Adhesive Joints

Wulff Possart holds the Chair for Adhesion and Interphases in Polymers at the Saarland University in Saarbrücken, Germany. Having obtained his PhD in Physics from the Academy of Sciences of the GDR in Berlin and his habilitation from the University Potsdam, Germany, he spent most of his research career at the Academy of Sciences and the Fraunhofer Institute for Applied Materials Research in Bremen, Germany, before taking up his present professorship at the Saarland University.Professor Possart has authored more than 140 scientific publications in the fields of adhesion, polymer science, surface science and ageing. He has received prestigious scientific awards from the Adhesion Societies in the US, Great Britain and France as well as multiple guest professorships in France,the honorary professorship from the Heilongjiang Academy of Science and the visiting professorship at the Beijing University of Chemical Technology in China. Markus Brede is head of the department Materials Science and Mechanical Engineering at the Fraunhofer Institute for Applied Materials Research in Bremen, Germany. His main field of activity covers mechanics and mechanical behavior of adhesive joints with respect to design and lifetime of bonded structures. He has authored more than 70 papers related to mechanical behavior of adhesive joints. Markus Brede obtained his PhD in physics from the University of Göttingen and spent several years as a postdoctoral fellow at the Massachusetts Institute of Technology (Cambridge, USA) and the Max-Planck-Institute for Iron Research in Düsseldorf, Germany. At that time his main research interests included fracture and plasticity of silicon, inter-metallic alloys and the development of new iron-chromium-aluminum alloys with high temperature corrosion resistance.

• Preface xvSection A Initial State of Adhesive Joints 1A.1 Adhesion and Interphases: The Basic Ideas in Brief 3Wulff PossartA.1.1 Introductory Remarks and General Concepts 3A.1.2 Fundamental Adhesive Interactions – the Microscopic Origin and Further Concepts 4A.1.2.1 Physical Intermolecular Forces 4A.1.2.1.1 Bi-Molecular Interactions 5A.1.2.1.2 Physical Interactions Between Condensed Phases 9A.1.2.2 Chemical Adhesion Mechanisms 11A.1.2.2.1 A Brief Sketch of MO Theory 12A.1.2.2.2 An Extension to Macromolecules and Solids – the Electron Band Structure 13A.1.2.2.3 Chemical Reactions – General Aspects 14A.1.2.2.4 Chemical Adhesion Mechanisms in Reactive Epoxies on Inorganic Solids 16A.1.2.2.5 Chemical Adhesion Mechanisms in Reactive Polyurethanes on Inorganic Solids 18A.1.2.3 The Electrostatic Component of Adhesion 21A.1.2.3.1 Mobile Charge Carriers and the Electric Double Layer 22A.1.2.3.2 Continuum Model for the Electric Double Layer Built of Mobile Electrons 23A.1.2.4 Microscopic Adhesion Mechanisms – Co-action at the Phase Boundary 26A.1.2.5 Mechanical Interlocking 27A.1.3 The Interphase – Elemental State of the Adhesive–Adherend Phase Boundary 28A.1.3.1 Polymer Adhesives on Impenetrable Solids 28A.1.3.2 Polymerisation on Solids 32A.1.3.3 The Contact Between Viscoelastic Polymers 34A.1.4 Closing Remarks: Fundamental vs. Practical Adhesion 35References 36Further Readings 41A.2 Adhesive Network Formation: Continuum Mechanical Modelling and Simulation 43Gunnar Possart and Paul SteinmannA.2.1 Introduction 43A.2.2 Phenomenological Observations in Polymer Curing 44A.2.3 One-dimensional Linear Viscoelastic Curing at Small Strains 45A.2.4 Three-dimensional Linear Viscoelastic Curing at Small Strains 52A.2.5 Three-dimensional Curing at Large Strains 55A.2.5.1 Elastic Simulation Framework and Thermodynamic Consistency 55A.2.5.2 Elastic Neo-Hookean Curing Model 58A.2.5.3 Viscoelastic Simulation