FATIGUE CLASS NOTES FOR MECHANICAL ENGINEERING

 

FATIGUE CLASS NOTES

FOR MECHANICAL ENGINEERING

It is the failure of material under reversal of stress. Fatigue reduces the strength of a material.

Notable Fatigue Failures

  1. Versailles train disaster
  2. The 1862 Hartley Colliery Disaster
  3. De Havilland Comet crash
  4. Alexander L. Kierland oil platform capsizing
  5. The 1919 Great Molasses Flood
  6. The 1948 Northwest Airlines Flight 421 crash
  7. The 1957 of Philippine President aircraft crash
  8. The 1965 capsize of UK’s first offshore oil plate form
  9. The 1968 Los Angles Airways Flight 417 crash
  10. The 1968 Mac Robertson Miller Airlines Flight 1750 crash,\
  11. The 1977 Dan-Air Boeing 707 crash
  12. The 1980 Lot Flight 7 crash
  13. The 1985 Japan Airlines Flight 123 crash
  14. The 1988 Aloha Airlines Flight 243 crash
  15. The 1989 United Airlines Flight 232 crash
  16. The 1992 EI AI Flight 1862 crash
  17. The 1998 Enschede train disaster
  18. the 2000 Hatfield rail crash
  19. the 2002 China Airlines Flight 611
  20. the 2005 Chalk’s Ocean Airways Flight 101 crash
  21.  the 2009 Viareggio train derailment

 

 

All these failures were  fatigue failure in one part or the other. There are many more to quote.

CAUSES OF FATIGUE FAILURES

 There are various types of mechanical failures. Some of these are buckling, corrosion, creep, fatigue, fracture, impact, wear, yielding and mechanical overload. However 90 % of the service failures are due to fatigue alone of one or the other type.  Fatigue failure is thus the most important. It is due to any one of the following cyclic- loading:

  1. Tensile load increases from zero to maximum and then back to zero
  2. Compressive load increases from zero to maximum and then back to zero
  3. Shear load increases from zero to maximum and then back to zero
  4. Tensile load increases from zero to maximum and then back to zero. Then to maximum compressive and back to zero. Maximum tensile being equal to maximum compressive. It is repeatable.
  5. Tensile load increases from zero to maximum and then back to zero. Then to maximum compressive and back to zero. Maximum tensile is not equal to maximum compressive.
  6. Completely or partially reversible torsion load

Thus the cyclic loads can be static, repeated and reversed, fluctuating and shock or impact.