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Fatigue Resistance Test
What IS a FATIGUE ?
2
Fatigue is a form of failure that occurs in
structures subjected to dynamic and fluctuating
stresses (e.g., bridges, aircraft, machine
components).
Fatigue
 This type of failure normally occurs after a lengthy
period of repeated stress or strain cycling.
 The process occurs by the initiation and propagation
of cracks, and typically the fracture surface is
perpendicular to the direction of an applied tensile
stress.
Cyclic Stresses
 The applied stress may be axial (tension–compression), flexural
(bending), or torsional (twisting) in nature.
 Three different fluctuating stress–time modes are possible.
Cyclic Stresses
 reversed stress cycle
 repeated stress cycle
 randomly Stress Cycle
Reversed Stress
Cycle:
The amplitude
is symmetrical
about a mean
zero stress
level.
Repeated Stress
cycle:
The maxima and
minima are
asymmetrical
relative to the
zero stress
level.
Random Stress
Cycle:
The stress level
may vary
randomly in
amplitude and
frequency
Reversed Stress Cycle
Repeated Stress Cycle
Random Stress Cycle
Fatigue Resistance Testing
The sequence of stress amplitude. The nature of the test-piece.
Constant-
amplitude
test
Variable-
amplitude
tests
Specimens Component
Routine
life test
Short
life test
Long
life test
Fatigue Testing Machines:
Rotating Bending Testing Machine
Axial loading (push-pull) type
fatigue tester
Rotating Bending Testing Machine
Rotating Bending Testing Machine
• This type of machine gives S-N curve
• The motor is turning at a constant
revolution per minute or frequency
• To create a failure on the specimen, a
constant-stationary force is applied on the
specimen, which creates a constant bending
moment.
Working Principle
A stationary moment applied to a rotating specimen
causes the stress at any point on the outer surface of the
specimen to go from zero to a maximum tension stress,
back to zero and finally to a compressive stress.
The process is repeated.
Axial loading (push-pull) type fatigue
tester
Axial loading (push-pull) type fatigue
tester
In this type the specimen is not exposed to bending
but to pure axial (tensile or compressive) loading.
Specimen is held at two ends and loaded cyclically
between two extreme (maximum and minimum)
values.
Fatigue Test for LDPE
Fatigue Test for LDPE
Fatigue rsistance test

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Fatigue rsistance test

  • 2. What IS a FATIGUE ? 2 Fatigue is a form of failure that occurs in structures subjected to dynamic and fluctuating stresses (e.g., bridges, aircraft, machine components).
  • 3. Fatigue  This type of failure normally occurs after a lengthy period of repeated stress or strain cycling.  The process occurs by the initiation and propagation of cracks, and typically the fracture surface is perpendicular to the direction of an applied tensile stress.
  • 4. Cyclic Stresses  The applied stress may be axial (tension–compression), flexural (bending), or torsional (twisting) in nature.  Three different fluctuating stress–time modes are possible.
  • 5. Cyclic Stresses  reversed stress cycle  repeated stress cycle  randomly Stress Cycle Reversed Stress Cycle: The amplitude is symmetrical about a mean zero stress level. Repeated Stress cycle: The maxima and minima are asymmetrical relative to the zero stress level. Random Stress Cycle: The stress level may vary randomly in amplitude and frequency
  • 9. Fatigue Resistance Testing The sequence of stress amplitude. The nature of the test-piece. Constant- amplitude test Variable- amplitude tests Specimens Component Routine life test Short life test Long life test
  • 10. Fatigue Testing Machines: Rotating Bending Testing Machine Axial loading (push-pull) type fatigue tester
  • 12. Rotating Bending Testing Machine • This type of machine gives S-N curve • The motor is turning at a constant revolution per minute or frequency • To create a failure on the specimen, a constant-stationary force is applied on the specimen, which creates a constant bending moment.
  • 13. Working Principle A stationary moment applied to a rotating specimen causes the stress at any point on the outer surface of the specimen to go from zero to a maximum tension stress, back to zero and finally to a compressive stress. The process is repeated.
  • 14. Axial loading (push-pull) type fatigue tester
  • 15. Axial loading (push-pull) type fatigue tester In this type the specimen is not exposed to bending but to pure axial (tensile or compressive) loading. Specimen is held at two ends and loaded cyclically between two extreme (maximum and minimum) values.