Advanced Materials Research Vols. 189-193

Abstract: This paper presents the prediction of a statistically analyzed model for the surface roughness,R_a of end-milled Machinable glass ceramic (MGC). Response Surface Methodology (RSM) is used to construct the models based on 3-factorial Box-Behnken Design (BBD). It is found that cutting speed is the most significant factor contributing to the surface roughness value followed by the depth of cut and feed rate. The surface roughness value decreases for higher cutting speed along with lower feed and depth of cut. Additionally, the process optimization has also been done in terms of material removal rate (MRR) to the model’s response. Ideal combinations of machining parameters are then suggested for common goal to achieve lower surface roughness value and higher MRR.

Abstract: Porous Silk Fibroin Films(PSFFs) as dermis implant were used widely in biomaterials. To investigate angiogenesis in rat at different time after PSFFs implanting, CD34 was observed. Immunohistochemistry showed new blood vessels were mainly formed by sprouting next to PSFFs after 7 days operation. Microvessel Density (MVD) in PSFFs was 0, 3.54, 11.6, 24.5 after 1day, 7days, 15 days and 25days implantation respectively.

Abstract: Microstructures and creep properties of AM80 alloy with calcium and strontium additions have been investigated by using OM, X-ray diffraction, SEM and creep tests. The results indicate that the as-cast microstructure of the AM80 alloy consists of the α-Mg matrix, bones-shaped Mg17Al12 and lamellar second precipitation phase at grain boundaries. Calcium and strontium can refine the grain size and the secondary phases. Calcium addition results in the formation of a fishbone Al2Ca eutectic phase in AM80 alloy. With the increase of calcium, reticular Al2Ca phase distribute at the grain boundaries. The creep resistance of the AM80 alloy is significantly improved by a small amount of strontium and calcium addition due to the formation of a grain boundary network consisting of the high melting point Al2Ca phase. Microstructure observations performed on the sample after creep testing reveal that the phase is distorted during creep, reflecting its formation in the as-cast microstructure is unbeneficial to creep properties of the AM80 alloy. The creep resistance of the alloy at elevated temperatures was remarkably increased when calcium was added combined with strontium. The highest creep resistance was obtained from the alloy with xSr and y3Ca addition and its steady state creep rate reached as low as 3.941×10-8s-1, one order of magnitude lower than that of alloy AM80 without strontium and calcium additions.

Abstract: Electrical discharge machining (EDM) is relatively modern machining process having distinct advantages over other machining processes and able to machine Ti-alloys effectively. This paper attempts to investigate the effects of process parameters on output response of titanium alloy Ti-6Al-4V in EDM utilizing copper tungsten as an electrode and positive polarity of the electrode. Mathematical models for material removal rate (MRR), electrode wear rate (EWR) and surface roughness (SR) are developed in this paper. Design of experiments method and response surface methodology techniques are implemented. The validity test of the fit and adequacy of the proposed models has been carried out through analysis of variance. It can be seen that as the peak current increases the TWR decreases till certain ampere and then increases. The excellent surface finish is investigated in this study at short pulse on time and in contrast the long pulse duration causes the lowest EWR. Long pulse off time provides minimum EWR and the impact of pulse interval on EWR depends on peak current. The result leads to wear rate of electrode and economical industrial machining by optimizing the input parameters. It found that the peak current, servo voltage and pulse on time are significant in material removal rate and surface roughness. Peak current has the greater impact on surface roughness and material removal rate.

Abstract: The press forging of AZ31 magnesium-alloy sheets for producing thin-walled structural components used in the electronics industry was examined by both the finite element analysis and the experimental approach in the present study. The experimental results obtained from the compression tests and ring compression tests were employed in the finite element simulations to investigate the effects of process parameters, such as forming temperature, friction condition, embossment location, and sheet thickness on the formation of embossments in a press forging process. The finite element simulation results reveal that a cost-effective press forging process of AZ31 magnesium-alloy requires an optimum combination of the above parameters. The detailed examination of the effects of the process parameters on the formation of embossments made in the present study could provide a design guideline for a press forging process of AZ31 magnesium-alloy sheets.

Abstract: A family of spherical parallel mechanisms which have fully decoupled motions is presented in this paper. The condition required for synthesizing the fully decoupled parallel mechanism is derived from the screw formulation of Jacobian matrix. According to this condition, several novel decoupled spherical parallel mechanisms are obtained. The decoupled motions are validated by the simulation of the prototype of spherical parallel mechanism.

Abstract: A kinetic model based on the thermal decomposition of 1,3,5-trinitro-1,3,5-triazmane (RDX) was constructed via differential scanning calorimetry (DSC), well-known kinetic equations, curve-fitting analysis, and simulations of thermal analysis. Our objective was to analyze thermokinetic parameters derived from heating rates used in DSC and compare simulations of thermal decomposition under various kinetic models. Experimental results were strongly dependent on the validity of the kinetic model, which was based on an appropriate mathematical model and a proper method for the evaluation of kinetics. Through six types of kinetic algorithms, a reasonable value of the Ea of the thermal decomposition of RDX was obtained. Finally, this study established a novel green technology for the thermal analysis of reactions and obtained information on the characteristics of thermal decomposition and reaction hazards of RDX.

Abstract: This study fully exploited the advantages of the similarities between chitosan and nitrocellulose (NC), their non-toxicity, superior germproof effects, and the characteristic of restraining fungal growth, to prevent NC’s biodegradation. In a comparison between NC’s Ea, the differences among them were dealt with or not with germproof chitosan by differential scanning calorimetry (DSC). We also observed specific functional groups with Fourier transform infrared (FT-IR) spectrometer to characterize the functional group transformation of NC under various thermal conditions.

Abstract: A phase-field approach which incorporates mass and momentum and solute conservation equations for simulation of Al-Cu binary alloy solidification is studied. The effect of force convection on the double dendrite growth and solute profile during the solidification of binary alloy were investigated. The results indicate that dendritic grows unsymmetrically under a forced flow, the growth velocity of the upstream tip is faster than the downstream tip. The downstream tip of the first dendrite and the upstream tip of the second dendrite are influenced each other, the upstream tip of the second dendrite will Coarsen, and the concentration at the boundary between them is the highest. Moreover, the interaction between the two dendrites is more and more obvious with the increasing of the flow speed.

Abstract: Signal measuring is an important link in machine fault diagnosis. Accurate and reliable fault signals can be achieved by reasonable signal measuring. When the distance between sensor and measuring gear or bearing is comparatively far, the collected signals became weak and disturbed by other vibratory signals in equipments on bearing and gear fault analysis. Useful signals often were submerged in powerful noise, so caused difficult in extracting fault feature. In this paper, according to the feature of vibratory signals in machine test, wavelet analysis basic theory was applied on researching basic feature of wavelet analysis. By selecting suitable wavelet function and applying wavelet elimination noise technology the signal to noise ratio of signal was raised, thus the vibratory impact component can be measured in weak signals. Finally, wavelet analysis was applied on bearing fault diagnosis.