Cyclic fatigue can be defined as
the stress, strain, and deformation induced in a material by cyclic loading
. Cyclic fatigue life is the number of loading cycles which produce a rupture or breakage in the material.
What are the three stages of fatigue?
There are three stages of fatigue fracture:
initiation, propagation, and final rupture
.
What is cyclic loading in fatigue?
Cyclic loading is
the application of repeated or fluctuating stresses, strains, or stress intensities to locations on structural components
. The degradation that may occur at the location is referred to as fatigue degradation.
What is cyclic fatigue failure?
A machine part or structure will,
if improperly designed and subjected to a repeated reversal or removal of an applied load, fail at a stress much lower than the ultimate strength of the material
. This type of time-dependent failure is referred to as a cyclic fatigue failure.
What is cyclic fatigue test?
Cyclic fatigue tests produce
repeated loading and unloading in tension, compression, bending, torsion or combinations of these stresses
. Fatigue tests are commonly loaded in tension – tension, compression – compression and tension into compression and reverse.
What is the reason for fatigue failure during cyclic loading?
Most fatigue failures are caused by cyclic loads significantly below the loads that would result in yielding of the material. The failure occurs due to
the cyclic nature of the load which causes microscopic material imperfections (flaws) to grow into a macroscopic crack (initiation phase)
.
Which is example of cyclic loading?
Cyclic loading is defined as the loads that are applied, removed, and reapplied, for example
on a pavement
, in a relatively rapid and repetitive form.
What does a fatigue failure look like?
A quick analysis of the fracture surface of a fatigue failure will often show features casually referred to as “
beach marks
”. These indicate the propagation of the failure from the initial cracks. Once the crack size has reached a critical level, it will propagate very rapidly until the fracture is complete.
How do I know if I have fatigue failure?
Fatigue failure is identified as starting
at a stress raiser or defect
, then the crack generates through the material before causing sudden failure. The crack progress is shown as smooth, rippled formation known as striations or beach marks, whilst the sudden failure is a classic brittle fracture with rough appearance.
Where do most fatigue cracks start?
Fatigue cracks of metals usually initiate from
the surface of a component
, where fatigue damage initiates as shear cracks on crystallographic slip planes. The surface shows the slip planes as intrusions and extrusions.
How can cyclic fatigue be prevented?
Premature fatigue failure is prevented by
careful attention to detail at the design stage
to ensure that cyclic stresses are sufficiently low to achieve the required endurance. Stress concentrations should be avoided where possible; a design with smooth ‘flowing’ lines is usually the optimum.
Is fatigue failure ductile or brittle?
Fatigue failure is
brittle-like
(relatively little plastic deformation) – even in normally ductile materials. Thus sudden and catastrophic! Applied stresses causing fatigue may be axial (tension or compression), flextural (bending) or torsional (twisting).
What are the main types of cyclic loading that lead to fatigue?
The process of fatigue consists of three (3) stages: a) Initial fatigue damage loading to crack nucleation and crack initiation. b)
Progressive cyclic growth of a crack (crack propagation)
until the remaining uncracked cross-section of the part becomes too weak to sustain the loads imposed.
Can blood tests show fatigue?
Your doctor may feel you should have some blood tests
to rule out physical causes for tiredness
. In most cases these turn out to be normal. This might include tests to rule out: Low iron levels (anaemia).
What is the fatigue test used for?
Fatigue tests are performed to
measure the reduction in stiffness and strength of materials under repeated loading and to determine the total number of load cycles to failure
. Fatigue tests are performed by repeated tension–tension, compression– compression, tension-compression or other combinations of cyclic loading.
What is the typical laboratory test used for fatigue?
The following instrumentation is typically used on a fatigue test:
strain gauges
.
accelerometers
.
displacement gauges
.
