Applied Mechanics and Materials Vol. 377

Abstract: In the present paper, sulfur, RE (rare earth) and bismuth were added to an austenite stainless steel. Low environmental impact machining processes of free cutting austenitic stainless steels was investigated by machinability testing. The results show that a significant amount of grey and dispersed inclusions were found in steel B. The inclusions are typical sulfide inclusions, and bismuth element is attached to double end of manganese sulfide inclusions. Some inclusions exhibit globular shape due to the presence of rare earths elements in steel B. Chip morphology was improved in steel B under the same turning conditions. The machinability of steel B is much better than that of steel A. This is attributed to the presence of free-cutting additives of sulfur, RE and bismuth in the austenitic stainless steels. Satisfactory mechanical properties were also obtained under the conditions of our experiments. The reasons why satisfactory mechanical properties were obtained may lie in that the sulfides and bismuth are soft phase, and the presence of rare earths elements contributes to the improvement of the toughness of the austenitic stainless steels.

Abstract: Acrylic is easy to machine. In addition to the advantages derived from the use of mill Computer Numerical Control (CNC) machine on acrylic sheet, there are at least two serious problems that need attention especially in cutting a small part with many vertices. These problems are the presence of excessive heat due to friction between the cutting tool with acrylic sheet on high RPM of spindle rotation, and soft acrylic flakes trapped in crevices of the cutting tools’flute.Generally, the cutting process using a mill CNC machine often is a practice of trial and error. At least nine basic technical parameters need to be optimized. The effectiveness of the parameter values are determined by observing and measuring the actual cutting time using mill CNC machine at given parameter settings, surface texture quality, the level of clarity of the cuts, characteristics of chip formation, and edge roughness.The experimental results showed that the adhesion of acrylic sheet and cutting tools is relatively low. However, the heat of cutting tool due to high spindle rotation, low feed rate, and relatively low melting point of acrylic, tend to form very small, soft, and hot flakes. The acrylic chips have great potential entering the crevices of cutting tools’ flutes, and reducing the cutting power significantly. In other condition, the cutting tool could even be broken if feed rate is too high. Some technical values of these parameters are recommended to obtain optimal CNC based cutting operation and surface quality on acrylic sheet.

Abstract: In the present paper, controlled cooling of Fe-C-Mn-Si multiphase steel was conducted by a laboratory hot rolling mill. The results show that polygonal ferrite, granular bainite and the stable retained austenite can be obtained through hot deformation and subsequent two steps cooling pattern. The amount of ferrite increased with the duration of intermediate air cooling during controlled cooling. The formation of the bainitic ferrite resulted in the carbon concentration enrichment in austenite further during the simulated coiling. This increases the stability of the remaining austenite. Satisfactory mechanical properties can be obtained through hot rolling process and two steps cooling pattern in this work due to the TRIP effect of the stable retained austenite.

Abstract: Rare earth elements (REE) are harmless for human health. REE addition contributes to the improvement of the machinability of the steels. In the present paper, machining characteristics of austenitic stainless steels without lead addition were investigated by adding free-machining elements, such as sulfur, REE and bismuth. The results have shown that large numbers of rounded, globular shaped inclusions were obtained for both steels. The machinability of steel B is better than that of steel A, and the cutting forces of steel B are lower than those of steel A at various cutting speeds. Lead can be substituted by REE and bismuth in free machinable austenitic stainless steels. REE significantly affects machining characteristics of austenitic stainless steels without lead addition. The mechanical properties of both steels were similar, and their fracture exhibited ductile characteristics. Satisfactory machinability and mechanical properties can be obtained for both steels.

Abstract: The injection molding process of plastic parts is simulated and analyzed through a three-dimensional model of bottom cover of USB (Universal Serial Bus) extender obtained by Pro/E software and MPI module of Moldflow software. Orthogonal test is applied to analyze the influence of press time, press pressure, mold temperature and melt temperature on the warpage of plastic parts. Those being influenced by factors above are listed in order as press pressure, melt tempreture, mold tempreture and press time. The optimum parameters are obtained by analyzing effect trend that the four factors can influence on warpage.

