Mechanical behavior of electrophoretically modified CFRP composites at elevated temperatures: An assessment of the influence of graphene carboxyl bath concentration

The study aims at investigating the mechanical behavior of carbon fiber reinforced polymer (CFRP) composites modified with graphene carboxyl at elevated temperature (ET-110°C) and understanding the effect of electrophoretic deposition bath concentration (0.5 g/L, 1.0 g/L, and 1.5 g/L) on their mechanical behavior at ET. The 1.5 g/L composite has revealed a maximum improvement in energy absorbed before failure of 33.25% at RT and 22.54% at ET for flexural testing and ∼35% at RT for short beam shear testing, over neat CFRP composite. The modified composites have shown an improved flexural strain to failure at both RT and ET, with 1.5 g/L composite exhibiting maximum enhancement of 12.41% at RT and 26.52% at ET over neat composite. However, at ET, modified composites exhibited lower flexural strength and interlaminar shear strength values in comparison to that of neat. Viscoelastic behavior of all composites was studied to understand bath concentration's effect on thermal behavior via dynamic mechanical thermal analysis. Differential scanning calorimetry was employed for governing the glass transition temperature of composites. Fractography of tested samples (both ET and RT) was performed utilizing a scanning electron microscope to determine the prominent failure mode.     

Influence of nucleation and growth mechanisms on the heat deflection temperature of a reactively processed polypropylene nanocomposite

The development of a reactively processed polypropylene nanocomposite (PPNC) with consequential improvements in the heat deflection temperature (HDT), Vicat softening temperature (VST), and crystallization peak temperature (T_c) is reported herein. Neat PP without nanoclay was also reactively processed to elucidate the effects of fillers on the improvement in physical properties. The results show a considerable improvement in the HDT of PPNC (77.9 °C) compared to those of neat PP (62.6 °C) and reactively processed branched PP (BPP; 69.2 °C). Moreover, the T_c of PP in PPNC improved by ~14% compared to that of neat PP. Various models of nonisothermal crystallization kinetics were employed to elucidate the nucleation and crystal growth mechanisms, and to correlate them with the observed HDT improvement in PPNC. Thermal transitions investigated by modulated differential scanning calorimetry explained the changes observed in the VSTs of all the samples. To the best of our knowledge, this is the first report on a significant improvement in HDT along with a marked increase in Tc. Such simultaneous improvements in HDT, VST, and T_c are highly desirable for applications involving the use of PP-based materials in rigid packaging.     

Effect of austenitization on austempering of copper alloyed ductile iron

A ductile iron containing 0.6% copper as the main alloying element was austempered at a fixed austempering temperature of 330 °C for a fixed austempering time of 60 min after austenitization at 850 °C for different austenitization periods of 60, 90, and 120 min. The austempering process was repeated after changing austenitization temperature to 900 °C. The effect of austenitization temperature and time was studied on the carbon content and its distribution in the austenite after austenitization. The effect of austenitization parameters was also studied on austempered microstructure, structural parameters like volume fraction of austenite, X _γ , carbon content C _γ , and X _γ C _γ , and bainitic ferrite needle size, d _α after austempering. The average carbon content of austenite increases linearly with austenitization time and reaches a saturation level. Higher austenitization temperature results in higher carbon content of austenite. As regards the austempered structure, the lowering austenitization temperature causes significant refinement and more uniform distribution of austempered structure, and a decrease in the volume fraction of retained austenite.     

The influence of nickel and copper on the austempering of ductile iron

In the present investigation, the effect of alloying elements on the austempering process, austempered microstructure, and structural parameters of two austempered ductile irons (ADI) containing 0.6% Cu and 0.6% Cu/1.0% Ni as the main alloying elements was investigated. The optical metallography and x-ray diffraction were used to study the changes in the austempered structure. The effect of alloying additions on the austempering kinetics was studied using the Avrami equation. Significantly more upper bainite was observed in the austempered Cu-Ni alloyed ADI than in Cu alloyed ADI. The volume fraction of retained austenite (X _γ), the carbon level in the retained austenite (C _γ), and the product X _γ C _γ in an austempered structure of Cu-alloyed ADI are higher than in Cu-Ni-alloyed ADI. The austempering Kinetics is slowed down by the addition of Ni.     

In situ repair welding of steam turbine shroud for replacing a cracked blade

A root-cracked blade in a high-pressure steam turbine of a nuclear power plant had to be replaced with a new blade by cutting the shroud to remove the cracked blade. This necessitated in situ welding of a new shroud piece with the existing shroud after the blade replacement. The in situ welding of the shroud, a 12% Cr martensitic stainless steel with tempered martensite microstructure, was carried out using gastungsten arc welding and 316L austenitic stainless steel filler metal followed by localized postweld heat treatment at 873 K for 1 h using a specially designed electrical resistance-heating furnace. Mock-up trials were carried out to ensure that sound welds could be made under the constraints present during the in situ repair welding operation. In situ metallography of the repair weld after postweld heat treatment confirmed the adequate tempering of the martensitic structure in the heat-affected zone. Metallurgical investigations carried out in the laboratory on a shroud test-piece that had been welded using the same procedure as employed in the field confirmed the success of the in situ repair operation. The alternate option available was replacing the cracked blade and the shroud piece to which it is riveted with a new one, reducing the height of all the blades attached to the shroud by machining, riveting the blades with reduced height to the new shroud, and, finally, dynamic balancing of the entire turbine after completion of the repair. This option is both time-consuming and expensive. Hence, the successful completion of this repair welding resulted in enormous savings both in terms of reducing the downtime of the plant and the cost of the repair. The turbine has been put back into service and has been operating satisfactorily since December 2000.     

