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A Study Of The Effects of Laser Shock Peening (LSP) On the Fatigue Life Of Ti-6Al-4V (ELI) Spinal Implant Rods

Subramanian, Sethuraman
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1337888224

Abstract Details

2012, MS, University of Cincinnati, Engineering and Applied Science: Materials Science.
Solid implant rods made of Ti-6Al-4V (ELI) are currently used in spinal implant devices. Due to the high stiffness of these solid rods, the implant devices are unable the meet the needs for increased flexibility over a wide range of human activities owing to changes in lifestyles and in human work environments, thereby, necessitating the need for more flexible rods. Hence, designing, developing, manufacturing and testing flexible spinal implant rods is the aim of this project. In this project, increased flexibility has been achieved by reducing the cross-section of the solid rods. Since reduction in cross-section leads to reduced load bearing capacity, the fatigue endurance level of the flexible rods is lowered. In order to increase the endurance levels of these flexible rods, Laser Shock Peening (LSP) has been used. As a part of this project, the Ohio Center for Laser Shock Processing of Advanced Materials and Devices (LSP Center) has been set-up at the University of Cincinnati through the Ohio State Third Frontier Wrights Projects funding. This project is a collaborative effort between the LSP Center and X-Spine Systems Inc., an implant devices manufacturer based in Miamisburg, Ohio. All the experimental and modeling work pertaining to this project were carried out at the LSP Center. To begin with, flexible rods were designed using finite element modeling. After considering models like flat rods and flute rods, the final design was chosen as grooved rods. Based on this design, grooved rods were machined by X-Spine Systems Inc. Also, a fatigue model to predict the effect of LSP on the fatigue life of the flexible grooved rods was developed. Based on the model, fatigue experiments were designed and carried out. Per requirements outlined by X-Spine Systems Inc, the flexible implant rods were required to demonstrate endurance level (run-out) for 5 million cycles in construct fatigue testing at -160N. This load is higher than the current industrial standard of -150N for solid rods in constructs. These tests were carried out per standard procedures recommended in ASTM F-1717 04. Results from the construct tests showed that the construct with grooved rods endured -160N for 5 million cycles. Static 4-point bending tests carried out on the flexible single rods showed a 10% reduction in stiffness as compared to the rigid solid rods. After successful construct testing, fatigue testing of flexible rods in 4-point bending showed that LSP improved endurance level by a small extent. To study the extent of LSP on the rods, residual stress measurements as a function of depth were performed on LSP treated rods. The results from residual stress measurement indicated that LSP gives rise to 5 X deeper compressive stress regimes as compared to conventional shot peening techniques. Fatigue fractured rods were observed in Scanning Electron Microscope (SEM) to study the fractographic features under different treatments and loading conditions. The overall results showed that flexible grooved rods meeting all the specifications were successfully developed and tested in this project. Results pertaining to these are presented and discussed.
Vijay Vasudevan, PhD (Committee Chair)
Dong Qian, PhD (Committee Member)
Rodney Roseman, PhD (Committee Member)
121 p.
Materials Science
laser shock peening; implant rods; Ti-6Al-4V; fatigue; ; ;

Recommended Citations

Citations

  • Subramanian, S. (2012). A Study Of The Effects of Laser Shock Peening (LSP) On the Fatigue Life Of Ti-6Al-4V (ELI) Spinal Implant Rods [Master's thesis, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1337888224

    APA Style (7th edition)

  • Subramanian, Sethuraman. A Study Of The Effects of Laser Shock Peening (LSP) On the Fatigue Life Of Ti-6Al-4V (ELI) Spinal Implant Rods. 2012. University of Cincinnati, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1337888224.

    MLA Style (8th edition)

  • Subramanian, Sethuraman. "A Study Of The Effects of Laser Shock Peening (LSP) On the Fatigue Life Of Ti-6Al-4V (ELI) Spinal Implant Rods." Master's thesis, University of Cincinnati, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1337888224

    Chicago Manual of Style (17th edition)

ucin1337888224
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© 2012, all rights reserved.
This open access ETD is published by University of Cincinnati and OhioLINK.