A three-dimensional dislocation field crystal plasticity approach applied to miniaturized structures

Material size effects are predicted for idealized planar micromanufactured structures, as a consequence of the competitive contributions of strain gradient strengthening and loss of microstructural constraints with diminishing dimensions, assuming a constant grain size. Simulations are carried out using a three-dimensional strain gradient crystal plasticity model which intrinsically accounts for the influence of differently oriented crystals within the material. By distinguishing between different crystallographic slip boundary conditions, the influences of surface layer passivity, internal grain boundaries and back stresses are assessed under externally applied in-plane tension and through-thickness bending loading conditions. Analyses are carried out on samples with a size that is representative of micromanufacturing processes. The simulations reveal a competitive process between first-order constraints, generally inducing a weakening behaviour as the number of grains decreases, and second-order strengthening resulting from the strain gradients