The Failure Analysis Process: An Overview Debbie Aliya, Aliya Analytical Introduction FAILURE ANALYSIS is a process that is performed in order to determine the causes or factors that have led to an undesired loss of functionality. This Volume primarily addresses failures of components, assemblies, or structures, and its approach is one consistent with the knowledge base of a person trained in materials engineering. The contribution of the materials engineer to the advancement of the scientific foundation of failure analysis has been great in the last few decades. This can be shown by the fact that many people define the causes of failure in a rather binary manner: was the part defective or was it abused? Obviously there are many types of defects, including those that come from a deficient design, poor material, or mistakes in manufacturing. Whether those"defects"exist in a given component that is being subjected to the failure analysis process can often only be determined by someone with a materials background. The reasons for this are related to the fact that many of the"defects"that people are looking for are visible only in a microscope of ome sort. While microscopes may be widely available, the knowledge required to interpret the images is less widely available. The other major type of defects, those related to design issues, may also require the assessment of a materials engineer. This is because many design engineers are not very familiar with the natural variations within a material grade. Evaluation of the adequacy of a material or process specification is often best performed by a materials engineer Thus, materials experts have been in an excellent position to gain experience in the failure analysis process. The advent of more and more powerful and widely available scanning electron microscopes has helped provide a more fact based foundation for opinions that may have been heavily speculative in the past. Some materials engineers have become very experienced in failure analysis. As materials engineers have worked on some very pectacular failures or on failures that have caused great pain and loss, they have been led to ask deeper and broader questions about the causes that lead to failures. In many cases it becomes clear that there is no single cause and no single train of events that lead to a failure. Rather, there are factors that combine at a particular time and place to allow a failure to occur. Sometimes the absence of any single one of the factors may have been enough to prevent the failure. Sometimes, though, it is impossible to determine, at least within the resources allotted for the analysis, whether any single factor was key. If failure analysts are to perform their jobs in a professional manner, they must look beyond the simplistic list of causes of failure that some people still promote. They must keep an open mind and always be willing to get help when beyond their own perience Many beginning practitioners of failure analysis may have their projects defined for them when they are handed a small component to evaluate and, thus, may be able to follow an established procedure for the evaluation This is especially true for someone working within an original equipment manufacturer. If there is someone who has a lot of experience and knowledge of the physical factors that tend to go wrong with the object and an established procedure exists, then a particular analysis may not require extensive pretesting work. However, for the practitioner who works in an independent laboratory or who is looking at a wide variety of components, following a predefined set of instructions for a failure analysis will generally prove to be an inadequate guideline for the investigation. Established"recipe type" procedures are generally inadequate for the more dvanced and broad-minded practitioner as well Although the failure that we are investigating is that of a physical component, assembly, or structure, the failures that lead to such physical failure happen on many levels. In other words, a failure should not be viewed as a single event. It is more useful to view both the failure and the failure analysis as multilevel processes that can be explored in many useful ways. The physical failure-a fracture, an explosion, or component damaged by heat or corrosion-is the most obvious. However, there are always other levels of failures that allow the physical event to happen. For example, even a simple failure whose direct physical cause was an improper hardness value has human factors that allowed the improperly hardened component to be manufactured and used. These human factors are generally very difficult to investigate within a manufacturing organization
The Failure Analysis Process: An Overview Debbie Aliya, Aliya Analytical Introduction FAILURE ANALYSIS is a process that is performed in order to determine the causes or factors that have led to an undesired loss of functionality. This Volume primarily addresses failures of components, assemblies, or structures, and its approach is one consistent with the knowledge base of a person trained in materials engineering. The contribution of the materials engineer to the advancement of the scientific foundation of failure analysis has been great in the last few decades. This can be shown by the fact that many people define the causes of failure in a rather binary manner: was the part defective or was it abused? Obviously, there are many types of defects, including those that come from a deficient design, poor material, or mistakes in manufacturing. Whether those “defects” exist in a given component that is being subjected to the failure analysis process can often only be determined by someone with a materials background. The reasons for this are related to the fact that many of the “defects” that people are looking for are visible only in a microscope of some sort. While microscopes may be widely available, the knowledge required to interpret the images is less widely available. The other major type of defects, those related to design issues, may also require the assessment of a materials engineer. This is because many design engineers are not very familiar with the natural variations within a material grade. Evaluation of the adequacy of a material or process specification is often best performed by a materials engineer. Thus, materials experts have been in an excellent position to gain experience in the failure analysis process. The advent of more and more powerful and widely available scanning electron microscopes has helped provide a more fact based foundation for opinions that may have been heavily speculative in the past. Some materials engineers have become very experienced in failure analysis. As materials engineers have worked on some very spectacular failures or on failures that have caused great pain and loss, they have been led to ask deeper and broader questions about the causes that lead to failures. In many cases it becomes clear that there is no single cause and no single train of events that lead to a failure. Rather, there are factors that combine at a particular time and place to allow a failure to occur. Sometimes the absence of any single one of the factors may have been enough to prevent the failure. Sometimes, though, it is impossible to determine, at least within the resources allotted for the analysis, whether any single factor was key. If failure analysts are to perform their jobs in a professional manner, they must look beyond the simplistic list of causes of failure that some people still promote. They must keep an open mind and always be willing to get help when beyond their own experience. Many beginning practitioners of failure analysis may have their projects defined for them when they are handed a small component to evaluate and, thus, may be able to follow an established procedure for the evaluation. This is especially true for someone working within an original equipment manufacturer. If there is someone who has a lot of experience and knowledge of the physical factors that tend to go wrong with the object and an established procedure exists, then a particular analysis may not require extensive pretesting work. However, for the practitioner who works in an independent laboratory or who is looking at a wide variety of components, following a predefined set of instructions for a failure analysis will generally prove to be an inadequate guideline for the investigation. Established “recipe type” procedures are generally inadequate for the more advanced and broad-minded practitioner as well. Although the failure that we are investigating is that of a physical component, assembly, or structure, the failures that lead to such physical failure happen on many levels. In other words, a failure should not be viewed as a single event. It is more useful to view both the failure and the failure analysis as multilevel processes that can be explored in many useful ways. The physical failure—a fracture, an explosion, or component damaged by heat or corrosion—is the most obvious. However, there are always other levels of failures that allow the physical event to happen. For example, even a simple failure whose direct physical cause was an improper hardness value has human factors that allowed the improperly hardened component to be manufactured and used. These human factors are generally very difficult to investigate within a manufacturing organization
