From a fundamental standpoint, there are only two modes, or ways, in which metals can fracture under single, or monotonic, loads: shear and cleavage. There are fracture modes other than shear and cleavage. These include intergranular and quasi-cleavage fracture modes for single-load applications, and fatigue for multiple-load applications. Each of these fracture modes are discussed in this chapter. The factors affecting the ductile brittle relationship are also covered.

A brittle fracture occurs at stresses below the material's yield strength (i.e., in the elastic range of the stress-strain diagram). This chapter focuses on brittle fracture in metals and, more specifically, ferrous alloys. It lists the factors that must all be present simultaneously in order to cause brittle fracture in a normally ductile steel. The chapter then discusses the macroscale characteristics and microstructural aspects of brittle fracture. A summary of the types of embrittlement experienced by ferrous alloys is presented. The chapter concludes with a brief section providing information on mixed fracture morphology.

A compressor blade made of titanium alloy fractured during an engine test. The material and processing conditions of the blade were found to be satisfactory, turning the focus of the investigation to operating anomalies and human error. A photograph of the failed blade shows well-defined chevron marks along the fracture surface that end in a shear lip on the convex side. Further examination using a SEM shows that the failure was due to overload. Based on these observations and the results of tensile testing and microstructural analysis, investigators concluded that a sudden impact load on the concave side of the blade caused it to fracture.

This chapter summarizes the various kinds of gear wear and failure and how gear life in service is estimated and discusses the kinds of flaws in material that may lead to premature gear fatigue failure. The topics covered are alignment, gear tooth, surface durability and breakage of gear tooth, life determined by contact stress and bending stress, analysis of gear tooth failure by breakage after pitting, and metallurgical flaws that reduce the life of gears. The chapter briefly reviews some components in the design and structure of each gear and/or gear train that must be considered in conjunction with the teeth to enhance fatigue life.

This article depicts typical fractographic features for a number of different composite materials, covering interlaminar and translaminar fracture characteristics in composite materials.

This chapter provides an overview of factors that must be considered in the design of structural components for satisfactory service performance in terms of mechanical behavior of steel castings. The chapter discusses designing against yielding, excessive deflection, and creep and stress rupture. The chapter describes the three main approaches to evaluating and designing structures relative to fatigue resistance: the S-N curve approach for high cycle fatigue, the strain range approach for low cycle fatigue, and the fracture mechanics approach. Two approaches to design against brittle fracture are described, the ductile to brittle transition concept and the fracture mechanics approach. The chapter also discusses several types of corrosion behavior and emphasizes the need to interact with corrosion specialists in the design process. It illustrates the unique advantages that designers may gain by designing components as castings to achieve low stress concentrations economically.

This chapter reviews the concepts of fracture mechanics and their application to materials evaluation and the design of cryogenic structures. Emphasis is placed on an explanation of technology, a review of fracture mechanics testing methods, and a discussion on the many factors contributing to the fracture behavior of materials at cryogenic temperatures. Three approaches of elastic-plastic fracture mechanics are covered, namely the crack opening displacement, the J-integral, and the R-curve methods. The chapter also discusses the influence of thermal and metallurgical effects on toughness at low temperatures.