Adhesive Joints: Ageing and Durability of Epoxies and Polyurethanes

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

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