Low-Deflection Loss And Hysteresis Measurements On A Spacecraft Test Joint

Report Number: WL-TR-91-3078 Volume III, p. IBC-1 thru IBC-19
Author(s): Austin, Eric M., Flora, Timothy L., Goodding, James C.
Corporate Author(s): CSA Engineering, Inc., Lockheed Missiles and Space Company, Inc.
Date of Publication: 1991-08
Pages: 19
DoD Task:
Identifier: This paper is part of a conference proceedings. See ADA241313

Abstract:
Passive damping has been demonstrated to be an effective and efficient means for limiting the effects of on-board excitations on the dynamics of space vehicles. High-precision applications require these treatments to both be effective at very low excitation levels and not affect the dimensional stability of the structure under quasistatic and thermal-mechanical loads. This work documents a study of two important issues facing structures damped with viscoelastic materials: hysteresis and loss at low deflection levels. The test article is an I-beam-like structure designed to simulate an experimental method of fabricating graphite-epoxy /honeycomb structures without using any mechanical fasteners. After identifying the most critical vibrational modes from a separate system-level analysis, a damping treatment was designed for the test joint using standard finite element techniques. A modal test using very low random excitation levels was performed on the resulting damped structure. Statistical methods were used to determine that the maximum displacement level of the free-free structure was of the order of nano-meters. Subsequently, hysteresis tests were performed on the same damped beam. Laser interferometry was used to measure displacements of the joint after undergoing cyclic static loads of varying magnitudes. Percent hysteresis was measured while the joint was loaded in three-point bending. Hysteresis behavior during displacements as small as 150 nano-meters was recorded.