Contents INTRODUCTION 1 Part 1 Structure Design Basis for Wind Turbine Blade Chapter 1 BASIC PRINCIPLES 9 1.1 DESIGN COORDINATION 9 1.2 DESIGN BASIS 12 1.3 STRUCTURE DESIGN 13 1.4 STRUCTURE WEIGHT AND COST CONTROL 15 Chapter 2 COMPOSITE BASIS 17 2.1 BLADE COMPOSITE STRUCTURE COMPONENTS 21 2.2 BLADE STRUCTURAL MATERIAL 25 2.3 REINFORCED FIBRE 25 2.4 RESIN 27 2.5 OTHER STRUCTURAL MATERIALS 28 2.6 MATERIAL SELECTION 30 2.7 MECHANICAL TEST OF COMPOSITES 30 2.7.1 Testing Techniques of Composites 30 2.7.2 Test Process of Composites 34 2.8 MANUFACTURABILITY OF COMPOSITES FOR BLADE 36 Chapter 3 STRUCTURE DESIGN BASIS 43 3.1 DESIGN BASIS 43 3.1.1 Airfoil Contour 43 3.1.2 Load Characteristics 45 3.1.3 Load-carrying Forms 57 3.2 CONFIGURATION DESIGN 59 3.3 STRUCTURE DESIGN PROCESS 61 Part 2 Structure Design for Wind Turbine Blade Chapter 4 STRUCTURAL COMPONENT DESIGN 67 4.1 SPAR CAP DESIGN 67 4.1.1 Configuration Categories for Spar Cap 70 4.1.2 Spar Cap of Glass-fibre Fabric 72 4.1.3 Spar Cap of Carbon-fibre Fabric 74 4.1.4 Spar Cap of Laminated Bamboo-wood 76 4.1.5 Spar Caps Made of Mixed Material 78 4.1.6 Structure Design for Spar Caps 78 4.1.7 Spar Cap Manufacturing Process Description 79 4.2 DESIGN OF WEB AND FLANGE ADHESIVE BONDING 83 4.2.1 Web Configuration Types 84 4.2.2 Web Arrangements 88 4.2.3 Web Structure Design 89 4.2.4 Prospect of Web Processing 96 4.3 SKIN DESIGN 96 4.3.1 Configuration Design for Skin 97 4.3.2 Summary of Skin Process 98 4.4 SANDWICH STRUCTURE DESIGN 99 4.4.1 Sandwich Structure Configurations 101 4.4.2 Sandwich Structure Design 101 4.4.3 Summary of Sandwich Structure Processes 104 4.5 LEADING EDGE UD DESIGN AND LEADING EDGE ADHESIVE BONDING 105 4.5.1 Structure Design for Leading edge UD 106 4.5.2 Adhesive Bonding Forms 108 4.6 TRAILING EDGE UD DESIGN AND TRAILING EDGE ADHESIVE BONDING 108 4.6.1 Design for Trailing Edge UD Configuration 109 4.6.2 Structure Design for Trailing Edge 111 4.6.3 Summary of Trailing Edge Processing 119 4.7 ROOT REINFORCEMENT DESIGN 121 4.7.1 Structure Design for Root Reinforcement 121 4.7.2 Process Overview of Blade Root Reinforcing Layer 122 4.8 CONNECTION DESIGN OF BLADE ROOT 123 4.8.1 Different Method for Mounting Bolt 124 4.8.2 Configuration Design of Embedded Bolts 126 4.8.3 Structure Design for Embedded Bolts 130 4.8.4 Structure Design for T-bolt 137 4.8.5 Overview of Blade Root Process Test 138 4.9 DISCUSSION ABOUT OPTIMIZATION DESIGN 138 4.9.1 Influence of Optimization and Non-optimization 138 4.9.2 Structure Index 138 Chapter 5 DESIGN OF FUNCTIONAL PARTS 140 5.1 BLADE TIP DESIGN 140 5.2 LIGHTNING PROTECTION DESIGN 140 5.2.1 Air-termination System 142 5.2.2 Lightning Protection Tests on Blades 143 5.3 GEL COATS AND PAINTS 144 5.4 DESIGN OF REINFORCED LAYERS FOR TRANSPORTATION 145 5.5 BLADE ROOT COVER DESIGN 145 5.6 DESIGN OF BALANCING CHAMBERS 146 5.7 RAIN DEFLECTOR DESIGN 146 5.8 PE PIPES CONNECTED WITH DOUBLE WEBS 147 5.9 OTHER DESIGNS 147 Part 3 Structure Design Methods for Wind Turbine Blade Chapter 6 STRUCTURE VERIFICATION PRINCIPLES 151 6.1 GENERAL PRINCIPLES OF STRUCTURE VERIFICATION 152 6.2 BLADE STRUCTURE VERIFICATION METHODS 152 6.3 GENERAL INTRODUCTION OF BLADE STRUCTURE