Claas Bierwisch, Hanna Lagger, Michael Moseler

We present the development of smoothed particle hydrodynamics (SPH) simulations for the investigation of the industrial application of abrasive flow machining (AFM). This process cannot be observed in-situ in experiments and therefore demands for numerical simulations at a grain-size process scale. There are only a few numerical models available for the AFM process, which are strongly simplified. In order to optimize the machining, an explicit approach of including individual grains in the abrasive suspension is essential. These grains are simulated by individual clusters of SPH particles, which are integrated in time by a rigid body solver. For the correct force transmission between the suspended abrasive particle and the workpiece, a realistic representation of the stress in the fluid model of the suspension is necessary. Therefore, the rheology of the fluids, containing the abrasive grains, has been experimentally characterized. Since the tested suspensions show a viscoelastic behavior, we have employed a viscoelastic fluid model and have used experimentally gathered data for the calibration of the applied numerical model. The abrasive process on a workpiece and the removal of material from its surface is modeled by the Johnson-Cook ductile flow stress model in combination with a strain-based failure criterion. We show that the particle method can reproduce key aspects for the simulation of the process of abrasive flow machining. By the application of the Johnson-Cook model, we are able to determine wear contacts between solid materials on a microscopic scale.

The discovery of the cosmic acceleration (Perlmutter & Riess, 1999; Perlmutter et al., 1999; Riess et al., 1998) along with the presence of dark matter is one of the most intriguing puzzles in modern physics and cosmology. Up to now, only 5% percent of the energy density in the universe can be explained by the physics that we know of. The other 95% are split up into 25% dark matter and 70% dark energy. For both energy densities there is still no reasonable physical explanation for their occurrence, only observational evidence. Another vividly discussed topic is the requirement for the occurrence of life in our galaxy and in the universe. There are studies by von Bloh et al. (2003) and Franck et al. (2007) trying to investigate the early spreading of life, especially by panspermia effects, throughout the Milky Way galaxy. In order to derive their results, they determine the number of stellar systems containing habitable planets as a function of time. Combining the results by Perlmutter & Riess (1999); Perlmutter et al. (1999), Riess et al. (1998) and von Bloh et al. (2003), Franck et al. (2007), there appears to be temporal correlation between the onset of cosmic acceleration and the formation of stellar systems containing habitable planets.The question is: is this just a mere coincidence, or is there a causal connection by a yet to be discovered physical mechanism?