Chemical analyses(bulk, local, surface corrosion products, and deposits or coatings) Testing under simulated service conditions Finally, the investigation concludes with a synthesis and interpretation of results. This step may actually require reiteration of previous steps or the introduction of new steps. Similar to design, failure analysis can be an iterative process of discovery and reexamination. Failure analysis can also be a multidisciplinary process and that may require consulting with experts in other disciplines throughout the investigation. Once all information has been assembled, then the final step is to synthesize all the evidence and formulate conclusions. This requires writing a report with follow-up recommendations on preventing future failures. The goal of every failure analyst is to determine not only the failure mechanism but also the root cause, which may be related to misuse, poor maintenance practices, or improper application, or related to the material properties, design,or manufacture of the product In cases that involve personal injury or will most likely involve legal pursuit of compensation from another company, care must be taken in preserving the scene and physical evidence. Accidental or deliberate the evidence, even though they may not have caused the original failure e to the person or company destroying destruction of evidence can result in diverting the legal liability of a failure to the Practices in Failure Analysi Collection of Background Data and Samples The failure investigation should include gaining an acquaintance with all pertinent details relating to the failure, collecting the available information regarding the design, manufacture, processing, and service histories of the failed component or structure, and reconstructing, insofar as possible, the sequence of events leading to the failure. Collection of background data on the manufacturing and fabricating history of a component should begin with obtaining specifications and drawings and should encompass all the design aspects of the failed part as well as all manufacturing and fabrication details---machining, welding, heat treating, coating, quality-control records, and pertinent purchase specifications Additional information on upfront planning of investigations is also described in the article"Organization of a Failure Investigation"in this volume Collecting Data and Samples On-Site Investigation. In the investigation of failures, it is also often desirable for the analyst to visit the scene, but for the nalysis of some components it may be impractical or impossible for the failure analyst to visit the failure site. Under hese circumstances, data and samples may be collected at the site by field engineers or by other personnel under the direction of the failure analyst. A field failure report sheet or checklist can be used to ensure that all pertinent information regarding the failure is recorded There also are situations where it is essential to perform failure analyses on the site. While it is recommended that examination be done in a laboratory, the requirements for on-site testing may involve the use of portable laboratories with metallographic equipment for grinding, mechanical polishing, and etching. Small specimens can be cut from a part on the site for preparation, examination, and photography immediately or upon return to a fully equipped laboratory Photography is, of course, essential; it should be performed by the analyst or perhaps a professional photographer in the case of a large-scale accident scene. Other considerations for on-site examination at an accident scene are also discussed in more detail in the article"Modeling and accident Reconstruction in this volume It is also frequently desirable to make acetate tape replicas or room-temperature-vulcanized(rTv) rubber replicas of fracture surfaces or of wear patterns of large parts during an on-site failure analysis. Several replicas should be made of the fracture-origin region using acetate tape softened in acetone, dried, then carefully stripped from the fracture surface Upon return to the laboratory, the replicas may be gold coated and examined with a scanning electron microscope(sEM Foreign particles removed from the fracture surface also may be analyzed The RTV rubber replica can be applied over a rather large area with less chance of missing a critical spot. A combination of acetate tape and rtV rubber replicas can assure the investigator of better coverage of the area in question. room- temperature-vulcanized rubber does not provide the sensitivity of an acetate replica, and a setup time of several hours is required. However, the added area can be very important in an investigation Thefileisdownloadedfromwww.bzfxw.com· Chemical analyses (bulk, local, surface corrosion products, and deposits or coatings). · Testing under simulated service conditions Finally, the investigation concludes with a synthesis and interpretation of results. This step may actually require reiteration of previous steps or the introduction of new steps. Similar to design, failure analysis can be an iterative process of discovery and reexamination. Failure analysis can also be a multidisciplinary process and that may require consulting with experts in other disciplines throughout the investigation. Once all information has been assembled, then the final step is to synthesize all the evidence and formulate conclusions. This requires writing a report with follow-up recommendations on preventing future failures. The goal of every failure analyst is to determine not only the failure mechanism but also the root cause, which may be related to misuse, poor maintenance practices, or improper application, or related to the material properties, design, or manufacture of the product. In cases that involve personal injury or will most likely involve legal pursuit of compensation from another company, care must be taken in preserving the scene and physical evidence. Accidental or deliberate destruction of evidence can result in diverting the legal liability of a failure to the person or company destroying the evidence, even though they may not have caused the original failure. Practices in Failure Analysis Collection of Background Data and Samples The failure investigation should include gaining an acquaintance with all pertinent details relating to the failure, collecting the available information regarding the design, manufacture, processing, and service histories of the failed component or structure, and reconstructing, insofar as possible, the sequence of events leading to the failure. Collection of background data on the manufacturing and fabricating history of a component should begin with obtaining specifications and drawings and should encompass all the design aspects of the failed part as well as all manufacturing and fabrication details—machining, welding, heat treating, coating, quality-control records, and pertinent purchase specifications. Additional information on upfront planning of investigations is also described in the article “Organization of a Failure Investigation” in this Volume. Collecting Data and Samples On-Site Investigation. In the investigation of failures, it is also often desirable for the analyst to visit the scene, but for the analysis of some components it may be impractical or impossible for the failure analyst to visit the failure site. Under these circumstances, data and samples may be collected at the site by field engineers or by other personnel under the direction of the failure analyst. A field failure report sheet or checklist can be used to ensure that all pertinent information regarding the failure is recorded. There also are situations where it is essential to perform failure analyses on the site. While it is recommended that examination be done in a laboratory, the requirements for on-site testing may involve the use of portable laboratories with metallographic equipment for grinding, mechanical polishing, and etching. Small specimens can be cut from a part on the site for preparation, examination, and photography immediately or upon return to a fully equipped laboratory. Photography is, of course, essential; it should be performed by the analyst or perhaps a professional photographer in the case of a large-scale accident scene. Other considerations for on-site examination at an accident scene are also discussed in more detail in the article “Modeling and Accident Reconstruction” in this Volume. It is also frequently desirable to make acetate tape replicas or room-temperature-vulcanized (RTV) rubber replicas of fracture surfaces or of wear patterns of large parts during an on-site failure analysis. Several replicas should be made of the fracture-origin region using acetate tape softened in acetone, dried, then carefully stripped from the fracture surface. Upon return to the laboratory, the replicas may be gold coated and examined with a scanning electron microscope (SEM). Foreign particles removed from the fracture surface also may be analyzed. The RTV rubber replica can be applied over a rather large area with less chance of missing a critical spot. A combination of acetate tape and RTV rubber replicas can assure the investigator of better coverage of the area in question. Room￾temperature-vulcanized rubber does not provide the sensitivity of an acetate replica, and a setup time of several hours is required. However, the added area can be very important in an investigation. The file is downloaded from www.bzfxw.com