Uncertainty in geometry of fibre preforms manufactured with Automated Dry Fibre Placement and its effects on permeability

Abstract

Resin transfer moulding is one of several processes available for manufacturing fibre-reinforced composites from dry fibre reinforcement. Recently, dry reinforcements made with Automated Dry Fibre Placement have been introduced into the aerospace industry. Typically, the permeability of the reinforcement is assumed to be constant throughout the dry preform geometry, whereas in reality, it possesses inevitable uncertainty due to variability in geometry. This uncertainty propagates to the uncertainty of the mould filling and the fill time, one of the important variables in resin injection. It makes characterisation of the permeability and its variability an important task for design of the resin transfer moulding process. In this study, variability of the geometry of a reinforcement manufactured using Automated Dry Fibre Placement is studied. Permeability of the manufactured preforms is measured experimentally and compared to stochastic simulations based on an analytical model and a stochastic geometry model. The simulations showed that difference between the actual geometry and the designed geometry can result in 50% reduction of the permeability. The stochastic geometry model predicts results within 20% of the experimental values.

Stochastic Resin Transfer Molding Process

“…In most cases of practical interest permeability k(x, y) (and hence the hydraulic conductivity K(x, y)) is anisotropic [8,30,39,18,24,26]. Consequently, it is important to model the hydraulic conductivity K(x, y) as a random tensor.…”

“…It is widely accepted (see e.g. [13,14,18,24,26,29,40,49,54] and references therein) that composite manufacturing processes are accompanied by uncertainties. The origins of these uncertainties include (a) variability of fiber placements due to imperfections of stages (i)-(ii) of RTM; (b) variability of fiber properties; (c) variability of resin properties; and (d) variability of environment during stages (i)-(iv) of RTM.…”

“…We note in passing that (2.13) is often used in experiments for estimating an effective macroscopic hydraulic conductivity (and hence effective permeability) via observing time to fill of samples of a material (see e.g. [26]). But it is not difficult to see that when the hydraulic conductivity is not perfectly correlated, (2.13) might not be a good way to estimate the mean and variance of hydraulic conductivity (cf.…”

Impact of stitching on permeability and mechanical properties of preforms manufactured by dry fiber placement

“…Still, the gap size range in which this is applicable is not mentioned despite this approach is unable to describe preforms without gaps, as the resulting permeability would be zero. Another recent research work also deals with gaps introduced to optimize permeability, and the variability of observed gap width differing from intended gap width leading to a variability of permeability.…”

Influence of test fluids on the permeability of epoxy powder bindered non-crimp fabrics

“…During draping the structure and geometry fixation are accomplished, while also accommodating for shearing and compaction processes that are inherent to this procedure [13]. Other methods that are summarized under direct preforming are 3Dweaving [14], 3D-knitting [15], automated dry fiber winding [16] and automated dry fiber placement [17,18].…”