behaviour and strength.
PW
SAT5
SAT8
plain weaves
5 harness satin
8 harness satin
CCM-TEX 3-D Weave
2-step braids
4-step braids
yes
µTex-10
µTex-20
general
user provides
yes
SAWC plain weave
(FE code general)
yes stiffness
discount
yes
TEXCAD 2D weaves
2D braids
user defined
yes shear
hardening,
stiffness
discount
yes
WEAVE 3D interlock weaves
BINMOD 3D interlock weaves yes not
directly
6.5 Notched Strength
Notch sensitivity in textile composites is limited by two mechanisms: splitting
parallel to the load axis, which isolates the notched material from adjacent material; and the
formation of blunting damage bands (Section 4). Models for splitting have been developed
extensively to deal with a similar effect in continuous fiber ceramic matrix composites and
layered systems, including tape laminates [6.22]. Nonlinear damage bands can be modeled
as cohesive zones or bridged cracks, much like craze zones in polymers or damage zones in
concrete [6.23-6.27]. Unfortunately, very few models have been formulated for dealing
with either splitting or cohesive zones in textile composites, where they are generally far
more important than in any other class of material. In fact, their unusual characteristics in
textile composites are the source of the extraordinary notch insensitivity these materials
possess (Section 4).
The crucial material property in a cohesive zone is the relation, p(u), between the
tractions, p, acting across the damage band and the effective opening displacement, 2u.
One would expect that the characteristics of p(u) that are essential to notch sensitivity
should be contained in no more than two parameters, for example, the critical stress, p
c
, for
the onset of damage and either the work of fracture, W
f
= 2∫pdu, or the critical opening
displacement, u
c
, beyond which p vanishes. The length of the cohesive zone is then
characterized approximately by the length scale, l
ch
, of Equation (3.2). Notch sensitivity is
generally restricted to holes or notches that are larger than l
ch
. The parameters (p
c
, W
f
) or
(p
c
, u
c
) should be evaluated by a set of standard tests, for example of notched strength.
Strength in parts of general shape should then be predicted by application of the calibrated
cohesive zone model. In the absence of developed codes, notched strength in textile
composites can receive no further treatment in this edition of the handbook. This problem
requires further work.
