What is Fatigue (material)?
[[File:Pedalarm Bruch.jpg|thumb|Fracture of an aluminium crank arm. Dark area of striations: slow crack growth. Bright granular area: sudden fracture.]] When a [[material]] starts to become weakened, because of heavy use, this is known as '''material fatigue'''. Fatigue in fracture mechanics refers to the gradual weakening and eventual failure of materials under repeated loading. Several key factors affect how quickly and severely fatigue damage occurs: === Factors Influencing Fatigue Behavior in Fracture Mechanics === Fatigue in fracture mechanics isn’t just about materials wearing out—it’s a complex process influenced by a variety of factors. When a material experiences repeated loading and unloading, tiny cracks can form and grow over time, eventually causing the structure to fail. The speed and likelihood of this happening depend on several things, including how the material is stressed, the properties of the material itself, and the surrounding environment. Let’s break down these factors in simple terms and understand how they shape the fatigue behavior of materials. ==== 1. Stress Levels and Loading Conditions ==== * '''Stress Range''': Larger differences between maximum and minimum stress accelerate crack initiation and growth. * '''Mean Stress''': Higher average stress reduces fatigue life by keeping materials under constant [[Tension (mechanics)|tension]]. * '''Loading Frequency''': Faster loading cycles increase damage, especially when combined with heat, causing '''thermal fatigue'''. ==== 2. Material Properties ==== * '''Microstructure''': Fine-grained materials resist fatigue better as cracks spread more slowly. * '''Surface Finish''': Smooth surfaces prevent crack initiation, while rough ones create stress concentrators. * '''Residual Stresses''': [[Compressive stress|Compressive]] residual stresses delay crack growth, while [[tensile stress]] speed it up. ==== 3. Environmental Conditions ==== * '''Temperature''': High temperatures cause '''thermal fatigue''' by expanding and contracting the