Applied Mechanics and Materials Vol. 761

Abstract: This article presents the tool wear mechanism when machining Aluminium alloy 6061-T6 with PVD coated carbide under dry cutting condition. Cutting parameters selected were cutting speed, Vc = 115-145 m/min; feed rate fz = 0.15-0.2 mm/tooth and depth of cut, ap = 0.5-0.75 mm. The result showed the tool life of PVD TiAlN ranged from 11 to 97 min. Full factorial approach was employed to exhibit relationship between parameter input and output. From the analysis, cutting speed was found to be the most significant factor for tool performance followed by feed rate and depth of cut. It was also found that most of failure modes occurred were notch wear and flaking near those found near depth of cut line.

Abstract: Fused deposition modeling (FDM) is an additive manufacturing (AM) process that has been used in various manufacturing fields. However, the drawback of FDM is poor surface finish of parts produced, leading to surface roughness and requires hand finishing. In this study, ultrasonic technology will be integrated into a desktop FDM system.Ultrasound has been applied in various conventional machining processes and shows good machined surface finish. However, very little research regarding the application of ultrasound to AM has been carried out. Our previous research found that the extrusion nozzle of the FDM system could withstand the high vibration transmitted at 40 kHz of frequency from an ultrasonic transducer. The aim of this paper is to discuss three novel setups of using ultrasound devices attached to a desktop FDM system to study its feasibility to improve the surface finish of parts produced. A comparative study was made and it was found that the second setup (Concept 2) was most suitable due to its safety and reliability aspects.

Abstract: Fused deposition modeling (FDM) is an additive manufacturing (AM) process that has an economical advantage compared to other AM processes. However, its biggest drawback is that it requires post processing to achieve a good surface finish. Ultrasound has been applied in various conventional machining processes and produces a good surface finish. However, the application of ultrasound to AM has not been sufficiently explored. This research aims to investigate the application of using ultrasound technology for a desktop FDM system. The idea is to transmit high vibration from the ultrasonic transducer to the FDM system's nozzle, and the objective is to examine whether the nozzle is able to withstand the high vibration being transmitted. Computer-aided design (CAD) software used to develop the 3D model of the extrusion nozzle component and a computer-aided engineering (CAE) software was used to perform static and vibration analysis. A frequency range of 20 to 30kHz and 30 to 40kHz was applied to the nozzle and it was found that the nozzle was able to withstand frequencies up to 40 kHz of vibration. In addition, the lowest Factor of Safety (FoS) obtained was 18.8975, concluding that the nozzle of FDM can withstand the high vibration transmitted from the ultrasonic transducer.

Abstract: Risk assessment of complex rotating equipment is costly and time consuming process. Due to the reason, only critical equipment should be considered for detailed risk assessment. In this study, a semi-quantitative risk assessment model was developed to assess the risk of rotating equipment. The model consists of four main parts, initial risk screening, risk assessment, Failure Mode and Effect Analysis (FMEA) and maintenance strategy planning based on reliability concept. The model was used to assess risk of rotating equipment of power generation unit. Initial risk screening indicated compressor, combustion chamber, turbine and lube oil system of the power generation system as critical equipment under serious risks. Risk assessment using Borda ranking minimized the risk ties and showed compressor, combustion chamber and turbine were more critical as compared to lube oil system. Failure modes were identified using FMEA, 68% of the downtime was due to compressor, combustion chamber and turbine failure modes. Only 32% of the downtime was due to lube oil subsystems failure modes. Maintenance interval for compressor, combustion chamber and turbine was calculated 2 months and 5 months for lube oil system to reduce risk.

Abstract: This paper presents the performance between silicon germanium (SiGe) and crystalline germanium (Ge) solar cells in terms of their simulated open circuit voltage, short circuit current density, fill factor and efficiency. The PC1D solar cell modeling software has been used to simulate and analyze the performance for both solar cells, and the total thickness is limited to 1μm of both SiGe and Ge solar cells. The Si_0.1Ge_0.9 thickness is varied from 10nm to 100nm to examine the effect of Si_0.1Ge_0.9 thickness on SiGe solar cell. The result of simulation exhibits the SiGe solar cell give a better performance compared to Ge solar cell. The efficiency of 9.74% (V_OC = 0.48V, J_SC = 27.86mA/cm², FF =0.73) is achieved with Si_0.1Ge_0.9 layer of 0.1μm in thickness whilst 2.73% (V_OC = 0.20V, J_SC = 27.31mA/cm², FF =0.50) efficiency is obtained from Ge solar cell.

