Issue 37

K. Yanase et alii, Frattura ed Integrità Strutturale, 37 (2016) 101-107; DOI: 10.3221/IGF-ESIS.37.14 101 Focussed on Multiaxial Fatigue and Fracture High cycle torsional fatigue properties of 17-4PH stainless steel K. Yanase Fukuoka University, B.M. Shönbauer University of Natural Resources and Life Sciences (BOKU) , M. Endo Fukuoka University, A BSTRACT . Sensitivity to small defects under torsional fatigue loading condition is examined in the high cycle fatigue regime. Fatigue crack initiation and small crack growth behaviors were observed during fatigue testing and fractographic investigations were performed. The results are compared to the data obtained in the uniaxial fatigue tests, which allows the effect of biaxial stresses on the surface of material to be discussed. Finally, an approach for predicting the fatigue limit of 17-4PH stainless steel under torsional and tension-compression fatigue loadings is presented. K EYWORDS . 17-4PH; Small defect; Torsion; Biaxial fatigue; Fatigue limit. I NTRODUCTION recipitation-hardened chromium-nickel-copper stainless steel 17-4PH possesses high strength, toughness and good corrosion resistance. Therefore, it is widely used in applications where good corrosion resistance as well as high strength are required, e.g., in the aerospace, chemical, food processing, paper and power industry. In the last few decades, a number of investigations on the uniaxial fatigue properties of 17-4PH have been performed; however, no results of torsional fatigue tests are presently available. In practice, there are several applications for the material in which components (e.g., bearing outer rings, propeller shafts and pressure safety valve springs) are exposed to torsional fatigue loading and where a high number of load cycles is accumulated within service life. Given the substantial knowledge on uniaxial fatigue, it is of practical merit to propose a predictive method that can connect the fatigue strength under multiaxial loading with that under uniaxial loading. In our previous studies [1,2], a series of tension-compression fatigue tests were carried out to elucidate the uniaxial fatigue properties of 17-4PH stainless steel in the high and very high cycle fatigue regimes. It was found that the material exhibits interesting properties that are different from those noted for conventional steels. For example, the defect tolerance under cyclic loading is highly dependent on the notch root radius, which makes the prediction of the fatigue strength in the presence of small flaws challenging. P