Abstract
Numerical and experimental investigations of evolution of slip fields in notched Ni-base superalloy single crystal tensile specimens are presented as functions of load and secondary (notch) orientation. Three crystallographic orientations were investigated with the primary (load) orientation fixed along the [0 0 1] direction while the notch directions are parallel to [ 1 ¯ 10 ] / [ 1 1 ¯ 0 ] , [ 0 1 0 ] / [ 0 1 ¯ 0 ] , and [ 3 ¯ 1 0 ] / [ 3 1 ¯ 0 ] , respectively. A three-dimensional elastic anisotropic finite element analysis (FEA) was used to compute the triaxial stress fields in the neighborhood of the notch. The elastic solution is successful in identifying which slip systems are activated initially. Interestingly this procedure was found to be also successful in predicting slip evolution at higher loads, because of slip localization in the superalloy tested. Based on this analysis, the concept of “dominant slip system” is introduced and defined as the single slip system that experiences the highest resolved shear stress (RSS) at a given point near the notch. The dominant slip systems are seen to persist with increasing load and inhibit the activation of new slip systems, which implies that when plasticity is initiated in the dominant slip systems, either softening takes place and/or the rate of increase in RSS on the other slip systems is reduced significantly. The distribution of dominant slip systems in the neighborhood of the notch and on the surface is used to accurately predict the evolution of activated slip sectors and sector boundaries observed experimentally. The activated stress fields are shown to vary strongly through the specimen thickness. Elastic anisotropy governs the development of the elastic stress field and controls which slip systems become initially dominant/activated. Therefore inclusion of elastic anisotropy was found to be important for the prediction of stress field evolution as functions of load and crystal orientation.
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