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KEY TERMS:
NASGRO 
FLAGRO
life assessment
crack growth
fracture
mechanics
damage tolerance
structural integrity
analysis
materials
database
consortium
software
stress intensity
factor
boundary element
method
fracture control
critical crack size
NASA

NASGRO® 4.0 User's Manual
Table of Contents

TABLE OF CONTENTS
SUMMARY 1
1.0 Introduction 3
2.0 Fatigue Crack Growth Analysis 5
      2.1 Theoretical Background 5
            2.1.1 Crack Growth Relationship 5
            2.1.2 Fatigue Crack Closure 7
            2.1.3 Threshold Stress Intensity Factor Range 10
            2.1.4 Fracture Toughness 14
            2.1.5 Criteria for Failure 16
            2.1.6 Yielding Checks 17
            2.1.7 Crack Growth under Load Interaction 18
                     2.1.7.1 Generalized Willenborg Model 18
                     2.1.7.2 Modified Generalized Willenborg Model 19
                     2.1.7.3 Chang-Willenborg Model 20
                     2.1.7.4 Strip Yield Model 21
                     2.1.7.5 Constant Closure Model 30
                     2.1.7.6 Notes on Using the Load Interaction Models 30
      2.2 Details of Crack Growth Analysis 39
            2.2.1 Choosing the Crack Geometry 40
            2.2.2 Transition of Crack Geometry 40
            2.2.3 Entering the Initial Flaw Size 42
            2.2.4 Selecting the Material Properties 60
                     2.2.4.1 Entering Material Properties Data from File 62
                     2.2.4.2 Entering Material Properties Data Manually 63
            2.2.5 Entering the Load Spectrum 64
                     2.2.5.1 Defining the Block Cases 65
                     2.2.5.2 Setting the range-pair counting option 70
                     2.2.5.3 Setting the Keac Check 70
                     2.2.5.4 Scaling the Stresses 71
                     2.2.5.5 Setting the Limit Stress Checks 72
                     2.2.5.6 Combining the Block Cases to Form a Schedule 72
            2.2.6 Output Options 73
            2.2.7 Computations and Postprocessing 74
3.0 Critical Crack Size Calculations 77
      3.1 Theoretical Background 77
      3.2 How to Run a Critical Crack Size Calculation 78
4.0 Stress Intensity Factor Calculations 79
      4.1 Theoretical Background 79
      4.2 How to Run a Stress Intensity Factor Calculation 79
            4.2.1 SIF Calculations Using Linear Stresses 80
            4.2.2 SIF Calculations Using Nonlinear Stresses 81
5.0 Sustained Stress (da/dt) Analysis of Glass 83
      5.1 Theoretical Background 83
      5.2 How to Run a Sustained Stress Analysis 83
            5.2.1 Material Properties 85
            5.2.2 Entering the Sustained Load Schedule 86
6.0 Crack Growth Data Analysis 87
      6.1 Entering a vs. N or da/dN vs. ΔK Data for Curve Fitting 87
      6.2 Obtaining the Constants 88
      6.3 Entering and processing fracture toughness data 89
7.0 Boundary Element Method Analysis 91
      7.1 The Data Input Interface 91
            7.1.1 The Input Philosophy, or: How to build the model 92
                     7.1.1.1 Points 92
                     7.1.1.2 Boundary segments 93
                     7.1.1.3 Boundaries 94
                     7.1.1.4 Zones 94
                     7.1.1.5 Crack segments and cracks 95
                     7.1.1.6 Boundary conditions and concentrated
                                 (or point) loads		 95
                     7.1.1.7 Materials 97
                     7.1.1.8 Special case geometries 97
                     7.1.1.9 Stress analysis 98
            7.1.2 The Menu Tree 98
                     7.1.2.1 Top level menu 98
                     7.1.2.2 General hints and notes on using the menu
                                 tree and input.		 99
      7.2 Numerical Limits on Input Items; or, How big can the
            model be?		 100
      7.3 Stress Analysis 100
            7.3.1 Stresses in the Interior 101
            7.3.2 Stresses on the Boundary 102
            7.3.3 Stresses in the Boundary Layer 103
      7.4 Program Output and Files Used 103
      7.5 Future Enhancements 104
ACKNOWLEDGMENTS 105
REFERENCES 107
Appendix A - Flow Diagrams A-1
Appendix B - Net-section Stress Computations B-1
Appendix C - Stress Intensity Factor Equations and Tables C-1
Appendix D - Instructions for Adding Crack Cases D-1
      D.1 Changes to Subroutines D-1
Appendix E - User-Defined Files E-1
Appendix F - Interpolation Routines F-1
Appendix G - List of Materials with Constants for NASGRO 4.0 Equation G-1
Appendix H - Loading Spectra for Acceptance Vibration Tests H-1
      H.1 Sinusoidal Sweep Vibration Test H-1
            H.1.1 Narrow band Response - Methodology and Results H-1
            H.1.2 Wide band Response - Methodology and Results H-3
      H.2 Sinusoidal Dwell Vibration Test H-4
      H.3 Random Vibration and Acoustic Tests H-5
            H.3.1 Methodology H-5
            H.3.2 Results H-6
      H.4 References H-6
Appendix I - System Requirements, Software Requirements, and Program Installation I-1
      I.1 PC Version of NASGRO I-1
            I.1.1 PC Installation Information I-2
            I.1.2 PC Execution I-2
      I.2 NASGRO for Computers other than PC I-3
            I.2.1 Source Code I-4
Appendix J - Unit Conversion factors J-1
Appendix K - Stress Quantities in Fatigue Load Spectra K-1
Appendix L - List of Materials with Constants for Walker Equation L1-1

 

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