Vibration Damping on Graphite and KEVLAR(R)Composites Using Piezoceramic Powder Coatings: A Review

Abstract

Some researchers have studied passive vibration damping using thin hybrid layer(s) of magnetostrictive powder coatings on a wide gamut of composite laminates. Although these magnetostrictive materials can be used for damping of thin flexible structural systems, in practice their use is limited in the domain of microwave spacecraft antenna applications because of electromagnetic interference (EMI) and electromagnetic coupling (EMC) issues at higher transmit and receive radio frequencies (RFs). Ultra-lightweight, high-frequency satellite reflectors made of high specific stiffness/high specific strength graphite and KEVLARcomposites, with stringent precision design requirements with respect to (w.r.t.) the root mean square surface error; pick up post-launch microvibrations in the deployed condition because of the movement of the three-axis gyros of the spacecraft or because of altitude correction exercises along with steep thermal gradients in the space domain. These vibrations at elevated temperatures need to be damped out, particularly in the passive domain, without affecting the overall stability of the spacecraft. Therefore, it is proposed to use particularly non-magnetic, thin hybrid piezoceramic powder coating(s) on one side of the graphite and KEVLAR® composites to cater for the microvibration suppression issue of the spacecraft reflectors. Moreover, at elevated temperatures, the adhesion of thin layers of piezoceramic materials on graphite and KEVLAR® composites also becomes an important issue, which needs to be addressed separately and has been reviewed at length. Therefore, in this paper, an attempt has been made to thoroughly review and investigate experimentally the use of the surface activation technique of RF plasma corona on composites along with coatings of thin hybrid layer(s) of high-sensitivity ferroelectrically soft, non-magnetic piezoelectric ceramic material for achieving passive vibration damping benefits on KEVLAR® and graphite composites with embedded KEVLAR® flexcore at varying temperatures. The surface activation has been performed using the plasma-etching approach to obtain improved adhesion of the piezoceramic material with composites at elevated temperatures. KEVLAR® and graphite composites were treated with RF plasma to modify the surface properties such that they contribute to the adhesion enhancement between plasma-treated polymer surfaces and the piezoceramic material coatings. We have referred to American Society for Testing and Materials (ASTM) standards for the finalization of test specimen sizes for the experimental work. Strain-dependent material damping in the thin piezoceramic passive layers on KEVLAR® and graphite composites leads to a typical nonlinear behavior at varying temperatures. Therefore, an Oberst vibrating beam technique has been chosen for experimentation on a cantilever specimen made of graphite and KEVLAR® in order to estimate the composite loss factor at elevated temperatures. The thin hybrid layer(s) of non-magnetic piezoceramic materials when coated on KEVLAR® and graphite substrates (on one side only) have given improved results w.r.t. passive structural damping at elevated temperatures with almost negligible weight penalty; this is with practically no EMI/EMC issues when tested separately for Ku-band frequencies at the Space Applications Centre, Indian Space Research Organization, Ahmedabad. The encouraging results, w.r.t. the enhanced passive damping at resonant frequencies for piezoceramic powder coated high specific stiffness/high specific strength graphite and KEVLAR® composites at elevated temperatures, may make the present investigation and review on piezocoated composites a possible candidate for high-frequency applications in future w.r.t. the microvibrations experienced in orbit by the reflectors of today's sophisticated Earth observation satellites, which are designed for stringent pointing accuracies and resolutions.