ADVANCED MATERIALS & PROCESSES | NOVEMBER/DECEMBER 2025 26 failed fastener was given to the plant metallurgist for examination with little to no history regarding the failure. Visual examination of the failed fastener revealed that the fastener had failed due to a torsional overload. Subsequent testing revealed that the fastener met all specifications and no material or manufacturing defects were found. The metallurgist examining the failed fastener fortunately continued the investigation and interviewed the mechanic who had installed the fastener. After some discussion it was found that the mechanic was new to the job, had not been instructed to use a calibrated torque wrench as required, and had simply over torqued the fastener, which caused the failure. Unfortunately, a lot of investigations would have stopped when the TRC for the failure had been found i.e., the mechanic over torqued the fastener and it broke. The mechanic would then be instructed on proper assembly techniques and the issue would be considered resolved. Stopping the investigation at that point would be premature and would not provide assurance to the organization or the customer that the problem had been effectively resolved. When the investigation determined the TRC of the failure, several “red flags” should have gone up and the investigation should have continued with the corrective phase of the investigation. Several questions should be asked and answered. Sample failure investigation questions include: • If the mechanic over torqued this fastener, then what about the other fasteners that were potentially compromised? • How long had the mechanic been on the job? • How many other units had the mechanic assembled and not followed the correct method? • Have any assemblies this mechanic worked on been shipped to the customer? • Why was the mechanic not trained on proper assembly techniques? • What would be the consequences of other comprised fasteners? • Was there any potential for damage to the components in the assembly? • What additional questions arise from the previously identified concerns that may need to be addressed? Further investigation may reveal that other critical fasteners have been damaged resulting in improper joint strength or compromised fasteners that may fail prematurely. At the beginning of this example, the investigation “team” consisted of just the analyst and the mechanic. As the investigation should have evolved, additional team members such as upper management, marketing, sales, distribution center staff, assembly supervision, training instructors, and more may be added to the team. Considering the answers to the additional questions, it could be found that this same mechanic had not utilized the required torque wrench and torque requirements on many other assemblies that are already in service with a potential for loss of property and/or life. It is vitally important to remember that the investigation is not complete until the TRC of the failure has been identified, and the cause and ramifications of the failure have been identified, addressed, and corrective/preventative action implemented. Seeing the investigation to its completion and asking all the right questions ensures that the investigation has been effectively accomplished. In the above example, it becomes easy to see how a seemingly simple failure with a known cause can evolve into a serious organizational concern. The failure investigator must be diligent and not end the investigation until it has been effectively concluded or until all investigative efforts have been exhausted. Imagine the questions from upper management for the investigator in the above example if the investigation had stopped prematurely with only the identification of the failure mode and material specification compliance. the basis for improvements to future designs and manufacturing methods. Initiating product improvements may not be necessary in all failure investigations. However, this step in the process and purpose of the investigation must be considered before closure of the investigation. PROTECT LIFE AND PROPERTY The third and extremely critical purpose for properly conducting a failure investigation is to protect life and property. Some failures have obvious causes that might be of little consequence, amounting to nothing more than an annoyance. Other failures may have catastrophic consequences resulting in significant loss of life and property. Even with an apparent simple and obvious failure cause, it is necessary to ensure that the TRC of the failure was found and the potential negative influences on other components or systems are analyzed and proven to no longer be a concern. Accomplishing the objectives and addressing the three reasons for a failure investigation requires a detailed and systematic process. A detailed model for such a process will be presented in the third article in this series. TAKING THE INVESTIGATION TO COMPLETION It must also be understood that merely finding the TRC is not the end of the process. An effective corrective action plan to eliminate the TRC must be initiated and completed. The following example illustrates how a relatively simple failure can evolve into a potentially significant issue if the identification of the TRC and the corrective action portion of the process are not taken to completion. A FAILURE INVESTIGATION SCENARIO Consider that a mechanic working on a fairly complex assembly over tightened a fastener and the fastener fractured. Thinking he did nothing wrong, he asked to have the fastener checked to ensure it was in compliance with the engineering specifications. The
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