What is low cycle fatigue test?
Low cycle fatigue (LCF) is low-cycle endurance testing, where components are subject to mechanical cyclic plastic strains that cause fatigue failure within a short number of cycles.
What is low cycle fatigue failure and high cycle fatigue failure?
The difference between low cycle fatigue (LCF) and high cycle fatigue (HCF) has to do with the deformations. LCF is characterized by repeated plastic deformation (i.e. in each cycle), whereas HCF is characterized by elastic deformation.
When does low cycle fatigue occur?
In turbine engines this occurs during takeoff and landing for an aero-turbine or startups and shutdowns of a power generating turbine. A common example of an extreme form of low cycle fatigue is illustrated in Figure 1; extreme because the paperclip is bent back and forth well into the plastic deformation regime.
What is low cycle fatigue where is it used why is it important?
LCF is characterized by high amplitude, low-frequency plastic strains. Low cycle fatigue can be particularly useful in industries that rely on materials in temperature-varying and cyclic conditions including aerospace, architecture, automotive, oil and gas, and power generation industries.
What is the cause of low cycle fatigue failure?
LCF is a type of fatigue caused by large plastic strains under a low number of load cycles before failure occurs. High stresses greater than the material yield strength are developed in LCF due to mechanical or thermal loading.
What are the characteristics of low cycle fatigue?
Low cycle fatigue has two fundamental characteristics: plastic deformation in each cycle; and low cycle phenomenon, in which the materials have finite endurance for this type of load.
What is low cycle fatigue failure?
LCF is a type of fatigue caused by large plastic strains under a low number of load cycles before failure occurs. High stresses greater than the material yield strength are developed in LCF due to mechanical or thermal loading. The stresses may exceed the yield strength and cause large plastic deformation.
What is high cycle fatigue failure?
High cycle fatigue is a type of fatigue caused by small elastic strains under a high number of load cycles before failure occurs. The stress comes from a combination of mean and alternating stresses. HCF requires a high number of loading cycles to reach fatigue failure mainly due to elastic deformation.
What decreases the fatigue strength?
Decarburisation diminishes the fatigue resistance of steel components by: diminishing the local fatigue strength due to the decreased density of the surface layer, increased grain size and diminished fracture toughness and yield strength (Chernykh 1991; Todinov, 2000b).
How can fatigue failure 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.
What are the stages of fatigue failure?
There are three stages of fatigue fracture: initiation, propagation, and final rupture. Indeed, this is the way that most authors refer to fatigue fracture, for it helps to simplify a subject that can become exceedingly complex.
What is the main reason for fatigue failure?
Fatigue failure is the formation and propagation of cracks due to a repetitive or cyclic load. Most fatigue failures are caused by cyclic loads significantly below the loads that would result in yielding of the material.
Why do I have low cycle fatigue ( LCF )?
Common factors that have been attributed to low-cycle fatigue (LCF) are high stress levels and a low number of cycles to failure. Many studies have been carried out, particularly in the last 50 years on metals and the relationship between temperature, stress, and number of cycles to failure.
Which is an example of strain controlled fatigue?
Strain-controlled fatigue can be an important consideration in the design of industrial products. It is important for situations in which components or portions of components undergo either mechanically or thermally induced cyclic plastic strains that cause failure within relatively few (that is, approximately < 10 5) cycles.
How are thermal stresses related to low cycle fatigue?
Thermal stresses originating from an expansion or contraction of materials can exacerbate the loading conditions on a part and LCF characteristics can come into play. A commonly used equation that describes the behavior of low-cycle fatigue is the Coffin-Manson relation (published by L. F. Coffin in 1954 and S. S. Manson in 1953):
Can a nonzero mean strain affect fatigue life?
Likewise, the presence of nonzero mean strains and varying environmental conditions may alter fatigue life as compared with the constant-amplitude, fully reversed fatigue tests. Care must be exercised in analyzing and interpreting data for such cases.