Structural analysis of an elastomeric bellow seal in unsteady conditions: simulations and experiments

The present work describes a study carried out to characterize the constitutive and operating behavior of a rubber membrane, to be used as an air-oil separator in vibration dampers of helicopter rotor blades. The membrane is mounted inside the main damper tube through a manual reversal movement, has to withstand a differential pressure and elongation/shortening cycles without tearing, while complying with the dimensions allowed by the damper structure. FE analyses were used extensively, taking into account large displacements, as well as the hyperelastic, viscoelastic and pseudo-elastic characteristics of the rubber material. Material models were properly tuned relying on experimental evidence. The mechanical behavior of the membrane was simulated, starting from the very first loading cycles up to the assigned service life. Additionally, membrane samples and a damper mock-up were used to conduct several experimental tests, in the attempt to reproduce the mounting and operation phases of the component. A detailed comparison between experimental and numerical results, for validation purposes, yielded in all cases a good level of agreement.