Framework 59A.2.5.4 Viscoelastic Neo-Hookean Curing Model 59A.2.5.5 The Consideration of Curing Shrinkage 64A.2.6 Material Parameter Evolutions During Curing 65A.2.6.1 Shear Modulus/Second Lamé Parameter 𝜇 66A.2.6.2 Poisson’s Ratio 𝜈 67A.2.6.3 Bulk Modulus 𝜅and First Lamé Parameter 𝜆 67A.2.6.4 Relaxation Time T 68A.2.6.5 Curing Shrinkage s 68A.2.6.6 Degree of Cure 68A.2.7 Epoxy–Ceramics Composite: Photoelasticity and Curing Shrinkage 69Bibliography 73A.3 Mechanical Interphases in Adhesive Joints: Characterisation Methods and FE-Simulations 79Gunnar Possart and Paul SteinmannA.3.1 Introduction 79A.3.2 High-Resolution Shear Testing by Scanning Electron Microscopy 84A.3.2.1 Specimen Preparation and Experimental Set-up 84A.3.2.2 Results and Discussion 88A.3.2.3 FE-Simulations of Adhesive Layers with Interphases 91A.3.2.3.1 Simulation Set-up and Mesh Dependency Study 92A.3.2.3.2 Elastic Interphases 97A.3.2.3.3 Elastoplastic Interphases 101A.3.2.4 Can Curing Shrinkage Fake Interphases? 106A.3.3 Nanoindentations Across Adhesive Joints 110A.3.3.1 Introduction and Experimental Data 110A.3.3.2 Determination of Stiffness and Hardness According to Oliver&Pharr 113A.3.3.3 FE-Simulations of Nanoindentations Across Adhesive Joints 114A.3.3.3.1 Simulation Set-up 114A.3.3.3.2 Results and Discussion 117A.3.4 Scanning Brillouin Microscopy 120A.3.4.1 Introduction and Experimental Set-up 120A.3.4.2 Results and Discussion 123A.3.5 Conclusions and Outlook 126Acknowledgements 128Bibliography 128A.4 Fracture Mechanics of Adhesive Joints 135Markus BredeA.4.1 Introduction 135A.4.2 Linear-elastic Fracture Mechanics 137A.4.3 Fracture in Materials with Energy Dissipation 143A.4.4 The Cohesive Zone Model and Fracture of Joints with Toughened Adhesives 145A.4.5 The Micro-structure of Toughened Adhesives 156A.4.6 Conclusions 161Acknowledgements 162References 162Section B Artificial Ageing and Failure of Adhesive Joints 167B.1 Ageing Phenomena in Polymers: A Short Survey 169Alexander Herzig, Michael Johlitz and Alexander LionB.1.1 What Is Ageing? A Brief Introduction to the Deterioration of Polymers 169B.1.2 Different Types of Polymer Ageing 171B.1.3 Experimental Investigations on the Ageing Behaviour of Polymers 181B.1.4 Influence of Ageing on the Properties of Polymers 191References 200B.2 Continuum Modelling of Ageing Adhesive Joints 205Stefan Diebels, Florian Goldschmidt and Frederik ScherffB.2.1 Outline 205B.2.2 Continuum Mechanics of Single-phase Materials 206B.2.2.1 Kinematics 206B.2.2.2 Balance Equations 211B.2.2.3 Constitutive Equations 214B.2.2.4 Viscoelasticity 217B.2.2.5 Example 220B.2.3 Additional Fields 222B.2.3.1 Diffusion of Tracers 223B.2.3.2 Formation of Interphases 225B.2.4 Summary 226References 226B.3 Crack Growth in Adhesive Joints: Balance of Energy for Mode I Crack Propagation 229Olaf Hesebeck, Udo Meyer, Andrea Sondag and Markus BredeB.3.1 Introduction 229B.3.1.1 Dissipation in TDCB Tests 230B.3.1.2 New Approach 232B.3.2 Estimate of Plastic Work Using Finite Element Simulation 233B.3.2.1 Aim 233B.3.2.2 Tensile Tests and Material Model 234B.3.2.3 Choice of Modelling Method 237B.3.2.4 Simulation and Evaluation of Plastic Strain Energy 238B.3.2.5 Evaluation of TDCB Test Results Using the Simulation 244B.3.3 TDCB Tests with Infrared Camera 248B.3.3.1 Aim and Measurement Principle 248B.3.3.2 Experimental Observations 249B.3.3.3 Thermo-Elastic Effect 254B.3.3.4 Estimate of Generated Heat 256B.3.4 Discussion 258B.3.4.1 Estimate of Energy Balance 258B.3.4.2 Limits of Method and Possible Extensions 259B.3.5 Summary 262Acknowledgement 262References 262B.4 Joints with a Basic Epoxy Adhesive: Ageing Processes 265Léo Depollier, Jesus Ernesto Huacuja-Sánchez and Wulff PossartB.4.1 Introduction 