Comparison of appearance,microstructure and tensile properties during friction stir welding processes of Al–Si alloys

The scope of this paper is to evaluate and discuss the flow phenomena of Al–2Si and Al–12Si alloys, which were joined through friction stir welding processes. The feed rate of 50mm/min and tool rotation of 600, 900, and 1200 rpm were selected for the processes. There was much change in the surface morphology with smoothness for Al–2Si alloy and roughness for Al–12 Si alloys. The microstructure studies on the weld zone were performed. The mechanical properties like tensile strength and hardness are discussed in detail.     

Effect of Co γ-ray irradiation on electrical properties of GaAs epilayer and GaAs p-i-n diode

GaAs epilayers and p-i-n diodes structures grown using metal-organic vapor phase epitaxy were irradiated at room temperatures by ⁶⁰Co γ-ray radiation with varying the dose up to 50 kGy. The carrier concentration and mobility on GaAs epilayer decreases while leakage current of p-i-n diode increases at higher radiation dose (10-50 kGy). However at lower dose (<6 kGy) carrier mobility remain same but leakage current still shows significant increase. Furthermore carrier mobility of irradiated GaAs epilayers recovers partially (68%) after annealing at 300 °C while leakage current of p-i-n diode does not show any noticeable recovery. These effects are mainly due to the creation of more deep levels compared to shallow levels as determined from photoluminescence, Hall, current-voltage and electrochemical capacitance voltage analysis.     

石膏板干墙系统与建筑防火

<正>轻钢龙骨石膏板隔墙和吊顶系统,统称石膏板干墙系统,凭借着其安装快速简便、可灵活造型、轻质、美观等特性已成为室内装修不可缺少的系统。其实,干墙系统除了这些优秀的装饰特性外还具备很强的建筑构件必备的保温隔热、隔声、吸声和防火等功能。     

Electrical resistivity as a measure of change of state in substrates: Design, development and validation of an automated system

Intrinsically smart structural composites are materials, which can perform function such as sensing strain, stress damage or temperature. Electrical resistance could potentially serve as an indicator of structural well-being or damage in the structure. To this end, the development of an automated resistance measurement system is desired. An automated nodal electrical resistance acquisition circuitry (NERAC) was designed, and interfaced to a laptop for measurement of electrical resistance/impedance from the substrate of interest. Measurements were carried out using DC/AC method with four-point probe technique. Baseline reading before damage was noted and compared with the resistance measured after damage. The device was calibrated and validated on three different substrates: PVDF samples, composite panels and smart concrete. Results conformed to previous work done on these substrates, validating the effective working of the NERAC device. Change of state of the substrate, after damage was assessed by measurement of resistance/impedance.     

Plasma effects in semiconducting nanowire growth

Three case studies are presented to show low-temperature plasma-specific effects in the solution of (i) effective control of nucleation and growth; (ii) environmental friendliness; and (iii) energy efficiency critical issues in semiconducting nanowire growth. The first case (related to (i) and (iii)) shows that in catalytic growth of Si nanowires, plasma-specific effects lead to a substantial increase in growth rates, decrease of the minimum nanowire thickness, and much faster nanowire nucleation at the same growth temperatures. For nucleation and growth of nanowires of the same thickness, much lower temperatures are required. In the second example (related to (ii)), we produce Si nanowire networks with controllable nanowire thickness, length, and area density without any catalyst or external supply of Si building material. This case is an environmentally-friendly alternative to the commonly used Si microfabrication based on a highly-toxic silane precursor gas. The third example is related to (iii) and demonstrates that ZnO nanowires can be synthesized in plasma-enhanced CVD at significantly lower process temperatures than in similar neutral gas-based processes and without compromising structural quality and performance of the nanowires. Our results are relevant to the development of next-generation nanoelectronic, optoelectronic, energy conversion and sensing devices based on semiconducting nanowires.     

Quantification and modeling of the dynamic changes in theabsorption coefficient of water at λ = 2.94 μm

A stable, high-energy Q-switched Er:YAG laser operating at 2.94 μm with a nearly diffraction-limited spatial beam profile was used to quantify the dynamic changes in the absorption coefficient of liquid water as a function of incident fluence. The data from transmission measurements across water layers of known thicknesses shows that the effective absorption coefficient of water decreases by almost an order of magnitude for fluence levels less than 2 J/cm². From the measured transmission data, we have developed a phenomenological, finite-difference absorption model (the dynamic saturable absorption model) that can, at least to a first-order approximation, accurately predict the dynamic and effective absorption coefficient of water at the wavelength λ = 2.94 μm. The model developed in the present study should prove useful in efforts to understand the underlying mechanisms of laser-tissue interaction in applications such as skin resurfacing and corneal sculpting, wherein Er:YAG lasers are used to target water as the dominant chromophore     

Prediction of gel-time in the cure of unsaturated polyester resins: Phenomenological modeling vs. statistical analysis

A series of kinetic and rheological measurements were carried out using a differential scanning calorimeter (DSC) and a Rheometrics Dynamic Analyzer (RDA). The effects of temperature, inhibitor level, initiator level, and initiator type on the curing of unsaturated polyester resins were investigated. Two models based on the free radical polymerization mechanism were developed for predicting the time to reach liquid-solid transition. These models adapted a concept that gelation occurred at a critical radical concentration. The applicability of these models was compared to that of a statistical analysis.     

Stochastic fracture analysis of laminated composite plate with arbitrary cracks using X-FEM

In this paper, second order statistics of mixed mode stress intensity factors (MSIFs) and crack propagation analysis of the symmetric angle ply laminated composite plate with through thickness arbitrary curve cracks subjected to tensile and shear stress is presented. The fracture behaviour is analysed using extended finite element method (X-FEM). The cracks like line, semi elliptical, semi circular and arbitrary curves are considered for the detailed numerical study. The material properties, lamination angle, loading, crack width and crack depth are modelled as independent, combine uncorrelated and correlated input random Gaussian variables. The interaction integral (M-integral) is adopted for calculating the MSIFs. The second order perturbation technique and Monte Carlo simulations are proposed to obtain the mean and coefficient of variance of MSIFs by random change in input system parameters. This work signifies the accurate and realistic evaluation of fracture response by handling the various levels of uncertainties. The effect of crack propagation on MSIFs using tensile and shear stresses using global tracking algorithm is also highlighted.