Fabric structure and mold curvature effects on preform permeability and mold filling in the RTM process. Part II. Predictions and comparisons with experiments
S. Bickerton et al., Fabric structure and mold curvature effects on preform permeability and mold filling in the RTM process. Part II. Predictions and comparisons with experiments, COMPOS P A, 31(5), 2000, pp. 439-458
Citations number
30
Categorie Soggetti
Material Science & Engineering
Journal title
COMPOSITES PART A-APPLIED SCIENCE AND MANUFACTURING
In Part I, an experimental study was completed in a series of five molds, e
ach having corners of different radii (from 0.06 to 8.0 in.). The primary g
oal of this work has been to determine whether corners in LCM molds signifi
cantly affect the filling process, by altering the structure of the preform
locally in such regions. Consistent trends were found for each series of e
xperiments completed in the mold, for which the same preform type, and numb
er of layers were used. For constant Row rate injection, the required injec
tion pressures to fill the two molds with tighter radii was significantly i
ncreased as compared to the other molds. Composite parts were manufactured
in these molds, measurements made on these parts revealing design flaws, th
e cavity thicknesses not being equal in all sections of the molds. Several
numerical simulations are presented in this paper, the goal being to separa
te any effects due to the varying thicknesses from effects due to the corne
rs present. Careful simulations have been completed, taking into account th
e actual thicknesses in each mold, and the resulting preform volume fractio
n. Experimentally measured permeability data was employed, and the predicte
d injection pressures match very well for all four molds studied, seeming t
o indicate that the corners present have not affected the filling. A simple
model for preform compression in corners has been developed, which predict
s local permeability modifications due to in-plane compression of the fabri
c layers. These predictions have been employed in conjunction with an exist
ing tool to analytically predict the permeability components of a preform i
n a Rat cavity. This code requires from the user a geometrical model of a p
reform unit cell, this data being measured from samples cut from the parts
manufactured. The resulting predictions for injection pressure are good for
an entirely predictive approach, underpredicting experimental values by on
ly 30-60%. Sensitivity analyses have demonstrated the strong relationship b
etween permeability and the details of the preform cell. Two numerical stud
ies were completed to determine how sensitive the injection pressure curves
are to reduced permeabilities in the corner regions. For the two injection
schemes having two different gate locations, pressures were not significan
tly affected, while the permeabilities in this region were reduced up to 10
0 times. Though the molds used were not ideal for isolating effects on mold
filling due to corner radii, the evidence presented does not show the exis
tence of any strong behavior related to mold radii. (C) 2000 Elsevier Scien
ce Ltd. All rights reserved.