Advances in Structures Analysis

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作者: Ali Messabhia, Naceur Hassounet
摘要: The concrete works, during their exploitation are exposed to operation or environmental conditions which can inflict certain degradations to them. Establishing a good diagnosis needs a particular knowledge of the behavior of concrete when exposed to aggressive agents, especially the mechanical behavior. The determination of the causes of degradation is a complex matter and the interaction between different pathologies makes it more difficult. The choice of the materials and techniques used to repair the damages is also very important to succeed in the intervention. Our objective is the development of a knowledge base which will be used as a base to formulate the rules used to organize, rationalize and optimize the diagnosis process of these pathologies. The knowledge base gathers the majority of known phenomena related to the degradation of the concrete works. It is organized according to a reasoning which enables to describe or to identify most damages and degradations of chemical or mechanical origins or of implementation. Used with an expert system it will enable us to evaluate the importance of the damage, the need to intervene and finally to propose recommendations about the appropriate procedures and materials needed to repair the damage.
作者: D. Popovici, Veronica Paltanea, Gheorghe Paltanea, Gabi Jiga
摘要: In many industrial and biomedical applications (laser scanning displays, optical switch matrices and biomedical imaging systems) the sensing and actuation components are realized using micro-mirrors fabricated by MEMS technology. In this paper is evaluated, through numerical methods, the structural mechanical properties of the actuation mechanism of a ring shape micro-mirror. For the lift-off of the structure there are used four springs simulating a prestressed cantilever beam.
作者: A. Meksem, M. El Ghorba, A. Benali, A. El Barkany
摘要: The metallic cables are used for various applications in many industrial fields, such as the aircraft industry, the systems of lifting, the electric lines… In addition, according to the application considered and the conditions of use, the metallic cables undergo degradations whose direct consequences are the strong modifications of the geometrical and mechanical characteristics of the components. What induces a notable reduction of the resistant capacity of the cable according to time, able to bring to failure. In particular at the time of the cyclic requests of loading and unloading where the cable undergoes a phenomenon of tiredness. For safety reasons and an optimal use, it is important to anticipate any brutal rupture. Our work consists in finding a method which allows the optimization of the critical damage and the prediction of its useful life expectancy to be able to change it at convenient time. An analysis making it possible to evaluate the effect of the factors affecting the performance of the long-term cable constitutes the principal work in our lab. It consists in developing a modelling making it possible to envisage the capacity resistant of a cable to various levels of damage of its components, the estimate of the residual life expectancy, the evaluation of the risk of rupture for a level of request given, a mechanical model describing the state of damage by tiredness and another mathematics describing the reliability and finally to an analytical modeling of the relation Damage-Reliability to predict the phenomenon of tiredness of the hoisting cables. The adopted approach is an approach multi-scales with a total decoupling between the scale of the wire and that of the cable. The criterion of the failure in fatigue for the cable is more complex than that applied to the continuous structures, where the measures of length of the crack or a simple observation of the loss of integrity can be enough. These criteria are based on a mixture of former experiment, personal preferences, and of damage, for each particular type of application of cable. The occurrence of the unacceptable number of the cuts of wire is, by far, the most common action adopted for the evaluation of the damage in fatigue of the cable, which justifies our choice. This relation makes it possible to connect the reliability to the damage through the fraction of life expectancy; this led to associate at each stage of damage corresponding reliability. In fact, the theory of the damage considers that the damage reached its maximum value 1 when there is appearance of a macroscopic crack; but the cable keeps a resistance translated by a no null reliability. The latter becomes it when the cable is completely broken. Optimization by the reliability of the damage is a technique which supports knowledge and a follow-up of the state of an entity requested during time. Thing was being able to have interest for a possible application in industrial maintenance. In this context, this work and other works of the same tendency were worked out to manage to establish the bond between reliability as being a statistical size, and the damage by tiredness observed and caused by the cyclic requests.
