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Finite-Element Analysis on the Stability of Geotextile Tube-Reinforced Embankments under Scouring
Kim, Hyeong-Joo,ASCE, A.M.,Won, Myoung-Soo,Jamin, Jay C. CRC Press, LLC 2015 International journal of geomechanics Vol.15 No.2
<P> Scouring is a significant problem on river bank and coastal protection systems. Severe scouring can cause damaging consequences to geotextile tube embankment structures. In this study, five case scenarios of an embankment system supported by stacked geotextile tubes were analyzed using a commercially available finite-element analysis software. These case scenarios include (1) conventional geotextile tube stacking on ground base foundation; (2) geotextile tube stacking on gravel bedding foundation; (3) geotextile tube stacking on excavated foundation; (4) geotextile tube stacking on excavated foundation with gravel bedding; and (5) fortification of stacked geotextile tubes by riprap protection. Each case scenario is simulated under normal loading and critical loading conditions with and without scouring at the base toe of the embankment system. Results suggest that the potential problems that occur during scouring and critical states of the embankment system instigate failures that could destabilize the geotextile tube retaining structure. Among all the case scenarios considered, additional fortification by riprap increases the performance and global stability of the geotextile tube embankment system. </P>
Predicting Powder-Polymer Mixture Properties for PIM Design
Kate, K.H.,Enneti, R.K.,Park, S.-J.,German, R.M.,Atre, S.V. CRC PRESS LLC 2014 CRITICAL REVIEWS IN SOLID STATE AND MATERIALS SCIE Vol.39 No.3
Powder injection molding (PIM) is a high-volume manufacturing technique for fabricating ceramic and metal components that have complex shapes. In PIM design, it is important to know the injection molding behavior at different powder-polymer compositions so as to understand the trade-offs between ease-of-fabrication, process throughput, and part quality at the design stage. A limited database of materials properties at different powder-polymer compositions is a significant challenge that needs to be addressed in order to conduct accurate computer simulations that aid part and mold design in PIM. However, accurate material property measurements are expensive and time-consuming. In order to resolve these conflicting challenges it is hypothesized that experimental measurements of material properties of a filled polymer at a specific filler content combined with similar measurements of unfilled polymer will be adequate to estimate the dependence of properties on filler content using rule-of-mixture models. To this end, this article focuses on a literature review of experimental data obtained from measurements of rheological, thermal, and mechanical properties for a wide range of powder-polymer mixtures at various filler volume fractions. The experimental data were compared to property estimates using various predictive models. It is expected that the current review will be valuable in selecting appropriate predictive models for estimating properties based on the input data requirements for commercially available mold-filling simulation platforms such as Moldflow (R) and PIMSolver (R). The combined protocol will be useful to design new materials and component geometries as well as optimize process parameters while eliminating expensive and time-consuming trial-and-error practices prevalent in PIM.
Processing, Structure, Properties, and Applications of PZT Thin Films
Izyumskaya, N.,Alivov, Y. -I.,Cho, S. -J.,Morkoç,, H.,Lee, H.,Kang, Y. -S. CRC PRESS LLC 2007 Critical Reviews in Solid State and Materials Scie Vol.32 No.3
<P> There has been a resurgence of complex oxides of late owing to their ferroelectric and ferromagnetic properties. Although these properties had been recognized decades ago, the renewed interest stems from modern deposition techniques that can produce high quality materials and attractive proposed device concepts. In addition to their use on their own, the interest is building on the use of these materials in a stack also. Ferroelectrics are dielectric materials that have spontaneous polarization in certain temperature range and show nonlinear polarization-electric field dependence called a hysteresis loop. The outstanding properties of the ferroelectrics are due to non-centro-symmetric crystal structure resulting from slight distortion of the cubic perovskite structure. The ferroelectric materials are ferroelastic also in that a change in shape results in a change in the electric polarization (thus electric field) developed in the crystal and vice versa. Therefore they can be used to transform acoustic waves to electrical signal in sonar detectors and convert electric field into motion in actuators and mechanical scanners requiring fine control. In a broader sense the ferroelectric materials can be used for pyroelectric and piezoelectric sensors, voltage tunable capacitors, infrared detectors, surface acoustic wave (SAW) devices, microactuators, and nonvolatile random-access memories (NVRAMs), including the potential production of one transistor memory cells, and applications requiring nonlinear optic components. Another set of potential applications seeks to exploit the ferroelastic properties in stacked templates where they are juxtaposed to ferromagnetic materials. Doing so would allow the control of magnetic properties with electric field, which is novel. Such templates taking advantage two or more properties acquired a new name and now goes by multiferroics. After a brief historical development, this article discusses technological issues such as growth and processing, electrical and optical properties, piezo, pyro, and ferroelectric properties, degradation, measurements methods, and application of mainly lead-zirconate-titanate (PZT = PbZr1-xTixO3). The focus on PZT stems from its large electromechanical constant, large saturation polarization and large dielectric constant.</P>