Simulation of air bubble’s creation, compression, and transport phenomena in resin transfer moulding

Abstract

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.

Process Induced Defects in Liquid Molding Processes of Composites

“…Cure induced defects, on the other hand, originate during the crosslinking reaction of the LCM, and include microcracks, distortions and void growth (Anders et al, 2016;Aaboud et al, 2017). Microcracks occur generally in the matrix due to thermal degradation and residual stresses.…”

“…A careful selection of temperature and pressure variation is crucial to ensure the production of a properly cured part with minimum or no cure related defects. Typical defects induced during LCM cure include microcracks, distortions and void growth (Aaboud et al, 2017;Anders et al, 2016;Nawab et al, 2015;Ruiz and Trochu, 2005;Svanberg, 2005).…”

“…Volatile species in thermoset resins include dissolved air and moisture, residual solvents and vaporized monomers among other byproducts. These volatiles can vaporize from the resin during cure causing existing voids to grow or creating new voids, often on the surface of the molded composite (Aaboud et al, 2017;Anders et al, 2016;Ledru et al, 2010). Before gelation, voids can be expanded, shrunk or even dissolved depending on the balance between their internal pressure and the hydrostatic pressure of the surrounding resin.…”

Flow-speed-controlled quality optimisation for one-shot-hybrid RTM parts

“…Depending on the flow front velocity either micro or macro voids are built. While a too slow injection leads to macro voids, situated in between the fibre bundles, a too fast injection leads to micro voids inside the fibre bundles of the textile [25][26][27]. While the micro impregnation of the fibre bundles is driven by capillary forces, the macro impregnation is driven by the injection pressure.…”

“…Former studies have shown that controlling the resin flow front velocity can reduce the amount of voids in liquid composite moulded (LCM) parts [24,[35][36][37]. As long as the resin system is liquid and further resin is injected the produced voids are transported along the flow path [27,35,38]. As the injection near area is flushed by more resin the void content usually increases along the flow path [35,39,40].…”