because cultures that allow a particular type of failure to occur will generally not have systems in place that allow simple remedies to be enacted for the deeper level causes. For example, if someone in an organization wants to investigate causes beyond the simple fact of improper hardness, it may be discovered that the incoming (receiving) inspection clerk was not properly trained to take note of reported hardness values Changing a corporate culture to include better training and education is generally very difficult; many corporations are structured so that the people who are responsible for training do not have an open line of communication to those doing the investigation. This only increases the difficulty of implementing change to prevent failures Professionally performed failure analysis is a multilevel process that includes the physical investigation itself and much more. This Section of this Volume is intended to showcase some of the latest thinking on how the different"layers" of the failure analysis process should work together, so that when the analysis or larger investigation is complete, the people involved will have useful knowledge about how to avoid future occurrences of similar problems Failure analysis of the physical object is often defined as a part of a larger investigation whose intent is to prevent recurrences. If we are to take the broadest view of what is required to prevent failures, there is one answer that stands out: education. Education needs to happen at multiple levels and on multiple subjects within an organization, within larger cultural groups, and within humanity in general, if we are to reduce the frequency of failures of physical objects Education, of which job training is a single component, is what allows people at all levels of an organization to make better decisions in time frames stretching from momentary to career long. There are many books now available that have exercises that help the reader to restructure knowledge into a more useful and accessible form(see, for example, titles in the Selected Reference list for this article). There are other books available that help the reader learn to recognize incorrect lines of reasoning; one such book is Ref 1 Specific levels of failure causes have been defined by Failsafe Network as follows I Phy 2. Human 3. Latent 4 Root Clearly, many people involved with failure analysis today call something a root cause when what they are referring to is a simple physical cause. If failure analysis tasks are performed adequately and with luck, at the end the analyst should be able to take the causes found, show that the failure would have happened the way it did, and also show that if something different had happened at some step along the way, the failure would not have occurred or would have occurred differently. The fact that is often revealed at the end of an investigation is that this is not possible. Even a long and involved investigation leaves unknowns. The honest analyst is left to make a statement of the factors involved in allowing conditions that promoted the likelihood of failure. This still a useful task, perhaps more useful than something that pins"blame"on a particular individual or group Understanding the factors that promoted a failure can lead to an understanding of what is required to have a real improvement in durability of products, equipment, or structures. Understanding goes beyond knowledge of facts. Understanding requires integration of facts into the knowledge base of an individual so that the facts may be transformed into knowledge and then into product and/or process improvement By now it should be clear that failure analysis is a task that requires input from people with many areas of expertise. A simple physical failure of a small object may be analyzed by a single individual with basic training in visual evaluation of engineered objects. However, going to the level of using the failure analysis to improve products and processes requires expertise in the various aspects of human relations and education, at the least Failure analysis of a complex or catastrophic failure requires much more people who perform failure analysis as part of their job function need to have an awareness of how their legal obligations are defined People who perform destructive testing on a component that has failed may sometimes be held accountable for the destruction of evidence on a personal level. Company employees need to learn to protect themselves. Investigators who were just doing the job"have been successfully sued by parties that the judicial system determined had a legitimate interest in the outcome of the failure analysis project The days where anyone unquestioningly agrees to destructively test a component that they know or can see has failed " should be over. This places the destructive testing technician or engineer in a difficult position, as it Thefileisdownloadedfromwww.bzfxw.com
because cultures that allow a particular type of failure to occur will generally not have systems in place that allow simple remedies to be enacted for the deeper level causes. For example, if someone in an organization wants to investigate causes beyond the simple fact of improper hardness, it may be discovered that the incoming (receiving) inspection clerk was not properly trained to take note of reported hardness values. Changing a corporate culture to include better training and education is generally very difficult; many corporations are structured so that the people who are responsible for training do not have an open line of communication to those doing the investigation. This only increases the difficulty of implementing change to prevent failures. Professionally performed failure analysis is a multilevel process that includes the physical investigation itself and much more. This Section of this Volume is intended to showcase some of the latest thinking on how the different “layers” of the failure analysis process should work together, so that when the analysis or larger investigation is complete, the people involved will have useful knowledge about how to avoid future occurrences of similar problems. Failure analysis of the physical object is often defined as a part of a larger investigation whose intent is to prevent recurrences. If we are to take the broadest view of what is required to prevent failures, there is one answer that stands out: education. Education needs to happen at multiple levels and on multiple subjects within an organization, within larger cultural groups, and within humanity in general, if we are to reduce the frequency of failures of physical objects. Education, of which job training is a single component, is what allows people at all levels of an organization to make better decisions in time frames stretching from momentary to career long. There are many books now available that have exercises that help the reader to restructure knowledge into a more useful and accessible form (see, for example, titles in the Selected Reference list for this article). There are other books available that help the reader learn to recognize incorrect lines of reasoning; one such book is Ref 1. Specific levels of failure causes have been defined by Failsafe Network as follows: 1. Physical 2. Human 3. Latent 4. Root Clearly, many people involved with failure analysis today call something a root cause when what they are referring to is a simple physical cause. If failure analysis tasks are performed adequately and with luck, at the end the analyst should be able to take the causes found, show that the failure would have happened the way it did, and also show that if something different had happened at some step along the way, the failure would not have occurred or would have occurred differently. The fact that is often revealed at the end of an investigation is that this is not possible. Even a long and involved investigation leaves unknowns. The honest analyst is left to make a statement of the factors involved in allowing conditions that promoted the likelihood of failure. This is still a useful task, perhaps more useful than something that pins “blame” on a particular individual or group. Understanding the factors that promoted a failure can lead to an understanding of what is required to have a real improvement in durability of products, equipment, or structures. Understanding goes beyond knowledge of facts. Understanding requires integration of facts into the knowledge base of an individual so that the facts may be transformed into knowledge and then into product and/or process improvement. By now it should be clear that failure analysis is a task that requires input from people with many areas of expertise. A simple physical failure of a small object may be analyzed by a single individual with basic training in visual evaluation of engineered objects. However, going to the level of using the failure analysis to improve products and processes requires expertise in the various aspects of human relations and education, at the least. Failure analysis of a complex or catastrophic failure requires much more. People who perform failure analysis as part of their job function need to have an awareness of how their legal obligations are defined. People who perform destructive testing on a component that has failed may sometimes be held accountable for the destruction of evidence on a personal level. Company employees need to learn to protect themselves. Investigators who were “just doing the job” have been successfully sued by parties that the judicial system determined had a legitimate interest in the outcome of the failure analysis project. The days where anyone unquestioningly agrees to destructively test a component that they know or can see “has failed” should be over. This places the destructive testing technician or engineer in a difficult position, as it The file is downloaded from www.bzfxw.com
