Applied Mechanics and Materials Vols. 284-287

Abstract: Since the spot welding process was completed in a very short time and there were many factors affecting the generation of welding defects, it was difficult to control all experimental factors of welding. Additionally, it was hard to monitor the distribution of stress in practical cases such as vehicle bodies. The purpose of this study was to investigate the applicability of infrared thermography for the evaluation of spot weldability in the view of fatigue life. In this research, infrared(IR) stress analysis adopting an infrared thermography as nondestructive evaluation of spot weldability was investigated. Using temperature and IR stress distribution obtained by an infrared camera from adiabatic heat expansion under a repeated load of sinusoidal waves, we estimated the fatigue quality index(FQI) of spot welded specimens. We also evaluated in terms of FQI and corrected the S-N curve from the original fatigue life curve of base metals.

Abstract: In this study, fixed mole number proportion of CuCl, ZnCl2, SnCl2‧2H2O and sulfide compounds and the reacted solution are added to the autoclave, then the CZTS powders are prepared by changing the heating temperature and time. It is found from the experimental results that better result with less secondary phase can be obtained at the heating temperature 250°C and heated time of 36 hours.

Abstract: This is a preliminary study on the viscosity characteristics of polyalphaolefin (PAO)-based γ-Fe2O3 under zero magnetic fields. By varying the concentration of magnetic nanoparticles (MNPs), PAO-based γ-Fe2O3 with different concentrations were synthesized by co-precipitation method. The effect of this factor on the viscosity characteristic of γ-Fe2O3 (< 30 nm) was investigated on the basic of a series of rheological measurement. The use of oleic acid (OA) as a coating agent and surfactant was also investigated by varying its concentration. The results show the concentration of MNPs and the amount of OA has obvious effect on viscosity characteristics of PAO-based γ-Fe2O3. In the case of comparison between the concentrations of MNPs, higher concentration of MNPs increased the viscosity of the PAO-based γ-Fe2O3 and exhibit nearly Newtonian behavior. The large amount of OA also exhibits the increment on viscosity characteristic of MNPs. The experimental data were compared with the Bingham and Casson model and the results revealed that the rheology of the polyalphaolefin (PAO)-based γ-Fe2O3 fitted the Casson model better.

Abstract: Cationic magnetic nanoparticles are prepared by covalently binding spermidine and polyethylenimine onto the surface of nanoparticles via a glutaraldehyde coupling method. Nanoparticles modified by spermidine or polyethylenimine were characterized using Fourier-transformed infrared spectra, transmission electron microscopy and scanning electron microscopy. In this study, cationic magnetic nanoparticles were prepared by covalently conjugating cationic ligands onto the surface of nanoparticles. The plasmid DNA adsorption by the surface-modified magnetic nanoparticles was analyzed by Freundlich, Temkin, and Langmuir models. The maximal adsorption capacities in Langmuir model for polyethylenimine- and spermidine- modified nanoparticles are 341 and 116 μg/mg, respectively. Overall, the results demonstrated that the polyethylenimine-modified magnetic nanoparticles has the potential for purification of plasmid.

Abstract: The effects of annealing at various annealing temperature on hydrophobic AlN coatings were investigated. AlN coatings were deposited in Ar/N2 plasma by using reactive magnetron sputtering process. Two medium frequency (MF) powered Al targets were used. AlN coatings were annealed in air at 300°C, 600°C, 700°C, 800°C, 900°C, 1000°C and 1100°C, respectively. The hydrophobic and hydrophilic properties were evaluated by using water contact angle (WCA) measurement. Microstructure and morphology were observed using X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray Photoelectron Spectrometer (XPS), respectively. According to the results revealed by XRD and SEM, AlN possess hexagonal close-packed (hcp) structures and good crystallization. The morphology of AlN coating after annealing at 800°C is still similar to the as-deposited AlN coating. As the annealing temperature increases to 1000°C, the XRD peaks of Al2O3 phase can be clearly identified. The main XRD peaks of the AlN coatings still can be found after annealing at 1100°C. The as-deposited AlN coating exhibits hydrophobic behavior and the highest WCA of 119°. As the annealing temperature increases to 300°C, the WCA decreases sharply to 77°. The lower WCA of AlN coatings obtained after annealing is related to the Al2O3 thin films upon AlN coatings.

