Applied Mechanics and Materials Vol. 835

Abstract: Steel sheet joining were dominantly by resistance spot welding (RSW) method. It is the most implemented in automotive mass production in which the heat is applied to the materials. Joining different material with different properties is a challenge. Thicker material needs more current and time. Meanwhile, the thinner material may burn and weaken if the excessive parameters apply. The purpose of this study is to identify the optimum spot weld parameters for joining dissimilar materials with different thickness that involve high tensile strength steel and low carbon steel in the automotive application. In this study, weld parameters with varying electrode forces, welding currents, and welding times are analyzed by applying a Taguchi robust method for the design of experiment (DOE). The L9 orthogonal array has been chosen due to the particular material specimen and time constraint. In the analysis, the higher value of signal-to-noise (S/N) ratio indicates the good responses of testing parameter when the level changed. Base of the plotted S/N ratio graph for each factor, Taguchi robust method has suggested that A3 (5000V), B3 (25 cycle), and C2 (150N) as the optimum weld parameters. The confirmation test afterward, finally proved that the Taguchi robust method was a liable DOE method and has been successfully optimized the spot weld parameters.

Abstract: Rapid prototyping (RP) has been known as one of the advanced technology that grows tremendously over the few years. Fused Deposition Modeling (FDM) is one of the RP technologies, which is commonly used in producing three dimensional products. The study focus on the effect of dies angle in FDM nozzle and finds the optimum angle know as natural convergent angle (2θ_o).Polylactic acid (PLA) has been chosen as the material due to lots of advantages including biodegradability and acts as the base material for reconstructive structure for bone material. Extruding PLA material effectively is utilized under simulation method and the data obtain has been recorded. Die angle has been varied from 80^o until 160^o and it shows a different effect in pressure drop. Pressure drop need to be observed as it affects the road width of scaffold design, thus affecting the quality of the extruded part. The natural convergence angle (2θ_o) should be closed as to the die angle (2α) in order to get stability and consistency scaffold design. The natural convergent angle is found at 130^o and can be considered as optimum die angle.

Abstract: By method of dynamic calorimetry, in the temperature range between 298,15 and 673 K, isobaric heat capacity of polycrystalline ferrites Bі₂СаFe₄O₁₀, BіMgFe₂O_5.5, Bі₂MgFe₄O₁₀ was experimentally studied. Mathematical processing of experimental data made it possible to derive polynomial equation of temperature dependence of ferrites heat capacity for respective temperature ranges, in dependencies C⁰_p~f (T) of ferrite Bі₂СаFe₄O₁₀ a jump was detected in heat capacity at 625K associated with phase transitions of type II. The values of the thermodynamic functions C⁰_p(Т), H⁰(T) – Н⁰(298,15), C⁰(T), F^hh(Т) have been calculated. Standard values of thermodynamic functions were determined using the method of ion increments. The results obtained broaden thermodynamic data bank for complex inorganic crystalline compounds.

Abstract: The purpose of this research is to investigate the optimum conditions of cationization on hemp fabric which affect staining with natural dye solution extracted from Arabica coffee ground. For this work, three conditions for cationization on hemp fabric were investigated including temperature, time and concentration of cationic with liquor ratio of 1:100. Then, the cationized fabrics were dyed with 50% on weight fabric (owf) of coffee ground dye at 90°C for 60 min by using liquor ratio of 1:100. Dyed fabrics were measured color strength (K/S value) and color value (CIELAB color-different value) to indicate staining and to compare to non-cationized hemp fabric. It was found that the optimum conditions of cationization on hemp fabric for staining were 5%owf of cationic concentration at 90°C for 30 min providing the highest K/S value.

Abstract: The isolation of microcryostalline cellulose (MCC) from rice husk (RH) via acid hydrolysis process has been successfully prepared by using different molarity of nitric acid (HNO₃) and hydrochloric acids (HCl). The properties of MCC obtained such as tapping and bulk densities, thermal stability and percentage crystallinity were studied. Tapping and bulk densities shown comparable results regardless of different acid used that reflecting the potential of MCC as reinforcement filler in composite fabrication. The usage of 2M HNO₃ gives highest percentage crystallinity (69%) in comparison with 2M HCl (49%). The result indicates the stability of MCC-RH obtained using HNO₃ has great potential to replace strong acid in acid hydrolysis process.