作者: M. Bouazza, A. Tounsi, E.A. Adda-Bedia, A. Megueni
摘要: Thermal buckling behaviour of FGM square plates with simply supported edges has been studied in this note using the classic plate theory (CPT). It is assumed that the nonhomogeneous mechanical properties of the plate, graded through thickness, are described by a power-law FGM (simply called P-FGM) and sigmoid FGM (S-FGM). The plate is assumed to uniform temperature rise. Resulting equations are employed to obtain the closed-form solutions for the critical buckling temperature change of FGM. The results are compared with the results of the first order shear deformation theory.
作者: Mohammed Diany, Hicham Aissaoui
摘要: The like-rubber O-ring gaskets are widely used in hydraulic and pneumatic equipments to ensure the sealing of the shaft, the pistons and the lids. The correct operation is due to the good tightening of the joint that generate a sufficient contact pressure able to confine the fluids inside rooms or to prevent their passage from one compartment to another. Several studies are carried out to model the O-ring behavior but without taking in account the effect of the relaxation and creep phenomena. In this article, an axisymmetric finite element model is proposed to study the O-ring relaxation during the first hours of its installation in the unrestrained axial loading case. The results of the numerical model are compared with an analytical approach results based on the classical Hertzian theory of the contact. The effects of the o-ring mechanical and geometrical characteristics are examined. The contact stress profiles and the peak contact stresses are determined versus the time relaxation in order to specify the working conditions thresholds.
作者: W. El Alem, A. El Hami, Rachid Ellaia
摘要: The aim of this paper is to study the implementation of an efficient and reliable methodology for shape optimization problems where the objective function and constraints are not known explicitly and are dependent on the Finite Element Analysis (FEA). It is based on the Simultaneous Perturbation Stochastic Approximation (SPSA) method for solving unconstrained continuous optimization problems. We also propose Penalty SPSA (PSPSA) for solving constrained optimization problems, the constraints are handled using exterior point penalty functions within an algorithm that combines SPSA and exact penalty transformations. This paper presents a new structural optimization methodology that combines shape optimization, geometric modeling, FEA and PSPSA method to successfully optimize structural optimization problems. Several tests have been performed on some well known benchmark functions to demonstrate the robustness and high performance of the suggested methodology. In addition, an illustrative two-dimensional structural problem has been solved in a very efficient way. The numerical results demonstrate the robustness and high performance of the suggested methodology for structural optimization problems.
作者: Emmanuel Lacoste, Sylvain Fréour, Frédéric Jacquemin
摘要: The present work aims to investigate the validity of Eshelby-Kröner self-consistent model [1] for thermoelastic behaviour, in the case of a material reinforced by inclusions randomly oriented in the ply plane. The model provides predictive information on the properties and multi-scale mechanical states experienced by the material, accounting for its constituents properties, but also their morphology. However, it cannot reliably account for multiple inclusion morphologies (shape and orientation) in the material [2, 3, 4]. A study of the two applicable formulations and their limits leads to suggest a mixed formulation as an acceptable compromise between those alternatives. The results of this original approach are also described in the case of a thermo-mechanical load.
作者: Fouzia Khadraoui, Moussa Karama
摘要: Creep in cementitious materials is an important part of the delayed strains. It is a complex phenomenon in which many physical and chemical parameters are involved. In this paper, an experimental program was conducted to clarify the creep performance of CFRP strengthened mortar. The main parameters under study are the age at the time of loading and the drying. Specimens are tested at a sustained load of 30% of the ultimate strength. These investigations show the interest of the reinforcement by CFRP of the prismatic mortar specimens, this one allows a notable improvement of the creep behavior.
作者: Joël Bonneville, Dimitri Charrier, Christophe Coupeau
摘要: We report in the present paper a practical situation where the use of atomic force microscopy allowed an irrefutable insight in material plasticity for discriminating between different modelling hypotheses concerning the yield stress anomaly of Ni3Al intermetallic compounds with the L12 ordered structure. The contribution of AFM to a better understanding of elementary rate controlling mechanisms as well as collective dislocation motions is highlighted.