Applied Mechanics and Materials Vols. 284-287

Abstract: With a relatively low liquidus temperature, the eutectic Sn-Zn alloy is suitable replacement for conventional eutectic Sn-Pb solder in the electronic industry. One of the most important materials as a lead-frame is Fe-42Ni alloy (Alloy 42) in the microelectronic packaging. The Sn-Fe-Zn ternary phase diagram is a powerful and useful tool to understand the interfacial reactions between Sn-Zn alloy and Alloy 42 substrate (Fe-rich alloy). The isothermal section of the Sn-Fe-Zn ternary system was experimentally investigated at 270oC in this study. Ternary Sn-Fe-Zn alloys were prepared and annealed at 270 oC to determine the isothermal section of the Sn-Fe-Zn ternary system. The experimental results revealed that no ternary intermetallic compound was formed, and noticeable Zn solubility was observed in the FeSn2 phase. The isothermal section of the Sn-Fe-Zn ternary system consists of nine single-phase areas, thirteen two-phase areas, and seven tie-triangles at 270 oC

Abstract: The leakage and fatigue characteristics of polyvinylidene fluoride (PVDF) are investigated for flexible electronics. The crystallization, frequency responses, leakage currents, current-voltage characteristics, and fatigue characteristics of PVDF film are measured using X-ray diffraction and an electrometer. Results show that a PVDF model with a resistive load exhibits high-pass filter characteristics. The frequency band of PVDF film increases with increasing resistive load and capacitance. The break frequencies for 100 kΩ, 300 kΩ, 700 kΩ, and 1 MΩ at the break frequency are 611, 207, 88, and 61 Hz, respectively. The hysteresis area of ΔH slightly increases with increasing input voltage. The leakage current of PVDF film is higher for a lower delay time under a given applied electric field. The average leakage currents for delay times of 10 and 1000 ms are 0.565 and 73.8 pA, respectively. The magnitude of the current values increases with decreasing delay time at a given drive voltage. PVDF film induced larger degradation when the number of stress cycles was increased to about 105 cumulative cycles.

Abstract: This paper reports experimental results of compression test on non-tapered rectangular shaped micro-pillar fabricated by focused ion beam techniques. The pillar is composed of electrodeposited nickel in additive-free Watts bath emulsified with supercritical carbon dioxide. We found that the electroplated film does not contain any defects or pores and has grain size of 8 nm. Maximum compression flow stress exceeds 3.5 GPa without any failure up to 9 % of permanent strain. This is 10 times higher than the strength of the single crystal nickel counterparts fabricated using the same focused ion beam techniques loaded along . This is because of the enhanced mechanical properties by grain boundary strengthening in nanocrystalline nickel and defect-free nickel film. Carbon impurity observed in the nickel film fabricated by electroplating with supercritical carbon dioxide emulsion enhances cohesion of the grain boundary and inhibits grain boundary sliding, which is the predominant deformation mechanisms in this grain size regime.

Abstract: In this present work, nanodiamond (ND) particles were successfully prepared from commercial micron diamond powder at room temperature by high energy ball milling process using an oscillatory mill (SPEX8000). The size reduction and structural evolutions of the milled samples were investigated as a function of the milling time by means of X-ray diffraction, and field emission scanning electron microscopy. The line broadening technique was used to determine the crystallite size and lattice strain. After 40 h of milling, obtained ND particles possessed uniform shape and 25 nm of average particle size. Also, energy dispersive X-ray results revealed the high purity of ND and demonstrated that the purification process using harsh acid mixture were effective to remove metal and non-diamond carbon impurities produced in milling stage. All results propose a scalable method to preparation ND particles as well as nanocrystalline materials.

Abstract: In this paper, nonlinear dynamic characteristics of giant magnetostructive nanofilm-shape memory alloy (SMA) composite beam in axial stochastic excitation were studied. Von del Pol nonlinear difference item was introduced to interpret the hysteresis phenomenon of the strain-stress curve of SMA, and the hysteretic nonlinear dynamic model of giant magnetostructive nanofilm-SMA composite beam in axial stochastic excitation was developed. The steady-state probability density function and the joint probability density function of the system were obtained in quasi-nonintegrable Hamiltonian system theory. The result of simulation shows that the stability of the trivial solution varies with bifurcation parameter, and stochastic Hopf bifurcation appears in the process. The result is helpful to stochastic bifurcation control to giant magnetostructive nanofilm-SMA composite beam.

