Dictionary FailureMaterial FailureFatigue Loading Fatigue Loading Last updated: January 22, 2020 What Does Fatigue Loading Mean? Fatigue loading is the changes observed in a material under the influence of stress generated during cyclic loading. This is generally represented by plotting a stress cycle curve (S-N curve), where S represents stress and N represents the number of cycles to failure. There is progressive and localized structural damage when fatigue loading occurs, and if the local stresses are high enough leads to the initiation of a crack, the growth of the crack and finally fracture. Fatigue can exacerbate structural damage in the presence of corrosive environments. Advertisement Corrosionpedia Explains Fatigue Loading In materials science, fatigue is the weakening of a material, and fatigue loading means continuously loading a material with some force until it experiences a crack. It is a cumulative effect that causes a material to fail after repeated applications of stress, none of which exceeds the ultimate tensile strength. The term fatigue is based on the concept that a material becomes "tired" and fails at a stress level below the nominal strength of the material. In a corrosive environment, if a material experiences fatigue loading, it leads to corrosion fatigue due to the combined action of cycling (or alternating) stresses and a corrosive environment. The fatigue process is thought to rupture the protective passive film, after which corrosion is accelerated. If the metal is simultaneously exposed to a corrosive environment, then the failure can take place at even lower loads and after a shorter time. Fatigue occurs when a material is subjected to repeat loading and unloading. If the loads are above a certain threshold, microscopic cracks form at the stress concentrators such as the surface, persistent slip bands (PSBs) and grain interfaces. Eventually, when a crack reaches a critical size, the crack propagates suddenly, and the structure fractures. The shape of the structure significantly affects the fatigue life — square holes or sharp corners lead to elevated local stresses where fatigue cracks can begin. Fatigue loading causes fatigue failure, which occurs in three stages: Crack initiation Slow, stable crack growth Rapid fracture The majority of engineering failures are caused by fatigue. The greatest concern in circuit boards, engines and many industrial applications is thermal fatigue. Thermal fatigue can arise from thermal stresses produced by cyclic changes in temperature. Related Question How can I determine and measure steel's endurance limit? Advertisement Share This Term> Related Terms Fatigue Corrosion Fatigue Fatigue Wear Fatigue Strength Cyclic Stress Corrosion Fatigue Strength Thermal Fatigue Ultimate Tensile Strength Stress Concentration Factor Lateral Loading Related Reading 6 Tests to Measure a Material’s Strength 21 Types of Pipe Corrosion & Failure High Pressure Fastener Coating Practices Under Fire: Ian MacMoy Speaks Out Calculating Tensile Stress: Why It Needs to Be Done Now Understanding the 3 Types of Tensile Strength The Relationship Between Corrosion Fatigue and Stress Corrosion Cracking Tags Materials Selection Failure Equipment Substances Substance Modification Metals Material Modification Material Failure Engineering and Spec Writing Corrosion Failure Trending Articles Corrosion An Introduction to the Galvanic Series: Galvanic Compatibility and Corrosion Chemical Compound 5 Most Common Types of Metal Coatings that Everyone Should Know About Asset Management Understanding Aluminum Corrosion Asset Management If Copper is a Noble Metal then Why Are My Pipes Corroding?