Lesson 4: The failure and the typical failure modes

In this lesson, we will delve into the concept of failure, understand its nature, and explore typical failure modes that can occur in various systems.

The Failure

  • According to ISO IEC 50(191):1992, a failure is a state in which a product cannot perform its intended function unless it happens during preventive maintenance or planned activity or is due to a lack of external resources.
  • Failure is essentially a process where a product transitions from a working state to a failure state.
  • Various technical failures, such as wear, stretching, deformation, cracking, or breaking, can occur during the wear and tear process of components, affecting the system’s reliability and serviceability.
  • Failure indicates a change in the quality of a component during operation, resulting from identifiable causes.

The Nature of Failure

  • Failure is not the same as a technical defect, as defects can occur during manufacture or repair and are not necessarily failures; they are merely preconditions for failure.
  • While failure is undesirable, it is a natural part of operation, and reliability is closely related to it.
  • The higher the reliability, the lower the probability of failure.
  • Understanding the most common causes of failure is crucial to reduce the likelihood of failures and identify root causes.

Typical Failure Modes

  • Failure analysis aims to identify the causes of failures, which can be categorized into direct causes (primary causes directly leading to the inability to perform a function) and indirect causes (triggers or reinforcers of direct causes).
  • Failures can be simple (caused by a single homogeneous defect) or complex (caused by multiple, often indirect, factors).
  • A systematic approach is essential to identify and examine failure causes comprehensively.
  • Failure modes can be classified based on several criteria, but one system groups them into categories based on their nature and origin.

Categories of Failure Modes

  • Faults caused by external factors: These occur independently of the manufacturer’s or user’s actions and intentions and include natural disasters, unauthorized or incorrect interventions, and other external factors.
  • Product defects: Arising within the manufacturer’s activities, these include design defects, manufacturing defects, material failures, failures of other components, and other product-related issues.
  • Defects due to natural wear and tear: These result from natural processes on machinery designed, constructed, and maintained correctly according to industry standards and conditions. Categories include wear, fatigue, aging, corrosion, and other wear and tear phenomena.
  • Maintenance defects: These stem from deficiencies in maintenance activities, such as maintenance design failures, daily maintenance issues, technical inspection or diagnostic failures, repair failures, modification failures, storage or warehousing problems, errors by external service providers, and other maintenance-related errors.
  • Operational errors: These occur during product use and are categorized into handling errors, abnormal use, and other operational errors.


  • Failure is an essential concept that denotes a condition where a product cannot perform its intended function.
  • Understanding failure modes and their causes is crucial for maintaining reliability and preventing failures.
  • Categorizing failure modes based on their nature and origin helps in systematic failure analysis and addressing the root causes.
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