Delamination in Wood, Wood Products and Wood-Based Composites (eBook)

Foreword 5
Preface 7
Acknowledgements 9
Contents 10
Contributors 12
Part I General Aspects 14
1 Introduction 15
1.1 Background 15
1.2 Solid Wood 17
1.3 Wood-Based Composites 21
1.4 Summary 24
References 25
2 Terms for Delamination in Wood Science and Technology 29
2.1 General Terms 29
2.2 Terms for Delamination in Solid Wood 30
2.3 Terms for the Delamination in the Cell Wall 31
2.4 Terms for the Delamination in Laminated Wood Products 31
2.5 Terms for the Delamination in Wood-Based Fibre and Particle Panels 37
2.6 General Classification of Delamination 38
2.7 Summary 41
References 41
3 Delamination Detection -- A Vibration-Based Approach 44
3.1 Introduction 44
3.2 Delamination Detection with an Ultrasonic Technique 44
3.3 Delamination Detection with a Model-Based Method 49
3.3.1 Linear Behavior 49
3.3.2 Nonlinear Behaviour 51
3.4 Some Practical Aspects 55
3.5 Summary 56
References 57
4 Initiation and Growth of Delamination in Wood and Wood-Based Composites, a Fracture Mechanics Approach 62
4.1 Introduction 62
4.2 Links with Fracture Mechanics 63
4.2.1 Linear Elastic Fracture Mechanics 71
4.2.2 Nonlinear Fracture Mechanics 83
4.3 Micro-structural Aspects in Wood 90
4.4 Micro-structural Aspects in Wood-Based Composites 95
4.5 Fracture Mechanics Parameters for Ecological Relevance 102
4.6 Summary 102
References 103
5 A Theoretical Model of Collapse Recovery 112
5.1 Introduction 112
5.2 Repeating Cell Unit Model with Cyclical Constrains 113
5.2.1 Cell Wall Layer Properties 113
5.2.1.1 Viscoelastic Material Model (S1, and S3) 114
5.2.1.2 The Non-linear (Elastic plastic) Material Properties (S2, and CML) 115
5.2.2 Circular Based Cell Model 115
5.2.3 Squared Based Cell Model 117
5.3 Summary 129
References 130
Part II Methodology for Delamination Detection and Factors Inducing and Affecting Delamination 131
6 Delamination of Wood at the Microscopic Scale: Current Knowledge and Methods 132
6.1 Anatomical Features of Wood Delamination 133
6.1.1 Weathering and Decay 135
6.1.2 Internal and Intra-Ring Checking 137
6.1.3 Resin Pockets 137
6.1.4 Shelling 137
6.1.5 Reaction Wood 138
6.1.6 Induced Delamination 139
6.2 Ultrastructural Features of Cell Wall Delamination 139
6.2.1 Ultrastructure of Wood Cell Walls 139
6.2.2 Location of Cell Wall Delamination 140
6.2.3 Mechanism of Delamination 143
6.2.4 Influence of Microfibril Angle 143
6.2.5 Influence of Delignification and Pulp Refining 144
6.2.6 Influence of Species 144
6.2.7 Influence of Moisture Content 145
6.2.8 Influence of Temperature 146
6.3 Microscopic Methods for Evaluation of Delamination in Wood 146
6.3.1 Light Microscopy 146
6.3.2 Confocal Microscopy 147
6.3.3 Electron Microscopy 147
6.4 Summary 148
References 148
7 Probing the Wood Coating Interface at High Resolution 154
7.1 Introduction 154
7.2 Confocal Laser Scanning Microscopy (CLSM) 156
7.2.1 High Resolution CLSM Examination of Wood-Coating Interface: Coating Penetration into Cell Wall Micro-Cracks 156
7.2.2 Combined Light Microscopy (LM), Confocal Laser Scanning Microscopy (CLSM) and Scanning Electron Microscopy (SEM) Reveals a Complex Wood-Coating Interaction in a Highly Textured Wood Surface-Coating Interface 158
