Investigation of Fatigue Crack Propagation in Nickel Superalloy Using Diffraction Contrast Tomography and Phase Contrast Tomography

Evaluation of superalloy component life in turbine engines requires a detailed understanding of how fatigue crack initiation and short crack propagation contribute to fatigue life. However most investigations have been carried out post-mortem and in two dimensions. New techniques are able to fully resolve cracks propagating in four dimensions (space and time), enabling characterisation of their local environments and allowing a much deeper understanding of fatigue mechanics. Nickel-based superalloys experiencing high cycle fatigue have shown a high sensitivity to microstructure during initiation and short crack propagation. Using high energy X-rays and the combination of Diffraction Contrast Tomography (DCT) and Phase Contrast Tomography (PCT), we followed a fatigue crack initiated from a Focused Ion Beam (FIB) milled notch at room temperature. Analyses have been carried out to fully characterise the crack and its environment. We tracked the evolution of the crack and interactions with the microstructure. Subsequently, post-mortem investigations have been carried out to corroborate results obtained from the tomographs and to provide more local information of fatigue crack propagation.

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Effects of Compressive Residual Stress Near Precrack on Fatigue Crack Propagation Behavior Bent from a Slant Precrack (Based on Discontinuous Displacement Measured along Short Crack Immediately after bending)

TRANSACTIONS OF THE JAPAN SOCIETY OF MECHANICAL ENGINEERS Series A ◽

10.1299/kikaia.72.624 ◽

2006 ◽

Vol 72 (717) ◽

pp. 624-631 ◽

Cited By ~ 1

Author(s):

YouLi MA ◽

Tashiyuki TORII ◽

Kenichi SHIMIZU

Keyword(s):

Residual Stress ◽

Fatigue Crack ◽

Crack Propagation ◽

Fatigue Crack Propagation ◽

Compressive Residual Stress ◽

Short Crack ◽

Fatigue Crack Propagation Behavior ◽

Propagation Behavior ◽

Discontinuous Displacement ◽

Crack Propagation Behavior

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Numerical Calculation of Fatigue Crack Growth for the Structures of Elbow and Tee Pipe Based on RCC-MR A16 Code

Volume 6B: Materials and Fabrication ◽

10.1115/pvp2018-85061 ◽

2018 ◽

Author(s):

Peng Tang ◽

Jiacheng Luo ◽

Pengzhou Li ◽

Lei Sun ◽

Juan Luo

Keyword(s):

Fatigue Crack ◽

Fatigue Crack Growth ◽

Crack Propagation ◽

Crack Growth ◽

Fatigue Crack Propagation ◽

High Energy ◽

Normal Operation ◽

Weak Links ◽

Pipeline System ◽

Safe Operation

As the transport artery for the reactor coolant, high-energy piping systems are the links that maintain the normal operation of each system and play a crucial role in ensuring the normal operation and safety of the reactor in nuclear power plants. During the long-term operation of the reactor, stress concentration may be induced at the weak links in the pipeline systems, such as the elbow and the tee pipe structures, under the loads of high temperature, high pressure, flow-induced vibration and so on, and finally resulting in crack defects. Due to the continuous fatigue load during the lifetime, the defects in the inner surface of the pipes may propagate rapidly and even penetrate through the wall thickness, leading to the leakage of coolant and seriously affecting the safe operation of the reactor. In order to ensure the normal function of the pipeline system and meet the service requirements, this paper studies the fatigue crack propagation problems in elbows and tee pipe in the reactor pipe systems to ensure the safe operation of the pipeline. According to the RCC-MR A16 code, the fatigue crack propagation calculation program is compiled for the elbow and tee pipe made of austenitic steel to study the fatigue crack growth process and the influencing factors of crack propagation.

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The Effect of a Complex Stress State on Fatigue Crack Propagation and the Orientation of the Cracking Plane in VT3-1 Aeronautical Titanium Alloy

Fatigue of Aircraft Structures ◽

10.2478/v10164-010-0011-0 ◽

2009 ◽

Vol 2009 (1) ◽

pp. 116-130

Author(s):

Dorota Kocańda ◽

Janusz Mierzyński

Keyword(s):

Titanium Alloy ◽

Fatigue Crack ◽

Stress State ◽

Crack Propagation ◽

Crack Growth ◽

Fatigue Crack Propagation ◽

Complex Stress ◽

Complex Stress State ◽

Short Crack ◽

Short Cracks

The Effect of a Complex Stress State on Fatigue Crack Propagation and the Orientation of the Cracking Plane in VT3-1 Aeronautical Titanium AlloyThe subject of the paper is the investigations of fatigue crack imitation and propagation in notched specimens made of the VT3-1 aeronautical russian titanium alloy under combined bending - torsion loading. The presence of short cracks was revealed at various ratios of bending to torsion. Experimental courses of short and long crack growth rates have been proved by the SEM and TEM micrographs which illustrated the changes in the mechanism of cracking in the examined specimens. The attempt was undertaken in order to explain partly brittle fracture that was observed in the range of fatigue short crack growth in the VT3-1 titanium alloy specimens. The results of the study of atmospheric hydrogen absorption capability and its ability for penetration inside the faces of nucleated and propagated microcracks in the surface layer allowed for suggestion that the cleavage mechanism of fracture found in the regime of short crack growth in the VT3-1 titanium alloy specimens was induced by hydrogen.

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Cyclic Deformation Induced Residual Stress Evolution and 3D Short Fatigue Crack Growth Investigated by Advanced Synchrotron Tomography Techniques

Materials ◽

10.3390/ma14061562 ◽

2021 ◽

Vol 14 (6) ◽

pp. 1562

Author(s):

Benjamin Dönges ◽

Melanie Syha ◽

Anne K. Hüsecken ◽

Ullrich Pietsch ◽

Wolfgang Ludwig ◽

...

Keyword(s):

Fatigue Crack ◽

Fatigue Crack Growth ◽

Residual Stresses ◽

Crack Propagation ◽

Crack Growth ◽

Cyclic Deformation ◽

Phase Contrast ◽

Crack Nucleation ◽

Short Fatigue Crack ◽

Phase Contrast Tomography

Diffraction and phase contrast tomography techniques were successfully applied to an austenitic–ferritic duplex stainless steel representing exemplarily a metallic material containing two phases with different crystal structures. The reconstructed volumes of both phases were discretized by finite elements. A crystal plasticity finite-element analysis was executed in order to simulate the development of the experimentally determined first and second order residual stresses, which built up due to the manufacturing process of the material. Cyclic deformation simulations showed the single-grain-resolved evolution of initial residual stresses in both phases and were found to be in good agreement with the experimental results. Solely in ferritic grains, residual stresses built up due to cyclic deformation, which promoted crack nucleation in this phase. Furthermore, phase contrast tomography was applied in order to analyze the mechanisms of fatigue crack nucleation and short fatigue crack propagation three-dimensionally and nondestructively. The results clearly showed the significance of microstructural barriers for short fatigue crack growth at the surface, as well as into the material. The investigation presented aims for a better understanding of the three-dimensional mechanisms governing short fatigue crack propagation and, in particular, the effect of residual stresses on these mechanisms. The final goal was to generate tailored microstructures for improved fatigue resistance and enhanced fatigue life.

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