Boundary Element Method for the dynamic evolution of intra-tow voids in dual-scale fibrous reinforcements using a Stokes-Darcy formulation

The Boundary Element Method (BEM) is implemented in the simulation of compression, displacement, migration and splitting of intra-tow voids in dual-scale fibrous reinforcements. The last three processes have not been simulated at mesoscopic scale in previous works due to the consideration of a constant pressure in the channels of the Representative Unitary Cell. In this work, both the channels and tows are modeled using the Stokes and Darcy equations, respectively, a pressure gradient is prescribed along the fluid motion, and full air compressibility is deemed, thereby allowing to consider these three processes. The void migration process from the weft towards the channel is analyzed in terms of the ratio between the average air migration velocity and the average liquid velocity, and of the normalized air rate from the weft towards the channel. According to BEM results, the bubble can migrate at both lower and higher velocities with respect to the liquid velocity, and the void removal out of the tows can occur after several stages of compression-displacement-migration-splitting; additionally, the bubble breaks up after several cycles of expansion and compression. BEM results also show that the liquid surface tension, pressure gradient and average channel pressure have important influence in the void migration process.