Effect Of Thickness Variation Research Articles

Effect of matrix voids, fibre misalignment and thickness variation on multi-objective robust optimization of carbon/glass fibre-reinforced hybrid composites under flexural loading

Abstract The robust and optimal design of carbon/glass fibre-reinforced epoxy hybrid composite laminates under the constraint of a specified minimum flexural strength was investigated in this study. Two conflicting objectives, minimizing material cost and weight, were considered with the design variables being fibre type, fibre orientation angle and fibre volume fraction of the laminas. Three sources of uncertainties, namely, fibre misalignment, lamina thickness variation and the presence of matrix voids were incorporated into the model. This multi-objective robust optimization problem was solved by combining a modified version of the non-dominated sorting genetic algorithm (NSGA-II) with a simple genetic algorithm (GA) as an anti-optimizer. Pareto optimal and robust solutions were found for different levels of minimum flexural strength and the significance of each uncertainty source on the optimal cost and weight of the optimal designs were investigated by conducting analysis of variance (ANOVA) tests. The results indicated that, in general, all three uncertainties affected the cost and weight of the optimal designs with the effect of voids being more critical for void contents of greater than 2%.

Vibration analysis of a cylinder with slight diameter and thickness variations

The cross section of circular cylinder in their dynamic model is always considered as a perfect circle, which means radii at every point on the circle are the same. In real engineering structure, there are slight fluctuations in shape of the circular cylinder which is different from those in ideal model. Meanwhile, effects of structural fluctuations on its dynamic characteristic are rarely analyzed before. To study problem mentioned above, the geometric shape of a typical, apparently symmetrical cylinder is examined experimentally to demonstrate that a small variation in diameter and thickness indeed exists in practice firstly. Because fluctuations in diameter and thickness of the cylinder are related to each other, we need to separate effects of a slight variation in its diameter and thickness on structural dynamic characteristics to search the key factor of influence. Then, two simplified modes, which are modeled by finite element method, are used to study the effects of diameter or thickness variation alone on the natural frequencies and modal shapes of the free cylinder. It is revealed that the diameter variation described by the simplified model captures the key influencing elements which affect the modal characteristics of the free cylinder. Finally, a free cylinder with both variations is analyzed numerically and the results are verified experimentally. This work illustrates that significant discrepancies inevitably exist between the measured results of an actual free cylinder and an assumed symmetrical model even if there is only a very slight variation in its geometric shape.

The effects of film thickness variations on the residual stress distributions in coated Cr thin films

AbstractGenerally, the residual stress of thin film coatings is calculated using Stoney's equation. However, variables in the manufacturing of the coated film, such as crystalline particle size and the unevenness of the thickness of the film, cause the radius of curvature of the beam to vary all over the beam. The cantilever beam curves not only in the axial direction but also in the transverse direction. Therefore, the residual stress in a film coating comprises not only axial residual stress but also transverse residual stress, and its distribution is also not uniform. Under such conditions, Stoney's equation must be modified. In this study, Si was used as a substrate in the production of cantilever beam specimens. Chromium thin films of various thicknesses were coated onto the Si substrates. The 3D digital image correlation technique was used to measure the out‐of‐plane displacement of the specimens at various positions. Then the modified Stoney's equation was used to obtain the axial and transverse residual stress at each measurement point to study the effect of variations in the thickness of the thin film on the magnitude and uniformity of the distribution of the residual stresses. Three thin film thicknesses 1, 2, and 3 μm were studied, and three specimens for each thickness were used. For each specimen, axial and transverse residual stresses were obtained at nine test points, and the equivalent residual stress was calculated. The results of this study reveal that as the difference between the thicknesses of the coating increased, average equivalent residual stress decreased and the distribution of stresses became more uniform. By comparing the corresponding results for the 1‐ and 3‐μm‐thick films revealed that the confidence levels in the average value and uniformity of the equivalent residual stress distribution, which increased with thickness, were 92.81% and 80.57%, respectively.

Tilt angle dependence of the modulated interference effects in photo-elastic modulators

The effect of the PEM tilt angle and incident polarization on the PEM interference is studied for a single axis photo-elastic modulator. The dc, 1ω, and 2ω components of the detector signal vary periodically as a function of PEM tilt angle. Although it is possible to adjust the PEM tilt angle to minimize the 1ω or 2ω detector signal at small tilt angles, it is not possible to null both of them simultaneously. For the case where no analyzer is used, the ac detector signals can be minimized simultaneously by adjusting the polarization angle of the light incident on the PEM and the PEM tilt angle. Direct observations of the detector signal indicate that the effects of refraction index and thickness variations are opposite consistent with a lower polarizability for compressive strain of the modulator.

