Advanced Materials Research Vols. 264-265

Abstract: Conventional AFM have difficulty achieving uniform roughness of an axial distribution in circular hole polishing due to limited unitary axial motion of abrasive media. Therefore, this work develops mechanism designs for different passageways to obtain multiple flowing paths of an abrasive medium, whose flowing behavior enhances polishing effectiveness by increasing the abrasive surface area and radial shear forces. The motion of the abrasive medium is studied by utilizing the design of the mold cores, which mold shapes include the circular passageway and helical passageway. The optimum design of the different passageways is then verified using CFD-ACE+ numerical software. Analytical results indicate that the optimum design is the mechanism with a passageway of six helices. Furthermore, surface roughness measurements demonstrate the increase in uniformity and the roughness improvement rate (RIR). Experimental results for surface roughness indicate that roughness deviation of six helices passageway of approximately 0.1001 m Ra is significantly better than those on a circular passageway of around 0.1760 m Ra. Additionally, the six helices passageway is also superior to circular passageway in reducing roughness improvement rate (RIR) by roughly 85% compared with RIR 75% for the circular passageway.

Abstract: Semi-solid processing (SSP) technology, due to its ability to provide near-net-shape components with properties far exceeding those of other casting technologies is considered as an alternative for forgings and investment castings. Conventional semi-solid forming, involving the use of heated billets, melt stirring or using cooling slopes require many processing steps and supplementary equipments. This article describes Narrow Melt Stream (NMS), as an alternative process for semi-solid processing of aluminum alloys that eliminates capital cost expenditures, reduces the number of steps required, and hence reduces the costs of making components with a globular structure. However, the applicability of this technique in producing globular structures in the large molds has not been explored. In the present study the results of a systematic investigation on the effects of mold size on the size and morphology of the globular structures formed by NMS processing of Al 356 alloy is reported. For this purpose, five different series of molds were employed. Each series consisted of three molds with identical volumes but different casting moduluses. By using these molds, the effects of casting modulus at constant casting size as well as the effect of casting volume on the size and shape factor of the globular structures in aluminum A356 samples prepared by NMS technique is reported.

Abstract: The Al/Gr/SiC hybrid composites have attracted a considerable attention owing to their high wear resistance combined with a low friction coefficient. In these composites graphite acts as a solid lubricating agent and lowers the friction coefficient. However, it reduces the mechanical properties of the composite. The presence of hard SiC particles in these hybrid composites increases the hardness and strength and compensates for the weakening effects of graphite. Powder metallurgy (P/M) is an important processing technique for processing of these MMCs but requires a relatively long mixing time for obtaining a uniform distribution of graphite and SiC particles in the matrix alloy. In the present study for the first time a new method, namely "in situ powder metallurgy (IPM)" is applied for preparation of Al/SiC/Gr hybrid composites. In this work, the effects of different contents (0-40 vol.%) of SiC particles on the morphology and size distribution of the IPM produced Al/Gr/SiC powder mixtures containing 9 vol.% of graphite particles was investigated. Then Al/Gr/SiC compacts were prepared by cold pressing of different powder mixtures and after sintering, the effects of SiC content on the density, microstructure, hardness and wear properties of the resultant hybrid composites was investigated.

Abstract: Due to performance improvement and the trend of miniaturized sizes in optical devices, the need for micro lenses is increasingly presented. In this paper, characteristic study of a micro aspheric mold having a diameter of only 0.3 mm was performed. According to the experimental results of rough cuttings using a diamond tool, the machined surfaces were with a mean peak-to-valley (PV) form error of 1.47 µm. The Taguchi Method was employed to determine the optimal cutting parameters by selecting the cutting depth, work spindle speed, and compensation ratio as the control factors. Experimental trials were conducted according to the L9(34) orthogonal array (OA), and a mean PV form error of 0.79 µm was obtained due to compensation cuttings. Based on signal-to-noise (S/N) ratios, the optimal levels of control factors were determined. By performing the confirmation test, the PV form error was reduced from rough cutting of 1.49 µm to 0.60 μm. The effectiveness of using the Taguchi Method was demonstrated. The systematic approach performed in this paper can be applied to micro-fabrications for precision components in molds and dies industry.

Abstract: In this experimental study, erosive wear behavior of epoxy-resin dipped composite materials reinforced with glass fiber and B2O3 (borax) under different impact velocities, erodent sizes, and erodent striking angles along the fiber direction were investigated. The tests which involved slightly rounded and irregular silicon oxide (SiO2) particles having two different sizes of approximately 250 and 500 , were conducted at two different impact velocities of approximately 20 m/s and 40 m/s, two different fiber directions (0o and 45o) and six different impingement angles of 15o, 30o, 45o, 60o, 75o and 90o. In the test results, erosion rates were obtained as functions of impact velocities, striking angles, fiber direction and particle sizes. In addition, the microscopic views showing worn out surfaces of the glass fiber reinforced epoxy composites were scrutinized.