VERIFICATION 154 6.3.1 Blade Topological Graph 154 6.3.2 Stress Characteristics of Blade Components 154 6.4 STRENGTH ANALYSIS 157 6.5 STABILITY ANALYSIS 157 6.6 DEFORMATION ANALYSIS 161 6.7 DYNAMIC CHARACTERISTIC ANALYSIS 162 6.8 ADHESIVE BONDING ANALYSIS 162 6.9 INTERLAMINAR ANALYSIS 162 6.10 FATIGUE ANALYSIS 163 6.11 ADVANCED ANALYSIS 164 Chapter 7 UNIDIMENSIONAL METHOD 165 7.1 I-BEAM THEORY 165 7.2 SIMPLIFICATION OF BLADE CROSS SECTION MODEL 168 7.3 CALCULATION OF BLADE CROSS SECTION STRENGTH 171 7.4 STRENGTH ANALYSIS OF BLADE CROSS SECTION 174 7.5 CALCULATION OF BLADE BENDING DEFORMATION 175 7.6 DEFLECTION ANALYSIS OF BLADE SECTION 177 7.7 DEVIATION ANALYSIS WITH UNIDIMENSIONAL METHOD 177 7.8 APPLICATION DEVELOPMENT OF UNIDIMENSIONAL METHOD 181 Chapter 8 2D METHOD 183 8.1 BLADE STRENGTH CALCULATION 184 8.1.1 Normal Stress Calculation of Thin-walled Airfoil Structure 184 8.1.2 Shear Stress Calculation of Thin-walled Airfoil 190 8.1.3 Calculation of Blade Deflection 197 8.2 CALCULATION OF BLADE NATURAL FREQUENCY AND CHARACTERISTIC MODE 201 8.3 EQUIVALENT FATIGUE LOAD METHOD FOR FATIGUE DAMAGE CALCULATION 203 8.4 2D ENGINEERING ALGORITHM 204 8.5 FINITE ELEMENT METHOD OF 2D UNIFORM CROSS SECTION 206 8.5.1 Finite element analysis of 2D shell model 206 8.5.2 Finite element verification of 2D solid model 209 Chapter 9 3D METHOD 211 9.1 FINITE ELEMENT ANALYSIS OF WIND TURBINE BLADES 212 9.2 FINITE ELEMENT MODELING OF BLADES 212 9.2.1 Geometrical Shape 213 9.2.2 The Coordinate System 214 9.2.3 Structural Configuration 216 9.2.4 Meshing 216 9.2.5 Element Normal and Element Coordinate System 218 9.2.6 Material Properties 219 9.2.7 Direction of Material 220 9.2.8 Spanwise Divisions 220 9.2.9 Element Properties 220 9.2.10 Mass of a Blade 222 9.3 LOCAL REFINEMENT OF BLADE FINITE ELEMENT MODEL 223 9.3.1 Refinement of TE Model 223 9.3.2 Adhesive Bonding of Web Flange and Shell 224 9.3.3 Blade Root Model 224 9.3.4 Adjacent Component of Root Model 225 9.3.5 Point Mass of Blade 225 9.4 FINITE ELEMENT BOUNDARY AND LOADING OF BLADE 226 9.4.1 Finite Element Boundary Conditions 226 9.4.2 Ultimate Loading Form in Blade FEA 226 9.4.3 Ultimate Envelop Load 227 9.4.4 Concentrated Force Ultimate Loading 230 9.4.5 Distributed Ultimate Loading 231 9.4.6 Loading Type of Test Load 240 9.4.7 Gravitational Load 243 9.4.8 Fatigue Load 243 Chapter 10 OTHER METHODS 244 10.1 PROCEDURE OF BLADE MOULDING 244 10.2 BLADE DATABASE 244 Part 4 Structure Component Design Methods for Wind Turbine Blade Chapter 11 BASIC VERIFICATION ANALYSIS 249 11.1 BASIC VERIFICATION OF BLADE 249 11.2 SAFETY FACTOR OF STRUCTURE VERIFICATION 250 11.2.1 Safety Factor of Structure Verification Defined in GL 2010 250 11.2.2 Safety Factor of DNV Structure Verification 252 11.3 STRENGTH VERIFICATION 254 11.3.1 Failure Criterion 254 11.3.2 Overall Ultimate Strength Verification 255 11.3.3 Strength Verification of Hoisting Condition 256 11.4 STIFFNESS VERIFICATION 259 11.4.1 Criterion of Deflection Analysis 259 11.4.2 Stiffness Distribution 260 11.4.3 Tip Deflection 261 11.5 ANALYSIS OF VIBRATION CHARACTERISTICS 262 11.5.1 Natural Frequency and Mode of Vibration 262 11.5.2 Campbell Chart of Blade