A methodology for measuring and modeling crystallographic texture gradients in processed alloys

The explicit representation of internal material structure in alloy process ing and in-service performance simulations is becoming increasingly prevale nt. This paper presents a methodology for characterizing and representing a spatially-varying orientation distribution function (ODF) that can be used in processing and performance simulations for alloys containing texture gr adients. We use thick AA 7050 aluminum plate, which is known to contain tex ture gradients, as a case study to demonstrate the methodology, which emplo ys a finite element representation of the ODF initialized using individual lattice orientation measurements taken using the electron backscatter patte rn (EBSP) technique. As expected, we find that the texture varies significa ntly through the plate thickness. We use the ODF to examine the effect of t he varying texture on the resulting yield strength distribution as embodied by the average Taylor factor. We find that the predicted yield strength an isotropy is different at different locations through the thickness of the p late. We examine the optimal number of orientation measurements necessary f or determining the ODF in the presence of this texture gradient. We find th at as we increase the number of orientations, the ODF quickly becomes stabl e but eventually starts to change under the influence of the texture gradie nt. We also investigate spatial interpolation of the ODF using the finite e lement representation, We find that, as with finite element representations of other fields, interpolation accuracy depends on the variation of the he ld variable and the discretization of the domain. In this case, gradients i n both physical space and orientation space affect the accuracy of the inte rpolation. Finally, the effects of the texture gradient on the mechanical r esponse of the material is demonstrated by employing the ODFs taken from va rious locations through the thickness of the plate in polycrystal plasticit y simulations of uniaxial tension and plane strain compression. (C) 2001 El sevier Science Ltd. All rights reserved.