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Engineered interfaces for toughening of advanced structural materials
Interfaces are ubiquitous in structural materials and often represent the weakest mechanical link. Improvement of interfacial strength and toughness is critical for increased durability of structural materials and composites. Geometry is known to affect fracture behavior at interfaces, however geometric toughening is insufficiently studied. The goal of this dissertation was to analyze the effects of interfacial topography on fracture behavior of interfaces at several scales. Corrugated interfaces with a broad range of corrugation aspect ratios were manufactured and studied experimentally under far-field Mode I, II and Mixed Mode loadings. Significant increases in critical loads were observed with the increase of aspect ratio. Numerical analysis was performed to identify mechanisms of toughening. Local mode mixity was found to be the main mechanism of improvement under Mode I loading, while crack tip shielding played the major role under Mode II loading. Beneficial effects of corrugations were preserved in bi-material specimens with unrestricted crack paths, mimicking fiber-matrix interfaces. Further analysis showed significant toughening at corrugated and micro-corrugated interfaces during stable crack propagation and under fatigue and dynamic impact loadings. Fiber-matrix interface geometry was also modified at nanoscale. Nano-corrugations on fiber surfaces were created by depositing and attaching continuous nanofibers using modified electrospinning process. The effect of modification was studied using the micromechanical test, which demonstrated increased frictional sliding resistance. Potential extent of improvements was studied experimentally and numerically on a series of cylindrical specimens with well-defined spiral corrugations. Results showed an increase of over 1000% in fracture resistance measured by apparent interfacial shear strength. A new, spiral type of crack propagation at the corrugated cylindrical interface was observed and analyzed for the first time. The results of this work provide new insights into mechanisms of toughening at interfaces and can be used for advanced interfacial design of future bioinspired multiscale heterogeneous structural materials and composites.
Desyatova, Anastasia, "Engineered interfaces for toughening of advanced structural materials" (2012). ETD collection for University of Nebraska - Lincoln. AAI3546868.