M.tech Project - Crack Growth Analysis and Propagation Life Prediction of Gas Turbine Rotor Discs

Aim/Goal

Setting up standard guidelines for crack propagation life estimation of gas turbine rotor discs using 3D crack modeling technique in finite element analysis.

Problem Definition

• Gas turbines are frequently employed in power generation due to their higher power to weight ratio and they usually rotate at high speeds and operate at high temperatures. So, these are heavily loaded due to mechanical and thermal loads.
• This leads to the generation of surface cracks at stress concentration zones or at pre-existing defects. The presence of crack can significantly reduce the life of component and components fails in brittle fashion even if it is ductile material.
• After reaching a critical state, these discs fracture into two or more number of parts due to the propagation of these cracks.
• Hence, turbine discs are considered as critical components in the engine and their crack propagation life estimation under fatigue loading is prime importance.
• Gas turbine rotor discs have complex geometries with cooling holes in different directions such as Axial, Radial or hybrid. This results in 3D stress field at many locations.
• For such complex geometries, 3D crack modeling technique and crack growth analysis using stress intensity factor & J-Integral is required to predict the realistic crack propagation life.

Objectives

• Initial FE and FM life (crack propagation life using fracture mechanics) assessment for standard components having standard crack geometries using 3D crack modeling technique and comparison with published or experimental results to setup the benchmark. 
• Next step involves FM life prediction of various cracks in different locations of gas turbine disc using 3D crack modeling technique in ANSYS. 
• Setting up standard guidelines for 3D crack modeling technique of GT rotor disks. 
• Comparison of FM life prediction by 2D analysis in IWM VERB and 3D crack modeling technique in ANSYS.

Methodology

• This work is focused on the crack propagation life estimation of gas turbine rotor discs under different service conditions using fracture mechanics concepts. 3D crack modeling technique and crack growth analysis using stress intensity factor & J-Integral is required to predict the realistic crack propagation life. 
• First, for benchmarking, stress intensity factors of surface and corner cracks in plates subjected to tensile loading are determined using 3D crack modelling technique in ANSYS. These results have been Compared with published results and good agreement was observed.Next, crack growth analysis and FM life estimation simulation is performed on plate having surface crcak and compared with results available and achieved excellent agreement.
• 3D crack modeling, Stress intensity factors estimation and FM life prediction is performed for gas turbine disc which has been taken from the literature. Predicted life is compared with experimental results to validate the methodology and the results are very good.
• Same methodology using 3D crack modelling is used for different gas turbine disc locations to predict the life of component.
• Until now, this work is performed under LEFM (linear elastic fracture mechanics) conditions. From now onwards, it will be carried out under EPFM (elastic-plastic fracture mechanics) conditions.
• This work is not completed yet. So, changes to the existing content are possible.

Result

This is the result of analysis performed on the literature disc.

Conclusions

• 3D crack modeling technique is very effective for estimating accurate stress intensity factors, crack propagation life and critical crack length. 
• Life from 2D analysis in IWM VERB is very much below the life estimated from Ansys.  
• If  accurate life and the critical crack length is known, inspection periods and maintenance can be scheduled accordingly.  

Downloads 

will be updated soon

Acknowledgemnet

Project guide : Dr K S R Krishna Murthy, IIT Guwahati
Mentors in SIEMENS :
Mr. Siddharth Jain,
Mr. Pritam Kondalwar
Mr. Manish Kumar Purohit
Mr. Sunder Raman Mohan 

I thank above all for their guidance and support during this work.

Suggested links

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Read about my B.tech project on fracture mechanics here

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