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- ISBN: 9781905209545 | 1905209541
- Cover: Hardcover
- Copyright: 11/3/2006
Practical problems in structural design and service inspection are addressed in this handbook to dealing with fatigue design of welded structures. Details of how to use calculation tools on an Excel spreadsheet are included for application in realistic industrial cases.
Tom Lassen is a professor at Agder University College–Grimstad and an aircraft maintenance teacher for the Norwegian Royal Air Force. He is a former visiting professor at UniversitT Blaise Pascal–Clermont-Ferrand. Naman Recho is a professor at the University Blaise Pascal–Clermont-Ferrand and at the Centre des Hautes +tudes de la Construction–Paris. He is also a guest Professor at the Hefei University of Technology.
Abbreviations | p. xv |
Common Practice | p. 1 |
Introduction | p. 3 |
The importance of welded joints and their fatigue behavior | p. 3 |
Objectives and scope of the book | p. 4 |
The content of the various chapters | p. 5 |
Other literature in the field | p. 7 |
Why should the practicing engineer apply reliability methods? | p. 8 |
How to work with this book | p. 9 |
About the authors | p. 10 |
Basic Characterization of the Fatigue Behavior of Welded Joints | p. 11 |
Introduction and objectives | p. 11 |
Fatigue failures | p. 11 |
Basic mechanisms of metal fatigue | p. 15 |
Parameters that are important to the fatigue damage process | p. 17 |
External loading and stresses in an item | p. 17 |
Geometry, stress and strain concentrations | p. 19 |
Material parameters | p. 20 |
Residual stresses | p. 24 |
Fabrication quality and surface finish | p. 25 |
Influence of the environment | p. 25 |
Important topics for welded joints | p. 26 |
General overview | p. 26 |
Various types of joints | p. 30 |
Plated joints | p. 30 |
Tubular joints | p. 34 |
References | p. 35 |
Experimental Methods and Data Analysis | p. 37 |
Introduction and objectives | p. 37 |
Overview of various types of tests | p. 38 |
Stress-life testing (S-N testing) of welded joints | p. 38 |
Test specimens and test setup | p. 38 |
Preparations and measurements | p. 41 |
Test results | p. 46 |
Testing to determine the parameters in the strain-life equation | p. 49 |
Crack growth tests - guidelines for test setup and specimen monitoring | p. 50 |
Elementary statistical methods | p. 55 |
Linear regression analyses | p. 55 |
References | p. 60 |
Definition and Description of Fatigue Loading | p. 61 |
Introduction and objectives | p. 61 |
Constant amplitude loading | p. 62 |
Variable amplitude loading | p. 63 |
Overview | p. 63 |
Rain-flow cycle counting of time series | p. 64 |
The energy spectrum approach | p. 69 |
References | p. 73 |
The S-N Approach | p. 75 |
Introduction and objectives | p. 75 |
Method, assumptions and important factors | p. 76 |
Statistics for the S-N approach, median and percentile curves | p. 76 |
Discussion of S-N curves-important factors | p. 78 |
The threshold phenomenon | p. 78 |
Mean stress and loading ratio | p. 79 |
Stress relieving | p. 79 |
The thickness effect | p. 80 |
Misalignment | p. 81 |
Post-weld improvement techniques | p. 82 |
Corrosive environment | p. 83 |
Mathematics for damage calculations | p. 84 |
Linear damage accumulation; load spectrum on a histogram format | p. 84 |
Discussion of the validity of the linear damage accumulation | p. 86 |
Definition of the equivalent stress range | p. 88 |
Load spectrum on the format of a Weibull distribution | p. 88 |
S-N curves related to various stress definitions | p. 91 |
Nominal stress, geometrical stress and weld notch stresses | p. 92 |
Geometrical stresses in tubular joints | p. 96 |
Fatigue life estimate based on the weld notch stress approach | p. 98 |
Conclusions on the various stress approaches | p. 101 |
Some comments on finite element analysis | p. 104 |
Current rule and regulations | p. 110 |
General considerations | p. 110 |
The original fatigue classes and S-N curves from DoE | p. 112 |
S-N life predictions according to Eurocode 3-Air environment | p. 117 |
S-N life predictions according to HSE | p. 119 |
S-N life predictions according to NORSOK and DNV | p. 120 |
S-N life predictions for ship structures | p. 122 |
The industrial case: an offshore loading buoy | p. 130 |
References | p. 136 |
Applied Fracture Mechanics | p. 139 |
Introduction | p. 139 |
Objectives of this chapter | p. 142 |
