Design of Threaded Fatigue Test Specimen for Machining

Design and machining of the fatigue test specimens have significant effects on the duration and reliability of fatigue test. Fatigue test specimens essentially consist of three parts: the center or critical test section, which is the region where required conditions are simulated as closely as possible, and the two ends, which serve to transfer the load from the grips to the center section. When high strength materials are used for a complex geometry, such as a thread need to be tested, design and manufacturing of the specimens become more influential on the reliability and duration of the tests. Threaded fatigue test specimens were designed, machined, and tested in a four-point rotary bending fatigue testing machine. An innovative threaded fatigue test specimen that consistently fails at the critical test section was designed, machined, and tested successfully to give the required fatigue notch factor. Because of full scale fatigue testing with threaded parts is very expensive and sometimes dangerous, evaluated threaded fatigue specimen can be used in fatigue testing and it reduces duration of the experiment more than 60% for machined threaded specimens.