Study of MA Effect on Yield Strength and Ductility of X80 Linepipe Steels Weld

Multipass GMAW (Gas Metal Arc Welding) welding was used to join X80 linepipe materials using two weld metals of slightly different compositions. Welding wires with diameters of 0.984 and 0.909 mm were used while applying the same heat input in each pass. The slight difference in the wire diameters resulted in different HAZ microstructures. The microstructures in the doubly reheated HAZ of both welds were found to contain bainite-ferrite. However, etching also revealed a difference in martensite-austenite (MA) fraction in these reheated zones. The MA exhibited twice the hardness of ferrite when measured by nanoindentation. Tensile testing from the reheated zone of both welds revealed a difference in yield strength, tensile strength and elongation of the transverse weld specimens. In the reheated zone of weld A, (produced with a 0.984 mm wire) a higher fraction of MA was observed, which resulted in higher strength but lower elongation compared to weld B. The ductility of weld A was found severely impaired (to nearly half of weld B) due to formation of closely spaced voids around the MA, along with debonding of MA from the matrix, which occurs just above the yield stress.

     

Intensity-dependent Phase Shifts in Nonlinear Coupling Devices

Abstract

For nonlinear coupling devices, general solutions using Stokes parameters fail to give complete information of phase shifts, as they only provide the phase-shift difference between the two outputs of coupling waveguides (or two cores for fibre coupling devices). Thus the standard Stokes parameter formulation is not sufficient for some applications in which the nonlinear phase shifts through the devices are of great concern. The analysis given here presents complete and exact solutions for nonlinear phase shifts in optical coupling devices for the first time. This reveals unusual behaviour of the nonlinear phase shifts because, in a certain input power range, a small change of input power can bring about a large change in the nonlinear phase shift. Some basic characteristics of the nonlinear phase shifts and their potential influence on application of coupling devices to all-optic signal processing are discussed.     

SAKE: Software attestation for key establishment in sensor networks

This paper presents a protocol called Software Attestation for Key Establishment (SAKE), for establishing a shared key between any two neighboring nodes of a sensor network. SAKE guarantees the secrecy and authenticity of the key that is established, without requiring any prior authentic or secret cryptographic information in either node. In other words, the attacker can read and modify the entire memory contents of both nodes before SAKE executes. Further, to the best of our knowledge, SAKE is the only protocol that can perform key re-establishment after sensor nodes are compromised, because the presence of the attacker’s code in the memory of either protocol participant does not compromise the security of SAKE. Also, the attacker can perform any active or passive attack using an arbitrary number of malicious, colluding nodes. SAKE does not require any hardware modification to the sensor nodes, human mediation, or secure side channels. However, we do assume the setting of a computationally-limited attacker that does not introduce its own computationally-powerful nodes into the sensor network.SAKE is based on Indisputable Code Execution (ICE), a primitive we introduce in previous work to dynamically establish a trusted execution environment on a remote, untrusted sensor node.     

Correlation between MgAl2O4-spinel structure,processing factors and functional properties of transparent parts (progress review)

Efforts were and are made to develop performant fabrication technologies, for transparent polycrystalline spinel – a material used for armor, infrared windows and other products. Significant progress was made – during some fifty years of research – regarding the understanding of the structure of spinel, at various scales, and the best ways to correlate processing with the relevant structural features so as to improve properties. This review compiles and comments the results of this progress, using as sources the literature and the author's own work. As of now the best specimens obtained combine submicron grains with an optical transmission close to the theoretical and a Vickers hardness of 15 GPa (size ≤25 cm). Larger plates, more than 0.5 m in size, but with coarse microstructure and lower hardness, have also been produced, together with quite large dome shaped parts, exhibiting highly uniform optical properties.     

