Abstract
A fatigue crack initiation model based on damage accumulation via a fatigue memory surface in conjunction with a plastic strain energy parameter was evaluated for thermomechanical fatigue loading in a gas turbine disc alloy. The accumulated damage in each hysteresis loop was summed up, and it was assumed that the damage at the stable state is repeated until failure occurs. Crack initiation occurs when enough fatigue damage has been obtained, and the number of cycles can thus be directly determined. The fatigue damage is highly coupled to the constitutive behaviour of the material, where the constitutive behaviour was modelled using a non-linear hardening description. Based on this, a stable state was achieved and the obtained damage could be extracted. A user-defined material subroutine was implemented, incorporating both the constitutive description and the fatigue damage accumulation. The framework was adopted in a finite element context to evaluate the thermomechanical fatigue crack initiation life of the disc alloy RR1000. From the evaluation it could be seen that a good prediction of the thermomechanical fatigue life was achieved compared to performed experiments.
Highlights
In the field of energy production and aircraft propulsion, with the use of gas turbines, thermomechanical fatigue (TMF) is one of the most damaging conditions that can possibly arise in a component
By extracting a set of internal variables at a stable state, number of cycles to crack initiation according to some defined life function that has been calibrated to experiments can be predicted
A satisfactory response of the constitutive behaviour compared to the experiments was obtained
Summary
In the field of energy production and aircraft propulsion, with the use of gas turbines, thermomechanical fatigue (TMF) is one of the most damaging conditions that can possibly arise in a component. One commonly used model to predict the fatigue crack initiation life is the Smith-Watson-Topper model [5] It is an energy-based model that accounts for mean stress influence and assumes that damage is brought on by the maximum tensile stress. Another energy-density model that was used for low-cycle fatigue with dwell time at elevated temperatures is the model introduced by Ostergren [6]. The maximum tensile stress and the plastic strain range are used It was shown by Kulawinski et al [7] that both the Smith-Watson-Topper model and the Ostergren model were able to predict the TMF life with satisfactory results for Waspaloy, with a slightly better prediction using the Ostergren model. The model was further enhanced by combining the plastic stress-strain hysteresis with the initiation model by Zamrik and Renauld [8] and an Arrhenius term to yield even better correlation to the experiments
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
