Dynamic stability of a porous cylindrical shell

This paper is devoted to a closed cylindrical shell made of a porous-cellular material. The mechanical properties vary continuously on the thickness of a shell. The mechanical model of porosity is as described as presented by Magnucki, Stasiewicz. A shell is simply supported on edges. On the ground of assumed displacement functions the deformation of shell is defined. The displacement field of any cross section and linear geometrical and physical relationships are assumed in cylindrical coordinate system. The components of deformation and stress state were found. Using the Hamilton's principle the system of differential equations of dynamic stability is obtained. The forms of unknown functions are assumed and the system of a differential equations is reduced to a simple ordinary equation of dynamic stability of shell (Mathieu's equation). The derived equation are used for solving a problem of dynamic stability of porous-cellular shell with intensity of load directed in generators of shell. The critical loads are derived for a family of porous shells. The unstable space of family porous shells is found. The influence a coefficient of porosity on the stability regions in Figures is presented. The results obtained for porous shell are compared to a homogeneous isotropic cylindrical shell. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Source mechanism model for ground motion simulation

A simple analytical model for computing ground motion in a layered half-space due to a buried seismic source is presented in this paper. The buried earthquake source is represented as a distribution of double couples varying in time as a ramp function on the fault plane. The analysis is simplified by first decoupling the governing equations into P-SV and SH problem by a coordinate transformation in the frequency-wave number domain. These two problems are solved separately and the final solution is obtained by the sum of solutions of these individual problems. Explicit expressions for ground motion in a layered half-space due to an impulsive double couple are derived. In the sequel, Green’s function for the displacement field in an infinite medium is also presented. The developed source mechanism model is also demonstrated by simulating ground motion for the Kucth earthquake (M_w = 7.7) of 26th January 2001.     

Application of a hybrid meshless technique for natural frequencies analysis in functionally graded thick hollow cylinder subjected to suddenly thermal loading

A hybrid meshless technique based on composition of meshless local Petrov–Galerkin method (for spatial variables) and Newmark finite difference method (for time domain) is developed for natural frequencies analysis of thick cylinder made of functionally graded materials (FGMs). The FG cylinder is assumed to be under suddenly thermal loading, axisymmetric and plane strain conditions. The dynamic behaviors and time history of displacements are obtained in time domain using Green–Naghdi (GN) theory of coupled thermo-elasticity (without energy dissipation). Using fast Fourier transform (FFT) technique, the displacements are transferred to frequency domain and all natural frequencies are illustrated for various grading patterns of FGMs. The variations of mechanical properties in FG thick hollow cylinder are considered to be in nonlinear volume fraction law through radial direction. The presented hybrid meshless technique furnishes a ground to analyze the effects of various grading patterns of FGMs on natural frequencies, which are obtained employing GN coupled thermo-elasticity governing equations. Also, the frequency history and natural frequencies are illustrated for various grading patterns at several points across thickness of cylinder.     

Mechanical properties of cold sprayed Titanium and Nickel based coatings

Cold spray is an innovative coating technology. Very fine particles are accelerated, then sprayed on a substrate in condition very far from material melting. The unique mechanical properties experienced by the sprayed material are due to the severe plastic deformation acting during particle impact. In the present paper, the microstructural and mechanical behavior of Ti- and Ni-based nanocomposites coatings produced via cold spray are presented. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Unscented Kalman filter for time varying spectral analysis of earthquake ground motions

A novel parametric time-domain method for time varying spectral analysis of earthquake ground motions is presented. Based upon time varying autoregressive moving average (ARMA) modeling of earthquake ground motion, unscented Kalman filter (UKF) is used to estimate the time varying ARMA coefficients. Then, time varying spectrum is yielded according to the time varying ARMA coefficients. Analysis of the ground motion record El Centro (1940, N–S) shows that compared to Kalman filter (KF) based method, short-time Fourier transform (STFT) and wavelet transform (WT), UKF based method can more reasonably represent the distribution of the seismic energy in time–frequency plane, which ensures its better ability to track the local properties of earthquake ground motions and to identify the systems with nonlinearity. Analysis of the seismic response of a building during the 1994 Northridge earthquake shows that UKF based method can be potentially a useful tool for structural damage detection and health monitoring. Lastly, it is found that the theoretical frequency resolving power of ARMA models usually neglected in some studies has considerable effect on time varying spectrum and it is one of the key factors for ARMA modeling of earthquake ground motion.     

