Global Fracture Analysis of Laminated Composite Materials for Aerospace Structures

Citation

González Liñero, Luis (2002) Global Fracture Analysis of Laminated Composite Materials for Aerospace Structures. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/FCJ8-EW63. https://resolver.caltech.edu/CaltechTHESIS:05032011-085654224

Abstract

The failure process of laminated composite materials originating from precut sharp cracks, as well as their propagation, is studied from a "global" perspective, appropriate for structural analysis. The size effect in the damage development is explored and the question of "scaling" of the results is addressed. Two globally orthotropic sets of panels with the notches aligned along the axes of orthrotopy are studied. The internally evolving damage in the crack tip region is examined through enhanced x-ray radiographic inspection and surface strain fields are measured by means of the Digital Image Correlation method (the applicability and limitations of which are analyzed and discussed). The results obtained from these two experimental techniques are joined to assess the feasibility of identifying internal damage solely from surface measurements. The shape of the region of influence of the crack is described and its extension measured. A simplified model for damage progression analysis is proposed. The process of initiation of the damage propagation is described in detail and the different responses for the two different layups are discussed. The maximum stress/strain and the Tsai-Hill failure criteria are compared with the experimental results on the laminates, and their reliability and limitations are addressed. The effective properties of the two sets of laminates are measured at three different loading rates and compared to theory, and the relevance of the time dependence of the material is studied.

Thesis Files