fatigue in aircraft structures-221113192308-0ad6dc8c.pptx
- 2. Contents • Introduction • Aircraft Materials • Types of Loading on Aircraft Structures • Causes of Fatigue Failures • Typical Fatigue in Aero structures • Testing of structures under fatigue loading 2
- 3. Introduction • Material fatigue is a phenomenon where structures fail when subjected to a cyclic load. This type of structural damage occurs even when the experienced stress range is far below the materials strength. Fatigue is the most common source behind failures of Aero structures • Often, machine members are found to have failed under the action of repeated or fluctuating stresses • The most distinguishing characteristic of these failures is that the stresses have been repeated a very large number of times. Hence the failure is called a fatigue failure. 3
- 4. Some Cyclic Loads on Aircrafts • Push back (on landing gear) • Turning (high stresses on landing gear) • Taxy • Take off • Cabin pressurization • Landing impact • Undercarriage loading • Turbulence • Gust and maneuvers 4
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- 7. Aircraft Materials 7 Steel Titanium Aluminum Laminate Composites Sandwich honeycomb Structures
- 9. 9 Types of Loading on Aero Structure
- 10. Causes of Fatigue Failure Pre Manufacturing • Oversize hole • Porosities • Incorrect fastener pitch • Alternative fastener type • Part out of tolerance • False cut • Alternative material used 10
- 11. Causes of Fatigue Failure 11 Post manufacturing • Corrosion damages • Cracks , Dents, Nicks & Scratches • Temperature Variations • Sonic or Acoustic effects • Debonding between skin and core (sandwich) • Free edge damages (Delamination's, notches etc.) • Impact damages • Fretting
- 12. 12 Typical Fatigue in Aero structures • Cyclic Fatigue Stress, strain and deformation Induced in a material by cyclic loading. Aircrafts are in a complex fatigue condition because the magnitude, frequency and Duration of some of the loading changes randomly.
- 13. 13 Typical Fatigue in Aero structures • Corrosion Fatigue Corrosion fatigue is fatigue in a corrosive environment. It is the mechanical degradation of a material under the joint action of corrosion and cyclic loading. It is accelerated by surface corrosion and penetrates inwards.
- 14. 14 Typical Fatigue in Aero structures • Fretting Fatigue Fretting fatigue is the phenomenon of crack initiation and propagation from the region of stress concentration in reciprocating frictional contacts.
- 15. 15 Typical Fatigue in Aero structures • Thermal Fatigue Thermal fatigue is a specific type of fatigue failure mechanism that is induced by cyclic stresses from repetitive fluctuations in the temperature of equipment. The degree of damage is affected by the magnitude and frequency of the temperature swings.
- 16. 16 Typical Fatigue in Aero structures • Sonic Fatigue Sonic Fatigue is caused by high frequencies noise generally emitted from aero engines which cause stress fluctuations and vibrations.
- 17. 17 Testing of Fatigue loaded structures • Visual Testing with aids (Borescope)
- 18. 18 Testing of Fatigue loaded structures • Dye Penetration Testing
- 19. 19 Testing of Fatigue loaded structures • Magnetic Particle Testing
- 20. 20 Testing of Fatigue loaded structures • Radiographic Testing
- 21. 21 Testing of Fatigue loaded structures • Ultrasonic Testing
- 22. 22 Testing of Fatigue loaded structures • Tap Testing
- 23. 23 Thank You