Investigation of porous polydimethylsiloxane structures with tunable properties induced by the phase separation technique

This article reports the fabrication and characterization of porous polydimethylsiloxane (PDMS) structures developed by the solvent evaporation-induced phase separation technique. Ternary systems containing water/tetrahydrofuran (THF)/PDMS with various concentrations are produced to form a stable solution. The porous PDMS structures are formed by removing the solvent (THF) and nonsolvent (water) phases during the stepping heat treatment procedure. The analytical ternary phase diagram is constructed based on the thermodynamic equilibrium state in the polymer solution to explain the stable/unstable formulations and the possible composition change path. The results show that the isolated pores with the adjustable pore size ranging from 330 to 1900 μm are obtained by tuning the water to the THF ratio. The mechanical properties of the porous PDMS structures are determined by conducting the tensile tests on the prepared dog bone-shaped specimens. A wide range of elastic modulus ranging between 0.49 and 1.05 MPa was achieved without affecting the density of the porous sample by adjusting the solvent and non-solvent content in the solution. It is shown that the flexibility of the porous structures can be improved by reducing the ratio of water to THF and decreasing the PDMS content. The porosity measurements reveal that the PDMS concentration is the major phase controlling the porosity of the structure, while the effect of water/THF is negligible.     

A knowledge based approach to automate forging design

This paper describes a method and a system to automate the design of forging geometries. The method is derived from the principles and the actual practices of forging design used by experienced forging designers. Due to the diversity of the knowledge and problem solving techniques required for forging design, a combination of knowledge-based and algorithmic techniques was employed to implement the AFD (automated forging design) system. Given a set of design specifications, that is, machined part geometry, processing conditions, and special design considerations, the AFD system designs the forging section geometry automatically. Initial results from AFD show that it can be a powerful tool for designing geometries for the rib-web type of forgings.     

Uniaxial tensile properties of TiO2 coated single wool fibers by sol‐gel method: The effect of heat treatment

Single wool fibers were coated with TiO₂ by using the sol‐gel method. The uniaxial tensile properties of TiO₂ coated single wool fibers heated at different temperatures from 25 to 200°C were investigated and compared with those of uncoated single wool fibers. It was observed that the shape of the stress–strain curve of TiO₂ coated wool fibers became the same as uncoated wool fibers and showed a similar tendency of change to uncoated wool fibers with increasing temperature. But, the TiO₂ coated wool fibers obtained higher rigidity than uncoated wool fibers and up to their rupture points; they obtained higher stress levels in three deformation regions in the stress–strain curves, which indicates stronger wool fibers. Although the breaking extension of TiO₂ coated wool fibers decreased little by about 8%, the Young's modulus of TiO₂ coated wool fibers increased significantly by 19%, which was caused mostly by an increment in the stiffness of the cuticle layer of the wool fiber, and remained relatively higher than that of uncoated wool fibers after heat treatments. Structural changes in both uncoated and TiO₂ coated single wool fibers due to thermal effect, which caused the changes in the uniaxial tensile properties and the thermal behaviors of these fibers were discussed by using spectroscopic and thermal analysis methods in detail. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 898‐907, 2013     

Computational and experimental study of high-speed impact of metallic Taylor cylinders

High-speed impact of metallic Taylor cylinders is investigated computationally and experimentally. On the computational side, a modular explicit finite element hydrocode based on updated Lagrangian formulation is developed. A non-classical contour integration is employed to calculate the nodal forces in the constant strain axisymmetric triangular elements. Cell and nodal averaging of volumetric strain formulations are implemented on different mesh architectures to reduce the incompressibility constraints and eliminate volumetric locking. On the experimental side, a gas gun is designed and manufactured, and Taylor impact tests of cylinders made of several metallic materials are performed. Computational predictions of the deformed profiles of Taylor cylinders and experimentally determined deformed profiles are compared for verification purposes and to infer conclusions on the effect of yield strength, strain hardening and strain rate on the material response. The article also compares the performance of different plastic flow stress models that are incorporated into the hydrocode with the experimental results and results provided by previously reported simulations and tests.     

