This article addresses macroscale fracture appearances, microscale fracture-surface appearances or morphologies, fracture mechanisms, and those factors that influence fractures and fracture appearances. Some of the macroscopic and microscopic features identified by the failure analyst to evaluate the fracture surfaces of metals and plastics are described and compared.

Fracture surfaces can provide an important and indispensable record of many factors in simple or complex failures. Visual examination of fracture surfaces can reveal the type and direction of loading, with fracture-surface features often providing definitive evidence of torsion, tension, bending, and compressive loads. This article discusses tools and techniques of visual examination and characteristic features of fracture features. A brief review of ductile and brittle fracture-surface features is provided. The article also describes macroscopic features that can be used to identify fracture-initiation sites, locations of final overload, and the directions of crack propagation. In addition, the use of these features to characterize loading at the time of failure is also described.

This article provides practical guidance for interpreting macroscale fracture appearances. It focuses on metallic fracture features. The article covers the important distinctions between ductile and brittle fracture and the influence of the type of loading on the facture-surface orientation. It discusses both ductile fracture and brittle fracture macroscale features. Finally, it delves into fracture-initiation sites and metal-processing effects on fracture appearance, including castings, powder metals, additive manufacturing, and surface treatments.

In this article, a basic summary of fracture mechanisms in carbon and alloy steels is presented, along with numerous examples of these fractures. These examples include ductile fracture, brittle cleavage fracture, intergranular fracture, fatigue fracture, and environmentally assisted failure mechanisms.

Fracture of aluminum alloys can occur due to several failure types and/or fracture morphologies, including overload, intergranular fracture, fatigue, corrosion, and mixed-mode fracture. This article provides a detailed discussion on these failure types and/or fracture morphologies. It also presents the differences between wrought and cast aluminum products.

This article focuses on the following common fracture mechanisms observed in copper alloys: dimple overload, corrosion-related fractures such as corrosion fatigue and stress-corrosion cracking, and intergranular fracture. The effects of loading conditions and temperature on copper and copper alloys are discussed.

This article reviews the mechanical behavior and fracture characteristics that discriminate structural polymers from metals, including plastic deformation. It provides overviews of crack propagation and fractography. The article presents the distinction between ductile and brittle fracture modes. Several case studies of field failure in various polymers are also presented to illustrate the applicability of available analytical tools in conjunction with an understanding of failure mechanisms.

With any polymeric material, chemical exposure may have one or more different effects. Some chemicals act as plasticizers, changing the polymer from one that is hard, stiff, and brittle to one which is softer, more flexible, and sometimes tougher. Often these chemicals can dissolve the polymer if they are present in large enough quantity and if the polymer is not crosslinked. Other chemicals can induce environmental stress cracking (ESC), an effect in which brittle fracture of a polymer will occur at a level of stress well below that required to cause failure in the absence of the ESC reagent. Finally, there are some chemicals that cause actual degradation of the polymer, breaking the macromolecular chains, reducing molecular weight, and diminishing polymer properties as a result. This article examines each of these effects. The discussion also covers the effects of surface embrittlement and temperature on polymer performance.

The discussion on the fracture of solid materials, both metals and polymers, customarily begins with a presentation of the stress-strain behavior and of how various conditions such as temperature and strain-rate affect the mechanisms of deformation and fracture. This article describes crazing and fracture in polymeric materials, with a review of the behavior of the elastic modulus as a function of temperature or time parameters, emphasizing the importance of the viscoelastic nature of their deformation and fracture. The discussion covers the behavior of polymers under stress, provides information on ductile and brittle behaviors, and describes craze initiation in polymers and crack formation and fracture by crazing. Macroscopic permanent deformation of polymeric materials caused by shear-yielding and crazing, which eventually can result in fracture and failure, is also covered.

A detailed fracture mechanics evaluation is the most accurate and reliable prediction of process equipment susceptibility to brittle fracture. This article provides an overview and discussion on brittle fracture. The discussion covers the reasons to evaluate brittle fracture, provides a brief summary of historical failures that were found to be a result of brittle fracture, and describes key components that drive susceptibility to a brittle fracture failure, namely stress, material toughness, and cracklike defect. It also presents industry codes and standards that assess susceptibility to brittle fracture. Additionally, a series of case study examples are presented that demonstrate assessment procedures used to mitigate the risk of brittle fracture in process equipment.

Life assessment of structural components is used to avoid catastrophic failures and to maintain safe and reliable functioning of equipment. The failure investigator's input is essential for the meaningful life assessment of structural components. This article provides an overview of the structural design process, the failure analysis process, the failure investigator's role, and how failure analysis of structural components integrates into the determination of remaining life, fitness-for-service, and other life assessment concerns. The topics discussed include industry perspectives on failure and life assessment of components, structural design philosophies, the role of the failure analyst in life assessment, and the role of nondestructive inspection. They also cover fatigue life assessment, elevated-temperature life assessment, fitness-for-service life assessment, brittle fracture assessments, corrosion assessments, and blast, fire, and heat damage assessments.

