Theses and Dissertations

Issuing Body

Mississippi State University

Advisor

Myers, Oliver J.

Committee Member

Schneider, Judith A.

Committee Member

Luck, Rogelio

Committee Member

Jha, Ratneshwar

Committee Member

Daniewicz, Steven R.

Date of Degree

12-13-2014

Document Type

Dissertation - Open Access

Major

Mechanical Engineering

Degree Name

Doctor of Philosophy

College

James Worth Bagley College of Engineering

Department

Department of Mechanical Engineering

Abstract

Reinforced fiber polymer composites are a class of materials that are composed of multiple constituents that work together to create a material specific for applications. By combining different fibers and matricies, laminates can be created that meet demands for high specific stiffness, damping specifications, and electrical resistance. However, their internal complexity subjects them to a number of internal failure modes that have the potential to fail the laminate. Those failure mechanisms are fiber breaking, microcracking in the matrix, debonding of the fibers from matrix, and delamination of ply layers. To assess these failures, nondestructive evaluation methods have been developed to detect internal damage before catastrophic failure occurs. This dissertation investigates an in-situ magnetostrictive based nondestructive method for monitoring delaminations in carbon fiber reinforced polymer laminates by using embedded Terfenol-D particles. The objective is to characterize how laminate ply count and delamination presence affect sensing through the mechanical and magnetic parameters that influence the induced voltage or sensing signal. In addition, the effect of magnetostriction on the formation and propagation of cracks on the sensor boundaries are also investigated. Methods used to characterize this behavior involve experimental testing, analytical, and numerical modeling. From the results, a threedimensional finite element analysis model reveals how the sensor interacts mechanically with the host structure through lower stresses in the delaminated region due to the absence of adhesive forces. The stress variation results in a local magnetic permeability change which influences the induced voltage. The experimental nondestructive testing show that the key parameter influencing the sensing signal for this setup was the particle density, which is controlled by fabrication process. An attempt to analytically model the experimental sensing signal with a first order differential equation using a multi-step process was successful, but there is poor correlation with the experimental results. Finally, analytical mechanics are developed to evaluate the interlaminar failure under a magnetostrictive stress of 55MPa, and was found to not cause interlaminar failure or delamination propagation in Section-A.

URI

https://hdl.handle.net/11668/18993

Comments

magnetostriction||Terfenol-D||delamination||carbon fiber||nondestructive evaluation

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