Theoretical and experimental investigation of cartilage replacement material for medical applications

Soft tissues are commonly applied in surgery to replace the injured articular cartilage. Many biological researches were carried out through mechanical and histological experiments. They focus on the function, degeneration and regeneration of the articular cartilage and fibrocartilage. The aim of the presented work is to develop a method to characterize the mechanical properties of different kinds of soft tissues and to trace the evolution of elastic properties in implants during the remodeling process. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Modeling the moisture and temperature dependent material behavior of adhesive bonds

Although bonding has been known for a long time, the mechanical behavior of adhesive bonded joints comes more and more into the focus of scientific attention. During usage, adhesives are exposed to environmental influences like temperature, moisture and radiation. Due to the fact that adhesives usually consist of polymers, these influences change their mechanical behavior. In the presented work, a viscoelastic cross-linked polyurethane that behaves incompressible is investigated. A three-dimensional mechanical model is presented, which takes into consideration influences of changes in temperature as well as in the moisture concentration inside the adhesive layer and its thickness on the mechanical behavior. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Design and Fabrication of Composite Smart Structures with High Electric and Mechanical Performances for Future Mobile Communication

In this paper, we have developed a load-bearing outer skin for antennas, which is termed a composite smart structure (CSS). The CSS is a multilayer composite sandwich structure in which antenna layers are inserted. A direct-feed stacked patch antenna is considered. A design procedure including the structure design, material selection, and design of antenna elements in order to obtain high electric and mechanical performances is presented. An optimized honeycomb thickness is selected for efficient radiation and impedance characteristics. High gain conditions can be obtained by placing the outer facesheet in the resonance position, which is at about a half wavelength distance from the ground plane. The measured electrical performances show that the CSS has a great bandwidth (over 10%) and a higher gain than an antenna without a facesheet and has excellent mechanical performances, owing to the composite laminates and honeycomb cores. The CSS concept can be extended to give a useful guide for manufacturers of structural body panels and for antenna designers.     

Experimental and theoretical investigation of PLC bands

In this paper, the nucleation and propagation of PLC deformation bands in AlMg3 alloy are studied experimentally and theoretically. The morphology and kinematics of PLC bands are investigated using both mechanical and thermal measurement methods. In particular, the latter is based on the use of a thermal camera which captures the temperature changes resulting from mechanical dissipation during nucleation and propagation of PLC bands. On the modeling side, two models are investigated via finite-element and finite-difference methods. Here, attention is focused on the influence of the specimen geometry and the thermomechanical coupling on PLC band nucleation and propagation. A comparison of experimental and simulation results is presented. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Finite element solution of the Kohn-Sham equations

Many properties of condensed matter as for example electric conductivity, magnetism as well as the mechanical response upon external excitations are determined by the electronic structure of the material. Its evaluation represents a coupled, quantum mechanical many body problem, consisting of the positively charged atomic cores and the negatively charged, fermionic electrons. By the Hohenberg-Kohn theorem a method was established to calculate the ground state electron density through a density functional. Then the Kohn-Sham equations resemble a nonlinear, single electron problem with an effective potential, accounting for the Coulomb interactions between the particles as well as for quantum mechanical effects. They can be solved within a self consistent field procedure. In this work a real space formulation for the calculation of the electronic structure in the context of density functional theory is shown. In a first step a finite element based solution algorithm for the Kohn-Sham equations is developed, based upon which the electron density is obtained in a non-periodic setting. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

FE-simulation of spatially graded gelation during adhesive's curing

In this contribution main aspects of material characterization and modelling of a curing adhesive are denoted. It is pointed out how to deal with the exothermic heat generation during curing, both, how to obtain it experimentally as well as how to account for it in the continuum mechanical an FE-modelling framework. Furthermore, a strategy to simulate spatially graded gelation processes in ANSYS® is presented. An academic simulation example completes this work. By the help of this simulation tool a better understanding of a novel manufacturing process of smart semi-finished light weight structures is ensured. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Material modelling of a sheet-layered lamination stack by homogenization

In electrical machines, sheet-layered lamination stacks play an important role for the mechanical behavior of the system. Especially the interlayer between individual sheets and their interaction have a severe influence on the structure. In the context of performance and computational effort, it is desirable to avoid a full FE simulation of a lamination stack with every single sheet. Therefore, homogenization techniques are presented to identify a transversely isotropic surrogate material model, while Zero-Thickness elements are utilized during this process to cover the interplay of single sheets. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

XFEM-modelling of stationary magnetic and coupled magneto-mechanical boundary value problems

