Mechanical Behavior Of Structures Research Articles

The second prototype design of the upper body of Archie

Abstract: In this paper, we have shown the second prototype design of the upper body of Archie, and we have discussed the dimensions giving calculated values of length of links, the weight and centre of weight of these links. During the design of second prototype, we have taken into account mechanical requirements, simplicity of the design, price, the natural appearance and design to be in accordance with the design of the lower part of the robot (which existed). A simulation refers to behaviour of mechanical structure of design, through graphs obtained through SimMechanics tool.

A Determination of Material Properties of Flexible Structures Using EMA and FEM Analysis

Dynamic behavior of mechanical structures results from complex interactions between applied forces and the stiffness properties of the structure. Currently, many problems of structural dynamic analysis are solved using Finite Element Method (FEM). However, in recent years, the implementation of the Fast Fourier Transform (FFT) in low cost computer-based signal analyzers has provided a powerful tool for acquisition and analysis of vibration data. This article discusses combination of two approaches to structural dynamics testing; the experimental part which is referred to as Experimental Modal Analysis (EMA), respectively the analytical part, which is realized by Finite Element Analysis (FEA). Main goal of the paper is calculation of material properties from experimentally determined modal frequencies.

Boundary Condition Identification of a Plate on Elastic Support

The behaviour of mechanical structures in low frequencies is strongly affected by the existence of the boundary conditions. It is not usually possible to provide ideal boundary conditions, i.e. simply supported or clamped, for structures. Therefore the real structures are mostly constrained by elastic supports. Constructing an accurate mathematical or numerical model for a structure requires the knowledge of the support parameters. In this paper, a new method is proposed for the parameter identification of a rectangular plate constrained by elastic support. The method relies on the free vibration solution of the plate dynamics subjected to elastic boundary conditions and employs the optimization toolbox of MATLAB.

A Semiautomatic Large-Scale Detection of Simple Geometric Primitives for Detecting Structural Defects from Range-Based Information

Buildings in Cultural Heritage environments exhibit some common structural defects in elements which can be recognized by their differences with respect to the ideal geometric model. The global approach consists of detecting misalignments between elements corresponding to sections perpendicular to an axis, e.g. The local approach consists of detecting lack of verticality or meaningful differences (facades or internal walls) in curved elements with typical components (apses or vaults, e.g.) appearing in indoor environments. Geometric aspects concern to the basic model which supports successive layers corresponding to materials analysis and mechanical structural behaviour. A common strategy for detecting simple shapes consists of constructing maps of normal which can be extracted by an appropriate sampling of unit normal vectors linked to a points cloud. The most difficult issue concerns to the sampling process. A profusion of decorative details or even the small variations corresponding to small columns which are prolonging the nerves of vaults generate a dispersion of data which can be solved in a manual way by removing notrelevant zones for structural analysis. This method can be appropriate for small churches with a low number of vaults, but it appears as tedious when we are trying to analyse a large cathedral or an urban district. To tackle this problem different strategies for sampling information are designed, where some of them involving geometric aspects have been implemented. We illustrate our approach with several examples concerning to outdoor urban districts and indoor structural elements which display different kinds of pathologies.

Study on Shear-Mode of Piezoelectric Patch/Complete Layer in Smart Laminated Shell Panels

Finite element solution is presented for finitely long, simply-supported, orthotropic, piezoelectric shell panel under pressure and electrostatic excitation. The influence of the piezoelectric layers on the mechanical behavior of structures is studied. The direct piezoelectric effect of the piezoelectric material in ordinary (normal) and shear mode application are investigated. Numerical examples are presented for [0/90/P] laminations, where P indicates the piezoelectric layer. Piezoelectric layer can be completed or patch form. Finally the results are compared together and the shear mode advantages are discussed.

Simulation of Thermo Mechanical Behavior of Structures by the Numerical Resolution of Direct Problem

The aim of our study is to develop an approach to both experimental and numerical modeling to the thermal behavior of a material by identifying these thermal parameters. The theoretical part is based on the finite element method which is a starting point to solve a two-dimensional inverse heat. The experimental measurements are performed by infrared thermography. All these experimental and numerical techniques give this method properties valued in the industrial world as the non-intrusive measurements and real-time calculations. For this, we have supported a system of equations and the temperature field, so before starting the inverse problem, we addressed the direct problem by finite element method that has been compared to measures experimental infrared thermography well to check the validity of equations, so it’s the purpose of this work.