265B.4.2 Experimental Strategy 266B.4.2.1 Basic Epoxy Adhesive 266B.4.2.2 Metal Substrates 268B.4.2.3 Sample Preparation 268B.4.2.3.1 Bulk Specimens 268B.4.2.3.2 Adhesive Joints 268B.4.2.3.3 Epoxy Curing Protocol 269B.4.2.3.4 Caloric Glass Transition in Cured EP65:35 270B.4.2.4 Conditions of Artificial Ageing 271B.4.3 Water Diffusion in EP Bulk and Adhesive Joints 273B.4.3.1 Diffusion in Basic Epoxy EP65:35 273B.4.3.2 Water Concentration Profiles in Adhesive Joints 278B.4.4 Mechanical Properties of Fresh and Aged Adhesive Joints 279B.4.4.1 Tensile Tests for Dry Epoxy Bulk Samples 279B.4.4.2 Shear Tests for Freshly Bonded Joints 280B.4.4.3 Bonded Sample Stiffness and Glass Transition During Ageing 286B.4.5 Chemical Ageing Processes 288B.4.5.1 De-bonding due to Corrosion of the Metal Substrates 288B.4.5.2 Chemical Ageing in Metal Joints Bonded with Basic Adhesive EP65:35 291B.4.5.3 Chemical Ageing in EP65:35 Bonded Joints – Liquid Water Versus Moist Air 297B.4.5.4 The Role of the Metal Surface 298B.4.6 Chemical Ageing Versus Physical Plasticisation 299B.4.7 Basic Epoxy Versus Commercial Epoxy Adhesives 300B.4.8 Summary and Conclusions 304Acknowledgement 306References 306B.5 Steel Joints with a Basic Polyurethane Adhesive – Ageing Processes 309Jesus E. Huacuja-Sánchez, Philipp Engel and Wulff PossartB.5.1 Introduction 309B.5.2 PU Adhesive and Sample Preparation 313B.5.2.1 Monomer Mix for the Basic PU Adhesive 313B.5.2.2 PU Bulk Samples and PU–Steel Adhesive Joints 314B.5.3 Artificial Ageing Conditions 314B.5.4 Ageing of Bulk Polyurethane Adhesive PU9010 in Water 315B.5.4.1 Chemical Ageing 315B.5.4.1.1 The Virgin PU9010 Network 316B.5.4.1.2 The Ageing PU9010 Bulk 323B.5.4.1.3 Summary: Chemical Ageing in PU9010 Bulk at Moderate Conditions 329B.5.4.2 Physical Ageing of PU9010 Bulk Samples 330B.5.5 Ageing in Adhesive Joints PU9010–Corundum Blasted Mild Steel S235 331B.5.5.1 Water Diffusion in the Adhesive Joint 331B.5.5.2 Chemical Ageing in the Adhesive Joint 331B.5.5.2.1 Corrosive Attack on the Corundum Blasted Steel in the Adhesive Joint 333B.5.5.2.2 Chemical Ageing of PU9010 in the Adhesive Joint with Steel S235 335B.5.5.3 Physical Ageing in the Adhesive Joint PU9010–Corundum Blasted Steel S235 336B.5.5.3.1 Caloric Glass Transition in the Adhesive Joint 337B.5.5.3.2 Mechanical Modulus in the Adhesive Joint – Evolution During Artificial Ageing 338B.5.6 Conclusions 346Acknowledgement 348References 348B.6 Viscoelasticity in Ageing Joints – Experiments and Simulation 355Florian Goldschmidt, Stefan Diebels, Frederik Scherff, Léo Depollier, Jesus Ernesto Huacuja-Sanchez and Wulff PossartB.6.1 Motivation 355B.6.2 Transport Processes in Adhesives 355B.6.2.1 Fick’s Law of Diffusion 356B.6.2.2 Langmuir-type of Diffusion 356B.6.3 Constitutive Equations 358B.6.3.1 Temperature 359B.6.3.2 Water in the Adhesive 360B.6.3.3 Chemical Ageing 361B.6.3.4 Size Effects 362B.6.3.5 Damage Evolution Model 363B.6.4 Data Evaluation and Results 364B.6.4.1 Data Evaluation 365B.6.4.2 Results – Polyurethane Adhesive 366B.6.4.2.1 Basic Elasticity 366B.6.4.2.2 Viscoelasticity 367B.6.4.3 Results – Epoxy Adhesive 371B.6.5 Summary 372References 373B.7 On the Energy Release Rate of Aged Adhesive Joints 375Markus Brede, Andrea Sondag, Olaf Hesebeck and Barbara SchneiderB.7.1 Introduction 375B.7.2 Experimental and Definitions 376B.7.3 Ageing of Polyurethane Adhesive Joints 385B.7.4 Ageing of Epoxy Adhesive Joints 394B.7.5 Summary and Conclusions 403Acknowledgements 404References 404B.8 Cohesive Zone Model for Moist Adhesive Joints 405Olaf Hesebeck, Florian Goldschmidt and Stefan DiebelsB.8.1 Introduction 405B.8.2 Transfer from Continuum to Cohesive Zone Model 406B.8.2.1 Viscoelasticity 407B.8.2.2 Damage Behaviour 