Semester

Fall

Date of Graduation

2006

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Nithi T. Sivaneri.

Abstract

An improved two-sublaminate model based on first-order shear deformation theory is implemented in a general-purpose finite element software (ANSYS) to study delaminated composite plates. Double cantilever beam and end-notched flexure models of unidirectional and multidirectional composite plates with mid-plane and offset delaminations are analyzed. The total strain energy release rate and the mode-I, mode-II and mode-III components are evaluated using a plate-theory-based crack-closure technique.;The effects of variation of material properties, ply thickness, fiber orientation, coefficient of friction between the crack surfaces, finite element mesh density and virtual crack-closure length and applied load on the mixed-mode strain energy release rates are studied using Monte Carlo simulations. The statistics and trends are analyzed and quantified using sensitivity plots and scatter plots. Anderson-Darling goodness-of-fit tests are performed on the results to fit them to a two-parameter Weibull, normal or log-normal distribution and the statistically-based design values are calculated. Three-dimensional contour plots are also generated to study the overall variation in the strain energy release rate distribution along the delamination front.;In the case of double cantilever beam specimens, the ply thickness has a significant influence on the total and average strain energy release rate. Fiber misalignment controls the amount of mode-II and mode-III components observed. The maximum and minimum values are also highly dependent on the virtual crack-closure length. For unidirectional end-notched flexure models, sliding friction effects are found to be negligible and occur only adjacent to the supports. For the symmetric and unsymmetric end-notched flexure models studied, the energy loss due to sliding friction controls the total strain energy release rate for friction coefficients greater than 0.16 and 0.24, respectively.

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