Publication Date


Document Type


Committee Members

Tarun Goswami (Committee Co-chair), Bor Zeng Jang (Committee Chair), Ravi Penmetsa (Committee Member), Raghavan Srinivasan (Committee Member)

Degree Name

Master of Science in Engineering (MSEgr)


There is an economic need to reduce the conservatisms of current lifing methods and extend component life. Extending component usage increases the probability of failure during operation. Therefore, the risk of continued service must be quantified before life extension concepts can successfully be implemented. The current FAA approved software for the certification of new rotor designs, only accounts for defects present prior to service. Defects due to the handling of components during inspection and material fatigue will induce defects during service and need to be included in any analysis of component life extension. Component life extension analysis of an Inconel 718 late stage turbine disk was conducted which accounted for manufacturing, handling, and fatigue defects. The probability of fracture due to manufacturing defects has a large effect prior to the first inspection. After the first inspection, these defects have a negligible effect due to the significant sensitivity and reliability of component inspection methods. It is shown that the effect of handling induced defects on the probability of fracture is dependent on their occurrence rate and size. It was concluded that handling has a limited effect on the probability of fracture. Past the low cycle fatigue life limit, fatigue of the material will continue to induce defects. The cycles to failure of the defects present at this limit will determine the first, post low cycle fatigue life limit inspection interval. Fatigue defects that initiate shortly before an inspection have a low probability of detection. If future inspection intervals are not adjusted, these undetected defects will grow to failure and have a large impact on the probability of fracture. To account for these undetected defects, future inspection intervals must be shorted to prevent such failures. The effect of applying an inspection timing distribution and percentage of components inspected is also evaluated.

Page Count


Department or Program

Department of Mechanical and Materials Engineering

Year Degree Awarded