scholarly journals Crack Growth of a Polycrystalline Nickel Alloy under TMF Loading

2014 ◽  
Vol 891-892 ◽  
pp. 1302-1307 ◽  
Author(s):  
Christopher J. Pretty ◽  
Mark T. Whittaker ◽  
Steve J. Williams
Keyword(s):  
Crack Growth ◽  
Growth Rates ◽  
Peak Stress ◽  
Potential Drop ◽  
Polycrystalline Nickel ◽  
Testing Method ◽  
Transgranular Crack ◽  
Engine Components ◽  
Crack Growth Rates ◽  
Time Dependent Crack Growth

Thermo-mechanical fatigue (TMF) is an important factor for consideration when designing aero engine components due to recent gas turbine development, thus understanding failure mechanisms through crack growth testing is imperative. In the current work, a TMF crack growth testing method has been developed utilising induction heating and direct current potential drop techniques for polycrystalline nickel-based superalloys, such as RR1000. Results have shown that in-phase (IP) testing produces accelerated crack growth rates compared with out-of-phase (OOP) due to increased temperature at peak stress and therefore increased time dependent crack growth. The ordering of the crack growth rates is supported by detailed fractographic analysis which shows intergranular crack growth in IP test specimens, and transgranular crack growth in 90° OOP and 180°OOP tests. Isothermal tests have also been carried out for comparison of crack growth rates at the point of peak stress in the TMF cycles.

Mechanical Factors Affecting Stress Corrosion Crack Growth Rates in Buried Pipelines

2000 ◽  
Author(s):  
S. B. Lambert ◽  
J. A. Beavers ◽  
B. Delanty ◽  
R. Sutherby ◽  
A. Plumtree
Keyword(s):  
Crack Growth ◽  
Growth Rates ◽  
Electrical Potential ◽  
Potential Drop ◽  
Maximum Load ◽  
Load Test ◽  
Factors Affecting ◽  
Transgranular Crack ◽  
Groundwater Environment ◽  
Crack Growth Rates

Over the past several years, investigations have been carried out into the rate of crack growth in pipeline steels in simulated, near-neutral pH, groundwater environment (NS4 solution). Pre-cracked specimens were subject to constant amplitude loading under various frequencies, maximum loads and R-ratios (minimum/maximum load). Test times varied from about 20 to 400 days. Transgranular crack features, similar to those found in service, have been observed. The extent of crack growth was monitored using either electrical potential drop or detailed metallographic examinations at two laboratories. The resulting crack growth rates from both labs are consistent with a superposition model based on a summation of fatigue (Paris Law) and static (SCC) crack growth rates. Differences between the results at the two laboratories are discussed.

A Superposition Approach for Time-Dependent Fatigue Crack Growth

2012 ◽  
Author(s):  
Fashang Ma
Keyword(s):  
Stress Intensity Factor ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Intensity Factor ◽  
Crack Growth ◽  
Growth Rates ◽  
Time Dependent ◽  
Crack Growth Rates ◽  
Time Dependent Crack Growth

High temperature fatigue crack growth is a combination of fatigue, creep and environmental attack, which greatly enhance fatigue crack growth. In order to understand the damage mechanisms and develop a physically based crack growth model, systematic experimental research has been conducted under various loading conditions for different specimen geometries made from a high strength nickel alloy. Test results from this work showed that time-dependent fatigue crack growth rates differ significantly from those observed in conventional fatigue crack growth tests. Crack geometry and loading history significantly affect fatigue crack growth rate. These results suggest the need for a change in the K based superposition approach for time-dependent crack growth modeling. A phenomenological model has been developed to predict time-dependent crack growth under various loading histories and crack geometries. In this model an effective stress intensity factor is defined to account for the effects of constraint loss of fracture mechanics due to crack-tip plasticity, and the creep stress relaxation on stress intensity factor. It is found the model can accurately predict the dwell crack growth rates for different crack geometries under various loading conditions.

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.

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