Dual-time scale crystal plasticity FE model for cyclic deformation of Ti alloys

A dual-time scale finite element model is developed in this paper for simulating cyclic deformation in a Titanium alloy Ti-6242. The material is characterized by crystal plasticity constitutive relations. Modeling cyclic deformation using conventional time integration algorithms in a single time scale can be prohibitive for crystal plasticity computations. Typically 3D crystal plasticity based fatigue simulations found in the literature are in the range of 100 cycles. Results are subsequently extrapolated to thousands of cycles, which can lead to considerable error in fatigue predictions. However, the dual-time scale model enables simulations up to a significantly high number of cycles to reach local states of damage initiation leading to fatigue crack growth. This formulation decomposes the governing equations into two sets of problems, corresponding to a coarse time scale (low frequency) cycle-averaged problem and a fine time scale (high frequency) oscillatory problem. A statistically equivalent 3D polycrystalline model of Ti-6242 is simulated by the crystal plasticity finite element model to study the evolution of local stresses and strains in the microstructure with cyclic loading. The comparison with the single time scale reference solution shows excellent accuracy while the efficiency gained through time-scale compression can be enormous.     

Hybrid composites made of carbon and glass woven fabrics under quasi-static loading

Experimental studies are presented on in-plane mechanical properties for two types of hybrid composites made using 8H satin weave T300 carbon fabrics and plain weave E-glass fabrics with epoxy resin. Results are also presented for 8H satin weave T300 carbon/epoxy and plain weave E-glass/epoxy. Studies are carried out under both tensile and compressive in-plane quasi-static loading. It is observed that for hybrid composites, placing glass fabric layers in the exterior and carbon fabric layers in the interior gives higher tensile strength and ultimate tensile strain than placing carbon fabric layers in the exterior and glass fabric layers in the interior. Quantitative data is given for different mechanical properties.     

Effect of salinity on the IFT between aqueous surfactant solution and crude oil

The effect of salts and different surfactants on the equilibrium as well as dynamic interfacial tension (DIFT) between crude oil and water was investigated. Three different types of surfactants with identical hydrophobic chain length C₁₂: Sodium Lauryl Ether Sulphate (SLES), Dodecyl Trimethyl Ammonium Bromide (DTAB), Polyoxyethylene (23) lauryl ether (C₁₂E₂₃) were used in this study. SLES shows better synergism of salt and surfactant mixture amongst the surfactants studied. The order of synergism of salts with the surfactant observed was MgCl₂>CaCl₂> NaCl. The results obtained from partition coefficient study show that the addition of salts favours the partition of surfactants into the oil phase hence reduce IFT more effectively. DIFT results reveal that, salt accelerates the surfactant migration towards the interface, hence, reducing the t^* value.     

In situ and real-time metrology during rinsing of micro- and nano-structures

A new technology, called electro-chemical residue sensor (ECRS), has been developed for the in situ and real-time measurement of the residual impurities left on the wafer surface and in the fine structures of patterned wafers during typical rinse processes. The key components of this technology, which consist of the sensor hardware and a process model, are described. The testing results of the ECRS show that the residual impurity concentration is significantly different from what is typically provided by the bulk water resistivity, which is usually employed for determining the progress of the rinse. As a case study, the new metrology method has been applied to the removal of sulfate ions from patterned wafers; the importance of various surface interactions, charge effects, and transport processes is determined. Two examples of the use of the ECRS for the development of novel rinse recipes to reduce water usage are also discussed.     