Vibration 266 11.6 OVERALL BUCKLING OF BLADE 270 Chapter 12 LAMINATE ANALYSIS 272 12.1 THEORY OF LAMINATE 272 12.1.1 The Theory of Shell Theory to Composite Material 273 12.1.2 Feature of Laminate 275 12.1.3 Performance and Stiffness of Laminate 276 12.1.4 The Strength Analysis of Laminate 279 12.1.5 The Design Value for Structure 280 12.2 DESIGN OF LAMINATE 281 12.2.1 The Stiffness Prediction and Design of Laminate 281 12.2.2 Preliminary Design of Laminate 282 12.2.3 Consideration of Environmental Influence 282 12.3 BUCKLING OF THE LAMINATE 283 12.3.1 Buckling Calculation Method 284 12.3.2 Boundary Conditions 286 12.3.3 Examples of Theoretical Solution 286 12.3.4 Engineering Algorithm 290 12.3.5 FEM Example 292 12.3.6 FEA of Laminate 293 12.4 FIBRE FAILURE ANALYSIS 294 12.5 RESIN FAILURE ANALYSIS 296 12.6 APPLICATION OF LAMINATES ON BLADES 300 Chapter 13 ANALYSIS OF SANDWICH STRUCTURE 302 13.1 BASIS OF SANDWICH STRUCTURE 302 13.2 SANDWICH STRUCTURE DEAIGN 303 13.2.1 Design Principle of Sandwich Structure 303 13.2.2 Design Key Points 304 13.3 ANALYSIS OF SANDWICH STRUCTURE 304 13.3.1 Basic Parameters 304 13.3.2 Analysis of Local Failure 305 13.4 ANALYSIS METHODS OF SANDWICH STRUCTURE 307 13.4.1 Sandwich with Isotropic Panels 307 13.4.2 Sandwich with Orthotropic Panels 315 13.4.3 Engineering Algorithm of Local Instability 316 13.4.4 Finite Element Analysis 318 13.4.5 Local Secondary Analysis Method 319 13.5 APPLICATION OF SANDWICH STRUCTURE ON BLADES .320 13.6 ANALYSIS OF WEB BUCKLING 320 13.7 ANALYSIS OF BLADE LOCAL BUCKLING 325 13.8 BUCKLING ANALYSIS OF BLADE CROSS SECTION 327 Chapter 14 ANALYSIS OF ADHESIVE BONDING 328 14.1 ADHESIVE BONDING 328 14.1.1 Adhesive Characteristics 329 14.1.2 Advantages and Disadvantages of Composite Bonding 330 14.2 DESIGN OF ADHESIVE BONDING 332 14.2.1 General Design Principles 332 14.2.2 Basic Failure Modes 332 14.2.3 Basic Bonding Methods 333 14.2.4 Selection of Geometric Parameters 334 14.2.5 Fibre Direction 336 14.2.6 Design of Bonding Detail 337 14.3 BONDING ENGINEERING ALGORITHM 338 14.3.1 Calculation of Static Strength 338 14.3.2 Durability Analysis 342 14.4 ANALYSIS OF ADHESIVE BONDING 343 14.5 ADHESIVE BONDING APPLICATION ON BLADE 345 14.5.1 Bonding between Web Flanges and Shells 346 14.5.2 Bonding of Trailing Edge 347 14.5.3 Control of Bonding Processing 348 Chapter 15 ANALYSIS OF BOLTED CONNECTION 349 15.1 STRUCTURE VERIFICATION OF BLADE ROOT WITH MBEDDED INSERTS 350 15.1.1 Types of the Root End 350 15.1.2 Global Finite Element Analysis 354 15.1.3 Local Analysis of Contact Surface 359 15.2 STRUCTURE VERIFICATION OF T-BOLT PROCESSING 369 15.2.1 Structure Analysis Procedure 369 15.2.2 Global Finite Element Analysis 370 15.2.3 Bolt Engineering Method 372 Part 5 Special Subject for Structure Design of Wind Turbine Blade Chapter 16 FATIGUE ANALYSIS 377 16.1 THEORETICAL BASIS 377 16.1.1 Cyclic Load 378 16.1.2 Fatigue Lifetime 379 16.1.3 Stress ratio 379 16.1.4 S-N curve 381 16.1.5 Diagram of Fatigue Limit 381 16.2 FATIGUE OF COMPOSITES 383 16.2.1 Model of fatigue accumulated damage 384 16.2.2 Estimation Method of Fatigue Lifetime 386 16.3 VERIFICATION PROCESS OF BLADE FATIGUE 387 16.4 FATIGUE