Research Papers

Crystal Plasticity Analysis of Stress Partitioning Mechanisms and Their Microstructural Dependence in Advanced Steels

[+] Author and Article Information
Chao Pu

Department of Materials Science
and Engineering,
University of Tennessee,
Knoxville, TN 37996

Yanfei Gao

Department of Materials Science
and Engineering,
University of Tennessee,
Knoxville, TN 37996
Materials Science and Technology Division,
Oak Ridge National Laboratory,
Oak Ridge, TN 37831

Manuscript received October 29, 2014; final manuscript received January 9, 2015; published online January 23, 2015. Editor: Yonggang Huang.

J. Appl. Mech 82(3), 031003 (Mar 01, 2015) (6 pages) Paper No: JAM-14-1505; doi: 10.1115/1.4029552 History: Received October 29, 2014; Revised January 09, 2015; Online January 23, 2015

Two-phase advanced steels have an optimized combination of high yield strength and large elongation strain at failure, as a result of stress partitioning between a hard phase (martensite) and a ductile phase (ferrite or austenite). Provided with strong interfaces between the constituent phases, the failure in the brittle martensite phase will be delayed by the surrounding geometric constraints, while the rule of mixture will dictate a large strength of the composite. To this end, the microstructural design of these composites is imperative especially in terms of the stress partitioning mechanisms among the constituent phases. Based on the characteristic microstructures of dual phase and multilayered steels, two polycrystalline aggregate models are constructed to simulate the microscopic lattice strain evolution of these materials during uniaxial tensile tests. By comparing the lattice strain evolution from crystal plasticity finite element simulations with advanced in situ diffraction measurements in literature, this study investigates the correlations between the material microstructure and the micromechanical interactions on the intergranular and interphase levels. It is found that although the applied stress will be ultimately accommodated by the hard phase and hard grain families, the sequence of the stress partitioning on grain and phase levels can be altered by microstructural designs. Implications of these findings on delaying localized failure are also discussed.

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Fig. 1

(a) RVE for DP 980 steel. The RVE model size is 100 μm×100 μm×100 μm consisting of 10×10×10 cubic units. Black elements denote the martensitic phase, while colored elements correspond to ferritic grains. (b) Each cubic unit consists of 3×3×3 C3D8 solid elements including one martensite grain and one ferritic grain. Due to the martensitic phase transformation during annealing, these martensitic phases are located at the grain boundaries. A two-dimensional cut of the RVE mesh is shown to compare with the SEM image in Ref. [4].

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Fig. 2

Schematic illustration of CPFEM model of multilayered steel. One eighth of the model is meshed due to symmetric considerations.

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Fig. 3

Crystal plasticity finite element simulations of lattice strain evolution in DP 980 steel (solid lines), as compared to experimental data (discrete markers [4]) and viscoplastic self-consistent simulations (dash curves)

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Fig. 4

Lattice strain evolution in multilayered steel, with the comparisons of CPFEM simulations in this work and experimental data in Ref. [5]. A dashed ellipse indicates the deviation of modeling from experimental data.

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Fig. 5

(a) Schematic illustration of the cubic unit used in the fictitious DP material that consists of martensite and austenite phases. (b) Direct comparisons of {211} lattice strain evolution in the fictitious DP material and multilayered steel of martensite and austenite phases.




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