JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 41
The Bondline Control Technology
Fig. 4: Topology of a
surface pre-treated
via the BCT, laser
scanning confocal
microscope image
dry specimen condition that could only be
detected in wet specimen condition with the
DCB test. At the same time, the BCT is less
prone to substrate damage since no bending
stresses are introduced in the substrate.
Robust surface pre-treatment
The mesh fabric can either be bonded onto
a solid structure via adhesive to perform the
peel test or it can be applied on a FRP component in the initial manufacturing process.
In both cases, peeling of the embedded fabric
serves as a highly effective method for surface
pre-treatment that is reproducible and operator-independent. The joining surface created
this way provides optimum properties for
a subsequent bonding process without any
further processing steps.
Several test programmes were conducted
to verify the effectiveness of the surface
pre-treatment for various material combinations, including high-, intermediate- and
room-temperature curing epoxy adhesives
and matrix resins. DCB specimens and
slotted single-lap shear specimens incorporating an interface produced by peeling of
mesh fabrics showed excellent performance
under all conditions relevant for aerospace
applications. This comprised testing of dry
and moisture-saturated specimens at low,
ambient and high temperatures. Figure 3
illustrates normalised DCB test results of an
out-of-autoclave repair configuration. The
numerical results highlight that specimens
produced with the BCT have a very high
fracture toughness that exceeds the reference
value. Even in wet condition and at low
temperature, the bonded specimens feature
excellent performance. The fracture patterns
observed are predominantly of the cohesive
type with no failure at the interface produced
by the BCT. The outstanding test results
obtained underline the performance of the
optimised joining surface that is generated by
the BCT.
Figure 4 shows a typical surface topology
of fractured resin after peeling of a mesh
fabric. The surfaces produced by the BCT
are highly textured with the true surface
area ranging between two and three times
the geometric area, depending on the fabric
specification used. The surface enlargement
Feature Aeronautics
Fig. 3: Test results
of DCB specimens.
Reference vs. BCT
pre-treatment
promotes the formation of a strong bond, as
more sites are available for interaction with
an adhesive polymer. The elevated portions
of the surface consist of cohesively-broken
resin that is guaranteed to be clean and ready
to form covalent bonds due to the presence
of functional groups and radicals. The test
results confirm that the smooth fibre imprints
that surround the cohesively-broken areas are
also able to form strong covalent bonds when
in contact with epoxy adhesive.
This was verified with additional series of
DCB specimens that were manufactured
from substrate panels pre-treated using a new
type of peel foil (patent pending) that consists
of a similar material as the mesh fabrics. These
peel foils leave behind a quasi-infinite imprint
without cohesion fracture, texturisation or
undercuts and still achieve the formation
of perfect bond quality. The explanation for
this is that the interaction between the liquid
resin and the foil material featuring a high
surface energy leads to an orientation of the
polar functional groups of the monomers
towards the surface of the foil. By peeling the
foil from the cured resin, a reactive surface is
exposed that is capable of cross-linking with
the adhesive applied in the joining step. This
way, a strong and durable bond is formed just
like in a co-curing process.
Figure 5 illustrates the cross-section of a
co-bonded joint produced by means of the
BCT. Depending on the fabric specification
used, the resin layer remaining on the precured adherent can be rather thick or it can
be very thin, with a mean thickness of less
than 30 µm. The grooves and undercuts created in the pre-treatment step result in strong
mechanical interlocking in the bondline,
which provides load transfer via positive fit in
shearing and also in the peeling direction of
the final joint. DCB tests performed on prebond contaminated BCT surfaces still reach
sufficiently high fracture toughness values in
the absence of strong adhesion. This shows
that the alternative load transfer mechanism
provides inherent redundancy in the bondline, making the adhesive layer itself fail-safe.
Results show that the surface pre-treatment
provided by the BCT results in a very high
process reliability of the adhesive bonding
process that remedies the criticality of local
adhesion defects. This can potentially enable
the certification of boltless bonded joints for
safety-critical applications in aerospace.
/ jec composites magazine
41
N°135 July - August 2020
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020
Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020
Cover
Edito
“We include composite materials in order to offer the most efficient protection”
Contents
NEWS
In brief
Agenda
BUSINESS
China - What is the impact of the Covid-19 crisis on chemical groups in China?
Startup - UBQ introduces the greenest thermoplastic material
Finance - Finding funding
MANUFACTURING
Simulation - Virtual design of a mediacal auto-injection
Method - The importance of FRP process specifications
FEATURE AERONAUTICS - Can composites help restart activity?
- Additive manufacturing: Printing continuous carbon fibre in true 3D
- Thermoplastics: A thermoplastic T-profile with effective lay-up in one shot
- Maintenance: Automated adaptive machining of aircraft composite structures
- OOA: Out-of-autoclave manufacturing processes for composite aerostructures
- Process: Overmoulded interfaces for composite aircraft parts
- Bonding: The Bondline Control Technology
- Interview: “Don’t miss the shift to Green and the chance to make a positive impact on the environment!”
- Testimonials: Aeronautics: now what?
- Natural fibre: A satellite panel reinforced with natural fibres for cleaner space exploration
SOLUTIONS
Autonomous human flight - Sky is no limit for inventors
Building & construction - Building reality with composites
Aerospace - Lightweight liner-less carbon composite subscale cryotank
TECHNOLOGY
Design - Developing CFRP components for machine tools
Inside the lab - Advanced Composites Laboratory,c Texas State University
FEA - Optimization approach for designing composite components
Index
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JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - Cover
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 2
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - Edito
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - “We include composite materials in order to offer the most efficient protection”
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 5
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - Contents
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 7
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - In brief
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 9
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 10
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - Agenda
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - China - What is the impact of the Covid-19 crisis on chemical groups in China?
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 13
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - Startup - UBQ introduces the greenest thermoplastic material
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 15
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - Finance - Finding funding
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 17
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - Simulation - Virtual design of a mediacal auto-injection
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 19
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 20
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 21
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - Method - The importance of FRP process specifications
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 23
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - - Additive manufacturing: Printing continuous carbon fibre in true 3D
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 25
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 26
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - - Thermoplastics: A thermoplastic T-profile with effective lay-up in one shot
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 28
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 29
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - - Maintenance: Automated adaptive machining of aircraft composite structures
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 31
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 32
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - - OOA: Out-of-autoclave manufacturing processes for composite aerostructures
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 34
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 35
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 36
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - - Process: Overmoulded interfaces for composite aircraft parts
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 38
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 39
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - - Bonding: The Bondline Control Technology
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 41
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 42
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 43
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - - Interview: “Don’t miss the shift to Green and the chance to make a positive impact on the environment!”
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 45
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - - Testimonials: Aeronautics: now what?
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 47
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 48
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 49
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 50
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - - Natural fibre: A satellite panel reinforced with natural fibres for cleaner space exploration
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 52
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - Autonomous human flight - Sky is no limit for inventors
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 54
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 55
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - Building & construction - Building reality with composites
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 57
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - Aerospace - Lightweight liner-less carbon composite subscale cryotank
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - Design - Developing CFRP components for machine tools
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 60
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 61
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - Inside the lab - Advanced Composites Laboratory,c Texas State University
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 63
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - FEA - Optimization approach for designing composite components
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 65
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - Advertisers
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 67
JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 68
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