Damage Localization Using Ultrasonic Methods in Multi-Layered Metallic Structures

Results are presented from a highly collaborative project that builds on previous research designed to improve ultrasonic (UT) localization of damage in mutli-layer metallic structures. One of the primary objectives of the project is to test existing acoustic models for cracks around fastener holes, and further develop a model as necessary to achieve the accuracy required for Air Force applications. For the first phase of the project, CIVA modeling results have been compared to ultrasonic measurements on aluminum plates with fatigue cracks and EDM notches at different locations around through-thickness holes. Variables include the diameter of the holes, length/width of notches/cracks, position of notches/cracks on the hole (angle with respect to the probe) and position in depth (surface, mid bore, backwall and through thickness). Baseline measurements have also been made on side-drilled and spherical-tip holes. Modeling challenges include accurately accounting for reflections arising from the cracks and the specimen geometry, mode conversion, contact conditions between fasteners and fastener holes, and reflection/transmission coefficients at interfaces between layers.