The Effects of Specimen Geometry on the Plastic Deformation of AA 2219-T8 Aluminum Alloy Under Dynamic Impact Loading

The effects of specimen geometry on shear strain localization in AA 2219-T8 aluminum alloy under dynamic impact loading were investigated. The alloy was machined into cylindrical, cuboidal and conical (frustum) test specimens. Both deformed and transformed adiabatic shear bands developed in the alloy during the impact loading. The critical strain rate for formation of the deformed band was determined to be 2500 s^?1 irrespective of the specimen geometry. The critical strain rate required for formation of transformed band is higher than 3000 s^?1 depending on the specimen geometry. The critical strain rate for formation of transformed bands is lowest (3000 s^?1) in the Ø5 mm × 5 mm cylindrical specimens and highest (> 6000 s^?1) in the conical specimens. The cylindrical specimens showed the greatest tendency to form transformed bands, whereas the conical specimen showed the least tendency. The shape of the shear bands on the impacted plane was also observed to be dependent on the specimen geometry. Whereas the shear bands on the compression plane of the conical specimens formed elongated cycles, two elliptical shaped shear bands facing each other were observed on the cylindrical specimens. Two parallel shear bands were observed on the compression planes of the cuboidal specimens. The dynamic stress–strain curves vary slightly with the specimen geometry. The cuboidal specimens exhibit higher tendency for strain hardening and higher maximum flow stress than the other specimens. The microstructure evolution leading to the formation of transformed bands is also discussed in this paper.     

Pressure control system for electrospinning process

Electrospinning is used to produce micro‐ and nano‐sized synthetic fibers through the use of electrostatic forces. Commercially, viable production of fibers requires high throughput of uniform fibers that are free of defects. To achieve greater control over the process variables that affect the fiber formation, a scalable closed loop control system that can maintain a constant pressure at the capillary tip was designed and tested. Two sensing technologies, infrared and ultrasonic, were used and compared for their ability to detect the height of polymer solution in the electrospinning fluid container. The air pressure above the solution was measured with a pressure transducer and adjusted through a controllable syringe pump. The closed loop electrospinning system was successful at controlling and maintaining a constant pressure at the capillary tip to within 2% of the specified pressure continuously. The controlled pressure at the capillary tip showed a strong correlation to fiber diameter and uniformity for polydimethylsiloxane‐based polyurethane/DMF‐based fibers. However the control system was less effective to control fiber diameter for polyethylene oxide/Water‐based fibers. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Fabrication of co-PVDF/modacrylic/SiO2 nanofibrous membrane: Composite separator for safe and high performance lithium-ion batteries

Highly porous free-standing co-poly(vinylidene fluoride)/modacrylic/SiO₂ nanofibrous membrane was developed using electrically-assisted solution blow spinning method. The performance and the potential of the membrane as a lithium-ion battery separator were investigated. The addition of modacrylic enhanced the solution spinnability that resulted in defect-free membranes. Moreover, the presence of modacrylic enhanced the dimensional and thermal stabilities, while the addition of hydrophilic SiO₂ nanoparticle enhanced both mechanical property and ionic conductivity. Combustion test results illustrated that the presence of modacrylic provide flame retarding property over a set of different polymeric-based membranes. Electrochemical performance results showed that the developed membrane can increase the battery capacity compared with the commercial separator.     

Transferrin-Decorated Niosomes with Integrated InP/ZnS Quantum Dots and Magnetic Iron Oxide Nanoparticles: Dual Targeting and Imaging of Glioma

The development of multifunctional nanoscale systems that can mediate efficient tumor targeting, together with high cellular internalization, is crucial for the diagnosis of glioma. The combination of imaging agents into one platform provides dual imaging and allows further surface modification with targeting ligands for specific glioma detection. Herein, transferrin (Tf)-decorated niosomes with integrated magnetic iron oxide nanoparticles (MIONs) and quantum dots (QDs) were formulated (PEGNIO/QDs/MIONs/Tf) for efficient imaging of glioma, supported by magnetic and active targeting. Transmission electron microscopy confirmed the complete co-encapsulation of MIONs and QDs in the niosomes. Flow cytometry analysis demonstrated enhanced cellular uptake of the niosomal formulation by glioma cells. In vitro imaging studies showed that PEGNIO/QDs/MIONs/Tf produces an obvious negative-contrast enhancement effect on glioma cells by magnetic resonance imaging (MRI) and also improved fluorescence intensity under fluorescence microscopy. This novel platform represents the first niosome-based system which combines magnetic nanoparticles and QDs, and has application potential in dual-targeted imaging of glioma.     

Relative brittleness characterization of some selected granitic building stones: Influence of mineral grain size

Being crystalline materials, brittleness may be an important issue for granitic rocks, especially when they are subject to certain loading conditions. Therefore, in practice, more specifically in their usage as a natural building stone, there is a need for their brittleness characterization. This paper reports a study carried out on some selected granitic rock types in order to determine their relative brittleness index values and relate it to their mineral grain size. For this purpose, three different types of granitic rocks similar in mineral composition, but diverse in grain sizes were selected for the execution of the study. The relative brittleness index values of the studied rock types were determined from the size effect method by using the point load test apparatus. Based on the results of this investigation it is was concluded that, rather than the proportions of the rock forming minerals such as quartz and feldspars, the grain size of feldspars could be the dominant parameter affecting relative brittleness values of the tested rocks.     

Effect of curing under pressure on compressive strength development of cemented paste backfill

The mechanical performance of cemented paste backfill (CPB) placed in underground openings (e.g., mine stopes) often differs from laboratory-predicted performance, even under the same atmospheric curing conditions (ambient temperature and relative humidity). This is probably due to the specific self-weight consolidation, different drainage conditions and confinement pressures encountered in the paste backfilled stopes. A new test system named CUAPS (Curing Under Applied Pressure System) was designed at the Université du Québec en Abitibi-Témiscamingue (UQAT) to assess the hydro-mechanical performance of in situ CPB samples at laboratory scale. The CUAPS apparatus allows the effective curing of CPB samples subjected to an assortment of vertical pressure applications (curing under stresses) that can mimic in situ placement and consolidation conditions. The compressive strength development of CPB samples prepared from sulphide-rich mine tailings from Garpenberg polymetallic mine (Sweden) was investigated using CUAPS apparatus and conventional plastic moulds (unconsolidated undrained samples) in parallel. The effect of curing stress (i.e. simulating different consolidation conditions) on resultant geotechnical index parameters and hydromechanical properties of CPB samples was analyzed. The primary observation is the confirmation that the compressive strength development of the consolidated CPB samples is higher than that of unconsolidated undrained ones. It could be attributed to the removal of excess pore water mainly due to the applied pressure during the effective curing process, which seems to improve consolidation process of the CPB material. The results also account for the differences in the CPB strength observed between laboratory samples and in situ samples. Thus, CUAPS would be more suitable than conventional plastic moulds to collect data for preliminary and final design of CPB systems.