Thermal Mechanical Fatigue Crack Growth. An Application for Fracture Mechanics Analyses of Gas Turbine Engine Disks.

1985 ◽  
Author(s):  
Dale A. Wilson ◽  
John R. Warren
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Gas Turbine ◽  
Crack Growth ◽  
Gas Turbine Engine ◽  
Turbine Engine ◽  
Thermal Mechanical Fatigue ◽  
Mechanical Fatigue

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.

A Thermo-Mechanical Fatigue Crack Growth Accumulative Model for Gas Turbine Blades and Vanes

2016 ◽  
Author(s):  
Andrea Riva ◽  
Alessio Costa ◽  
Dalila Dimaggio ◽  
Paolo Villari ◽  
Karl Michael Kraemer ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Crack Propagation ◽  
Gas Turbine ◽  
Crack Growth ◽  
Turbine Blades ◽  
Gas Turbine Blades ◽  
Mechanical Fatigue ◽  
Safety Margins

Heavy duty gas turbine blades and vanes are operated at high temperatures and high stresses, condition where several damage mechanisms can simultaneously be present. For example creep, fatigue and oxidation play an important role in the propagation of existing cracks. Crack growth models are employed for assessment criteria, interpretation of the field feedback and non-conformities management and they are required to be as accurate as possible when predicting crack propagation under the combined effect of all the three phenomena. In this work, a Linear Elastic Fracture Mechanics (LEFM) model based on isothermal experimental tests and validated by Thermo-Mechanical-Fatigue Crack Growth tests (TMFCG), is employed to predict crack propagation of a cast Ni-base superalloy used in gas turbine blades and vanes. When calculating the individual propagation fractions of creep and fatigue crack growth, the model accounts for the instantaneous stress state and temperature in transient regime (i.e. a complete cycle of start-up, base-load and shut-down). The loss of γ’- precipitates at the crack tip due to surface oxidation is interpreted as environmental damage fraction. A complete workflow for the systematic use of the approach, comprising an in-house software, has been defined and developed. Stress intensity factors used for LEFM calculations are determined either using tabulated weight functions or with the aid of Finite Element Analysis (FEA). This flexible approach is consistent with the industrial need of a given fracture mechanics calculation, which might require different levels of accuracy and resources/time consumption case by case. The software identifies the fraction of propagation caused by oxidation, creep crack growth or fatigue crack growth. This allows checking the physical realism of the results by comparing to metallographic analysis of fracture surfaces from broken TMFCG test specimen and/or real component damage information from field. Besides, this feature can be helpful to support the engineer in residual life evaluation under damage tolerant approach because it allows the identification of the type of operational regime that minimizes crack propagation. The software also allows the execution of sensitivity analyses via Monte-Carlo calculations, identifying for a given component and operational condition the more relevant calculation inputs. This feature also quantitatively supports the engineers in the identification of the most appropriate safety margins.

Probabilistic Fretting Fatigue Assessment of Aircraft Engine Disks

2009 ◽  
Author(s):  
Michael P. Enright ◽  
Kwai S. Chan ◽  
Jonathan P. Moody ◽  
Patrick J. Golden ◽  
Ramesh Chandra ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Gas Turbine ◽  
Crack Growth ◽  
Stress Gradient ◽  
Random Variables ◽  
Aircraft Engine ◽  
Fretting Fatigue ◽  
Turbine Engine ◽  
Engine Components

Fretting fatigue is a random process that continues to be a major source of damage associated with the failure of aircraft gas turbine engine components. Fretting fatigue is dominated by the fatigue crack growth phase and is strongly dependent on the magnitude of the stress values in the contact region. These stress values often have the most influence on small cracks where traditional long-crack fracture mechanics may not apply. A number of random variables can be used to model the uncertainty associated with the fatigue crack growth process. However, these variables can often be reduced to a few primary random variables related to the size and location of the initial crack, variability associated with applied stress and crack growth life models, and uncertainty in the quality and frequency of non-deterministic inspections. In this paper, an approach is presented for estimating the risk reduction associated with non-destructive inspection of aircraft engine components subjected to fretting fatigue. Contact stress values in the blade attachment region are estimated using a fine mesh finite element model coupled with a singular integral equation solver and combined with bulk stress values to obtain the total stress gradient at the edge of contact. This stress gradient is applied to the crack growth life prediction of a mode I fretting fatigue crack. A probabilistic model of the fretting process is formulated and calibrated using failure data from an existing engine fleet. The resulting calibrated model is used to quantify the influence of inspection on the probability of fracture of an actual military engine disk under real life loading conditions. The results can be applied to quantitative risk predictions of gas turbine engine components subjected to fretting fatigue.

Probabilistic Fretting Fatigue Assessment of Aircraft Engine Disks

2010 ◽  
Vol 132 (7) ◽  
Author(s):  
Michael P. Enright ◽  
Kwai S. Chan ◽  
Jonathan P. Moody ◽  
Patrick J. Golden ◽  
Ramesh Chandra ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Gas Turbine ◽  
Crack Growth ◽  
Stress Gradient ◽  
Random Variables ◽  
Aircraft Engine ◽  
Fretting Fatigue ◽  
Turbine Engine ◽  
Engine Components

Fretting fatigue is a random process that continues to be a major source of damage associated with the failure of aircraft gas turbine engine components. Fretting fatigue is dominated by the fatigue crack growth phase and is strongly dependent on the magnitude of the stress values in the contact region. These stress values often have the most influence on small cracks where traditional long-crack fracture mechanics may not apply. A number of random variables can be used to model the uncertainty associated with the fatigue crack growth process. However, these variables can often be reduced to a few primary random variables related to the size and location of the initial crack, variability associated with applied stress and crack growth life models, and uncertainty in the quality and frequency of nondeterministic inspections. In this paper, an approach is presented for estimating the risk reduction associated with the nondestructive inspection of aircraft engine components subjected to fretting fatigue. Contact stress values in the blade attachment region are estimated using a fine mesh finite element model coupled with a singular integral equation solver and combined with bulk stress values to obtain the total stress gradient at the edge of contact. This stress gradient is applied to the crack growth life prediction of a mode I fretting fatigue crack. A probabilistic model of the fretting process is formulated and calibrated using failure data from an existing engine fleet. The resulting calibrated model is used to quantify the influence of inspection on the probability of fracture of an actual military engine disk under real life loading conditions. The results can be applied to quantitative risk predictions of gas turbine engine components subjected to fretting fatigue.

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