Modal performance degradation of naturally aged NBR

Abstract

Damping is often an invisible requirement for a good mechanical design. To render the long-term service of viscoelastic dampers, it is essential for design engineers to estimate the degradation of the damping characteristics with age. Nitrile butadiene rubber (NBR) is a widely used damping and sealing material. Viscoelastic sandwich beam configurations have been used to mount electronic components for various automobile and aerospace applications. The present work emphasizes the estimation of modal parameter degradation of NBR with age in an oxidative environment. NBR is assumed to be homogeneous and isotropic and is allowed to age naturally with no load under ambient conditions. Fourier-transform infrared spectroscopy (FTIR) was used to detect age-related changes in the functional groups of the NBR material with age. Dynamic mechanical analysis (DMA) tests were performed to relate the complex properties of naturally aged materials to those of virgin materials in the frequency and temperature domains. Mechanical tests were performed to determine the hardness, elongation break, and failure stress of the virgin NBR and naturally aged NBR. The damping ability of the NBR was investigated using an unconstrained sandwich cantilever beam with aluminum as the base material. For sinusoidal sweep excitation, the influence of viscoelasticity on structural damping was investigated. Based on the experimental results, the damping ability of the NBR has been observed to degrade with age. As the age increased, the damping ability of the NBR decreased by 8% at the first resonance frequency and by 34% at the third resonance frequency.

Keywords

• Damping
• DMA
• FTIR
• NBR
• Viscoelasticity