Overview
ISO 8642:2008 - Aerospace - Self-locking nuts with maximum operating temperature greater than 425 °C - Test methods - defines standardized test methods for metric self-locking nuts with MJ threads intended for use in aerospace applications where the maximum operating temperature exceeds 425 °C. The standard describes the required test devices and step‑by‑step methods for each inspection. It applies when referenced by the dimensional standard, drawing or procurement specification and is intended to be used in conjunction with ISO 8641.
Key Topics and Requirements
ISO 8642:2008 organizes a comprehensive set of mechanical and functional tests. Key topics include:
- Scope and applicability: metric MJ-thread self-locking nuts for aerospace use at >425 °C; applies only when specified in procurement documents.
- Test device definitions: standardized fixtures and mandrels for reproducible testing.
- Hardness test: authorized methods (Rockwell, Vickers, microhardness) and guidance on measurement zones and specimen preparation.
- Dimensional and fit tests: bearing surface squareness using a sliding collar/mandrel device.
- Mechanical performance tests:
- Axial load test (80 % and 100 % variants; includes procedures after heat soak at maximum operating temperature).
- Wrenching feature test for wrenchable nuts.
- Torque‑out test for multi‑part nuts (floating or assembled bodies).
- Push‑out, swaging and captive washer rotation tests.
- Self‑locking torque tests at ambient temperature and after heat soak.
- Permanent set test and vibration test for durability and retention performance.
- Test conditions: many tests are performed at ambient temperature; several call for heat soak at the specified maximum operating temperature before re‑testing.
- Conformance and dispute resolution: alternative methods may be used, but in disputes the ISO 8642 procedures take precedence.
Applications and Who Uses It
ISO 8642:2008 is essential for stakeholders involved with high‑temperature aerospace fasteners:
- Fastener manufacturers designing and qualifying self‑locking nuts for high‑temperature service
- Aerospace OEMs and suppliers specifying procurement and acceptance criteria
- Qualification and test laboratories performing standardized mechanical and thermal tests
- Quality assurance and certification bodies assessing compliance with procurement specifications
Typical use cases include qualification of locknut designs for high‑temperature aerospace environments (for example, hot‑section assemblies), ensuring consistent performance after thermal exposure, and verifying retention, torque and vibration resistance.
Related Standards
Relevant referenced standards include:
ISO 8642:2008 provides a practical, repeatable test framework for validating the high‑temperature performance of self‑locking nuts in aerospace applications.
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