Studies of fracture in thin -wall and thin -film structures by use of cohesive zone model approach
Abstract
The cohesive zone model approach is applied to studies of failure in structure with members of small thickness: thin walled sheet metal structures and thin film coating structures. Special attention is paid to situations in which the interaction between buckling and crack extension is important. Crack propagation is studied for through cracks in thin sheet aluminum. Multi-site damaged panels are analyzed especially with respect to the size effect phenomena during crack link-up. The good agreement found between the predicted and experimental data demonstrates that the cohesive zone model approach is attractive in investigation of structural integrity of thin-walled structures, and provides a solution to the problem of geometry and size dependence of conventional crack growth parameters. For coating system consisting of a ductile coating on an elastic substrate, the initiation and growth of interface delamination induced by indentation is studied. Instability is an important issue for this kind of structure, including those present at delamination initiation and coating buckling. Several existing methods for interface toughness evaluation are compared with the results obtained from the numerical studies. Improved methods for interface toughness determination are proposed for strong and weak interface cases. Dimensional considerations introduce size effects via the interface constitutive relation. The hardness at delamination initiation is shown to be dependent on the coating thickness. As the ratio between coating thickness and cohesive length decreases, the coating substrate system becomes stronger. Size effects based on the strain gradient plasticity theory are considered in the simulations. The results predict a hardness increase for small indentation depths, but a reduced maximum hardness when compared to simulations with classical flow plasticity.
Degree
Ph.D.
Advisors
Siegmund, Purdue University.
Subject Area
Mechanical engineering|Mechanics
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