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 |  موضوع: كتاب Finite Element Based Fatigue Calculations الإثنين 30 أبريل 2012, 6:46 pm | |
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تذكير بمساهمة فاتح الموضوع : أخوانى فى الله
أحضرت لكم كتاب
Finite Element Based Fatigue Calculations
Authors:
Dr NWM Bishop & Dr F Sherratt
ويتناول الموضوعات الأتية :
Contents
1 Introduction 1
2 Why FEA Based Fatigue Design? 5
2.1 The Elements of a Life Estimation System. 5
2.2 An Overview of the FEA Based Fatigue Environment 8
2.3 FE Hints and Tips – Why FEA 12
3 Different Philosophies and Life Estimation Models. 15
3.1 Design Philosophies 15
3.1.1 Safe-Life. 15
3.1.2 Fail-Safe. 16
3.1.3 Damage-Tolerant. 16
3.1.4 Integrated Durability Management 17
3.2 Life Prediction Methods 17
3.2.1 Stress-Life (S-N, or Nominal Stress) Approach. 18
3.2.2 Strain-Life (Crack-Initiation or Critical-Location Approach) 19
3.2.3 Crack Propagation Models. 20
3.3 Linking Life Estimation Methods With Design Philosophies. 20
3.4 FE Hints and Tips – Alternative Philosophies 21
4 The Stress-Life (S-N) Approach. 23
4.1 Defining Stress Cycles 23
4.2 The S-N Curve 24
4.3 Limits of the S-N Curve 26
4.4 The Role of Stress Concentration. 26
4.4.1 Example: Simple Fatigue Strength Estimates 28
4.5 The Influence of Mean Stress 29
4.5.1 Example: Correcting For Mean Stress Effects 31
4.6 Variable Amplitude Response – Block Loading and Palmgren-Miner 33
4.6.1 Example: Palmgren-Miner Cumulative Damage Calculation 34
4.7 Variable Amplitude Loading – Rainflow Cycle Counting 35
4.7.1 Presentation of Rainflow Counts 37
4.7.2 Example: Rainflow Cycle Counting 374.8 Material and Component S-N Curves 38
4.8.1 Material S-N Curves 39
4.8.2 Component S-N Curves 39
4.9 FE Hints and Tips – S-N approach 41
4.9.1 Component S-N Curves 41
4.9.2 Nodal vs Element Averaging 41
4.9.3 Spot Welds 42
4.9.4 Welds 42
4.9.5 KTand Kf Values Within an FE Model 44
5 The Strain-Life (e-N) Approach. 45
5.1 The Stress-Strain Curve 47
5.1.1 Elastic and Plastic Strain. 47
5.1.2 Cyclic Stress-Strain Behaviour 49
5.1.3 Cyclic Loading Under Strain Control 50
5.1.4 Hysteresis Loop Shape 50
5.1.5 Example: Calculating Cyclic Stress-Strain Response 51
5.1.6 Estimating a Strain-Time History. 54
5.1.7 Retaining Mean Stress Information 56
5.2 The Strain-Life Curve 57
5.2.1 The Effect of Mean Stress 60
5.2.2 The Morrow Mean Stress Correction 60
5.3 FE Hints and Tips – e-N Approach 61
5.3.1 Element vs Nodal Results 61
5.3.2 Weld Analysis, Component Material Curves and Composites 61
6 Crack Propagation Analysis Using LEFM 63
6.1 How Fatigue Cracks Start 63
6.2 The Concept of Stress Intensity 64
6.3 Fatigue Crack-Propagation and LEFM 66
6.4 Stresss Intensity Factor K Versus Compliance-Function Y 68
6.5 What is the Meaning of “Nominal Stress” as Used With a ComplianceFunction in FE Based Crack Growth Calculations? 69
6.6 What is the Role of FEA in Generating Compliance-Functions? 70
6.7 Using Fracture Mechanics in Damage-Tolerant Design. 70
