Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Department of Defense, Washington Headquarters Services, Directorate for Information SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR'S ACRONYM(S)USAF, AFRL AFOSR / PKC SPONSOR/MONITOR'S REPORT875 Randolph St. Room 3112 NUMBER(S)Arlington, VA 22203 DISTRIBUTION / AVAILABILITY STATEMENT SUPPLEMENTARY NOTES ABSTRACTThe project explores application of magneto-elastic active sensors (MEAS) for structural health monitoring (SHM) of responsive space satellite systems. Design, development and fabrication procedures for MEAS are presented and associated electrical and mechanical characteristics are discussed. MEAS miniaturization efforts are highlighted. Examples of MEAS-enabled SHM testing in aerospace structures of simple and complex geometry, such a honeycomb and realistic satellite panels, are provided. Nonlinear SHM methodologies using MEAS are considered and its use for acousto-elastic assessment of bolted joints is recommended. A new SHM methodology -magneto-mechanical impedance (MMI) testing is suggested and explored from both theoretical and practical perspectives. The MMI measurement technique demonstrates ability for non-contact structural dynamic measurements and effectiveness in detection of fatigue damage at early stage, well before onset of fracture and crack development. Analytical and numerical models of MEAS and MMI are suggested. Finally, MEAS capability for recording dynamics of payload during sub-orbital space flight is validated. The results of the sub-orbital flight measurements suggest feasibility of using MEAS in space environment although characterization of dynamic events was not possible due to limitation of the on-board data acquisition system. It is advocated that MEAS could find its own niche in traditional and innovative SHM methodologies. SUBJECT TERMSStructural health monitoring, magnetic, magneto-elastic, embedded ultrasonics, nonlinear diagnostics, space structures, structural joints, sub-orbital. ABSTRACTThe project explores application of magneto-elastic active sensors (MEAS) for structural health monitoring (SHM) of responsive space satellite systems. Design, development and fabrication procedures for MEAS are presented and associated electrical and mechanical characteristics are discussed. MEAS miniaturization efforts are highlighted. Examples of MEAS-enabled SHM testing in aerospace structures of simple and complex geometry, such a honeycomb and realistic satellite panels, are provided. Nonlinear SHM methodologies using MEAS are considered and its use for acousto-elastic assessment of bolted joints is recommended. A new S...

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Many structural damage detection methods utilize piezoelectric sensors. While these sensors are efficient in supporting many structural health monitoring (SHM) methodologies, there are a few key disadvantages limiting their use. The disadvantages include the brittle nature of piezoceramics and their dependence of diagnostic results on the quality of the adhesive used in bonding the sensors. One viable alternative is the utilization of Magneto-Elastic Active Sensors (MEAS). Instead of mechanically creating elastic waves, MEAS induce eddy currents in the host structure which, along with an applied magnetic field, generate mechanical waves via the Lorentz force interaction. Since elastic waves are generated electromagnetically, MEAS do not require direct bonding to the host structure and its elements are not as fragile as PWAS. This work explores the capability of MEAS to detect damage in aluminum alloy. In particular, methodologies of detecting fatigue cracks in thin plates were explored. Specimens consisted of two identical aluminum plates featuring a machined slot to create a stress riser for crack formation. One specimen was subjected to cyclic fatigue load. MEAS were used to transmit elastic waves of different characteristics in order to explore several SHM methodologies. Experiments have shown that the introduction of fatigue cracks created measurable amplitude changes in the waves passing through the fatigued region of the aluminum plate. The phase indicated sensitivity to load conditions, but manifestation in the cracked region lacked stability. Nonlinear effects were studied using plate thickness resonance, which revealed birefringence due to local stresses at the site of the fatigue crack. The resonance spectrum has also shown a frequency decrease apparently due to stiffness loss. Preliminary results suggest opportunities for fatigue damage detection using MEAS. Application of MEAS for the diagnosis of complex structures is currently being investigated.

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