Rachid Nasri

Robust electromechanical finite element updating for piezoelectric structures effective coupling prediction

A robust electromechanical updating methodology for piezoelectric structures effective coupling prediction is first presented. It combines a finite element design experiment–based a priori sensitivity analysis, a response surface method–based meta-modelling and a genetic algorithm–based multi-objective optimization procedure. Then, this methodology is applied to cantilever aluminium thick plate and thin beam structures that are bonded, respectively, with two oppositely poled large and oppositely and same poled small piezoceramic patches on their upper and lower surfaces. In order to correlate corresponding first few effective modal electromechanical coupling coefficients, a mechanical updating is first considered; it consists of identifying the stiffness parameters of linear springs, modelling the clamp, so that relative deviations between the first few experimental and finite element short-circuit frequencies are minimized; then, an electric updating is considered; it consists of finding the patches’ relative transverse blocked dielectric constants that minimize the first few experimental and finite element open-circuit frequencies relative deviations. Free vibrations are simulated using ANSYS®-coupled piezoelectric three-dimensional finite element. The obtained results have partially confirmed those from a former ad hoc updating method since the sensitivity analyses led to same stiffness parameters’ irreducible number and only some effective modal electromechanical coupling coefficient test–model correlations were enhanced.

Experimental and numerical study on optimization of the single point incremental forming of AINSI 304L stainless steel sheet

AINSI 304L stainless steel sheets are commonly formed into a variety of shapes for applications in the industrial, architectural, transportation and automobile fields, its also used for manufacturing of denture base. In the field of dentistry, there is a need for personalized devises that are custom made for the patient. The single point incremental forming process is highly promising in this area for manufacturing of denture base. The single point incremental forming process (ISF) is an emerging process based on the use of a spherical tool, which is moved along CNC controlled tool path. One of the major advantages of this process is the ability to program several punch trajectories on the same machine in order to obtain different shapes. Several applications of this process exist in the medical field for the manufacturing of personalized titanium prosthesis (cranial plate, knee prosthesis...) due to the need of product customization to each patient. The objective of this paper is to study the incremental forming of AISI 304L stainless steel sheets for future applications in the dentistry field. During the incremental forming process, considerable forces can occur. The control of the forming force is particularly important to ensure the safe use of the CNC milling machine and preserve the tooling and machinery. In this paper, the effect of four different process parameters on the maximum force is studied. The proposed approach consists in using an experimental design based on experimental results. An analysis of variance was conducted with ANOVA to find the input parameters allowing to minimize the maximum forming force. A numerical simulation of the incremental forming process is performed with the optimal input process parameters. Numerical results are compared with the experimental ones.

Experimental Investigation for Forced Vibration of Honeycomb Sandwich Beams

The present paper deals with vibration analysis of laminated sandwich beams made of Honeycomb cores. An experimental investigation of two sandwich beams made of Aluminum and Nomex cores is proposed. The vibration tests were performed for clamped-free boundary conditions using forced vibration method. A series of measurements varying excitation and response points are carried out. Experimental results have been presented leading to perform the vibration characteristics of Honeycomb sandwich beams in terms of natural frequencies, damping factors and vibration amplitudes.

Theoretical and Experimental Analysis of the Vibrational Behavior of a Polyester Composite Material

Polyester composite materials are being used increasingly in numerous and diversified activities, they are often subjected to harmful vibrations. The molding techniques of the polyester composite materials have been developing increasingly, among these techniques we name: contact molding and projection molding. This work aims to study the vibrational behavior of two polyester composite beams obtained using the two mentioned techniques. To this end, we proceed to an experimental study to determine the mechanical characteristics of the polyester composite beams, and we conduct a vibrational analysis. Besides, we proceed to a theoretical study using a polynomial field of displacement based on trigonometric series, and we apply the Hamilton’s principle. The experimental results allow adjusting the analytical method used, and comparing the two molding techniques of polyester composite materials.

