ADVANCED MATERIALS & PROCESSES | JANUARY 2026 25 incorrect plating/coating, or incorrect assembly. Environment. Incorrect corrosive or thermal factors. Incorrect Material. Material mix from suppliers or in-house storage, or supplying the incorrect material for production. Failure to Meet Material Speci- fications. Outside supplier errors, material mixes in house, or ineffective inspection of supplied material. Failure to Meet Dimensional Specifications. Incorrect operation routings, improper inspection, or incorrect gauging equipment. There may be a few sources and causes not included in this list and the TRC may be a combination of two or more sources. A successful failure investigation will have identified the failure source(s) (TRC) and implemented corrective actions. FAILURE MECHANISMS The second stage of a failure event is the failure mechanism or propagation. This phase can become confusing with regard to the terms used to describe failures. Review of published works on failure analysis and failure investigations will reveal that the terms “failure mechanisms” and “failure modes” are sometimes used interchangeably as though they have the same meaning. They do not. They are two entirely different entities and must be treated as such to accurately describe the failure event. The difference between the two is that a failure mechanism is the “how” and the failure mode is the “what” as illustrated previously in Fig. 1. Confusion of the terminology can also occur when a specific word is used to describe two distinct things. A prime example of this confusion is the word “fatigue” when differentiating between failure mechanism and failure mode. The confusion can result from the fact that the word “fatigue” can be a noun, a verb, or an adjective depending of its usage in a sentence[3]. When distinguishing between a failure mechanism and a failure mode consider the following usage examples. Fatigue used as a Noun Identi- fying a Failure Mode. The component was determined to have failed by reverse bending fatigue. Fatigue used as a Verb Identifying a Failure Mechanism. The fracture origin was initiated at a sharp notch and propagated via low stress high cycle fatigue for 80% of the cross-section before final rupture via ductile fracture. UNDERSTANDING FAILURE MECHANISMS AND FAILURE MODES It is important to address the distinction between failure mechanisms and failure modes and the types of each. Failure Mechanisms. There are essentially four primary failure mechanisms. Each failure mechanism can additionally have multiple subcategories. The four primary failure mechanisms are corrosion, erosion/wear, fatigue, and overload. The failure mechanism is the phase of the failure event that defines how the failure progresses from initiation until the final failure mode. Failure Modes. There are essentially 12 primary failure modes. As previously stated, the failure mode is the “what” of a failure. The failure mode is the final phase of the failure event and is the starting point of the failure investigation. The 12 primary failure modes are fatigue, brittle fracture, ductile fracture, wear failure, corrosion failure, buckling failure, stress evidence of how the failure progressed (failure mechanism). The correct identification of the failure mode(s) and mechanism will ultimately lead to the determination of the TRC “why” (the source) of the failure. Let’s examine each of the three stages of a failure event. The first stage of the failure progression is fairly straightforward by definition: that is, the source or the initiation of the failure. The source of a failure can occur at any stage of the product’s life. The relationship of a failure source to the failure mechanism that results in a specific failure mode is the key to determining the “why” or the TRC of the failure. The following is a list of potential failure sources and a brief description of each[2]. Design. Incorrect design parameters used for the intended application. Design Revisions. Revisions to an existing design that fail to recognize changes in application. Application. Having a component or assembly placed in an application that the design did not anticipate or intend. Abuse. Operation of a component or assembly beyond its design limits. Material Defects. Manufacturing or inherent defects in a material used for the manufacture of a component. Manufacturing Processes. Incorrect machining, incorrect manufacturing process, incorrect heat treatment, Fig. 1 — Progression of a materials failure investigation.
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