Mohamed Haboussi

Panel flutter characteristics of sandwich plates with CNT reinforced facesheets using an accurate higher-order theory

Abstract In this paper, the flutter characteristics of sandwich panels with carbon nanotube (CNT) reinforced face sheets are investigated using QUAD-8 shear flexible element developed based on higher-order structural theory. The formulation accounts for the realistic variation of the displacements through the thickness, the possible discontinuity in the slope at the interface, and the thickness stretch affecting the transverse deflection. The in-plane and rotary inertia terms are also included in the formulation. The first-order high Mach number approximation to linear potential flow theory is employed for evaluating the aerodynamic pressure. The solutions of the complex eigenvalue problem, developed based on Lagrange׳s equation of motion are obtained using the standard method for finding the eigenvalues. The accuracy of the present formulation is demonstrated considering the problems for which solutions are available. A detailed numerical study is carried out to bring out the efficacy of the higher-order model over the first-order theory and also to examine the influence of the volume fraction of the CNT, core-to-face sheet thickness, the plate thickness and the aspect ratio, damping and the temperature on the flutter boundaries and the associated vibration modes.

Free vibrations of thick laminated anisotropic non-circular cylindrical shells

Abstract Here, the free vibration characteristics of thick laminated composite non-circular cylindrical shells are analyzed using higher-order theory. The formulation accounts for the variation of the in-plane and transverse displacements through the thickness, abrupt discontinuity in slope of the in-plane displacements at the interfaces, and includes in-plane, rotary inertia terms, and also the inertia contributions due to the coupling between the different order displacement terms. The accurate strain–displacement relations are used for the evaluation of strain energy. The governing equations are solved employing the finite element procedure. Detailed study is made to highlight the influences of length and thickness ratios, eccentricity parameters, ply-angles and number of layers on the free vibration characteristics of non-circular shells.

Numerical study of the influence of material parameters on the mechanical behaviour of a rehabilitated edentulous mandible.

OBJECTIVES The study dealt with full dental prosthetic reconstruction on four implants. The aim was to analyse the influence of material parameters on the mechanical behaviour of the restored mandible compared to the natural mandible. METHODS A finite element model of an edentulous mandible with prosthetic rehabilitation was established. Four materials were investigated for the framework of the prosthesis (zirconia, titanium, gold and nickel-titanium (NiTi)), as well as three cortical bone thicknesses. Various muscles were employed to simulate the main stages of mastication. Three distinct phases of mastication were modelled: maximum intercuspation, incisal clench and unilateral molar clench. RESULTS The zirconia framework demonstrated the highest stresses and NiTi the weakest. The highest stresses in the framework were obtained during maximum intercuspation. The highest stresses at the bone-implant interface were recorded on the working axial implant during unilateral molar clench and on tilted implants during maximum intercuspation. The influence of the frameworks material stiffness on the stresses at the bone-implant interface was insignificant for axial implants (except the right implant during unilateral molar clench) and slightly more significant for tilted implants. Mandibular flexion decreased with an increase of the cortical bone thickness and the stiffness of the prosthetic frameworks material. CONCLUSIONS Among all materials, NiTi allowed a better preservation of the mandibular flexure, during all the mastication stages. Compared to stiffer materials, NiTi also permitted physiological mechanical conditions at the bone/implant interface, in almost all mastication stages.

Predictive model of the prostate motion in the context of radiotherapy: A biomechanical approach relying on urodynamic data and mechanical testing.

In this paper, a biomechanical approach relying on urodynamic data and mechanical tests is proposed for an accurate prediction of the motion of the pelvic organs in the context of the prostate radiotherapy. As a first step, an experimental protocol is elaborated to characterize the mechanical properties of the bladder and rectum wall tissues; uniaxial tensile tests are performed on porcine substrates. In a second step, the parameters of Ogden-type hyperelastic constitutive models are identified; their relevance in the context of the implementation of a human biomechanical model is verified by means of preliminary Finite Elements (FE) simulations against human urodynamic data. In a third step, the identified constitutive equations are employed for the simulations of the motion and interactions of the pelvic organs due to concomitant changes of the distension volumes of the urinary bladder and rectum. The effectiveness of the developed biomechanical model is demonstrated in investigating the motion of the bladder, rectum and prostate organs; the results in terms of displacements are shown to be in good agreement with measurements inherent to a deceased person, with a relative error close to 6%.

Analysis of Elliptical Cracks in Static and in Fatigue by Hybridization of Green's Functions

A hybrid weight function technique is presented. It consists of dividing an elliptical crack into two zones, then using the appropriate weight function in the area where it is more efficient. The proportion between zones is determined by optimizing two crack parameters (axis ratio and curvature radius). Stress intensity factors are hence computed by a self developed computer code. Static and fatigue loadings are considered. The results found by the present approach are in good correlation with the analytical and experimental solutions (when available) as well as with those obtained numerically by other researchers.

Mixed Mode Static and Dynamic Modeling in Fracture Mechanics for Plane Composite Materials by X-FEM

In this paper, static and dynamic fracture behaviors of cracked orthotropic structure are modeled using extended finite element method (X-FEM). In this approach, the finite element method model is first created and then enriched by special orthotropic crack tip enrichments and Heaviside functions in the framework of partition of unity. The mixed mode stress intensity factor (SIF) is computed using the interaction integral technique based on J-integral in order to predict cracking behavior of the structure. The developments of these procedures are programmed and introduced in a self-software platform code. To assess the accuracy of the developed code, results obtained by the proposed method are compared with those of literature.

Modeling of Planar Embedded Cracks of Arbitrary Shape under Non Uniform Mode I Loadings

A numerical method using the weight function technique is proposed in order to evaluate the stress intensity factors for planar cracks of an arbitrary shape under non uniform mode I loadings. In accordance with the crack front perturbation theory of Rice, the SIFs are calculated in an incremental way, from a known initial crack shape (circle) which we make evolve until the final form is reached. Due to the non uniform character of the loading a surface integral term reappears during the calculation of the SIF which disappeared in the uniform case. This surface integral contribution to the calculation of the SIF depends on a kernel function which we propose to approximate by an empirical weight function that was developed by Oore and Burns (OB) for embedded cracks of any shape. The OB weight function introduces new singularities in the SIF evaluation that we propose to treat numerically. Several tests of validation are proposed to appreciate the predictive capacity of the proposed model.

FINITE ELEMENT MODELLING OF PELVIC INTERACTIONS AND PROSTATE MOTION

Finite Element (F.E.) simulations of the pelvic organ motions and interactions have been developed, in the framework of the prostate cancer therapy. From a medical point of view, the aim of the predictive simulations of the prostate motion is the shrinking of the margins around the clinical target volume (C.T.V.) inside the gland during radiation therapy, in order to keep away the neighbouring organs from any hazardous radiations.