To analyse a composite material with magnetically switchable stiffness properties, the coupling between the magnetic and the mechanical field has to be considered. Here the mechanical as well as the magnetic problem are computed using the eXtended Finite Element Method (XFEM). After a brief introduction of the framework, some results are presented focusing on the ability to calculate correct loads and displacements as well as on convergence rates. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Mechanical Synchronization in Dual-Rotor Vibroactuator

In the present work the mechanical behaviour of a dual-rotor vibrotactor has been investigated with special attention to its stationary motions and their linear stability. After the introduction of the used mechanical model, the formulae for the stationary motions are given, and characteristic stablity charts are presented. The linear stability is investigated for uncontrolled and controlled system as well. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Modeling of fiber-reinforced PMMA at different scales

This paper deals with the modeling of fiber-reinforced PMMA. Focus is on the macroscopic mechanical response with emphasis on the fracture properties such as the ultimate strength and the fracture energy. In order to capture the macroscopic mechanical response of PMMA, a finite element formulation is presented. While the elastic response of the fibres and that of the surrounding matrix are modelled in standard manner, i.e., by standard bulk material models, the relevant failure modes such as cracking of the fibres are accounted for by means of the so-called Strong Discontinuity Approach (SDA). Since the fibres are relatively small, their fracture mechanical properties crucially depend on their geometry, i.e., they show a pronounced size effect. Based on numerical analyses of fibres with different geometries, the aforementioned size effect is naturally incorporated into the formulation [1]. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

A reformulation of the nonsmooth approaches of M. Frémond and J.J. Moreau for rigid body dynamics

This paper deals with the nonsmooth dynamics of a rigid bodies system. The proposed theory is inspired by the formalism of J.J. Moreau and that of M. Frémond and relies on the notion of percussion which is the integral of the contact force during the duration of the collision. Contrary to classical discrete element models, it is here assumed that percussions can be expressed as a function of only the velocity before the impact. This assumption is checked for the usual mechanical constitutive laws for collisions derived from a pseudopotential of dissipation or the Coulomb friction law. Motion equations are then reformulated taking into account simultaneous collisions of solids. A mathematical study of the new model is presented: the existence and uniqueness of the solution are discussed according to the regularity of both the forces (Lebesgue‐density occurring during the regular evolution of the system) and the percussions (Dirac‐density describing the collision). In the light of the principles of thermodynamics, a condition on the internal percussion assuring that the collision is thermodynamically admissible, is established. Finally, an application of this new model to the motion of a system of rigid disks, including simultaneous collisions is presented.     

Design and simulation of a carbon nanotube-based adjustable nano-electromechanical shock switch

In this paper, design and simulation of a carbon nanotube-based nano-electromechanical shock switch is reported. The switch is represented by a carbon nanotube placed over a ground electrode. Response of the nano-switch based on nonlinear beam theory is studied using Galerkin’s method. Up to five mode shapes have been utilized to capture the response of system and results are validated by comparing with Molecular Dynamics (MD) simulation. Due to their high stiffness, CNTs cannot be actuated to pull-in (switch ON) state by conventional mechanical shocks in range of 10–1000 g under one-step voltage. Here, a multi-steps voltage modification is applied to enhance the actuation. Employing this method, a nano-switch with fixed geometry can be adjusted to be triggered by wide rang of mechanical shocks (10–1000 g).     

Elements on the Concept and Design of a Tracked Mini Robot – “ROBO GENIU” – Destined for Special Applications

The authors of this paper aim to highlight issues related to the organology and the integration of the hardware component in the mechanical structure of a tracked mini robot, called Robo Geniu, part of the unmanned ground vehicles category having the ability to act autonomously and enabling its endowment with means of observation, listening, tapping, relaying and jamming. This paper reveals, in detail, the composing parts of the hardware component, as well as the way they are assembled in the mechanical structure of the mini robot under study. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Fast partial differential equation de‐noising filter for mechanical vibration signal

A novel approach for mechanical vibration signal de‐noising filter using PDE and its numerical solution were presented. The proposed method is computationally fast compared with other conventional PDE‐based de‐noising methods. It enables: (i) by incorporating unconditional stable finite difference backward Euler scheme, the de‐noising process has no requirements of grid ratio; (ii) developing variational matrix‐based fast filter while the de‐noising process can be completed instantly, which will be accomplished by only one iteration; and (iii) effective de‐noising method for mechanical vibration signal interfered by Gauss white noise. The method is performed efficiently, and the de‐noising tests on different artificial Gauss white noise as well as natural mechanical noise are conducted. Experimental tests have been rigorously compared with different de‐noising methods to verify the efficacy of the proposed method. Copyright © 2015 John Wiley & Sons, Ltd.