Autumn Semester 2020 takes place in a mixed form of online and classroom teaching.
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151-0349-00L  Fatigue Strength of Materials, Components and Structures

SemesterAutumn Semester 2016
LecturersM. Guillaume, R. E. Koller
Periodicityyearly recurring course
Language of instructionGerman


AbstractFatigue of materials is playing a key role in light weight structures. All applications are affected that are exposed to oscillating loads. The lecture will present the most important methods for analyzing the fatigue strength under service load conditions. This starts with the conventional assessment of a components endurance limit and ends with the application of the damage tolerance philosophy.
ObjectiveGoals of the lecture

An introduction to the most important terms and phenomena related to fatigue damages of metallic components will be given and explained by practical examples. Methods for assessment of endurance strength, finite life fatigue strength, crack initiation and crack growth will be discussed. The lecture shall demonstrate how to solve fatigue problems in practice.
Examples like the ICE disaster at Eschede or structural problems of the Combino tram demonstrate the significance of this subject. The fatigue behavior of lightweight structures for vehicles and aircrafts has to be considered during the component design process. Designing the static strength of a component alone is not sufficient since fatigue damages of such components may cause extremely high costs.
Structural components of modern aircraft like Airbus A380 or A400M are designed with respect to crack growth using the damage tolerance philosophy.
Understanding fatigue strength and its phenomena requires broad knowledge of material behavior, services loads, manufacturing effects as well as of analysis and test methods. Fatigue strength is a highly interdisciplinary area of work. For this the most important tools and methods shall be presented.
Content1. INTRODUCTION, OVERVIEW, MOTIVATION
1.1 Preface (General introduction and history survey) (Schijve; Chapter 1)
1.2 Standards and Guidelines
1.3 Examples of damage events • Comet-Accident (Pressure cycles, stress concentration)
• Aloha-Incident at Hawaii (Multiple site damage)
• Accident of an aerial passenger tramway (Fretting corrosion on axle)
• ICE-Accident (Wheel failure)
1.4 Presentations
• DVD "MTW Materialermüdung (1995, 21')",
• DVD "F/A-18 Full Scale Fatigue Test (2004, 12')",
• DVD "Sicherheit von Seilbahnen (1996, 7')" with discussion

2. LOADING
2.1 Fatigue strength overview
2.2 Significance of operational loading
2.3 Types of load histories(Schijve; Chapter 9)
2.4 Terms and definitions (Schijve; Chapter 9)
2.5 Measurement of operational loadings (Schijve; Chapter 9)
2.6 Counting algorithms (Schijve; Chapter 9)
2.7 Frequency distributions or spectra (Schijve; Chapter 9)
2.8 Impact of spectrum shape
2.9 Design Spectra (Schijve; Chapter 13)

3. MATERIAL
3.1 Fatigue strength overview
3.2 Evaluation of material properties for cyclic loading (Schijve; Chapter 13)
3.3 Fatigue properties (Schijve; Chapter 6)
3.4 Wöhler-Diagram (Schijve; Chapter 6, 7)
3.5 Scatter of fatigue properties (Schijve; Chapter 12)
3.6 Mean stress effect (Schijve; Chapter 6)
3.7 Damage mechanisms & matierial selection (Schijve; Chapter 2)
3.8 Environmental effects (Schijve; Chapter 16, 17)
3.9 Specific fatigue properties (Schijve; Chapter 6)

4. STRUCTURAL COMPONENT
4.1 Fatigue strength overview
4.2 Notches (Schijve; Chapter 3, 7)
4.3 Residual stresses (Schijve; Chapter 4)
4.4 Size effect
4.5 Surface condition and surface layers (Schijve; Chapter 7, 14)
4.6 Fretting corrosion (Schijve; Chapter 15)
4.7 Summary of fatigue strength improving methods (Schijve; Chapter 14)

5. SAFETY FACTORS (Schijve; Chapter 19)

6. FATIGUE STRENGTH ASSESSMENT
6.1 Fatigue strength overview
6.2 Assessment concepts for fatigue lifetime prediction
6.3 Assessment of the endurance strength
6.4 Finite life fatigue strength assessment using the nominal stress concept (Schijve; Chapter 10)
6.5 Local stress-strain concept (Schijve; Chapter 10)
6.6 Fracture mechanics concept (Schijve; Chapter 5, 8, 11)
6.7 Accuracy of concepts for fatigue lifetime assessment

7. STRUCTURAL INTEGRITY CONCEPTS
7.1 Safe life design (Mirage III, Pressure Vessel)
7.2 Fail safe design (modern aircraft construction)
7.3 Damage tolerance (approach according to US Air Force)
7.4 F/A-18 design philosophy
7.5 Summary

8. EXPERIMENTAL FATIGUE STRENGTH
8.1. In case of interesting current tests laboratory visitation at Empa
Lecture notesAll lecture chapters are on Powerpoint presentations. The chapters will be available as presentation handouts at the first day for a fee of CHF 20.-
LiteratureRecommended books as supplement to the lecture:

Schijve, Jaap
Fatigue of Structures and Materials
Springer Verlag, Berlin, ISBN 978-1-4020-6807-2 (Hardcover)

Broek, David
The Practical Use of Fracture Mechanics
Springer Netherlands, ISBN 978-90-247-3707-9 (Hardcover)
Prerequisites / NoticeDepending on actual fatigue tests a Laboratory visitation at Empa in Dübendorf may be organized.