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.comA 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