Applied Mechanics and Materials Vol. 493

Abstract: Dual phase steels are an important advanced high strength steel, which have been widely used in the automotive industry for vehicle components requiring light weight and safety. In this study, the formation of dual phase structure with various volume fraction of martensite in a low carbon steel SS400 during intercritical annealing were investigated. It was found that intercritical annealing temperature and holding time affected the microstructure and mechanical properties of dual phase low carbon steel. The specimens were heated at intercritical annealing temperature of 750°C, 775°C, 800°C and 825°C, for holding periods of 6-18 minutes, followed by water quenching in order to get a dual phase ferrite and martensite. After quenching, it was obtained the optimal annealing conditions at 800°C with a holding periods of 10 minutes. In this condition, the tensile strength was increased up to 621 N/mm² or 39.24% higher than the initial condition, while the elongation decreased up to 13.8%. The hardness of specimens increased from 127.7 to 235.83 HVN or up to 84.67% higher than the initial condition. Meanwhile the volume fraction of martensite was 24.08%. The higher the temperature of the heating value of grain growth rate constant (K) increases. In addition, at the optimal poin, the value of K (grain growth rate constant) and n (Avramis exponent) were 0.263 and 0.318, respectively, with activation energy (Q) of 3.98 J/mol.

Abstract: This study is aimed at investigating the performance of saramet compared to other austenitic stainless steel (SS) types. Saramet is a type of austenitic SS which contains Silicon (Si) higher than others. The research treatment was divided into 2 activities which were at room temperature and high temperature. The material used were saramet, SS 304 and SS 316L. Corrosion test was conducted by using weight losing method and electrochemical. The findings show that saramet is more resistant to corrosion compared to SS 304 and SS 316L both at high and room temperature. Saramet has better performance at high temperature.

Abstract: This study investigates the variation of sulphuric acid concentration, temperature, and time towards the corrosion rate of saramet using response surfacemethod. Method used in this study is true experimental research. Sarametis material which is included into type of austenitic stainless steel which contains high amount of silicon. Starting at these past 2 years, the material has been widely used.This research used weight loss method. It has been found that minimum corrosion rate is achieved at concentration combination of 89.49% in 3.682 hoursandat temperature of 106,8 °C. From the variation combination, it is seen that the low concentration will decrease ion mobility corrossive ion from saramet.The long period of exposure supports the forming of passive layer which prevent the corrosive ions gets into the steel surface. As a result, corrosion rate decreases. At high temperature, steel which has high silicon content will be stable in terms of its atomic bound which therefore makes it posses high corrosion resistance.

Abstract: Technology of Friction Stir Welding (FSW) is a relatively new technique for joining metal. In some cases on Aluminum joining, FSW gives better results compared with the arc welding processes, including the quality of welds and less distortion. The purpose of this study is to analyze the parameters effect of high speed tool rotation on micro Friction Stir Spot Welding (μFSSW) to the shear strength of welds. In this case, Aluminum material A1100, with thickness of 0.4 mm was used. Tool material of HSS material was shaped with micro grinding process. The spindle speed was fixed at 30000 rpm. Tool shoulder diameter was 3 mm, and a length of pin was 0.7 mm. The parameter variations used in this study were the variable of pin diameter (1.5 mm, 2.0 mm, and 2.5 mm), a variable of plunge speed (2 mm/min, 4 mm/min, 6 mm/min), and the variable of dwell time (2 seconds, 4 seconds, 6 seconds). Where the variation of these parameters will affect to the mechanical properties of welds (as response) was the shear strength. Response Surface Methods (RSM) was used to analyze μFSSW parameters with the shear strength of welds. From the result of experiment and analysis, it is shown that the important welding parameters in high speed μFSSW process are pin diameter and plunge speed.

