Key Engineering Materials Vols. 462-463

Abstract: In this study, the classification of modes of failure, the observation of microscopic failures and the mechanical properties of Semantan bamboo strips were investigated. Specimens were loaded in bending and shear parallel to grain. Specimens were taken from internodes and node parts in bottom, middle and top portions of bamboo culms. From the classification, different modes of failure occurred in different parts of Semantan bamboo culms loaded in bending and shear. From the microscopic observation, the failures occurred in both parenchyma and vascular bundles regions for all classified failure modes from all tests, except for Even Splitting Mode from shear. This mode exhibited failure in parenchyma only, without any failure in vascular bundles regions. The Maximum Stress (σml) values between failure modes for both tests were significantly different. Generally, anatomical behaviour at different culm’s parts had influenced the different modes of failure and microscopic failures of Semantan bamboo strips loaded in bending and shear.

Abstract: Thermo-mechanical stresses analysis of laminated hollow circular cylinder with finite length are carried out in this study based on the theory of laminated composites. The hollow circular cylinders with finite length are simply supported at four edges and are subjected to nonuniform thermal and mechanical loadings on the inner and outer surfaces. Analytical solutions of temperature distribution and thermo-mechanical stress fields are derived by using variable separation approach and series solving method. A four -layer laminated hollow circular cylinder with finite length is numerically analyzed by using the present method. All results are graphically presented and briefly discussed.

Abstract: Several different groups of filler metal are known to be compatible in welding of AA6xxx series. The aim of this investigation is to study the effects of different filler alloys toward mechanical properties and microstructure of welded AA6061 aluminium alloy using gas metal arc welding. Single V butt joint configuration has been used for joining the plate’s. Butt-joint welds were made on 6 mm thick plates using 21 – 22 V arc voltage. Tensile test was carried out using 100kN, electro-mechanical controlled hydraulic Instron 8801 universal testing machine. The results showed that the yield strength of base metal were 330 MPa and while the yield strength of ER5356 joints and ER4043 joints were 200 MPa and 235 MPa, respectively. The difference properties of strength in both weld metal was due to the difference major element in the both filler composition. The amount of silicon content in ER4043(Al-Si5%) filler is believed to play a role in the mechanical strength on weld metal. Microstructural examination was carried out using a light optical and electron microscope. The different filler alloys give different weld metal microstructure.

Abstract: Underfilling is the vital process to reduce the impact of the thermal stress that results from the mismatch in the co-efficient of thermal expansion (CTE) between the silicon chip and the substrate in Flip Chip Packaging. This paper reported the pattern of underfill’s hardness during curing process for large die Ceramic Flip Chip Ball Grid Array (FC-CBGA). A commercial amine based underfill epoxy was dispensed into HiCTE FC-CBGA and cured in curing oven under a new method of two-step curing profile. Nano-identation test was employed to investigate the hardness of underfill epoxy during curing steps. The result has shown the almost similar hardness of fillet area and centre of the package after cured which presented uniformity of curing states. The total curing time/cycle in production was potentially reduced due to no significant different of hardness after 60 min and 120 min during the period of second hold temperature.

Abstract: Carbon nanofiber (CNF) has good electrical conductivity. Addition of a few percentages of carbon nanofiber to polymer yields electrical conductivity but hardly affects the mechanical properties of polymer. This conductive polymer may be useful for sensing applications such as strain sensors and chem-resist sensors. Many researchers have reported on the electrical conductivity, but the electrical resistance change under strain of the carbon nanofiller composites is not fully investigated. In this study, the electrical resistance change under strain of CNF/flexible-epoxy composites was investigated experimentally. More than 100% of quasi-static strain can be measured by using CNF/flexible-epoxy composite with Young’s modulus of less than 1MPa. Cyclic and unloading behaviors were also measured and discussed. It was found that the cyclic behavior was strongly affected by viscoelasticity and damage.

Abstract: A large number of rubber products are formed into their final shape by vulcanization. In particular, curing process of rubber is the final step in manufacturing many rubber products and determines both the quality of the resulting product as well as production costs. This paper is devoted to the simulation of rubber curing process in a three-dimensional model. The effects of final temperature of mold are investigated on curing process and quality of final product. The results were compared with the experimentally measured data, which confirmed the accuracy and applicability of the method.

Abstract: The present work studies the crack behavior along the surface of the friction stir welded (FSW) joint of 2024-T351 aluminum alloy. The surface engineering of shot peening and skimming are used to enhance the fracture characteristics of the joint. Then multiple crack initiation is detected within FSW zones by scanning electron microscopy, while plastic replication technique is used to monitor the crack propagation. The variation of residual stress is measured (using hole drilling technique) as well as hardness characteristic (using standard method of Vicker) to study the fatigue life of the FSW by two models of Pearson and Nicholls, incorporating crack closure and stress relaxation.

Abstract: Improving crashworthiness of vehicles is considered to be one of the main concerns in traffic safety. The study focused on new designs that can be incorporated into existing vehicles. The paper presents a crashworthiness design of a bi-tubular thin walled column for different dimension profiles. To formulate the complex crashworthiness design problem, the response surface method (RSM) was utilized. The design of experiments of the factorial design is used to construct the response surface for the specific energy absorption (SEA). This surface was optimized for SEA. Results from a finite element analysis of elastic plastic square bi-tubular steel tubes subjected to dynamic axial impact load are reported. The bi-tubular design has shown good potential as an efficient energy absorber in comparison to existing conventional energy absorbing structures.

Abstract: Effect of peak-aged and over-aged Cu particles on wear behaviour of ferritic iron was investigated by means of Pin-on-Disc wear test under dry sliding condition. It was found that hardness of the peak-aged sample was higher than the over-aged sample. The specific wear rates of peak-aged samples were in the range of 0.20 × 10-4 to 0.89 × 10-4 mm3/(Nm) while the over-aged samples were in the range of 0.21 × 10-4 to 1.29 × 10-4 mm3/(Nm). Although both samples possessed moderate wear behaviours, the peak-aged samples had better wear resistance. Scanning Electron Microscopy observation found that most wear mechanism were due to plastic ploughing phenomenon. Transferred materials from the counterface tool was also proven by Energy Dispersive Spectroscopy test. However, the roughness test showed that the peak-aged sample surface was finer than the over-aged sample surface. Average roughness of peak-aged samples were in the range of 0.49 to 1.79 μm while the over-aged samples were in the range of 3.28 to 4.02 μm. Hence, it can be concluded that the peak-aged Cu particles can improve the wear resistance of steel.

Abstract: A general method is developed to deal with the compressibility of air film and to predict the linear dynamic stiffness and damping coefficients of air-lubricated bearings over the whole range of frequency. Numerical results reveal that both stiffness and damping coefficients are functions of not only the static parameters such as eccentricity and attitude angle, but also the frequency of disturbance. The coefficients are continuous and tend to certain values even when the frequency approaches zero or positive infinity. In general, the direct terms of the dynamic stiffness increase with the increase of the frequency, while the cross-coupling terms tend to an equal value when the frequency becomes infinite, and all the damping coefficients decrease in the higher frequency region and vanish when the frequency approaches positive infinity.