Basic concepts of linear elastic fracture mechanics | p. 142 |
The local stress field ahead of the crack front | p. 142 |
Fracture criterion due to extreme load | p. 152 |
Mixed mode rupture | p. 153 |
The R6 criterion and critical crack size | p. 154 |
Fatigue threshold and fatigue crack growth | p. 156 |
Crack growth models | p. 156 |
Parameters C and m | p. 159 |
Residual stresses | p. 160 |
Some notes on the size of the initial cracks | p. 161 |
Geometry function and growth parameters given in BS7910 | p. 161 |
The geometry function | p. 162 |
Parameters C and m | p. 163 |
Fracture mechanics model for a fillet welded plate joint | p. 165 |
Basic assumptions and criteria for the model | p. 165 |
Data for crack growth measurements (database 1) | p. 166 |
Data for fatigue lives at low stress levels (database 2) | p. 167 |
Procedure and curve fitting | p. 167 |
Growth parameters C and m | p. 169 |
The initial crack depth a[subscript 0] | p. 172 |
Prediction of crack growth histories and construction of S-N curves | p. 173 |
Conclusions for fillet joints with cracks at the weld toe | p. 175 |
Fatigue crack growth in tubular joints | p. 176 |
Discussion of current models | p. 179 |
Conclusion on the empirical fracture mechanics model | p. 183 |
Proposal for model improvements | p. 183 |
A brief overview of stiffened panels | p. 184 |
Units and conversion for fracture mechanics parameters | p. 186 |
Industrial case: fatigue re-assessment of a welded pipe | p. 186 |
Introduction | p. 186 |
Description of the loading buoy with steel pipe | p. 187 |
Replacement and inspection strategy | p. 189 |
Re-assessment based on the S-N approach | p. 190 |
Re-assessment based on fracture mechanics | p. 191 |
References | p. 193 |
Stochastic Modeling | p. 197 |
Stochastic Modeling | p. 199 |
Introduction and objectives | p. 199 |
Overview of models and methodology | p. 200 |
Sources of uncertainty | p. 200 |
Introduction to the random variable model and related methods | p. 201 |
Requirements for a stochastic model | p. 203 |
The concept of the limit state function and the safety margin | p. 204 |
The first and second order reliability methods (FORM/SORM) | p. 206 |
Elementary reliability models | p. 207 |
General considerations | p. 207 |
The Lognormal distribution | p. 208 |
The Weibull distribution | p. 209 |
The random variable model using simulation methods | p. 212 |
General considerations | p. 212 |
The realization of a random variable by the Monte Carlo method | p. 213 |
Random variable models based on the S-N approach | p. 215 |
The lognormal format for the S-N fatigue life | p. 215 |
Example: full-penetration butt joint in an offshore structure | p. 217 |
Monte Carlo Simulation of the S-N fatigue life | p. 219 |
Random variable models based on fracture mechanics | p. 220 |
General considerations | p. 220 |
Taking account for future inspections and inspection results | p. 221 |
Characterization of the performance of the non-destructive inspection technique | p. 223 |
Simulation with account for future planned inspections | p. 225 |
A first approximation to the inspection problem | p. 225 |
Full stochastic simulation | p. 226 |
Simulation of planned inspections for a fillet welded joint | p. 229 |
Updating based on inspections results | p. 231 |
The Markov chain model | p. 235 |
Basic concepts | p. 235 |
Simple illustration on how the model works | p. 235 |
Elaboration of the model | p. 242 |
Influence of scheduled inspection and repair | p. 244 |
Parameter estimation | p. 246 |
Hybrid model to account for additional scatter | p. 248 |
Analysis of a fillet welded joint | p. 249 |
Short review and elaboration of database 1 | p. 250 |
Determination of parameters in the Markov model | p. 251 |
Reliability results and discussion | p. 253 |
A damage tolerance supplement to rules and regulation | p. 255 |
Introduction | p. 255 |
An industrial case study: single anchor loading system | p. 260 |
Example 1: butt weld in upper pipeline | p. 262 |
Example 2: welded brackets on the main plates | p. 263 |
Conclusions for the damage tolerance supplement | p. 263 |
Risk assessments and cost benefit analysis | p. 264 |
Reliability and risk assessment for the riser steel pipe | p. 267 |
References | p. 268 |
Recent Advances | p. 271 |
Proposal for a New Type of S-N Curve | p. 273 |
Introduction and objectives | p. 273 |
General considerations for the conventional S-N approach | p. 275 |
Basic assumptions | p. 275 |
