Theoretical and experimental modelling of multiple site damage in plate components.

Fracture and fatigue assessment of structures weakened by multiple site damage (MSD), such as two or more interacting cracks, currently represents a challenging problem. The lifetime prediction of structural components with MSD is still largely based on 2D single crack solutions available in various handbooks or derived from the simplified finite element analysis. Such simplifications could often result in non-conservative predictions, overestimating the actual fatigue life of the structural components. Therefore, there is a strong motivation for the development of more advanced modelling approaches, which could incorporate the effects of the interaction between multiple cracks, 3D and other nonlinear phenomena. The primary objective of this study is to develop analytical and numerical models for the evaluation of the residual strength and fatigue crack growth of two through-the-thickness cracks in a plate of finite thickness subjected to monotonic and cyclic loading. The selected problem represents the simplest type of MSD, however the obtained results can serve as benchmark solutions for modelling and assessment of more complicated practical MSD problems. The nonlinear interactions between the cracks as well as the 3D effects, such as the effect of the plate thickness, are investigated with the help of the classical strip yield model, plasticity induced crack closure concept and fundamental 3D solution for an edge dislocation in an infinite plate. The computational procedure is based on the Distributed Dislocation Technique and Gauss-Chebyshev quadrature method, which provide an effective way for obtaining highly accurate solutions to fracture mechanics problems. An experimental study was conducted to evaluate the effect of the plate thickness and crack interaction on the residual strength levels and fatigue crack growth rates of two closely spaced through-the-thickness cracks in aluminium plate specimens. The outcomes of the experimental study were also utilised to validate the theoretical approach and estimate the accuracy of the analytical and numerical predictions. The major outcomes of the thesis can be formulated as follows: • An original analytical 3D model for the evaluation of residual strength of two collinear cracks of equal length was developed and compared with the existing 2D models and outcomes of the experimental program conducted by the candidate; • Analytical and numerical models for the assessment of the fatigue crack growth of two collinear through-the-thickness cracks subjected to a constant amplitude cyclic loading were developed; • The effects of the nonlinear interactions between two cracks, plate thickness and plasticity induced crack closure on fatigue crack growth rates were identified and analysed using the developed theoretical and experimental techniques; • Further recommendations for analytical and numerical modelling of MSD were provided.

Author dc:creator

• Chang, Donghoon

Advisors dc:contributor.advisor

• Kotousov, Andrei Georgievich
• Codrington, John David

• multiple site damage; strip yield model; crack interaction

Handle dc:identifier.uri

http://hdl.handle.net/2440/92539

OAI identifier oai:identifier

oai:digital.library.adelaide.edu.au:2440/92539