JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 40

FEATURE
bonding

The Bondline Control Technology

Dipl.-Ing. Lennert Heilmann,
Research Associate
German Aerospace Center (DLR)

J

oining fibre-reinforced plastics (FRPs)
via adhesive bonding enables optimum
material utilisation and optimised designs
in terms of manufacturing, aerodynamics and
weight. In aviation, however, the use of this
joining technology is restricted since adhesion defects cannot be reliably detected with
non-destructive testing methods (NDT). In
the case of critical joints, fail-safe design is
implemented in the form of additional bolts
or structural redundancy, resulting in reduced
efficiency in the manufacture and operation
of the aircraft. To solve this issue, DLR invented the BCT, a novel method for bondline testing and surface pre-treatment (international
patents pending). The proof test is capable
of detecting any defects present in a bonded
interface with a very high sensitivity. And the
surface treatment produces a joining surface
that is guaranteed to be bondable and that is
highly robust against the formation of critical

The Bondline Control Technology (BCT) comprises several
innovative methods that substantiate proper bond quality
in adhesive joints. It unlocks the use of adhesive bonding in
safety-critical applications and offers a variety of benefits for
lab testing, production and bonded repair of FRPs.

bonding defects. The proof test and surface
pre-treatment can be performed in combination or separately to meet the requirements of
various application scenarios.
Novel proof test
The quality and properties of a joint between
an adhesive and a solid adherent are assessed
by means of the novel proof test. The mechanical test is performed by bonding a mesh
fabric onto the adherent and by successively
peeling it out of the cured adhesive, see Figure
1. The peeling of the fabric generates a high
mechanical stress that reveals any bondline
defect present, regardless of its cause. Defects
are recognised by an invalid fracture pattern
or as a deviation from the nominal peeling resistance. In case of a proper bond, the peeling
resistance reaches a reference value and a thin
layer of tested adhesive remains on the adherent. Due to the flexibility and drapeability of
the mesh fabric, the test can be performed on
rigid materials with a flat or curved surface
and even on complex-shaped surfaces such as

Fig. 1: Crosssectional view of the
BCT peel test

40

jec composites magazine / N°135 July - August 2020

Fig. 2: Test results of defective bonds: BCT vs. DCB

stepped repair geometries.
In the framework of the FACTOR project
supported by the German Federal Ministry
of Economics and Technology, several test
programmes were conducted to assess the
sensitivity of the BCT with respect to the
detection of different types of bonding
defects. Figure 2 illustrates the results of a
comparative analysis between the BCT and
the double cantilever beam test (DCB or "GIC
test"), which is deemed the most sensitive
state-of-the-art test for interfacial defects.
The tests were performed on CFRP panels
with different degrees of pre-bond contamination of the joining surface (S1 to S4). The
contaminant was a silicone-based release
agent that was applied homogeneously via
the dip-coating method at Fraunhofer IFAM.
The results showed that for each degree of
contamination, the amount of adhesion
failure detected is comparable between the
two methods. Similarly positive results were
obtained for other types of bondline defects
such as cohesion defects of the adhesive and
surface-near defects in the substrate.
The sensitivity of the BCT peel test was
found to be so high that it detects defects in



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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