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J. Eng. Mater. Technol. 136, 041001 (2014) (10 pages);   Paper No: MATS-13-1154;   doi:10.1115/1.4027857

The prediction of temperature-dependent fatigue deformation and damage in directionally solidified and single-crystal nickel-base superalloy components used in the hot section of gas turbine engines requires a constitutive model that accounts for the crystal orientation in addition to the changing deformation mechanisms and rate dependencies from room temperature to extremes of the use temperature (e.g., 1050 °C). Crystal viscoplasticity (CVP) models are ideal for accounting for all of these dependencies. However, as the models become more physically realistic in capturing the true cyclic deformation mechanisms, increases the requirements to achieve an accurate model calibration. As a result, CVP models have yet to become viable for life analysis in industry. To make CVP models an industry relevant tool, the calibration times must be reduced. This paper explores methods to reduce the calibration time. First, a series of special calibration experiments are conceived and conducted on each relevant orientation and microstructure. Second, a set of parameterization protocols are used to minimize parameter interdependencies that reduce the amount of iteration required during the calibration. These experimental and calibration protocols are exercised using the CVP model of Shenoy et al. (2005, “Thermomechanical Fatigue Behavior of a Directionally Solidified Ni-Base Superalloy,” ASME J. Eng. Mater. Technol., 127(3), pp. 325–336) by calibrating a directionally solidified Ni-base superalloy across an industry relevant temperature range of 20 °C to 1050 °C.

J. Eng. Mater. Technol. 136, 041002 (2014) (7 pages);   Paper No: MATS-14-1042;   doi:10.1115/1.4028006

It is the objective of this study to conduct realistic simulations of the arc-height development in shot-peened Almen strips using the finite element (FE) method. Unlike our earlier work which is devoted to relaxation of shot peening induced residual stress, in this paper, the focus is on peen forming as a result of repeated spherical impingement. Specifically, a 3D FE model with 1500 randomly distributed shots bombarding an Almen strip was developed. Strain rate dependent plasticity was considered and an artificial material damping was applied to control the undesired high-frequency oscillations. The solution further adopts both explicit dynamic and implicit quasi-static analyses to simulate the entire arc-height development in the Almen strips. Quantitative relationships between the resulting equivalent plastic strain and the associated residual stress distribution for a given shot velocity and shot numbers are established and discussed. The work also considers the effect of repeated impacts upon the induced residual stress field using a large number of random shots. Attention was further devoted to the effect of the strip constraint upon the outcome of the impingement. Our results indicate that the proposed FE model is a powerful tool in investigating the underlying mechanisms of the peening treatment.

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