Abstract: A new method of prediction based on smooth support vector regression (SSVR) is introduced to resolve the slump flow modelling of self-compacting concrete (SCC). The slump flow is a function of the content of all concrete ingredients, including cement, silica fume, water, superplasticizer, coarse and fine aggregate. In this paper, the basic ideas underlying SSVR are reviewed, and the potential of the SSVR for multiple regression (modelling) problems is demonstrated by applying the method to model of slump flow from experimental data. The results of experimentation indicate that SSVR has excellent performance on slump flow prediction. Compared with traditional prediction method such as second order regression, SSVR has much more accurate and effective to prediction of slump flow and it is very promising result.

Abstract: Hydrophobic silica coating on copper (Cu) has been successfully prepared byelectrophoretic deposition (EPD) of silica sol prepared from waterglass. trimethyl chlorosilane (TMCS) was used as the modifying agent to produce hydrophobic coating by replacing the silanol groups on the silica surface with alkyl groups. The hydrophobicity was indicated by the contact angle of water droplet on the coating surface. It has been shown that TMCS concentration plays an important role in the preparation of hydrophobic coating. However, higher concentration of TMCS made the copper corroded before coated with silica due to the production of Cl-ions when TMCS reacted with water and silanol groups during electrophoretic deposition. In addition, the electricfield intensity, silica concentration and deposition time also influence the hydrophobicity of the coating. Increasing the three parameters produces silica coating with higher hydrophobicity. Thecontact angle of the silica coating can reach 130°. EIS analysis showed that the silica coating is very porous.

Abstract: Plasma nitriding is a widely used technique to improve the mechanical properties and tribological properties of AISI 316L steel because it has many advantages over other surface treatment techniques. One of this advantage is plasma nitriding allows nitrogen introduce to steel at low temperature (below 500°C).In this study, nitriding of an AISI 316L was performed in high density plasma nitriding system using 70%N₂:30%H₂ gas mixture at 400°C and 480°C for 2, 4, and 8 hours. Optical Emission Spectroscopy (OES) with optical probe was used for plasma diagnosis. The properties of nitrided sample were investigated through microhardness measurement. The results show that N₂ ions and radicals are species predominantly formed in plasma.

Abstract: The oxidation kinetics of hot-dip aluminized AISI 1020 steel with Na₂SO₄ deposit was investigated at 700 °C for 49 h in static air. The scale morphologies were observed by means of metallograpy, scanning electron miscroscopy (SEM), electron dispersive spectroscopy (EDS) and X-ray analyses. The accelerated oxidation of aluminized steel was attributed to the formation of aluminum-sulphides which allowed the rapid diffusion of Fe ions in the aluminide layer to the formation of iron oxide. In addition, the Al-sulphides precipitations in the alumina scale causes the Al-depletion such that Al₂O₃ layer fails to form a protective layer. Consequently, the kinetics rate of aluminized was increased.

Abstract: Korea is expected to one of countries with water shortages, and thus must secure high-quality water resources and strictly maintain them. However, water is frequently polluted and there is still a lack of water treatment technologies and facilities to provide safe water. To remove pollutants, membrane-based methods are being widely used for water treatment. It needs high pressure and energy to capture the pollutants by pore size. In this study, electrostatic force is used to increase the efficiency of filtration and decrease pressure loss. By electro spinning, nanoelectret filter is made with 100 nm in diameter and positive charge potential. Surface potential is measured by electrostatic voltmeter system with nanoelectret filter by three conditions of applied voltage. For the filtration performance, filtration efficiency is measured by filter test system with 0.5 and 1.0 PSL. Also pressure loss of nanoelectret filter is measured by comparing PC membrane.

Abstract: Critical strain energy release rate in CFRP composites characterizes the delamination resistance. More study is still needed to measure the critical strain energy release rate in sliding shear mode (G_IIC) considering various factors that influence its measurement. This study evaluates one of the influencing factors, the starter defect. Two types of on thin, unidirectional CFRP composites with one having thin film insert as starter defect and another one with pre-crack under Mode II loading were prepared and tested in three point bending end notch flexure (3ENF) test. It was found that the (G_IIC) of the former was more than twice higher than that of the latter, supposedly due to the presence of resin rich region in the former.