Long-wave interfacial instabilities in a thin electrolyte film undergoing coupled electrokinetic flows: a nonlinear analysis

Spatiotemporal deformations of the free charged surface of a thin electrolyte film undergoing a coupled electrokinetic flow composed of an electroosmotic flow (EOF) on a charged solid substrate and an electrophoretic flow (EPF) at its free surface are explored through linear stability analysis and the long-wave nonlinear simulations. The nonlinear evolution equation for the deforming surface is derived by considering both the Maxwell’s stresses and the hydrodynamic stresses. The electric potential across the film is obtained from the Poisson–Boltzmann equation under the Debye–Hückel approximation. The simulations show that at the charged electrolyte–air interface, the applied electric field generates an EPF similar to that of a large charged particle. The EOF near the solid–electrolyte interface and the EPF at the electrolyte–air interface are in the same (or opposite) directions when the zeta potentials at the two interfaces are of the opposite (or same) signs. The linear and nonlinear analyses of the evolution equation predict the presence of travelling waves, which is strongly modulated by the applied electric field and the magnitude/sign of the interface zeta potentials. The time and length scales of the unstable modes reduce as the sign of zeta potential at the two interfaces is varied from being opposite to same and also with the increasing applied electric field. The increased destabilization is caused by a reverse EPF near the free surface when the interfaces bear the same sign of zeta potentials. Flow reversal by EPF at the free surface occurs at smaller zeta potential of the free surface when the film is thicker because of less influence of the EOF arising at the solid–electrolyte boundary. The amplitude of the surface waves is found to be smaller when the unstable waves travel at a faster speed. The films can undergo pseudo-dewetting when the free surface is almost stationary under the combined influences of EPF and EOF. The free surface instability of the coupled EOF and EPF has some interesting implications in the development of micro/nano fluidic devices involving a free surface.     

Self adaptive animation based on user perspective

In this paper we present a new character animation technique in which the animation adapts itself based on the change in the user’s perspective, so that when the user moves and their point of viewing the animation changes, then the character animation adapts itself in response to that change. The resulting animation, generated in real-time, is a blend of key animations provided a priori by the animator. The blending is done with the help of efficient dual-quaternion transformation blending. The user’s point of view is tracked using either computer vision techniques or a simple user-controlled input modality, such as mouse-based input. This tracked point of view is then used to suitably select the blend of animations. We show a way to author and use such animations in both virtual as well as augmented reality scenarios and demonstrate that it significantly heightens the sense of presence for the users when they interact with such self adaptive animations of virtual characters.     

Analysis of electro‐optical properties of polymer‐stabilized OCB and the application to TFT‐LCDs

Abstract— A 9‐in. full‐color polymer‐stabilized OCB TFT‐LCD with stable bend alignment in the absence of an electric field was developed. The condition of the polymer stabilization, the characteristics of UV‐curable monomers, and their influence on the configurations of the polymer network in the cell were studied. Possible models of the configuration were proposed and their relationship to the electro‐optical properties was analyzed using a novel simulation method considering the distribution of anchoring effects from both alignment surfaces and the polymer network. It was suggested that a good performance such as high contrast ratio and fast response could be expected in the polymer network originating from newly developed monomers composed of multifunctional LC acrylates due to a relatively weak‐anchoring effect and presumably its localization near the alignment surfaces. By using the newly developed monomers under the optimized polymer‐stabilizing process, a high contrast ratio of 250:1 and fast response nearly equal to that of a conventional OCB cell were achieved.     

Supervised Self-Organization of Homogeneous Swarms Using Ergodic Projections of Markov Chains

This paper formulates a self-organization algorithm to address the problem of global behavior supervision in engineered swarms of arbitrarily large population sizes. The swarms considered in this paper are assumed to be homogeneous collections of independent identical finite-state agents, each of which is modeled by an irreducible finite Markov chain. The proposed algorithm computes the necessary perturbations in the local agents' behavior, which guarantees convergence to the desired observed state of the swarm. The ergodicity property of the swarm, which is induced as a result of the irreducibility of the agent models, implies that while the local behavior of the agents converges to the desired behavior only in the time average, the overall swarm behavior converges to the specification and stays there at all times. A simulation example illustrates the underlying concept.     

An application of PSO technique for harmonic elimination in a PWM inverter

Harmonic elimination problem in PWM inverter is treated as an optimization problem and solved using particle swarm optimization (PSO) technique. The derived equation for computation of total harmonic distortion (THD) of the output voltage of PWM inverter is used as the objective function in the PSO algorithm. The objective function is minimized to contribute the minimum THD in the voltage waveform and the corresponding switching angles are computed. The method is applied to investigate the switching patterns of both unipolar and bipolar case. While minimizing the objective function, the individual selected harmonics like 5th, 7th, 11th and 13th can be controlled within the allowable limits by incorporating the constraints in the PSO algorithm. The results of the unipolar case using five switching angles are compared with that of a recently reported work and it is observed that the proposed method is effective in reducing the voltage THD in a wide range of modulation index. The simulated results are also validated through suitable experiments.