GROWTH – DEDICATED CALL – 10/00
TOPIC IV.11
Assessing long term durability of bonded automotive metallic
structures.
1. CONFORMITY WITH THE WORK PROGRAMME
This topic falls under the Competitive and Sustainable Growth Programme, generic
activity Measurement and Testing. Specifically, it is related to Objective GROW-20006.2.1 Methodologies to Support Standardisation and Community Policies for which
expressions of interest have been called.
This topic is also related to Generic Activity Materials, specifically related to objective
1.1.3-5.1 Cross-cutting generic materials technologies and objective 1.1.3-5.4
Expanding the limits and durability of structural materials.
In addition, this topic relates to Key Action 3 Land transport and marine technologies
under objective 1.1.3-3.1.1 Efficient, clean, and intelligent road and rail transport
vehicle technologies and 1.1.3-3.1.2 Innovative and safe road and rail transport vehicle
concepts.
2. KEYWORDS
Lightweight vehicles - weld bonded structures - adhesive bond durability assessment integrated corrosion cycle and fatigue testing - reliability and safety.
3. SUMMARY OF OBJECTIVES AND JUSTIFICATION
Industrialised countries agreed in Kyoto in 1997 to reduce CO2 emissions. Passenger
cars are a significant source of CO2 emissions and the EU is fully committed to meet its
targets by reducing emissions from new cars. This has moved the European car
industry into looking at novel manufacturing techniques to reduce vehicle weight.
In July 1997 the European Commission presented a proposal for a European Directive
on End-of-Life Vehicles (ELVs) with a view to limiting the environmental impact of
vehicles at the end of their life. The proposal suggested introducing targets for the reuse and recovery of such vehicles, measures to ensure environmentally friendly
treatment, and, in particular, the objective to work towards better prevention of waste
from vehicles. An increase in the use of aluminium alloys would enable these targets to
be met.
Adhesive bonding is viewed as a key enabling technology in the development of
lightweight vehicles. Adhesive bonding can be used to stiffen designs in spot welded
steel designs and remains a principal construction method for aluminium designs.
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Unlike spot welded structures, design analysis methodologies are not yet available for
bonded structures.
Currently there is a lack of confidence in long term durability testing leading to slow
uptake of a key enabling technology. For the opportunities of adhesive bonding to be
taken in automotive structures a standard accelerated laboratory test methods for
assessing long term durability of bonded automotive metallic structures should be
developed. Work in this area has begun, as described below, but it is now required to
take this technology further, to conduct pre-normative research to increase the reliability
of this approach leading to standardisation. A standard method that is accepted and
used would give the automotive companies, their suppliers and the consumer confidence
in the use of lightweight vehicles.
4. BACKGROUND
Under an agreement between the European Commission and the European Automobile
Manufacturers Association (ACEA) the average of new cars sold in the EU by
European manufacturers in the year 2008 will emit about 25% less CO2 than in 1995
(1). Programme areas that have been developed to meet these targets include R&D
towards Mass Reduction using aluminium and other materials and R&D in Joining and
Assembly Technology. The use of adhesive bonding would allow "lightening and
modularity improvement for car body by high strength steel and aluminium sheets"1.
The European Aluminium Association is active in developing a new range of
lightweight products for the transportation sector. The use of aluminium in automotive
applications is expected to double in the next decade (2). Extensive use of aluminium
can result in up to 300 kg weight reduction in a medium size vehicle (1400kg). For
every 100 kg reduction in the automotive sector, there is a cut of 0.6 litres per 100 km in
fuel consumption leading to 20% lower exhaust gas emissions and proportional running
costs. Aluminium can be repeatedly recycled without quality loss. Its high scrap value
ensures reclamation and recycling: 95% of aluminium in cars is currently collected and
recycled and accounts for over 50% of the material value of a vehicle at the end of its
life
Existing standard methods for fatigue and durability assessment of bonded joints for
thin gauge metals are inadequate for automotive applications. Fatigue tests based on
standard lap joints allow comparison of different adhesives but do not provide data for
design analysis because they are geometry dependent. Durability tests using lap joints
(3), peel joints (4) or wedge tests (5) generally involve static loading which is not
relevant for automotive structures that are primarily fatigue loaded. Durability tests do
not include the influence of fatigue loads while testing under the environment (6).
A consortium of car companies and their suppliers have been investigating the use of
fracture mechanics to develop an integrated environmental and fatigue assessment
method. This method focused around a new test method called the Reinforced Double
Cantilever Beam (RDCB) and a novel multi-station durability testing machine
developed as a prototype (7). These tests have the advantage of being used for both
durability assessment and for design purposes. These developments have shown
promise and now require further prenormative research leading to a common European
standard ensuring repeatability and reproducibility. Further work is required to ensure
the corrosion durability cycle is relevant to the applications and in making the test
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method more robust. Once achieved this would result in making the methodology
available for wider use within the industry and its suppliers. Involvement of the
relevant CEN/ISO committee at an early stage in this project would help dissemination
to other can companies and suppliers.
