Lucien Laiarinandrasana

Anisotropic (Continuum Damage Mechanics)-based multi-mechanism model for semi-crystalline polymer

In this work, the anisotropic damage of semi-crystalline polymers is investigated. The model, developed within a thermodynamic framework, includes the following features: (i) the degree of crystallinity; (ii) the hydrostatic pressure effect; and (iii) the damage anisotropy. The adopted tensorial damage variable is based on the Continuum Damage Mechanics approach under the energy equivalence assumption. For the quantification of the anisotropy, a parameter called “shape factor” is defined as the ratio between the void mean diameter and the void mean height. This parameter is linked to the main axial and the main radial damage components. Experimental data taken from the recent literature using the tomography technique were selected to assess the model capability. Finite element simulations of notched round bar specimens subjected to tensile test stopped at three key loading stages are systematically compared with experimental data. The proposed model was able not only to accurately simulate the macroscopic response of the material, but more interestingly, to reproduce the spatial distribution of the shape factor. This demonstrates the anisotropy effects of the material under study induced at different stages of the deformation.

Modelling of Failure of Woven Composites. Part 2: Experimental and Numerical Justification of the Interzone Concept

AbstractThe failure of woven composites has been examined. This study is presented in two parts: Modelling of failure of woven composites. Part 1: nomenclature defining the interzone concept;Modelling of failure of woven composites. Part 2: experimental and numerical justification of the interzone concept. In the first part, the concepts of the interzone and the geometry of an interzone have been defined in a general way for a large panel of woven composites. In the second part, it has been shown that the failure of woven composites is well described by using the interzone concept. The load transfer between intact interzones and broken interzones has been evaluated for two types of loadings (tensile loading and loading in bending). The analysis of these load transfers explains why in the case of a tensile loading the failure is of a sudden-death type whereas in the case of bending loading the failure is progressive. The concept of failure of an interzone has been also defined.

Modelling of failure of woven composites. Part 1 : Nomenclature defining the interzone concept

AbstractThe failure of woven composites has been examined. This study is presented in two parts: Modelling of failure of woven composites. Part 1: nomenclature defining the interzone concept;Modelling of failure of woven composites. Part 2: experimental and numerical justification of the interzone concept. In the first part, the concepts of the interzone and the geometry of an interzone have been defined in a general way for a large panel of woven composites. In the second part, it has been shown that the failure of woven composites is well described by using the interzone concept. The load transfer between intact interzones and broken interzones has been evaluated for two types of loadings (tensile loading and loading in bending). The analysis of these load transfers explains why in the case of a tensile loading the failure is of a sudden-death type whereas in the case of bending loading the failure is progressive. The concept of failure of an interzone has been also defined.

Multiaxial stress state assessed by 3D X-Ray tomography on semi-crystalline polymers

This work aims at linking the microstructural evolution of semi-crystalline polymers to the macroscopic material behaviour under multiaxial stress state. Tensile tests on notched round bars, interrupted after different stages of deformation before failure, were supposed to have undergone various states of stress in the vicinity of the net cross-section. They were examined using synchrotron radiation tomography. A sample obtained from a test stopped at the end of stress softening stage showed elongated axi-symmetric columns of voids separated by thin ligaments of material. This special morphology allowed investigating the distributions of voids in terms of both volume fraction and orientation. This distribution was compared with the theoretical multiaxial stress/strain field. The combination of the tomographic images analyses and the continuum mechanics approach results in a determination of the principal mechanical parameter driving voids evolution.