Overview
ISO 23886:2021 specifies a torque and preload test method for threaded, self-locking collars used in aerospace applications. The standard defines how to measure key performance parameters - locking torque, breakaway torque, torque off and preload - using calibrated torque/tension test benches or torsion machines. It was prepared by ISO/TC 20/SC 4 (Aerospace fastener systems) and includes procedural details, data processing and recommended test fixtures.
Key topics and technical requirements
- Scope and purpose: Test method for measuring torque and preload characteristics of threaded collars (self-locking).
- Test apparatus: Use a torque-tension test bench, torsion machine or equivalent precision equipment calibrated within 12 months.
- Test bolt: The bolt used with the collar must comply with the applicable product specification.
- Test accessories and interface:
- Collar bearing surface material: alloy steel.
- Surface roughness: Ra = 0.4 µm to 0.8 µm.
- Hardness of contact washer: 50 HRC to 60 HRC.
- Test procedure (high level):
- Install test bolt and collar; measure initial geometry and compute cycles.
- Rotate collar at (10 ± 2) r/min until seating (hex portion twists off).
- Release axial load, clamp unlocking area, reverse torque at (10 ± 2) r/min to measure disassembly behavior.
- Data capture and processing:
- Record torque, tension and rotation angle to produce torque‑angle and tension‑angle curves.
- From curves determine locking torque, preload, torque off and breakaway torque.
- Test reporting: Reports shall include part/lot/manufacturer, test machine model/serial/calibration date, measured torque/preload values and results.
Applications
- Aerospace fastener qualification: Verifying self-locking collar performance for aircraft and space vehicle assemblies where controlled preload and locking behavior are critical.
- Design validation: Engineers use the method to confirm design margins, friction behavior and seating characteristics of collars in structural and dynamic assemblies.
- Quality control and acceptance testing: Manufacturers and suppliers apply the procedure during production testing and lot acceptance to ensure consistent locking performance.
- Failure analysis: Test data (torque‑angle and tension‑angle curves) support investigations into unexpected loosening or seating issues.
Who should use this standard
- Aerospace fastener manufacturers and suppliers
- Mechanical and structural engineers working on bolted joints
- Test laboratories performing torque/preload characterization
- Quality and certification teams in aviation and space programs
Related standards
ISO 23886:2021 complements other aerospace fastener and torque/preload standards and should be used alongside applicable product specifications and industry fastener standards used by designers, procurement and test labs.
