Applied Mechanics and Materials Vol. 776

Abstract: Effect of addition of theobroma cacao peels extract (TCPE), a new proposed green inhibitor, on tensile and hardness properties, and related microstructure of mild steel exposed in solution of 1.5M HCl was investigated in order to know the contribution of this kind of inhibitor in controlling mechanical properties, in addition to reducing corrosion attack. Corrosion behaviors including inhibition mechanism and adsorption process during exposure were then discussed. Corrosion rate and inhibitory efficiency of mild steel samples containing 0.3%C were determined using weight loss method. The samples were exposed in the acid solution with and without addition of 0.5-2.5% the TCPE. Tensile and hardness tests were subsequently performed on the samples to determine the change of mechanical properties of the metal prior and after addition of the extracts. Sample surface morphologies and chemical composition as well were observed by a scanning electron microscopy equipped with energy dispersive X-ray spectroscopy (SEM-EDX). The results show that the strength, hardness and elongation of mild steel drop significantly due to heavy damage in the surface after immersion in the HCl solution for 32 days. However, these mechanical properties gradually increase with increasing concentration of the extract following the increase of surface coverage and inhibition efficiency. The increase of the tensile properties and hardness is due mainly to the ability of the inhibitor to cover mild steel surface through formation of metal-organo complexes protection layer in the surface of the mild steel. Although total carbon level in the surface of the mild steel also increases significantly, there is no any proof of carbon difussion into the mild steel. The addition of polar extract of theobroma cacao peels into a solution of 1.5 M HCl is, therefore, not only effective to minimize the degradation on the mild steel surface, but it also diminishes the mechanical properties reduction of the mild steel.

Abstract: This research is concerned with the effect of different carburizers on hardness distribution, effective case depth and microstructure of low carbon steel after pack carburizing process. Carburizers to be used were combination of energizer (BaCO₃), goat bone charcoal and bamboo charcoal with five different compositions. The specimens were heated to temperature of 950°C, soaked at the temperature for 4 hours and quenched in the water. After the process, microstructures of specimen were observed, the hardness was measured using Vikers method and effective case depths were calculated. The results obtained showed that for all types of carburizer used, the hardness were scattered from surface to the core with lower hardness level. Carburizer composition of 20% BaCO₃ + 80% goat bone charcoal produced the highest hardness ( 789.273 HV₁) at 0.2 mm from the surface, however, it yielded the lowest effective case depth (0.52 mm). The highest effective case depth of 1 mm was obtained using carburizer composition of 20% BaCO₃ + 60% goat bone charcoal + 20% bamboo charcoal. Meanwhile, the original structures of raw material which consist of ferrite and pearlite transformed to hard martensite constituent in the surface after pack carburizing.

Abstract: This study was designed to determine the effect of the solidification rate on the acoustic properties of the bronze alloy of 20% wt. Sn. Copper and commercially pure tin is melted in a furnace to a temperature 1000, 1100 and 12000C. The melted metal is poured into molds variation temperature of 200, 300 and 4000C. Materials castings were cut and machined for specimen damping capacity test. The results showed that the reduction in mold temperature leads to an increase solidification rate, which causes the shortness of the solidification time. The variation of the solidification rate affects on the morphology of the microstructure and acoustical properties of the material. By increasing the solidification rate influence on the secondary dendrite arm spacing (SDAS) decreases. It causes the material hardness increases and the damping capacity of material decreases. There is a significant correlation between the material hardness and the damping capacity of materials.

Abstract: This study was aimed at evaluating morphological and crystalline structures of anodic and hydrothermal titanium oxide thin films formed on Ti6Al4V alloy in a mixture of glycerol phosphate disodium salt (GP) and calcium acetate (CA) solution at various forming environments such as CA molarity and applied voltage. Anodic oxide films were hydrothermally treated and their morphological surfaces, crystal structures and chemical compositions were characterized. It was found that TiO₂ film was formed in all surfaces of Ti6Al4V alloy specimen with porous and rough morphology and the crystal structures were mainly anatase. The anodized film morphology and the crystals structure were dependent on CA molarity and anodizing voltage. Increasing CA molarity from 0.15 to 0.30M increased the number and size of micro porous and the intensity of anatase crystals, but further increasing to 0.45M, the number and size did not change and the intensity of anatase peaks became weak. Except in 0.45M-CA, the number and size of micro porous and the intensity of anatase crystals increased gradually with increasing anodizing voltage. Ca-P crystals were precipitated on the surface of hydrothermally treated films. CA molarity associated to the crystal shape while anodizing voltage related to the amount and size precipitated crystals. CA molarity was also associated to the atomic compositions of Ca and P that precipitated on the hydrothermally treated surface film.

Abstract: The cement industry has remarked as an intensive consumer of energy. The amount of energy consumed in the cement manufacturing has a correlation to the increasing of CO2 emission. It is reported that the cement Industry has contributed to 5–7% of the total CO2 emission in the world. Thus, there is a need to make an innovation in order to overcome the environmental problem. One of effort can be made is by using chemical grinding aids (CGA) as an additive material in the cement production process. This study aimed to determine the optimal clinker factor of the cement production by the addition of chemical grinding aids (CGA). The experiments are conducted in PT Semen Padang consisting of four variable of the clinker factor without CGA and with CGA addition 300 ppm. The clinker factor varies from 78.3% to 72.9%. The results show that the optimal clinker factor is at 74.5% with the CGA addition 300 ppm. It can improve the cement fineness to 3848cm2/gr and decrease the sieving R45μ to 10%. In addition, the strength of the cement produced is higher than the standard. The findings show the chemical grinding aids (CGA) addition in the cement production process can reduce the clinker factor as well as reducing the CO₂ emissions. It can aid the cement industry to achieve the higher performance in green manufacturing and so as to increase the competitiveness.