Analysis of nonlinear stability and post-buckling for Euler-type beam-column structure

Based on the assumption of finite deformation, the Hamilton variational principle is extended to a nonlinear elastic Euler-type beam-column structure located on a nonlinear elastic foundation. The corresponding three-dimensional (3D) mathematical model for analyzing the nonlinear mechanical behaviors of structures is established, in which the effects of the rotation inertia and the nonlinearity of material and geometry are considered. As an application, the nonlinear stability and the post-buckling for a linear elastic beam with the equal cross-section located on an elastic foundation are analyzed. One end of the beam is fully fixed, and the other end is partially fixed and subjected to an axial force. A new numerical technique is proposed to calculate the trivial solution, bifurcation points, and bifurcation solutions by the shooting method and the Newton-Raphson iterative method. The first and second bifurcation points and the corresponding bifurcation solutions are calculated successfully. The effects of the foundation resistances and the inertia moments on the bifurcation points are considered.

The modified couple stress functionally graded Timoshenko beam formulation

In this paper, a size-dependent formulation is presented for Timoshenko beams made of a functionally graded material (FGM). The formulation is developed on the basis of the modified couple stress theory. The modified couple stress theory is a non-classic continuum theory capable to capture the small-scale size effects in the mechanical behavior of structures. The beam properties are assumed to vary through the thickness of the beam. The governing differential equations of motion are derived for the proposed modified couple-stress FG Timoshenko beam. The generally valid closed-form analytic expressions are obtained for the static response parameters. As case studies, the static and free vibration of the new model are respectively investigated for FG cantilever and FG simply supported beams in which properties are varying according to a power law. The results indicate that modeling beams on the basis of the couple stress theory causes more stiffness than modeling based on the classical continuum theory, such that for beams with small thickness, a significant difference between the results of these two theories is observed.

Investigation of the size effects in Timoshenko beams based on the couple stress theory

In this paper, a size-dependent Timoshenko beam is developed on the basis of the couple stress theory. The couple stress theory is a non-classic continuum theory capable of capturing the small-scale size effects on the mechanical behavior of structures, while the classical continuum theory is unable to predict the mechanical behavior accurately when the characteristic size of structures is close to the material length scale parameter. The governing differential equations of motion are derived for the couple-stress Timoshenko beam using the principles of linear and angular momentum. Then, the general form of boundary conditions and generally valid closed-form analytical solutions are obtained for the axial deformation, bending deflection, and the rotation angle of cross sections in the static cases. As an example, the closed-form analytical results are obtained for the response of a cantilever beam subjected to a static loading with a concentrated force at its free end. The results indicate that modeling on the basis of the couple stress theory causes more stiffness than modeling by the classical beam theory. In addition, the results indicate that the differences between the results of the proposed model and those based on the classical Euler–Bernoulli and classical Timoshenko beam theories are significant when the beam thickness is comparable to its material length scale parameter.

Efficiency factor and modulus of elasticity of lightweight concrete with expanded clay aggregate

Nowadays lightweight concrete is used on a large scale for structural purposes and to reduce the self-weight of structures. Specific grav- ity, compressive strength, strength/weight ratio and modulus of elasticity are important factors in the mechanical behavior of structures. This work studies these properties in lightweight aggregate concrete (LWAC) and normal-weight concrete (NWC), comparing them. Spe- cific gravity was evaluated in the fresh and hardened states. Four mixture proportions were adopted to evaluate compressive strength. For each proposed mixture proportion of the two concretes, cylindrical specimens were molded and tested at ages of 3, 7 and 28 days. The modulus of elasticity of the NWC and LWAC was analyzed by static, dynamic and empirical methods. The results show a larger strength/ weight ratio for LWAC, although this concrete presented lower compressive strength.

