ADVANCED MATERIALS & PROCESSES | JANUARY 2026 24 This is the second installment of a three-part series designed to provide an understanding of materials failures and outline an approach to the investigative process for resolving them. A systematic and effectively conducted investigation is the key to resolving failures of materials and systems. Materials failures are the result of a specific sequence of events that cause a material, component, or system to become unable to perform as designed. Materials failures begin with a source, identified as the true root cause (TRC), then propagate via a failure mechanism, and end via a failure mode. The identification of each of these events requires a systematic process to analyze and correct the cause or source of the failure. FAILURE DEFINED The word failure does not instill images of a positive nature. What exactly constitutes a failure? Looking up the word failure in a dictionary reveals that it is a noun that can have different meanings depending on usage. The various definitions and uses for the word failure, according to the Merriam- Webster Dictionary include 1a) omission of occurrence or performance, 1b) a state of inability to perform a normal function, 1c) a fracturing or giving way under stress, 2a) a lack of success, 2b) a failing in business, 3a) a falling short, 3b) a deterioration or decay, and 4a) one who has failed[1]. FAILURE INVESTIGATIONS: A SYSTEMATIC PROBLEMSOLVING PROCESS, PART II This second part in an article series provides an overview of various phases of a failure examination and clarifies terminology used in metallurgical failures. Jeffrey L. Hess, Fort Wayne, Indiana is paramount to preventing the failure from reoccurring. PROGRESSION OF A METALLURGICAL FAILURE Failures of a component or system have a beginning and an end. The beginning or initiation, is the source or the TRC and the end is the final failure, specifically the failure mode(s). The progression of a failure from the beginning to the final failure is referred to as the failure mechanism or propagation. These three stages of the failure are also identified as the “why,” “how,” and “what” of the failure event as described in Table 1. As illustrated in Fig. 1, the failure investigation process is actually the reverse of the failure progression. After a failure has been identified, the failed component or assembly is examined to determine the failure mode(s). Once the failure mode or modes are identified the investigation proceeds to find This article will only consider definition 1c) a fracturing or giving way under stress as in a structural failure. Review of the available literature on metallurgical failures reveals a number of definitions for a failure depending on the author’s perspective. Much of the literature comes to the same conclusion or definition, but with slightly different wording. It is this author’s belief that the statement that best defines a metallurgical failure is simply: A failure is the point at which a material, component or system is no longer capable of performing its intended function. With that definition as a guide, it follows that a failure doesn’t necessarily mean there was a catastrophic event and fracture of parts, assemblies, or structures. A failure can be the result of a component wearing out. Failures can be as simple as a broken bolt from over torquing or as complex as an aircraft crash. In all failures, finding the TRC or the “why” of the failure TABLE 1 — STAGES OF A MATERIALS FAILURE Stage Failure progression Question addressed Initiation Source of the failure (TRC) Why Propagation Failure mechanism How Final failure Failure mode What
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