Droplet Spreading on Unidirectional Fiber Beds

Patricio Martinez,Bo Cheng Jin,Steven Nutt

doi:10.3390/jcs5010013

Patricio Martinez, Bo Cheng Jin + Show 1 more

Open Access

https://doi.org/10.3390/jcs5010013

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Abstract

This study reports a method to analyze parametric effects on the spread flow kinetics of fluid droplets on unidirectional fiber beds. The investigation was undertaken in order to guide the design of droplet arrays for production of an out-of-autoclave (OoA) prepreg featuring discontinuous resin distribution, referred to here as semi-preg. Volume-controlled droplets of a resin facsimile fluid were deposited on carbon fiber beds and the flow behavior was recorded. The time to full sorption (after deposition) and the maximum droplet spread distance were measured. Experiments revealed that fluid viscosity dominated time to full sorption—doubling the viscosity resulted in an 8- to 20-fold increase in sorption time, whereas doubling fabric areal weight increased the time only by a factor of three. Droplet spread distance was nearly invariant with fiber bed architecture and fluid viscosity. A series of droplet arrays were designed, demonstrating how the results can be leveraged to achieve different resin distributions to produce semi-preg optimized for OoA cure.

Highlights

We investigate the effects of fiber bed architecture on the anisotropic flow behavior of fluid droplets on and into unidirectional (UD) fiber beds
These images show that as fabric areal against fractions of time to full sorption, t. These images show that as fabric areal h0 against fractions of in-plane time to spreading full sorption, th0. These images showmore thatrapidly, as fabric weight increased, of droplets generally occurred theareal weight increased, in-plane spreading of droplets generally occurred more rapidly, the onlythe weight in-plane spreading droplets generally more rapidly, only increased, exception being the fabric with theofheaviest areal weight
We have demonstrated the effects of unidirectional fiber beds on droplet flow on the surface

Summary

Introduction

We investigate the effects of fiber bed architecture on the anisotropic flow behavior of fluid droplets on and into unidirectional (UD) fiber beds. We determine the effects of fiber bed areal weight and fluid viscosity on sorption time and spread distance. The work is motivated by a need to support the design of prepreg formats with discontinuous resin distributions (semi-pregs). Conventional out-of-autoclave (OoA) prepregs typically feature continuous resin films partially impregnated into the fiber bed and rely on “edge breathing” for air removal [1,2,3]. Compared to autoclave prepregs processing of OoA prepregs lacks robustness, in challenging conditions, such as poor vacuum, ply ramps, embedded doublers and large parts [4,5]. Semi-pregs [6] feature discontinuous resin distributions that impart high through-thickness permeability and increase process robustness compared to conventional OoA prepregs [5,7,8,9]. Previous methods of fabricating semi-preg include hot-rolling resin onto the tow overlaps of woven fiber beds [10], using a release film mask to press a discontinuous film onto dry fibers [8] and dewetting a continuous resin film, pressing onto dry fibers [7]

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Discussion

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