Modeling of Size Effects on the Flow Stress of Type 304 Stainless Steel and Application in Coining Process

Application of microforming in various research areas has received much attention due to the increased demand for miniature metallic parts that require mass production. For the accurate analysis and design of microforming process, proper modeling of material behavior at the micro/meso-scale is necessary by considering the size effects. Two size effects are known to exist in metallic materials. One is the “grain size” effect, and the other is the “feature/specimen size” effect. This study investigated the “feature/specimen size” effect and introduced a scaling model which combined both feature/specimen and grain size effects. Predicted size effects were compared with experiments obtained from previous research and showed a very good agreement. The model was also applied to forming of micro-features by coining. A flow stress model for Type 304 stainless steel taking into consideration the effect of the grain and feature size was developed and implemented into a finite element simulation tool for an accurate numerical analysis. The scaling model offered a simple way to model the size effect down to length scales of a couple of grains and extended the use of continuum plasticity theories to micro/meso-length scales.

Failure Analysis of a Fibrous Composite Half-Space Subjected to Uniform Surface Line Load

Uni-Directional Fiber-Reinforced Plastic (UD-FRP) laminates have been modeled previously as an equivalent quasi-homogeneous monoclinic half-space subjected to an inclined line load on the surface using Lekhnitskii’s formulation simulating the orthogonal edge trimming loads in UD-FRPs. In continuation, failure analysis of the aforementioned composite half-space has been carried out in the present investigation based on Tsai-Wu criterion. In particular, the failure behavior of the half-space laminate with respect to the fiber orientation, load inclination angle and spatial coordinates has been examined in detail. The motivation behind such a study lies in correlating the failure behavior of the half-space laminate with the damage progression observed during orthogonal edge trimming experiments. The present work strives at identifying this relationship and in the process, understanding the physics of orthogonal cutting mechanisms in UD-FRP laminates.

Effect of Carbon Nanotube on Electrical, Thermal and Mechanical Properties of Epoxy

In this study, electrical, thermal and mechanical properties of multi-walled carbon nanotubes (CNTs) reinforced Epon 862 epoxy have been evaluated. Firstly, 0.1 wt%, 0.2 wt%, 0.3 wt%, and 0.4 wt% CNT were infused into epoxy through a high intensity ultrasonic liquid processor and then mixed with EpiCure curing agent W using a high speed mechanical agitator. The trapped air and reaction volatiles were removed from the mixture using a high vacuum. Neat epoxy sample also was made as reference. Electrical conductivity, dynamic mechanical analysis (DMA, three point bending tests and fracture tests were performed on unfilled, CNT-filled epoxy to identify the loading effect on the properties of composites. Experimental results show significant improvement in electric conductivity. The resistivity of epoxy decreased to 15Ωm with 0.4% CNT. DMA studies revealed that filling the carbon nanotube into epoxy can produce a 90% enhancement in storage modulus and a 17° C increase in Tg, but CNT has little effect on decomposing temperature. Mechanical test results showed that modulus increased with higher CNT loading percentages, but the 0.3 wt% CNT-infusion system showed the maximum strength and fracture toughness enhancement. The decrease in strength and fracture toughness in 0.4% CNT/epoxy was attributed to poor dispersions of nanotubes in the composite.

Modeling and Characterization of a Chemomechanical Actuator Based on Protein Transporters

Plants and animal cells are naturally occurring actuators that exhibit force and motion driven by fluid transport through the cell membrane. The protein transporters embedded in the cell membrane serve as the selective gateway for ion and fluid transport. The actuator presented in this work generates force and deformation from mass transport through an artificial membrane with protein transporters extracted from plant cell membranes. The artificial membrane is formed from purified 1-Palmitoyl-2-Oleoyl-sn-Glycero-3-[Phospho-L-Serine] (Sodium Salt) (POPS), 1-Palmitoyl-2-Oleoyl-sn-Glycero-3-Phosphoethanolamine (POPE) lipids and supported on a porous substrate. The protein transporter used in the actuator membrane is a proton-sucrose cotransporter, SUT4, extracted from yeast cells that genetically modified to grow the cotransporter in their cell membranes. The SUT4 transporter conducts proton and sucrose from the side of the membrane with higher concentration and carries water molecules across the membrane. It is observed from transport characterization experiments that fluid flux through the membrane varies with the applied sucrose concentration and hence is chosen as the control stimulus in the actuator. A modified four-state facilitated diffusion model is applied to the transport characterization data to compute the two characteristic parameters for fluid transport, saturation concentration and translocation rate, through the membrane. The flux rate through the membrane is observed to increase with the concentration till a particular value and saturates at a higher concentration. The concentration at which the flux rate through the membrane saturates is referred to as the saturation concentration. The saturation concentration for the actuator is experimentally found to be 6±0.6mM sucrose on the side with lower pH. The corresponding maximum translocation rate is found to be 9.6±1.2 nl/μ.cm2.min. The maximum steady state deformation produced by the actuator is observed at 30 mM sucrose that corresponds to a force of 0.89 mN.

Novel Processing of Structural Epoxy for Shielding and Structural Applications

In this study we investigate the shielding effectiveness of a structural epoxy against high energy protons. To study the influence of material texture on its radiation shielding effectiveness we induced orientations in the epoxy using a high magnetic field of 15 T, and exposed it to proton beams of energy 6 MeV-15 MeV. The micro structures of the samples were characterized using ESEM microscopy. The effect of the radiation on the mechanical properties of the samples was measured using nanoindentation tests. The findings of this study can lead to an optimal processing path for multifunctional epoxy that can be utilized as structural and shielding component in future space missions.

