Influence of effective stress intensity factor range on mixed mode fatigue crack propagation

A new technique is described for determining the critical stress intensity factor required for fatigue crack propagation to occur. It enables data to be obtained more rapidly and with fewer testpieces than existing techniques. Initial results obtained for En 3A mild steel are in excellent agreement with published data.

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Experimental Investigations of Fatigue Crack Propagation for Pipe Under Torsional Loading

ASME 2010 Pressure Vessels and Piping Conference: Volume 1 ◽

10.1115/pvp2010-25831 ◽

2010 ◽

Author(s):

Motoki Nakane ◽

Satoshi Kanno ◽

Shota Hashimoto ◽

Takayuki Watanabe ◽

Yukio Takahashi

Keyword(s):

Stress Intensity Factor ◽

Fatigue Crack ◽

Stress Intensity ◽

Intensity Factor ◽

Crack Propagation ◽

Crack Growth ◽

Fatigue Crack Propagation ◽

Growth Rates ◽

Torsional Loading ◽

Crack Growth Rates

This study discusses methods for evaluating fatigue crack propagation under torsional loading for pipes. To achieve this objective, fatigue crack propagation tests were carried out on both stainless steel and carbon steel used in piping systems of nuclear power plants. Two different kinds of pipes were tested in this study. These pipes had the same shape but the diameter and thickness of the larger pipe were twice those of the smaller pipe. The nominal shear stress amplitudes applied to the specimen were set between 50 and 100 MPa depending on the dimension of the specimen and desired crack growth rates. All fatigue tests were conducted under pure torsional loading with stress ratio R = −1 and at room temperature. The geometrical correction factors for the specimen were derived from elastic J-integral calculated by the FEM. The fatigue crack propagation tests results show that the crack growth rates estimated by the elastic stress intensity factor with the geometrical correction factor were much faster than curves prescribed in The Japan Society of Mechanical Engineers (JSME) codes. These results suggest that elastic plastic fracture parameters should be considered into the stress intensity factor because yield stresses for torsional loading would be smaller than those of uniaxial loading. The plastic zone correction method and modified reference stress method were examined as alternative methods. The crack growth rates estimated by the proposed methods almost totally correspond to the JSME curves. The two proposed methods were found to be quite effective at correctly evaluating the crack growth rates under torsional loading.

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Fully Automated SCC and Fatigue Crack Propagation Analyses on Deep Semi-Elliptical Flaws

Volume 1B: Codes and Standards ◽

10.1115/pvp2013-97678 ◽

2013 ◽

Cited By ~ 2

Author(s):

Kota Sugawara ◽

Hirohito Koya ◽

Hiroshi Okada ◽

Yinsheng Li ◽

Kazuya Osakabe ◽

...

Keyword(s):

Residual Stress ◽

Stress Intensity Factor ◽

Finite Element ◽

Fatigue Crack ◽

Stress Intensity ◽

Intensity Factor ◽

Crack Propagation ◽

Fatigue Crack Propagation ◽

Surface Flaw ◽

Stress Fields

In this paper, some results of crack propagation analyses of deep initially semi-elliptical flaws under assumed residual stress fields are presented. The crack propagation analyses were performed by using a software system that has been developed by Okada and his colleagues. It is based on a conventional finite element program but uses the quadratic tetrahedral finite elements to model the structure with the crack. The finite element model with the crack can be generated in an automated manner. The stress-intensity factor computations are performed by using the virtual crack closure-integral method (VCCM) for the quadratic tetrahedral finite element which was also proposed by Okada and his colleagues. The automatic meshing scheme for the crack propagation analyses has also been developed by the authors. By the authors’ previous publication, it was shown that the stress intensity factor of deep semi-elliptical surface flaw under assumed residual stress field reached its maximum value at the mid-depth of the crack. Hence, in present study, in order to investigate the feature of the crack propagation of deep surface cracks, we are conducting crack propagation analyses that can predict the crack extension from each point along the crack front for an arbitrary shaped surface flaw. It can also account for material anisotropy in the crack propagation behavior. Then, the SCC crack propagation analyses for a deep semi-elliptical surface flaw in a plate under assumed residual stress fields are being conducted. The results of the crack propagation analyses suggest that the shapes of the crack after the SCC crack propagation may not be exact semi-elliptic in its shape. In this paper, the analytical procedures and some results are presented. The same analytical procedures can be adopted to perform fatigue crack propagation analyses.

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