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FROM:
Christopher Klobedanz (Mechanical Engineering, Rensselaer Polytechnic Institute, Hartford, Connecticut, USA), “A study of the effect of delamination size on the critical sublaminate buckling load in a composite plate using the Ritz method”, M.S. Thesis, December 2014
ABSTRACT: This project analyzes the effect of delamination size on the localized critical buckling load of a partially delaminated composite plate sublaminate under uniform, uniaxial compression. The plate being analyzed is a square, 24-layered, symmetric graphite/epoxy laminate composite of uniform thickness, with a centrally-located circular delamination between the fourth and fifth layers. A model, based on the code outlined in Reference (1), was built in the symbolic computation program Maple to conduct this analysis. The model first applies Classical Laminate Plate Theory to define the composite behavioral response to compression. It then applies the Ritz variational method to minimize the total potential energy of the system and create an expression from which the critical buckling load of the composite sublaminate can be predicted. The potential energy term is initially expressed in terms of known geometric dimensions and material properties, and unknown polynomial coefficients. The Newton-Raphson method solves for the values of the polynomial coefficients, which can then be substituted back into the sublaminate stress, strain, and displacement equations to fully describe the sublaminate behavior. By conducting this analysis at various loads, a load-strain plot illustrates the critical buckling load as a maximum point in the resulting curve. This process was repeated for delaminations of various diameters to understand the relationship between delamination size and the compressive-tolerance capabilities of composites. This analysis was validated by recreating the results of a model created in the Reference (1) study. After verifying the Maple model, the initial study was able to be expanded to support the goals of this project. Ultimately the project determined that as the delamination size increases, the strength of the composite can be severely reduced.
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