Ph.D. Defense

Daniel Okegbu

(Advisor: Prof. George A. Kardomateas)

"Large Deflection Effects on the Energy Release Rate and
Mode Partitioning of Face/Core Debonds in Sandwich Composites"

Tuesday, August 29, 2023

1:00 p.m. EST

Price Gilbert Library 4222

 Meeting Link: URL Link

Meeting ID: 964 6479 8061

Abstract

This study investigates the effects of large deflections on the energy release rate and mode partitioning of face/core debonds for the Single Cantilever Beam Sandwich Composite testing configuration, which is loaded with an applied shear force and/or bending moment. Studies on this topic have been done by employing geometrically linear theories (either Euler-Bernoulli or Timoshenko beam theory). This assumes that the deflection at the tip of the loaded debonded part is small, which is not always the case. To address this effect, we employ the elastica theory, which is a non-linear theory, for the debonded part. An elastic foundation analysis and the linear Euler-Bernoulli theory are employed for the "joined" section where a series of springs is employed to represent the interfacial bond between the face and the substrate (core and bottom face). The derivation/solution is done for a general asymmetric sandwich construction. A J-integral approach is subsequently used to derive a closed-form expression for the energy release rate. Furthermore, in the context of this Elastic Foundation model, a mode partitioning measure is defined based on the transverse and axial displacements at the beginning of the elastic foundation. The results are compared with finite element results for a range of core materials and show very good agreement. Specifically, the results show that large deflection effects reduce the energy release rate but do not have a noteworthy effect on the mode partitioning. A small deflection assumption can significantly overestimate the energy release rate.

Committee Members:

• Prof. George A. Kardomateas (Advisor), School of Aerospace Engineering, Georgia Institute of Technology
• Prof. Julian J. Rimoli (Co-Advisor), Department of Mechanical and Aerospace Engineering, UC Irvine
• Prof. Claudio V. Di Leo, School of Aerospace Engineering, Georgia Institute of Technology
• Prof. Christos E. Athanasiou, School of Aerospace Engineering, Georgia Institute of Technology
• Prof. Gbadebo M. Owolabi, Department of Mechanical Engineering, Howard University
• Dr. Jaret C. Riddick, Center for Security and Emerging Technology, Georgetown University