is sometimes difficult to see that something has failed. Corporate cultures that are highly structured and hierarchical can be particularly difficult environments for the failure analysis practitioner, as it may be difficult to even find out if the component has failed. Even if that information is given, relevant background details are often very difficult to obtain, even if the analyst tries. Pressure to finish the analysis in a shorter time frame than is desirable for a quality investigation is commor Those who perform failure analysis work must realize that many people are still unaware of what failure analysts have to offer in terms of allowing clients or fellow employees to replace speculation with facts. The people who request failure analysis work may not be aware that rushing ahead into the destructive portion of an investigation may well destroy much information. The remainder of this article and the following articles in this Section of the Volume are intended to demonstrate proper approaches to failure analysis work. The goal of the proper approach is to allow the most useful and relevant information to be obtained. Readers of the various articles will see many points of view demonstrated. All the valid approaches require planning, defining of objectives, and organization prior to any destructive testing. Simultaneous preservation of evidence is also required. It should now be clear that proper failure analysis cannot be done with input from only a single individual. Even someone only participating in the"straightforward" portions of the investigation of physical failure needs to know how his or her contribution fits into a bigger picture. This is the intent of this Section while the next Section of this Volume is intended to provide an introduction to the vast array of technical tool and information available to the failure analyst The competent failure analyst needs to know more than the failure analysis process and the tools used to support it. The competent failure analyst needs to understand the function of the object being analyzed and to be familiar with the characteristics of the materials and processes used to fabricate it. The failure analyst needs to understand how the product was used and the culture in which it was used. Communication skills are a When you ask a question, do you know for certain what the answer"yes"means? In some cultures, the yes"means"I heard the question"and does not imply that the answer is actually affirmative. The failure analyst must al ways be well versed in multiple disciplines The failure analysis process is something that can be approached in many different ways. Most people who do failure analysis of structural components or larger scale structures and assemblies have probably run into someone who wanted to do a failure analysis without considering a contribution from an experienced materials ngineer. While the analyst may reach a conclusion in this manner, its value should be questioned. A reliable understanding of what happened and why it happened requires the input of a competent materials engineering practitioner. Every"failed"object is made of some material, and some common materials can lose more than 90% of their usual strength if they are not processed properly. Clearly, prior to reaching a conclusion as to the most significant causes of the failure, someone should determine if the correct material d and if it was processed properly. This often requires both an investigation of documentation and a series of physical tests This Volume focuses on the definition of and requirements for a professionally performed failure analysis of a physical object or structure. However, many of the concepts for investigation that are described in this Section have much greater utility than for investigations of physical objects failure. The concepts in learning how to define objectives, negotiate scope of investigation, look at the physical evidence, structure both the investigation and the data that it reveals, and perform general problem solving have broad applicability in other areas of business, manufacturing, and life in general. The examples of how competent materials engineers can use these concepts in a failure analysis or failure investigation are emphasized here Reference cited in this section D. Levy, Tools of Critical Thinking: Metathoughts for Psychology Allyn and Bacon, 1997 The Failure Analysis Process: An Overview Debbie Aliya, Aliya Analytical Principles and Approaches in Failure Analysis Work
is sometimes difficult to see that something has failed. Corporate cultures that are highly structured and hierarchical can be particularly difficult environments for the failure analysis practitioner, as it may be difficult to even find out if the component has failed. Even if that information is given, relevant background details are often very difficult to obtain, even if the analyst tries. Pressure to finish the analysis in a shorter time frame than is desirable for a quality investigation is common. Those who perform failure analysis work must realize that many people are still unaware of what failure analysts have to offer in terms of allowing clients or fellow employees to replace speculation with facts. The people who request failure analysis work may not be aware that rushing ahead into the destructive portion of an investigation may well destroy much information. The remainder of this article and the following articles in this Section of the Volume are intended to demonstrate proper approaches to failure analysis work. The goal of the proper approach is to allow the most useful and relevant information to be obtained. Readers of the various articles will see many points of view demonstrated. All the valid approaches require planning, defining of objectives, and organization prior to any destructive testing. Simultaneous preservation of evidence is also required. It should now be clear that proper failure analysis cannot be done with input from only a single individual. Even someone only participating in the “straightforward” portions of the investigation of physical failure needs to know how his or her contribution fits into a bigger picture. This is the intent of this Section, while the next Section of this Volume is intended to provide an introduction to the vast array of technical tools and information available to the failure analyst. The competent failure analyst needs to know more than the failure analysis process and the tools used to support it. The competent failure analyst needs to understand the function of the object being analyzed and to be familiar with the characteristics of the materials and processes used to fabricate it. The failure analyst needs to understand how the product was used and the culture in which it was used. Communication skills are a must. When you ask a question, do you know for certain what the answer “yes” means? In some cultures, the word “yes” means “I heard the question” and does not imply that the answer is actually affirmative. The failure analyst must always be well versed in multiple disciplines. The failure analysis process is something that can be approached in many different ways. Most people who do failure analysis of structural components or larger scale structures and assemblies have probably run into someone who wanted to do a failure analysis without considering a contribution from an experienced materials engineer. While the analyst may reach a conclusion in this manner, its value should be questioned. A reliable understanding of what happened and why it happened requires the input of a competent materials engineering practitioner. Every “failed” object is made of some material, and some common materials can lose more than 90% of their usual strength if they are not processed properly. Clearly, prior to reaching a conclusion as to the most significant causes of the failure, someone should determine if the correct material was used and if it was processed properly. This often requires both an investigation of documentation and a series of physical tests. This Volume focuses on the definition of and requirements for a professionally performed failure analysis of a physical object or structure. However, many of the concepts for investigation that are described in this Section have much greater utility than for investigations of physical objects failure. The concepts in learning how to define objectives, negotiate scope of investigation, look at the physical evidence, structure both the investigation and the data that it reveals, and perform general problem solving have broad applicability in other areas of business, manufacturing, and life in general. The examples of how competent materials engineers can use these concepts in a failure analysis or failure investigation are emphasized here. Reference cited in this section 1. D. Levy, Tools of Critical Thinking: Metathoughts for Psychology Allyn and Bacon, 1997 The Failure Analysis Process: An Overview Debbie Aliya, Aliya Analytical Principles and Approaches in Failure Analysis Work
