Damage Detection in Bolted Space Structures

To overcome the current limitations of satellite operation timelines, responsive space satellites are being developed for rapid configuration and assembly. Time spent for assembly, integrating, and verifying a satellite ready for launch and on-orbit operations must be reduced to less than a week. Structural health monitoring is seen as a possible avenue for real-time assessment of satellite integrity and qualification before launch. Embedded ultrasonics and magneto-mechanical impedance (MMI) are considered as potential candidates for diagnostics of critical system elements. Piezoelectric wafer active sensors in conjunction with acousto-elastic SHM methods are used for assessing aerospace structures with bolted joints. In the present analysis, the acousto-elastic behavior of the joint is used as an indicator of structural integrity. Experimental data show changes in the acoustic signal phase as a result of differing bolt torques. Localization potential of the acousto-elastic technique is demonstrated in a complex structure analogous to a typical satellite panel. The MMI method has shown utility in assessing the condition of bolted joints in complex satellite structures. Experimental data reveal changes in position of impedance peaks induced by the difference in structural loads applied to the joint. Repeatability of the MMI measurements is evaluated and spectral energy representation suitable for automation of MMI diagnostics is suggested. It is advocated that both the acousto-elastic and MMI methods have indicated possibilities for detecting and characterizing damage in satellite bolted joints.