409B.8.2.3 Validation 411B.8.2.3.1 Tensile Tests of Butt Joints 411B.8.2.3.2 Validation of the Viscoelastic Model 413B.8.2.3.3 Validation of Transfer to Cohesive Zone Model and Damage Model 416B.8.3 Simulation of Diffusion 418B.8.3.1 Finite Element Simulation of Diffusion 418B.8.3.2 Closed-Form Solutions of Diffusion 419B.8.4 Automation of Model Extension 420B.8.4.1 Procedure 420B.8.4.2 Application Tests 422B.8.4.3 Extensibility 423B.8.5 Summary 424Acknowlegdement 425References 425Section C Weathering of Adhesive Joints and Life Time Prediction 427C.1 Adhesive Application Under High-power Ultrasound: Effects on Durability 429Barbara Schneider, Jens Holtmannspötter, Markus Spallek and Jürgen von CzarneckiC.1.1 A Power Ultrasound Process for Contamination-tolerant Adhesive Application on Critical Surfaces 429C.1.2 Effects of Power Ultrasound 431C.1.2.1 Cavitation 431C.1.2.2 Viscosity Changes 432C.1.3 Determination of the Cleaning Behaviour by Power Ultrasound 433C.1.3.1 Experimental 433C.1.3.2 Weakening of Adhesion by an Applied Contamination 433C.1.3.3 Effect of the Contamination on the Surface Free Energy 434C.1.3.4 Adjustment of the Ultrasonic Process 436C.1.3.5 Results of Mechanical Testing (Single Lap Shear Test) 437C.1.3.6 Cleaning and Improvement of the Ageing Resistance by Using Power Ultrasound 438C.1.3.7 Effects of Ultrasonic Treatment on the Adhesive Assessed by EIS 439C.1.4 Application 442C.1.4.1 Ultrasound-Assisted Primer Application 442C.1.4.2 Automated Removal of Release Agents from Reinforced Plastics by Power Ultrasound 444C.1.5 Summary 446References 447C.2 Long-term Behaviour of Adhesively Bonded Timber–Concrete Composites 449Werner Seim and Lars EisenhutC.2.1 Introduction 449C.2.2 Hygro-thermal Impact 450C.2.3 Numerical Description of Hygro-thermal Phenomena 452C.2.3.1 Material Models 453C.2.3.2 Mechanical Material Properties 454C.2.3.3 Moisture Transport in Wood 457C.2.4 Experimental Studies 459C.2.4.1 Small-scale Samples Under Artificial Climatic Conditions 460C.2.4.2 Full-scale Specimens Under Natural Climatic Conditions 463C.2.5 Model Validation 464C.2.5.1 Wood Moisture Content 464C.2.5.2 Deflection of the Full-scale Specimens 465C.2.6 Summary and Conclusion 467References 467C.3 Adhesive as a Permanent Shear Connection for Composite Beams 471Wolfgang Kurz, Markus Kludka, Ruben Friedland and Paul-Ludwig GeißC.3.1 Materials 472C.3.2 Description of the Small-scale Specimens 473C.3.2.1 Steel–Steel Connection 473C.3.2.2 Concrete–Concrete Connection 474C.3.2.3 Steel–Concrete Connection 474C.3.3 Ageing of Lap Shear Specimens 475C.3.3.1 Outdoor Weathering 475C.3.3.2 Accelerated Ageing 475C.3.4 Test Results 476C.3.4.1 Epoxy Adhesive Hilti HIT-RE 500 476C.3.4.1.1 Steel–Steel Specimens 477C.3.4.1.2 Concrete–Concrete Specimens 477C.3.4.2 Polyurethane Adhesive Körapur 666/90 479C.3.5 Large-scale Composite Beams 481C.3.5.1 Testing of the Composite Beams 481C.3.5.2 Test Procedure of the Large Specimens 481C.3.5.3 Test Results of the Composite Beams 483C.3.5.4 Evaluation of the Test Results 484C.3.5.4.1 Evaluation of the Strain Gauges 486C.3.6 Analytical Calculation of the Adhesive Stress in Composite Beams 487C.3.6.1 Effect of the Joint Compliance on the Load–Deformation Behaviour of Composite Beams 490C.3.6.2 Transferability of Small-scale Test Results on Large Components 491C.3.6.3 Analytical Determination of the Deformation Behaviour of Composite Beams in View of an Accelerated Ageing of Adhesives 492C.3.6.4 Analytical Determination of the Tested Composite Beam Results 494C.3.6.5 Complementing the Segment Method by the Method of Lamellae 496C.3.7 Conclusions 498References 498C.4 Concluding Remarks 501Wulff Possart, Stefan Diebels and Markus BredeIndex 513