JEC COMPOSITES MAGAZINE - Issue #78 - January/February 2013 - 28

resin

not only provides beneficial processing
characteristics, it also imparts significant
mechanical performance improvements
with both glass and carbon fibre. Compared with classical infusion systems, compressive strength increases by 25%, and
C-fibres infused with this system approach
90% of C-fibre prepreg performance
(Figure 1).

Shell infusion system
In many rotor blade designs made from
glass fibre reinforced epoxy, the transverse
tensile (i.e. interfibre failure, IFF) properties are a design-limiting factor. The
structural stiffness of a rotor blade is provided by the spar caps, which incorporate
unidirectional (UD) glass fibre fabrics. The
shell structure provides torsional stiffness
as well as the aerodynamic contour and
is typically constructed of a ±45° biaxial
layup. The interfibre failure properties of
the shell laminate determine the maximum
allowable strain level in the main load
direction (flapwise).
A matrix resin that provides enhanced
transverse tensile properties, such as the
new Epikote RIM245 infusion system
[2], allows for higher tolerable strain
levels and thus a reduction of the spar cap
dimensions. This volume decrease results
in significant weight savings, enabling the
construction of longer blades, as well as raw
material cost reductions. A reduced blade
weight results in significantly decreased
fatigue loads and can positively influence
the overall turbine design as well, by reducing pitch bearing dimensions and so on.
The transverse tensile performance of the
new Epikote RIM245 system was tested
on various roving types and fabrics. Two
glass fibre roving types commonly used in
the wind energy industry – the PPG2002
and the 3B SE1500 type – were employed
as glass fibre reinforcements. The wellestablished Momentive Epikote RIM135
infusion resin system (with curing agent
RIMH137) served as a reference. In Figure
2, the transverse tensile strain (strain to
first crack) values, as well as the transverse
tensile strength (stress at first crack) values

Fig. 2: a) Mean transverse tensile strain and b) mean transverse tensile strength values of the RIM135
and RIM245 systems, tested on a PPG2002 roving (Kuempers fabric HPT 1040) at a fibre volume content
of 52%

of the RIM135 and RIM245 systems are
displayed for a Kuempers HPT1040 fabric
with the standard PPG2002 roving. It
should be noted that the fabric contained
8% 90° fibres (stabilizers) oriented in
the testing direction. A +53% increase in
transverse tensile strain was found (from
0.42% to 0.64%) when comparing the
industry benchmark RIM135 system with
the new RIM 245 system. The transverse
strength value increased from 50.6 to 65
MPa (+28%).
Very similar results were found on glass
fibre reinforcement with SE1500 sizing
(3B fibreglass), which is also widely used
in the wind energy industry. The fabric was
a Saertex UD (type V105180), with a 90°
fibre weight proportion of only 3%. With
the RIM 245 system, the strain to failure
was improved by 29% (0.42% vs. 0.54%)
and the transverse tensile strength by 35%
(36.7 MPa vs. 49.8 MPa), when compared
with the RIM135 reference system.
In a rotor blade design study by EUROS
Entwicklungsgesellschaft für Windkraftanlagen mbH [3], the calculated weight
saving potential of a rotor blade using the
Epikote RIM245 system as a shell matrix
system instead of the standard infusion
system was approximately 1 metric ton for
a 59 m blade. This translates to a reduction
of 19,000 kg∙m of static moment or a 10%
reduction in fatigue loads.
In the same study, a rotor blade design
consisting of a UD carbon fibre spar cap
infused with the RIM145 system and a
shell structure infused with the RIM245
system was compared with a standard glass

28 jec composites magazine / No78 January - February 2013

fibre design infused with a standard system.
A weight saving of 4.4 metric tons could
be achieved with the new infusion systems
and a carbon fibre spar cap [3].

Bonding paste system
Enhanced mechanical performance as
well as cycle time reductions via improved processing characteristics are also the
main features of the new Epikote BP435
bonding paste system. This system offers
superior processing properties, such as
improved rheology for better control of the
bonding process and a faster cure speed. A
structural adhesive in rotor blade manufacturing should develop mechanical strength
as well as heat resistance (glass transition
temperature, Tg) quickly when cured, yet
provide a pot life long enough to allow for
a controlled application process. Figure 3
shows the improved glass transition temperature development of the Epikote BP435
bonding paste as compared with that of
the industry standard Epikote BP135/
G3 system. Cycle time reductions of 2-4 h
were achieved during full-scale rotor blade
manufacturing.
Furthermore, the BP435 bonding paste
system provides improved rheological properties. Full-scale application tests showed
that closure forces during the bonding
process could be significantly reduced,
without sacrificing sag resistance. This
improvement allows better control of bond
line quality.
The new adhesive system was especially
designed to meet the needs of the offshore
market segment. Therefore, a major design

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

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