P/M PROCESSING AND CHARACTERIZATION OF CONTROLLED TRANSFORMATION TEMPERATURE NiTi

Double vacuum arc remelted NiTi ingots were vacuum induction remelted and subsequently atomized using a high-pressure gas stream. Powders were collected, loaded into cans, and hot isostatically pressed (HIP'ed). Prior to HIP'ing, powders of various known transformation temperatures (As), were precisely blended to achieve a desired intermediate transformation temperature (As). This intermediate As follows an empirical relationship which approximates a rule of mixtures based on weight fraction. As were measured using differential scanning calorimetry (DSC). Results for HIP'ed and high temperature annealed specimens indicate that this technique was accurate and reproducible for measuring the transformation temperature of smooth, nearly symmetrical DSC curves. DSC/DTA thermograms in the literature typically show a double peak exothermic-martensitic reaction which was different than the smooth peaks observed for the HIP'ed condition. The specific thermomechanical history performed on the P/M material resulted in the double peak exothermic reaction. To interpret the peaks, thermal arrest experiments were conducted on both exothermic peaks, the results of which clearly support the existence of a premartensitic reaction. Thermal arrest experiments were also performed to analyze incomplete thermal cycles on both heating and cooling. Thermal arrest of the martensite reaction resulted in reduced energy absorbed for completion of the austenite reaction. Conversely, martensite energy was reduced by an arrest of the austenite reaction. However, reheating the sample revealed that the arrest split the austenite reaction into two distinct peaks, the split occurring at the temperature of the prior thermal arrest. These results and results of additional DSC experiments serve to emphasize the influence of thermomechanical history on the kinetics and energetics of the SME transformation. The P/M blending process technique was found to result in unprecedented control of the As temperature. Scientific/engineering considerations justify P/M processing and mechanical blending as opposed to conventional cast/wrought processing to achieve accurate As temperatures

MONOTONIC AND THERMOMECHANICAL TESTING OF P/M NiTi

P/M NiTi for the test program was manufactured by the Special Metals powder metallurgy process and converted to wire by hot swaging and wire drawing. The mechanical test program was undertaken in order to investigate the performance of NiTi both for scientific reasons and for better understanding of material performance as it specifically pertains to shape memory effect (SME) devices. Two types of mechanical tests, monotonic deformation/recovery and thermomechanical cyclic deformation, were used to characterize performance. As anticipated, monotonic mechanical properties were equivalent to cast/wrought properties. Individual NiTi wire specimens were deformed in an incremental series up to 30 percent total engineering strain. These prestrained specimens followed three experimental thermal cycles which monitored deflection, load, and energy during the shape recovery-heating cycle. The aforementioned three techniques were used to provide a more complete understanding of the shape recovery response. Each measurement technique demonstrated a maximum in the recovery resulting from an 8 to 12 percent total input strain. Monotonic results indicate that the maximum recovery strain is a measure of SME capacity to provide a single output of deflection (or force), which are potentially useful data for SME devices performing monotonically. Thermomechanical testing was conducted using a servo-hydraulic test machine in conjunction with a controlled temperature environmental chamber in an attempt to simulate a cyclic SME device. After deformation to a predetermined strain, stroke position was held constant as the specimen was thermally cycled above Af and the resulting load was monitored (strain control). This test mode resulted in permanent damage and loss of SME with each thermomechanical cycle, manifested as a decrease in load and available work delivered by the specimen. In load control, the specimen was deformed to a predetermined strain, the load reduced, and maintained at approximately zero during the thermal cycle above Af. This load control technique proved to be much less damaging to the specimen. Load control testing was clearly the superior technique for evaluating performance of cyclic SME devices

Plasma Sources in Planetary Magnetospheres: Mercury

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Bringing optical networks to the Cloud: an architecture for a sustainable future Internet

Over the years, the Internet has become a central tool for society. The extent of its growth and usage raises critical issues associated with its design principles that need to be addressed before it reaches its limits. Many emerging applications have increasing requirements in terms of bandwidth, QoS and manageability. Moreover, applications such as Cloud computing and 3D-video streaming require optimization and combined provisioning of different infrastructure resources and services that include both network and IT resources. Demands become more and more sporadic and variable, making dynamic provisioning highly needed. As a huge energy consumer, the Internet also needs to be energy-conscious. Applications critical for society and business (e.g., health, finance) or for real-time communication demand a highly reliable, robust and secure Internet. Finally, the future Internet needs to support sustainable business models, in order to drive innovation, competition, and research. Combining optical network technology with Cloud technology is key to addressing the future Internet/Cloud challenges. In this context, we propose an integrated approach: realizing the convergence of the IT- and optical-network-provisioning models will help bring revenues to all the actors involved in the value chain. Premium advanced network and IT managed services integrated with the vanilla Internet will ensure a sustainable future Internet/Cloud enabling demanding and ubiquitous applications to coexist