MESO‐MECHANICAL CHARACTERIZATION OF TRIAXIALLY BRAIDED COMPOSITES
MESO‐MECHANICAL
MESO MECHANICAL CHARACTERIZATION OF TRIAXIALLY BRAIDED COMPOSITES
1
1
1
1,2
p
,, J. Xu
p ,,C. González
A García Carpintero
A. García‐Carpintero
J Xu ,, C.S. Lopes
C S Lopes
C González
alejandro garcia@imdea org
[email protected]
1
IMDEA‐Materials Institute
IMDEA
Materials Institute
2 Polytechnic University of Madrid
Polytechnic
y
Universityy of Madrid
Motivation
Braided preforms are manufactured over a cylindrical
mandrel. A single layer of a 2
2-D
D braid consists of either two or
th
three
i t t i dy
intertwined
yarns. The
Th braided
b id d y
yarns follow
f ll
th +φ
the
φ and
dφ direction while interlacing in the desired pattern.
pattern A 2-D
2D
Triaxial braided consists of axial yarns in addition to the offaxis braider yarns. The axial yarns follow the longitudinal
di ti and
direction
d are inserted
i
t d between
b t
th braider
the
b id y
yarns,, Fig
Fig 1.
1
Due to the new weight
g requirements in the aeronautic sector,
sector
fabric-reinforced “textile”
textile composites manufactured with
high strength fibers are promising lightweight solutions.
solutions They
possess better
p
b tt
out-of-plane
t f pl
stiffness,
tiff
, strength
t gth and
d
toughness
g
properties
p
p
than tape
p and unidirectional laminates.
laminates
They are also amenable to automated and efficient
manufacturing techniques.
techniques
However,, the
H
th architecture
hit t
off a textile
t til composite
p it is
i complex
pl
and therefore,
and,
therefore the parameters controlling its mechanical
properties are numerous.
numerous This necessitates development of
analytical and numerical models to predict the mechanical
properties
p
p ti off textile
t til composites.
p it
Objectives
•
R p d
Reproduce
th repetitive
the
p titi unitit cellll ((RUC)) g
geometry.
ty
•
Remove the tow interpenetrations
realistic fiber volume fraction.
fraction
•
X ray computer tomography
X-ray
h (XCT) and
d micrographs
i
h to
d t
determine
i
/ validate
lid t the
th p
parameters
t
th t controls
that
t l the
th
complexity of the architecture
•
Develop a numerical methodology to predict the
mechanical
h i lp
properties
p ti off the
th braided
b id d composites
p it
•
Experimental validations.
validations
and obtain a
Fig 1.
1 2x2 biaxial (left) and triaxial (right) fabric architecture
M
Manufacturing
f t i g process
p
Mi g ph
Micrographs
Fib volume
Fiber
l
fraction
f ti
In order to determine the number of filaments present in the
tows local fiber volume fraction and in
tows,
in-plane
plane dimensions of
the
h yarns, a optical
i l microscope
i
was used,
d Fig
Fi 4.
4
Th yarns were braided
The
b id d over a cylindrical
li d i l mandrel,
d l Fig2.
Fi 2 The
Th
desired p
preform thickness was
as achieved
achie ed by
by over
o er braiding
g
layers; there are no through-the-thickness
through the thickness fibers,
fibers Fig 3.
3
Following the ASTM D2584-02,
D2584 02 the panel
fiber volume fraction was calculated,
calculated Fig 5.
5
Fig 5.
5 Residues from the ignition process
Fi 2.
2 Braid
B id preform
f
f t i process
Fig
manufacturing
Fig 3.
3 T
i i lb
id d preform
f
Fig
Triaxial
braided
Fiber volume Fraction
Fiber volume Fraction
After braiding,
braiding the preforms were removed from the mandrel,
mandrel
slit along the 0
0º fiber direction, flattened, and border stitched
to
t minimize
i i i fiber
fib shifting.
hifti g The
Th resin
i was introduced
i t d
d via
i a resin
i
transfer moulding (RTM) process.
process
Experimental
Methods
X Ray CT
Data Sheets
CAD software
Analytical
55.1
55 1 %
Development of a reliable methodology:
Thermal expansion
expansion-compression
compression
A methodology to fully obtain the triaxial
braided
b
aid
ded
du
unititt ce
cellll has
has bee
b
been
d eloped
developed.,
de
d , Fig
Fig 6
6.
R.
R NAIK NASA
REPORT
54.5 %
54 5 %
Fig
g 4. Micrographs
g p of the cross-section of a 12 layers
y
triaxial braided composite
p
panel.
p
Geometry roadmap
Analytical
y
Formulas
Experimental
The objective is to obtain a more realistic representation of the unit cell
without
ith t tow
t
i t
interpenetrations
t ti
and
d with
ith a fiber
fib volume
l
f ti similar
fraction
i il to
t
the experimental
p
values,
g 9.
e perimental
al es Fig
9
Fig 7. Ideal geometry modeled with a CAD software
Micrographs
Textile Generator
Fig
Ideall geometry
Fi 8.
8 Id
t modeled
d l d with
ith a ttextile
til generator
t
Geometry
Fig 6.
6 A schematic of the different approaches to obtain the geometry.
geometry
Limitations:
Low
fiber
fraction
Li it ti
L
fib volume
l
f ti (30 – 40 %)
and to
tow interpenetrations
interpenetrations.
p
Fig 9.
9 Ideal-scaled
Ideal scaled dry fabric architecture
architecture.
Fi it Element
El
t Model
M d l
Finite
Th main
i objective
bjj ti is
i to
t obtain
bt i a desirable
d i bl unitit
The
cell meshed in which p
periodic boundaryy
conditions are going to be applied,
applied Fig 12.
12
Limitations: Fiber volume fraction up to 50 %.
%
Fig 12.
12 Top and front views of the mesh of the triaxial braided unit cell
cell.
Experimental
E
p i
t l Tests
T t
Transverse tensile load/unload il l d// l d
600
Tensile tests on 12 layers laminate coupons has been
carried
i d outt in
i the
th axial
i l and
d transverse
t
di ti
directions.
500
esss (M
Mp
Stre
paa)
400
300
200
100
0
0
0 003
0.003
0 006
0.006
0 009
0.009
Strain
0 012
0.012
0 015
0.015
0 018
0.018
Fig
g 10. Virtual geometry
g
y after the thermal expansion-compression
p
p
test. (top),
( p),
displacements in the axial direction (left) and in the transverse direction (right)
Fig 13.
13 Transverse (top) and longitudinal (bottom) tensile specimens
specimens.
Tensile tests 12 layers (6K/3K)
Tensile tests 12
layers (6K/3K)
Conclusions
• Thermal expansion to fill the free spaces in the ideal-scaled
ideal scaled
geometry and compression showed a more realistic
representation of the structure of the braided composite.
• Due to the limitations of the single
single-ply
ply model, several effects as
nesting
ti g and
d fiber
fib shifting
hifti g are nott taken
t k
i t accountt and
into
d could
ld
affect in the overall fiber volume fraction.
fraction
Longitudinal modulus L
i di l
d l E1 E1
(GPa)
45 71
45.71
Transverse modulus E2 Transverse modulus E2
(GP )
((GPa)
43.28
Longitudinal Strength Xt (MPa)
701.39
701 39
Transverse strength Yt Transverse
strength Yt
(Mpa)
677.71
Fig 11
11. Dry fabric geometry with the compression plates after the virtual tests