Combined Analytical and Finite Element Beam Model for Wind Turbine Blades

Finite element method (FEM) has been widely used in recent years to analyze fiber-reinforced polymer (FRP) beams such as wind turbine blades. Although it is generic and convenient, FEM does little to shed light on the mechanical behavior of structures. Moreover, it is inefficient in calculation. This study presents a combined analytical and finite element beam (CAFB) model with an inclination angle correction to solve the non-prismatic, blade-like FRP beam problem. It not only substantially reduces computational time, but also helps us comprehend the mechanical behavior. Also, the inclination angle correction is supposed to correct the overestimated axial stiffness due to the topology of beams. In the presented cases, the CAFB model can accurately analyze the FRP thin-walled beams with all results being certified by finite element analysis software, and the correction is especially effective in small fiber orientation angles.

Corrosion behaviour of reinforced concrete: Laboratory experiments and archaeological analogues for long-term predictive modelling

In the context of the nuclear waste storage, reinforced concrete will be used for various purposes such as cell structures and some types of containers (e.g. for intermediate level wastes). These structures are required to be safe and reliable in varying environments for long periods of time (up to several hundred years). This paper presents a specific approach that is developed in France at CEA and EDF for the prediction of long-term behaviour of such structures. It discusses the experimental and theoretical approaches which have been developed. It is based on interactive studies dedicated to short term experimentations (corrosion and mechanical behaviour of structures), characterization and specific tests on archaeological analogues, both used to develop mechanistic understanding and modelling of corrosion and mechanical behaviour of reinforced concrete. Advantages and limits of these different and complementary aspects are presented and discussed. Moreover the prediction results of a specific mechanistic model have been confronted to real structures exposed to atmospheric conditions for many years.

On the dynamic behavior of piezoelectric sensors and actuators embedded in elastic media

Embedded piezoelectric sensors can be used to monitor the mechanical behaviour of structures for damage detection. This paper provides an analytical study of the dynamic behaviour of piezoelectric sensors embedded in elastic media under high frequency electromechanical loads induced by piezoelectric actuators. A generalized sensor/actuator model taking account of the deformation in both transverse and longitudinal directions of the piezoelectric sensor/actuator is developed. The dynamic load transfer between the sensors/actuators and the host medium is studied using Fourier transform method and solving the resulting integral equations in terms of the interfacial normal and shear stresses. Detailed numerical simulation is conducted to study the relation between the deformation of the sensor and that of the host medium under different loading conditions. The results show the significant effect of the geometry, the material combination and the loading frequency upon the behaviour of the sensor.

A GENETIC ALGORITHM FOR THE SHAPE OPTIMIZATION OF PARTS SUBJECTED TO THERMAL LOADING

In many technical situations, the optimization of the mechanical behavior of structures proceeds from the search for the ideal shape satisfying thermal, mechanical, technological, and geometrical constraints. In this article, the shape optimization of mono- and two-dimensional structures is handled by means of a new genetic algorithm (GA). The method is in general well suited to the resolution of nonconstrained optimization problems: The algorithm presented here has been modified by taking into account the imposed design constraints in the selection of the "individuals" belonging to a given population. The crossover operation between individuals and the mutation process in their original forms are applied to derive the optimal shape of parts subjected to thermal loadings. The algorithm exhibits a good convergence toward the optimal solution and the numerical results of its application show a good numerical accuracy.

Speckle interferometry from fiber-reinforced materials:A fractal geometry approach

Summary Speckle field studies were performed on fiber-modified Portland cement-based microconcrete beam models subjected to flexural loading. The resulting speckle fields were analyzed in terms of their associated mass fractal dimension by using digital image processing techniques. The experiments showed a change in the fractal dimension of the speckle fields as a function both of the loading and the structure of the microconcrete beams. A study was also conducted on the free-damped frequencies of the beams, which allowed to draw a fractal dimension vs. frequency plot on each loading cycle. These results allow to foresee the use of fractal geometry as a promising tool for better understanding the mechanical behavior of structures.

Recent developments in fire design

Developments in fire safety engineering now allow a better assessment of fire risk and consequently better design of steel structures for improved fire resistance. By using numerical modelling the various physical phenomena occurring in a fire can be predicted with a fair degree of accuracy. These models cover fire development, temperature distribution within heated structural elements and the mechanical behaviour of structures at elevated temperatures. With such tools it is possible to assess the global behaviour of steel structures, taking into account the real risk of fire and considering the thermal elongation effect and possible redistribution of loads between hot and cold members. The fire parts of Eurocode I (actions in case of fire) and of Eurocode 3 (structural fire design of steel structures) cover a large part of this fire engineering discipline. Some useful definitions are given at the end of this review.

