PSI - Issue 17

Available online at www.sciencedirect.com Structural I tegrity Procedia 00 (2019) 000 – 000 Available online at www.sciencedirect.com ScienceDirect Structural Integrity Procedia 00 (2019) 000 – 000 Available online at www.sciencedirect.com ScienceDirect

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Procedia Structural Integrity 17 (2019) 758–765

ICSI 2019 The 3rd International Conference on Structural Integrity Structural Integrity Analysis and Life Estimation of a Gas Turbine Bladed-Disc Shahnawaz Ahmad a , A Suman b , T Sidharth b , Ganesh Pawar b , Vikas Kumar a , N. S. Vyas b a Defence Metallurgical Research Laboratory Kanchanbagh, Hyderabad, India b Indian Institute of Technology, Kanpur, India Turbine blades in an aero-engine are subjected to severe conditions of high temperature and pressure, which cause high levels of stress leading to crack formation and subsequent failure in service. We have investigated the influence of crack on vibration parameters of a typical aero-engine gas turbine blade and have described a life assessment approach for blades and bladed discs. A typical transport aircraft AMT (Accelerated Mission Test) cycle has been utilized for getting operating parameters. Material data is taken from tests conducted on specimens extracted from turbine disc of a transport aircraft. Initial studies are carried out on idealizations involving cantilever beams with uniform cross-section; the procedures are then extended to free-standing turbine blades with asymmetric airfoil cross section mounted at a stagger angle on a rotating disc. Dynamic characteristics of the blade are estimated and free vibrations analysis has been carried out for healthy blades and those with cracks of different sizes. Influence of crack size on natural frequencies and mode shapes is studied. Results show a difference of less than 1% in frequency for cracks less than 1mm in length; for larger crack lengths the frequency shifts are higher. Analytical results are compared with experimental tests on a Laser Doppler Vibrometer set-up. Subsequently, forced vibration analysis is performed and a methodology, using Lazan’s law ,is developed to extract modal damping ratios from the strain energy of the blade under nozzle excitation pressure fluctuations. Modal damping ratios, thus obtained, are indicative the energy dissipation in the component under such stress conditions. The ratios show differences of the order of 5% between healthy and cracked blades for the second mode. These observations lead illustrate that modal damping has strong correlation with blade structural integrity. The possibility of employing these modal damping ratios as indicators for the presence of cracks / defects is discussed. ICSI 2019 The 3rd International Conference on Structural Integrity Structural Integrity Analysis and Life Estimation of a Gas Turbine Bladed-Disc Shahnawaz Ahmad a , A Suman b , T Sidharth b , Ganesh Pawar b , Vikas Kumar a , N. S. Vyas b a Defence Metallurgic l Re earch Laborat ry Kanchanbagh, Hyderabad, India b Indian Institute of Technology, Kanpur, India Abstract Turbine blades in an aero-engine are subjected to severe conditions of high temperature and pressure, which cause high levels of stress leading to crack formation and subsequent failure in service. We have investigated the influence of crack on vibration parameters of a typical aero-engine gas turbine blade and have described a life assessment approach for blades and bladed discs. A typical transport aircraft AMT (Accelerated Mission Test) cycle has been utilized for getting operating parameters. Material data is taken from tests conduct d on specimens extracted from turbi e disc of a transport aircraft. Initial studies re carried out on idealizations involving cantilever beams with uniform cross-section; the procedures are then extended to free-standing turbin blad s with asymmetric airfoil cross section mounted at a stagger angle on a rot ting disc. Dynamic characteristics of the blade are estimated nd free vibrations analysis has been carried out for healthy blades and those with cracks of different sizes. Influence of crack size on atural frequencies and mode s apes is studied. Results show a difference of l ss than 1% in frequency for cracks less than 1mm in length; for larger crack l ngths the frequency shifts are higher. Analytic l results ar c pared with experimental tests on Laser Doppler Vibrometer set-up. Subsequently, forced vibr tion analysis is performed and a method logy, using Lazan’s law ,is developed to extract modal damping ratios from the strain energy of the blade under n zzle excitation pressure fluctuations. Modal damping ratios, thus obtained, are indicative the energy dissipation in the component under such stress conditions. The ratios s ow differences of the order of 5% between ealthy and cracked blades for the second mode. These observations lead illustrate that mod l damping has strong correlation with blade structural integrity. The possibility of employing these modal damping ratios as indicators for the presence of cracks / defects is discussed. Abstract

© 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the ICSI 2019 organizers. © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the ICSI 2019 organizers. © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the ICSI 2019 organizers. Keywords:Aerodynamic load assessment, Massing hypothesis, Paris Law Keywords:Aerodynamic load assessment, Massing hypothesis, Paris Law

Corresponding author Email: shahnawaz@dmrl.drdo.in Corresponding author Email: shahnawaz@dmrl.drdo.in

2452-3216© 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the ICSI 2019 organizers. 2452-3216© 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the ICSI 2019 organizers.

2452-3216  2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the ICSI 2019 organizers. 10.1016/j.prostr.2019.08.101