Abstract: This research analyzed the results of flexural strength of dense and porous mullite ceramic prepared from kaolin clay by using two-parameter Weibull probability distribution with different estimates. Chemical and physical characterizations of the clay were conducted using XRF, XRD and FESEM. The samples were tested using three point bending tests. The different estimates used in analyzing the results include mean rank, median rank, modified Kaplan Meier and Kaplan Meier. Among the estimates, Kaplan Meier was found to give the best fit with the highest correlation coefficient (R²) value. The porous ceramic had the higher value of Weibull modulus in comparison to the dense ceramic, while the characteristic strength (scale parameter) of the dense ceramic was higher than that of the porous ceramic. The micrograph of the porous ceramic showed a relatively balanced distribution of rounded pores, which is associated with the higher Weibull modulus in the porous ceramic.

Abstract: Al7075 was recycled using the powder metallurgy technique to determine the effect of particle size distribution on the mechanical and microstructure of materials. Analysis of the microstructure, green density and microhardness was conducted to evaluate the performance of the recycled aluminium. The Al7075 was added with 4% of alumina and Al₂O₃ (3-4μm). The results showed that the green density of recycled Al7075 was lower than the pure Al7075. The average size distribution of the aluminium powder decreased with the increase in the ball mill time. As the temperature of sintering process increased, the green density decreased. The alloy’s microstructure sintered at 650°C has the lowest density, indicating a larger and more frequent porosity. The hardness of the samples with the addition of alumina was higher than the samples without the alumina. Sintering at 650°C also caused the hardness of the sample to increase in the range of approximately 50-62 Hv.

Abstract: Mechanical properties of an industrial based rubber mat compound were optimized via response surface methodology (RSM). Interaction between two factors: accelerators (0.04-3.50 phr) and fillers (0-18.29 phr) were investigated using a full factorial design. The accelerators consisted of a combination of mercaptobenzothiazole disulphide (MBTS) as the primary accelerator, and diphenyl guanidine (DPG) and Zn-2-mercaptobenzo thiazole (ZMBT) as the secondary accelerators. Meanwhile, silane functionalized hybrid precipitated silica/calcined clay (f-PSi/ClCy) was used as the fillers. Regression models for optimum mechanical properties against the accelerator and filler factors were generated by Design Expert software. It was recommended that the level of accelerators and fillers at 1.77 phr and 0.65 phr as the optimum parameter to achieve tensile strength of ~14 MPa and ~2 N/mm, respectively. Further, a comparison between the recommended formulation and the original rubber mat formulation affirmed that the mechanical properties via statistical design were in good agreement with the experimental results with deviations of only + 8.8 % and 0 % for tensile strength and tear strength respectively.

Abstract: Copper (Cu) wire bonding on the pre-plated leadframes with Ni/Pd/AuAg plating has been applied extensively in the semiconductor industry for the interconnection of integrated-circuit (IC) packaging due to the lower material cost of Cu and its excellent electrical properties. Furthermore, the Cu wire bonding on the preplated leadframe has advantages, such as the tin whisker prevention and the robust package for automotive application. Nevertheless, a stitch bondability of Cu wire-preplated leadframe is facing several challenges, such as the Cu oxidation, the high hardness of Cu wire and the very thin AuAg plating on the leadframes. This paper discusses the effect of AuAg plating thickness in roughened pre-plated leadframe on the stitch bonding of Cu wires with the leadframe. The stitch bonding integrity was assessed using Dage 4000 shear/pull tool at a key wire bond responses of stitch pull at time zero (T₀). Results show that the stitch pull strength of the Cu-leadframe stitch bonding increases with the increase thickness of AuAg layer. FESEM images of the stitch bonding between the Cu wires and the pre-plated leadframes of different AuAg plating thickness did not show any defect in microstructures, thus it suggests that the bonding property is determined by diffusion mechanism at the Cu wire/AuAg stitch bonding interface. Finally, a brief discussion is provided on the stitch bondability of high performance Au-flashed palladium-coated copper wires on the pre-plated leadframe with different AuAg thickness.

Abstract: Commercially available Multiwalled Carbon Nanotubes (MWCNTs) were refluxed with nitric acid in order to improve the density of the acidic surface functional groups. The formation of oxygen containing functional groups may lead to surface enhancement of MWCNTs for further modifications. The crude MWCNTs were refluxed in nitric acid at 100 °C for time ranging between 3 to 24 h. The influence of treatment time on crystalline structure was investigated using X-Ray Diffraction (XRD); the results confirmed that all treated MWCNTs are crystalline. The density of the surface functional groups on treated MWCNTs was examined by Fourier Transform Infrared (FTIR). The FTIR spectrums revealed a strong vibration band at 1739, 1219, 1369 cm^-1 that indicates covalently bound acidic surface functional groups existed on the treated MWCNTs. The amount of acidic groups increased with the reflux time up to 15 h treatment as measured by an acid-base Boehm titration. The vibrational spectroscopy of these functional groups also increased with the increasing reflux time.