Fluid Structure Interactions
Research Group
Hygrothermal ageing and the implications on adopting sustainable
composite materials for structural marine applications
Mari Malmstein – M.Malmstein@soton.ac.uk
Supervisors: Dr. James Blake and Dr. Alan Chambers
BACKGROUND
AIM & OBJECTIVES
Exposing composite materials to the marine
environment tends to degrade the material’s
mechanical properties. Recently, new sustainable
materials have been introduced due to
environmental concern and societal awareness.
However, the high structural performance end of
the market seen in the marine industry (Figure 1)
has little confidence in the performance of these
emerging materials. Manufacturing petroleum
based resins has higher environmental impact than
fibres. Hence, this research seeks to determine the
viability of using glass fibre reinforcements with two
candidate plant oil-based resins, linseed oil and
castor oil resins (Figure 2), for marine structures.
The aim of the project is to investigate the issues of
environmental degradation and durability of
composite materials in the marine environment.
This leads to the following objectives:
• Investigating the effect of water uptake on the
durability of glass reinforced natural resins in
comparison to epoxy resin through accelerated
conditioning tests (hygrothermal ageing);
• Increasing the understanding of the processes
behind the reduction of mainly flexural properties
of composite materials;
• Using visual inspection techniques to relate
moisture uptake and storage areas to the failure
modes of composites.
Figure 1: example application for
sustainable composites – Beneteau
Oceanis
Figure 2: castor oil resin
VISUAL INSPECTION
Accelerated ageing (36 weeks)
Non-accelerated ageing (16 weeks)
Water
Distilled
Distilled & salt
Water temp
40 ˚C
20 ˚C
Specimens
Glass/epoxy, castor & linseed oil Glass/linseed oil
• Flexural tests were carried out with 2 week intervals for the
first 10 weeks of ageing to monitor reduction of properties
• Computed tomography and scanning electron microscope
were used to investigate the changes in flexural failure modes
due to moisture uptake in glass/epoxy and glass/linseed oil
600.0
4.50
Glass/Epoxy
Flexural failure stress, MPa
Moisture uptake, %
Glass/Epoxy
Glass/Epoxy 26 weeks
Glass/Castor oil
Glass/Castor oil 22 weeks
Glass/Linseed oil
Glass/Linseed oil 26 weeks
Glass/Linseed oil
Glass/Castor oil
3.00
2.50
2.00
1.50
1.00
0.50
500.0
400.0
300.0
533.8
200.0
100.0
0.00
0
1
2
3
√weeks
4
Cracks
90˚ fibres
0˚ fibres
Compression
5
6
Figure 3: moisture uptake comparison of
glass/epoxy, glass/linseed and glass/castor oil
243.4
295.7
233.8
147.1 40.35
0.0
Figure 4: reduction of flexural strength
over 20+ week ageing period
Reduction in flexural failure
stress, %
• The flexural properties of glass/castor oil compared better to
glass/epoxy than glass/linseed oil (Figure 4), especially after
ageing
• Degradation of glass/linseed oil was most rapid during the first
2 weeks of ageing
90
80
2 weeks
4 weeks
Non-accelerated ageing
70
15 weeks
15 weeks
60
• Non-accelerated ageing
6 days 8 weeks
8 weeks
50
40
showed that reduction of
Glass/Linseed oil @ 40˚C distilled water
3 days
30
Glass/Linseed oil @ 20˚C distilled water
flexural strength is related
20
Glass/Linseed oil @ 20˚C salt water
10
to water content rather
0
0
0.5
1
1.5
2
2.5
3
than water temperature or
Moisture content, %
Figure 5: reduction of flexural strength vs.
chemistry (Figure 5)
moisture uptake under accelerated and nonaccelerated conditions
• Failure of glass/linseed oil changes from a tensile/compressive
mode into a compressive one after 3 days of ageing (Figure 7)
Tension
Cracks
1 mm
Compression
1
mm
Accelerated ageing
• Water uptake of glass/epoxy reaches moisture equilibrium
content after 6 weeks of immersion, glass/castor oil after 25
weeks (Figure 3); up to 6 weeks of immersion the water uptake
of glass/epoxy and glass/castor oil is very similar
• The moisture uptake of glass/linseed oil kept increasing even
after 36 weeks of immersion (Figure 3) due to blistering
3.50
Tension
Figure 6: unaged glass/epoxy (left) and 10 weeks aged glass/epoxy (right) showing changes
from tensile/compressive into a tensile failure mode
FLEXURAL PROPERTIES
4.00
Computed tomography (CT)
• CT provides 3D overview of the damage occurring inside the
materials after flexural failure
• Failure of glass/epoxy changes from a tensile/compressive
mode into a tensile failure after 10 weeks of ageing (Figure 6)
1 mm
Ageing 
1 mm
METHODOLOGY
0˚ fibres
Compression
90˚ fibres
Tension
Figure 7: unaged glass/linseed (left) and 3 days aged glass/linseed (right) showing changes
from tensile/compressive into a compressive failure mode dominated by delamination
Scanning Electron Microscope
(SEM)
• SEM
showed
that
in
glass/epoxy specimens the
interface has degraded already
after 3 weeks of immersion
Figure 8: unaged (left) and 3 weeks aged
glass/epoxy (right). Clean fibres in aged
material indicate interfacial damage
CONCLUSIONS
Moisture uptake causes rapid loss of strength in all tested
materials. Glass/castor oil compares better to glass/epoxy than
glass/linseed oil. The reduction of strength can partially be
attributed to changes in flexural failure modes due to water
ingress. While the failure of glass/epoxy remains mainly
tensile/fibre dominated, the failure of glass/linseed oil changes
from a tensile/compressive into a compressive failure.
FUTURE WORK
Investigating the possibility of using CT for detecting moisture
storage areas and relating them to the failure modes.
Sustainable Composites Ltd and Bioresin are acknowledged for providing the natural resin systems
IMarEST is acknowledged for providing additional funding for the project
FSI Away Day 2012