Ahmet Unal

Date of Award


Document Type


Degree Name

Master of Science in Engineering (MSE)


Mechanical and Aerospace Engineering

Committee Chair

Gang Wang

Committee Member

Mark Lin

Committee Member

Q. H. Ken Zuo


Structural analysis (Engineering), Elastic analysis (Engineering), Elasticity


Multi-layered elastic structures are widely used in engineering applications due to their high strength, fatigue resistance and their ability to be tailored to meet different design requirements. Although they provide many benefits compared to their metallic counterparts, they are also susceptible to damage. In most cases, the damage detection in a multi-layered structure is challenging due to its complex structure and construction (e.g. delamination). Lamb wave based structural health monitoring has been successfully implemented in metallic beam and plate structures. Damage location, amount and the extent can be determined by comparing baseline signatures of wave propagation in the structure. However, it is very challenging to characterize the dynamic behavior of a multi-layered structure and to extend wave based SHM to a multi-layered structure, in which the wave propagation characteristics must be well understood. Accurate prediction of high frequency wave response using conventional finite element method requires a large number of elements in the structural problem, resulting in computational effort and cost. A new high fidelity, efficient, and accurate model, and a solution approach are needed to capture the dynamic behavior of such multi-layered structures. In this thesis, the spectral finite element model (SFEM) is developed to predict the dynamic behavior of a multi-layered beam structure. First, a higher order multi-layered beam model is developed. For a beam that has n number of layers, each layer of the beam is idealized by a Timoshenko beam, in which shear deformation as well as rotational inertia are included. Mathematical model is developed based on this higher order theory, which is critical to capture high frequency response of the multi-layered beam structures. A set of fully coupled governing equations and associated boundary conditions are obtained by the application of Hamilton's principle. Secondly, semi-analytical solutions of these equations are determined in order to formulate the SFEM. The predictions of the SFEM are compared to the NASTRAN results and other data in literature. Fewer elements are required in the SFEM, compared to conventional finite element based approaches, which substantially benefits the ultrasonic frequency simulations. Finally, the newly developed SFEM is applied to the structural health monitoring demonstration in a multi-layered beam. Accurate wave propagation predictions in undamaged and damaged cases are captured.



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