Abstract: The net-inserted metal matrix composite strip could be cast by a twin roll caster at only one process. The net could be inserted in the strip or lower surface of the aluminium alloy strip. The matrix was Al-12mass%Si, and inserted net was made from SUS304 stainless steel. The diameter of the wire of the net was 0.29mm, and distance between the wires was 0.98mm (#20). The roll speed was 30m/min. The net was not reacted with the matrix, and there was not gap between the matrix and the net. The mechanical property of the net-inserted composite strip was affected by the direction of the wire of the net. When the angle of the wire against the tensile direction was 45 degrees, elongation of the composite became better than that of the matrix from 14% up to 23%. This reason was improvement of the local contraction of the composite strip. The net-inserted composite strip could be cold rolled. The reduction of the net was smaller than that of the strip. The reduction of the wire at rolling direction was larger than that of the wire at lateral direction.

Abstract: In this study, the roll casting of Al-40%Sn-1%Cu alloy was tried by an unequal diameter twin roll caster. The unequal diameter twin roll caster could continuously cast the strip. The casting load of the roll was small to prevent the flow out of the Sn. The roll-load was 0.1kN/mm(unit width). The roll casting of 400mm-width strip of 8mm-thick was tried, and it was attained. The gravity segregation of Sn did not occur. The as-cast strip could be cold rolled down to 1mm. However, this strip had much porosity. The rapid solidification was useful to prevent the porosity. The copper roll was better than steel roll to increase cooling ability. The copper roll was suitable to prevent the porosity. The temperature of solidified metal was important factor which influenced the porosity. The 4mm-thickness strip with little porosity was could be cast at the speed of 30m/min.

Abstract: A 6061 aluminium alloy and an alloy with increased Fe content, representing recycled 6061 aluminium alloy were cast into strips at speed of 30m/min by an unequal diameter twin roll caster. The Fe content of 6061 aluminium alloy and the model of recycled 6061 aluminium alloy was 0.36 mass% and 0.59 mass%, respectively. Ripple marks, which are typical surface defect of roll cast strips, did not occur on the surface of both as-cast strips. Fe content did not influence the surface condition of the roll-cast-strip. The as-cast strip was cold rolled down to 1 mm, T4 heat treatment was conducted, and then subjected to180 degrees bending test. The result of 180 degrees bending test shows that roll cast 6061 aluminium alloy and 6061 aluminium alloy with increased Fe as recycled had bending ability as same as that of roll-cast 6022 aluminium alloy. In the strip cast by the twin roll caster of the present study, increased Fe content did not influence on the result of the180 degrees bending test.

Abstract: The characteristics of natural yarns are inconsistent in their mechanical property. The tensile strength of jute yarns is an intricate parameter, which can not be fully described using single value. This necessitates the study of the jute yarn strength distribution and efficient experimental methods for its measurement. Here Weibull model is used to describe the statistical nature of the tensile strength. However, the experimental process widely uses for obtaining the two parameters Weibull model which is described for this experiment. The Weibull modulus of the untreated and NaOH treated jute yarns were determined and it suggests that the treated yarns are better than the untreated yarns. The tensile strength of NaOH treated jute yarns increased to 219.93 MPa compared to the untreated yarns which was 177.32 MPa. For the treated yarns the coefficient value R2 is 0.9829, which indicates good degree of linearity.

Abstract: Due to the environmental issue, natural fibers are day by day becoming attractive to researchers. Natural fiber contains cellulose, hemicelluloses, lignin etc, which are hygroscopic in nature and biodegradable. The lack of surface feature diminishes its properties. So, the surface properties of the jute yarns need to be modified. In the present study, jute yarns were cleaned using 2% detergent and chemically modified by 5, 15 and 25% NaOH solution both at room temperature and 700C for 2 hours and dried in air. The structural and morphological studies of the treated and untreated yarns were carried out using Fourier transform infrared spectroscopy (FT-IR) and Scanning electron microscopy (SEM). The thermal and mechanical behaviour of the yarns were analyzed using Differential scanning calorimetry (DSC) and Instron Universal testing machine. The results show the improvement in mechanical strength of the yarns due to the change in crystalinity after alkali treatment. Also, the thermal decomposition temperature of raw jute yarns decreased from 357.30C to 349.60 C after alkali treatment.