Using impact modulation to identify loose bolts in a satellite structure
Abstract
Quickly-assembled, on-demand satellites are being developed to meet the needs of responsive space initiatives. The short testing times and rapid assembly procedures associated with these satellites create the need for an efficient method to verify the satellite's structural integrity. In particular, the ability to identify loose bolts within the satellite structure is of interest. In this work, Impact Modulation (IM) is explored as a possible means of detecting loose bolts. First, a simple two-beam, one-bolt assembly is studied to establish guidelines for the implementation of IM. Then, theoretical and analytical models are developed to provide a basis for applying IM to bolted joints. Two analysis methods for identifying loose bolts within a structure are then proposed. These methods are demonstrated on a three-beam, two-bolt structure; a four-beam, three-bolt structure; and a realistic satellite structure. The results of IM testing on the two-beam, one-bolt assembly showed that the nonlinear response of the system is significantly affected by the underlying linear characteristics of the system, that nonlinear stiffness and damping contribute to the response, that IM is an effective method for differentiating the responses of the bolted structure with different bolt torque levels, and that changes in boundary conditions do not diminish the effectiveness of IM testing. It was demonstrated that the first analysis method was able to identify the presence of loose bolts within increasingly complex structures without the use of historical data by using a dot product analysis to quantify the difference in response amplitudes at the natural frequencies and those at the sideband frequencies across an array of impact locations. The second analysis method successfully tracked changes in bolt torque by comparing the area under the response spectra in the modulation range to a baseline reference.
Degree
Ph.D.
Advisors
Adams, Purdue University.
Subject Area
Mechanical engineering
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