Ductile fracture results from the application of an excessive stress to a metal that has the ability to deform permanently, or plastically, prior to fracture. Careful examination and knowledge of the metal, its thermal history, and its hardness are important in determining the correct nature of the fracture features. This chapter is a detailed account of the general characteristics and microstructural aspects of ductile fracture with suitable illustrations. It describes some of the complicating factors extraneous to the fracture itself.

This chapter discusses the causes and effects of ductile and brittle fracture and their key differences. It describes the characteristics of ductile fracture, explaining how microvoids develop and coalesce into larger cavities that are rapidly pulled apart, leaving bowl-shaped voids or dimples on each side of the fracture surface. It includes SEM images showing how the cavities form, how they progress to final failure, and how dimples vary in shape based on loading conditions. The chapter, likewise, describes the characteristics of brittle fracture, explaining why it occurs and how it appears under various levels of magnification. It also discusses the ductile-to-brittle transition observed in steel, the characteristics of intergranular fracture, and the causes of embrittlement.

In order to understand how various types of single-load fractures are caused, one must understand the forces acting on the metals and also the characteristics of the metals themselves. All fractures are caused by stresses. Stress systems are best studied by examining free-body diagrams, which are simplified models of complex stress systems. Free-body diagrams of shafts in the pure types of loading (tension, torsion, and compression) are the simplest; they then can be related to more complex types of loading. This chapter discusses the principles of these simplest loading systems in ductile and brittle metals.