Abstract: We analyzed the degradation mechanism of GaInP/GaInAs/Ge triple junction solar cells without coating any protective film. Gradual degradation in the dark and light I-V characteristics of the solar cells were observed after the step stress accelerated degradation tests (SSADT) were conducted on these devices sequentially at 90, 110, 130 and 150°Cfor 25, 55, 85 and 135 hours, respectively. The recombination current in the depletion region at the chip perimeter of solar cells, resulting in the decrease of open-circuit voltage (VOC), fill factor (FF) and efficiency, is suggested to be the important degradation mechanism for GaInP/GaInAs/Ge triple junction solar cells.

Abstract: To provide a simple and fast alternative in measuring soil water content (SWC), a spectrometer was used to detect SWC because of different soil water contents, leading to different reflectance spectrums. Two commonly seen soil types in Taiwan are red soil and younger alluvial soil, which were used as test materials in this study. Fifty red soil samples and 50 younger alluvial soil samples were used as testing samples for comparative study. The root mean square error of SWC estimation of red soil and younger alluvial soil is 3.65 and 7.26, respectively. The results show that the estimation accuracy of red soil is higher than that of younger alluvial soil. The estimation error is random for red soil, and decreases exponentially for younger alluvial soil. Spectrometers have the potential to detect soil water content, especially in red soil. After full development of this technology, remote sensing will be applied to detect soil water content or even water-induced landslides.

Abstract: Dry machining is a clean machining process and it will be considered as a necessity for manufacturing industries in future. Dry machining is environmental friendly and safe to be performed. Regardless of decreasing tool life due to lack of lubricants, choosing dry machining over wet machining may be a wiser choice since the cost of purchasing and disposing the cutting fluids can contribute to a higher cost. Tool wear intensities of TiN and TiCN coated tools using both dry and traditional wet machining was studied with the aim in finding the optimum cutting speed from three different cutting speeds (318, 394 and 490 m/min) with a feed rate of 0.6 mm/rev and depth of cut of 0.4 mm. Tool tip temperature was also analyzed to see the effect of temperature rise at the tool-chip interface. TiCN coated tool performed better than TiN coated tool since the wear rate for TiCN coated tool is smaller by 40-48 % when compared to TiN coated tool for dry machining for all three cutting speeds. The optimum cutting speed for dry machining of T6061 Aluminium alloy using TiN and TiCN coated tools is 394 m/min. Tool tip temperature for dry machining is also slightly higher than wet machining by 19 and 32 % for TiN and TiCN coated tools respectively at the optimum cutting speed. Dry machining of T6061 Aluminium alloy can be a more suitable eco-friendly machining process particularly at high cutting speed for interrupted cutting operations.

Abstract: Molecular dynamic simulation for Fe sliding on Fe substrate with textured surface is investigated in this work. The textured surfaces on sliding are discussed to elucidate the physics of friction at the small scale. The modified embedded-atom method many-body potential is modeled to describe the interaction of Fe-Fe atoms. We find that a textured surface can reduce the friction because the former can entrap wear particles, effectively reducing the contact area. In addition, the friction force increases almost linearly in the low sliding speed with the increasing of sliding speeds. However, the friction force decreased as the increasing speed exceeds the 300 m/s.

Abstract: Intermolecular interactions are of fundamental importance to fully comprehend the formation mechanism of a nanostructure created by peptides. Four peptides, segmented from human neuropeptide Y (hNPY), were synthesized in this work to study the interaction between species. Information about intermolecular interactions was extracted from their self-assembly behaviors. The results from pulsed field gradient NMR data revealed that one of the peptides may undergo a more favorable self-assembly as temperature was increased, while other three peptides were found to form larger self-assemblies at lower temperatures and continuously dissociate into the monomeric form with increasing temperature. We characterized the changes of the oligomeric states with respect to temperature to infer the effects of entropy and interacting energetics on the self-assembly behavior. We demonstrated that an extended C-terminal helix may improve the binding of TFE, and as a result, entropy is gained via the transfer of the TFE cluster from the interface between monomeric peptides into the bulk solvent. This observation suggests that the self-assembly behavior may be modulated by the entropy and the energetics contributed by the helical segments in a self-assembly process.