Lattice Rotation Patterns and Strain Gradient Effects in Face-Centered-Cubic Single Crystals Under Spherical Indentation

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.

1979 ◽  
Vol 21 (4) ◽  
pp. 263-273 ◽  
Author(s):  
T. V. Duggan ◽  
M. T. Lowcock ◽  
B. C. Staples

This paper discusses the parameters likely to influence the crack-formation life of components. In particular, the relationship between the fatigue life of plain and notched specimens is considered, and a mathematical model for predicting the crack-formation life of components is proposed. This allows for the effects of mean stresses and strains and is dependent upon the determination of local material behaviour. The approach is original in that it makes allowances for the influence of the degree of plasticity around a notch, represented in terms of the strain gradient. The Neuber method is evoked, suitably modified to allow for strain gradient effects, and strain gradients are estimated by differentiating Neuber's rule in the immediate vicinity of the notch. Experimental studies have been conducted to determine strain distributions, strain gradients and cyclic lives, and the results compared with predicted values; correlation is good.


1966 ◽  
Vol 92 (5) ◽  
pp. 67-86
Author(s):  
F.D. Day ◽  
Yechiel Weitsman

2010 ◽  
Vol 58 (4) ◽  
pp. 542-557 ◽  
Author(s):  
Christian F. Niordson ◽  
Brian Nyvang Legarth

Sign in / Sign up

Export Citation Format

Share Document