Ductile Fracture and Stress-Induced Defects in Multiscaled Plastic Deformation

Abstract

Fracture failure, as one of the main failure modes in product engineering, has been fully recognized and extensively studied in the past a few decades. Product fracture failure can happen in different stages of product life cycle including manufacturing, service, and maintenance. In manufacturing, especially for the parts and components made via plastic deformation of materials or the so-called metal-forming processes, the existence of fracture and fracture defects in the metal-deformed parts is a critical and tantalized issue to be addressed. Any fracture defects formed in forming process would reduce the load-carrying capacity, deteriorate the performance of product in service, and thus disqualify the produced parts. In the traditional metal-forming arena, the size scale of metal-formed parts is mostly large scale and the plastic deformation process is the so-called macroscaled forming. For the large-scaled parts made via plastic deformation, ductile fracture often occurs in the process and has been extensively studied with the intended goal of defect-free production. The systematic knowledge in terms of fracture formation mechanism, affecting factor, prediction criterion, classification, etc., has also been well established. When the part size is scaled down to microscale, however, the well-established knowledge and the insights into this widely used manufacturing process may not be fully valid in microscaled plastic deformation or microforming, so is the knowledge of ductile fracture and stress-induced defects. The barrier of this knowledge transfer from macro- to microscale plastic deformation is generally believed to be caused by the size effect, which is a ubiquitous and unique phenomenon in many engineering processes. This is a relatively new topic and has not yet been extensively explored and investigated.