Overview of constitutive laws, kinematics, homogenization and multiscale methods in crystal plasticity finite-element modeling: Theory, experiments, applications

http://meyersgroup.ucsd.edu/papers/journals/meyers 213.pdf

The onset of twinning in metals: a constitutive description

We investigate the effect of grain size and grain orientation on deformation twinning in a Fe–22 wt.% Mn–0.6 wt.% C TWIP steel using microstructure observations by electron channeling contrast imaging (ECCI) and electron backscatter diffraction (EBSD). Samples with average grain sizes of 3 μm and 50 μm were deformed in tension at room temperature to different strains. The onset of twinning concurs in both materials with yielding which leads us to propose a Hall–Petch-type relation for the twinning stress using the same Hall–Petch constant for twinning as that for glide. The influence of grain orientation on the twinning stress is more complicated. At low strain, a strong influence of grain orientation on deformation twinning is observed which fully complies with Schmid's law under the assumption that slip and twinning have equal critical resolved shear stresses. Deformation twinning occurs in grains oriented close to 〈1 1 1〉//tensile axis directions where the twinning stress is larger than the slip stress. At high strains (0.3 logarithmic strain), a strong deviation from Schmid's law is observed. Deformation twins are now also observed in grains unfavourably oriented for twinning according to Schmid's law. We explain this deviation in terms of local grain-scale stress variations. The local stress state controlling deformation twinning is modified by local stress concentrations at grain boundaries originating, for instance, from incoming bundles of deformation twins in neighboring grains.

The effect of grain size and grain orientation on deformation twinning in a Fe-22 wt.% Mn-0.6 wt.% C TWIP steel

A dislocation-based constitutive law for pure Zr including temperature effects

This article investigates the microstructural variables influencing the stress required to produce deformation twins in polycrystalline fcc metals. Classical studies on fcc single crystals have concluded that the deformation-twinning stress has a parabolic dependence on the stacking-fault energy (SFE) of the metal. In this article, new data are presented, indicating that the SFE has only an indirect effect on the twinning stress. The results show that the dislocation density and the homogeneous slip length are the most relevant microstructural variables that directly influence the twinning stress in the polycrystal. A new criterion for the initiation of deformation twinning in polycrystalline fcc metals at low homologous temperatures has been proposed as (σ
 tw
 −σ
 0)/G=C(d/b)A, where σ
 tw
 is the deformation twinning stress, σ
 0 is the initial yield strength, G is the shear modulus, d is the average homogeneous slip length, b is the magnitude of the Burger’s vector, and C and A are constants determined to have values of 0.0004 and −0.89, respectively. The role of the SFE was observed to be critical in building the necessary dislocation density while maintaining relatively large homogeneous slip lengths.

Influence of grain size and stacking-fault energy on deformation twinning in fcc metals

The stress-strain behavior of pure Zr was studied systematically at various temperatures and strain rates. At 76 K, Zr deforms predominantly by twinning, whereas above room temperature (RT), slip is the controlling deformation mode. A transition in the rate-controlling deformation mode from slip to twinning has been observed to occur at intermediate temperatures during the course of plastic deformation. Above 373 K, slip dominates the entire course of deformation. The transition from slip to twinning in the stress-strain behavior is linked to differing strain-hardening rates and temperature sensitivities of the two deformation modes.

Influence of temperature and strain rate on slip and twinning behavior of zr

Mechanical tests and microstructural examinations performed on a SiC-particle-reinforced 6061-A1 matrix composite indicate that particle cracking during mechanical testing significantly affects the failure mechanisms of the composite. Microcracks were observed to nucleate and propagate on stacking faults and interfaces between the 4H (or 3C) and 6H hexagonal phases within the SiC particle reinforcements. These planar defects were the predominant defects seen in the SiC particles. Partial dislocations, having a 1/3 (10άrc10) Burgers vector, were also observed bounding the stacking faults in the reinforcement phase.

Stacking faults in sic particles and their effect on the fracture behavior of a 15 Vol Pct SiC/6061-AI matrix composite

Static and Dynamic mechanical tests, and microstructural examinations performed on a SiC particle reinforced 6061-Al matrix composite indicated that particle cracking significantly affected the strength, strain hardening, and failure mechanism of the composite Cracks were observed to nucleate and propagate on stacking faults and interfaces between the various phases within the reinforcing SiC particles Planar defects were the predominant artifacts seen in the SiC particles Partial dislocations were also observed bounding the stacking faults within the reinforcement phase

/pdf/the-effect-of-structural-defects-in-sic-particles-on-the-20hhj55y1m.pdf

S. G. Song

Papers

Influence of temperature and strain rate on slip and twinning behavior of zr

Stacking faults in sic particles and their effect on the fracture behavior of a 15 Vol Pct SiC/6061-AI matrix composite

The effect of structural defects in SiC particles on the static & dynamic mechanical response of a 15 volume percent SiC/6061-Al matrix composite