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The increasing pressure on reducing costs has lead to light-metal designs which demand diverse joining techniques, such as adhesives, riveting, screwing and welding. Over the last years the adhesive joint technology has seen a significant increase in interest, due to remarkable advantages compared to other joining techniques. The growing usage of adhesive joints i.e. in the automotive industry also leads to increased demand for simulation methods for structure, crash and fatigue analyses of bonded components. The awakened interest is reflected by the growing number of CAE-based methods for durability designs of bonded components. The lecture introduces a fracture mechanics-based method to predict the durability of bonded metal components applying on the J-integral solution approach, which is implemented in the modern, process-oriented software nCode DesignLife of HBM. Inputs of the analysis are results of a standard FE solver, material fatigue data and cyclic loading. The energy release rate is determined at the crack tip, where a concentration of local plastic deformation is observed. Based on these conditions the line integral (J-integral approach) could be employ to the combination of adhesive and bonded metal components. In the conventional analytical way the combination can be regarded as a layered composite. The theoretical principles of the method were developed in a research project in UK.
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European Altair Technology Conference, June 24 – 26, 2014
Fracture mechanics-based method for prediction of
safety factors of adhesive bondings
Dr.-Ing. Stephan Vervoort
Hottinger Baldwin Messtechnik GmbH
Agenda
1. Motivation
2. CAE based analysis process
3. FEM Guidelines
4. Adhesive Joints Calculation Method
5. Example
6. Correlation
7. Acknowledgements
2 European Altair Technology Conference, June 24 – 26, 2014
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• Lightweight designs
• Weight minimization induced by material utilization
• Material substitution (sheet metals -> composites)
• Component designs consist of multiple material (steels, aluminum, composites,
plastics)
• Increased use of adhesive joints in automotive engineering:
• 15 kg adhesives in average car
• Examples of automotive engineering:
• Audi A6: Bond seam approx. 90 m
• Daimler A-Class: Bond seam approx. 120 m
• BMW 7-Series: Bond seam approx. 150 m
Motivation
European Altair Technology Conference, June 24 – 26, 2014
Source: Audi
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• Example: Adhesive joints in automotive engineering
Motivation
Source: www.volkswagen-forum.com
European Altair Technology Conference, June 24 – 26, 2014
Bond seams of
Audi TT
Source: http://wiki.zimt.uni-siegen.de
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• Advantages
• Nondestructive joining technology
• Preservation of material properties
• Prevention of thermal damage
• Cold-heat equalization
• Integration of additional functions
• Tightness
• Damping (crash)
• Disadvantages
• Long-term set-up times (e.g. for cleaned
surfaces)
• Long cure times (could be improved by use
of weld/adhesive- or rivet/adhesive-
combinations)
• Need clarification in respect of fatigue
• Repairing of bonded car
• Aging
Adhesives
European Altair Technology Conference, June 24 – 26, 2014
Welds
Rivets
Adhesive
Joints
Source: TU Dresden, Fraunhofer, IWS, 3.Workshop, TGZ, 2009
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CAE based analysis process
Transfer line forces to
analytical sandwich model Line forces and moments
on flange edge
Global model Simple joint modeling
European Altair Technology Conference, June 24 – 26, 2014
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FEM Guidelines
• FE Guidelines:
• Congruent homogeneous mesh
• 4-node linear shell elements are preferred for the sheets (approx. 10 mm)
• Adhesive joint is modeled by beam elements (radius approx. 5 mm)
• Beam elements represent the edge of the adhesive joint
• Required FE results: Grid Point Forces
Upper shell
Lower shell
Shell normal
Local
coordinate system
Calculation point
European Altair Technology Conference, June 24 – 26, 2014
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Adhesive Joint Calculation Process
European Altair Technology Conference, June 24 – 26, 2014
L2
L1
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Adhesive Joint Calculation Process
Initial Condition: Initial flaw size has to be specified
Thickness
Moduli
Poisson Ratios
Local
coordinate system
Path for J-integral
evaluation
Sandwich model (schematic)
European Altair Technology Conference, June 24 – 26, 2014
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Adhesive Joint Calculation Process
• Sandwich model
• Shell elements
Rotation of the cross beam
section
Second moment of area
Shear moduli
with
European Altair Technology Conference, June 24 – 26, 2014
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Adhesive Joint Calculation Process
• J-integral equation:
• for each point of loading time series
• Calculation of safety factor:
Gth = Threshold strain energy release rate
European Altair Technology Conference, June 24 – 26, 2014
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Automotive Example
European Altair Technology Conference, June 24 – 26, 2014
• Typical kind of adhesive joint
• CAE based process for coach peel specimen
• Initial condition
• Technical crack size: 0.4 mm
• Adhesive thickness: 0.3 mm
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Correlation
Fatigue test simulation results and
corresponding cracking on test
Test rig with Jaguar XJ body-in-white
SAE Paper 2012-01-731
A Fracture Mechanics Approach to Durability Calculations for Adhesive Joints
Peter Heyes (HBM UK, Ltd.),
Gunnar Björkman (Volvo Technology),
Andrew Blows and Tim Mumford (Jaguar/Land Rover Cars),
Paul Briskham (Coventry University)
European Altair Technology Conference, June 24 – 26, 2014
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• The testing and software implementation work described in this paper was
carried out as part of the “Bonded Car” collaborative research project, the
partners being Jaguar Land Rover, HBM UK Ltd (nCode), Coventry Uni-
versity, Warwick University, Innoval Technology, Henrob and Stoke Golding
Applied Research.
• The project was co-funded by the Technology Strategy Board's
Collaborative Research and Development program, following an open
competition. The Technology Strategy Board is an executive body estab-
lished by the UK Government to drive innovation. It promotes and invests
in research, development and the exploitation of science, technology and
new ideas for the benefit of business - increasing sustainable economic
growth in the UK and improving quality of life.
• The theoretical basis of the work presented here was developed as part of
an earlier project conducted by the Volvo Group, whose contribution is
gratefully acknowledged.
Acknowledgements
European Altair Technology Conference, June 24 – 26, 2014
measure and predict with confidence
www.hbm.com/ncode
Dr.-Ing. Stephan Vervoort
HBM nCode Produkte
Tel: +49 (0)89 9605372 18
Fax: +49 (0)89 9605372 21
Email: [email protected]
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Thanks for Your Attention
Questions ?!
