scholarly journals Lattice Rotation in Fe-20%Cr Alloy Single Crystals Subjected to Sliding Wear

2015 ◽  
Vol 64 (4) ◽  
pp. 281-286
Author(s):  
Yoshihisa KANEKO ◽  
Mutsumi NISHII
2015 ◽  
Vol 82 (6) ◽  
Author(s):  
Y. F. Gao ◽  
B. C. Larson ◽  
J. H. Lee ◽  
L. Nicola ◽  
J. Z. Tischler ◽  
...  

Strain gradient effects are commonly modeled as the origin of the size dependence of material strength, such as the dependence of indentation hardness on contact depth and spherical indenter radius. However, studies on the microstructural comparisons of experiments and theories are limited. First, we have extended a strain gradient Mises-plasticity model to its crystal plasticity version and implemented a finite element method to simulate the load–displacement response and the lattice rotation field of Cu single crystals under spherical indentation. The strain gradient simulations demonstrate that the forming of distinct sectors of positive and negative angles in the lattice rotation field is governed primarily by the slip geometry and crystallographic orientations, depending only weakly on strain gradient effects, although hardness depends strongly on strain gradients. Second, the lattice rotation simulations are compared quantitatively with micron resolution, three-dimensional X-ray microscopy (3DXM) measurements of the lattice rotation fields under 100 mN force, 100 μm radius spherical indentations in 〈111〉, 〈110〉, and 〈001〉 oriented Cu single crystals. Third, noting the limitation of continuum strain gradient crystal plasticity models, two-dimensional discrete dislocation simulation results suggest that the hardness in the nanocontact regime is governed synergistically by a combination of strain gradients and source-limited plasticity. However, the lattice rotation field in the discrete dislocation simulations is found to be insensitive to these two factors but to depend critically on dislocation obstacle densities and strengths.


1996 ◽  
Vol 44 (9) ◽  
pp. 3477-3488 ◽  
Author(s):  
T. Zhai ◽  
J.W. Martin ◽  
G.A.D. Briggs ◽  
A.J. Wilkinson

Author(s):  
Nithyanand Kota ◽  
Anthony D. Rollett ◽  
O. Burak Ozdoganlar

With the increased application of micromachining, including micromilling and microdrilling, the need to develop accurate models for machining at the microscale has been recognized. In particular, the crystallographic effects that are generally neglected in the macroscale cutting models must be incorporated into the micromachining models. Diamond turning and mechanical nanomanufacturing techniques also require an understanding of crystallographic effects during material removal. This work presents a rate-sensitive plasticity-based machining (RSPM) model that is used to determine the specific energies (and thus forces) for orthogonal cutting of face-centered cubic (fcc) single-crystals. The RSPM model uses kinematics and geometry of orthogonal cutting for an ideally sharp cutting edge. The total power is expressed in terms of the plastic power, which is spent for shearing the material within a finite shear zone, and the friction power, which is spent for overcoming the friction at the rake face. In calculating the shearing power, rate-sensitive plastic behavior of fcc metals is considered. In addition, realistic effects of lattice rotation and strain hardening are included in the model. Subsequently, the total power is minimized within the space of geometrically allowable shear angles to determine the shear angle solution, and associated cutting and thrust specific energies, as a function of cutting plane orientation, cutting direction (with respect to the crystal orientation), rake angle, and the coefficient of friction. The calibration procedure for and the experimental validation of the model are provided in Part II.


Author(s):  
Nithyanand Kota ◽  
Anthony D. Rollett ◽  
O. Burak Ozdoganlar

For a range of precision machining and micromachining operations, the crystallographic anisotropy plays a critical role in determining the machining forces. Part II of this work presents the calibration and validation of the rate-sensitive plasticity-based machining (RSPM) model developed in Part I. The five material parameters, including four hardening parameters and the exponent of rate sensitivity, for both single-crystal aluminum and single-crystal copper are calibrated from the single-crystal plunge-turning data using a Kriging-based minimization approach. Subsequently, the RSPM model is validated by comparing the specific energies obtained from the model to those from a single-crystal cutting test. The RSPM model is seen to capture the experimentally observed variation of specific energies with crystallographic anisotropy (orientation), including the mean value, symmetry, specific trend, amplitude, and phase of the peak specific energy. The effects of lattice rotation, hardening, and material-parameter variations on the predicted specific energies is then analyzed, revealing the importance of both lattice rotation and hardening in accurately capturing the specific energies when cutting single-crystals. Using the RSPM model, the effects of crystallographic orientation, rake angle and friction angle on specific energies are also analyzed. Lastly, a simplified model that uses Merchant’s shear angle, thereby circumventing the minimization procedure, is constructed and evaluated.


Author(s):  
Krzysztof Pieła ◽  
Andrzej Korbel

Abstract This paper is focused on the mechanism of kink band formation. In the general case, lattice rotation in a kink band may be realized by two sequentially activated simple elastic shears in nearly perpendicular planes. In the case of zinc crystals, compressed along (0001) plane at the temperature 523 K, the first shear may result from stress-induced temporary lattice instability (movement of atoms towards metastable positions in tetrahedric holes), while the second shear occurring along a temporary ‘new-positioned’ basal plane immediately ‘rebuilds’ the stable lattice.


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