Deducing the Fatigue Crack Growth Rates of Natural Flaws in Silicon Nitride Ceramics: Role of R -Curves

2013 ◽  
Vol 96 (8) ◽  
pp. 2593-2597 ◽  
Author(s):  
Martin Härtelt ◽  
Stefan Fünfschilling ◽  
Thomas Schwind ◽  
Heinz Riesch-Oppermann ◽  
Theo Fett ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Silicon Nitride ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Nitride Ceramics ◽  
Crack Growth Rates

An Assessment of Low Alloy Steel EAC Corrosion Fatigue Relationships for BWR Environment

2005 ◽  
Author(s):  
Hardayal Mehta ◽  
Ron Horn
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Water Chemistry ◽  
Crack Growth ◽  
Corrosion Fatigue ◽  
Growth Rates ◽  
Ferritic Steels ◽  
Asme Code ◽  
Crack Growth Rates

The fatigue crack growth rates for ferritic steels in water environments given in A-4300 of Appendix A, Section XI, ASME Code, were developed from data obtained prior to 1980. Subsequently, updated assessments by Eason, et al. and recent laboratory test results from Seifert and Ritter demonstrated that under certain conditions, ferritic steels exposed to oxygenated water environments may be susceptible to high fatigue crack growth rates that exceed the current disposition curves. In the light of ASME adopting Code Case N-643 for PWRs, there is a need for a similar Code Case for the BWR water environments (for both the normal water chemistry and hydrogen water chemistry/NobleChem) that takes into account these findings. This could mean modification of current EAC curves in the ASME Code. A joint program of EPRI and GE was developed to address this need for updated evaluations of the corrosion fatigue. The program’s first task has been to re-assess the role of rise time, environment, alloy, heat treatment and impurity levels on the established ASME codified disposition curves/methodologies. The data was then used as a basis to assess the impact of on modified cyclic curves on the disposition approaches that are currently used to evaluate postulated flaws in the BWR reactor pressure vessel or RPV head and the feed water nozzle regions. The presentation would include a discussion of the appropriate BWR plant transients and the GE process for performing evaluations. The role of the evaluations on the establishment of inspection intervals currently determined using NUREG-0619 and the latest BWROG Report would also be presented. Finally, the relationship between cyclic load and constant load behavior in these steels are discussed in the context of the mechanisms for environmentally assisted cracking.

scholarly journals Advantageous Description of Short Fatigue Crack Growth Rates in Austenitic Stainless Steels with Distinct Properties

Metals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 475
Author(s):  
Lukáš Trávníček ◽  
Ivo Kuběna ◽  
Veronika Mazánová ◽  
Tomáš Vojtek ◽  
Jaroslav Polák ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Stainless Steels ◽  
Growth Rates ◽  
Large Scale ◽  
J Integral ◽  
Scale Yielding ◽  
Residual Fatigue ◽  
Crack Growth Rates

In this work two approaches to the description of short fatigue crack growth rate under large-scale yielding condition were comprehensively tested: (i) plastic component of the J-integral and (ii) Polák model of crack propagation. The ability to predict residual fatigue life of bodies with short initial cracks was studied for stainless steels Sanicro 25 and 304L. Despite their coarse microstructure and very different cyclic stress–strain response, the employed continuum mechanics models were found to give satisfactory results. Finite element modeling was used to determine the J-integrals and to simulate the evolution of crack front shapes, which corresponded to the real cracks observed on the fracture surfaces of the specimens. Residual fatigue lives estimated by these models were in good agreement with the number of cycles to failure of individual test specimens strained at various total strain amplitudes. Moreover, the crack growth rates of both investigated materials fell onto the same curve that was previously obtained for other steels with different properties. Such a “master curve” was achieved using the plastic part of J-integral and it has the potential of being an advantageous tool to model the fatigue crack propagation under large-scale yielding regime without a need of any additional experimental data.

Thermo-mechanical fatigue crack growth behaviour of Ti-6246

2021 ◽  
Author(s):  
◽  
Jennie Palmer
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Gas Turbine ◽  
Crack Growth ◽  
Growth Rates ◽  
Turbine Engine ◽  
Mechanical Fatigue ◽  
Test Conditions ◽  
Materials Used ◽  
Crack Growth Rates

Within the gas turbine engine, the high transient thermal stresses developed due to variations in power requirements during a typical flight cycle give rise to the phenomenon of thermo-mechanical fatigue (TMF). Associated with higher operating temperatures, the study of TMF within the gas turbine engine has mainly been focused on materials used in the latter turbine sections. However, the increasing temperatures to improve operating efficiency have led to the requirements for an understanding of the TMF behaviour in materials used for the later stages of the compressor. As such, fatigue crack growth rates are required to be evaluated under non-isothermal conditions along with the development of a detailed understanding of related failure mechanisms. In the current study a bespoke TMF crack growth (TMFCG) test set up has been developed and validated to investigate the TMFCG behaviour of the titanium alloy, Ti-6246. The study has explored the effects of phasing between mechanical loading and temperature, as well as the effects of maximum cycle temperature. Results show in-phase (IP) test conditions to have faster crack growth rates than out-of-phase (OP) test conditions, due to increased temperature at peak stress and therefore increased time-dependent crack growth. Fractography evidences subtle differences in fracture mechanisms and the microstructural analysis along the crack path has aided the characterisation of damage mechanisms in IP and OP test conditions.

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