7.3 Wood-Coating Interface Examined by Field Emission Scanning Electron Microscope (FE-SEM) in Combination with Backscattered Electron Imaging (BEI) 161
7.4 Summary 164
References 165
8 Delamination in Timber Induced by Microwave Energy 167
8.1 Introduction 167
8.2 The Mechanism of Wood Delamination Induced by Microwaves 168
8.3 Dielectric Properties of Wood 170
8.4 Solid Wood Delaminations in Various Microwave Applications 171
8.4.1 Impregnation 172
8.4.2 Drying 173
8.4.3 Bending 173
8.5 Controlling the Microwave Delamination Zone in Solid Timber 175
8.6 Conclusions 177
8.7 Summary 177
References 178
9 Delaminations Induced by Weathering in Wood and Wood-Based Composites Panels 181
9.1 Background 181
9.2 Delamination Induced by Weathering in Solid Wood 183
9.2.1 Methods of Measurements 184
9.2.2 Factors of Influence 185
9.2.3 Structural Aspects 186
9.2.3.1 Natural Outdoor Exposure 186
9.2.3.2 Artificial Exposure 194
9.3 Delamination Induced by Weathering in Wood-Based Composites Panels 199
9.3.1 Natural Outdoor Exposure 199
9.3.2 Artificial Exposure 200
9.4 Summary 200
References 201
10 Delamination in Timber Induced by Drying 205
10.1 Introduction 205
10.2 Influence of Temperature, Relative Humidity and Rate of Air Circulation on Drying 207
10.2.1 Temperature 207
10.2.2 Relative Humidity 208
10.2.3 Air Circulation Rate 208
10.3 Wood Drying Methods 208
10.3.1 Air Drying 209
10.3.2 Kiln Drying 209
10.4 Kiln Drying Schedules 211
10.5 Drying Defects 212
10.6 Prediction of Drying Stress and Strain Using Mathematical Models 213
10.6.1 Hardwood 215
10.6.2 Softwood 216
10.6.2.1 Low Temperature (LT) to Accelerated Conventional Temperature (ACT) 217
10.6.2.2 High Temperature Drying (HT) 218
10.7 Summary 219
References 220
Part III Delamination in Different Products 221
11 Industry Prospective of Delamination in Wood and Wood Products 222
11.1 Introduction 222
11.2 The Unique Wood Structure 224
11.3 The Raw Materials: Tree and Stem/Log 227
11.4 The Manufacturing Processes 230
11.4.1 Solid Wood Products (SWP) 230
11.4.2 Engineered Wood Products (EWP) 233
11.5 Product Failure and Product Durability 237
11.5.1 Product Failure 238
11.5.2 Product Durability 239
11.6 Summary 243
References 243
12 Internal Checking During Eucalypt Processing 244
12.1 Introduction 244
12.2 Why is Drying Slow and Collapse High in Eucalypts 245
12.3 Causes of Surface and Internal Checking in Eucalypts 248
12.4 Eucalypts Species Prone to Collapse 253
12.5 Collapse Recovery and Check Closure 255
12.6 Dimensional Analysis and Predictions from Heat-Transfer Theory 257
12.7 Effect of Reconditioning on Internal Checking 259
12.8 Summary 259
References 260
13 Acoustic Tomography for Tension Wood Detection in Eucalypts 262
13.1 Introduction 262
13.2 Ultrasonic Methods 264
13.2.1 Materials 264
13.2.2 Ultrasonic Methods 264
13.3 Tension Wood Detection with Ultrasonic Velocity Method 267
13.4 Acoustic Imaging with Stress Wave Technique 268
13.4.1 Imaging with Radial Stress Waves Velocities 269
13.4.2 Imaging with Tangential Stress Waves Velocities 269
13.5 Summary 273
References 273
14 The Hygroscopic Warping of Cross-Laminated Timber 276
14.1 Introduction 276
14.2 Material and Methods 278
14.2.1 Moisture Measurements 278
14.2.2 Warp Measurements 279
14.3 Material Data 281
14.3.1 Moisture Model 281
14.3.2 Mechanical Model 283
14.4 Results and Discussion 284