Abstract: The Composite sandwich plate is made of two laminated face-sheets and one core material. Since such a kind of structure has many advantages, they have been widely used in structural manufacturing industry. However, when sandwich plates are impacted by transverse loadings, damages that are usually invisible would occur inside the sandwich plate and those damages would potentially reduce the structural safety. Therefore, it is necessary to elucidate the failure mechanism and how they affect the failure behaviors of sandwich structures for safety purpose. To this end, the present study is to investigate the impact failure behaviors of sandwich plates subjected to a rigid spherical impactor. Numerical simulation approach is carried out by finite element method. To predict the initial failure, several failure criteria to face-sheets and core material are proposed. In addition, to further simulate the progressive failure behaviors, a stiffness modification method is proposed and incorporated into the finite element software. The analytical results show that the local failure including fiber breakages, delamination, core cracking and plasticity is the main failure mechanism of cases studied. Furthermore, parametric study is also conducted and discussed in the paper.

Abstract: This study utilized the reaction of O₂/N₂ gases and Al_0.67Ti_0.33/Cr (99.9%) dual targets to synthesize (Ti,Al)ON/CrON multilayered coatings on AISI M2 steel by cathodic arc deposition system. Thermal stability and corrosion resistance of the multilayered coatings for aluminum die casting applications, along with coating structure were investigated. The results showed that the structure of multilayered coatings was a B1 NaCl type. The formation of oxide phases by introducing oxygen to react with Al, Cr, and Ti elements was confirmed by XPS. The thermal stability of oxygen-doped AlTiN/CrN coatings was higher than that of one without oxygen. After the immersion tests in Al-alloy melt, the oxygen-doped AlTiN/CrN coatings deposited at the O₂/N₂ ratio value of 0.3 had the best improvement on the corrosion resistance among all the coated specimens.

Abstract: In electrical engineering, electrical discharge can occur in gaseous, liquid or solid insulating medium. Localized dielectric breakdown that occur at a small portion of a solid or fluid electrical insulation under high voltage stress is called partial discharge (PD). This phenomenon can cause the material to breakdown if there is no proper action taken. Usually it begins within voids, cracks, or inclusions within a solid dielectric, at conductor-dielectric interfaces within solid and in bubbles within liquid dielectrics. In order to modify electrical properties of the original structure then nanocomposite need to be introduced. Nanocomposite is the original structure that has been inserted by nano component (nanofiller) such as silicone dioxide and titanium dioxide. Nanocomposites are also found in nature, for example in the structure of the abalone shell and bone. By adding nano component inside the original component, it can change the mechanical and electric properties. In this study, PD characteristics of polymer-natural rubber blends nanocomposite have been investigated. The samples of nanocomposites were developed by using extrusion method. The high voltage is applied at the electrode arrangement of the test sample. The signals of partial discharges are detected by CIGRE Method II and RC detector and the signals are transferred to the personal computer using LabViewTM software. The result from the software is analyzed to find out the PD characteristics. The results revealed that the highest PD numbers are compositions with no filler while the lowest PD numbers come from sample that use 4% SiO2 as its nanofiller. The physical morphology observation is also conducted to investigate the degradation of the samples.

Abstract: Sr0.4Ba0.6Nb1.85Ta0.15O6 (SBNT) ceramic was used as a target and SBNT thin films were deposited at room temperature. After deposition, the SBN thin films were annealed in conventional furnace (CFA) and in an oxygen atmosphere for 1h by changing the temperature from 700oC to 900oC. The thicknesses of the SBN thin films were calculated by SEM and they were about 450nm independent on the annealing temperature. From the XRD patterns, the as-deposited SBNT thin films displayed amorphous phase, whereas as CFA-treatment was used, the SBNT thin films displayed smooth surfaces. The grain sizes also increased with increasing CFA-treated temperature. In addition, the remanent polarization and saturation polarization increased and coercive field decreased with increasing CFA-treated temperature. Finally, the lnJ-E1/2 curves of the SBNT thin films was developed to find that the linear variations of leakage current densities correspond either to the Schottky emission mechanism or to the Poole-Frenkel emission mechanism.

Abstract: Spot welds have been widely used in vehicle body assembly, and can affect the performance of a vehicle. This paper studies the mechanical properties of spot weld and utilizes those properties in the numerical simulation to predict the failure behavior of a spot-welded component. The mechanical properties of a spot weld are not easy to obtain due to the size of spot weld, and the non-uniformity around the weld zone. The study utilized the hardness measured on and around the spot weld, heat treated samples with the same hardness, and then performed the tensile tests on those heat treated specimens to obtain the corresponding mechanical properties. With those testing data, the numerical simulation model was then created based on the properties obtained. A single-spot-welded part was used to correlate the results of hardware tests and numerical simulation. The study compared the results of three different modeling schemes with those of the hardware test. The results showed that the simulation model with material properties assigned to their corresponding region provided better correlation with the hardware testing results.