Key Engineering Materials Vol. 446

Abstract: The aim of this paper is to present a new methodology for the evaluation of the statistical proprieties of the response of structures, based on The Finite Element Analysis (FEA) coupled with the Probabilistic Transformation Method (PTM). Uncertainty modelling with random variables motivates the adoption of advanced PTM for reliability analysis to solve problems of mechanical systems. The PTM is readily applicable in the case where the expression between input and output of structures are available in explicit analytical form. However, the situation is much more involved when it is necessary to perform the evaluation of implicit expression between input and output of structures through numerical models. For this we propose technique that combines the FEA software, and the PTM program to evaluate the Probability Density Function (PDF) of the response where the expression between input and output of structures is implicit. This technique is based on the numerical simulations of the FEA and the PTM by making an interface between Finite Element software and Matlab. Some problems of structures are treated in order to demonstrate the applicability of the proposed technique.

Abstract: In structural design optimization, numerical techniques are increasingly used. In typical structural optimization problems there may be many locally minimum configurations. For that reason, the application of a global method, which may escape from the locally minimum points, remain essential. In this paper, a new hybrid simulated annealing algorithm for global optimization with constraints is proposed. We have developed a new algorithm called Adaptive Simulated Annealing algorithm (ASA); ASA is a series of modifications done to the Basic Simulated Annealing algorithm ( BSA) that gives the region containing the global solution of an objective function. In addition, the stochastic method Simultaneous Perturbation Stochastic Approximation (SPSA), for solving unconstrained optimization problems, is used to refine the solution. We also propose Penalty SPSA (PSPSA) for solving constrained optimization problems. The constraints are handled using exterior point penalty functions. The proposed method is applicable for any problem where the topology of the structure is not fixed, it is simple and capable of handling problems subject to any number of nonlinear constraints. Extensive tests on the ASA as a global optimization method are presented, its performance as a viable optimization method is demonstrated by applying it first to a series of benchmark functions with 2 - 30 dimensions and then it is used in structural design to demonstrate its applicability and efficiency. It is found that the best results are obtained by ASA compared to those provided by the commercial software ANSYS.

Abstract: The objective is to design a joint, suitable for use from low to high temperature by combination of two adhesives along the overlap length in single lap joint. This mixed modulus concept is called Multi-module Bond line (MMBL). At high temperatures, a brittle adhesive (high modulus) in the middle of the joint retains the strength and transfers the entire load. At low temperatures, a ductile adhesive at the ends of the joint is the load-bearing adhesive. The first part of this work deals with the formulation of adhesives with differend stiffnesses to be used in the MMBL concept. Starting from a DGEBA resin/DETDA hardener system, different contents of amine terminated polysiloxane modifiers are added to the original mixture. A phase-separated structure is observed via scanning electron microscopy. The thermal, mechanical and dynamic viscoelastic properties of polysiloxane modified epoxy networks are studied. The second part of this paper will present the infinite element study of the assembly with two formulated adhesives in order to verify if they respect the MMBL concept.

Abstract: The aim of this study is to gain knowledge concerning the process and its physics, as well as to become able to optimize the fabrication of large and complex composite parts in aeronautics appli- cations. Composite materials have many advantages and the use of this technology is increasing in the aeronautic industry. In the L.R.I. process, dry textile preforms are impregnated by a thermoset liquid resin. All the elements are enclosed in a vacuum bag of known pressure. Once preforms are totally impregnated, the resin system begins the curing reaction to obtain the composite part. This study contains two major sections. Firstly, numerical modeling was done with the Pam- Rtm nite element code to determine the evolution of the ow front during the infusion. Simulations were performed to analyse the infusion of sandwich composite parts with a perforate foam, which allows the inferior skin to be impregnated in the same operation. Secondly, experimental work was conducted to conrm the numerical results.

Abstract: The use of composite materials in large structures has increased in recent years. Aircraft industry has recently begun to investigate the field of Liquid Composite Molding (LCM) through research programs because of its ability to produce large parts at low cost. The present paper focuses on modeling a 3D radial impregnation through an anisotropic fibrous perform. As a preliminary work, it is assumed an isothermal flow and no hydro-mechanical coupling. Governing equations are Darcy’s law and mass conservation. Simulation is performed combining Boundary Element Method (BEM) with a lagrangian moving mesh method. An analytical solution is developed to assess the numerical model.

Abstract: In this work the dynamic responses of bonded top hat stiffened panel have been studied by using finite element analysis model (Abaqus). A symmetrical 2D model was performed and used in the simulations. In the first part, dynamic behavior and impact speed effects at such composite structure have been studied. In the second part, other simulations were carried out by using cohesive elements proposed to predict the delamination might happen under such loading.

Abstract: The aim of this paper is to study the machinability of a new titanium alloy: Ti-5AL-5Mo-5V-3CR used for the production of new landing gear. First, the physical and mechanical properties of this material will be presented. Second, we show the relationship between material properties and machinability. Third, the Ti5553 will be compared to Ti64. Unless Ti64 is α+β alloy group and Ti5553 is a metastable, we have chosen to compare these two materials. Ti64 is the most popular of titanium alloys and many works were been made on its machining. After, we have cited the Ti5553 properties and detailed the behavior laws. They are used in different ways: with or without thermal softening effect or without dynamic terms. The goal of the paper is to define the best cutting force model. So, different models are compared for two materials (steel and titanium alloy). To define the model, two methods exist that we have compared. The first is based on machining test; however the second is based on Hopkinson bar test. These methods allow us to obtain different ranges of strain rate, strain and temperature. This comparison will show the importance of a good range of strain rate, strain and temperature for behavior law, especially in titanium machining.

Abstract: The numerical simulation based on the Finite Element Method (FEM) is widely used in academic institutes and in the industry. It is a useful tool to predict many phenomena present in the classical manufacturing forming processes such as necking, fracture, springback, buckling and wrinkling. But, the results of such numerical model depend strongly on the parameters of the constitutive behavior model. In the first part of this work, we focus on the traditional identification of the constitutive law using oriented tensile tests (0°, 45°, and 90° with respect to the rolling direction). A Digital Image Correlation (DIC) method is used in order to measure the displacements on the surface of the specimen and to analyze the necking evolution and the instability along the shear band. Therefore, bulge tests involving a number of die shapes (circular and elliptic) were developed. In a second step, a mixed numerical–experimental method is used for the identification of the plastic behavior of the stainless steel metal sheet. The initial parameters of the inverse identification were extracted from a uniaxial tensile test. The optimization procedure uses a combination of a Monte-Carlo and a Levenberg-Marquardt algorithm. In the second part of this work, according to some results obtained by SEM (Scaning Electron Microscopy) of the crack zones on the tensile specimens, a Gurson Tvergaard Needleman (GTN) ductile model of damage has been selected for the numerical simulations. This model was introduced in order to give informations concerning crack initiations during hydroforming. At the end of the paper, experimental and numerical comparisons of sheet metal forming applications are presented and validate the proposed approach.