This paper aims to investigate the joining of polypropylene using friction stir welding (FSW). FSW parameters were the rotation speed of 620 rpm, the travel speed of 7.3 mm/min, and 13 mm/min. The tensile test was performed using a universal testing machine, and the results of the tensile test were related to the crystallite size and degree of crystallinity. X-ray diffraction (XRD) was performed to examine the crystallite size and degree of crystallinity while thermal analysis was carried out using TGA/DSC. Besides, the effect of the degree of crystallinity on the thermal stability at the weld nugget area due to travel speed is explained in this paper. The findings showed that FSW with a travel speed of 7.3 mm/min had a higher crystallite size and degree of crystallinity than that with a travel speed of 13 mm/min, because there is a fusion of crystals and also recrystallization occurs, as an effect of the difference in the length of time exposed to heat during the FSW process. From the study results, it can be seen that the FSW with a 7.3 mm/minute travel speed has a higher crystal size and degree of crystallinity compare with the use of 13 mm/minute travel speed. The reason for that, the difference in heat exposure time during FSW affects crystal fusion and recrystallization. A sample with a travel speed of 7.3 mm/min had high tensile strength because it obtains sufficient heat for a more complete joint. In terms of thermal stability, the specimen with a lower travel speed showed a higher stability level than the specimen with a higher travel speed in that of the higher degree of crystallinity.
The effects of preheat temperature on mechanical properties and the microstructure of friction stir welded (FSW) aluminum alloy 5052 joints were studied in the present work. Heated air from Hot Gun was applied in front of the FSW tool to give the preheat on friction stir welding process. Preheat temperature was set 150°C, 250°C and 300°C. Mechanical properties were correlated and analyzed according to tensile strength, macro and microstructure. Defect free weldswere obtained at all preheat variations. The increasing preheat temperature produced the coarser grain size, it influencedthe little decrease both the tensile strength and hardness of joints.
This study aims to investigate the influence of weather exposure on the physical and mechanical characteristics of rHDPE matriced composites reinforced with zalacca midrib fibers. The specimens were fabricated using the compression molding method into 3 variations which include the neat rHDPE as control as well as the untreated and alkaline-treated zalacca fiber-reinforced rHDPE composites at 30 % vf. Moreover, the weathering exposure was conducted under a tropical climate for 6 months after which all the specimens became chalky and showed significant changes in color. The FTIR results indicated that carbonyl groups of rHDPE emerged due to the weathering exposure while the thermogravimetry test showed no significant change in thermal stability. It was also discovered that their flexural and impact strength were enhanced by the alkaline treatment but the effect diminished after weathering. The micrograph observation showed some gaps between fibers and matrix, breakage of the fibers and matrix bonds, and cracks on matrix around the fibers. Furthermore, the fracture of the neat rHDPE was observed to be more brittle after exposure and this means the neat rHDPE and rHDPE-ZF composites are suitable for indoor applications but not recommended for outdoor uses.
Di masa pandemi COVID-19 seperti sekarang ini, dianjurkan untuk selalu menaati protokol kesehatan. Salah satunya adalah dengan menggunakan masker. Penggunaan masker pada atlet, khususnya atlet difabel memiliki dampak yang buruk bagi tubuh atlet itu sendiri. Karena dalam keberjalanan latihan, para atlet akan melakukan pekerjaan yang berat, sehingga membutuhkan suplai oksigen yang mencukupi. Dalam kasus ini, masker dapat menyebabkan berkurangnya efektivitas pernapasan atlet karena terjadi hypoxia. Hypoxia merupakan kondisi di mana tubuh kekurangan kadar oksigen. Untuk mencegah hypoxia pada atlet yang harus tetap melaksanakan latihan dengan protokol kesehatan COVID-19 adalah dengan menggunakan masker yang dapat mengatur sirkulasi udara dengan baik. Oleh karena itu, muncul sebuah ide untuk membuat masker aerator yang dapat membantu sistem pernapasan dan dapat mencegah atlet terkena gangguan hypoxia selama latihan di kala pandemi, karena masker aerator yang dibuat ini dilengkapi dengan dual fan yang dapat menyuplai oksigen dengan baik, sehingga atlet dapat melakukan latihan tanpa takut mengalami gangguan hypoxia dan tetap patuh dengan protokol kesehatan.
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