Modeling and Optimization of Materials and Structures

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Authors: Nikolaos D. Alexopoulos, Vangelis Migklis, Stavros K. Kourkoulis, Zaira Marioli-Riga
Abstract: In the present work, an experimental study was performed to characterize and analyze the tensile and constant amplitude fatigue mechanical behavior of several aluminum alloys, namely 2024 (Al-Cu), 2198 (Al-Li) and 6156 (Al-Mg-Si). Al-Li alloy was found to be superior of 2024 in the high cycle fatigue and fatigue endurance limit regimes, especially when considering specific mechanical properties. Alloy 6156 was found to have superior constant amplitude fatigue performance that the respective 6xxx series alloys; more than 15% higher endurance limit was noticed against 6061 and almost 30% higher than 6082. Alloy 6156 presented only a marginal increase in fatigue life for the HCF regime.
Authors: A. Baazaoui, T. Fourcade, Olivier Dalverny, Joel Alexis, Moussa Karama
Abstract: This paper deals with an identification methodology of the interfacial fracture parameters to predict the lifetime of a metallic brazed joint. The methodology is based on an experimental-numerical study whereby the optimal parameters are obtained. The experimental data, using the scanning electron microscope analysis, allowed approving that failure of the assembly based AuGe solder seems first to appear near the interfaces. These results were confirmed by micrographs analysis of the solder/insert and solder/substrate interfaces. Then, using shear test results and parametric identification coupled with a finite elements model (FEM) simulation, the damage constitutive law of the interfacial fracture based on a bilinear cohesive zone model are identified. The agreement between the numerical results and the experimental data shows the applicability of the cohesive zone model to fatigue crack growth analysis and life estimation of brazed joints.
Authors: Shi Jie Zhu, Abel Cherouat, Houman Borouchaki, Xiao Lu Gong
Abstract: The compression characteristics of open-cell aluminum foams were experimentally and numerically investigated. It is found that the mechanical parameters, such as collapse stress and absorbed energy, are dependent on the porosity of aluminum foams. Three macroscopic models were chose to predict the compression behavior of open-cell foams. During simulation of metal foam compression, the finite elements distort severely at the local regions with high gradient of physical field such as stress, strain due to these problems. The procedure integrates Explicit solver of ABAQUS, OPTIFORM mesher and python script program transfer to execute step by step the incremental deformation process. At each step, the meshes are refined and coarsened automatically based on geometrical and physical error estimations; the physical fields are transferred from old to the new one using advanced algorithm.
Authors: Abel Cherouat, Guillaume Montay, Florent Ilczyszyn
Abstract: Hemp fibres are using as reinforcement for compounds based on polymer in different industrial manufacturing (aerospace and automotive) for their interesting mechanical and ecological properties. The hemp fibres present a non-constant cross section and complex geometry that can have a high effect on their mechanical properties. In this study, a micro-traction test coupled with a numerical imaging treatment and a finite elements method are used. The mechanical tensile test allows to determinate the evolution of the traction load in function of the displacement until the fibre crack. The used fiber are incorporate in plastic material is order to obtained PP/hemp reinforcement composite part. Static and dynamic tests are proposed in order to study trhe behaviour of green material subjected to tensile load.
Authors: Yasir Nawab, Chung Hae Park, Abdelghani Saouab, Romain Agogué, Pierre Beauchêne
Abstract: Process induced residual stresses in thermoset composite parts is one of significant issue faced by the industry. Its Modelling is a coupled multiphysics phenomena. Precise information about the chemical shrinkage, thermal expansion coefficient, cure kinetics, heat transfer and constitutive equation are required for an accurate simulation. In this article, spring-in angle induced in woven carbon/epoxy composite bracket is modelled by solving the thermo-kinetics and thermo-mechanics coupling simultaneously in a commercial finite element software. The obtained values of spring-in angle using numerical simulation are compared with those found in the literature and both are found in agreement.
Authors: Khalil El-Hami, Abdelkhalak El-Hami
Abstract: In this investigation, we reported that single walled carbon nanotube can act as a sharpest tip where the electric field strength is highly concentrated at the edge. Therefore, we study the effects of the physical and geometrical parameters of an applied electric field gradient to various electrode structures. Results showed that carbon nanotubes presented a strongest electric field value at the edge which makes them suited for applications as unidirectional electric field or serving as nanoelectrode with a diameter of about one nanometer to be used for conductivity nanotest and to determine the electrical properties of single molecules or clusters.Keywords: single walled carbon nanotube, nan-electrode, tip, electric field lines, surface charge density.
Authors: Khalil El-Hami, Abdelkhalak El-Hami
Abstract: Nanocomposites from carbon nanotubes (CNT) and ferroelectric polymers/CNT provide new generation of nanomaterial with high electromechanical properties and allow polymers to exhibit enhanced actuating. Based on relative motion of nanotubes walls incorporated in polymer matrix, CNT are considered for various electromechanical applications such as nanoactuator, nanopump, nanothermometer, nanoresistor, nanomotor...In this investigation we determine the experimental correlation between the electrical and mechanical coupling of the nanocomposite based single walled carbon nanotubes (SWCNT).A strain refereed as a mechanical deformation was determined to be 10-3 under an applied electrical voltage of 6V.
Authors: Hind Haji, Abdelghani Saouab
Abstract: We present numerical simulation of particle filled resin flow through a fibrous media taking into account dual scale porosity in LCM (Liquid Composite Molding) processes. During the flow, a strong interaction between the particle motion and the fluid flow takes place at the porous medium wall or at the fiber bundle surface. A model is developed to describe the particle retention and filtration in the porous media. In this study, the Stokes-Darcy equation is solved to describe the resin flow in a mesoscopic scale. The particle retention mechanism is extensively studied taking into account the influences from such parameters as size and concentration of particles. The particle filled resin flow through a fibrous media simulation is performed to demonstrate the effect on the retention and filtration mechanism during the composites manufacturing by LCM processes.
Authors: Abdelkhalak El Hami, Bouchaib Radi
Abstract: In this paper, an original method is presented for evaluating the probability of failure in a precise manner in the tube hydroforming process (THP). This process consists to apply an inner pressure combined to an axial displacement to manufacture the part. During the manufacturing phase, inappropriate choice of the load paths can lead to failure. Our approach is to determine the space failure probability for each item in the area is critical. It is defined by identifying the critical element, and then a patch is defined on this item that represents the area of the most probable failure. The identification of the critical element for each failure mode is done by reference the state of strain on the forming limit curve (FLC) of the material. Access to the probability of space failure allows to give an idea on the stability of the process and also to predict the most likely area where plastic instability can appear. The failure probability estimation based on a characterization probabilistic principal strains (major and minor) for each failure mode and for each element. Access to this probability of failure in a direct manner is impossible given the complexity of the treated problem and the huge number of calculations by finite elements necessary. To compensate for this problem, approximation techniques have been used to replace the real model by metamodel that enables to evaluate the response quickly and allows us to get an idea on the stability of the process.Keywords: Hydroforming process, metamodels, random, forming limit curve (FLC), failure mode, finite element.

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