Void transport during resin flow through fibrous reinforcements: a semi-analytical approach
Topic(s) : Manufacturing
Co-authors :
Joao MACHADO (PORTUGAL), Paulo GONÇALVES (PORTUGAL), Nuno CORREIA (PORTUGAL)Abstract :
In composite material manufacturing, namely in Liquid Composite Moulding, the void content is of major concern because it influences the final quality of the component. Post-filling strategies such as resin bleeding, are reported to contribute to the global reduction of void content. This is attributed to void transport phenomena because voids are mobilized through the fibrous reinforcement due to the hydrodynamic pressure provided by the resin flow [1]. Void mobility, which is the quotient between void velocity and the volume average superficial fluid flow velocity, is a commonly employed measure to describe void transport [2].
However, not all voids show the same behaviour, as due to surface tension effects, void size in combination with local fibre volume fractions and fluid flow conditions can lead to different observed mobilities, or in worst case scenario, void entrapment [3]. The Young-Laplace equation can lead to quantitative approximations of the necessary process parameters to minimize void entrapment [4], but there is still a lack of models capable of mapping the influence that process parameters impose on void mobility. Therefore, the development of models that allow an accurate prediction of void mobility, given a set of process parameters, is paramount to devise more efficient bleeding strategies.
The present study aims to minimize this knowledge gap, investigating void transport phenomena at the microscale and establishing quantitative relations between void size and manufacturing process variables, such as: fibre volume fraction, resin flow rate, density, viscosity, and surface tension. A semi-analytical model was formulated to describe the dynamics of voids at the micro-scale, allowing a fast computation of void kinematics, and the post-processing of relevant variables such as void mobility. This allows to conduct a full parametric analysis on void mobility, given different variables, such as void size, fibre volume fraction and fluid flow conditions, given from processing parameters. The results obtained from the semi-analytical model were compared against Computational Fluid Dynamics (CFD) numerical simulations, in which good agreement was found.
The results obtained in this study should prove useful in designing process conditions in which void removal is enhanced, leading to higher quality composite material parts.
However, not all voids show the same behaviour, as due to surface tension effects, void size in combination with local fibre volume fractions and fluid flow conditions can lead to different observed mobilities, or in worst case scenario, void entrapment [3]. The Young-Laplace equation can lead to quantitative approximations of the necessary process parameters to minimize void entrapment [4], but there is still a lack of models capable of mapping the influence that process parameters impose on void mobility. Therefore, the development of models that allow an accurate prediction of void mobility, given a set of process parameters, is paramount to devise more efficient bleeding strategies.
The present study aims to minimize this knowledge gap, investigating void transport phenomena at the microscale and establishing quantitative relations between void size and manufacturing process variables, such as: fibre volume fraction, resin flow rate, density, viscosity, and surface tension. A semi-analytical model was formulated to describe the dynamics of voids at the micro-scale, allowing a fast computation of void kinematics, and the post-processing of relevant variables such as void mobility. This allows to conduct a full parametric analysis on void mobility, given different variables, such as void size, fibre volume fraction and fluid flow conditions, given from processing parameters. The results obtained from the semi-analytical model were compared against Computational Fluid Dynamics (CFD) numerical simulations, in which good agreement was found.
The results obtained in this study should prove useful in designing process conditions in which void removal is enhanced, leading to higher quality composite material parts.