Tensile fatigue behavior of plain-weave reinforced Cf/C–SiC composites

The fatigue behavior of plain-weave C_f/C–SiC composites prepared by liquid silicon infiltration (LSI) was studied under cyclic tensile stress at room temperature. The specimens were loaded with stress levels of 83% and 90% of the mean static tensile strength for 10⁵ cycles. The cross-sections and fracture surfaces of the fatigued specimens were examined by optical microscopy (OM) and scanning electron microscopy (SEM), respectively. The results show that the specimens can withstand 10⁵ fatigue cycles with a stress level of 90% of the static tensile strength. The retained strengths after fatigue for 10⁵ cycles with stress levels of 83% and 90% are about 19% and 11% higher than the static tensile strength. Due to the observation of the microstructures a relief of the thermal residual stress (TRS) caused by stress-induced cracking is probably responsible for the enhancement. Furthermore, the fracture surfaces indicate that the fatigue stress results in interfacial debonding between the carbon fiber and matrix. Additionally, more single-fiber pull out was observed within the bundle segments of fatigued specimens.     

Photon statistics anomalies in adiabatic transfer between two cavity modes

Adiabatic transfer between two degenerate cavity modes is investigated theoretically using a counter-intuitive pulse sequence. Several measures of successful state transfer are shown to correlate strongly with anomalous values of the photon statistics of the initial mode. The detailed behaviour of theses anomalies originate from the way the state approaches vacuum and their features are found to give a good indication of the effciency and robustness of the state transfer.     

MY RECOLLECTIONS OF G.2 A.6

Abstract

In this article, we consider an attack on the SIGABA cipher under the assumption that the largest practical keyspace is used. The attack highlights various strengths and weaknesses of SIGABA and provides insight into the inherent level of security provided by the cipher.     

Optimization of the working fluid for a sorption-based Joule–Thomson cooler

Sorption-based Joule–Thomson coolers operate vibration-free, have a potentially long life time, and cause no electromagnetic interference. Therefore, they are appealing to a wide variety of applications, such as cooling of low-noise amplifiers, superconducting electronics, and optical detectors. The required cooling temperature depends on the device to be cooled and extends into the cryogenic range well below 80 K. This paper presents a generalized methodology for optimization in a sorption-based JT cooler. The analysis is based on the inherent properties of the fluids and the adsorbent. By using this method, the working fluid of a JT cooler driven by a single-stage sorption compressor is optimized for two ranges of cold-tip operating temperatures: 65–160 K and 16–38 K. The optimization method is also extended to two-stage compression and specifically nitrogen and carbon monoxide are considered.     

A robust hybrid method for maximum power point tracking in photovoltaic systems

In this paper a new hybrid method for maximum power point tracking in PV systems has been proposed. This method combines offline and online methods in order to estimate duty cycle of converter in maximum power point. In the offline phase, temperature and radiation intensity are the inputs of the system to estimate the approximate maximum power based on analytical equations of solar cell. These equations which give the relation of maximum power with temperature and irradiation can be derived from characteristics of cell provided by manufacturer or experiments. Afterwards the duty cycle of converter would be estimated using circuit equations of measured Thevenin model of the load and battery. Measuring Thevenin equation results in robustness of method respecting variations of load and battery. In the online phase, the classic perturbation and observation (P&O) method will be utilized for fine tuning and tracking of maximum power point. The proposed method has been simulated in MATLAB/SIMULINK workspace and compared with some other MPPT methods. The results reveal that this hybrid method outperforms other methods in term of performance and speed of tracking.     

