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Fatigue crack growth behaviour under intermittent overstressing was investigated in dry air with a low carbon steel under tension-compression and tension-tension loading with different mean stress levels. A very small number of cycles of overstress applied intermittently during a very large number of cycles of understress below threshold caused, in all cases, a significant acceleration in crack growth rate as compared to the case of steady cyclic stress. The acceleration for the case with tensile mean stresses was a little smaller than in the case without mean stress and it was related to a little higher crack closure level in the former case. Stress history in the precracking process had some effect on crack closure and, consequently, on the acceleration. A fairly good correlation was obtained between the acceleration and

Lightweight structures have widely been used due to their weight saving. Aluminum alloys are among the alternative for their material, and they are mostly manufactured by employing welding process using the same filler material as the base metal. Aluminum welding process can be conducted employing 2-layer semiautomatic MIG when the thickness of the plate is no more than 5 mm. Porosity in aluminum alloy welding is considerably difficult to avoid due to hydrogen and oxygen environment. Macro-micro analyses on 2-layer semiautomatic MIG welding of AA5052 material using ER5356 electrode have been carried out. A pair of AA5052 plates of 400 mm x 75 mm x 5 mm were clamped at three points of one side and welded using 2-layer semiautomatic MIG welding using ER5356 filler such that angular distortion can happen. Welding speed of 6, 7, and 8 mm/s using electrical voltage of 23 Volt, current of 130 Ampere, filler diameter of 0.8 mm, and shielded using argon gas. After completion of the welding, angular distortion was measured using dial indicator possessing accuracy of 0.01 mm. Welding result was micro-Vickers (VHN0.1) hardness, tension and Charpy impact, as well as micro structure using OM and SEM-EDS. The highest tensile strength was found at welding speed of 7 mm/s, angular distortion of 6.780, average VHN0.1 of the BM, HAZ, and WM of 47.82, 49.14, and 51.75, respectively. Tensile strength of 156.5 MPa and joint efficiency of 70%, BM failure strain of 17%, Charpy impact of 0.26 J/mm2. SEM-EDX at spot shows that the amount of Mg is not significant for being Al2Mg3 precipitate such that Vickers hardness distribution do not show any difference among BM, HAZ, and WM.

Simultaneous double-sided MIG welding as alternative method for joining the skin-stringer T-joints were investigated. The microstructure and mechanical properties of the welded joints were examined. Our study showed that a distance of 27-mm (torch to surface) results in the best weld appearance. Shorter distance produces higher heat input and causes the material stringers to melted with the filler, while longer distance increases the number of porosity and prevents the formation of a complete fusion zone.

Anodizing is one way of coating oxidation on aluminum, which is carried out by anodic oxidation at room temperature with the help of an electric current so that a chemical reaction occurs so that a layer is produced that can protect the metal from the effects of corrosion. The objective of this study was to determine the characterization of variations in electric voltage on surface hardness in the anodizing aluminum series 6. Specimens were made with dimensions of 50 mm × 25 mm with a thickness of 10 mm, then the cleaning process was carried out with a solution of sodium carbonate (Na 2 CO 3 ) with a concentration of 50 gr/100 ml of reverse osmosis (RO) water. The etching, desmut, and anodizing processes were continued with a solution concentration of 400 ml of sulfuric acid (H 2 SO 4 ) and 600 ml of RO water. The electric voltage variables used were 20, 24, and 28-V with a current of 2 A and an immersion time of 10 min. The results of the highest hardness test on a variable voltage of 20-V with a Vickers hardness value of 59.117 VHN. This proves that anodizing treatment on the surface of aluminum material with a variable voltage of 20 V will produce a high Vickers hardness value. These results indicate that the toughness of the material on the anodized specimen is also affected by the magnitude of the electric voltage.

The problems facing the world, in relation to the increasing consumption of petroleum and its limited sources, as well as pollution by fuel-related gases, such as CO, have sparked research on the application of biogasoline as an environmentally friendly alternative fuel. Our research aimed to determine engine performance through mixtures of biogasoline and gasoline to measure torque, power, and fuel consumption rate, and to determine the effect of the mixture on the level of air pollution. The biogasoline used was previously prepared from cooking oil through a Cr-zeolite-catalyzed process. The testing methods on the fuel mixture as a working substance included engine performance and exhaust emission tests, applied to four-stroke engines with mixtures with gasoline and biogasoline ratios of 95:5, 90:10, and 85:15. The engine performance test results showed that the highest values of torque, power, and average effective pressure were of the fuel with a composition of 85:15. CO and HC, the two emitted gases with high toxicities, based on the air quality standard, should not be more than 5.5% by volume and 2400 ppm, respectively. In this research, the findings indicated that both substances, not exceeding 3.0% by volume and not more than 200 ppm, respectively, are safe and environmentally friendly.

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The tandem metal inert gas (MIG) process uses two wires that are continuously fed through a special welding torch and disbursed to form a single molten pool. Within the contact tip of the modern approach, the wires are electrically insulated from one another. This study identified the effect of welding electrode spacing on the distortion of AA5052 aluminum plates and different mechanical properties including hardness and thermal cycle using grey relational analysis. Plate distortion was subsequently predicted using the grey prediction model GM (1, 6). This research used a pair of 400 mm × 75 mm × 5 mm of AA5052 plates and electrode distances of 18, 27, and 36 mm. The welding current, voltage, welding speed, and argon flow rate were 130 A, 23 V, 7 mm/s, and 17 L/min, respectively. The temperature was measured using a type-K thermocouple at 10, 20, 30, and 40 mm from the center of the weld bead. The smallest distortion at an electrode distance of 27 mm was 1.4 mm. At an electrode distance of 27 mm, the plate may reach a proper peak temperature where the amount of heat input and dissipation rate are similar to those for electrode distances of 18 mm and 36 mm. The highest relative VHN of 57 was found in the BM, while the lowest, 46, was found in the WM, showing good agreement with their respective grain sizes. Six parameters were designed using grey relational analysis (GRA) and subsequently employed in the grey prediction model GM (1, 6). Process evaluation results show that predictions for welding distortions are consistent with actual results, thus, the GM (1, 6) model can be used as a predictive model for welding distortions of 5052 aluminum plates.