Lebensdauer-Vorhersage für Elastomerbauteile mit variabler Vorspannung und Temperaturabhängigkeit

Abstract

Elastomers are able to deform elastically under tensile and compressive loads up to large deformations. For this reason they are often used for industrial purposes (tire production, rubber bands, sealing rings, etc.). The structural design and dimensioning of elastomer components from a fatigue and lifetime prediction related viewpoint is still a challenge. A correlated lifetime prediction concept for load cases without static preload, which argues with crack growth and particle size distribution from 3D computer tomography, has been introduced by Ludwig [1]. This method is extended here to consider temperature effects and load cases with a static preload dependency. Fatigue tests for dumbbell specimens in force control and crack growth investigation for SENT specimens in displacement control are carried out under dynamic loading with preload variation as well temperature dependency. Carbon black reinforced HNBR, EPDM and NR elastomers show a correlation between the W¨ohler curve and the Paris-Erdogan plot. An extension of the empirical Paris-Erdogan equation considering static preload and temperature environment dependency allows the prediction of uniaxial lifetime statistics by means of particle size distribution.

Due to the viscoelastic nature of the material, the cyclically introduced energy is partly dissipated. This is more pronounced at high amplitudes causing an increase in sample temperature, which generally leads to a reduction of lifetime. It is shown that considering the hysteresis at each load stage the frequency can be adjusted to achieve similar dissipation power density. With the resulting thermally adjusted Wöhler curves significant corrections between measured and predicted lifetime cycle numbers were found. The evaluated temperature distribution by FEM simulation considering homogeneous and inhomogeneous deformation field for verification shows reasonable accordance with experimental findings.