Item – Thèses Canada

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Numéro d'OCLC
881138073
Lien(s) vers le texte intégral
Exemplaire de BAC
Exemplaire de BAC
Auteur
Landry, Benoit,
Titre
Effet du vieillissement hygrothermique et modélisation du délaminage dans un composite carboneépoxy.
Diplôme
Thèse (M. Sc. A.)--Université de Moncton, 2011.
Éditeur
Ottawa : Library and Archives Canada = Bibliothèque et Archives Canada, [2012]
Description
2 microfiches.
Notes
Comprend des références bibliographiques.
Résumé
<?Pub Inc> This thesis studies the problem of delamination in composite materials. It consists of two parts : an experimental study and the development of a numerical model. In the experimental part, results of an investigation on the influence of long term hygrothermal exposure on the delamination growth in an aerospace grade carbon/epoxy composite (G40-800/5276-1) are presented. Specimens made from this unidirectional composite were immersed in water at 70 °C until saturation. Delamination tests were performed with the double cantilever beam (DCB) configuration in mode I and the four-point bend end-notched flexure configuration (4ENF) in mode II, under quasi-static and fatigue loading conditions. For each loading mode, I and II, the effect of moisture absorption was evaluated in the three regions of the typical fatigue delamination growth curve. First, quasi-static tests were conducted to determine the delamination toughness, 'Gc'. Subsequently, fatigue tests results in the stable growth region were plotted in the form of delamination growth rate curves. Finally, fatigue delamination onset tests were conducted to determine the characteristics of the subcritical growth region. All tests were performed with dry specimens and specimens saturated with moisture. In addition, a group of specimens saturated with moisture was dried and subsequently tested in order to assess the degree of reversibility of the measured effects. Results showed that in mode I, moisture decreases the delamination toughness, ' GIc', and the delamination growth threshold, 'G Ith', in addition to increasing the delamination growth rate in the studied material. In mode II, moisture had the effect of decreasing the delamination toughness and the number of cycles required for fatigue delamination onset, and increasing the delamination growth rate. Micrographs taken with a scanning electron microscope indicated that these results were due to degradation of the fiber/matrix interface by moisture. On the other hand, compared to wet specimens, better performances were measured with the dried specimens, demonstrating that the degradation due to moisture is partially reversible. The second objective of this work was to develop an interface finite element based on the cohesive zone approach to simulate the progressive delamination in a composite subjected to quasi-static loading and fatigue loading regimes of varying amplitude. The proposed formulation combines damage mechanics and fracture mechanics, and directly employs material properties, such as the delamination toughness and the fatigue delamination growth rate. The cohesive element was inserted along the delamination path in a finite element model to simulate delamination in a composite. A calibration method of the cohesive zone parameters was proposed, where they were identified using a quasi-static test. In addition, a method was suggested to evaluate the energy release rate, ' GImax', during the numerical simulation. A validation test of the numerical model was carried out in mode I, where five different loadings (two quasi-static and three in fatigue) were applied experimentally and numerically to a DCB specimen. These loadings were more realistic than those applied to delamination models presented in the literature, which are limited to fatigue loadings ('Gmax') of constant amplitude. A comparison between the experimental and numerical results showed that model predictions agree well with experimental results. Such a model could be used to predict the service life of structural composite part subjected to complex fatigue regimes.
ISBN
9780494812051
0494812052