Measurements of Displacement Cross Section of Tungsten under 389-MeV Proton Irradiation and Thermal Damage Recovery

For validating the number of displacements per atom (dpa) for tungsten under high-energy proton irradiation, we measured displacement cross sections related to defect-induced electrical resistivity changes in a tungsten wire sample under irradiation with 389-MeV protons under 10 K. The Gifford–McMahon cryocooler was used to cool the sample using a conductive coolant via thermal conduction plates of oxygen-free high-conductivity copper and electrical insulation sheets of aluminum nitride ceramic. In this experiment, the displacement cross section was 1612 ± 371 b for tungsten at 389 MeV. A comparison of the experimental displacement cross sections of tungsten with the calculated results obtained using Norgett–Robinson–Torrens (NRT) dpa and athermal recombination-corrected (arc) dpa cross sections indicates that arc-dpa was in better agreement with the experimental data than NRT-dpa; this is similar to the displacement cross sections of copper. From the measurements of damage recovery of the accumulated defects in tungsten through isochronal annealing, which is related to the defect concentration of the sample, approximately 20% of the damage was recovered at 60 K. This trend was similar to those observed in other experimental results for reactor neutrons.

An Indirect Method of Micromagnetic Structure Estimation in Microwires

The tunable magnetic properties of amorphous ferromagnetic glass-coated microwires make them suitable for a wide range of applications. Accurate knowledge of the micromagnetic structure is highly desirable since it affects almost all magnetic properties. To select an appropriate wire-sample for a specific application, a deeper understanding of the magnetization reversal process is required, because it determines the measurable response (such as induced voltage waveform and its spectrum). However, the experimental observation of micromagnetic structure of micro-scale amorphous objects has strict size limitations. In this work we proposed a novel experimental technique for evaluating the microstructural characteristics of glass-coated microwires. The cross-sectional permeability distribution in the sample was obtained from impedance measurements at different frequencies. This distribution enables estimation of the prevailing anisotropy in the local region of the wire cross-section. The results obtained were compared with the findings of magnetostatic measurements and remanent state analysis. The advantages and limitations of the methods were discussed.

Quartz Enhanced Conductance Spectroscopy for Polymer Nano-Mechanical Thermal Analysis

A fast and highly sensitive polymer nano-mechanical thermal analysis method for determining the melting temperature (Tm) of polymer microwires was proposed. In this method, a small-size, low-cost quartz tuning fork was used as a piezoelectric transducer to analyze the thermodynamics of polymer microwires at the nanogram level without changing its own properties. Due to the thin wire sample, which has a length of 1.2 mm and a diameter of ~5 µm, which is bridged across the prongs of the tuning fork, the nanogram-level sample greatly reduces the thermal equilibrium time for the measurement, resulting in a fast analysis for the melting temperature of the polymer sample. Compared with the traditional method, the analysis method based on the quartz enhanced conductivity spectrum (QECS) does not require annealing before measurement, which is an essential process for conventional thermal analysis to reduce the hardness, refine the grain, and eliminate the residual stress. In this work, the melting temperatures of three of the most commonly used polymers, namely polymers polymethyl methacrylate, high-density polyethylene, and disproportionated rosin, were obtained under the temperature from room temperature to >180 °C, proving the QECS method to be a useful tool for nano-mechanical thermal analysis.

Dripping Behavior of Wire Fire under Varying Pressure and Electric Current

Dripping of polymer insulations is a different type of hazardous behaviors in wire fire, which has a potential risk of igniting adjacent combustible material and causing the dramatic growth and spread of fire in buildings, aircraft, spacecraft and nuclear power plant. To improve the fire-safety strategy, bench scale tests are conducted to study the dripping phenomenon using thin wire sample under various atmosphere pressure and electric current. The results show that the variation of flame front has a slight fluctuation during molten dripping, while the flame size (especially flame height) changes significantly. Moreover, dripping frequency (f) decreases with pressure (Ρ) due to a sufficient burning effect, but it increases with electric current (Ι) because of a stronger accumulating effect.