Anomalous Transconductance in Long Channel Halo Implanted MOSFETs: Analysis and Modeling

In this paper, we report anomalous behavior of transconductance ( ${g}_{m}$ ) in halo implanted MOSFET for linear and saturation regions across both gate and body biases. The ${g}_{m}$ characteristics undergo sharp change of slope in saturation which cannot be modeled by conventional compact models. The cause of such behavior is identified and explained using the TCAD simulations of source side halo, drain side halo (DH), both side halos, and uniformly doped transistors. An analytical model, based on the equivalent conductance of the halo device, is developed to understand the ${g}_{m}$ behavior. It is shown that the commonly used approach where only the DH region is considered in saturation, is insufficient to model the atypical ${g}_{m}$ behavior. The effect of oxide thickness ( ${T}_{\text {ox}}$ ) variation on ${g}_{m}$ is also studied, which demonstrates a deviation from the conventional $g_{m}$ behavior for halo implanted devices with thicker ${T}_{\text {ox}}$ . A computationally efficient SPICE model is proposed to model ${g}_{m}$ characteristics which shows excellent matching with the measured data.

Vibration analysis of a rotating variable thickness bladed disk for aircraft gas turbine engine using generalized differential quadrature method

In this paper, free vibration analysis of rotating variable thickness annular bladed disk suitable to be used in aircraft gas turbine engine is investigated. The numerical generalized differential quadrature method is introduced in this paper as a fast and efficient numerical method to be used for vibration analysis of bladed disks of real gas turbine engines. The boundary conditions are supposed to be similar to those of the real bladed disk used in the aircraft engines i.e. clamped for the inner edge and free for the outer edge. Considering the thickness of the disk to vary as a power function and the blades of the bladed disk to be rigid, the numerical solution is performed and the effects of thickness variation, geometric parameters, angular velocity, and number of blades on the natural frequencies and critical speeds are investigated. The obtained numerical results are compared with those reported in the literature indicating a good agreement.

Effect of Thickness variation on The Optical Properties of (Poly Vinyl Alcohol : Green Methyl) Films

Effect of Thickness variation on The Optical Properties of (Poly Vinyl Alcohol : Green Methyl) Films

Effect of InGaN thickness on assisted trap recombination and behaviour of InGaN/AlGaN double heterostructure LED

This work is dedicated to the study of InGaN based LED on the thickness variation effect. The operating voltage, total emission rate, efficiency droop and spontaneous recombination rate was improved by increasing the thickness of InGaN layer of InGaN/AlGaN electron blocking layer (EBL). Based on optical and electrical results, the thicker InGaN layer could have lower operating voltage and higher total emission rate. LED with 5nm thick InGaN layer also could prevent electron leakage into p-region and improve hole injection efficiency. As a result it decreases 60% of efficiency droops and reduces the trap assisted recombination in InGaN/AlGaN active light emitting region. This indicates that InGaN layer may decrease the non-radiative recombination

Effect of spin-coated i-layer properties on electrical and optical characteristics of p-i-n structured all-Silicon Quantum Dot Solar Cell

Spin coating is a well-developed and established method for the application of thin films on the substrates. Key benefits of spin coating method are repeatability, ease of process, and the control over film parameters. Hydrogen Silsesquioxane (HSQ) materials are useful as spin-on-glass (SOG) dielectrics for fabrication of quantum confined Nano-size semiconductors. The paper reports some preliminary results of the electrical and optical characterization of all-Si Quantum Dot Solar Cell (QDSC), having a p-i-n structure and fabricated using ‘top-down’ approach. Spin coated intrinsic layer of the cell accommodates Si QDs synthesized on sonication of freestanding porous silicon film prepared using anodization technique. After spin coating, the device is cured on furnace treatment at 400°C for 1 hour in the presence of N2. Curing decreases, the number of Si-H bonds present in HSQ turning HSQ into porous hydrogenated silicon oxide having a network structure. To achieve higher intrinsic layer thickness, multiple coats of the ‘i-(QDs),’ layers are applied. All the variants of the QDSC fabricated, are tested for photovoltaic effect using I-V characterization. Effect of variation in bandgap due to change in the size of quantum dot and effect of variation in intrinsic layer thickness on quantum efficiency is observed using external quantum efficiency analysis.

Modeling localized corrosion with an effective medium approximation

A model of localized corrosion is developed, in which the effective local properties of the electrolyte are adjusted based on a continuously variable porosity parameter that permits penetration of the electrolyte into the corroding medium in an average sense. The model is applied to corrosion of multilayer aluminum alloy electrodeposits in salt water, and compared to experimental results on several different coatings. The model can accurately reproduce a number of phenomena specific to localized corrosion, including the effects of variations in film thickness, dissolution through a barrier, and relative lifetimes of different coatings in immersion conditions.

