Fracture Appearance and mechanisms of Deformation and fracture W.T. Becker, University of Tennessee, Emeritus; S. Lampman, ASM International Introduction FAILURE(briefly described as loss of function) occurs in multiple ways for multiple reasons and does not always result in fracture. Types of failure for which fracture does not occur are considered in other sections of this Volume. while this article introduces the section on fracture. However. it should be remembered that some nonfracture-failure scenarios may ultimately lead to fracture. Wear processes, for example, can ultimately lead to fracture by galling and/or fretting fatigue. Other examples include fatigue crack initiation at surface pits from corrosion, cyclic loading in a corrosive environment (stress-corrosion fatigue) and elastic buckling. Elastic buckling may cause parts to contact, causing seizure of a rotating system, but it may also lead to plastic buckling and ultimately to fracture The purpose of this article is to introduce the subject of fractography and how it is used in failure analysis Fractography is the science of revealing loading conditions and environment that caused the fracture by a three- dimensional interpretation of the appearance of a broken component. If the specimen is well preserved and if the analyst is knowledgeable, the fracture appearance reveals details of the loading events that culminated in fracture. An understanding of how cracks nucleate and grow microscopically to cause bulk(macroscale fracture is an essential part of fractography. The ability to accomplish this resides in interpretation of fracture surface features at both the micro- and macroscales. It is important that examination of the fracture surface and adjacent component sur face be done starting at low magnification with sequential examination of features of interest at increasing magnification. It is only in this way that significant features are identified as to location on the macroscale fracture surface. Stated differently, potential explanations for cause for failure must be consistent with both macroscopic and microscopic features The ultimate purpose of fractography and the other methods of failure analysis is the determination of the technical) root cause of failure, which may arise from various conditions such as inappropriate use,an unanticipated operating environment, improper prior fabrication, improper or inadequate design, inadequate maintenance or repair, or combinations thereof. Possible root causes also include design mistakes such as inadequate stress analysis, alloy selection, improper mechanical/thermal processing, improper assembly, and failure to accommodate an adverse operating environment. Fractography provides a unique tool to determine potential causal factors such as Whether a material was used above its design stress Whether the failed component had or did not have the properties assumed by the design engineer Whether a discontinuity was critical enough to cause failure This article introduces the topic of fractography and the interpretation of fracture surfaces. The basic types of fracture processes(ductile, brittle, fatigue, and creep) are described briefly, principally in terms of fracture appearances(as sometimes affected by the microstructure). More in-depth coverage on specific types of fracture(processes such as ductile and brittle fracture, fatigue, creep, and complex environmentally assisted cking from stress-corrosion cracking and hydrogen embrittlement) is in other articles in this Volume Articles on the fractographic appearances of polymeric and ceramic materials are also included. Fractography of electronic components, which is addressed in detail in Ref 1, is not covered in this Volume Tables I and 2 list some general types of macroscale and microscale fractographic features, which are described in more detail in this article. In summary form, the following are key features in distinguishing between montonic versus fatigue fracture and ductile versus brittle fractures(on either a macroscale or microscale) Thefileisdownloadedfromwww.bzfxw.comFracture Appearance and Mechanisms of Deformation and Fracture W.T. Becker, University of Tennessee, Emeritus; S. Lampman, ASM International Introduction FAILURE (briefly described as loss of function) occurs in multiple ways for multiple reasons and does not always result in fracture. Types of failure for which fracture does not occur are considered in other sections of this Volume, while this article introduces the section on fracture. However, it should be remembered that some nonfracture-failure scenarios may ultimately lead to fracture. Wear processes, for example, can ultimately lead to fracture by galling and/or fretting fatigue. Other examples include fatigue crack initiation at surface pits from corrosion, cyclic loading in a corrosive environment (stress-corrosion fatigue) and elastic buckling. Elastic buckling may cause parts to contact, causing seizure of a rotating system, but it may also lead to plastic buckling and ultimately to fracture. The purpose of this article is to introduce the subject of fractography and how it is used in failure analysis. Fractography is the science of revealing loading conditions and environment that caused the fracture by a three￾dimensional interpretation of the appearance of a broken component. If the specimen is well preserved and if the analyst is knowledgeable, the fracture appearance reveals details of the loading events that culminated in fracture. An understanding of how cracks nucleate and grow microscopically to cause bulk (macroscale) fracture is an essential part of fractography. The ability to accomplish this resides in interpretation of fracture surface features at both the micro- and macroscales. It is important that examination of the fracture surface and adjacent component surface be done starting at low magnification with sequential examination of features of interest at increasing magnification. It is only in this way that significant features are identified as to location on the macroscale fracture surface. Stated differently, potential explanations for cause for failure must be consistent with both macroscopic and microscopic features. The ultimate purpose of fractography and the other methods of failure analysis is the determination of the (technical) root cause of failure, which may arise from various conditions such as inappropriate use, an unanticipated operating environment, improper prior fabrication, improper or inadequate design, inadequate maintenance or repair, or combinations thereof. Possible root causes also include design mistakes such as inadequate stress analysis, alloy selection, improper mechanical/thermal processing, improper assembly, and failure to accommodate an adverse operating environment. Fractography provides a unique tool to determine potential causal factors such as: · Whether a material was used above its design stress · Whether the failed component had or did not have the properties assumed by the design engineer · Whether a discontinuity was critical enough to cause failure This article introduces the topic of fractography and the interpretation of fracture surfaces. The basic types of fracture processes (ductile, brittle, fatigue, and creep) are described briefly, principally in terms of fracture appearances (as sometimes affected by the microstructure). More in-depth coverage on specific types of fracture (processes such as ductile and brittle fracture, fatigue, creep, and complex environmentally assisted cracking from stress-corrosion cracking and hydrogen embrittlement) is in other articles in this Volume. Articles on the fractographic appearances of polymeric and ceramic materials are also included. Fractography of electronic components, which is addressed in detail in Ref 1, is not covered in this Volume. Tables 1 and 2 list some general types of macroscale and microscale fractographic features, which are described in more detail in this article. In summary form, the following are key features in distinguishing between montonic versus fatigue fracture and ductile versus brittle fractures (on either a macroscale or microscale): The file is downloaded from www.bzfxw.com