a key principle of failure analysis is, first and foremost, to preserve evidence-the analyst must make sure that any necessary information from the subject part or assembly in the as-received condition is captured before anything is done to alter its condition. This principle can be summarized by the following guidelines First, preserve evidence Perform tests in order of less destructive to more destructive in nature Know the limitations of one's personal knowledge Know how to ask for help Do not attempt a failure analysis if the basics of specimen preservation, collection, and selection have not been studied Know when to say no to performing a destructive test Destructive testing obviously includes anything that requires cutting the part. However, even moving fragments of an explosion may cause loss of information that might have been determined from the position of the fragments. Cleaning components can also be problematic; not cleaning can lead to damage by corrosion in the case of many common materials, while cleaning may remove the substances that caused or contributed to the failure or that shed light on the nature of any physical degradation of the components. Sometimes, cleaning of dangerous or toxic substances from the debris of a failure is necessary for the safety of the investigator. The practitioner should also keep in mind that many tests described as"nondestructive are only relatively nondestructive. There are numerous investigations during which the analysts representing different parties have spent long periods of time trying to figure out whether the dye penetrant residue that they detected is a result of the test done after the failure or before the last service period. Again, the phrase nondestructive should be iewed as a relative term It should also be recognized that the problem of failure analysis can be approached in different ways, depending the required depth and scope of analysis. another key principle in failure analysis work is knowing how to lefine the scope of the investigation at the proper time, so that the investigation has the highest chance of allowing the answers to the questions posed to become known. The circumstances of failure problems can be diverse, and even the"simple"principles of failure analysis may be subject to interpretation and examination Even the principle of preserving evidence may involve judgments, as noted in the preceding paragraph. Even the experienced analyst can make mistakes. For example, consider a situation in which an analyst received a bearing from a regular client. The bearing had worn out prematurely in a durability test. The analyst was requested to photograph the wear marks and check the hardness and quality of heat treating of the races and balls. The bearing was covered with a black greasy substance. When analyzing wear failures, it is often the lubricant properties and the wear particles that offer the most information about the wear process. The analyst informed the client of this, and the client made the decision to sacrifice the"dirty grease in the interest of completing the investigation in a shorter time. The client just wanted to know if the part met the specification and whether there was evidence of gross misalignment or dimensional problems. After the investigation was finished, and the grease had been dissolved in solvent and discarded, another individual at that company requested detailed information on the actual wear mechanism. At that point, it was too late to analyze the lubricant. If either the client or the analyst had taken more time, a sample of this material could have been set aside and preserved Another key principle of failure analysis is that for all but the simplest routine investigations, there may be multiple, legitimate approaches. Selecting the most appropriate of these approaches to problem solving in failure investigations. some of which are described later in this article and elsewhere in this volume is an important skill. The classical approach is to follow a list of steps, which generally include planning the investigation, performing background research, and writing the report, as well as the actual physical tests and evaluations to which the component in question is subjected. Even though a recipe of procedures has many merits, especially for the beginners in the practice of failure analysis, performing a series of tests does not always produce results that allow the analyst to reach a clear conclusion with ease. Also, if failure analysis is presented exclusively as a series of steps or recipes, the repetitive steps may be conducive to carelessness. If the process of failure analysis is viewed as just a routine series of procedures, the practitioner may not notice the presence of new or different features. This is not to say that structured approaches are bad. However, the importance of paying attention to detail and learning to ask oneself whether each detail is consistent with the other previously noted details can hardly be overemphasized to the beginning failure analyst. Failure analysis is Thefileisdownloadedfromwww.bzfxw.com
A key principle of failure analysis is, first and foremost, to preserve evidence—the analyst must make sure that any necessary information from the subject part or assembly in the as-received condition is captured before anything is done to alter its condition. This principle can be summarized by the following guidelines: · First, preserve evidence. · Perform tests in order of less destructive to more destructive in nature. · Know the limitations of one's personal knowledge. · Know how to ask for help. · Do not attempt a failure analysis if the basics of specimen preservation, collection, and selection have not been studied. · Know when to say no to performing a destructive test. Destructive testing obviously includes anything that requires cutting the part. However, even moving fragments of an explosion may cause loss of information that might have been determined from the position of the fragments. Cleaning components can also be problematic; not cleaning can lead to damage by corrosion in the case of many common materials, while cleaning may remove the substances that caused or contributed to the failure or that shed light on the nature of any physical degradation of the components. Sometimes, cleaning of dangerous or toxic substances from the debris of a failure is necessary for the safety of the investigator. The practitioner should also keep in mind that many tests described as “nondestructive” are only relatively nondestructive. There are numerous investigations during which the analysts representing different parties have spent long periods of time trying to figure out whether the dye penetrant residue that they detected is a result of the test done after the failure or before the last service period. Again, the phrase nondestructive should be viewed as a relative term. It should also be recognized that the problem of failure analysis can be approached in different ways, depending on the required depth and scope of analysis. Another key principle in failure analysis work is knowing how to define the scope of the investigation at the proper time, so that the investigation has the highest chance of allowing the answers to the questions posed to become known. The circumstances of failure problems can be diverse, and even the “simple” principles of failure analysis may be subject to interpretation and examination. Even the principle of preserving evidence may involve judgments, as noted in the preceding paragraph. Even the experienced analyst can make mistakes. For example, consider a situation in which an analyst received a bearing from a regular client. The bearing had worn out prematurely in a durability test. The analyst was requested to photograph the wear marks and check the hardness and quality of heat treating of the races and balls. The bearing was covered with a black greasy substance. When analyzing wear failures, it is often the lubricant properties and the wear particles that offer the most information about the wear process. The analyst informed the client of this, and the client made the decision to sacrifice the “dirty grease” in the interest of completing the investigation in a shorter time. The client just wanted to know if the part met the specification, and whether there was evidence of gross misalignment or dimensional problems. After the investigation was finished, and the grease had been dissolved in solvent and discarded, another individual at that company requested detailed information on the actual wear mechanism. At that point, it was too late to analyze the lubricant. If either the client or the analyst had taken more time, a sample of this material could have been set aside and preserved. Another key principle of failure analysis is that for all but the simplest routine investigations, there may be multiple, legitimate approaches. Selecting the most appropriate of these approaches to problem solving in failure investigations, some of which are described later in this article and elsewhere in this Volume, is an important skill. The classical approach is to follow a list of steps, which generally include planning the investigation, performing background research, and writing the report, as well as the actual physical tests and evaluations to which the component in question is subjected. Even though a recipe of procedures has many merits, especially for the beginners in the practice of failure analysis, performing a series of tests does not always produce results that allow the analyst to reach a clear conclusion with ease. Also, if failure analysis is presented exclusively as a series of steps or recipes, the repetitive steps may be conducive to carelessness. If the process of failure analysis is viewed as just a routine series of procedures, the practitioner may not notice the presence of new or different features. This is not to say that structured approaches are bad. However, the importance of paying attention to detail and learning to ask oneself whether each detail is consistent with the other previously noted details can hardly be overemphasized to the beginning failure analyst. Failure analysis is The file is downloaded from www.bzfxw.com
