Processing and Probability Analysis of Pulsed Terahertz NDE of Corrosion under Shuttle Tile Data
This paper examines data processing and probability analysis of pulsed terahertz NDE scans of corrosion defects under a Shuttle tile. Pulsed terahertz data collected from an aluminum plate with fabricated corrosion defects and covered with a Shuttle tile is presented. The corrosion defects imaged were fabricated by electrochemically etching areas of various diameter and depth in the plate. In this work, the aluminum plate echo signal is located in the terahertz time-of-flight data and a threshold is applied to produce a binary image of sample features. Feature location and area are examined and identified as corrosion through comparison with the known defect layout. The results are tabulated with hit, miss, or false call information for a probability of detection analysis that is used to identify an optimal processing threshold.
Comparison of two non-destructive inspection techniques on the basis of sensitivity and reliability
Abstract Two non-destructive inspection (NDI) methods have been used to determine the damage tolerance life prediction of aero-engine turbine discs. For this purpose, low cycle fatigue cracks were examined in the compressor discs of tie bolt holes. The successful implementation of damage tolerance design method strongly depends on the sensitivity and reliability of applied NDI method. The result of this study indicated that the manual eddy current inspection method is more sensitive and more reliable than the liquid penetrant inspection method in terms of detection of small cracks in the compressor discs.
Gas turbine engine disk cyclic life prediction
Major disk design criteria are identified with emphasis on the life limiting design and the application of life prediction techniques. Design for low-cycle fatigue (LCF) capability includes consideration of operator usage, material characteristics, temperature, and stress analysis. Analytical stress analysis methods are discussed and related to experimental testing of both specimen and full-scale components. The role of initiation time in the total component life is discussed with emphasis given to analytical techniques, including finite element, finite difference, and the role of stress concentrations on fatigue life. The fatigue life initiation system and its inter-relationship with the flight profile including the effects of time, temperature, stress, and material characteristics are highlighted. Attention is focused on the role of crack propagation in the disk design system including the design of disks for internal defects. The general role of fatigue crack propagation and subcritical flaw growth is highlighted along with the inter-relationship with nondestructive inspection techniques for surface and sub-surface defects. The future of initiation-propagation relationship to total disk life concept is explored in light of improved NDI, advanced fracture mechanics analysis, and the potential for disk retirement for cause.