Abstract: The poly (ethylene terephthalate)/poly (trimethylene terephthalate) (PET/PTT) blends were prepared and their phase morphology, mechanical and thermal properties were investigated by scanning electron microscopy (SEM), polarized optical microscopy (POM), universal material testing machine, differential scanning calorimetry (DSC), wide-angle X-ray (WAXD), respectively. The glass transition and SEM results suggest apparently that the PET and PTT have good miscibility at amorphous state. The blends with more PET content less likely undergo a melting/recrystallization process during DSC heating scan. In the blends, PET component with higher supercooling degree crystallizes first, and then the crystallites of PET will be the nucleating agents for PTT, which greatly improves the crystallization rate of PTT. Because of the interaction between the PET and PTT, there are much smaller spherulites formed in blends with increasing PET component. The blend with more PET contents has larger tensile strength and modulus.

Abstract: The effects of the montmorillonite clay surface modified with 25-30 wt% of methyl dihydroxyethyl hydrogenated tallow ammonium (Clay-MHA) on morphology and mechanical properties of poly(lactic acid) (PLA)/acrylonitrile-butadiene rubber copolymer (NBR)/Clay-MHA composites were investigated. The composites of blends of PLA/NBR with Clay-MHA were prepared by melt mixing in an internal mixer and molded by compression molding. The ratio of PLA and NBR was 80/20 by weight and the Clay-MHA content was 1, 3, 5 and 7 phr. The results showed Young’s modulus and stress at break of the composites increased with increasing Clay-MHA content. While the tensile strength and strain at break of the composites decreased with increasing Clay-MHA content. Scanning electron microscopy analysis showed that the addition of Clay-MHA could improve the miscibility of PLA and NBR to be homogeneous blends and the pore in polymer blends was disappeared.

Abstract: Coconut shell-based activated carbon (CSAc) was prepared by chemical activation method using microwave-induced KOH technique. The activation process was successfully carried out with varying microwave power ranging from 100 to 1000 W and impregnation ratio of 1.0 to 3.0. The surface area, pore sizes, surface morphology and specific capacitance of the produced activated carbon were analyzed by using an automatic quantachrome instrument (Autosorb1C) volumetric sorption analyzer, scanning electron microscope (SEM) and automatic battery cycler. The optimum activation power and impregnation ratio were found at 600 W and 1.5, respectively. The resulted product, C3 has maximum surface area and specific capacitance value of 1768.8 m² g^-1 and 156.33 F g^-1 respectively, with carbon yield of 58 %.

Abstract: The pyrolysis kinetics of the Jordanian Lajjun oil shale kerogen was investigated inside a TGA reactor. Kerogen samples (extracted by mineral digestion) were non-isothermally heated at rates varying from 1 to 50^°C/min under 350-550C in N₂ atmosphere. Friedman, Kissinger-Akahira-Sunose (KAS) and Flynn-Wall-Ozawa (FWO) models were employed to estimate the kinetic parameters at isoconversional points ranging from 0.1 to 0.9. The value of the calculated apparent activation energy (E) was found to vary with both the employed model and the conversion (x). Using the three models, the calculated increased with from 10 to 30% (low level), and then decreased with from 30 to 60% (medium level). At high level (60 to 90%), however, increased with increase using both KAS and FWO models, while it continuously dropped with increase using Friedman model. The frequency factor (k₀) calculated form each model was found to linearly correlate with E. Compared to KAS and FWO models, Friedman' provided a more accurate fit to the experimental data.

Abstract: In this paper, we report the first principles Density Functional Theory (DFT) calculation to study the structural, energetic, and electronics properties of the 6–Bromo–4–Oxo–4H–Chromene–3–Carbaldehyde, C₁₀H₅BrO₃ molecular framework. Geometry optimization technique was carried out to find the local energy minimum of the title compound using four hybrid DFT functionals with the basis set of 6–311++G**. The optimized molecular structure of C₁₀H₅BrO₃ cluster was then used to determine the HOMO–LUMO gaps, Molecular Electrostatic Potential (MEP), Mulliken atomic charges, and others. Using the four hybrid DFT techniques, the optimized geometries of C₁₀H₅BrO₃ molecular cluster is close to that of measurement data. Our calculation results also show that the total energies obtained are close to each other with the four hybrid DFT procedures. The diagram of electrostatic potential surface show that the regions of negative electrostatic potential around the oxygen atoms, O₁ and O₂. Using the scheme of Mulliken Population Analysis (MPA), the distributions of atomic charges follow the same arguments for the B3LYP/6–311++G**, B3PW91/6–311++G**, M06/6–311++G**, and PBE1PBE/6–311++G** simulation approaches. For example, the atom of C₅ has the highest positively charge, whereas the highest negatively charge was found in the C₄ atom. For Br atom, the atomic charge values obtained are –0.158, –0.222, –0.277, and –0.224, respectively for the B3LYP/6–311++G**, B3PW91/6–311++G**, M06/6–311++G**, and PBE1PBE/6–311++G** computational methods.