Vibration of higher-order-shearable pretwisted rotating composite blades

The free and forced vibration of a rotating, pretwisted blade modeled as a laminated composite, hollow (single celled), uniform box-beam is studied. The structural model includes transverse shear flexibility, restrained warping, and centrifugal and Coriolis effects. A key element of this model is its ability to satisfy the zero shear–traction requirement on the external bounding surfaces. The governing system possesses complicated and eigenvalue-dependent natural boundary conditions. Hence an extended Galerkin method using admissible functions is employed. Free-vibration results obtained for the present higher-order shearable model are compared with those of the existing first-order shearable and the non-shearable models. For the data considered, the present theory provides conservative predictions. This suggests that through-the-thickness variations of transverse shear strains are significant and should be considered when pursuing non-resonant designs. The effect of pretwist, while marginal for the lowest eigenfrequency, is substantial for the higher ones especially for lower rotation speeds and larger ply angles. A combination of softening and stiffening effects are also possible for the same eigenfrequency when pretwist is varied. Tailoring studies using the present model show an enhancement of eigenfrequency characteristics and also reveal the potential for passive mitigation of forced response.     

Numerical investigation of the stress field near a crack normal to ceramic-metal interface

Ceramic-metal interfaces are often present in composite materials. The presence of cracks has a major impact on the reliability of advanced materials, such as fiber or particle reinforced ceramic composites, ceramic interfaces and laminated ceramics. The understanding of the failure mechanisms is very important, as is as the estimation of fracture parameters at the tip of the crack approaching an interface and crack propagation path. A cracked sandwich plate loaded with axial uniform normal stress was numerically investigated using plane strain Finite Element Analysis. The numerical results for the singularity orders were compared with the analytical solution. The influences of the material combination and crack length on the radial and circumferential stresses and displacement distributions were investigated. The Stress Intensity Factors were determined based on numerical results using a displacement extrapolation method. The results for the non-dimensional stress intensity factors show that at lower crack lengths the influence of material mismatch is lower, but this influence increases with increasing crack length.     

The Dufort-Frankel Chebyshev method for parabolic initial boundary value problems

A pseudospectral explicit method for solving parabolic problems is presented. A stability theorem is proved for model equations, and numerical experiments discussed.     

Highly Crosslinked Polysilane–Schiff Base

Summary N,N-Bis(4-hydroxysalicylidene)ethylendiamine (salen) was attached to a poly[iodopropyl(methyl)-co-diphenylsilane)chain. Due to intermolecular crosslinking reactions, a high molecular weight polymer formation was observed. The resulted material was doped with metal cations through complexation reactions. The chemical structure of the polysilane-Schiff base metal complex was investigated by spectral analysis (IR, ¹H-NMR, ¹³C-NMR, UV), thermogravimetric analysis (TGA) and gel permeation chromatography (GPC).     

Sensitivity of static noise margins to random dopant variations in 6-T SRAM cells

The random dopant induced fluctuations of static noise margins (SNM) in 6-T SRAM cells are analyzed by using the formalism of doping sensitivity functions, which show how sensitive the SNM are to variations of the doping concentration at different locations inside the cell. The technique presented in this article is based on a full circuit perturbation theory at the level of each device transport model. It provides important information for the design and optimization of SNM and can capture correlation effects of doping fluctuations inside the same semiconductor device and between more devices. The bias points and the magnitude of random dopant induced fluctuations are computed by solving the Poisson, current continuity, and density–gradient equations for all the devices self-consistently (mixed-mode simulation). Simulation results for a well scaled SRAM cell with 30 nm channel length transistors show that the most sensitive regions to doping fluctuations extend for approximately 10 nm below the oxide/semiconductor interface and are located in the middle of the conduction channels for both the p-channel and n-channel transistors. It is apparent that random dopant induced fluctuations can significantly impinge on the yield and reliability of SRAM circuits and constitute a fundamental limit for further scaling unless these devices are properly optimized.     

Design of random doping fluctuation resistant structures of semiconductor devices

An automated technique is presented for the computation of the doping profiles that minimize the intrinsic fluctuations of various parameters induced by random doping fluctuations in semiconductor devices. The technique is based on the computation of the doping sensitivity functions of the parameters under consideration and the constrained minimization of the standard deviation of fluctuations by using the Lagrange multipliers technique. The technique is then applied to the minimization of the random doping induced fluctuations of the threshold voltage in 40-nm channel length MOSFET device.     

Bending vibrations of adaptive cantilevers with external stores

The vibrational behavior of cantilevers carrying externally mounted stores and featuring adaptive capabilities is investigated. The structure is modeled as a thin-walled beam, and the adaptive capabilities are provided by a system of piezoactuators bonded or embedded into the structure. Based on the converse piezoelectric effect, the piezoactuators produce a localized strain field in response to an applied electric field and, as a result, an adaptive change in the dynamic response characteristics is achieved. Implementation of a control law relating the applied electrical field to one of the mechanical quantities characterizing the motion of the beam, enables one to obtain the free vibration characteristics as a function of the applied voltage (or in other terms, of the feedback gain).The obtained numerical results suggest that the application of this technology can play a major role in the enhancement of the dynamic response and the control of free vibration characteristics of this type of structures.     

Modeling and bending vibration control of nonuniform thin-walled rotating beams incorporating adaptive capabilities

This paper addresses the problems of modeling and bending vibration control of tapered rotating blades modeled as nonuniform thin-walled beams and incorporating adaptive capabilities. The blade model incorporates non-classical features such as transverse shear, secondary warping and includes the centrifugal and Coriolis force fields. For the non-adaptive system, an assessment of a number of non-classical features including the taper characteristics is accomplished. The adaptive capabilities are provided by a system of piezoactuators bonded to the structure surface and spread over the entire span of the beam. Based on the converse piezoelectric effect and on the out-of-phase actuation, the piezoactuators produce a localized strain field in response to the applied voltage, and consequently, a change of the dynamic response characteristics is induced. A combined feedback control law relating the piezoelectrically induced transversal bending moment at the beam tip with the kinematical response quantities appropriately selected is used, and the beneficial effects upon the closed-loop dynamic characteristics of the blade are highlighted.     

Modeling and dynamic behavior of rotating blades carrying a tip mass and incorporating adaptive capabilities

Summary The problems of the mathematical modeling and dynamical behavior of rotating blades carrying a tip mass and incorporating adaptive capabilities are considered. The blade is modeled as a thinwalled beam incorporating non-classical features such as anisotropy, transverse shear, secondary warping, and includes the centrifugal and Coriolis force fields. For non-adaptive rotating blades, a thorough validation of the structural model and solution methodology is accomplished. The adaptive capabilities provided by a system of piezoactuators bonded or embedded into the structure are also implemented. Based on the converse piezoelectric effect, the piezoactuators produce a localized strain field in response to an applied voltage, and, as a result, an adaptive change of the dynamic response characteristics is obtained. A combined feedback control law relating the piezoelectrically induced bending moment at the beam tip with the kinematical response quantities appropriately selected is used, and its beneficial effects upon the closed-loop eigenvibration characteristics are highlighted.Dedicated to Prof. Dr. Dr. h. c. Franz Ziegler on the occasion of his 60th birthday     

Phosphate esters with a complex structure of an alkyl‐aryl type considered as base oils

This paper presents results of work carried out to produce phosphate esters of the alkyl‐aryl type. Three new triesters of mixed structure have been synthesised using a special alcohol with an aryl content, e.g., 2‐phenoxy ethanol, and a very long branched alcohol, e.g., isotridecanol. The influence of the aryl content and the effect of the long aliphatic chain on the main tribological properties have been investigated.