NATURAL FREQUENCY CONSTRAINED OPTIMAL STRUCTURAL MODIFICATION USING A SENSITIVITY DERIVATIVE OF DYNAMICALLY CONSTRAINED MASS AND STIFFNESS MATRICES

Structural dynamic modification (SDM) problems involve local modifications with lumped masses, stiffeners, dampers and beam elements, etc., to improve the dynamic behaviour of existing structures. Many proposals have been presented earlier [1-3] which identify the optimal parameter of the system. The need for quantification of identified optimal parameters for a desired natural frequency has been stressed by Snoeys et al. [4]. Reanalysis techniques for finding the geometrical dimensions of structural members have been investigated by Wang [5]. The modification techniques reviewed above offer no guarantee that the chosen modification is the most appropriate. Depending upon the dynamicist's intuition and other factors, the modification may be acceptable, but not necessarily optimal. This is the reason why sensitivity analysis together with modification techniques form useful tools for the optimum modification of the dynamic behaviour of mechanical structures. These techniques, based on the calculation of derivatives of the modal parameters, provide the most effective parameter changes such that the desired dynamic behaviour can be obtained in one modification cycle. The calculation of derivatives of modal parameters in turn requires the sensitivity derivatives of the spatial parameters, namely mass and stiffness matrices of the structure [6, 7]. Usually, these matrices are dynamically condensed corresponding to the co-ordinates of interest [8]. The finite difference calculation of sensitivity derivatives is easy to implement but the accuracy of this method is greatly influenced by the choice of step size. The present work addresses itself to analytical determination of sensitivity derivatives of dynamically condensed mass and stiffness matrices of structures which are modelled with beam elements [8]. These derivatives are used to find derivatives of eigenvalues and thereby predict optimal values of modifications such that the modified structure has the desired shifted natural frequency. For a dynamicist, it is desirable that none of the natural frequencies coincide with excitation frequencies. The present note deals with shifting of an undesirable natural frequency in an optimum way. The proposed algorithm has an advantage that a shift in natural frequency and its prediction is accurate even when the magnitude of the desired frequency shift is large. A first step in this direction is the sensitivity analysis to identify effective parameters for modification. The present work utilizes the sensitivity derivatives of the natural frequency and also quantifies the effectiveness of various parameters. Further, optimal modification is approached as one of the two possible requirements.

Interactive shape optimization of continuum structures

A concept for interactive shape optimization of plane and axisymmetric continuum structures is presented. Interactive optimization is interpreted as a continuous optimization of the mechanical structural behaviour using a flexible optimization model that may be changed during the optimization process. Essential points of the concept are: the application of analytically formulated hybrid-mixed finite elements for structural and sensitivity analysis, the integration of an adaptive mesh generation scheme for the automatic derivation of the analysis model, and an interactively changeable boundary representation using nonuniform rational B-splines (NURBS) curves. The characteristics of the implementation, the shape optimization system PICASSO (prototype of interactive computer aided structural shape optimization), are discussed using an example.

Exact solution of orthotropic cylindrical shell with piezoelectric layers under cylindrical bending

An exact elasticity solution for an orthotropic cylindrical shell with piezoelectric layers is obtained in this paper. The stress and displacement distributions are presented. The influence of the piezoelectric layers on the mechanical behavior of structures is studied. Both the direct piezoelectric effect and the converse piezoelectrical effect of the piezoelectric material are investigated. Results presented in this paper can be used to study various approximate shell theories used in the numerical simulations of piezoelectric structures.

Scale Model Study of an Underground Opening in a Mine in Saudi Arabia

Physical scale model study of the mechanical behaviour of structures is of a vital importance in the design process and in the evaluation of performance of the prototypes. Important applications are in the fields of aeronautics, hydraulics, structural and mechanical engineering. It is also applied in mining engineering, particularly in relation to mine ventilation, the design of underground openings, evaluation of ground subsidence and slope stability. Criteria for the scaling of physical quantities involved in the model study of the deformation behaviour of underground openings are developed. The mechanical properties of the rock mass around an underground mine opening are determined and the corresponding properties of an equivalent model material are also assessed. The technique of scale model testing is described and the results of the model tests are compared with those of the measurement of deformation of the actual opening.