This is mainly applicable for short-lived devices where very large overloads may occur at low cycles. Typical examples include the elements of control systems in mechanical devices. A fatigue failure mostly begins at a local discontinuity and when the stress at the discontinuity exceeds elastic limit there is plastic strain. The cyclic plastic strain is responsible for crack propagation and fracture. Experiments have been carried out with reversed loading and | Module 3 Design for Strength Version 2 ME IIT Kharagpur Lesson 4 Low and high cycle fatigue Version 2 ME IIT Kharagpur Instructional Objectives At the end of this lesson the students should be able to understand Design of components subjected to low cycle fatigue concept and necessary formulations. Design of components subjected to high cycle fatigue loading with finite life concept and necessary formulations. Fatigue strength formulations Gerber Goodman and Soderberg equations. Low cycle fatigue This is mainly applicable for short-lived devices where very large overloads may occur at low cycles. Typical examples include the elements of control systems in mechanical devices. A fatigue failure mostly begins at a local discontinuity and when the stress at the discontinuity exceeds elastic limit there is plastic strain. The cyclic plastic strain is responsible for crack propagation and fracture. Experiments have been carried out with reversed loading and the true stressstrain hysteresis loops are shown in . Due to cyclic strain the elastic limit increases for annealed steel and decreases for cold drawn steel. Low cycle fatigue is investigated in terms of cyclic strain. For this purpose we consider a typical plot of strain amplitude versus number of stress reversals to fail for steel as shown in . Version 2 ME IIT .
