TY - CONF A1 - Vöse, Markus A1 - Fedelich, Bernard ED - Maruyama, K. ED - Abe, F. ED - Igarashi, M. ED - Kishida, K. ED - Suzuki, M. ED - Yoshimi, K. T1 - Grain boundary cavitation under time-varying normal stresses N2 - In a polycrystal, the development of creep damage, especially for low extemal loads, is related to nucleation and difiüsive growth of cavities on the grain boundaries. For low stresses, the contribution to cavity growth by dislocation creep of the suirounding material can be neglected. However, grain boundaiy diffitsion is mainly driven by the local normal stiess acting on the grain boundaiy. Under creep conditions, even under a constant extemal load, an individual grain boundaiy generally experiences a time-varying normal stress, due to stress redistributions within the polycrystalline stiuctuie. Indeed, a constrained cavitating grain boundaiy is relieved, since matter is transported to and deposited in the grain boundaiy plane, which causes the adjoining giains to drill apart. A Simulation proceduie based on the use of complex holomoiphic fiinctions for solving the diffiision problem has been used to investigate multiple cavity growth on a grain boundaiy subjected to a constant normal stress. A simplified model has been developed to describe the cavitation behaviour observed in the simulations. Finally, the analysis of cavitation simulations with time-vaiying nomial stresses, including the cases with veiy low or negative stresses, has been used to extend the simplified cavitation model to more general normal stiess time profiles. T2 - 12th International Conference on Creep and Fracture of Engineering Materials and Structures CY - Kyoto, Japan DA - 27.05.2012 KW - Creep damage KW - Grain boundary diffusion KW - Cavitation KW - Simulation KW - Evolution equations PY - 2012 SP - 1 EP - 4 AN - OPUS4-27544 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kindrachuk, Vitaliy A1 - Fedelich, Bernard T1 - Simulation of non-isothermal mechanical tests on a single crystal nickel-basis superalloy N2 - An extension of the constitutive viscoplastic model of Meric and Cailletaud is presented. The new model accounts for coupling of plasticity and viscoplasticity to describe the rate dependence at low and moderate temperatures. The model contains two boundaries: an elastic one and a viscoplastic one. Between the boundaries, the only contribution to yielding is the rate dependent viscoplastic mechanism. Once the viscoplastic boundary is reached, an additional rate independent flow mechanism becomes active. However, the extended model is not able to predict properly both creep and long-term relaxation tests simultaneously. Therefore, a deformation-induced softening is assumed, which is supposed to mainly affect static recovery. The model has been calibrated with the mechanical tests on a single crystal nickel-basis superalloy. The uniaxial tests have been carried out in the temperature interval 600°C – 1100°C in [001], [011] and [111] specimens. The predicted creep, relaxation and non-isothermal cyclic tests exhibit reasonable agreement with the experimental observations. KW - Non-isothermal mechanical tests KW - Superalloys KW - Constitutive modeling PY - 2012 SN - 0232-3869 VL - 32 IS - 2-5 SP - 321 EP - 332 PB - Institut für Mechanik CY - Magdeburg AN - OPUS4-25925 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -