JEC COMPOSITES MAGAZINE - Issue #78 - January/February 2013 - 29

Tab. 2: GL minimum requirements and properties of the BP435 system, cure cycle
6h/70°C, single lap shear substrate: GF/epoxy composite, thickness 4.5 mm

Single lap shear

> 12 MPa

34.7 MPa (0.5 mm)
24.0 MPa (3.0 mm)

Lap shear creep

< 0.18 mm (0.5 mm)
< 1 mm (3 mm)

0.01-0.04 mm
0.02-0.06 mm

BP135/G3 system.
The Epikote BP435
bonding paste exhibits
superior fatigue
behaviour at all load
levels tested. In the
Fig. 3: Development of Tg midpoint at a cure temperature of 70°C. A Tg
high cycle regimen,
midpoint of 75°C is reached after ~3h with the new BP435 system, while
5-6h are needed with the reference BP135/G3 system
a factor of ~5 was
observed between
the performance of the new adhesive vs.
goal in its development was to achieve
the reference. At a maximum stress value
high fatigue resistance to offer added
of 6 MPa (R = 0.1), lifetimes on the order
value in durability, as many offshore wind
of 107 cycles were achieved. It should be
energy plant locations can only be accessed
infrequently for maintenance and service.
noted that the results presented here are
In designing the new bonding paste,
a conservative estimation of the potential
designers followed a different mechanical
of the new BP435 system, as the measureconcept than for the reference BP135/G3
ments were performed under load control.
system. As shown in Table 1, the values
In combination with a density about 10%
obtained from static tensile testing show a
lower than that of the benchmark, the exhigh ductility, with strain to failure values
cellent static and mechanical performance
of up to 11.8%. These material characterisof the BP435 system allows for further
tics are quite different from those of stanweight reduction in rotor blade design.
dard wind energy bonding pastes which
typically show a relatively brittle behaviour,
with strain to failure values < 5%. Furthermore, the new adhesive was designed
to be less stiff, exhibiting a comparatively
low Young’s modulus of around 2.7 GPa,
while state-of-the-art bonding pastes for
rotor blade manufacturing typically exhibit
values > 3.5 GPa (e.g. 4.5 GPa for BP135/
G3).
Fig. 4: Wöhler plot of the BP435 and BP135/G3
The Epikote BP435 system provides
bonding paste systems, bond line thickness 1
mm; R = 0.1; f = 5 Hz; cure cycle 6h/70°C; GF/
excellent static and dynamic bonding perepoxy substrate (t = 4.5 mm)
formance. Table 2 shows the static single
lap shear test results and Figure 4 shows the
fatigue performance of the BP435 bonding
Longer and lighter rotor blades
paste in comparison to the reference
Momentive’s new epoxy infusion system
– the Epikote RIM145 system – exhibits
Tab. 1: Tensile properties of the BP435
improved properties that allow wind
system, cured for 2h at 80°C
turbine rotor blade manufacturers to use a
VARTM infusion process for carbon fibre
2720 ± 24
Young’s modulus [MPa]
structures, even thick ones, such as spar
Ultimate tensile strength [MPa] 48.7 ± 0.2
caps. The use of VARTM infusion results
11.82 ± 2.85
in significant cost savings compared with
Tensile strain at break [%]

the C-fibre prepreg process. The Epikote
RIM145 system with C-fibres approaches
90% of the compressive strength performance of the traditional C-fibre prepreg.
With the new Epikote RIM245 wind
energy infusion system, Momentive offers
a solution for lighter and longer blades, as
well as the potential for substantial cost
savings through decreased volume requirements for both fibre and resin. With this
system in use, transverse tensile strain and
strength values were shown to improve by
30-50% over the market benchmark.
With improved applicability, faster curing
cycles and excellent fatigue properties,
the new Epikote BP435 bonding paste
system is especially suited to the manufacture of offshore rotor blades. Cycle time
reductions of 2-4 hours were achieved in
full-scale rotor blade manufacturing. With
the reduction in density, weight savings of
more than 10% can easily be achieved. The
good mechanical performance provides
potential for further weight reduction.
These improvements are likely to result
in significant material and manufacturing
savings as well as longer, lighter rotor blades
that will drive wind energy’s acceptance as
an efficient, reliable energy source. n
More information
www.momentive.com/wind energy/
References
[1] Technical Whitepaper on the Momentive Epikote™ RIM145
infusion system, Momentive Specialty Chemicals Inc., www.
momentive.com/wind-energy/Contact-Us/
[2] Technical Whitepaper on the Momentive Epikote™ RIM245
infusion system, Momentive Specialty Chemicals Inc., www.
momentive.com/wind-energy/Contact-Us/
[3] S. Löser, A. Krimmer, Comparison of the potential for light
weight construction from different epoxy resin systems and
construction methods. R&D report, EUROS Entwicklungsgesell-

No78 January - February 2013 /

schaft für Windkraftanlagen mbH, 2012

jec composites magazine 29
http://www.momentive.com/wind-energy/ http://www.momentive.com/wind-energy/Contact-Us/ http://www.momentive.com/wind-energy/Contact-Us/
JEC COMPOSITES MAGAZINE - Issue #78 - January/February 2013

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