14.4.1 Moisture 284
14.4.2 Deformations and Stresses 285
14.5 Summary 290
References 291
15 Acoustic Emission Activity Induced by Delamination and Fracture of Wood Structure 293
15.1 Introduction 293
15.2 Parameters of the Acoustic Emission Signals 294
15.3 Parameter-Based Acoustic Emission Techniques 296
15.3.1 Species Effect 296
15.3.2 Grain Angle Effect 298
15.3.3 Annual Ring Structure 300
15.3.4 Tension Wood 303
15.3.5 Moisture Content 303
15.3.6 The Reused Old Wood 305
15.4 Some Aspects Related to the Energy of the Acoustic Emission Signals 307
15.5 Summary 308
References 310
16 Delamination Detection in Wood -- Based Composites Panel Products Using Ultrasonic Techniques 313
16.1 Introduction 313
16.2 Basic Aspects 315
16.2.1 Waves Propagation Paths 315
16.2.2 Linear Ultrasonic Inspection Techniques 317
16.2.2.1 Contact Techniques 318
16.2.2.2 Non-contact Techniques 322
16.2.3 Ultrasonic Transducers and Scanning Procedures 326
16.2.3.1 Contact Transducers 327
16.2.3.2 Non-contact Transducers 329
16.2.3.3 Scanning Procedures 329
16.2.4 Non-linear Ultrasonic Inspection Techniques 333
16.3 Delamination Detection in Wood-Based Composite Panels 335
16.3.1 Through Transmission Technique 335
16.3.1.1 Technique with the Transducers in Contact with the Specimen 335
16.3.1.2 Technique with Non-contact Ultrasonic Transducers 340
16.3.2 Plate Wave Technique 345
16.3.2.1 Technique with the Transducers in Contact with the Specimen 346
16.3.2.2 Technique with Non-contact Ultrasonic Transducers 346
16.3.3 Industrial Applications of Non-contact Technique 349
16.4 Summary 350
References 351
17 Delamination Evaluation of in-Service Glulam Beams and other Structural Members Via Ultrasonics 358
17.1 Introduction 358
17.2 Crack Types 360
17.2.1 Crack Between Lamellae 360
17.2.2 Crack Inside the Lamella Material 360
17.3 Crack Depth Detetrmination with Ultrasonics 361
17.4 Strength Prediction of Lamellas In situ 363
17.5 Detection of Other Internal Defects in Glulam 363
17.6 Shear Strength Determination Between the Lamellae 363
17.7 Delamination and Other Defects in Structural Element of Historic Buildings 365
17.8 Summary 368
References 369
18 Moisture Induced Stresses and Deformations in Parquet Floors 370
18.1 Introduction 370
18.2 Material and Methods 371
18.2.1 Tests on the Basic Material 371
18.2.2 Test on Parquet Planks 372
18.2.3 Analytical Model A: Calibration Model 373
18.2.4 Analytical Model B: Distortional Effects 375
18.2.5 Analytical Model C: Gap Opening 375
18.3 Deformations in Parquet Floors 376
18.3.1 Model A: Calibration and Comparison to Test Series 2 376
18.3.2 Model B: Cupping of the Parquet 378
18.3.3 Model C: Stresses in the Glue Line and Gap Opening 379
18.4 Conclusion 381
18.5 Summary 382
References 383
19 Glue Line Nondestructive Assessment in Timber Laminates with an Air-Coupled Ultrasonic Technique 384
19.1 Introduction 384
19.2 Theoretical Considerations 385
19.3 Material and Methods 386
19.3.1 Sample Preparation 386
19.3.2 Experimental Setup 387
19.4 Results and Discussion 388
19.4.1 Imaging of Glue Presence and Repeatability of Measurements 388
19.4.2 Influence of Natural Variability and Anisotropy of Wood 390
19.5 Conclusion 390
19.6 Summary 391
References 391
20 From Present Researches to Future Developments 393
References 395
Index 396