Abstract: In rolling-sliding contact, wear will occur when the accumulated plastic shear strain of the material at the surface exceeds its critical shear strain for failure. During rolling-sliding contact, the difference in relative velocities of two contacting components can cause slip in the contact (known as creep). The higher creep ratio may increase the severity of wear. In this work, the wear rate of the material and the behaviour of material just below the contact surface in rolling-sliding contact with various creep ratios were investigated. The carbon steel (about 0.65% C) was chosen as the test material and wear test was conducted using disc-to-disc contact testing machine with the maximum contact pressure of 1000 MPa and with various creep ratio of 1%, 5% and 7%. The results show the higher creep ratio causes the material to accumulate critical shear strain more quickly, resulting in the increase of wear (i.e., from about 0.0047μm/cycle for creep ratio of 1% up to about 0.0077μm/cycle for creep ratio of 7%). .

Abstract: The Finite Element model of Vickers indentation has been developed. The model was validated against published testing data. An approach to predict the P-h curves from constitutive material properties has been developed and evaluated based the relationship between the curvature and material properties and representative stress. The equation and procedure established was then successfully used in predict the full Vickers indentation P-h curve. FE Spherical indentation models of different radius have been developed and replay file model was developed that is able to produce data of different materials properties. Two new approaches to characterise the P-h curves of spherical indentation have been developed and evaluated. One is the full curve fitting approach while the other is depth based approach. Both approaches were proven to be adequate and effective in predicting indentation P-h curves. The concept and methodology developed is successfully used to predict hardness values (HV and HRB) of materials through direct analysis and validated with experimental data on selected sample of steels. The approaches (i.e. predict hardness from P-h curves) established was successfully used to produce hardness values of a wide range of material properties, which is then used to establish the relationship between the hardness values (HV and/or HRB) with representative stress. This provided a useful tool to evaluate the feasibility of using hardness values in predicting the constitutive material parameters with reference to accuracy and uniqueness by mapping through all potential materials ranges

Abstract: The application of steel products have been widely used and various research have been developed to find a good and appropriate quality of steel and can be produced in the country without have to be imported, for example alloy steels. One of the alloy steels that have been constantly developed is Ni-Cr-Mo alloy steel with additional nickel, chromium and molybdenum which can increase hardness, tensile strength, ductility and toughness. The effect during the production process is at the heating process that causes the formation of iron oxide layer (scale) and the loss of steel weight. Therefore, the selection of heat treatment methods and techniques are required to increase the mechanical properties of steel, such as hardness, tensile strength, and toughness, with the scale is about <5% of steel weight. In this research, the heat treatment was carried out at austenisation temperature of 800°, 850°, 900°C and at holding time of 20, 40, 60 minutes, then followed by a rapid cooling (quenching) to improve the mechanical properties of hardness. This research also tested the mechanical properties of steel that consist of hardness test and impact test, and metallographic observation that consist of micro structure observation and scale thickness observation. The micro structure from heat treatment process is martensite, it is due to a rapid cooling (quenching) that rapidly change the austenite phase into martensite. The data showed the highest hardness is 588.35 HVN at 850°C of temperature and 60 minutes of holding time, 8.5 Joules of impact energy, and 91.5 μm of scale thickness. While the lowest hardness is 539.34 HVN at 800°C of temperature, 5 Joules of impact energy, and 47.81 μm of scale thickness.

Abstract: Al/(SiCw+Al₂O₃p) composite was a blend of fine aluminum powder serving as a matrix while Silicon Carbid whiskers (SiCw) and Alumina (Al₂O₃p) as a reinforcement. Powder metallurgy was used for the manufacture of composites according to the shape of the test specimen. Parameter testing was conducted with varied sintering holding time of 1 h, 3 h and 6 h at a sintering temperature of 500°C and 600°C. This study was conducted to know hardness properties, density, porosity and SEM analysis. The results show that the sintering process which has been conducted affects the physical and mechanical properties of the composite. Increased hardness and density occur due to the stronger or more dense interface bonding between matrix and reinforcement which are affected by the increase in the holding time and sintering temprature, where the highest is at 6 hours with 600°C, while the porosity decreases inversely proportional to the density and the hardness that occur in composite materials.

Abstract: This research has been carried out in order to analyse the possibility of fiberglass woven roving used as an alternative material for the hull of of fishing boat. The standard used in this analyzing process was the Standard of Biro Klasifikasi Indonesia (BKI), especially to find how the forces applied to the boat. Once the forces were found, they would be applied to justify the possibility mentioned above. The justification process was done by theoretically analyzing the mechanical properties of some fiberglass woven roving composites using mathematical software. The composites have been made by varying the mixture volume fraction between 0% - 100% within 10% interval, fiber orientation angle between 0^o – 90^o within 5^o interval, and then the results which met the requirements according to BKI Standard would be justified by the results obtained from experimental analysis. Based on the experimental analysis results, it could be stated that the fiberglass woven roving with composition of 40% - 60% and fiber orientation angle 0^o can be used as an alternative material for the hull of fishing boat.