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Shin, E.J.,Jung, A.,Choi, S.H.,Rollett, A.D.,Park, S.S. Elsevier Sequoia 2012 Materials science & engineering. properties, micro Vol.538 No.-
A resolved shear stress (RSS) criterion and the microstructure-based-crystal plasticity finite element method (MB-CPFEM) were used to analyze the activation of twin variants in extruded AZ31 Mg alloys during ex situ uniaxial compression. The RSS criterion, which is simply based on the Schmid factor, failed to predict the activation of twin variants consisting of the second-highest RSS and the third-highest RSS. In contrast to the RSS criterion, the MB-CPFEM based on a quasi-3D finite element mesh successfully predicted the activation of twin variants consisting of the highest RSS and the second-highest RSS. The MB-CPFEM demonstrated that local fluctuation of the stress field induces the activation of twin variants with the second-highest RSS during uniaxial compression.
5754 Aluminum Sheet Deformed Along Bi-Linear Strain Paths
M.A. Iadicola,L. Hu,A.D. Rollett,T. Foecke 한국소성가공학회 2011 기타자료 Vol.2011 No.8
Sheet specimens of aluminum alloy 5754 were deformed along a series of bi-linear, equal-biaxial and uniaxial, strain paths while simultaneously measuring stress-strain behavior. Using the measured crystallographic texture before and after deformation, the VPSC model that incorporates texture evolution was used to simulate the flow stress and hardening behavior. Including latent hardening of multiple slip planes allowed the model to explain the decrease in flow stress when changing from equal-biaxial to uniaxial deformation. However, the model did not capture the details of the drop in flow stress nor the magnitude of the plastic hardening after the change in deformation mode. This is likely due to room temperature recovery between the two steps of testing.
Microtexture development during equibiaxial tensile deformation in monolithic and dual phase steels
Kim, D.H.,Kim, S.J.,Kim, S.H.,Rollett, A.D.,Oh, K.H.,Han, H.N. Elsevier Science 2011 ACTA MATERIALIA Vol.59 No.14
Subgrain texture and microstructure evolution in individual ferrite grains in single (so called interstitial-free) and dual phase (DP) steel sheets with various martensitic fractions during stepwise equibiaxial deformation was observed by high resolution electron backscatter diffraction (EBSD) measurement on a special deformation stage positioned inside a scanning electron microscope chamber. The micromechanical effect of hard martensite islands on adjacent ferrite grains in DP steels was analyzed by comparing the microstructural changes in the two steels. The strain partitioning between ferrite and martensite in DP steel, the development of orientation gradients in ferrite grains near martensite islands, and the surface height variation were observed via a combination of high resolution transmission electron microscopy, EBSD, and atomic force microscopy. From these microstructural and geometrical observations the main effect of the hard martensite islands was to shed strain into the adjacent ferrite, thus inducing strain gradients, orientation spread, geometrically necessary dislocations and increased surface height variation.
Liu, X.,Nuhfer, N.T.,Rollett, A.D.,Sinha, S.,Lee, S.B.,Carpenter, J.S.,LeDonne, J.E.,Darbal, A.,Barmak, K. Elsevier Science 2014 Acta materialia Vol.64 No.-
A transmission-electron-microscope-based orientation mapping technique that makes use of beam precession to achieve near-kinematical conditions was used to map the phase and crystal orientations in nanolamellar Cu/Nb composites with average layer thicknesses of 86, 30 and 18nm. Maps of high quality and reliability were obtained by comparing the recorded diffraction patterns with pre-calculated templates. Particular care was taken in optimizing the dewarping parameters and in calibrating the frames of reference. Layers with thicknesses as low as 4nm were successfully mapped. Heterophase interface plane and character distributions (HIPD and HICD, respectively) of Cu and Nb phases from the samples were determined from the orientation maps. In addition, local orientation relation stereograms of the Cu/Nb interfaces were calculated, and these revealed the detailed layer-to-layer texture information. The results are in agreement with previously reported neutron-diffraction-based and precession-electron-diffraction-based measurements on an accumulated roll bonding (ARB)-fabricated Cu/Nb sample with an average layer thickness of 30nm as well as scanning-electron-microscope-based electron backscattered diffraction HIPD/HICD plots of ARB-fabricated Cu/Nb samples with layer thicknesses between 200 and 600nm.
S-J Kim,D. H. Kim,K. H. Oh,A. D. Rollett,R. A. Lebensohn,H. N. Han 한국소성가공학회 2010 기타자료 Vol.2010 No.6
An efficient formula, which is based on fast Fourier transform (FFT) algorithm and orientation image, was implemented into an elasto-plastic finite element method, in order to calculate the plastic deformation of polycrystalline material with intracrystalline resolution for arbitrary deformation. This new finite element model will provide the changes in average orientation and intracrystalline misorientation as well as the stress and strain behavior for various polycrystalline materials under arbitrary deformation.