The Radially Asymmetric Dual Arc (RADA) Profile is a novel geometric configuration for the Elastomer of a Torsional Vibration Damper (TVD) that enhances the TVD’s fatigue-life while simultaneously improving the axial and radial run-outs between the two metallic components utilized therein. The RADA is a subtle geometric change, and can be implemented without any additional manufacturing costs (Figure 1).
TVDs reduce torsional vibrations inherent to rotating shafts and consequently enhance its fatigue-life while improving the system’s vibratory performance. The simplest TVD consists of a rigid structural bracket (Hub) that attaches it to the rotating shaft; an active inertial member (Ring) that enables vibration attenuation; and an elastomer member (Elastomer) that is inserted between the Hub and the Ring under compression holding them in place while simultaneously providing a spring-dashpot system for the TVD (Figure 1). The geometry of the compressed Elastomer post-assembly is determined by the axisymmetric cross-sectional shape of the gap defined by outermost diametric surface of the Hub and innermost diametric surface of the Ring. Two design paradigms universally accepted throughout the industry for such profiles are: (1) the straight Profile yields the best Maximum Principal Strain (MPS) response post-assembly; (2) the opposite walls of the Profile must be maintained mutually parallel through the majority of the TVD’s axial length.
The post-assembly MPS is calculated utilizing proprietary highly non-linear hyper-elastic Finite Element Analysis (FEA) techniques. The FEA results correlate to the fatigue-life of the Elastomer under a Resonant-Dwell Test (RDT) through internally developed proprietary threshold values. In the RDT, the Hub is oscillated at an angular amplitude with the frequency adjusted constantly based upon maintaining the relative phase-angle between the Hub and Ring oscillations at ninety degrees (i.e. at resonance).
The FEA based MPS results of the Elastomer insertion with standard Profiles yields two realizations: (1) the elastomer experiences higher MPS values at either axial periphery compared to the axial center-point; and (2) true to conventional wisdom, the straight Profile outperforms any curved Profile in MPS buildup so long as the opposite walls of the Profile are mutually parallel (Figure 2). The RADA Profile shifts this paradigm and defies convention design practice to yield a structurally superior TVD. By subtending two arcs with different radii and different but collinear center-points, a “marble-in-a-bowl” scenario is created where the spherical Hub-arc (marble) self-centers itself within the spherical Ring-arc (bowl); therefore providing a natural stability and equilibrium that enhances the axial and radial run-out of the TVD (Figure 1). Furthermore, the Elastomer is allowed to relax at the axial periphery and avoid the classical tear-drop type strain buildup common in traditional TVDs (Figure 3).
Empirical testing of the RADA Profile confirms that the FEA predicted MPS results correlate to the fatigue-life of the Elastomer under the RDT (explained above). This test yielded an average 320% fatigue-life improvement of TVDs with RADA Profiles over those with straight Profiles. Therefore, shattering the twin paradigm that the straight Profile yields the best fatigue-life response and that the Profile must have mutually parallel opposing sides.