an iterative and creative process, much like the design process, but with reversed roles of synthesis and analysis. See the article"Materials Selection for Failure Prevention "in this volume Knowing which approach to use is at least as important as knowing how to use it. This article describes some of he factors and conditions that might be considered when approaching a failure analysis problem. In any case, whichever approach is taken, it is always important to cultivate an open mind and to the temptation to reach a conclusion about the cause(s)of the failure before performing the analysis and evaluation. The science of critical thinking has a principle called the confirmation bias, which refers to the tendency to look only for what one expects to find: that is, "Ye shall find only what ye shall seek"(Ref 1). Humans have a general tendency to see what they expect to see or to perceive things according to preconceived expectations. As Mark Twain wrote, "To the man who wants to use a hammer badly, a lot of things look like nails that need hammering. If observation is limited to an expected outcome, helpful data may be overlooked. For example, one of the biggest mistakes that people make in failure analysis work is defining the investigation in binary terms of"was there a manufacturing defect or was the object abused? The professional analyst should not be confined to this small set of possible causes for the failure, because it may be difficult to become aware of the situation of not finding what he or she did not set out to find It is also important to appreciate the value of intuition and instinct. While the importance of observation and analysis can hardly be overemphasized, sometimes intuition can provide insights and a better appreciation of the big picture. For years, the great 19th-century Indian mathematician Ramanujan would, immediately upon awakening, write down theorems that had come to him in his dreams. many of these theorems remain unproven et useful to mathematicians and physicists today(Ref 2). Another example is the discovery of the structure of the benzene ring by F.A. Kekule. Many high-school science books report that during the period of time when he was trying to figure out how the carbon and hydrogen atoms were arranged within the molecule, he had a vision in a dream of intertwined serpents, each biting its own tail. Obviously, he and others went on to use more cientific methods to demonstrate the correctness of his theory. Likewise while any failure investigation must intuitive function in engineering and scientific work in genery orically, too little credit has been given to the stand or fall on the merits of the analytical work done, hi References cited in this section 1. D. Levy, Tools of Critical Thinking: Metathoughts for Psychology Allyn and Bacon, 1997 2. M. Kaku, Hyperspace, Oxford University Press, 1994 The Failure Analysis Process: An Overview Debbie Aliya, Aliya Analytica The Objectives of Failure Analysis The objective or purpose of a failure analysis project is often described to be preventing a recurrence of the failure. However, there are many different types of failure analysis projects. Where an injury lawsuit is involved, for example, it may be important to assign responsibility for an undesired event. There are other cases when there may never be a chance for a recurrence. For example, if the item that fails is unique, there may never be a repeat incident Another case in which the objective of the investigation may not be the prevention of recurrences is one involving a very minor failure of a low-value component. If there is no other damage, it may be difficult to justify a prevention-oriented project. It may be more economical to live with a certain level of failure than to devote resources to prevention. The work is still worthwhile, because if certain economic situations change, there is background information available to support a broader investigation, in a more efficient manner, at a later time. Also, the understanding gained may lead to an improved product that may be appropriate for particular market niche, for example, long- life light bulbs
an iterative and creative process, much like the design process, but with reversed roles of synthesis and analysis. See the article “Materials Selection for Failure Prevention” in this Volume Knowing which approach to use is at least as important as knowing how to use it. This article describes some of the factors and conditions that might be considered when approaching a failure analysis problem. In any case, whichever approach is taken, it is always important to cultivate an open mind and to minimize the temptation to reach a conclusion about the cause(s) of the failure before performing the analysis and evaluation. The science of critical thinking has a principle called the confirmation bias, which refers to the tendency to look only for what one expects to find: that is, “Ye shall find only what ye shall seek” (Ref 1). Humans have a general tendency to see what they expect to see or to perceive things according to preconceived expectations. As Mark Twain wrote, “To the man who wants to use a hammer badly, a lot of things look like nails that need hammering.” If observation is limited to an expected outcome, helpful data may be overlooked. For example, one of the biggest mistakes that people make in failure analysis work is defining the investigation in binary terms of “was there a manufacturing defect or was the object abused?” The professional analyst should not be confined to this small set of possible causes for the failure, because it may be difficult to become aware of the situation of not finding what he or she did not set out to find. It is also important to appreciate the value of intuition and instinct. While the importance of observation and analysis can hardly be overemphasized, sometimes intuition can provide insights and a better appreciation of the “big picture.” For years, the great 19th-century Indian mathematician Ramanujan would, immediately upon awakening, write down theorems that had come to him in his dreams. Many of these theorems remain unproven yet useful to mathematicians and physicists today (Ref 2). Another example is the discovery of the structure of the benzene ring by F.A. Kekulé. Many high-school science books report that during the period of time when he was trying to figure out how the carbon and hydrogen atoms were arranged within the molecule, he had a vision in a dream of intertwined serpents, each biting its own tail. Obviously, he and others went on to use more scientific methods to demonstrate the correctness of his theory. Likewise, while any failure investigation must stand or fall on the merits of the analytical work done, historically, too little credit has been given to the intuitive function in engineering and scientific work in general. References cited in this section 1. D. Levy, Tools of Critical Thinking: Metathoughts for Psychology Allyn and Bacon, 1997 2. M. Kaku, Hyperspace, Oxford University Press, 1994 The Failure Analysis Process: An Overview Debbie Aliya, Aliya Analytical The Objectives of Failure Analysis The objective or purpose of a failure analysis project is often described to be preventing a recurrence of the failure. However, there are many different types of failure analysis projects. Where an injury lawsuit is involved, for example, it may be important to assign responsibility for an undesired event. There are other cases when there may never be a chance for a recurrence. For example, if the item that fails is unique, there may never be a repeat incident. Another case in which the objective of the investigation may not be the prevention of recurrences is one involving a very minor failure of a low-value component. If there is no other damage, it may be difficult to justify a prevention-oriented project. It may be more economical to live with a certain level of failure than to devote resources to prevention. The work is still worthwhile, because if certain economic situations change, there is background information available to support a broader investigation, in a more efficient manner, at a later time. Also, the understanding gained may lead to an improved product that may be appropriate for a particular market niche, for example, long-life light bulbs