CFD Analysis of a Continuous Inkjet Print Head for Direct Write Fabrication

This paper investigates the fluid generation mechanism in a modified Continuous Inkjet Print (CIJ) method. The CIJ technique is utilized to deposit a variety of conductive nano particulate materials for building miniaturized devices that can sustain harsh environments. These include devices and structures that can sustain high temperature and humidity applications. Given the complex drop formation mechanism a CFD model is developed that is further validated using an ultrahigh speed photography experimental setup. Various input parameters such as frequency, voltage and fluid pressure can be tuned using the model for different fluid types to obtain an optimal drop formation. These findings can be useful for the fabrication of freeform miniaturized devices in 3 dimensional space.

Dynamic Rheology and Microstructure of Polypropylene/Clay Nanocomposites Prepared Under Sc-CO2 by Melt Compounding

The polypropylene (PP)/clay nanocomposites were prepared using a twin screw extruder with the aid of the supercritical carbon dioxide (Sc-CO2). The dynamic rheological properties were measured using a rheometer in the oscillatory mode. X-ray diffraction and transmission electron microscopy were used to characterize the microstructure of extruded nanocomposites. Results showed that an optimized CO2 concentration existed. When the CO2 concentration increased up to the optimized level, the nanocomposites tended to be more viscous, especially at low frequency. Whereas further increasing the CO2 concentration resulted in the decrease in the complex viscosity and dynamic moduli. The presence of Sc-CO2 with the concentration not higher than the optimized level was helpful to promote the degree of dispersion of the nano-clay in PP matrix, and overloaded CO2 would have negative effect on the clay dispersion.

Substrate Preparation by Magnetron Sputtering and CVD Growth of Carbon Nanotube Arrays

In this study we explored the use of magnetron sputtering as an alternative to e-beam deposition for preparation of the alumina intermediate layer and of the metal catalyst on an oxidized Si wafer. This approach offers large area deposition of the layered substrate including the intermediate alumina layer and the final catalyst film. The effects of the substrate design on the growth of long multi-wall carbon nanotube (MWCNT) arrays by CVD (Chemical Vapor Deposition) were also explored. The CNT synthesis was carried on in a hydrogen/ethylene/water/argon environment at 750 °C for different periods of deposition time. Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), Thermal Gravimetric Analysis (TGA) and Transmission Electron Microscopy (TEM) were employed to characterize the substrates and the CNT arrays. The study showed that for specific processing conditions the length of highly oriented CNTs strongly depends on the thickness of Al2O3 intermediate layer and on the catalyst film. The results obtained confirm that magnetron sputtering can be successfully employed as a tool for substrate preparation to grow 7 mm long CNT arrays with high purity. The aligned nanotubes do not suffer from limitations typical for powdered (spaghetti type) nanotubes which opens up new applications.

Analysis of the Piezoelectric Ceramics PLZT With ANSYS

Traditional electric servo system is disturbed by electromagnetic interference, so optical servo system is needed to build urgently in order to avoid electric signal and electrical wire. Therefore, photostrictive ceramics becomes promising material to realize the optic-signal transmission and photostriction. Lanthanum-modified lead zirconate titanate (PLZT) ceramics, which also belongs to piezoelectric ceramics, is one of the most promising photostrictive materials that can stretch with the light intensity. Photostriction is the combination of the photovoltaic and converse piezoelectric effect. Because of little knowledge about photostriction, the piezoelectric characteristic of PLZT, which is a portion of the photostriction, is studied by use of coupled-field analysis of the Finite Element Analysis (FEA) software ANSYS. The detailed steps of modeling are given. The performances of unilateralism and multilayer PLZT are described, such as displacement output, stiffness and dynamics characteristics. It can be concluded that ANSYS calculation value is very close to the theoretical results by comparing those two results, so ANSYS software can be used to preestimate before we research the characteristics of piezoelectric devices.

Process Optimization Studies on Ni-YSZ Anode Material for Solid Oxide Fuel Cell Applications

The characteristics of the Ni/YSZ anode material for the solid oxide fuel cells (SOFCs) were investigated in order to study the relation between the porosity and the conductivity of the cell. The nano-sized Yittria Stabilized Zirconia (YSZ) (∼ 60 nm), Nickel Oxide (NiO) (∼ 40 nm) and graphite (∼ 40 nm) particles were used as the raw materials. The graphite particles act as a pore former. The experiments were planned based on a response surface design (central composite design matrix). The graphite content and the sintering temperatures were varied based on the design chart, while the other variables like NiO/YSZ ratio, ball milling time, powder compaction pressure and reduction temperature values were fixed. Porosity and conductivity measurements were performed on the sintered and reduced anode material. The results indicated that the porosity values got decreased by increasing sintering temperature values, while the conductivity values were on the reverse scale. The conductivity values increase with increasing temperature. The scanning electron microscope (SEM) images showed that the sintering temperature had a visible impact on the microstructure. At elevated temperature, the microstructure showed visible particle growth and it formed a better Ni-network along the structure, compared to samples sintered at lower temperature. It is believed that the enhanced Ni-network at elevated temperature helps to increase the electrical conductivity of the Ni-YSZ anode cermet.