REAL-TIME SENSING OF FATIGUE CRACK DAMAGE FOR INFORMATION-BASED DECISION AND CONTROL
Open Access
- Author:
- Keller, Eric Evans
- Graduate Program:
- Mechanical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- December 15, 2004
- Committee Members:
- Donald Albert Koss, Committee Member
Asok Ray, Committee Chair/Co-Chair
Eric Russell Marsh, Committee Member
Shashi Phoha, Committee Member
Marc Carpino, Committee Member - Keywords:
- damage
ultrasonic
fatigue crack - Abstract:
- Information-based decision and control for structures that are subject to failure by fatigue cracking is based on the following notion: Maintenance, usage scheduling, and control parameter tuning can be optimized through real time knowledge of the current state of fatigue crack damage. Additionally, if the material properties of a mechanical structure can be identified within a smaller range, then the remaining life prediction of that structure will be substantially more accurate. Typically, neither the damage state nor the material properties are known precisely for any given structure. Decision systems for maintenance and usage scheduling are often based on analytically derived reliability and anticipated usage patterns. At best, if the anticipated and actual usages are approximately the same, these systems can only project worst-case remaining life that is considerably worse than the average case. Thus almost all structures must be inspected and repaired on a schedule that is more conservative than is required for a given margin of safety. However, in a very common scenario, usage is considerably more demanding than the design usage, and thus the systems are not conservative enough, leading to unexpected failures and safety concerns. Information-based decision systems can rely on physical models, estimation of material properties, exact knowledge of usage history, and sensor data to synthesize an accurate snapshot of the current state of damage and the likely remaining life of a structure under given assumed loading. Thus the future usage can be modified, either through mission planning or through damage mitigating control in order to optimally use the remaining life of a structure. The work outlined in this dissertation is structured to enhance the development of information-based decision and control systems. This is achieved by constructing a test facility for laboratory experiments on real-time damage sensing. This test facility make use of a methodology that has been formulated for fatigue crack model parameter estimation and significantly improves the quality of predictions of remaining life. Specifically, the dissertation focuses on development of an on-line fatigue crack damage sensing and life prediction system that is built upon the disciplines of Systems Sciences and Mechanics of Materials. A major part of the research effort has been expended to design and fabricate a test apparatus which allows: (i) measurement and recording of statistical data for fatigue crack growth in metallic materials via different sensing techniques; and (ii) identification of stochastic model parameters for prediction of fatigue crack damage. To this end, this dissertation describes the test apparatus and the associated instrumentation based on four different sensing techniques, namely, traveling optical microscopy, ultrasonic flaw detection, Alternating Current Potential Drop (ACPD), and fiber-optic extensometry-based compliance, for crack length measurements.