Friction Behavior Between Epoxy and Flexible Pipes Armor Wires

The offshore industry has presented an increasing demand over the last few decades, requiring the production in deep water fields. The end fittings (EF) are critical points within the production system. Therefore, structural and fatigue analyses are essential in the EF design, making it necessary to know the stress distribution experienced by the armor wires along the EF. Numerical and analytical models are often used in order to assess the stress state. However, characteristics like geometries, materials and interactions must be previously known in order to apply these models. The purpose of this work was to analyze the arithmetic mean surface roughness (Ra) and to determine the friction coefficient (μ) for two types of armor wires when in contact with resin used to fill the EF. The resin used in the interaction with the armor wires was an epoxy filled with metallic particles. For the experimental analysis straight carbon steel armor wires with different cross-sections, typically used in 2.5″ and 8″ flexible pipes were used. Surface profile was obtained for each wire by repeated measurements along two lines over each surface. A total of three repetitions were performed in each measure line. Longitudinal roughness was determined through these profiles. Finally, friction coefficients were obtained experimentally by means of a device that allows to simulate the wire pullout and sliding process. In this device, two epoxy pads were put in contact with the surface of the analyzed wire sample, and rigid bodies in contact with the pads were used to ensure that the normal load applied is transmitted uniformly through the contact surface. The displacement rate, contact pressure between the surface of the wire and the epoxy resin pads, and axial force were recorded. The roughness in the longitudinal direction of the wires was analyzed through descriptive statistic and compared by Student’s “t” test. The highest values were obtained on wires with larger sections. This behavior is exposed on the results obtained for the friction coefficient as a function of the contact pressure. Friction coefficient for both wires was analyzed and compared using a Mann-Whitney U test. Both friction coefficients have a positive slope, indicating a small increase as the contact pressure raise. The significance value obtained for the means comparisons was p = 0.0001 and confirms that the average friction coefficient of the two wires are really different. Because of that, we conclude that is necessary to treat the EF project for different flexible pipes differentially.

An Excess Heat Phenomenon Triggered by Pressure in a H-Pd Gas-Loading System

Some hydrogen atoms were being charged into metal palladium lattice and reached a certain ratio in a H-Pd gas-loading system under the pressure of PH2<1atm. The relationship between loading ratio, pressure and excess heat were studied at different reaction conditions. In one of the experiments the palladium wire was broken with a huge excess heat. The calculation results showed that about 2.2×104 Joules excess energy were released in that abnormal process, which was corresponding to 2.5×102eV for each palladium atom. Analysis on the surface of the melted broken section of palladium wire sample before and after the abnormal process with a scanning electron microscopy (SEM) and an energy dispersive spectrometer (EDS) revealed that new surface topographical features with concentrations of unexpected elements (Ag and Ca) were detected, which implied that the excess heat might come from a nuclear transmutation reaction

Infrared behavior of aluminum nanostructure sculptured thin films

ABSTRACTWe report on fabrication, structural and infrared optical characterization of nanostructure aluminum sculptured thin films prepared by glancing angle deposition (GLAD) and controlled substrate motion on p-type silicon. We discuss two structures, one with plate-like and one with screw-like (chiral) morphology. While the plate-like sample possesses a metal Drude behavior in the infrared spectral range, the chiral nanowire sample behaves non-metallic and reveals a series of intriguing resonances, which are equally spaced in frequency by ∼7.5 THz. We suggest that formation of 3D nano resonator circuits consisting of inductances and capacitances has occurred within the screw-like conductive aluminum wire sample, which might be responsible for the observed resonances. We suggest conductive GLAD nanostructures in combination with Schottky diodes to facilitate active or passive THz detector and transmitter devices.

Deformation Band Velocities and Local Strain Rates in a Ni-Cr-Fe Alloy (Inconel)

ABSTRACTNickel based alloys with nominal compositions similar to 78Ni -15Cr -7Fe, commonly referred to as “Inconel”, exhibit serrated flow (Portevin-LeChatelier effect) in the temperature interval of 230-730°C. Within this temperature range a series of thermally activated processes can also be observed when a wire sample of the alloy is heated with the direct resistance method under dead-weight loading while stressed above the room temperature yield. These processes include the expected initial period of plastic deformation at the start of heating followed by its complete arrest at a higher temperature, a behavior that is completely at odds with models for the thermal activation of plastic flow in metals. As the temperature is increased after this first arrest a cascade of two or three large plastic instabilities involving the high velocity propagation of narrow deformation bands is observed. Measurements of the band velocities using the time of flight within a 50.8 mm gage length extensometer indicate that they can exceed 2 m/s in some cases. Estimates of the maximum local strain rate attained within the deformation bands, obtained with a diametral extensometer, approach 15-18 s−1. The localization of plastic flow into narrow, high velocity bands in this material is the result of the collective behavior of dislocations interacting at a high density. As demonstrated by TEM examination of the complex dislocation structures associated with these various events, however, it is difficult to rationalize a specific mechanism for these effects. If one assumes that both serrated flow and the thermally activated strain bursts are manifestations of the same basic mechanism these observations pose a challenging problem for interpretation with models for the Portevin-LeChatelier effect in this material.

In Situ Studies of Coatings on Metal Wires by FT-IR External Reflectance Spectroscopy

Diffuse reflectance FT-IR spectroscopy was originally developed for particulate samples dispersed in KBr powders. Now, by using ellipsoid mirrors for scattered light collection, we have taken advantage of the collection efficiency of diffuse reflectance optics and have extended their use to an in situ study of coatings on metal wires and of the broken surface of a reinforcement wire as well. The result is that spectra of coatings on wire show good overall agreement with external reflection spectra of thin films. The technique we have developed has an advantage over infrared attenuated total reflection (ATR), in that there is no optical contact problem between the wire sample and ATR crystal.