It may be that there is no true product failure. In fact, one important question that may well be asked is: Did a failure really occur? It is possible to have an undesirable event that involves fracture, wear, deformation, or corrosion but that is not really a component failure. For example, discovering a fatigue crack in a 40-year-old structural component, in many cases, may be less of a surprise than finding one that is free from such cracks For these and similar reasons, it is good practice to avoid the use of terms such as failed part, at least until th investigation has revealed strong evidence that a failure has indeed occurred. The terms subject part, subject component, or physical evidence are preferred. It is also good to have an appreciation for what a failure is not The objectives of failure analysis can vary, as suggested by some of the different types of objectives listed in Table 1. Early in every investigation, those with an interest should determine exactly what their objective is or, have no legal obligation to do so, they still, parties have a genuine desire to prevent recurrences,even and timing considerations usually determine the scope of the investigation. Aside from the cost of the investigation itself, a sure answer that comes after repeat failures may be less valuable than a reasonably sound answer before repeat failures Table 1 Objectives in failure analysis Types of objective Possible precipitating situation Product life cycle Product development Demands of the market Prototyping I Product improvement i Warranty costs L Ongoing Assignment of eparations for financial/physical damage or bodily injury or After subject sponsibility death Prevention of recurrence Any After subject event However, despite these various ways of defining objectives and conclusions in failure analysis, it is still fundamentally worthwhile for the knowledge gained. Obviously, success is more satisfying than failure, but experienced practitioners of failure analysis have learned the value of taking the time to extract lessons about both the technical and people-related causes of the failure. When the challenge is to keep learning, every investigation adds to our competence. Often, problems cannot be solved from the same level of understanding in which they are created Thus, failure analysis may often require a keen and inquisitive outlook, which very good and satisfying way to keep learning on a technical, professional, and personal level for an entire career The Failure Analysis Process: An Overview Debbie Aliya, Aliya Analytical Scope and planning The scope of a failure analysis depends on the depth and complexity of the project. Many failure analysts have experienced being told to find the root cause of a particular failure in half an hour! Usually, this is impossible or leads to superficial results. The scope of the investigation must also be targeted toward finding the real root (physical or human) cause of the failure. Root-cause failure analysis has generated much attention in recent years,and it is a good development when the term root cause is given to mean the particular physical or human effect that precipitated or assisted in a failure. Sometimes the term root-cause analysis is misconstrued to mean figuring out whether a component meets a specification. If it does not meet specification, then the lack of conformity to the specification becomes a convenient"root cause. This use of the term is not only superficial but also invalid. Any approach that does not attempt to link the particular physical effect with the particular lack of conformity and its direct expected consequences is not a valid failure analysis approach During the planning stages on the possible scope of an investigation, it is sometimes useful to focus attention on the potential complexity of the problem and on when the physical cause may have occurred. Various categories of complexity are listed in Table 2. These categories of complexity are not exclusive. All failure analysis work must be founded on the physical causes. Sometimes one is asked to determine a cause based on the verbal Thefileisdownloadedfromwww.bzfxw.com
It may be that there is no true product failure. In fact, one important question that may well be asked is: “Did a failure really occur?” It is possible to have an undesirable event that involves fracture, wear, deformation, or corrosion but that is not really a component failure. For example, discovering a fatigue crack in a 40-year-old structural component, in many cases, may be less of a surprise than finding one that is free from such cracks. For these and similar reasons, it is good practice to avoid the use of terms such as failed part, at least until the investigation has revealed strong evidence that a failure has indeed occurred. The terms subject part, subject component, or physical evidence are preferred. It is also good to have an appreciation for what a failure is not. The objectives of failure analysis can vary, as suggested by some of the different types of objectives listed in Table 1. Early in every investigation, those with an interest should determine exactly what their objective is or, more likely, what their objectives are. If the parties have a genuine desire to prevent recurrences, even if they have no legal obligation to do so, they still need to decide how far they want to go toward this goal. Economic and timing considerations usually determine the scope of the investigation. Aside from the cost of the investigation itself, a sure answer that comes after repeat failures may be less valuable than a reasonably sound answer before repeat failures. Table 1 Objectives in failure analysis Types of objective Possible precipitating situation Product life cycle Product development Demands of the market Prototyping Product improvement Warranty costs Ongoing Assignment of responsibility Reparations for financial/physical damage or bodily injury or death After subject event Prevention of recurrence Any After subject event However, despite these various ways of defining objectives and conclusions in failure analysis, it is still fundamentally worthwhile for the knowledge gained. Obviously, success is more satisfying than failure, but experienced practitioners of failure analysis have learned the value of taking the time to extract lessons about both the technical and people-related causes of the failure. When the challenge is to keep learning, every investigation adds to our competence. Often, problems cannot be solved from the same level of understanding in which they are created. Thus, failure analysis may often require a keen and inquisitive outlook, which is a very good and satisfying way to keep learning on a technical, professional, and personal level for an entire career. The Failure Analysis Process: An Overview Debbie Aliya, Aliya Analytical Scope and Planning The scope of a failure analysis depends on the depth and complexity of the project. Many failure analysts have experienced being told to find the root cause of a particular failure in half an hour! Usually, this is impossible or leads to superficial results. The scope of the investigation must also be targeted toward finding the real root (physical or human) cause of the failure. Root-cause failure analysis has generated much attention in recent years, and it is a good development when the term root cause is given to mean the particular physical or human effect that precipitated or assisted in a failure. Sometimes the term root-cause analysis is misconstrued to mean figuring out whether a component meets a specification. If it does not meet specification, then the lack of conformity to the specification becomes a convenient “root cause.” This use of the term is not only superficial but also invalid. Any approach that does not attempt to link the particular physical effect with the particular lack of conformity and its direct expected consequences is not a valid failure analysis approach. During the planning stages on the possible scope of an investigation, it is sometimes useful to focus attention on the potential complexity of the problem and on when the physical cause may have occurred. Various categories of complexity are listed in Table 2. These categories of complexity are not exclusive. All failure analysis work must be founded on the physical causes. Sometimes one is asked to determine a cause based on the verbal The file is downloaded from www.bzfxw.com
description of a component. In some limited cases, this may be all that is possible, if the part is gone. However, the value of the failure analysis is limited in those cases. Also note that a failure problem is defined in a broader context going from top to bottom of Table 2. This is particularly important for failure analysis within a manufacturing organization. Today, many companies manufacture components or assemblies for other companies. The individuals at the contract manufacturing companies may not have any way of learning the importance of specified or unspecified requirements of the components that they are manufacturing until they have the opportunity to learn as a result of a failure investigation. Progressive companies have been taking advantage of their human resources for years by providing more training and education, because they know that it generally has a positive effect on the profitability of the company Table 2 Complexity of investigation Depth and Example Allowed effects of findings Part is found to be of the wrong Part gets rehardened. Maybe inspection cause(s)or hardness frequency is increased Individual Heat treat department employee does Heat treatment department employees are sent people causes not understand importance of to a basic metallurgy and testing class. hardness and does not check part Latent causes or Nobody tells furnace operator about Design and supervisory personnel are given factors the importance of hardness testing. It custom training by a competent materials does not matter that she fabricated engineer on the subject of how to specify test results, until the pyrometer fails, hardness test protocol. Maybe an investigation causing incorrect temperature into the heat treat furnace uniformity is exposure during austenitization. undertaken Culture-based Hardness runs on low end of Marketing people are given additional training root cause(s) specified range for years but never so that they do not give unreasonable causes a problem until someone, expectations of product performance.(It is due to economic downturn, decides recognized that an optimistic outlook is part of to use item for much longer than sales and marketing. The question is, where does the original expected service life one draw the line as to what is reasonable and unreasonable. Marketing people are given adequate resources to follow up with customers It is also important to keep in mind when root cause(s) could have been introduced. Table 3 lists some examples. It is often difficult to assign a failure to a single phase of problem creation. Many times, there are complex interactions. Only an integrated design approach will create robust processes and thus robust parts The designer must communicate with personnel from the sales department, as well as customers, maintenance personnel, manufacturing personnel, and material suppliers. Input from failure analysts who evaluate broken, worn,corroded, or deformed parts from durability testing is an important source of information that is often neglected by designers Table 3 Physical causes and time of occurrence Physical Example Likely effects of findings Alternative effect(s)of findings causes Raw material Excessive microsegregation Material supplier is Additional investigation is manufacturing causes inability to achieve blamed performed on how to improve post heat treat mechanical heat treat line to make process more robust. Design phase Designer does not know Heat treater is blamed for Designer reviews accuracy of hardness test poor process control specifications, and broadens and specifies a that is specification if that is too narrow to achieve acceptable based on
