Our singular quest to mimic nature has spawned tremendous excitement in synthesizing materials and constructing structures that aim at using some of the natural principles. The notion of the statement Smaller is Stronger has far reaching implications in engineering the materials that push the limits of structural performance. In crystalline metals, size-effects in the elasto-plastic behavior is important as our ability to design and manufacture structures at miniaturized length-scales and with nano-scaled internal structures continues to acquire higher levels of sophistication. Rapid increase in computational power in the recent decades has enabled performing computational simulations that supplement, or at times even motivate, experimental investigations into the physics and mechanics in crystalline materials at multiple length-scales, ranging from brute-force atomistics to enriched continuum mechanics.
Our current focus is on a small subset within the vast expanse of length-scale dependent behaviors. We are interested in some of the size-effects that prevail in the mechanical behavior of crystalline metals. A particular category of size-effects covered in this thesis pertains to crystalline plasticity that arises from interacting effects between dislocations and their ambience. For example, dislocations get stopped by hard boundaries or annihilate at free surfaces. In another scenario, dislocations talk to other dislocations in their neighborhood. All these events result in length-scale dependent macroscopic plastic responses that manifest as strengthening of a material. We probe some of these effects in heterogeneous crystalline microstructures of current interest through analytical and computational crystal plasticity.