(1) R&D Work programme on Automotive CO2 Emission Reduction 1998-2004,
ACEA, CLEPA, EUCAR.
(2) www.aluminium.org/pages/News/news.html#Press1
(3) ISO 4587 - Determination of tensile lap-shear strength of rigid-to-rigid bonded
assemblies.
(4) ISO 4578 - Determination of peel resistance of high strength adhesive bonds Floating- roller method.
(5) ISO 10354 - Characterisation of durability of structural- adhesive bonded
assemblies - Wedge rupture test.
(6) ISO 14615 - Durability of structural adhesive joints - Exposure to humidity and
temperature under load.
(7) Opportunities for Adhesive Bonding in Lightweight Vehicle Structures, 32nd
ISATA, 14-18 June 1999, Vienna - Materials for Energy Efficient Vehicles.
5. ECONOMIC AND SOCIAL BENEFITS
Markets
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Automotive manufacturers
Steel and aluminium suppliers
Adhesive suppliers
Component manufacturers and assemblers (Tier 1 and Tier 2 suppliers)
Other industries using spot welding or aluminium in structures that could adhesively
bonded - e.g. the railway industry.
Economical consequences
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Improved fuel consumption from lighter vehicles (savings for all drivers).
Reduction in use of fossil fuels by improved fuel efficiency - consequentially
reducing fuel imports.
Secure European jobs in the automobile industry supply chain and material suppliers
by increasing competitiveness of European manufactured cars.
Wider dissemination of adhesive bonding technology through Round Robin and
activity within CEN/ISO committees.
Increased life cycle of automobiles by further utilisation of aluminium alloys thus
helping meet EC Reduction in Waste Directives.
Support the use of a lighter materials (aluminium) in structural automobile
applications allowing alternative fuels to be considered.
Supporting the use of aluminium helping European aluminium suppliers find new
markets.
Reduced development time and time to market from presence of a standard method
to assess durability.
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Social benefits
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Lighter vehicles will aid towards the reduction of emissions and help meeting EC
emission reduction targets.
Give the European car industry a competitive technological lead.
Increase safety through reliable design and better understanding of adhesively
bonded joints in automotive applications, thus, reducing unexpected failure.
Develop CEN/ISO draft standard for subsequent progression through the standards
committees to ensure repeatability.
Aid recycling targets of automobiles.
6. SCIENTIFIC AND TECHNOLOGICAL OBJECTIVES
6.1
Technical objectives
The scientific and technological objectives of this work should aim to:
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6.2
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Develop accelerated test methods to determine durability of adhesive bonds.
To prove the robustness of the fracture mechanics method of assessing the durability
of bonded and weld bonded structures.
To prove the repeatability and reproducibility of the method via a Round Robin
exercise.
To publish a draft standard for submission to CEN/ISO committee to allow the
method to be adopted more widely.
To facilitate the progression of prototype technology into the main stream use of
automobile manufacture.
To increase the confidence in design and manufacturing of automobile bonding by
using standard methods.
To introduce technology to reduce weight of vehicles by stiffer design (Weld
bonding).
Work programme
Review, definition and set-up - Identify adhesive systems and test parameters of
interest (substrates, adhesives, surface preparation, test conditions, etc.). Including
generic systems for public dissemination and systems confidential to the partners.
Manufacture specimens.
Pre-standards research - Conduct test matrix to investigate effect of parameters
including: bond-line thickness, R-ratio, fillet preparation, curing schedule,
environment, protective coating, …
Development & installation of test equipment - Modifications to prototype
durability test equipment. Fabricated and installed at the partners. CE certification.
In-house installation and staff training.
Test method preparation - Based on results of Pre-standards research prepare
draft test methods.
Round robin stage 1 - Conduct stage 1 round robin to test the robustness of the
round robin using partners only. The public results will be disseminated through
EUCAR and ESIS (European Structural Integrity Society).
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Round robin stage 2 - Solicit members from ESIS and EUCAR to participate in a
final round robin to broaden the knowledge base of the test method and to develop
precision statements on accuracy.
Implementation - The resulting test method will be written up as an EUCAR
published standard. This will allow it to be implemented immediately by the
EUCAR participants. The method will also be submitted to ISO/CEN and
supported at an early stage to the relevance committee. Further funding will be
solicited for supporting the test methods through the balloting procedure.
7. TIME SCALE
Although no rigid timescale requirements apply to this project, based on the described
objectives, it is anticipated that this project will have a three-year duration. The support
of the draft standard through the balloting procedures to a published standard is outside
the scope of this project.
8. IMPORTANT ADDITIONAL INFORMATION
The proposal must demonstrate that:
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The method is applicable to the thin gauge metals used in the automotive
industry without the need for altering the surface preparation of the metals.
The method addresses the varied operating conditions of automobiles.
There will be participation from members of the supply chain and that the
method can be implemented into the manufacturing processes of the automobile
manufacturers.
This work should be carried out in cooperation with the relevant CEN/ISO
committee to ensure full dissemination of the work.