The presence of air bubbles impacts the quality of the produced composite part, by reducing its mechanical properties, and also it might degrade its surface finish. The modelling of air bubbles entrapment requires the consideration of three phenomena: air bubble’s creation, compression and transport. Very few studies have been conducted on this latter phenomenon. The model developed in this work is proposed for a unidirectional reinforcement. It is integrated into a simulation code of resin transfer moulding process, via the control volume finite element method. That model takes into account the dual scale pores in fibrous media, and simulates the three said phenomena highlighting the migration phenomenon and the coexistence of micro and macro air bubbles. As a result, the spatial distribution of created, compressed and transported air bubbles as well as its macro and micro remaining quantities, in the end of the injection are estimated.

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Tow bundles inside a quasi-unidirectional non-crimp fabric are maintained by sewing threads that induce variation in the bundles’ shape. Indeed, the sewing threads apply a light clamping force that gives a periodical and sinusoidal shape to the tow’s cross-sectional area. This tow cross-sectional area heterogeneity, as a function of position in the fabric, induces a variation of the permeability values. Consequently, while injecting liquid into the fibrous bed, preform's impregnation is influenced as well as the fabric’s void content. The aim of this paper is to consider the effect of tow cross-sectional area heterogeneity on the quality of the manufactured composite part. It leads to reveal the influence of the fibrous reinforcement’s microstructure on the air bubble creation and compression phenomena, especially in terms of process time and the micro and macro air bubble distribution.