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Loading parameters (frequency, amplitude ratio and waveform) are varied to determine their influence on fatigue crack growth in rubber. Up to three different rubber blends are investigated: one actual engineering material and two model materials. Fatigue crack growth curves and strain distributions of pure shear and faint waist pure shear samples are compared for a model material. Fatigue behavior is studied for three different frequencies (1 Hz, 3 Hz and 5 Hz). Amplitude ratio appears to be another important influence factor concerning fatigue crack growth in rubber. The beneficial effect of positive amplitude ratios (tensional loading conditions) is shown for different materials. However, fatigue crack growth is considerably increased for negative amplitude ratios (tensional-compressional loading conditions). Furthermore, the influence of the waveform is determined for three different waveform shapes. One is sinusoidal, and two have a square shape, including dwell periods and sinusoidal slopes. Special focus lies on heat build-up, which is substantial, especially for large loads, high frequencies and/or highly filled rubber blends. Plateau temperatures are determined for various loading conditions and rubber blends. A very simple linear relationship with dissipated energy per time and unit area is obtained. Results gathered with dynamic mechanical analyses show, likewise, a linear trend, but the heat build-up is very small, due to different sample geometries.

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Because of its capability for net-or near-net shape production, P/M technology is well suited for the production of complex shapes such as gears. Nevertheless, the usage of P/M parts has been limited for a long time on low to moderate stress applications due to their porosity. To improve the mechanical properties of P/M gears, the high stressed regions have to be densified. As the highest service stresses for gears occur in a thin layer below the surface, it's sufficient to densify just the cogs surface and keep porosity with its positive influence on weight and noise damping over the rest of the gear. Due to new surface treatment processes, which provide a local densification of high stressed areas up to full density, P/M components are now successfully used in high performance applications. One new idea for surface densification of P/M gears is the use of a specific radial forging process. To prove the applicability and to generate specific knowledge about the new process, FEM studies have been done before running pilot trials. The main purpose of the FEM studies is the investigation of the influence of preform and die design on surface densification and the expectable dimensional accuracy. Therefore different ways of forging the cogs have been investigated. The deduced basic coherences and process characteristics enable a demonstration of advantages and disadvantages of the planned process. Hence, basic conditions for an application of the radial forging process for gear productions are deduced.

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