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Investigating and Understanding the Role of Transformation Induced Residual Stress to Increase Fatigue Life of High Strength Steel Used in Transmission Gears

Freborg, Andrew M
http://rave.ohiolink.edu/etdc/view?acc_num=akron1374077405

Abstract Details

2013, Master of Science in Engineering, University of Akron, Mechanical Engineering.
It is well established that carburization of low alloy steels promotes compressive residual surface stress upon quenching, and that compressive surface stresses enhance fatigue life. A number of innovative steel processing techniques have been advanced to enhance material performance through manufacturing, processing and finishing. For applications where part life is limited by fatigue, significant life enhancement can be realized by introducing compressive stresses in the part surface, and by eliminating stress concentration factors. Of primary focus in this thesis is the use of heat treatment to control surface and subsurface residual compressive stresses, specifically to affect consequent part fatigue life. For fatigue critical rotorcraft gear applications, the alloy steel Pyrowear®53 is conventionally hardened by oil quenching, followed by deep freezing and double tempering. Residual compressive stress is generated in the carburized case because of the delay in surface martensite formation due to the high surface carbon content. In a number of research and production trials with steel parts, an intensive quenching process has been shown to produce surface compressive stresses on the order of 1.5 to 2 times more compressive than standard oil quenching methods. Recent work conducted under US Army AATD sponsorship has demonstrated the potential for up to 28% improvement in bending fatigue strength for carburized and intensively quenched 3-point bend coupons. Based on these findings, an evaluation has been made of the relationship between residual compressive stresses and bending fatigue resistance in gears. Using single tooth bend tests conducted on carburized and hardened spur gears processed using both standard oil quenching and intensive quenching, residual stress profiles in the gear roots, distortion/growth of the teeth, and single tooth bending fatigue life were compared. The physical studies were then supplemented by finite element simulation of the heat treatment and subsequent bending fatigue cyclic loading. The FEA results showed that the stress state in the root area is reduced by the presence of the deep surface compression. Furthermore, neglecting the presence of the compressive surface stress, which is the practice of the standard tooth stress calculation methods, results in calculated stresses that are in excess of the actual fatigue strength of the gear steel. This thesis work demonstrates the use of thermal processing to control residual compressive stresses, and how thermal processing can be used to increase the high cycle fatigue endurance limit in carburized Pyrowear53 gear steel evaluated under single tooth bending.
Tirumalai Srivatsan, Dr. (Advisor)
Craig Menzemer, Dr. (Committee Member)
Greg Morscher, Dr. (Committee Member)
Aerospace Materials; Engineering; Materials Science

Recommended Citations

Citations

  • Freborg, A. M. (2013). Investigating and Understanding the Role of Transformation Induced Residual Stress to Increase Fatigue Life of High Strength Steel Used in Transmission Gears [Master's thesis, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1374077405

    APA Style (7th edition)

  • Freborg, Andrew. Investigating and Understanding the Role of Transformation Induced Residual Stress to Increase Fatigue Life of High Strength Steel Used in Transmission Gears. 2013. University of Akron, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1374077405.

    MLA Style (8th edition)

  • Freborg, Andrew. "Investigating and Understanding the Role of Transformation Induced Residual Stress to Increase Fatigue Life of High Strength Steel Used in Transmission Gears." Master's thesis, University of Akron, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=akron1374077405

    Chicago Manual of Style (17th edition)

akron1374077405
4,499
© , some rights reserved.Creative Commons License Investigating and Understanding the Role of Transformation Induced Residual Stress to Increase Fatigue Life of High Strength Steel Used in Transmission Gears by Andrew M Freborg is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. Based on a work at etd.ohiolink.edu.
This open access ETD is published by University of Akron and OhioLINK.