Effect of temperature, stress and humidity on the collapse characteristics of mechanically fixed, welded and bonded assemblies

Directorate-General For Research And Innovation European Commission

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Properties and service performance
Industrial research and development

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• Sciences et techniques

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• Publié par: DIRECTORATE-GENERAL-FOR-RESEARCH-AND-INNOVATION-EUROPEAN-COMMISSION
• Nombre de lectures: 6
• Langue: English
• Poids de l'ouvrage: 4 Mo

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European Commission
technical steel research
Properties and service performance
Effect of temperature, stress and humidity on
the collapse characteristics of mechanically
fixed, welded and bonded assemblies
STEEL RESEARCH European Commission
technical steel research
Properties and service performance
Effect of temperature, stress and humidity on
the collapse characteristics of mechanically
fixed, welded and bonded assemblies
T. Jones, M. White
British Steel PLC — Welsh Technology Centre
Port Talbot
West Glamorgan SA13 2NG
United Kingdom
Contract No 7210-KC/812
1 July 1989 to 30 June 1992
Final report
Directorate-General XII
Science, Research and Development
1996 EUR 15838 EN LEGAL NOTICE
Neither the European Commission nor any person acting on
behalf of the Commission is responsible for the use which might be made of the
following information
Cataloguing data can be found at the end of this publication
Luxembourg: Office for Official Publications of the European Communities, 1996
ISBN 92-827-7201-2
© ECSC-EC-EAEC, Brussels • Luxembourg, 1996
Reproduction is authorized, except for commercial purposes, provided the source is acknowledged
Printed in Luxembourg SUMMARY
THE EFFECT OF TEMPERATURE, STRESS AND HUMIDITY ON THE COLLAPSE
CHARACTERISTICS OF MECHANICALLY FIXED, WELDED AND BONDED ASSEMBLIES
British Steel pic
ECSC Agreement No. 7210.KC/812
Final Summary Report
The need to reduce the weight of automotive assemblies to give improved fuel economy remains a major
driving force within the automotive industry. Weight reduction can only be achieved provided there is no
loss in the overall properties of the structure. The collapse resistance of box sections is an important
consideration in this context.
It was demonstrated that, for a low yield stress material, there is an optimum ratio between thè length of
the structure and the cross-sectional area which, when exceeded, leads to unstable collapse. Also for a
given section design, the primary factor governing both the radius and the number of folds obtained, at a
constant impact energy, is the cross-sectional area of the box. Changes in flange width, section length and
joining process did not lead to any significant change in either the number or radius of folds. The
positioning of triggers had little effect on the location of fold initiation.
The attachment of stiffeners to the vertical or horizontal webs of the box structure had little effect on
collapse resistance. In contrast, the attachment of right angled stiffeners to the corners of a structure led
to a significant enhancement in performance, allowing some potential for weight reduction. In addition,
the use of polyurethane foams led to a marked improvement in both the collapse resistance and stability of
collapse. Increasing the tensile strength of the steel led to a decrease in the amount of collapse and also led
to more stable collapse. There appeared to be a threshold value of yield stress to induce stable collapse
since instability was commonly observed at a yield stress of 164N/mm2 whereas a high level of stability
was observed for all steels of yield stress S 255 N/mm2.
Of the single joining techniques investigated, spot welding gave the best results with few welds failing,
even in the folded region, on impact. In contrast, rivets, press-formed joints and adhesives all failed in the
folded region during impact promoting high levels of instability and greater collapse. Use of hybrid
joining systems ie., weidbonding or riv-bonding led to an improvement in both the amount and stability of
collapse compared to any individual joining technique.
Temperature had a more profound effect on adhesive bonded than spot welded structures. At -40° C
adhesives performed in a brittle manner causing complete separation of the structure. Increasing the
temperature to 120°C led to a marked reduction in the modulus of the adhesive leading to a marked
reduction in collapse resistance. Where adhesives were used, a satisfactory performance was only
obtained over the full range of temperature when bonding was combined with spot welding. Similarly,
