Vibration monitoring via nano-composite piezoelectric foam bushings

Abstract

Most mechanical systems produce vibrations as an inherent side effect of operation. Though some vibrations are acceptable in operation, others can cause damage or signal a machine's imminent failure. These vibrations would optimally be monitored in real-time, without human supervision to prevent failure and excessive wear in machinery. This paper explores a new alternative to currently-used machine-monitoring equipment, namely a piezoelectric foam sensor system. These sensors are made of a silicone-based foam embedded with nano-and micro-scale conductive particles. Upon impact, they emit an electric response that is directly correlated with impact energy, with no electrical power input. In the present work, we investigated their utility as self-sensing bushings on machinery. These sensors were found to accurately detect both the amplitude and frequency of typical machine vibrations. The bushings could potentially save time and money over other vibration sensing mechanisms, while simultaneously providing a potential control input that could be utilized for correcting vibrational imbalance.

Effect of environmental and material factors on the response of nanocomposite foam impact sensors

“…Analyzing this data from a mechanical perspective offers little to help identify the underlying drift mechanism. Though humidity is known to influence the mechanical response of viscoelastic polymers [37,38], it has been shown to soften polyurethane foam at higher levels (by 0.8%/%RH) [39,40], which should increase both peak strain (by 0.57%/%RH) and peak voltage per impact (by the same 0.57%/%RH, assuming a linear relationship between peak strain and peak voltage) [1]. It is likely that this mechanical effect causes minor drift in the response (in the opposite direction), but it only serves to slightly weaken the dominating electrical effect.…”

“…Upon deformation from impact, interactions between these additives and the surrounding foam matrix produce a distinct voltage response (figure 2). Previous work has determined this response to be related to the magnitude of impact applied to the sensor [1][2][3]. This quasi-piezoelectric effect can be harnessed to measure impact directly from a component that imparts energy-absorbing and cushioning properties.…”

“…Certain NCF characteristics (such as foamed density, matrix material, and geometry) can be engineered to reach the mechanical performance required by a wide range of applications. To date, applications include self-sensing shoe insoles [3], football helmet pads [4], and health-monitoring bushings/pads for machine mounts [1].…”

Dual-Sensing Piezoresponsive Foam for Dynamic and Static Loading

“…Nanocomposite piezoresponsive foam (NCPF) is a recently developed self-sensing material that produces a voltage during rapid deformation, and hence can be utilized to characterize impacts for applications such as helmets, sports padding, shoe insoles, and vibration-isolating components [ 1 , 2 , 3 , 4 , 5 ]. However, there is currently no consensus on what specifically is being measured by a given foam sensor; i.e., what characteristic of the deformation (energy, impulse, velocity, etc.)…”

“…NCPF materials have been developed that undergo a constriction or expansion when a high voltage is applied [ 24 ]. The reverse effect—a charge arising from deformation—has only recently been discovered with nanocomposite foams that exhibit the quasi-piezoelectric (QPE) phenomenon during impact [ 1 , 2 ]. These NCPF materials have been tailored for use in a variety of applications including vibration monitoring [ 1 ], measuring ground reaction force in shoe insoles during running and walking [ 3 , 4 ], and detecting impact magnitude in football helmets [ 5 ].…”