Sr. Kalidindi et E. Franco, NUMERICAL EVALUATION OF ISOSTRAIN AND WEIGHTED-AVERAGE MODELS FOR ELASTIC-MODULI OF 3-DIMENSIONAL COMPOSITES, Composites science and technology, 57(3), 1997, pp. 293-305
The isostrain model is being widely used for predicting the elastic pr
operties of three-dimensional composites, i.e. composites in which the
reinforcement extends in the general three-dimensional space. Recentl
y, it has been suggested that a weighted average of the isostrain and
isostress model predictions yields better results, when compared to th
e predictions of the isostrain model alone. Critical evaluation of the
se models through experiments alone is expensive and time consuming ow
ing to the large number of material and geometric variables involved i
n these models. We have conducted a numerical study to evaluate the ac
curacies of these simplistic analytical models. A finite element model
, based on the commonly used representative volume element of the thre
e-dimensionally braided composite, was developed for this purpose. The
variables considered in this study included the type of loading, the
braid angle, the fiber volume fraction, and the yarn elastic propertie
s. The study revealed that a suitable weighted average of the isostrai
n and isostress model predictions is in better agreement with the corr
esponding finite element model predictions for the elastic moduli of 3
-D braided composites. Furthermore, the weighting factor was observed
to be fairly insensitive to braid angles, yarn volume fraction, and th
e type of loading, but strongly influenced by the non-axial elastic pr
operties of the yarn. (C) 1997 Elsevier Science Limited.