LOAD 389 16.5 SELECTION OF CRITICAL POINT OF FATIGUE 389 16.6 METHODS OF BLADE FATIGUE VERIFICATION 391 16.6.1 Coordinate System 392 16.6.2 Transformation Matrix of Stress 392 16.6.3 Equivalent Stress 393 16.6.4 Rain-flow Counting 394 16.6.5 Safety Factor of Fatigue Analysis 396 16.7 IDENTIFICATION OF BLADE FATIGUE DAMAGE 397 Chapter 17 ANALYSIS OF IMPACT RESISTANCE OF BLADE 399 17.1 ANALYSIS TECHNIQUES OF IMPACT DAMAGE 400 17.1.1 Methods of Engineering Analysis 401 17.1.2 Techniques of Load Processing 402 17.2 METHODS OF EXPLICIT TIME INTEGRATION 404 17.3 CONSTITUTIVE RELATION OF MATERIAL 405 17.3.1 Material of Bird-model Impact 405 17.3.2 Material of Hail Impact 405 17.4 VERIFICATION OF RESISTANCE FOR IMPACT OF BLADE 406 17.4.1 Impact-resistance Model of Blade 407 17.4.2 Analysis of Blade Resistance for Impact 407 17.5 TEST OF BLADE RESISTANCE FOR IMPACT 408 Chapter 18 ANALYSES OF FRACTURE MECHANICS AND INTER LAMINAR 409 18.1 FRACTURE ANALYSIS of COMPOSITE MATERIALS 409 18.2 MAIN PARAMETERS IN FRACTURE MECHANICS 410 18.3 FRACTURE MECHANICS CALCULATION METHOD 411 18.3.1 Theoretical Solution of a Center Cracked Finite Width Plate 411 18.3.2 The Stress Intensity Factor and Extrapolation 412 18.3.3 Domain Method J-integration and Equivalent Integration 417 18.3.4 Strain energy release rate and virtual crack method 419 18.4 DUMMY NODE FRACTURE ELEMENT 420 18.4.1 Dummy Node Fracture Element of Linear Crack 420 18.4.2 Dummy Node Fracture Element of a Plane Crack 424 18.5 INTERLAMINAR STRESS OF COMPOSITES 427 18.5.1 Shear Stress Distribution of Interlaminar Interface 430 18.5.2 Interlaminar Shear Stress Distribution Along Thickness Direction 431 18.5.3 Interlaminar Normal Stress 431 18.5.4 Distribution of Axial Displacement on the Surface of Laminates 432 18.6 INTERLAMINAR FAILURE AND FRACTURE FAILURE OF BLADE 433 Chapter 19 RELIABILITY ANALYSIS 434 19.1 COMPOSITES DAMAGE TOLERANCE 434 19.1.1 Overview 434 19.1.2 Three Elements of Damage Tolerance 435 19.2 RELIABILITY 437 19.2.1 Technical Basis of Reliability 438 19.2.2 Reliability Evaluation Index 439 19.2.3 Reliability Design of Structural System 440 Chapter 20 FULL-SCALE TESTING OF BLADES 442 20.1 OVERVIEW 442 20.2 MATERIAL TESTING AND COMPONENT TESTING 442 20.3 INTRODUCTION OF FULL-SCALE TESTING OF BLADES 445 20.3.1 Basic Principle and Relevant Standards 445 20.3.2 Test Items and Procedures 445 20.4 BLADE DATA AND REQUIREMENTS FOR SPECIMENS 446 20.4.1 Blade Data 446 20.4.2 Requirements for Specimens 447 20.5 TEST STAND 447 20.5.1 Loading Directions 447 20.5.2 Loading Types 448 20.5.3 Other Devices and Tooling 449 20.6 DESIGN LOAD AND TEST LOAD 452 20.7 FAILURE MODES 452 20.8 MASS AND DYNAMIC PROPERTY TESTS 453 20.9 STATIC STRENGTH TEST 454 20.10 FATIGUE TEST 457 20.11 DESTRUCTIVE TEST 458 Chapter 21 SUMMARY AND PROSPECT 459 21.1 DESIGN AND PROCEDURES 459 21.2 VERIFICATION AND EXPERIENCE 461 21.3 HORIZONS BEYOND DESIGN AND VERIFICATION 462 21.4 PROSPECTS FOR THE FUTURE 463 21.5 BACK TO THE ORIGIN-STRUCTURAL MECHANICS OF COMPOSITE THIN-WALLED BARS 468 REFERENCES 470 Appendix A COORDINATE SYSTEM 472 Appendix B BLADE WB45.3 475 INDEX 477
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