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FATIGUE TEST

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FATIGUE TEST EXPERIMENT # 5 Instructor: M.Yaqub FATIGUE FATIGUE LOADING Fluctuating or Cyclic loading (as shown in previous ) is referred as Fatigue loading. – PowerPoint PPT presentation

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Title: FATIGUE TEST


1
FATIGUE TEST
  • EXPERIMENT 5
  • Instructor M.Yaqub

2
FATIGUE
3
FATIGUE LOADING
  • Fluctuating or Cyclic loading (as shown in
    previous slide) is referred as
  • Fatigue loading.
  • A metal component may fail below stress
    corresponding to tensile strength or even below
    yield strength if it is subjected to Fatigue
    loading.
  • Most of the failure in engineering are because of
    fatigue loading.

4
FATIGUE TEST PROCEDURE
  • A Standard sample is used for the metal for which
    fatigue test is required.
  • Test procedure is explain in the handout.
  • A number of sample is used for the test and data
    plotted as applied stress (S) on Y-Axis and
    fatigue life (N) on X-Axis.
  • This curve is called S-N Curve.
  • Log-Log scale is used for S-N curve.
  • Few S-N curves are given in next slide.

5
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6
ENDURANCE LIMIT OR FATIGUE LIMIT
  • From S-N curve, it is clear that when applied
    stresses are reduces, the life of the part
    increases and vise versa.
  • For steel, a horizontal line at the end of the
    curve shows that the below this stress level, the
    metal will not have a fatigue failure.
  • This level of stress below which no fatigue
    failure is called ENDURANCE LIMIT OR FATIGUE
    LIMIT.
  • This can be observed in steel only.
  • What is endurance limit for steel in the previous
    slide.

7
FATIGUE STRENGTH
  • When there is no fatigue limit for metal, we
    define another stress called fatigue strength
  • Fatigue strength is defined as the stress
    corresponding to some definite life cycle usually
    taken as corresponding to 10 millions cycles.
  • Note that from S-N Curve first try to fine
    fatigue limit. If not possible, then find fatigue
    strength.
  • What is fatigue strength for Aluminum and Brass
    in previous slide.

8
DATA NOT COMPLETE
  • When there is no horizontal line for any S-N
    curve at the end and data is not available up to
    10 millions cycles, it means neither fatigue
    limit nor fatigue strength can be obtained from
    the curve.
  • In such cases, the data is not complete and few
    more sample has to tested to complete the data.

9
FACTORS EFFECTING FATIGUE LIFE
  • Stress
  • Temperature
  • Surface Finish
  • Corrosion
  • Stress Concentration
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