Reliability prediction, scatter-band analysis and fatigue limit assessment of high-cycle fatigue properties in EN-GJS700-2 ductile cast iron

Abstract

In this article, high-cycle fatigue properties of the EN-GJS700-2 ductile cast iron were experimentally examined, using the four-point rotary-bending fatigue machine. Such material has been widely utilized for manufacturing crankshafts in automotive industries. Therefore, standard specimens were extracted from the crankshaft to consider the manufacturing effect. The other aim of this work is to develop a model, anticipating the probabilistic behavior of the EN-GJS700-2 ductile cast iron. For such objective, the parametric analysis of the most commonly used statistical distributions were performed and compared. Based on the best fitted distribution function on experimental data, fatigue lifetime reliability specifications of the material were analyzed and represented through probabilistic modeling. In addition, the S-N diagram with its scatter-band were conducted at different values of the confidence level. As another investigation, the criterion for designing the crankshaft is the infinite lifetime, or in more practical terms, is the design with allowable stress levels, below the fatigue limit. Based on the staircase test methodology, fatigue endurance limit tests were conducted. Then, statistical trends of the fatigue limit were analyzed by the Dixon-Mood method, based on the maximum likelihood estimation. Obtained results represents that the fatigue limit was 211 MPa for the ductile cast iron.

Bending cyclic behavior and scatter-band analysis of aluminum alloys under beneficial and detrimental conditions through high-cycle fatigue regime

“…Usually, experimental fatigue data have high scattering, especially in the high-cycle fatigue regime. Therefore, the fatigue lifetime of materials is described by statistical functions such as Weibull or Normal [15][16][17]. For these distribution functions, the averaged value (  ) and the standard deviation (  ) are considered for recorded data.…”

“…However, in this research, Eq. (1) was utilized for the scatter-band analysis, which could be written as follows [16,17],…”

“…where the z value could be found from the literature [16,17] and the confidence level. In this research, the confidence level was considered as 85, 90, and 95% for the Normal distribution function.…”

“…When the confidence level increases, the scatterband will be wider. It should be noted that the z value is 1.44, 1.65, and 1.96 when the confidence level is 85, 90, and 95%, respectively [16,17]. Finally, the scatter-band could be written as     N z , where N is the fatigue lifetime at each stress level.…”