JEC COMPOSITES MAGAZINE - Issue #128 - May/June 2019 - 24

MANUFACTURlNG automotive

Optimizing leaf springs via
enhanced composite solutions

PASCAL ALBRECHT, Technical Manager Composites
JÜRGEN BECHER, Manager Application Testing
DR CHRISTOS DERDAS, Scientific Principal PD EU
Engineer, Global Engineering Center
MIKE WIENAND, Process Engineer for Composites
Henkel
JAN HINDAHL, New Products & New Markets Business
Unit Saertex

omposite leaf springs have been
used in automotive axle designs for
more than 50 years now.
However, despite their indisputable
weight benefits, their use has been limited to only a small group of car models.
Recently, the Volvo XC, S, V 90 & 60 series has been available as standard with
a transversal GFRP leaf spring based on
Henkel's Loctite Max 2 polyurethane
resin. However, many axle designs are
still using coil or leaf springs made of
steel. Two reasons for this are the poorly
understood fatigue performance of the
material, with limited literature available on this topic, and the processing
time and cost to reach competitiveness
in terms of cost per part. Both issues are
addressed in this paper.
In a joint research effort between
Saertex GmbH & Co. KG and Henkel
AG & Co. KgaA, leaf spring demonstrators were manufactured with different
fibre reinforcement architectures.
These reinforcement architectures were
designed to achieve an optimum combination of easy handling and fast and
good fibre wetting within the HP-RTM
process, using the road-proven Loctite
Max 2 PU resin.
Fatigue testing was performed both at
the coupon level and on full-size demonstrator parts to better understand the
influences of fabric architecture, resin

Leaf springs are a component that can be lightweighted using composites. The results of joint research between Saertex GmbH & Co. KG
and Henkel AG & Co. KgaA on how engineered preform architectures
and high fatigue resistance PU resins can enhance fatigue performance are presented in this paper.

type and manufacturing parameters and
to correlate small-scale standardized
testing with real-size parts performance.
Materials
Non-crimp fabrics (NCF) are characterized by a very low undulation of fibres
compared to woven fabric structures.
This results in high mechanical performance with reduced structural elongation at low stress levels. Additionally,
the textile construction of unidirectional NCFs can be produced in various
ways so as to ensure glass fibre retention
by modifying the stitching structure
and architecture. The influence of the
stitching structure on fatigue properties
is investigated in this paper.
To this end, eight different textile

structures were produced, all based on
3B's SE1500 glass fibre in a range of 950
g/m2 and pre-bindered with Henkel's
Loctite FRP2000 reactive powder
binder. The fibres were infiltrated with
the Loctite Max 2 high fatigue life
polyurethane resin from Henkel AG &
Co KgaA. Polyurethane resins such as
Loctite Max 2 provide many advantages
in current epoxy systems, such as a lower exothermic reaction, low viscosity at
injection temperatures and significantly
better fatigue performance due to a
unique chemistry that ensures high
fracture toughness. Small amounts of
the Loctite Max 2-301 accelerator and
the Loctite FRP 3000 internal mould
release agent were pre-mixed into the A
component of the resin system.

Fig. 1: Leaf spring demonstrator preform placed in the mould

jec composites magazine / N°128 May - June 2019

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #128 - May/June 2019