Dislocation nucleation and multiplication in small volumes: The onset of plasticity during indentation testing

While classical studies of dislocation behavior have focused on the motion and multiplication of dislocations, recent advances in experimental methods allow studies that probe relatively dislocation-free volumes of materials. When the dislocation concept was initially developed 75 years ago, researchers were not easily able to examine the ultra-fine size scales of materials that would allow the onset of plasticity to be examined. This paper will review some recent developments in the area of incipient plasticity in materials and provide a historical context for current interest in testing mechanical behavior at small scales.