Mechanical & Materials Engineering, Department of


Date of this Version

Summer 7-28-2011


A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Mechanical Engineering, Under the Supervision of Professor Linxia Gu. Lincoln, Nebraska: August, 2011

Copyright 2011 Ananth Ram Mahanth Kasavajhala


Understanding the behavior of fracture due to preliminary flaws in materials is essential to escalate the life and reliability of a structure. The present work is focused on investigating the influence of various structural parameters on the pre-crack growth stress state, initiation and propagation of flaws in two distinct fields of engineering that is, aging aircraft structural repair (aerospace) and the human aortic dissection (life sciences). Three dimensional finite element methodologies, coupled with linear elastic fracture mechanics (LEFM) formulation was utilized in both the cases.

A model of pre-cracked Al 7075 T6 plate was used to analyze pre- and post- crack growth behavior. Thereby the effectiveness of composite repair in recovering the residual strength of the assembly was validated using analytical formulation. Furthermore, the influence of composite material type, adhesive properties in maintaining the repair efficacy was also investigated. Finally, analytical fatigue life predictions were carried out on the pre-cracked plate with and without repair.

In case of aortic dissection, three dimensional models of human aorta and layered sections of artery with plaque were developed to study the effect of loading condition on the stress state as well as initiation of flaws. Thereby, crack propagation behavior in the intima layer was studied with varying material fracture resistance.

Advisor: Linxia Gu