Page 19 - T. Anderson-Fracture Mechanics - Fundamentals and Applns.-CRC (2005)

1656_FM.fm Page xvii Tuesday, May 3, 2005 5:49 PM

10.5.1 Linear Damage Model for Variable Amplitude Fatigue.......................................474
10.5.2 Reverse Plasticity at the Crack Tip.......................................................................475
10.5.3 The Effect of Overloads and Underloads ............................................................478
10.5.4 Models for Retardation and Variable Amplitude Fatigue.....................................484
10.6 Growth of Short Cracks......................................................................................................488
10.6.1 Microstructurally Short Cracks.............................................................................491
10.6.2 Mechanically Short Cracks...................................................................................491
10.7 Micromechanisms of Fatigue .............................................................................................491
10.7.1 Fatigue in Region II ..............................................................................................491
10.7.2 Micromechanisms Near the Threshold.................................................................494
10.7.3 Fatigue at High ∆K Values....................................................................................495
10.8 Fatigue Crack Growth Experiments ...................................................................................495
10.8.1 Crack Growth Rate and Threshold Measurement ................................................496
10.8.2 Closure Measurements..........................................................................................498
10.8.3 A Proposed Experimental Definition of ∆K ......................................................500
eff
10.9 Damage Tolerance Methodology........................................................................................501
Appendix 10: Application of The J Contour Integral to Cyclic Loading .................................504
A10.1 Definition of ∆J......................................................................................504
A10.2 Path Independence of ∆J........................................................................506
A10.3 Small-Scale Yielding Limit.....................................................................507
References ......................................................................................................................................507

Chapter 11
Environmentally Assisted Cracking in Metals ..............................................................................511
11.1 Corrosion Principles ...........................................................................................................511
11.1.1 Electrochemical Reactions....................................................................................511
11.1.2 Corrosion Current and Polarization......................................................................514
11.1.3 Electrode Potential and Passivity..........................................................................514
11.1.4 Cathodic Protection...............................................................................................515
11.1.5 Types of Corrosion................................................................................................516
11.2 Environmental Cracking Overview ....................................................................................516
11.2.1 Terminology and Classification of Cracking Mechanisms ..................................516
11.2.2 Occluded Chemistry of Cracks, Pits, and Crevices..............................................517
11.2.3 Crack Growth Rate vs. Applied Stress Intensity..................................................518
11.2.4 The Threshold for EAC ........................................................................................520
11.2.5 Small Crack Effects ..............................................................................................521
11.2.6 Static, Cyclic, and Fluctuating Loads...................................................................523
11.2.7 Cracking Morphology ...........................................................................................523
11.2.8 Life Prediction.......................................................................................................523
11.3 Stress Corrosion Cracking..................................................................................................525
11.3.1 The Film Rupture Model ......................................................................................527
11.3.2 Crack Growth Rate in Stage II .............................................................................528
11.3.3 Metallurgical Variables that Influence SCC..........................................................528
11.3.4 Corrosion Product Wedging..................................................................................529
11.4 Hydrogen Embrittlement ....................................................................................................529
11.4.1 Cracking Mechanisms...........................................................................................530
11.4.2 Variables that Affect Cracking Behavior..............................................................531
11.4.2.1 Loading Rate and Load History...........................................................531
11.4.2.2 Strength.................................................................................................533
11.4.2.3 Amount of Available Hydrogen ...........................................................535
11.4.2.4 Temperature ..........................................................................................535