Title:

Fatigue Life Estimation and Dominant Slip Systems in Single Crystal Nickel-Base Superalloy Turbine Blades

Speaker:

Prof. Nagaraj K. Arakere

Affiliation:

Mechanical & Aerospace Engineering, University of Florida

When:

Tuesday, April 27, 2010 at 11:00:00 AM   Add to Calendar

Where:

MRDC Building, Room 4211

Host:

Richard Neu
rick.neu@me.gatech.edu
404-894-3074

Abstract

Among the most demanding structural applications for high temperature materials are those of aircraft and rocket engine turbine blades, due to the combination of high operating temperature, corrosive environment, high monotonic and cyclic stresses, long expected component lifetimes and the enormous consequence of structural failure. Single crystal nickel-base superalloy turbine blades are being utilized in rocket engine turbopumps and turbine engines because of their superior creep, stress rupture, melt resistance and TMF capabilities over polycrystalline alloys. Contact fatigue damage can result because of the subsurface shear stresses induced by fretting action at damper contact and blade attachment regions can result in crystallographic initiation and crack growth along slip planes. Stresses in the airfoil and the attachment region are evaluated using a 3D elastic-anisotropic finite element model. Analytical techniques for evaluating subsurface stress fields in anisotropic contacts are presented. The concept of ¡§Dominant Slip System¡¨ defined as the single slip system that experiences the highest resolved shear stress (RSS) at a given point is introduced. The dominant slip systems are seen to persist with increasing load and inhibit the activation of new slip systems. A fatigue damage parameter based on the maximum shear stress amplitude on the dominant slip system is discussed. Stress intensity factors for anisotropic cracks subject to mixed-mode loading are presented based on KRSS. Fatigue crack growth based on a multiaxial ƒ´KRSS parameter is also presented. Results from an experimental and numerical investigation of 3D stress fields and evolution of plasticity and slip sector boundaries near notches in FCC single crystal tension test specimens are presented, using both elastic anisotropic and 3D crystal plasticity models.

Biography

Nagaraj K. Arakere is Associate Professor in the MAE department at the University of Florida. His research focus is on understanding the damage mechanics of structural materials such as single crystal superalloys, plastically graded bearing steels, aluminum alloys, and foams subject to multiaxial fatigue and tribological loading. He got his PhD in MAE at Arizona State University in 1988. He worked for many years at Allied-Signal Aerospace Company (now Honeywell) on fatigue life evaluation of rolling-element bearings, and rotordynamics, before joining academics. He is Fellow of ASME. Two of his papers on plasticity evolution and fatigue in single crystal blades were selected for ¡§Best Paper¡¨ award at the ASME/IGTI conferences, (2000 and 2004). His current research work is funded by NSF (CMII), AFRL (Propulsion Directorate), The Timken Co., Pratt & Whitney, and NASA MSFC.

Notes

Refreshments will be served.