6.8 Example: A Simple Damage-Tolerant Design Calculation 72
6.9 Example: Solving the Box for Fatigue Crack Growth Assessments 736.10 Aircraft Engine Mounting Lug FE Based Fatigue Analysis 75
6.10.1 S-N Analysis 75
6.10.2 Crack Growth Prediction 77
6.11 FE Hints and Tips – Crack Growth 79
6.11.1 The Use of Crack Tip Elements 79
6.11.2 Picking a Nominal Stress 79
7 Multi-axial Fatigue Analysis. 81
7.1 Multi-axial Stress-Strain States 81
7.1.1 Separate Tensile and Torsion Loading 82
7.1.2 Combined Tensile and Torsional Loading 84
7.2 Characterisation of Stress States 84
7.3 Proportional Multi-axial Responses 87
7.4 Equivalent Stress-Strain Approaches 89
7.5 Dealing with Non-Proportional Responses 90
7.6 FE Hints and Tips – Multi Axial Fatigue 92
7.6.1 3D, 2D and 1D Models 92
7.6.2 Multi Modal Response to Single Input Loading 92
7.6.3 Summary 92
8 Vibration Fatigue Analysis. 93
8.1 Alternative Descriptions of Engineering Processes 93
8.1.1 What is the Frequency Domain? 95
8.1.2 What is a Power Spectral Density (PSD)? 96
8.2 Characterization of Engineering Processes Using Statistical Measures 96
8.2.1 Time Histories & PSDs 96
8.2.2 Expected Zeros, Peaks and Irregularity Factor 97
8.2.3 Moments From a PSD 98
8.2.4 Expected Zeros, Peaks and Irregularity Factor From a PSD. 99
8.2.5 What is The Transfer Function? 99
8.3 What is a Modal Transient (Superposition) Fatigue Analysis? 101
8.4 Fatigue Life Estimation From PSDs 102
8.4.1 Time Domain Stress-Life Fatigue Life Estimation 102
8.4.2 S-N Relationship 103
8.4.3 Estimating Fatigue Life From a Stress pdf 103
8.4.4 The Frequency Domain Model 103
8.4.5 Narrow Band Solution 1048.4.6 Empirical Correction Factors (Tunna, Wirsching, Hancock, Chaudhury
and Dover) 106
8.4.7 Dirlik’s Empirical Solution for Rainflow Ranges 106
8.4.8 Bishop’s Theoretical Solution for Rainflow Ranges 107
8.4.9 Clipping Ratio as a Function of rms 107
8.5 A Simple Vibration Fatigue Hand Calculation 107
8.5.1 Time Domain By Hand. 108
8.5.2 Frequency Domain By Hand. 109
8.5.3 Computer Based Calculations Using MSC.Fatigue 109
8.6 An FEA Based Example 110
8.7 FE Hints and Tips – Vibration Fatigue 110
8.7.1 Calculation of Frequency Response Function (Transfer Function) 110
8.7.2 Verifying Vibration Fatigue Results 112
9 FE Model Building and Post Processing Issues. 113
9.1 Introduction 113
9.2 Process Issues 113
9.3 Model Building 117
9.3.1 Requirements 117
9.3.2 Observations 118
9.3.3 H vs P-type element choice 119
9.4 Meshing 120
9.5 Dealing with Loads. 120
9.6 FEA Based Global Analysis Options 121
9.6.1 Analysis Options 121
9.6.2 FE Results output type 123
9.7 FE Based Local Analysis Options 123
9.7.1 What is “Absolute Maximum Principal” Stress and “Signed Von Mises”?
9.7.2 The Choice of Element Centroid Versus Nodal Results 124
9.8 Pre Processing of Loading Data 125
9.9 Post Processing of FE Based Fatigue Results. 125
9.10 Accuracy of Fatigue Life Estimates 127
9.11 General Conclusions 128
10 Bibliography
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