ISO 4378-2:2017

Overview

ISO 4378-2:2017 - "Plain bearings - Terms, definitions, classification and symbols - Part 2: Friction and wear" defines the commonly used terminology and classification for friction and wear of plain bearings. The standard provides precise terms, definitions, classification schemes and symbols (with some accepted short forms) to reduce ambiguity in design, testing, documentation and communication across the bearing, tribology and machinery communities.

Key topics

The standard focuses on clear, standardized vocabulary and covers:

• General friction and wear terms: external/internal friction, friction force, coefficient of friction, friction angle, wear, wear rate and specific wear rate.
• Classification of friction:
  • By presence of relative motion: static, maximum static, dynamic.
  • By mode of motion: sliding, rolling, combined rolling/sliding, traction and related coefficients.
  • By lubrication condition: unlubricated (dry), lubricated, boundary, mixed-film and fluid friction.
• Wear types and mechanisms:
  • Mechanical wear: abrasive, adhesive, hydro-abrasive, fluid erosion, fatigue, cavitation, fretting.
  • Mechano-chemical wear: tribo-chemical wear, fretting corrosion, oxidative wear.
  • Other forms: electroerosive and thermal wear.
• Phenomena and failure modes: stick‑slip motion, adhesion, material transfer, seizure, scoring, scratching, spalling, pitting, running‑in, edge loading.
• Vibration-related terms for shafts on plain bearings: notably oil whirl and oil whip.
• Notation and symbols: commonly used symbols and permitted short forms where unambiguous. (The document includes figures illustrating many terms.)

Applications - who uses it and why

ISO 4378-2:2017 is a reference for professionals who require consistent terminology and classification when working with plain bearings and tribological systems:

• Bearing designers and mechanical engineers - for clear specification of friction and wear expectations in design documents.
• Tribologists and materials scientists - to standardize reporting of wear mechanisms and test results.
• Test laboratories and quality assurance - for consistent test reporting and interpretation of wear/failure data.
• Maintenance and reliability engineers - when diagnosing wear-related failures and specifying mitigation (lubrication regimes, running‑in procedures).
• Standards authors, procurement and technical writers - to ensure unambiguous contract and specification language.

Practical uses include preparing technical specifications, writing test reports, conducting failure analysis, training staff on wear mechanisms, and aligning multidisciplinary teams around common definitions.

Related standards

• ISO 4378 is a multi‑part series covering plain bearing terminology; a full list of parts is available on the ISO website.
• For terminological cross-references, ISO and IEC maintain online terminological databases (ISO OBP and IEC Electropedia).

Keywords: ISO 4378-2:2017, plain bearings, friction and wear, bearing terminology, tribology, wear classification, coefficient of friction, running-in, oil whirl.