Zinc tin oxide as high-temperature stable recombination layer for mesoscopic perovskite/silicon monolithic tandem solar cells

Perovskite/crystalline silicon tandem solar cells have the potential to reach efficiencies beyond those of silicon single-junction record devices. However, the high-temperature process of 500 °C needed for state-of-the-art mesoscopic perovskite cells has, so far, been limiting their implementation in monolithic tandem devices. Here, we demonstrate the applicability of zinc tin oxide as a recombination layer and show its electrical and optical stability at temperatures up to 500 °C. To prove the concept, we fabricate monolithic tandem cells with mesoscopic top cell with up to 16% efficiency. We then investigate the effect of zinc tin oxide layer thickness variation, showing a strong influence on the optical interference pattern within the tandem device. Finally, we discuss the perspective of mesoscopic perovskite cells for high-efficiency monolithic tandem solar cells.

Study on effect of back oxide thickness variation in FDSOI MOSFET on analogue circuit performance

In this study, the analogue performance of radio-frequency (RF) range amplifiers and ring oscillators designed using fully depleted silicon on insulator (FDSOI) metal–oxide–semiconductor field-effect transistors (MOSFETs) is studied for different back oxide (BOX) thickness. The analysis exemplifies the need for BOX thickness variation analysis for the superior analogue/RF performance. The analogue parameters of the circuit analysed for different BOX thickness are the bandwidth, the linearity and the power consumption. The study shows that for an FDSOI MOSFET-based amplifier circuit, with increasing BOX thickness the bandwidth increases and the gain decreases. Also an optimum value of gain–bandwidth product for the amplifier is proposed considering the BOX thickness and the gate length of the device. It is also shown that frequency of oscillation for the ring oscillators increases with increasing BOX thickness.

Effect of glass thickness variations on the performance of RPC detectors

The India-based Neutrino Observatory (INO) is planning to build a magnetized iron calorimeter detector (ICAL) in which Resistive Plate Chambers (RPCs) will be the active detector elements. A study of the performance of RPCs, made using electrodes of various thicknesses, is pivotal in optimizing the design parameters of the ICAL RPCs. We fabricated RPCs with glasses of various thicknesses and studied their performance in the same environmental conditions. A study of detector efficiency, noise rate, time resolution and charge distribution is presented in this paper.

Wall thickness variation effect on tank’s shape behaviour under critical harmonic settlement

The purpose of this study was to investigate the effect of wall thickness variation on tank’s wall buckling mode under the effect of critical harmonic settlement for open top tanks. The study was performed on four tanks which have the same geometric and material properties except wall thickness, for each case the tank was subjected to several settlement waves which has the same settlement amplitude, and the buckling mode and critical vertical settlement results were compared. For buckling mode, the results show that tanks with wall thickness at a close range have similar buckling mode behaviour and in case using too thick wall the buckling mode starts to change. And for the effect on critical vertical settlement, the results show that vertical settlement is sensitive to any variation in wall thickness beside that settlement value changes with the effected wave number and this variation could change the whole behaviour of the tanks. The study recommended that in case of performing analysis for a tank with neglecting the variation in wall thickness values, the value of chosen wall thickness should be the average of wall thickness values obtained from the designed equation.

Sub-5 μm-thick spalled single crystal Si foils by decoupling crack initiation and propagation

Spalling of a brittle semiconductor substrate is an attractive method for fabricating sub-50 μm thick single crystal semiconductor wafers in large area. Here, a spalling process to fabricate single crystal Si foils with controlled thicknesses ranging from sub-5 to 38 μm is demonstrated using electroplated Ni stressor layers on Si substrates. In this study, the thickness profile of the Ni stressor layer was varied by changing the Ni electroplating current density, and the effect of thickness variation on the crack initiation and propagation in the underlying Si substrate was evaluated. The critical Ni thickness for crack initiation in our Ni/Si bilayer system was determined and we also show that the crack propagation depth, i.e., spalled Si thickness, is proportional to the thickness of the Ni layer at the central area of the Si wafer. Ni layer plated using 40 mA/cm2 resulted in sub-5 μm thick Si foil. In addition, the spalling mechanics of a Ni/Si bilayer system was analytically explored to give insight into the requirements of the Ni stressor layer for crack initiation.

