers. However, due to the nature of the aviation parts industry, there are no established methods for modification of product shapes and parts. Studying the modification process would allow for increased productivity, such as shorter working hours, throughout the aviation industry. In this study, a method of predicting residual stress due to frictional heat generated during high-speed machining and applying a tensile force to a model deformed by residual stress was used to modify the product. Our analysis showed that a degree of deformation similar to the measured value was produced, and that the product was modified by applying a tensile load.

Abstract: An increase in power consumption density is related to the internal thermal characteristics of an electronic device, and the heat dissipation of the device is directly related to the high performance and miniaturization of the device. TIM (thermal interface material) with excellent internal heat dissipation performance are mainly used to improve the heat dissipation performance of electronic devices. Recently, the need for a high-efficiency TIM with high-performance thermal conductivity and low thermal contact resistance has increased. In this study, thermal grease was prepared by mixing Cu-Ni nanopowders with silicon oil, the thermal grease was then used as a heat transfer material. Compared to silicone thermal grease, the thermal conductivity of all prepared samples was excellent. In particularly, thermal conductivity was improved by about maximum 212% compared to that of thermal silicone of thermal grease mixed with Cu-Ni powder.

Abstract: There is a need to address the gap between the theoretical benefits and cost-efficient production of supercapacitors in the market in order to sway the preference of the industry from the current perishable energy sources and storage. More extensive exploration of sustainable fabrication methods and materials used for renewable energy storage are just some of the factors that would decrease this gap. A binder-free supercapacitor electrode made of NiCo₂O₄ and carbonized kapok fiber paper (CKFP) was successfully fabricated by hydrothermal process at relatively low temperatures. NiCo₂O₄ urchin-like structures were deposited on the surface of carbon fiber paper (CFP) and CKFP. XRD analysis confirmed the successful conversion of kapok fiber paper to CKFP after pyrolysis, as well as the growth of pure spinel NiCo₂O₄ nanostructures on CFP and CKFP. The cyclic voltammetry curves showed that the CFP-NiCo₂O₄ prepared at 140 °C had the highest specific capacitance of 143.51 Fg^-1 at 2 mVs^-1. The CKFP-NiCo₂O₄ synthesized at the same temperature yielded slightly higher specific capacitance of 146.29 Fg^-1 at 2 mVs^-1, and 508 Fg^-1 at 0.5 Ag^-1.

Abstract: Binderless supercapacitor electrodes are currently being employed to increase the surface contact between the active material and current collector, leading to enhanced capacitance. In binderless electrodes, the active material is directly grown on the surface of the current collector, omitting the use of insulative polymer-based binders. In this work, Cu foam was successfully electrodeposited on Cu sheet by dynamic hydrogen bubble templating (DHBT) using polyethylene glycol (PEG) and sodium bromide (NaBr) as additives. The current density was set at 3 A·cm^-2 and electrodeposition was performed for 20 s. At 200 mg/L PEG, increasing the NaBr concentration from 0 to 80 mM produced Cu foam with decreasing pores sizes of about 75.15 to 34.10 μm. However, the walls of the interconnected pores became thicker as the pore diameters were reduced. This indicates that NaBr promotes Cu deposition rather than hydrogen evolution reaction (HER), leading to smaller pore sizes. X-ray diffraction confirms the oxidation of the Cu foam under ambient conditions forming cuprous oxide (Cu₂O). The Cu₂O/Cu foam was then utilized as binderless electrode for supercapacitor, resulting to a specific capacitance of 0.815 F·cm^-2 at 5 mV·s^-1. Results show the potential of the fabricated Cu₂O/Cu foam as binderless electrode for pseudo-type supercapacitors.

Abstract: Machine learning (ML) has recently made a major contribution to the fields of Material Science (MS). In this study, ML algorithms are used to learn atoms types over structural geometrical data of anatase TiO₂ nanoparticles produced at different temperature levels with the density-functional tight-binding method (DFTB). Especially for this work, Random Forest (RF), Decision Trees (DT), K-Nearest Neighbor (KNN), Naïve Bayes (NB), which are among the most popular ML algorithms, were run to learn titanium (Ti) and oxygen (O) atoms. RF outperforms other algorithms, almost succeeding in learning this skewed data set close to perfect. The use of ML algorithms with datasets compatible with its mathematical design increases their learning performance. Therefore, we find it remarkable that a certain type of ML algorithm performs almost perfectly. Because it can help material scientists predict the behavior and structural and electronic properties of atoms at different temperatures.

