Key Engineering Materials Vols. 419-420

Abstract: The objective of this research is to develop soy-based polyurethane (PU) foam product reinforced with carbon nanotubes. The shortage of petroleum and the increasing concern on environmental issues have resulted in an interest in using renewable substances as building blocks for polymer applications. Multi-walled carbon nanotube (MWNT) was used in this study to reinforce the soy-based polyurethane foam. The compressive and mechanical properties of the composites were enhanced with adding carbon nanotubes. Neat polyurethane was used as a control. Soy-based polyurethane / carbon nanotubes composites with loadings of 0.5 and 1.0 wt% were fabricated. The compressive, flexural, and tensile properties of MWNTs-PU foams were improved by 24, 30 and 30 %, respectively, as compared with the neat PU foam. The greatest enhancements on compressive and flexural properties were shown at the 0.5 wt% MWNT loading, while the highest tensile stress enhancement of PU foam was shown at 1 wt% MWNT loading.

Abstract: This study applies the finite element method (FEM) in conjunction with an abductive network to predict springback of different strain-hardening material in U-shaped bending process.Springback is investigated for different material parameters, such as strength coefficient of material, strain-hardening exponent and Young’s modulus, by finite element analysis during U-shaped bending process. The abductive network is then applied to synthesize the data sets obtained from the numerical simulations. Prediction results of the springback of different strain-hardening material in U-shaped bending process are consistent with the results obtained from FEM simulation quite well. After employing the predictive model can provide valuable references in prediction of the springback of U-shaped bending process under a suitable range of material parameters.

Abstract: This paper presents a layer manufacturing technology called selective laser gelling (SLG) to fabricate metal-ceramic composites green parts which are difficult to construct using traditional methods for fabricating composites. When a layer of metal-ceramic slurry is scanned via Nd: YAG laser radiation, the metal particles are gelled together by the silica sol to form a composites part. In comparison with other composites processes, the features of this process include lower laser forming energy, faster fabrication speed, less dimensional variations. The material composition is mixing by the stainless steel powder and a silica sol in a proportion of 75 to 25 wt. %. A series of experiments was conducted to obtain the smallest pave-able layer thickness of 50 μm on an experimental rapid prototyping (RP) machine. The feasibility of this process was demonstrated by manufacturing a gear shaped prototype with a surface finish of 18μm under a laser energy density of 3.5 J/mm2.

Abstract: Two major analyses were conducted in this paper. In the first, experimental procedures are accomplished to measure the tensile mechanical properties of ultra thin gold wire (=1mil) before/after electric flame-off (EFO). Characteristics of free air ball (FAB), heat affected zone (HAZ) and as-drawn wire have been carefully investigated by nanoindentation, microhardness and self-design pull test fixture. Secondary, with the obtained experimental material data, a comprehensive finite element model using software ANSYS/LS-DYNA is successfully developed to simulate the wirebonding. Dynamic analysis is performed to evaluate the overall stress distributions on the underlay microstructure of Cu/low-k wafer. Special emphasizes are focused on the Copper via and the intermetal dielectric (IMD)/undoped silica glass (USG) dielectric microstructure.

Abstract: A combined effect of moisture diffusion, heat transfer, and hygro-thermo-vapor pressure modeling for pre-mold QFN CMOS Image Sensor (CIS) package has been developed in this study. Hygroscopic swelling properties such as saturation, coefficient of moisture expansion (CME) and activation energy can be extracted through TMA (Thermal Mechanical Analysis) and TGA (Thermal Gravitational Analysis) instruments. Fick’s second law of transient diffusion is solved by using finite element analysis (FEA) to evaluate the overall moisture distributions. With obtained experimental data, a three-dimensional FEA CIS model using the “thermal-wetness” technique is developed to predict the moisture absorption, moisture desorption, temperature distributions, hygro-thermo-vapor pressure mechanical coupled effect and the residual stress distributions at JEDEC pre-conditioning standard JESD22-A120.

Abstract: Dynamic mechanical analysis (DMA) tests are conducted on styrene-based shape memory polymer(SMP) to investigate its glass transition behaviors. The tensile tests at various temperatures are operated to detect the stress-strain relationship of styrene-based SMP. The material elastic moduli and yielding limits at 25oC, 30oC, 40oC, and 50oC are determined according to the results of tensile test. A new material parameter function is supposed to express the glass transition behavior of styrene-based SMP. The shape memory thermo-mechanical cycle of styrene-based SMP is numerically simulated by Tobushi’s constitutive equation coupled with the new material parameter function. Numerical results show the new material parameter function can express the thermo-mechanical properties of styrene-based SMP effectively.

Abstract: The basic theory of material point method (MPM), which is a new meshfree method,was briefly introduced in this paper.MPM takes advantage of both Eurlerian and Lagrangian methods. It avoids the mesh distortion and tangling issues associated with Lagrangian methods and the advection errors associated with Eulerian methods. A MPM computational code called MPM-EXPLICIT with the Von-mises material strength model and Shock equation of state was developed in FORTRAN 90, and was used to compute various impact problems. The calculated result and experimental result were compared to confirm the accuracy of the code. The results obtained by using the MPM, FEM and SPH were compared. It shows that MPM possesses many prominent features. This study indicates that the material point method is an efficient and promising method for simulating the impact problems.

Abstract: Both dynamic cutters installed on the shaft and fixed cutters installed on the shell has realized to form the high-pressured superimposition produced the high dynamic pressure and the static pressure due to the Reynolds effect during process of high-speed rotation, which forms high pressure required by super velocity centrifugal grinding, and raw material of the sawdust or fibrous fragments can be stricken and cut into the wood powders which are in line with granularity of requirement for power generation through treble percussion effect including percussion between the particles and the dynamic and fixed cutters, percussion between particles and particles, and percussion between the particles and the shell. Simultaneously, the disintegrator has realized integration between the main motor and the main spindle, which has many characteristics such as contact construction, low noise and slight vibration. This machine is possible to realize 3 kind of granularity that could be selected.

Abstract: Based on viscoelastic fluid mechanics, this paper presents a simulation model of the flow behaviour of thin polymer film during nanoimprint lithography (NIL). The polymer is imprinted at a constant temperature of 180oC and at a constant imprint speed of 100nm/s by using a tool with a single convex feature of 100 nm in width and 500 nm in height. At the imprint beginning, only a very limited area adjacent to the tool top is affected by the imprint, but subjects to a sudden change of pressure. With the imprint process forward, the wave-like polymer front and the trumpet-shaped profile are predicted to travel out from the imprint patterns. When the tool base intimately contacts the polymer film, another sudden change of the pressure occurs in the area under the interface between the polymer surface and the tool base. These results are of significance to understand the flow behaviour of NIL.

Abstract: The elastoplastic instability of the symmetrical double-arc ring-stiffened cylindrical shell was analyzed. The critical pressure was obtained for small deflection elastoplastic buckling of the cylindrical shell under hydrostatic pressure. The critical pressure for large deflection buckling of the cylindrical shell with initial geometric imperfections was determined under hydrostatic pressure by using nonlinear large deformation theory. The effects of hoop equivalent wave number, initial geometric imperfection and the central angle of circular arc on buckling mode and critical pressure of double-arc ring-stiffened cylindrical shell were analyzed. The results showed that the hoop equivalent wave number of arc cylindrical shell had an main effect on the critical pressure of the structure, designed equivalent hoop wave number of double-arc cylindrical shell should not be approach to the hoop wave number corresponding to minimum critical pressure, and the central angle of circular arc had less effect on critical pressure of the structure.