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International audienceThe crack onset configuration at damage onset in a four-layer plain weave glass fiber/epoxy matrix composite is studied at the mesoscopic scale using a coupled criterion based on both a stress and an energy condition. The possible crack shapes are selected based on optical microscope observations of damage mechanisms on a specimen edge during a tensile test. The crack location, length and orientation, the decohesion length and the strain at damage onset are determined. The damage onset strain is underestimated compared to the experimental value determined by acoustic emission if only a stress criterion is considered. The coupled stress and energy criterion leads to a more reasonable estimate of strain at damage onset

a b s t r a c tThe mechanical behavior of a four-layer plain weave glass fiber/epoxy matrix composite is modeled at the mesoscopic scale, taking into account the dry fabric preforming before resin injection, the relative shift and nesting between fabric layers, and the characteristic damage mechanisms, i.e., intra-yarn cracking and decohesion at the crack tips. The surface strain fields obtained numerically are similar to the strain fields observed at the surface of the specimen. Damage is modeled by introducing discrete cracks in the FE mesh of the representative unit cell of the composite. The crack locations are determined using a stress based failure criterion. The predicted locations are similar to those observed experimentally. The effects of intra-yarn cracks on the macroscopic mechanical properties show the same trends as the experimental data. Good quantitative agreement is obtained if yarn/yarn or yarn/matrix decohesions at the crack tips are taken into account.

OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. This is an author-deposited version published in : http://oatao.univ-toulouse.fr/ Eprints ID : 18105To link to this article : a b s t r a c tThe crack growth behaviour of Direct Aged Inconel 718 was studied at 550°C. Experiments were carried out under pure fatigue cycles, hold-time cycles of different durations and a mix of both. Hold-time cycles were systematically associated with complex crack front morphologies. A new numerical approach was developed to assess the effect of crack front morphology on the direct current potential drop technique, mechanical fields at the crack tip and ultimately, measured crack growth rates. Using this approach, a clear relation was established between crack front morphology and its evolution, and the crack growth behaviour under hold-time conditions. Complex crack front morphologies are demonstrated to be responsible for increased crack growth rates. From this, a crack growth mechanism under hold-time conditions is proposed. Finally, the numerical framework here presented is to be considered as a new, easily reproducible, way to properly analyse experimental data when dealing with complex loading cycles and complex crack front morphologies.⇑ Corresponding author at: Safran Aircraft Engines, établissement de Villaroche,

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