The S-N approach based on BS5400 and Eurocode 3 | p. 275 |
S-N curves based on a random fatigue limit model | p. 277 |
Experimental data for model calibration | p. 278 |
Data for fatigue life at high stress levels (database 1) | p. 278 |
Data for fatigue lives at low stress levels (database 2) | p. 279 |
Comparison between the F-class curve, the RFLM-based curve and the data | p. 279 |
Conclusions | p. 284 |
References | p. 284 |
Physical Modeling of the Entire Fatigue Process | p. 287 |
Introduction and objectives | p. 287 |
Modeling the fatigue crack initiation period | p. 289 |
Basic concept and equations for the local stress-strain approach | p. 289 |
Definition of the initiation phase and determination of parameters | p. 292 |
Local toe geometry and stress concentration factor | p. 292 |
Transition depth | p. 294 |
Cyclic mechanical properties and parameters in Coffin-Manson equation | p. 295 |
Constructing the S-N curve from the two-phase model | p. 297 |
Damage accumulation using the TPM | p. 301 |
The practical consequences of the TPM | p. 302 |
General considerations | p. 302 |
Life predictions and dimensions | p. 302 |
Predicted crack evolution and inspection planning | p. 303 |
Conclusions | p. 306 |
Suggestions for future work | p. 307 |
References | p. 308 |
A Notch Stress Field Approach to the Prediction of Fatigue Life | p. 309 |
A modified S-N approach | p. 309 |
General considerations | p. 309 |
The basic theory for the notch stress intensity factor | p. 311 |
S-N data analysis for fillet welded joints | p. 313 |
A modified crack growth approach | p. 315 |
References | p. 317 |
Multi-Axial Fatigue of Welded Joints | p. 319 |
Introduction and objectives | p. 319 |
Overview of theory and crack-extension criteria | p. 321 |
The crack box technique | p. 322 |
General considerations for finite element analysis and element mesh | p. 322 |
Methodology | p. 322 |
Examples | p. 324 |
Tentative mixed-mode model to crack propagation in welded joints | p. 325 |
Modeling the effect of the loading mode on the crack growth rate | p. 327 |
Modeling the effect of the residual stress due to the weld on the crack growth rate | p. 328 |
Measured effect of the loading angle on the crack growth rate | p. 329 |
Measured effect of weld on the crack growth rate | p. 331 |
Measured crack extension angle under mixed mode loading | p. 332 |
Validation of the model | p. 333 |
Verification of the models for non-welded steel specimens under mixed-mode loading | p. 334 |
Verification of the models for non-welded and welded steel specimens under mode I loading | p. 336 |
Verification of the models for welded steel specimens under mixed-mode loading | p. 337 |
Verification of the effect of the welded residual stress on the fatigue life | p. 338 |
Discussion and conclusions | p. 339 |
Extension to full test | p. 340 |
Modeling methodology | p. 341 |
Global calculation scheme | p. 341 |
The crack box technique | p. 343 |
Crack-propagation rate | p. 344 |
Description of experiments carried out | p. 345 |
Results | p. 345 |
Weld toe geometry | p. 346 |
Numerical calculations | p. 347 |
Crack initiation | p. 347 |
Crack growth | p. 349 |
References | p. 351 |
The Effect of Overloads on the Fatigue Life | p. 355 |
Introduction and objectives | p. 355 |
Residual stress opening approach at the crack tip following an overload during fatigue | p. 359 |
Numerical modeling | p. 362 |
Modeling aspects | p. 362 |
Finite element modeling choices | p. 363 |
Proposed deterministic approach to fatigue crack growth following an overload | p. 366 |
Reliability modeling including the effect of an overload | p. 370 |
Application of the reliability model to a fillet welded joint | p. 371 |
References | p. 375 |
Short Overview of the Foundations of Fracture Mechanics | p. 381 |
Introduction | p. 381 |
Elementary failure modes and stress situations | p. 383 |
Foundations of fracture mechanics | p. 383 |
Parameters characterizing the singular zone | p. 385 |
The stress intensity factor (SIF), K | p. 385 |
The energy release rate, G | p. 387 |
The J-integral | p. 388 |
The crack-opening displacement (COD) | p. 389 |
Asymptotic stress field in elastic-plastic media | p. 390 |
References | p. 391 |
Spreadsheet for Fatigue Life Estimates | p. 393 |
CG - Crack Growth Based on Fracture Mechanics | p. 395 |
CI - Crack Initiation Based on Coffin-Manson | p. 399 |
Index | p. 403 |
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