Nathan Klingbeil (Advisor)
Master of Science in Engineering (MSEgr)
A new theory of fatigue crack growth in ductile solids has recently been proposed based on the total plastic energy dissipation per cycle ahead of the crack. This and previous energy-based approaches in the literature suggest that the total plastic dissipation per cycle can be closely correlated with fatigue crack growth rates under Mode I loading. The goal of the current study is to extend the dissipated energy approach to steady-state crack growth under mixed-mode loading conditions, with application to cyclic delamination of ductile interfaces in layered materials. The total plastic dissipation per cycle is obtained by 2-D elastic-plastic finite element analysis of a stationary crack in a general mixed-mode specimen geometry under constant amplitude loading. Both elastic-perfectly plastic and bi-linear kinematic hardening constitutive behaviors are considered, and numerical results for a dimensionless plastic dissipation per cycle are presented over the full range of relevant mechanical properties and mixed-mode loading conditions. In addition, numerical results are presented for the case of fatigue crack growth along a bonded interface between materials with identical elastic, yet dissimilar plastic properties, including mismatches in both kinematic hardening modulus and yield strength. Finally, the approach is generalized to include mismatches in both elastic and plastic properties, and results for the dimensionless plastic dissipation per cycle are reported over the complete design space of bimaterial interfaces. The results of this thesis are of interest in soldering, welding, coating, electronic packaging, and a variety of layered manufacturing applications, where mismatches in both elastic and plastic properties can exist between the deposited material and the substrate.
Department or Program
Department of Mechanical and Materials Engineering
Year Degree Awarded
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