Buckling analysis of circular functionally graded plate under uniform radial compression including shear deformation with linear and quadratic thickness variation on the Pasternak elastic foundation

A numerical scheme for buckling analysis of functionally graded circular plate (FGCP) subjected to uniform radial compression including shear deformation rested on Pasternak elastic foundation is presented. The linear and quadratic thickness variation patterns with various boundary conditions are considered. A modified Euler–Lagrange equation is achieved and then solved by converting differential equation to a nonlinear algebraic system of equations. Also, based on traction–free surface without using shear correction factor, a new approach by considering shear deformation for buckling analysis of FGCP rested on elastic foundation is carried out. The stability equation based on shear stress-free surface is solved by the spectral Ritz method. The spectral Ritz method has good flexibility in the sense of satisfying the boundary conditions. The effects of both linear and quadratic thickness variations and Poisson’s ratio are investigated. By taking small numbers of the basis, the outcomes in literature are improved.

Experimental and finite element evaluations of debonding in composite sandwich structure with core thickness variations

An important failure mode in sandwich structures is the debonding between the core and facesheet, which can destroy the load capacity of the structure. This work addressed the critical interfacial modes and studied the effects of thickness variation of the core material. The single cantilever beam geometry is utilized for conducting experiments after optimizing the thicknesses of the core and facesheet by minimizing the difference in the bending stiffness matrix between the upper facesheet and the lower facesheet/core combination. Two different core material thicknesses were tested. The experimental results showed that the critical energy release rate could be influenced by core thickness variations. Furthermore, the cohesive zone method and elastic–plastic core material model in conjunction with fracture criteria were used to model the entire structure failure response. The validation results predicted load–extension curves in agreement with actual tests for both single cantilever beam geometry specimens. The model also had the ability to predict the crack initiation in the core materials which occurred under the interface zone as in the actual test. In addition, the mixed-mode ratios through the interface area were analyzed as function of crack length to assess its influence on both single cantilever beam thickness specimens.

Structural and metamagnetic transitions in thin films of Ce-doped Pr0.5Ca0.5MnO3 manganites

We have investigated the effects of Ce-doping, epitaxial strain and thickness variation on the physical properties of four series of manganite thin films of Pr0.5−xCexCa0.5MnO3 (x=0, 0.05, 0.10). Two series of films were deposited on LaAlO3 (001) substrates under compressive strain: one series with fixed thickness (~250nm) and varied Ce-doping, and another series with constant Ce-doping (x=0.05) and varied thickness. In similar manner, other two series of films were deposited on (LaAlO3)0.3(Sr2AlTaO6)0.7 (001) substrates with tensile strain. An important feature of this system is that the films (x=0.05) deposited on LaAlO3 show coherent compressive strain till the thickness as large as 700nm, albeit with a different structure. All the films under study are highly insulating and show unsaturated magnetic hysteresis loops with a very low magnetic moment (~ 0.6–0.7μB/f.u.). As we increase Ce-doping, a structural transition manifest in the films. At 2K, small step-like metamagnetic transition appears in magnetic hysteresis of compressively strained films with x=0.05. However, metamagnetic transition is absent in the films with tensile strain. Several films show pinched hysteresis loops indicating two co-existed ferromagnetic phases (soft and less soft) at low temperatures. The results are discussed in the framework of effects of Ce-doping, structural transition and epitaxial strain in thin films.

Buckling of Cylindrical Shells with Arbitrary Circumferential Thickness Variations Under External Pressure

AbstractThis paper presents an analytical study on the buckling of cylindrical shells with arbitrary circumferential thickness variations under external pressure. Firstly, based on the thin shell theory and separation of variables, corresponding ordinary differential equations of laterally pressured cylinders are obtained. Secondly, the general asymptotic formula of buckling load, which is in terms of thickness variation parameter up to arbitrary order, is derived by combining the perturbation method and Fourier series expansion. Thirdly, the effects of uniform and circumferential modal thickness variations on the buckling of cylindrical shells under external pressure are investigated, respectively, and the results agree well with those available in literature. Particularly, the buckling load reduction of cylinders with circumferential modal thickness variation obtained by the proposed method coincides with the numerical results presented by Gusic et al. This analytical method is applicable for evaluating the stability of laterally pressured cylindrical shells with arbitrary circumferential thickness variations, once the thickness variation is known.

Numerical study a broad low-loss pass-band optical metamaterials filter through tailoring dispersion

We present a theoretical and numerical study of a compound structure optical metamaterials filter in 14.8-19.8THz region. Effects of variations in thickness of dielectric layer H and structural parameters on the pass-band are surveyed. Simulated results indicate that the sidewall length of the main air hole and the nano-hole mainly define the impedance matching condition. The pass-band can be expanded due to impedance matching condition between the designed structure and air interface is achieved through optimizing the dimensional parameters of the designed structure. Meanwhile, the pass-band can be also expanded by reducing the thickness of dielectric layer.