adhesive, bonded structures performed poorly after weathering in a range of environments, where again a
satisfactory performance was only obtained with weldbonded structures.
A theoretical technique was developed to describe the collapse behaviour of both closed top-hat and double
box-structures under both static and dynamic conditions of loading. The theoretical results were found to
be in reasonable agreement with those obtained experimentally.
Ill CONTENTS Page
1. INTRODUCTION 1
2. PROGRAMME OBJECTIVES 3
3. EXPERIMENTAL PROCEDURE 6
3.1 BST- Welsh Laboratories
3.2 Impact Research Centre-Liverpool University
3.3 Criteria for Assessment of Results 8
4. WORK AT BRITISH STEEL TECHNICAL-WELSH LABORATORIES 9
4.1 Effect of Steel Strength 9
4.2 Influence of Section Design 11
4.3e of Weld Pitch in Spot Welded Structures 12
4.4 Effect of Joining Technique3
4.4.1 Adhesive Bonded Structures4
4.4.2 Weldbonded Structures 16
4.4.3 Riveted Structures7
4.4.4 Combined Mechanical Fixing/Adhesive Bonding 18
4.5 Influence of Test Temperature 20
4.5.1 Spot Welded Structures
4.5.2 Adhesive Bonded Structures1
4.5.3 Riveted Structures 22
4.6 Influence of Triggers and Inserted Stiff eners 23
4.6.1 Effect of Triggers
4.6.2 Effect of Stiffening Ribs5
4.7 Influence of Weathering
4.8 Side Impact Testing
4.9 Influence of Foam/Honeycombe Filling
4.10 Properties of Simple Joints 37
5. LIVERPOOL UNIVERSITY-IMPACT RESEARCH CENTRE 39
5.1 Static Crushing of Closed Top-Hat Structures 3
5.2 Dynamic Axial Crushing of Closed Top-Hat Structures 41
V 5.2.1 Influence of Flange Width 42
5.2.2e of Specimen Length3
5.2.3 Influence of Tup Mass4
5.2.4 Collapse Profiles of Closed Top-Hat Structures 4
5.2.4.1 Regular Progressive Collapse from One End6
5.2.4.2 Regulare Collapse from Both Ends7
5.2.4.3 Irregular Collapse Modes 48
5.3 Static and Dynamic Tests of both Double Box-Hat and Square
Structures9
5.4 Adhesive Bonded Structures 51
5.5 Use of High Strength Steels
5.6 Theoretical Analysis of the Static and Dynamic Axial Crushing
of Spot Welded Closed Top-Hat and Double Box-Hat Structures 54
5.6.1 Introduction
5.6.2 Analytical Solution for A Closed Top-Hat Structure
5.6.2.1 Type 1 or Symmetric Collapse
5.6.3 Simplified Solution for Strain Hardening Materials 58
5.6.4 Final Expression for Mean Load
5.6.5 Example of Calculation for Closed Top-Hat Structure 63
5.6.6 Analytical Solution for a Double Box-Hat Structure4
5.6.6.1 Type 1 or Symmetric Collapse 6
5.6.6.2 Material Strain Rate Effects5
5.7 Discussion of Final Results6
6. DISCUSSION 68
6.1 Geometric Factors 70
6.2 Effect of Strain Rate2
6.3 Inserted Stiffeners and Foam/Honycombe Filling 73
6.4 Material Types4
6.5 Joining Process5
6.6 Mathematical Model 76
7. CONCLUSIONS
8. REFERENCE
VI LIST OF TABLES
I Mechanical Properties of Steels Investigated
II Influence of Steel Strength on Mode of Collapse of Spot Welded Structures of
varying Weld Pitch
IIIe of Section Size on Amount and Mode of Collapse
IV Details of Adhesives Investigated
V Influence of Adhesive Type on the Collapse Resistance of Closed Top-Hat Structures
in 1.2mm Mild Steel
VI Collapse Performance of Adhesive Bonded Double Box-Hat Structures
VII Influence of Foam Density on Collapse Resistance of Closed Top-Hat Structures
VIIIe of Foam Density on Side Impact Performance of Foam Filled Structures Fabricated
in 0.7mm Thick Sheet Steel
IX Influence of Joining Process on the Energy Absorbed during Impact Tests on 1.2mm Mild
Steel and Hot-Dip Zinc Coated Steel Lap Shear Joints
X T-Peel Strengths for the Various Adhesives Investigated
XI Results of Static Crushing Tests on both Closed Top-Hat and Double Box-Hat Structures of
Varying Flange Width
XIIs of Impact Tests on Closed Top-Hat Structures - Flange Width 10mm
XIII Results of Impact Tests on Closed Top-Hat Structures - Flange Width 15mm
XIVs of Impact Tests on Closed Top-Hat Structures - Flange Width 20mm
XV Results of Impact Tests on Closed Top-Hat Structures - Flange Width 25mm
XVI Dynamic Crush Test Results for Double Box-Hat and Square Tube Structures
XVII Static Crush Test Results for Double Box-Hat and Square Tube Structures
XVIIIc Crush Test Results for 'Non Standard' Closed Top Hat Structures
XIX Dynamic Crush Test Results for Closed Top-Hat Structures Fabricated using Different
Joining Techniques
VII LIST OF FIGURES
1. Typical Trace from 1000Hz Butterworth Low Pass Filter
2. Symmetrical Collapse Profile
3. Tearing of Corner of Box-Hat Structure
4. Dimensions of (a) Closed Top-Hat and (b) Double Box-Hat Structure
5. Comparison between % Collapse for Closed Top-Hat and Double Box-Hat Structures in both
Uncoated Mild Steel and Zinc Coated Steel (a)
6. Schematic of Mode of Collapse of Corner of Top-Hat Structure
7. Influence of Weld Pitch on the Collapse Resistance of Spot Welded Box-Hat Section i