In addition to failures in shafts, this article discusses failures in connecting rods, which translate rotary motion to linear motion (and conversely), and in piston rods, which translate the action of fluid power to linear motion. It begins by discussing the origins of fracture. Next, the article describes the background information about the shaft used for examination. Then, it focuses on various failures in shafts, namely bending fatigue, torsional fatigue, axial fatigue, contact fatigue, wear, brittle fracture, and ductile fracture. Further, the article discusses the effects of distortion and corrosion on shafts. Finally, it discusses the types of stress raisers and the influence of changes in shaft diameter.

This article focuses on characterizing the fracture-surface appearance at the microscale and contains some discussion on both crack nucleation and propagation mechanisms that cause the fracture appearance. It begins with a discussion on microscale models and mechanisms for deformation and fracture. Next, the mechanisms of void nucleation and void coalescence are briefly described. Macroscale and microscale appearances of ductile and brittle fracture are then discussed for various specimen geometries (smooth cylindrical and prismatic) and loading conditions (e.g., tension compression, bending, torsion). Finally, the factors influencing the appearance of a fracture surface and various imperfections or stress raisers are described, followed by a root-cause failure analysis case history to illustrate some of these fractography concepts.

This article briefly reviews the factors that influence the occurrence of intergranular (IG) fractures. Because the appearance of IG fractures is often very similar, the principal focus is placed on the various metallurgical or environmental factors that cause grain boundaries to become the preferred path of crack growth. The article describes in more detail some typical mechanisms that cause IG fracture. It discusses the causes and effects of IG brittle cracking, dimpled IG fracture, IG fatigue, hydrogen embrittlement, and IG stress-corrosion cracking. The article presents a case history on IG fracture of steam generator tubes, where a lowering of the operating temperature was proposed to reduce failures.

This article aims to identify and illustrate the types of overload failures, which are categorized as failures due to insufficient material strength and underdesign, failures due to stress concentration and material defects, and failures due to material alteration. It describes the general aspects of fracture modes and mechanisms. The article briefly reviews some mechanistic aspects of ductile and brittle crack propagation, including discussion on mixed-mode cracking. Factors associated with overload failures are discussed, and, where appropriate, preventive steps for reducing the likelihood of overload fractures are included. The article focuses primarily on the contribution of embrittlement to overload failure. The embrittling phenomena are described and differentiated by their causes, effects, and remedial methods, so that failure characteristics can be directly compared during practical failure investigation. The article describes the effects of mechanical loading on a part in service and provides information on laboratory fracture examination.

As cast iron parts are extensively applied, fracture events will eventually take place. Consequently, it becomes essential to carry out failure analyses to identify the cause of fracture and to provide corrective actions that allow safe operation. This article presents a description of the main fracture modes and their characteristic fractographic features. It discusses the four principal fracture modes: dimple rupture (or fracture), cleavage, fatigue, and intergranular fracture. The article provides information on special cases of environmentally assisted fracture. It concludes with a description of fractographic analyses for identifying the direction of propagation of a crack.

This article describes the microstructure, properties, and performance of carburized steels, and elucidates the microstructural gradients associated with carbon and hardness gradients. It provides information on case depth measurement, the factors affecting case depth, and the formation and causes of microcracks. The article discusses the effects of alloying elements on hardenability, the effects of excessive retained austenite and massive carbides on fatigue resistance, the effects of residual stresses and internal oxidation on fatigue performance of carburized steels. In addition, the causes of intergranular fracture at austenite grain boundaries and their prevention methods are explored. The article also describes the major mechanisms of bending fatigue crack initiation in carburized steels.

This article describes the formation of residual stresses and distortion and the techniques for measuring residual stresses. It provides a discussion on the magnitude and distribution analysis of residual stresses and distortion in weldments. The article considers the effects of residual stresses and distortion on the brittle fracture and fatigue fracture of welded structures. The thermal treatments of weldments are also discussed.

This article discusses the visual and microscopic characteristics of fractures of cast alloys. These fractures include ductile rupture, transgranular brittle fracture, intergranular fracture, fatigue, and environmentally induced fracture. The article also describes the factors that affect fracture appearance.

This article provides an overview of the origin of metallography. It presents information on how to select a section from a specimen and prepare it for macroscopic analysis. The article describes the macroscopic analysis of steel fracture surfaces with emphasis on ductile, brittle, and fatigue fracture with illustrations. It discusses microanalysis with a focus on the method of light microscopy and includes information of scanning electron microscope in fractography. The article also explains the characteristics of solidification, transformation, deformation structures, and discontinuities that are present in a microstructure. It concludes with information on image analysis.