Experimental study of melting of LDPE/PS polyblend in an intermeshing counter‐rotating twin screw extruder

An experimental study is presented of the melting mechanism in a starve‐fed closely intermeshing counter‐rotating twin screw extruder of a modular Leistritz design. Various polymeric materials, semicrystalline low density polyethylene (LDPE), amorphous polystyrene (PS), and (LDPE/PS) polyblend were investigated at various operating conditions. A “screw pulling‐out” technique was used to investigate polymer behavior along the screw axis. In particular, the solid conveying, melting positions, the extent of starved character along the screw, and the fully filled regions were observed. Polymer samples were stripped off from each screw which was removed from the machine to investigate melting mechanism. Generally, it has been concluded that the melting mechanism revealed by White and Wilczyński for polyolefines has been proved for other polymeric materials under study. This mechanism consists of pellets being dragged into the calendering gap where they are melted due to calendering action. The molten polymer is expelled from the gap and pushes against the pellet bed which is continuously dragged into the gap. The composite modeling of an intermeshing counter‐rotating twin screw extrusion of polyblends has also been discussed. POLYM. ENG. SCI., 52:449–458, 2012. © 2011 Society of Plastics Engineers     

Capturing expert knowledge of mesh refinement in numerical methods of impact analysis by means of genetic programming

The mesh refinement decisions of an experienced user of high-velocity impact numerical approximation finite differences computations are discovered as a set of comprehensible rules by means of Genetic Programming. These rules that could automatically trigger adaptive mesh refinement to mimic the expert user, detect mesh cells that require refinement by evolving a formula involving cell quantities such as material densities. Various cell variable combinations are investigated in order to identify the optimal ones for indicating mesh refinement. A high-velocity impact phenomena example of a tungsten ball that strikes a steel plate illustrates this methodology.     

Correlation Between Experimental and Calculated Phase Fractions in Aged 20Cr32Ni1Nb Austenitic Stainless Steels Containing Nitrogen

A centrifugally cast 20Cr32Ni1Nb stainless steel manifold in service for 16 years at temperatures ranging from 1073 K to 1123 K (800 °C to 850 °C) has been characterized using scanning electron microscopy (SEM), electron probe micro-analysis (EPMA), auger electron spectroscopy (AES), and X-ray diffraction (XRD). Nb(C,N), M₂₃C₆, and the silicide G-phases (Ni₁₆Nb₆Si₇) were all identified in a conventional SEM, while the nitride Z-phase (CrNbN) was observed only in AES. M₂₃C₆, Z-phase and G-phase were characterized in XRD. Thermodynamic equilibrium calculations using ThermoCalc Version S, with the TCS Steel and Fe-alloys Database (TCFE6), and Thermotech Ni-based Superalloys Database (TTNI8) were validated by comparing experimental phase fraction results obtained from both EPMA and AES. A computational study looking at variations in the chemical composition of the alloy, and how they affect phase equilibria, was investigated. Increasing the nitrogen concentration is shown to decrease G-phase formation, where it is replaced by other intermetallic phases such as Z-phase and π-phase that do not experience liquation during pre-weld annealing treatments. Suppressing G-phase formation was ultimately determined to be a function of minimizing silicon content, and understabilizing the Nb/(C + 6/7N) ratio.     

Selective particle and cell clustering at air–liquid interfaces within ultrasonic microfluidic systems

In this study, we demonstrate particle and cell clustering in distinct patterns on the free surface of microfluidic volumes. Employing ultrasonic actuation, submersed microparticles are forced to two principal positions: nodal lines (pressure minima) of a standing wave within the liquid bulk, and distinct locations on the air–liquid interface (free surface); the latter of which has not been previously demonstrated using ultrasonic standing waves. As such, we unravel the fundamental mechanisms behind such patterns, showing that the contribution of fluid particle velocity variations on the free surface (acoustic radiation force) results in patterned particle clustering. In addition, by varying the size and density of the microparticles (3.5–31 μm polystyrene and 1–5 μm silica), acoustic streaming is found to increase the tendency for a smaller and lighter particle to cluster at the air–liquid interface. This selectivity is exploited for the isolation of multiple microparticle and cell types on the free surface from their nodally aligned counterparts. Free surface clustering is demonstrated in both an open microfluidic chamber and a sessile droplet, as well as using a range of biological species Escherichia coli, blood cells, Ragweed pollen and Paper Mulberry pollen). The ability to selectively cluster submersed microparticles and cells in distinct patterns on the free surface showcases the excellent suitability of this method to lab-on-a-chip systems.