Abstract: This study investigates the optimal charge and discharge capacity of the sintering process on the lithium battery spinel - LiMn₂O_4. Both Li₂CO₃ and Mn₃O₄ are utilized to synthesize the cathode material LiMn₂O₄ using the solid-state reaction. Cathode materials are processed to fabricate batteries at temperatures ranging from 800°C to 900°C. Test results reveal that the highest initial discharge capacity of 105.19 mAhg^-1 (theoretically at 148 mAhg^-1) has been obtained at the temperature of 850°C in the sintering process for synthesis of LiMn₂O₄. In addition, the initial discharge capacity can be increased to 140.51 mAhg^-1 with both overdosing the amount of lithium by 2% and increasing the range of operating voltage. The increasing of the charge voltage ranges from 4.5V to 4.8V and reducing of the discharge voltage ranges from 3.0V to 2.8V.

Abstract: A novel green-emitting phosphors Tb³⁺-doped LiLa2BO5 phosphor was synthesized by different methods: the solid-state reaction method and solgel method. The green phosphor was characterized by XRD. The green phosphor has a dominant excitation peak located at 280nm. The emission intensity was enhanced by Tb³⁺ doped ion, and decreased due to concentration quenching. Under the excitation wavelength of 280 nm, the relative intensity of the solgel derived phosphor is about 81% of solid-state reaction derived phosphor. The intense green emission of LiLa2BO5 under 280nm excitation suggests that Tb³⁺ -doped LiLa2BO5 phosphor is a potential green phosphor for near-UV LEDs.

Abstract: Ultrafine spherical yttrium aluminum garnet (YAG) powders have been synthesized via homogeneous precipitation method using urea as the precipitant. The precursor powders were calcinated at 1000°C or 1100°C for 4 hrs and then were studied by means of FE-SEM, XRD, FT-IR and TG-DTA. The result shows that the amount of ammonium sulfate has a significant effect on morphology and particle size of powders. Pure phase and spherical YAG particles with 350 nm in diameter can be obtained when the molar ratio of ammonium sulfate to aluminum nitrate is about 0.75 and the concentration of the metallic ions is 0.008M.

Abstract: TO/ZnPcSu-PCBM/Al heterostructure was prepared by ink-printing and studied by DC (current-voltage characteristics) and AC (dielectric spectroscopy) techniques (ZnPcSu means 3-diethylamino-1-propylsulphonamide substituted Zn phthalocyanine, PCBM phenyl-C61-butyric acid-methylester fullerene). At the Al contact a Schottky barrier was formed. To explain the shape of current-voltage characteristic two effects had to be taken into account, emission effect, overcoming the potential barrier effect, formed by the superposition of the image Coulombic, space-charge and external potentials, by charge carrier. Dielectric spectroscopy made possible to determine effective lifetime of charge carriers and characteristic time related to electron diffusion; lifetime of charge carriers was τ_d = 2.10^-5 s, and the electron mobility was of order 10⁴ cm²V^-1s^-1.

Abstract: 0.95 (K_XNa_1-X) NbO₃-0.05 LiSbO₃ (KNN-LS-X) (X=0.4-0.5) lead-free ceramics were prepared by conventional solid method. The effect of K/Na ratio on the dielectric, piezoelectric, pyroelectric and polymorphic phase transition was studied. The results show that the electrical properties strongly depend on the K/Na ratio. The KNN-LS-X(X=0.45) ceramics exhibit enhanced properties (ε_r=891.267, d₃₃=222pC/N, K_p =0.43517, Q_m=64.72, p=15×10^-4C/m²K). Enhanced electrical properties of the KNN-LS-X (X=0.45) ceramics could be attributed to the effect of K/Na ratio modifying the polymorphic orthorhombic-tetragonal phase transition temperature to room temperature, which could make KNN-LS-X (X=0.45) ceramics use as a new ferroelectric sensor.