The Role of Plasticity in the Transverse Lattice Strain Evolution of a Martensitic Steel
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neutron diffraction (ND), performed as a sample is held under mechanical load, has been successfully used to monitor the mechanical response in a range of crystalline materials. Insights into the evolutionary lattice strain (average elastic strain over a family of appropriately orientated grains), represented by the shift in diffraction peaks, have been gained in ferritic steels[1–6] under uniaxial loading conditions. In in-situ ND tests, lattice strains are typically presented as a function of macroscopic stress. If the material deforms in the linear elastic regime in an in-situ tensile test or if stress and strain are homogenous throughout the material, a linear relation will result between macroscopic stress and lattice strain. However, in the plastic regime, a nonlinear lattice strain response has been identified in both the longitudinal and transverse direc-
DONG-FENG LI, Postdoctoral Researcher, formerly with the Department of Mechanical, Aeronautical and Biomedical Engineering, Materials and Surface Science Institute, University of Limerick, Limerick, ireland, is now with the Mechanical Engineering School of Informatics and Engineering, National University of Ireland, Galway, Ireland. Contact e-mail: [email protected]; [email protected] BRIAN J. GOLDEN, Ph.D. Student, and NOEL P. O’DOWD, Professor, are with the Department of Mechanical, Aeronautical and Biomedical Engineering, Materials and Surface Science Institute, University of Limerick. SHU-YAN ZHANG, Instrument Scientist, is with the ISIS, STFC Rutherford Appleton Laboratory, Chilton Didcot, OX11 0QX Oxfordshire, U.K. VADIM DAVYDOV, Instrument Scientist, is with the Paul Scherrer Institute (PSI), Spallation Neutron Source SINQ, Materials Science and Simulations, NUM ASQ, WBBA/119, Villigen 5232, Switzerland. PETER TIERNAN, Senior Lecturer, is with the Department of Design and Manufacturing Technology, Materials and Surface Science Institute, University of Limerick, Limerick, Ireland. Manuscript submitted April 22, 2014. Article published online October 3, 2014 METALLURGICAL AND MATERIALS TRANSACTIONS A
tions, associated with nonlinear, locally inhomogeneous material response. As mechanical behavior at different length scales are measured in an in-situ ND test (stress and strain at the macroscopic level; lattice strains at the mesoscale/intergranular level), ND data, particularly those showing a strong nonlinear response, have the potential to validate computational models using, for example, the crystal plasticity method.[7–12] The nonlinear effect in the longitudinal direction has been examined elsewhere, e.g., in Reference 10. For metals, the nonlinear inelastic deformation is typically governed by the shear stress acting on the relevant material slip planes through the Schmid law.[13] Therefore, differently orientated grains exhibit heterogeneous response and consequently different loadcarrying capacities. When the material deformation transits from the linear elastic regime to the nonlinear plastic regime, local stress redistribution in relevant gr
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