description of a component. In some limited cases, this may be all that is possible, if the part is gone. However, the value of the failure analysis is limited in those cases. Also note that a failure problem is defined in a broader context going from top to bottom of Table 2. This is particularly important for failure analysis within a manufacturing organization. Today, many companies manufacture components or assemblies for other companies. The individuals at the contract manufacturing companies may not have any way of learning the importance of specified or unspecified requirements of the components that they are manufacturing until they have the opportunity to learn as a result of a failure investigation. Progressive companies have been taking advantage of their human resources for years by providing more training and education, because they know that it generally has a positive effect on the profitability of the company. Table 2 Complexity of investigation Depth and complexity of investigation Example Allowed effects of findings Physical cause(s) or factor(s) Part is found to be of the wrong hardness. Part gets rehardened. Maybe inspection frequency is increased. Individual people causes Heat treat department employee does not understand importance of hardness and does not check part. Heat treatment department employees are sent to a basic metallurgy and testing class. Latent causes or factors Nobody tells furnace operator about the importance of hardness testing. It does not matter that she fabricated test results, until the pyrometer fails, causing incorrect temperature exposure during austenitization. Design and supervisory personnel are given custom training by a competent materials engineer on the subject of how to specify hardness test protocol. Maybe an investigation into the heat treat furnace uniformity is undertaken. Culture-based root cause(s) Hardness runs on low end of specified range for years but never causes a problem until someone, due to economic downturn, decides to use item for much longer than the original expected service life. Marketing people are given additional training so that they do not give unreasonable expectations of product performance. (It is recognized that an optimistic outlook is part of sales and marketing. The question is, where does one draw the line as to what is reasonable and unreasonable.) Marketing people are given adequate resources to follow up with customers. It is also important to keep in mind when root cause(s) could have been introduced. Table 3 lists some examples. It is often difficult to assign a failure to a single phase of problem creation. Many times, there are complex interactions. Only an integrated design approach will create robust processes and thus robust parts. The designer must communicate with personnel from the sales department, as well as customers, maintenance personnel, manufacturing personnel, and material suppliers. Input from failure analysts who evaluate broken, worn, corroded, or deformed parts from durability testing is an important source of information that is often neglected by designers. Table 3 Physical causes and time of occurrence Physical causes Example Likely effects of findings Alternative effect(s) of findings Raw material manufacturing Excessive microsegregation causes inability to achieve post heat treat mechanical properties. Material supplier is blamed. Additional investigation is performed on how to improve heat treat line, to make process more robust. Design phase Designer does not know accuracy of hardness test and specifies a range that is too narrow to achieve. Heat treater is blamed for poor process control. Designer reviews specifications, and broadens specification if that is acceptable, based on
performance criteria, or modifies design as required. Manufacturing Part loader malfunctions, Heat treater is blamed for Product design manager is hase and a small fraction of the poor process control inspired to perform detailed load does not experience failure mode and effects proper thermal cycle, but analysis(FMEA) in presence none of the bad ones are in of mechanical. materials the test group manufacturing, and maintenance personnel, and Service phase Part is subject to Hardness data can be Product design manager unexpected and easy to misinterpret ired to perform detailed undetected heat, which leading to assignment of FMEA in presence of changes the hardness the same likely cause mechanical. materials listed above. if manufacturing, and microstructure analysis is maintenance personnel, and not included customers Avoiding Errors. The failure analyst needs to be aware that sorting out the causes of failures can cause economic and noneconomic(e.g, psychological) consequences to particular individuals or companies who are implicated for carelessness, negligence, simple ignorance, or other errors or omissions. Thus, it is important to avoid mistakes, as they could cause as much harm as, or more harm than, the original failure Analytical mistakes may be technical in nature, such as an incorrect measurement of a mechanical prope Analytical mistakes may also be subtle. An example may be not questioning a suspicious hardness composition data point. Another example error in judgment of the significance of something that normally a minor detail. If this causes one to overlook things that bear close scrutiny, an incorrect conclusion may be drawn. Making sure that all relevant details are examined can help point to a clear conclusion and is a key to competent failure analysis work In situations that involve loss of life, human injury, or large economic damage, professional analysts should be very careful to do work only within their areas of competence. It is important to know the limits of one 's own knowledge and to know when help is needed. In fact, input from people from many areas will probably be involved in all but the most basic physical-cause investigations. If the failure involves complex interactions of latent factors, an interdisciplinary approach is generally required to prepare prevention strategy recommendations Fear of overlooking important details is probably the biggest reason that many experienced analysts refuse to perform failure analysis work unless they are given the time and budget to do a complete investigation. It is very easy to draw the wrong conclusions if one does not consider the "big picture" from multiple angles. A broad view is more likely to lead to a coherent conclusion or set of conclusions. To emphasize this important point again, a failure analysis must include an evaluation of the consistency of results from different tests or analytical methods. A single test result does not constitute a legitimate foundation for a failure analysis. Other common pitfalls in failure investigations suggested by Dennies(Ref 3)include Jumping to conclusions Not understanding the problem Not understanding how the failed system is supposed to operate Not considering all possible failure causes Tearing system apart without a developed plan We need to tear it apart as soon as possible Failing to follow through Not asking for help Thinking it is so easy to do Destroying evidence due to lack of plar Failure analysis is a profession that is rarely perfected in a given individual, and even experienced practitioners should remain aware of these potential pitfalls. It is also important to understand that failure analysis is not(ref 3) Thefileisdownloadedfromwww.bzfxw.com
