A model for the axisymmetric growth and coalescence of small internal voids in elastoplastic solids is proposed and assessed using void cell computations. Two contributions existing in the literature have been integrated into the enhanced model. The first is the model of Gologanu-Leblond-Devaux, extending the Gurson model to void shape effects. The second is the approach of Thomason for the onset of void coalescence. Each of these has been extended heuristically to account for strain hardening. In addition, a micromechanically-based simple constitutive model for the void coalescence stage is proposed to supplement the criterion for the onset of coalescence. The fully enhanced Gurson model depends on the flow properties of the material and the dimensional ratios of the void-cell representative volume element. Phenomenological parameters such as critical porosities are not employed in the enhanced model. It incorporates the effect of void shape, relative void spacing, strain hardening, and porosity. The effect of the relative void spacing on void coalescence, which has not yet been carefully addressed in the literature. has received special attention. Using cell model computations, accurate predictions through final fracture have been obtained for a wide range of porosity, void spacing, initial void shape, strain hardening, and stress triaxiality. These predictions have been used to assess the enhanced model. (C) 2000 Elsevier Science Ltd. All rights reserved.

An extended model for void growth and coalescence - application to anisotropic ductile fracture

A review on machinability of carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP) composite materials

Une présentation de la méthode des éléments finis

This paper provides an overview of recent advances in research on the interfacial characteristics of carbon nanotube–polymer nanocomposites. The state of knowledge about the chemical functionalization of carbon nanotubes as well as the interaction at the interface between the carbon nanotube and the polymer matrix is presented. The primary focus of this paper is on identifying the fundamental relationship between nanocomposite properties and interfacial characteristics. The progress, remaining challenges, and future directions of research are discussed. The latest developments of both microscopy and scattering techniques are reviewed, and their respective strengths and limitations are briefly discussed. The main methods available for the chemical functionalization of carbon nanotubes are summarized, and particular interest is given to evaluation of their advantages and disadvantages. The critical issues related to the interaction at the interface are discussed, and the important techniques for improving the properties of carbon nanotube–polymer nanocomposites are introduced. Additionally, the mechanism responsible for the interfacial interaction at the molecular level is briefly described. Furthermore, the mechanical, electrical, and thermal properties of the nanocomposites are discussed separately, and their influencing factors are briefly introduced. Finally, the current challenges and opportunities for efficiently translating the remarkable properties of carbon nanotubes to polymer matrices are summarized in the hopes of facilitating the development of this emerging area. Potential topics of oncoming focus are highlighted, and several suggestions concerning future research needs are also presented.

/pdf/a-review-of-the-interfacial-characteristics-of-polymer-2xw2lbq2se.pdf

A review of the interfacial characteristics of polymer nanocomposites containing carbon nanotubes

We present a phase field formulation for fracture in functionally graded materials (FGMs). The model builds upon homogenization theory and accounts for the spatial variation of elastic and fracture properties. Several paradigmatic case studies are addressed to demonstrate the potential of the proposed modelling framework. Specifically, we (i) gain insight into the crack growth resistance of FGMs by conducting numerical experiments over a wide range of material gradation profiles and orientations, (ii) accurately reproduce the crack trajectories observed in graded photodegradable copolymers and glass-filled epoxy FGMs, (iii) benchmark our predictions with results from alternative numerical methodologies, and (iv) model complex crack paths and failure in three dimensional functionally graded solids. The suitability of phase field fracture methods in capturing the crack deflections intrinsic to crack tip mode-mixity due to material gradients is demonstrated. Material gradient profiles that prevent unstable fracture and enhance crack growth resistance are identified: this provides the foundation for the design of fracture resistant FGMs. The finite element code developed can be downloaded from www.empaneda.com/codes .

Phase field modelling of crack propagation in functionally graded materials

A modified FSDT-based four nodes finite shell element for thermal buckling analysis of functionally graded plates and cylindrical shells

Free vibration analysis of carbon nanotube-reinforced functionally graded composite shell structures

The main aim of this paper is to investigate the mechanical buckling behavior of functionally graded materials and carbon nanotubes-reinforced composite plates and curved panels. The governing equations are established using a double directors finite element shell model which induces a high-order distribution of the displacement field and takes into account the effect of transverse shear deformations. The effective material properties of functionally graded materials are estimated using a power law distribution and those of nanocomposites by an extended rule of mixture with some efficiency parameters. Uniform and four profiles of carbon nanotubes are considered to describe the distribution of these reinforcements through the thickness of the nanocomposite shell structure. A comparison study of the present results with those available in the literature is carried out for the isotropic case in order to prove the validity as well as the accuracy of the present model. Then, the results are extended to functionally graded materials and nanocomposites. The results reveal that the critical buckling load of plates and curved panels can be significantly increased as a result of a functionally graded reinforcement. They also show that the mechanical buckling behavior of such structures is significantly influenced by the plate aspect ratio, the length-to-thickness ratio, radius-to-thickness ratio, boundary conditions, power law index as well as the carbon nanotubes profiles and their volume fractions.

Fakhreddine Dammak

Papers

A modified FSDT-based four nodes finite shell element for thermal buckling analysis of functionally graded plates and cylindrical shells

Free vibration analysis of carbon nanotube-reinforced functionally graded composite shell structures

Mechanical buckling analysis of functionally graded power-based and carbon nanotubes-reinforced composite plates and curved panels

Dynamic analysis of functionally graded carbon nanotubes-reinforced plate and shell structures using a double directors finite shell element

Static analysis of functionally graded carbon nanotube-reinforced plate and shell structures