Electrochemical genosensor based on colloidal gold nanoparticles for the detection of Factor V Leiden mutation using disposable pencil graphite electrodes

Electrochemical genosensors for the detection of the Factor V Leiden mutation from polymerase chain reaction (PCR) amplicons using the oxidation signal of colloidal gold (Au) is described. A pencil graphite electrode (PGE) modified with target DNA, when hybridized with complementary probes conjugated to Au nanoparticles, responded with the appearance of a Au oxide wave at approximately +1.20 V. Specific probes were immobilized onto the Au nanoparticles in two different modes: (a) Inosine-substituted probes were covalently attached from their amino groups at the 5' end using N-(3-dimethylamino)propyl)-N'-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysulfosuccinimide (NHS) as a coupling agent onto a carboxylate-terminated l-cysteine self-assembled monolayer (SAM) preformed on the Au nanoparticles, and (b) probes with a hexanethiol group at their 5' phosphate end formed a SAM on Au nanoparticles. The genosensor relies on the hybridization of the probes with their complementary targets, which are covalently immobilized at the PGE surface. Au-tagged 23-mer capture probes were challenged with the synthetic 23-mer target, 131-base single-stranded DNA or denatured 256-base polymerase chain reaction (PCR) amplicon. The appearance of the Au oxidation signal shortened the assay time and simplified the detection of the Factor V Leiden mutation from PCR amplified real samples. The discrimination between the homozygous and heterozygous mutations was also established by comparing the peak currents of the Au signals. Numerous factors affecting the hybridization and nonspecific binding events were optimized. The detection limit for the PCR amplicons was found to be as low as 0.78 fmol; thus, it is suitable for point-of-care applications.     

Mechanical and Antibacterial Properties of Injection Molded Polypropylene/TiO2 Nano-Composites:Effects of Surface Modification

Polypropylene (PP)/titanium dioxide (TiO2) nano-composites were prepared by melt compounding with a twin screw extruder. Nanoparticles were modified prior to melt mixing with maleic anhydride grafted styrene-ethylene-butylene-styrene (SEBS-g-MA) and silane. The composites were injection molded and mechanical tests were applied to obtain tensile strength, elastic modulus and impact strength. Antibacterial efficiency test was applied on the injection molded composite plaques by viable cell counting technique. The results showed that the composites including SEBS-g-MA and silane coated TiO2 gave better mechanical properties than the composites without SEBS-g-MA. Antibacterial efficiency of the composites varied according to the dispersion and the concentration of the particles and it was observed that composites at low content of TiO2 showed higher antibacterial property due to the better photocatalytic activity of the particles during UV exposure.     

Prediction of forming limits and parameters in the tube hydroforming process

Determination of process limits and parameters for hydroforming was conducted applying widely known plasticity, membrane and thin-thick walled tube theories. Analytical predictions were compared with experimental findings. Simple but useful analytical models to predict buckling, wrinkling and bursting as well as axial force, internal pressure, counter force and thinning in tube hydroforming were verified with experimental results.     

The use of FEA and design of experiments to establish design guidelines for simple hydroformed parts

We present models to predict the protrusion height of “Tee-shaped” hydroformed parts, both because this information is of direct relevance to engineers attempting to build such parts and also to illustrate an advantageous process for developing design guidelines for tube hydroforming (THF) in general. A newly proposed design of experiments technique, Low Cost Response Surface Method (LCRSM), was utilized to facilitate the economical prediction and optimization of this height as a function of geometrical parameters subject to thinning of the wall thickness at the protrusion region. The same methodology is also proposed for the economical investigation of other geometries and conditions. As a result of this investigation, not only were known and expected trends of effect of parameters verified, but also numerical values within a practical range of parameters at certain conditions were obtained. In addition, interactions between factors were also revealed as predicted. Moreover, this information was gained from a substantially reduced number of finite element analysis (FEA) simulations via LCRSM compared to standard response surface method (RSM) or factorial techniques, avoiding costly physical experimentation.     

Effects of Laser-Cutting and Spark Erosion Techniques and Heat Treatment on the Magnetic Properties of Grain-Oriented Transformer Steels

Spark erosion and laser-cutting processes were examined in terms of their effects on the magnetic properties of grain-oriented electrical steels at working frequencies. The maximum permeability value in each case was considered a reference to determine the quantitative effect of cutting and eroding methods as well as the effects of heat treatment. To minimize the deterioration that appears after the piercing process is implemented, the specimens were subjected to heat treatment at the most appropriate temperature. The influence of stress-relief annealing could be observed throughout the domain refinement on the surface by using magneto-optical Kerr microscopy. Additionally, it was clearly seen that the domain contrast at the cut edge of the spark-eroded sample was more uniform than that provided by laser cutting upon applying a high AC-field amplitude.