Date of Award

8-2004

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Mechanical Engineering

Advisor

Roberto Lopez-Anido

Second Committee Member

Senthil Vel

Third Committee Member

Michael Peterson

Abstract

The hydromat test system (HTS), ASTM D6416, is a recent experimental approach to characterize the structural performance of sandwich composite panels. In this thesis, hydromat test panels were modeled using sandwich composite plate theory with a Navier's solution form. The complete methodology used to predict the response of a hydromat test panel is presented. In previous work dealing with hydromat tests of sandwich structures, the sandwich plate theory was oversimplified and therefore a formal application of classical lamination theory was not available. The analysis process from classical lamination theory to sandwich plate theory is illustrated and the solution is compared to the results from a finite element method (FEM) code. It was found that the proposed model overcomes the limitations of the existing HTS solutions and correlates very well with FEM results.

A combined experimental and numerical approach for determining bending and shear stiffness parameters of a sandwich composite panel evaluated with the hydromat test was developed. A method for computing the bending and shear stiffness parameters of an orthotropic sandwich composite panel using the hydromat test system is presented and verified. The method is considered to be robust for two reasons. First, it was found that when random additive noise was introduced into simulated field data, convergence to the known solution was attained. Second, it was found that the solution converged for initial seed values containing significant error.

To implement the inverse solution method experimentally, full-field strain and displacement data was required. A 3-D digital image correlation system capable of full field measurements of strains and displacements was utilized with the hydromat test system. The accuracy and precision of the 3-D digital image correlation system was quantified to allow use with the hydromat test system ensuring reliable measurements. The stiffness parameters of the sandwich composite plate were optimized based on the experimental displacement and in-plane strain measurements from image correlation. This combined experimental and numerical solution method when applied to E-glass balsa wood sandwich panels produced reliable results.

The relevance of this combined experimental-numerical method is that it could change the way composite material structures are evaluated, since it may be possible to determine relevant stiffness parameters from plate bending tests. This approach reduces the experimental effort required to characterize sandwich composite panels, while improving the reliability of the predictions.

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