Introduction to Adhesive Bonding

Eduardo A. S. Marques, Post-doctoral researcher, Institute of Science and Innovation in Mechanical and Industrial Engineering (INEGI), University of Porto, Portugal. Ana S. Q. F. Barbosa, Post-doctoral researcher, Institute of Science and Innovation in Mechanical and Industrial Engineering (INEGI), University of Porto, Portugal. Ricardo J. C. Carbas, Post-doctoral researcher, Institute of Science and Innovation in Mechanical and Industrial Engineering (INEGI), University of Porto, Portugal. Alireza Akhavan-Safar, Post-doctoral researcher, Institute of Science and Innovation in Mechanical and Industrial Engineering (INEGI), University of Porto, Portugal. Lucas F. M. da Silva, Full Professor and Director of the Integrated Master in Mechanical Engineering Program, Department of Mechanical Engineering, University of Porto, Portugal.

• Preface xi1 Benefits, Limitations, and Applications of Adhesive Bonding 11.1 Definition of Basic Concepts 21.2 Historical Context on Adhesive Bonding 31.3 Benefits and Limitations of Adhesive Bonding 41.4 Examples of Current Applications of Adhesive Bonding 81.4.1 Transportation 81.4.1.1 Aeronautical Industry 81.4.1.2 Road Transport and Rail Industry 111.4.1.3 Naval Industry 131.4.2 Civil Engineering 151.4.2.1 Tiling 151.4.2.2 Floor andWall Covering 151.4.2.3 Anchoring Systems 151.4.2.4 Building Facades 161.4.2.5 Wooden Construction 171.4.3 Labelling and Packaging Industry 181.4.3.1 Labelling of Consumable Products 181.4.3.2 Packaging 181.4.4 Medical Applications and Devices 191.4.5 Electronic Devices 231.4.6 Sport Equipment 231.4.7 Footwear 242 Principles of Adhesion 272.1 Forces Associated with Adhesion 282.2 Surface Roughness 312.3 Wettability 322.4 Adhesion and CohesionWork 352.5 Spreading 362.6 Adhesion Theories 372.6.1 Adsorption Theory 372.6.2 Mechanical Theory 382.6.3 Diffusion Theory 412.6.4 Electrostatic Theory 412.7 Defects andWeak Spots in Adhesive Joints 423 Surface Preparation 453.1 Objectives of Surface Preparation 453.2 Classes of Substrate Materials 473.2.1 Metals 473.2.2 Polymers 473.2.3 Composites 483.2.4 Other Materials 493.3 Surface Preparation Processes 493.3.1 Passive Processes 513.3.1.1 Passive Chemical Processes 513.3.1.2 Passive Mechanical Processes 553.3.2 Active Processes 593.3.2.1 Active Chemical Processes 593.3.2.2 Physical–Chemical Processes 623.3.3 Primers and Adhesion Promoters 653.4 Conservation of the Post-treatment Surface 674 Main Families of Adhesives and Adhesive Selection 694.1 Typical Composition of a Modern Adhesive 694.2 Methods for Adhesive Classification 704.2.1 Molecular Structure 704.2.1.1 Thermosets 714.2.1.2 Thermoplastics 714.2.1.3 Elastomers 724.2.1.4 Hybrid Materials 724.2.2 Physical Form 744.2.3 Mechanical Properties 744.2.4 Hardening and Implementation Method 754.2.4.1 Hardening by Chemical Reaction 754.2.4.2 Hardening via Physical Processes 764.2.4.3 Pressure-Sensitive Adhesives 764.2.5 Chemical Composition 774.3 Main Structural Adhesives 774.3.1 Epoxy Adhesives 774.3.2 Polyurethane Adhesives 784.3.3 Acrylic Adhesives 794.3.4 Phenolic Adhesives 804.3.5 Aromatic Adhesives 814.4 Main Non-structural Adhesives 814.4.1 Elastomeric Adhesives 814.4.2 Polyester Adhesives 824.4.3 Hot Melt Adhesives 824.4.4 Inorganic Adhesives 834.5 How to Select an Adhesive 834.5.1 Case Study: Adhesive Selection for the Automotive Industry 844.6 How to Test and Characterise an Adhesive 884.6.1 Mechanical Testing 884.6.1.1 Strength Tests 894.6.1.2 Fracture Tests 934.6.1.3 Testing Under Severe Environmental and Loading Conditions 984.7 Mechanical Properties of Adhesives 1025 Manufacture 1075.1 Adhesive Storage 1075.1.1 Storage Time 1085.1.2 Humidity 1095.1.3 Temperature 1095.1.4 Light and UV Radiation 1105.2 Adhesive Metering and Mixing 1105.2.1 Adhesive Metering 1115.2.2 Adhesive Mixing 1115.3 Adhesive Forms and Application 1145.3.1 Liquid Adhesives 1145.3.2 Paste Adhesives 1155.3.3 Film Adhesives 1165.3.4 Tapes 1175.4 Joint Assembly