Define endurance strength mechanical11/9/2023 ![]() For such cases, the load cycle is easily defined. In elastic materials, a cyclic load causes a periodic-cyclic stress response. For a superficial discussion, it can, however, be assumed that the fatigue-controlling state variable has the same value at the start and end of each load cycle. In a general case, all cycles do not have the same amplitude. A load cycle is defined as the duration from one peak in the studied variable to the next peak. The fatigue process is typically viewed as controlled by a specific such variable. The state at a point in the material can be described by many different variables such as stress, strain, or energy dissipation. Under the influence of a nonconstant external load, the state in the material also varies with time. Because the largest part of the component's life is spent before it is possible to observe a macroscopic crack, most designs aim to avoid ever encountering such damage. There is, however, some overlap between the disciplines and the measured number of cycles to fatigue often includes the last two stages as well. The term fatigue applies mainly to the first stage. The details of the last two stages are usually considered within the topic of fracture mechanics. A microscopic crack instead grows rapidly, causing sudden failure of the component. The cracked component breaks because it can no longer sustain the peak load.įor certain applications, the second stage cannot be observed.The macroscopic crack grows for each cycle until it reaches a critical length.During a large number of cycles, the damage develops on the microscopic level and grows until a macroscopic crack is formed.The process until a component finally fails under repeated loading can be divided into three stages: Fatigue is the most common source behind failures of mechanical structures. ![]() This type of structural damage occurs even when the experienced stress range is far below the static material strength. Material fatigue is a phenomenon where structures fail when subjected to a cyclic load. Structural Mechanics Material Fatigue What Is Material Fatigue? ![]()
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