performance criteria, or modifies design as required. Manufacturing phase Part loader malfunctions, and a small fraction of the load does not experience proper thermal cycle, but none of the bad ones are in the test group Heat treater is blamed for poor process control. Product design manager is inspired to perform detailed failure mode and effects analysis (FMEA) in presence of mechanical, materials, manufacturing, and maintenance personnel, and customers. Service phase Part is subject to unexpected and undetected heat, which changes the hardness Hardness data can be easy to misinterpret, leading to assignment of the same likely cause listed above, if microstructure analysis is not included. Product design manager is inspired to perform detailed FMEA in presence of mechanical, materials, manufacturing, and maintenance personnel, and customers. Avoiding Errors. The failure analyst needs to be aware that sorting out the causes of failures can cause economic and noneconomic (e.g., psychological) consequences to particular individuals or companies who are implicated for carelessness, negligence, simple ignorance, or other errors or omissions. Thus, it is important to avoid mistakes, as they could cause as much harm as, or more harm than, the original failure. Analytical mistakes may be technical in nature, such as an incorrect measurement of a mechanical property. Analytical mistakes may also be subtle. An example may be not questioning a suspicious hardness or composition data point. Another example is an error in judgment of the significance of something that is normally a minor detail. If this causes one to overlook things that bear close scrutiny, an incorrect conclusion may be drawn. Making sure that all relevant details are examined can help point to a clear conclusion and is a key to competent failure analysis work. In situations that involve loss of life, human injury, or large economic damage, professional analysts should be very careful to do work only within their areas of competence. It is important to know the limits of one's own knowledge and to know when help is needed. In fact, input from people from many areas will probably be involved in all but the most basic physical-cause investigations. If the failure involves complex interactions of latent factors, an interdisciplinary approach is generally required to prepare prevention strategy recommendations. Fear of overlooking important details is probably the biggest reason that many experienced analysts refuse to perform failure analysis work unless they are given the time and budget to do a complete investigation. It is very easy to draw the wrong conclusions if one does not consider the “big picture” from multiple angles. A broad view is more likely to lead to a coherent conclusion or set of conclusions. To emphasize this important point again, a failure analysis must include an evaluation of the consistency of results from different tests or analytical methods. A single test result does not constitute a legitimate foundation for a failure analysis. Other common pitfalls in failure investigations suggested by Dennies (Ref 3) include: · Jumping to conclusions · Not understanding the problem · Not understanding how the failed system is supposed to operate · Not considering all possible failure causes · Tearing system apart without a developed plan: “We need to tear it apart as soon as possible.” · Failing to follow through · Not asking for help · Thinking it is so easy to do · Destroying evidence due to lack of planning Failure analysis is a profession that is rarely perfected in a given individual, and even experienced practitioners should remain aware of these potential pitfalls. It is also important to understand that failure analysis is not (Ref 3): The file is downloaded from www.bzfxw.com
Give me your best guess Not identifying root cause(s) Reworking or repairing: It will be quicker to fix it Swapping parts: Remove and replace mentality Ignoring the problem: Wait until the problem goes away We were going to change it later anyway Band-aid fixes: Return to the supplier; scrap; another system, supplier, or inventory · Never happens:“Oops Reference cited in this section 3. D P. Dennies, Boeing Co., private communication Planning and Preparation It should be clear that the objectives and scope should be defined and understood early in every investigation. If resources for a complete and detailed investigation leading to a high degree of technical certainty are not available, the investigator is encouraged to clarify for himself or herself, as well as the others involved, what is oped to be determined after following a particular protocol. This clarification process should be done before any destructive testing Even a very limited investigation is by no means useless. Often, the people involved have two or three failure scenarios in mind. It is often possible for the trained analyst to rule out some of these scenarios with a small amount of work. A case in point is when an automotive repair shop owner wanted to know if employee negligence had caused a premature fracture in an externally threaded fastener. The fracture occurred two months after the repair job. The fracture was found by a different auto repair shop. There were no indications of progressive cracking. The people from the second repair shop accused the first shop of gross negligence. In this situation, it might be reasonable to suggest that something other than the first mechanic's negligence caused the fracture. Even without revealing the whole story, the information provided with a simple fractographic evaluation was useful to those involved Guidelines on the preparation of a protocol for a failure analysis may vary. For a part investigation, it may be a simple checklist(Fig. 1)that is included in a client report. In larger investigations, other methods(Table 4)may be considered to help plan and identify priorities. Each has advantages, drawbacks, and limitations in any given situation. When planning the actual step-by-step activities of the investigation, one should keep in mind that the degree of comprehensiveness necessary will be determined to a large degree not only by what the involved parties want to know but also by how strong their desire is to know it. In practice, the strength of the desire is measured in practical terms by the budget and timing considerations
· “Give me your best guess” · Not identifying root cause(s) · Reworking or repairing: “It will be quicker to fix it.” · Swapping parts: Remove and replace mentality · Ignoring the problem: “Wait until the problem goes away.” · “We were going to change it later anyway.” · Band-aid fixes: Return to the supplier; scrap; another system, supplier, or inventory · Never happens: “Oops” Reference cited in this section 3. D.P. Dennies, Boeing Co., private communication Planning and Preparation It should be clear that the objectives and scope should be defined and understood early in every investigation. If resources for a complete and detailed investigation leading to a high degree of technical certainty are not available, the investigator is encouraged to clarify for himself or herself, as well as the others involved, what is hoped to be determined after following a particular protocol. This clarification process should be done before any destructive testing. Even a very limited investigation is by no means useless. Often, the people involved have two or three failure scenarios in mind. It is often possible for the trained analyst to rule out some of these scenarios with a small amount of work. A case in point is when an automotive repair shop owner wanted to know if employee negligence had caused a premature fracture in an externally threaded fastener. The fracture occurred two months after the repair job. The fracture was found by a different auto repair shop. There were no indications of progressive cracking. The people from the second repair shop accused the first shop of gross negligence. In this situation, it might be reasonable to suggest that something other than the first mechanic's negligence caused the fracture. Even without revealing the whole story, the information provided with a simple fractographic evaluation was useful to those involved. Guidelines on the preparation of a protocol for a failure analysis may vary. For a part investigation, it may be a simple checklist (Fig. 1) that is included in a client report. In larger investigations, other methods (Table 4) may be considered to help plan and identify priorities. Each has advantages, drawbacks, and limitations in any given situation. When planning the actual step-by-step activities of the investigation, one should keep in mind that the degree of comprehensiveness necessary will be determined to a large degree not only by what the involved parties want to know but also by how strong their desire is to know it. In practice, the strength of the desire is measured in practical terms by the budget and timing considerations
Factor/Variable Observations/Comments Chemistry Conforms to AISI 1030 Microstructure Proeutectoid ferrite and pearlite as expected in a hypoeutectoid annealed/normalized plain carbon steel Grain Size Variable: coarse(1 to 2 ASTM grain size)in the heavy thickness and fine (3 to 5 grain size)in the thin web. Knoop Hardness web( Thin section):260,266,252,245,233(HK300 Avg=251 HK300(20HRC) Heavy section:275,248,309,241,273,301(HK300) Avg= 275 HK300(25HRC) Inclusions/Segregation Appears most probably The EDS spectra show presence of Sulfur(S), Phosphorus(P), Silicon(Si), Calcium(Ca) and other elements(Fe and Mn are expected). Some of the phosphorus nay have been contributed by the laboratory cleaning procedure Forging Defects No gross forging defects such as laps or folds were detected. Overheating/Burning Possible overheating causing grain growth and grain boundary precipitation/formation of sulfides/phosphides/oxides and other non-metallics Residual Stress/Tightening Unknown. Not expected to be significant Overload Operating Loads The concave side of brace is always under tension magnitude of forces unknown Hydrogen Damage Appears possible but secondary to grain growth due to overheating Hard spots Higher Knoop reading near cracked edge. Fracture Appearance The initiation region shows fine dimpled structure which is interpreted to be due to the presence of grain boundary precipitates formed during forging processing. The fracture way from the initiation area is a mixture of ductile and intergranular modes; and has a faceted appearance. Further into the core, the fracture mode is predominantly of the cleavage (less ductile or brittle, transgranular) type Fatig No fatigue striations were detected. It is believed the crack front traveled rapidly. Corrosion in Service Rust only. No evidence of any other form of corrosion detected Thefileisdownloadedfromwww.bzfxw.com
The file is downloaded from www.bzfxw.com