and Fixturing 1175.4.1 Moulds and Fixtures 1175.4.2 Adhesive Thickness Control 1195.4.3 Joint Assembly 1195.5 Adhesive Hardening 1205.5.1 Heat Curing Processes 1215.5.2 Evaporation-Based Processes 1255.6 Finishing Steps 1266 Quality Control 1276.1 Quality Control of the Incoming Materials 1286.1.1 Control of Adhesive Quality 1286.1.1.1 Mechanical Properties 1286.1.1.2 Viscosity 1286.1.2 Control of Adherend Quality 1296.1.2.1 Mechanical Properties 1296.1.2.2 Wettability, Contact Angle, and Surface Energy 1296.1.2.3 Surface Roughness 1316.2 Quality Control of the Manufacturing Process 1336.3 Quality Control on Bonded Structures 1376.3.1 Types of Defects Present in Bonded Joints 1376.3.2 Destructive Tests 1386.3.2.1 Proof Tests 1396.3.2.2 Fractography Analysis 1396.3.3 Non-destructive Tests 1416.3.3.1 Visual Inspection 1416.3.3.2 Tap Test 1426.3.3.3 Ultrasonic Test 1436.3.3.4 Acoustic Emission Test 1436.3.3.5 Radiography Test 1446.3.3.6 Eddy Current Test 1456.3.3.7 Thermal Infrared Method 1466.3.3.8 LambWave-Based Testing 1466.3.3.9 Electromechanical Impedance Spectroscopy 1466.3.3.10 Laser-Based Testing 1497 Environment, Health, and Safety 1517.1 Toxicity of Adhesives: Are Adhesives Really Toxic? 1537.2 General Precautions for Handling Adhesives 1537.2.1 Pictograms 1547.2.2 Training for Handling Adhesives 1577.2.3 Safety Eyewear 1587.2.4 Hand Protection – Gloves 1587.2.5 Safety Shoes 1597.2.6 Lab Coat 1597.2.7 Ventilation Systems 1597.3 Hazardous Characteristics of the Most Common Adhesives 1607.3.1 Structural Adhesives 1607.3.1.1 Epoxies 1607.3.1.2 Polyurethanes 1617.3.1.3 Acrylic Adhesives 1617.3.1.4 Phenolic Adhesives 1617.3.1.5 Aromatic Adhesives 1617.3.2 Non-structural Adhesives 1627.3.2.1 Synthetic Rubbers 1627.3.2.2 Polyesters 1627.3.2.3 Hot Melt Adhesives 1627.3.2.4 Inorganic Adhesives 1627.4 Surface Preparation Precautions 1627.5 Adhesive Application Precautions 1647.6 Environmental Protection 1647.6.1 Air 1657.6.2 Water 1657.6.3 Soil 1668 Design of Bonded Joints 1678.1 Main Loading Modes on Adhesive Joints 1688.2 Main Adhesive Joint Geometries 1698.3 Joint Strength Prediction Using Analytical Methods 1718.3.1 Determination of Stresses Acting on an Adhesive Joint 1728.3.2 Failure Criteria for Bonded Joints 1758.3.2.1 Failure in the Adhesive 1768.3.2.2 Failure in the Adherends 1778.4 Joint Strength Prediction Using Numerical Methods 1808.5 Parameters That Affect Joint Performance 1838.5.1 Effect of Adhesive Thickness 1838.5.2 Effect of Overlap Length 1848.5.2.1 Overlap Length and Adhesive Behaviour 1858.5.2.2 Overlap Length and Adherend Strength 1868.5.2.3 Overlap Length and Composite Adherends 1878.5.3 Effect of Temperature and Thermal Stresses 1878.6 Methods to Improve Joint Strength 1898.6.1 Adhesive Fillet 1898.6.2 Mixed Adhesive Joints 1908.6.3 Functionally Graded Joints 1908.6.4 Hybrid Joints 1918.7 Case Studies 1928.7.1 Case Study 1 – Effect of Adhesive Type on the Strength of Adhesive Joints 1928.7.2 Case Study 2 – Effect of Overlap Length and Adherend Type on the Strength of Adhesive Joints 1948.7.3 Case Study 3 – Effect of Adhesive Thickness on the Strength of Adhesive Joints 1978.7.4 Case Study 4 – Strength Prediction of Adhesive Joints with Composite Adherends 2018.7.5 Case Study 5 – Strength Prediction of an SLJ with Cohesive Zone Modelling 2058.7.6 Case Study 6 – Effect of Thermal Stresses on Adhesive Joints 2089 Durability of Adhesively Bonded Joints 2139.1 Environmental Effects 2149.1.1 Hygrothermal Ageing 2149.1.2 Temperature 2209.2 Loading Conditions 2219.2.1 Fatigue 2219.2.1.1 Total Fatigue Life (S–N) Approach 2239.2.1.2 Fatigue Crack Growth Approach 2259.2.2 Creep 22910 Case Studies 23510.1 Vehicle Construction 23510.2 Seat Fixation in Passenger Trains 23710.3 Aeronautical Applications 23910.4 Flexible Cooling Circuits 24110.5 Glass to Metal Bonding in Appliances 24310.6 Roof Coverings 24510.7 Shoe Manufacture 24610.8 Food Packaging 248Recommended Bibliography 251Referenced Bibliography 251Index 253