Wear and corrosion resistance and electroplating characteristics of electrodeposited Cr–SiC nano-composite coatings

Cr–SiC nanocomposite coatings with various contents of SiC nanoparticles were prepared by electrodeposition in optimized Cr plating bath containing different concentrations of SiC nanoparticles. Direct current electrocodeposition technique was used to deposit chromium layers with and without SiC nanoparticles on mild carbon steel. The effects of current density, stirring rate and concentration of nanoparticles in the plating bath were investigated. Scanning electron microscopy was used to study surface morphology. Energy dispersive analysis technique was used to verify the presence of SiC nanoparticles in the coated layers. The corrosion behaviors of coatings were investigated by potentiodynamic polarization and electrochemical impedance spectroscopy methods in 0.05 mol/L HCl, 1 mol/L NaOH and 3.5% NaCl (mass fraction), respectively. Microhardness measurements and pin-on-disc tribometer technique were used to investigate the wear behavior of the coatings.     

Geometrically Non-Linear Rapid Heating of Temperature-Dependent Circular FGM Plates

Based on the uncoupled thermoelasticity assumptions, axisymmetric thermally induced vibrations of a circular plate made of functionally graded materials (FGMs) are analyzed. Each thermomechanical property of the circular plate is assumed to be functions of temperature and thickness coordinate. Solution of the transient one-dimensional heat conduction equation with the arbitrary type of time-dependent boundary conditions is carried out employing the central finite difference method combined with the Crank–Nicolson time marching scheme. Afterwards, with the establishment of the associated Hamilton's principle and the accountancy of the von Kármán type of geometrical non-linearity, the motion equations are obtained with the aid of the conventional multi-term Ritz method. The solution of highly coupled non-linear motion equations is obtained utilizing a hybrid iterative Newton–Raphson–Newmark scheme. After validating the developed computer code, some parametric studies are accomplished to show the influences of various involved parameters. It is shown that temperature dependency, geometrical non-linearity, plate thickness, power law index, and the type of thermal in-plane and out-of-plane mechanical boundary conditions, all affect the temporal evolution of plate characteristics.     

32—THE SNARLING OF HIGHLY TWISTED MONOFILAMENTS. PART I: THE LOAD–ELONGATION BEHAVIOUR WITH NORMAL SNARLING

An account is given of an experimental investigation of the normal snarling of highly twisted monofilaments, those used being vulcanized rubber and nylon.

An earlier theoretical analysis is corrected, and the experimental results show that, after this correction, the theory put forward for the mechanical properties of the snarling mechanism holds reasonably well for elastic filaments. Although, as would be expected, there are larger deviations from the theory for viscoelastic filaments, the theory still gives a good indication of the behaviour of these filaments under torsion.     

Effect of tungsten addition on thermal conductivity of graphite/copper composites

Graphite/copper composites with high thermal conductivity were fabricated by tungsten addition, which formed a thin tungsten carbide layer at the interface. The microstructure and thermal conductivity of the composite material were studied. The results indicated that the insertion of tungsten carbide layer obviously suppressed spheroidization of copper coating on the graphite particles during the sintering process, and decreased the interfacial thermal resistance of the composites. Compared with the graphite/copper composites without tungsten, the thermal conductivity of the obtained composites was increased by 43.6%.     

Static and high-rate loading of single and multi-bolt carbon–epoxy aircraft fuselage joints

Single-lap shear behaviour of carbon–epoxy composite bolted aircraft fuselage joints at quasi-static and dynamic (5 m/s and 10 m/s) loading speeds is studied experimentally. Single and multi-bolt joints with countersunk fasteners were tested. The initial joint failure mode was bearing, while final failure was either due to fastener pull-through or fastener fracture at a thread. Much less hole bearing damage, and hence energy absorption, occurred when the fastener(s) fractured at a thread, which occurred most frequently in thick joints and in quasi-static tests. Fastener failure thus requires special consideration in designing crashworthy fastened composite structures; if it can be delayed, energy absorption is greater. A correlation between energy absorption in multi-bolt and single-bolt joint tests indicates potential to downsize future test programmes. Tapering a thin fuselage panel layup to a thicker layup at the countersunk hole proved highly effective in achieving satisfactory joint strength and energy absorption.