Holistic structural integrity process (HOLSIP) research for hybrid structure applications

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This proposal outlines research to investigate and model the physical crack growth processes that lead to failure in a "hybrid" structure under fatigue loading. A hybrid structure is defined here as a metal structure that has been reinforced or repaired using a bonded composite material. This composite "reinforcement" (for an uncracked metal structure) or "patch" (in the case of a cracked metal structure) is typically a multi-layer boron/epoxy or other high stiffness fiber-reinforced material. Significant potential exists for the use of hybrid structures for a variety of applications (e.g. aircraft, ships, pressure vessels, biomedical implants, vehicle structures, spacecraft, etc.), however their use for reliability-critical components is extremely limited as accurate analytical tools for reliably predicting failure do not currently exist. It is due to a lack of basic knowledge of the multiple and interacting failure process mechanisms within the hybrid structure (required for the creation of an accurate failure/life prediction model for structural integrity assessment) that limits their widespread use. This research will utilize knowledge, facilities and expertise previously developed at UBC to construct and test small-scale specimens to investigate the mechanisms and interaction between hybrid structure geometry, fatigue crack growth and disbonding rate in order to properly identify and model the failure mechanisms. The information obtained will be used to create a crack growth model for hybrid structures, required for development of a new risk/reliability analysis strategy for these complex structures. This new strategy - the HOLolistic Structural Integrity Process (HOLSIP) - will be developed with a specific focus on the application of bonded composite repairs for metal aircraft structures. The goal is to develop the necessary knowledge and prediction models to overcome existing barriers to the certification of this technology for repairing civilian aircraft structures. This research is crucial to obtaining economic benefit from the life-extension programs for the vast fleets of ageing civilian aircraft that currently exist, and will be increasing in the future due to reductions in aircraft purchases after the events of 9/11.