Elastic-plastic fracture analysis for small-scale yielding
Abstract
The objective of the present study was to develop a criterion to characterize the influence of plastic deformation around the crack tip. The first part of this dissertation explored the plastic crack tip fields estimated by linear elastic fracture mechanics, then they were compared to the results from numerical elastic-plastic analysis in order to establish a border-line that the plastic deformation can be included in the concept of linear elastic fracture mechanics. The elastic-plastic energy release rate was proposed as the sum of separation work and plastic dissipation which can be computed through numerical simulation of crack growth. Based on intensive investigations, a plastic zone ratio $r\sb{p}/a\ \approx$ 0.003 was chosen as the characterizing parameter for small scale yielding at which linear elastic fracture mechanics satisfactorily replaces elastic-plastic analysis. The elastic-plastic energy release rate calculated from two different finite element meshes and different nodal release techniques revealed no discrepancies; therefore, it could be regarded as being independent on a computational model, proving the validity of the modified energy balance concept. The feasibility of the elastic-plastic energy release rate in predicting mixed mode fracture behavior was verified through comparisons with existing fracture criteria and available experimental results. The direction of crack initiation was projected in the path of least plastic dissipation, and the combined load ratios were determined by the constant energy release rate, which resulted in different curves according to material properties.
Degree
Ph.D.
Advisors
Sun, Purdue University.
Subject Area
Aerospace materials
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