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A failure mode is a characterization of the way a product or process fails.

Rather than the simple description of symptoms that many product users or process participants might use, the term failure mode refers to a rather complete description, including the pre-conditions under which failure occurs, how the thing was being used, proximate and ultimate/final causes (if known), and any subsidiary or resulting failures that result.

The term is part of the engineering lexicon, especially of engineers working to test and debug products or processes. Carefully observing and describing failure conditions, identifying whether failures are reproducible or transient, and hypothesizing what combination of conditions and sequence of events led to failure is part of the process of fixing design flaws or improving future iterations.

There are many different kinds of mechanical failure, and they include overload, impact, fatigue, creep rupture, stress relaxation, stress corrosion cracking corrosion fatigue and so on. Each produces a different type of fracture surface, and other indicators near the fracture surface(s). The way the product is loaded, and the loading history are also important factors which determine the outcome.

Over time, as more is understood about a failure, the failure mode evolves from a description of symptoms and outcomes (that is, effects) to a systematic and relatively abstract model of how, when, and why the failure comes about (that is, causes).

The more complex the product or situation, the more necessary a good understanding of its failure modes is to ensuring its proper operation (or repair). Cascading failures, for example, are particularly complex failure modes. Edge cases and corner cases are situations in which complex, unexpected, and difficult-to-debug problems often occur.

• Failure analysis
• Failure mode and effects analysis (FMEA)
• Failure rate
• Forensic engineering
• Hazard analysis