Nahla Helmy


The scope of this research is to estimate the fatigue life of drill pipes subjected to multiaxial state of stress. Several approaches that model and estimate fatigue life under non-proportional multiaxial loading were investigated. The critical plane approach was chosen with Fatemi and Socie numerical model. A software program (Elrond) was constructed to estimate the fatigue life for non-proportional loading. The code was validated using previous researchers experimental fatigue data sets. The developed software was then applied to a real life drilling problem. The “Build and Hold” drilling job condition was analyzed using the developed software. Results were compared with the API RP7G fatigue design guidelines. Fatigue life charts were prepared using fatigue lives estimated by Elrond at several axial loading, dogleg severities and axial torque amplitudes. Also cumulative fatigue life charts using fatigue life values from Elrond were calculated according to the method of Hansford and Lubinski developed, and used in API RP7G. Elrond results were less conservative than the API results, especially for low values of axial torque.


Mechanical Engineering Department

Degree Name

MS in Mechanical Engineering

Graduation Date


Submission Date

September 2016

First Advisor

Younan, Maher

Committee Member 1

Megahed, Mohamed

Committee Member 2

Nassef_, Ashraf


115 p.

Document Type

Master's Thesis


The author retains all rights with regard to copyright. The author certifies that written permission from the owner(s) of third-party copyrighted matter included in the thesis, dissertation, paper, or record of study has been obtained. The author further certifies that IRB approval has been obtained for this thesis, or that IRB approval is not necessary for this thesis. Insofar as this thesis, dissertation, paper, or record of study is an educational record as defined in the Family Educational Rights and Privacy Act (FERPA) (20 USC 1232g), the author has granted consent to disclosure of it to anyone who requests a copy.

Institutional Review Board (IRB) Approval

Not necessary for this item