Temperature-Dependent Viscoelastic Energy Dissipation and Fatigue Crack Growth in Filled Silicone Elastomers

There has always been a need to investigate the mechanical properties and fracture behaviors of materials that are widely used commercially, such as filled silicone rubbers. In this work, a thorough study was performed to evaluate the temperature dependencies of viscoelastic energy dissipation and fatigue crack propagation. Small strain viscoelastic behavior was examined by using dynamic mechanical analysis (DMA), and larger strain viscoelastic dissipation was quantified by defining an effective viscoelastic phase angle from large-amplitude cyclic deformation. Pure shear mode I fatigue tests were performed for quantification of material toughness and crack propagation resistance. In addition, natural rubber with different filler levels was tested to provide a direct comparison between two important classes of filled rubber elastomers. Major differences were identified for the two elastomers. However, for both types of elastomers, a common power law relationship with an exponent of 1.5 describes the dependence of the fatigue crack growth per cycle on a normalized driving force obtained from the stored elastic energy. We found that the silicone rubber deviated from the 1.5 exponent power law relation at elevated temperature, and its prefactor in this power law was correlated to the crack morphology, with rough cracks providing a higher fatigue resistance than smooth cracks.