The fatigue limit is the maximum stress level a material can withstand for an infinite number of loading cycles without failing. This concept is crucial in engineering, especially for components subjected to repeated stress, such as in bridges or aircraft. Understanding the fatigue limit helps engineers design safer and more durable structures. Materials like steel and aluminum exhibit a fatigue limit, while others, like plastic, may not have a distinct limit. Testing for fatigue limits involves subjecting materials to cyclic loading until failure occurs, allowing engineers to predict the lifespan of components under operational conditions.