Prakash Patnaik

A Local Information Exchange Based Coverage-Preserving Protocol For Wireless Sensor Networks

Coverage preserving solutions have been reported and are basically based upon node scheduling and quality coverage. Node scheduling based solutions presents at least three challenging problems: 1) resolving conflicts when determining what nodes should be turned-off to save energy; 2) finding optimal wakeup strategies that avoid waking up more nodes than necessary; and 3) keeping connectivity and coverage of the network while optimizing the number of nodes. This paper presents a novel distributed solution that extends the coverage calculation method proposed by Tian and Georganas, referred here as C-PNSS scheme. The solution is based on local information exchange without the uncertainty of self-schedule algorithms. Our Optimal Coverage-Preserving Scheme (OCoPS) comprises a new Decision algorithm, devised to resolve the off-duty conflict problem for different network densities, and an energy aware Wakeup scheme that solves problems, such as coverage holes, that exist in current schemes. We discuss the implementation of OCoPS with the new Decision algorithm as an extension of LEACH. A set of simulation experiments was performed to evaluate OCoPS performance when compared to the C-PNSS scheme. Our results indicate that our solution outperforms C-PNSS by over 20% on network lifetime and by over 25% on network lifetime when the coverage rate is higher than 80%. The experimental results also show that our coverage scheme based on our extended coverage calculation method effectively limits the on-duty node number when compared the original C-PNSS scheme.

An Improved Wear-resistant PTA Hardfacing: VWC/Stellite 21:

A novel compound carbide, VWC, is designed to incorporate into Stellite 21, in order to achieve an improved wear-resistant composite, plasma transferred arc (PTA) hardfacing. Different contents of VWC in the composite, 5, 10, and 20% (in weight), are tested. The microstructures of the hardfacing specimens are studied using, scanning electron microscopy (SEM) plus, energy dispersive X-ray (EDX) and X-ray techniques. The influence of VWC additive on the mechanical properties of the Co solid solution in Stellite 21 matrix is investigated with a nano-indentation technique. The hardness and wear resistance of the hardfacing specimens are evaluated on a Wilson Rockwell machine and a ball-on-disc tribometer, respectively. It is found that the hardness and wear resistance of the VWC/Stellite 21 composite layer are much higher than those of pure Stellite 21. The presence of the VWC reinforcement changes the microstructure of the Stellite 21 matrix and strengthens the Co solid solution.

Effects of heat treatment on mechanical and tribological properties of cobalt-base tribaloy alloys

Cobalt-base Tribaloy alloys are important wear-resistant materials, especially for high-temperature applications, because of the outstanding properties of the strengthened cobalt solid solution and the hard Laves intermetallic phase that make up the alloys. The Laves intermetallic phase is so abundant (35–70 vol.%) in these alloys that its presence governs all of the material properties. Heat treatment may alter the volume fraction, the size/shape, and the distribution of the Laves phase in the microstructures as well as the phase and structure of the cobalt solid solution, thus influencing the mechanical and tribological properties of the alloys. In this work, the effects of heat treatment on two cobalt-based Tribaloy alloys, T-400 and T-200, were studied. The former is a well-known Tribaloy alloy, and the latter is a newly developed one. These two alloys were heat treated in different conditions. The phases and microstructures of the alloys before and after the heat treatments were analyzed using x-ray and scanning electron microscopy. The mechanical and tribological properties of the alloys were investigated using a nano-indentation technique and a pin-on-disc tribometer, respectively.

Instability Analysis for Thermal Barrier Coating by Fracture Mechanical Modelings

Two simplistic models based on fracture mechanics considerations are used to advance the understanding of instability conditions in TBC systems. First model assumes isostrain behavior at and prior to the onset of crack initiation and is based on elastic energy balance approach. The other model is used for layer buckling and crack propagation behavior. The analysis for crack initiation suggests that the crack tip driving force, KI can reach a high value that is comparable to the fracture resistance of the coating material at and near the TBC/TGO interface even for a small nominal applied stress. The stresses required for the crack driving force (KI or GI ) exceeding the fracture resistance of TBC materials are found to be in the range of 0.05 to 0.5 GPa. This appears to be an order of magnitude lower than the reported tangential tensile stress values of 1 to 2 GPa, but matches closely with the simulated transverse stress. High crack driving force resulting from low stress and small size defects (around 2 microns) facilitates early crack initiation in TBC system.© 2007 ASME

A Framework of Prognosis and Health Management: A Multidisciplinary Approach

A multi-disciplinary team covering mechanical, materials and information technologies are investigating and developing appropriate technologies for aircraft prognostics and health management (PHM) applications. To integrate the efforts, a framework for PHM has been developed with three major functional blocks: Life Prediction, State Awareness, and Information Management. This framework provides a hierarchy for development and implementation. Achievements and future plans within this framework are presented with specific applications to military legacy systems and future acquisitions. Opportunities are described within some new initiatives for development and implementation.© 2007 ASME