Low cycle fatigue (LCF)and High Cycle Fatigue (HCF) testings are necessary for a variety of industries that require analysis of a material that endures fatigue damage over its application. Applications in designing regarding size in aeronautics, architecture, and energy-producing industries are using LCF methods to analyse the integrity of materials under these types of pressure. For example, a building’s materials that often endures earthquakes may have a inite fatigue life possible and should be analysed using low cycle fatigue criteria. The LCF results allow engineers to study materials in greater depth to understand mechanical and metallurgical phenomena including crack growth, work-softening, strain concentration, and work hardening.
There are three stages to low cycle fatigue testing:
• The irst stage is designed to detect crack initiation on a polished specimen.
• The second stage is propagation life, which occurs after initiation.
• The third stage is failure, which is usually determined by some percentage of load drop from a stable condition.
The standards that cover Fatigue testing: ASTM Standard E 606 (LCF) and E 466 (HCF)
Fatigue Material Properties
Fatigue Life – The number of cycles that the material will survive in service with a given cyclic stress.
Fatigue Strength – If we only require a material to last for a certain number of cycles then the maximum stress can be determined under which the material will not prematurely fail.
Fatigue Limit – The stress can be determined for any given material for which failure never occurs.
Determination of this maximum stress is the preferred option for many applications as the material will therefore never require replacement.
Fatigue Ratio – Fatigue resistance is largely inluenced by the tensile strength of the material at its surface.
The ratio of fatigue limit to tensile strength is known as the fatigue ratio.