Abstract: The spokes of airless tire or non-pneumatic tire (NPT) are normally made with thermoplastic polyurethane (TPU), which is highly elastic material, to replace inflation pressure in conventional pneumatic tire. However there are limitation in designing of complex spoke geometries due to difficulty in manufacturing process, which normally involve molding process. Recently, the 3D printing technique has been improved and can be used to create highly complex geometries with wide range of materials. However the mechanical properties of printed spoke structure using 3D printing technique are still required to design and development of NPT. This research aim to study the mechanical properties of TPU while varying in printing conditions. The specimens were prepared from actual NPT spoke using waterjet cutting technique and 3D printing technique according to the testing standard ASTM D412 and D638, respectively. The tensile tests were performed on the specimens with corresponding crosshead speed. The testing speed of 3D printed specimen were also varied to 100 and 200 mm/min to study the effects of strain rate on mechanical properties. The stress-strain relationships were obtained from tensile testing and the important mechanical properties were then evaluated. The mechanical properties of specimens prepared from actual NPT spokes and 3D printed specimens were then compared. The ultimate stress of specimens prepared from actual NPT spokes in radial direction and 3D printed specimens with 100% infill were found to be 32.92 and 25.47 MPa, respectively, while the breaking strain were found to be 12.98 and 10.87, respectively. Thus, the information obtained from this research can be used to ensure the possibility in creating NPT spoke using 3D printing technique based on elastic material such as TPU.

Abstract: Due to a huge usage of plastics in the packaging industry, an abundant of plastics wastes is dumped at landfills. The environmental issue has given a serious impact to wildlife and humans. Hence, it is strongly advised to substitute the petroleum-based plastics with other plant-based polymers. One of the most popular bioplastics is polylactic acid (PLA). PLA can be biodegraded and recycled. The aim of this work is to investigate the effect of natural weathering ageing on the mechanical properties of virgin and recycled PLA. The investigation was focused on the tensile strength, transverse rupture strength (TRS) and impact energy. The samples were produced using the injection molding process. The samples were exposed to natural weathering continuously for 150 days. The sample inspection was monitored for every 30 days. The results showed that a decreasing in tensile strength of the recycled PLA was faster as compared to the virgin PLA. After 150 days exposed in natural weathering, there is about 41% reduction in the tensile strength of the recycled PLA. As for virgin PLA, the tensile strength is reduced approximately 11%. Similar trend was observed on the transverse rupture strength. The TRS for virgin PLA has dropped almost 14%. On the other hand, the TRS for recycled PLA declined at 17%. The diminishing in impact energy is more significant where it reduced 56% and 73% for virgin PLA and recycled PLA, respectively.

Abstract: Wood is the largest source of cellulose in the nature however it has a low strength. In other hand, bacteria cellulose as a pure cellulose has a higher tensile strength than wood. Wood reinforced with bacterial cellulose was produced by self-assembly approach with veneer soak into the fermentation medium. The product of this research is hybrid veneer processed thermos-hydro-mechanical treatment. It has been used to give a change in its mechanical properties. This research analyzed mechanical tensile test, Fourier transform infrared spectroscopy, and field emission scanning electron microscopy. The result showed that bacteria cellulose had impact to increase tensile strength of veneer and improve the molecular strength between cellulose fibers. Hydrogen bonds were formed between veneer fibers and bacterial cellulose then those bonds stick together and resulted in strong adhesion.

Abstract: The commercially available Curcuma mangga Val extract (CMVE) and poly (vinyl alcohol) (PVA) blends were studied by electrospinning. The result showed inadequate tensile properties of commercial CMVE/PVA nanofiber mats with very high modulus (220.0 MPa) and low strain (50%). The commercial CMVE was then replaced by a type of non-commercial CMVE to compare them with those of the commercial bandage. A non-commercial CMVE was prepared by simply extracting of the fresh Curcuma mangga Val (CMV) produced in a liquid extract. This non-commercial CMVE was then blended with 10% (w/w) PVA at various concentrations of CMVE (0, 2, 5, 10 and 15%) (w/w). The morphology and tensile properties of the mats were investigated. The findings indicated that the tensile strength and modulus increased with CMVE concentrations, decreased of the mean fiber diameter. In this study, a nanofiber mat with a concentration of 2% CMVE was selected and compared to others. This mat had lower average fiber diameter (187.50 nm), tensile strength (8.93 ± 0.36 MPa) and modulus (31.37 ± 4.91MPa), and higher tensile strain (90%) than the commercial CMVE/PVA. Compared to the tensile properties of the Hansaplast bandage, the current tensile strength was higher, the tensile modulus was equivalent and lower tensile strain.

Abstract: Extensive processes and costly precursors for the fabrication of existing sorbents for oil spills urges to look for more renewable sorbent sources. In this work, hollow, tubular, cellulosic fibers (kapok, Ceiba pentandra) were successfully converted to carbon sponges by pyrolysis at increasing temperature and time. Fourier Transform Infrared (FTIR) spectroscopy confirmed the complete carbonization of the kapok fibers at 800 °C. Scanning Electron Microscope (SEM) images revealed that the carbonized kapok fibers maintained their original tubular structures, suggesting high surface area. Water contact angle measurement showed improved hydrophobicity, with a maximum value of about 135°. The carbonized fibers were able to hold selected organic and oil solvents ranging from 16-20 times the weight of the fibers. The fiber pyrolyzed at 400 °C for 0.5 h showed the highest sorption capacity at 45.56 g/g for palm oil, almost matching that of raw kapok.