Session: 28-02 Lifing Applications using Probabilistic Methods

Paper Number: 82303

82303 - A Probabilistic Model for Forging Flaw Crack Nucleation Processes for Heavy Duty Gas Turbine Rotor Operations 

We developed a probabilistic model for quantifying the number of load cycles for nucleation of forging flaws into a crack under gas turbine rotor operation conditions. The model correlates low cycle fatigue (LCF) data, ultrasonic testing (UT) indication data, flaw morphology and type with the nucleation process. This paper is the third of a series [1,2] of publications where this modeling approach is presented progressively. It focuses on the effect of temperature variation on the nucleation life of forging flaws.

High temperature tests were performed on specimens that include forging flaws. Based on the morphology of the flaws and the observed number of cycles until crack nucleation. The flaws of different sizes and shapes are effectively described by an ellipsoidal finite element model at the respective temperature and stress levels. The resulting stress distributions are analyzed by a local probabilistic low-cycle fatigue model accounting for the statistical size effects.

This presented crack nucleation model is calibrated using the Maximum Likelihood Estimation (MLE) method applied to the flaw extension perpendicular to the fracture surface, which is not available experimentally. The MLE methodology is extended to account for experimental findings on secondary flaws which did not cause specimen failure and had no measurable nucleation time. These flaws are accounted for as censored data points.

The proposed probabilistic modeling approach is based on experimental data for realistic engine temperature and stress conditions for heavy duty gas turbine rotor components utilized in the energy sector. Our suggested approach can support component assessment under flexible gas turbines operation conditions driven by increased availability of intermittent renewable energy sources.

1)      Radaelli, Francesco, Kadau, Kai, Amann, Christian and Gumbsch, Peter. “Probabilistic Fracture Mechanics Framework Including Crack Nucleation of Rotor Forging Flaws.” Proceedings of ASME Turbo Expo 2019: pp. GT2019–90418. 2019. DOI 10.1115/GT2019-90418.

2)      Radaelli, Francesco, Amann, Christian, Ali Aydin, Igor Varfolomeev, Gumbsch, Peter, and Kadau, Kai, “A Probabilistic Model for Forging Flaw Crack Nucleation Processes” Proceedings of ASME Turbo Expo 2020: pp. GT2020–14606. 2020.

Presenting Author: Kai Kadau Siemens Energy

Presenting Author Biography: Senior Key Expert Probabilistic Analysis and Simulation

Authors:

Francesco Radaelli Siemens Energy Global GmbH & Co. KG
Christian Amann Siemens Energy Global GmbH & Co. KG
Ali Aydin Fraunhofer IWM
Igor Varfolomeev Fraunhofer IWM
Peter Gumbsch Karlsruhe Institute of Technology
Kai Kadau Siemens Energy