Experimental and Numerical Study on Force Reduction in SPIF by Using Response Surface

The single point incremental forming process is an emerging process which presents an alternative to the conventional sheet-metal forming processes like stamping and drawing. It is particularly suitable for prototyping and low production thanks to its flexibility and low cost. The objective of this paper is to study the incremental forming of titanium grade2 and AISI 304L stainless steel sheets. The forming force of sheet titanium grade2 and 304L steel parts formed by single point incremental process depends on different parameters (tool path, tool size, materials and shape, friction, etc.). During the process, considerable forces can occur which must be controlled to ensure the safe use of the CNC milling machine. The aim of this paper is to study the effect of different process parameters on the maximal force. Experimental and numerical studies are performed. An optimization method based on the use of an experimental design and response surface method is used to minimize the forming force.

Non-linear Model Reduction Method Applied to Viscoelastically Damped Sandwich Structures

The aim of this paper is to present an efficient non-linear model reduction method intended to temporal dynamic analysis of viscoelastic sandwich structures. The proposed non-linear model reduction method is based on the combination of modal synthesis method, as well known, substructuring technique and Guyan reduction method. Each substructure is analyzed and reduced separately as a linear finite element model. The viscoelastic behavior of the core, which depends on frequency, is represented by Golla-Hughes-Mc Tavish (GHM) model. This model allows a correct representation of viscoelastic materials characteristics through the addition of dissipative coordinates. Once obtained, the reduced models of each substructure are assembled taking into account the local nonlinearities in the junctions leading to perform the capacity of the proposed method to reproduce the original model with accuracy and (CPU) time gain. Numerical examples are presented to illustrate the ability of the proposed non-linear model reduction method to handle both viscoelasticity and large finite elements models.

Mechanical Vibration Elimination Using Friction Absorber

The work consists on studying the vibration reduction of mechanical systems using friction absorber, with and without viscous damping. The aim is to determine the influence of the friction absorber parameters on the mechanical system response. A study using a nonlinear friction force is conducted while varying the absorber parameters, which are: the mass, the stiffness, the friction coefficient, and the damping coefficient. The linearization of the friction force is then considered, and the results are compared. The effect of the primary system damping and the excitation parameters are also examined. The influence evaluation of the friction absorber parameters on the mechanical system vibration leads to conclude on the favorable absorber giving significant vibration decrease, and to advance design recommendations.

Mechanical Vibration Cancellation Using Impact Absorber

The free and forced vibrations of a mechanical system equipped with a ball absorber were studied. The modeling of the impact damping and the problem formulation and resolution were conducted. The effect of the absorber parameters on the vibration attenuation of the primary system was then examined. The absorber parameters considered are: the mass, the stiffness, the damping, the clearance, and the impact velocity. The excitation parameters were also evoked. Physical and mathematical modeling, then numerical simulation led to determine the free and forced responses of the considered system equipped with the impact absorber, for different situations. This helped to identify the absorber favorable parameters, leading to reduce considerably the primary system vibration, and to advance design recommendations.

Parametric Study on Energy Pumping of Mdof System Using Multiple Dynamic Absorbers

The concept of energy pumping is an innovative dynamic phenomenon. This phenomenon gives rise to a new generation of dynamic absorbers. Theoretical studies and feasibility tests are necessary for a better understanding of their dynamic behaviour and for them to be applied on real structures or machines.

Effects of Gyroscopic Coupling on the Dynamics of a Wind Turbine Blade with Horizontal Axis

It is about a wind turbine blade of five meters of length in composite material, Glass Fiber Reinforced Plastics (GRP), calculated using the finite elements method (FEM) to determine the influence of the gyroscopic coupling on its dynamic behavior. First, using the blade element momentum method (BEM) we wrote the aerodynamic forces applied on the blade, depending on the wind speed. Then we incorporated these expressions into the laws of structures behavior to reach a matrix formulation of the equations of motion of the blade taking into account the nonlinear deformation. The obtaining of the mechanical stiffness, geometric stiffness, mass and gyroscopic coupling matrices of the blade allows to simulate its dynamic response in transient and permanent phases under the action of its weight, and under a sudden variation of the wind speed.