Investigation of mechanical and fracture mechanical properties of elastomers filled with precipitated silica and nanofillers based upon layered silicates

The aim of this paper is to show possibilities of experimental methods of polymer diagnostics and fracture mechanics for quantitative characterization of crack initiation and propagation properties of elastomeric materials. At first, a general overview of methods of technical fracture mechanics is given. This is followed by a short discussion of some possibilities for determination of tearing energy T for elastomers. In the main part, results of various mechanical and fracture mechanics experiments on filled natural rubber vulcanizates are shown. The vulcanizates were filled with different contents (5-70 phr) of two filler types. The fillers were precipitated silica and an organic-modified nano-disperse layered silicate. Th aim of the experiments was to prove possibilities of several fracture mechanics testing methods for quantifying the influence of the filler content, filler type and additionally the specimen direction on the deformation and fracture behavior. Tear-analyzer results were used to assess the crack propagation behavior under fatigue-like loading conditions. Furthermore, instrumented tensile-impact tests were performed for the characterization of the crack resistance of the materials under impact-like loading conditions. To obtain information about the initiation and propagation of a stable crack, a quasi-static fracture mechanics test was applied, and crack resistance curves were recorded. Here, specimens with various thicknesses were investigated. Additionally, conventional tear tests were done and the results were compared to that of the fracture mechanics test. Generally, it was found that all methods are useful for the description of the fracture properties. Furthermore, the fracture behavior is influenced positively especially by high filler contents. Strong differences of several parameters were found depending on the filler type. Another important result is that again differences were found between the crack initiation and propagation behavior.