Optical wireless communication through fog in the presence of pointing errors

Terrestrial optical wireless communication (OWC) is emerging as a promising technology, which makes connectivity possible between high-rise buildings and metropolitan and intercity communication infrastructures. A light beam carries the information, which facilitates extremely high data rates. However, strict alignment between the transmitter and the receiver must be maintained at all times, and a pointing error can result in a total severance of the communication link. In addition, the presence of fog and haze in the propagation channel hampers OWC as the small water droplets scatter the propagating light. This causes attenuation due to the resultant spatial, angular, and temporal spread of the light signal. Furthermore, the ensuing low visibility may impede the operation of the tracking and pointing system so that pointing errors occur. We develop a model of light transmission through fogs of different optical densities and types using Monte Carlo simulations. Based on this model, the performance of OWC in fogs is evaluated at different wavelengths. The handicap of a transceiver pointing error is added to the model, and the paradoxically advantageous aspects of the transmission medium are exposed. The concept of a variable field of view receiver for narrow-beam OWC is studied, and the possibility of thus enhancing communication system performance through fog in an inexpensive and simple way is indicated.     

Room temperature observation of point defect on gold surface using thermovoltage mapping

In this work, we apply thermovoltage imaging using scanning tunneling microscope to observe atomic scale surface imperfections at room temperature. Thermovoltage mapping can provide high resolution (down to 1 nm) images of standing waves in metal at room temperature, thus avoiding the need for low temperature scanning tunneling microscopy for the investigation of the standing waves. In order to generate a thermovoltage between the sample and tip, the sample (Au(1 1 1)) is heated to about 40 °C above the room temperature and surface scanning is performed. Heating the sample is simpler than heating the tip by laser irradiation. The thermovoltage technique can be applied to estimate surface defect density and the severity of the surface defects in materials, which can be a useful tool for the reliability study of nano-scale materials and devices.     

Nanoparticle dispersed resins and composites under quasi‐static loading: Shear plugging behavior

Experimental studies are presented on the quasi‐static shear plugging behavior of nanoparticle dispersed materials viz symmetric balanced cross‐ply laminates made using unidirectional E‐glass fabric with epoxy resin, and neat epoxy resin. The nanoparticles used are nanosilica and multiwalled carbon nanotube for E‐glass/epoxy and nanosilica for epoxy resin. The effect of nanoparticle dispersion on shear plugging strength was evaluated. Shear plugging strength was enhanced up to 10.5% for E‐glass/epoxy and up to 17.0% for neat epoxy resin on addition of nanoparticles. Shear plugging strength of nanoparticle dispersed composites decreased with an increase in specimen thickness. POLYM. COMPOS., 37:3411–3415, 2016. © 2015 Society of Plastics Engineers     

Compositional mapping of the surface and interior of mammalian cells at submicrometer resolution

We present progress toward imaging of chemical species within intact mammalian cells using secondary ion mass spectrometry, including the simultaneous mapping of subcellular elemental and molecular species along with intrinsic membrane-specific cellular markers. Results from imaging both the cell surface and cell interior exposed by site-specific focused ion beam milling demonstrate that in-plane resolutions of approximately 400-500 nm can be achieved. The results from mapping cell surface phosphatidylcholine and several other molecular ions present in the cells establish that spatially resolved chemical signatures of individual cells can be derived from novel multivariate analysis and classification of the molecular images obtained at different m/z ratios. The methods we present here for specimen preparation and chemical imaging of cell interiors provide the foundation for obtaining 3D molecular maps of unstained mammalian cells, with particular relevance for probing the subcellular distributions of small molecules, such as drugs and metabolites.     

Effect of polar head surfactants on the demulsification of crude oil

Surfactants can act as demulsifiers to neutralize the stabilizing effect of natural emulsifiers in crude oil. Here, the effect of polar head group of surfactants with identical hydrophobic chain C₁₂ (SLES, SLS, C₁₂E₂₃, BKC, C₁₂E₇) on the demulsification of crude oil emulsion and its effect on water separation rate were studied at different temperature. The activation energy for destabilization was calculated. The results indicate that the rate of water separation increases with temperature and surfactant concentration. The emulsion destabilising activation energy decreases as the concentration of the surfactant increases. The Interfacial Tension (IFT) study showed that when the reduction in IFT was the highest, the water separation rate and efficiency achieved was the highest.