ISO 23887:2021

Overview

ISO 23887:2021 is an international standard published by the International Organization for Standardization (ISO) focused on aerospace fasteners. Specifically, it defines the test method for measuring the locking torque of blind fasteners, threaded type, self-locking. These blind fasteners, featuring internal threads and an external sleeve, are critical components in aerospace engineering, ensuring reliable and secure fastening where access is limited to one side of the assembly. The standard applies to blind fasteners composed of four main elements-drive nut, nut, sleeve, and corebolt-with a distinctive cross recess at the nut’s top.

Key Topics

• Scope and Applicability: The standard details testing procedures for blind fasteners with four components and specifies conditions for grip length, installation, and test coupon thickness based on product specs.
• Test Apparatus: Two essential tools are specified-torque wrenches calibrated within 12 months with ±4% accuracy, and torsion machines with ±2% accuracy. Both must use torque scales that capture readings between 20% and 90% of their capacity for reliable results.
• Test Fixture and Setup: A test fixture design is presented to hold the fastener and coupon securely. The installation hole size must align with the product’s specification or default to nominal diameter with ISO tolerance H11 if unspecified.
• Test Procedure:
  • Install the fastener to the point of corebolt fracture ensuring minimum upset diameter compliance.
  • Secure the nut in the fixture to prevent rotation during torque measurement.
  • Slowly disassemble the fastener either manually with torque wrenches or at 2-4 revolutions per minute with a torsion machine to accurately record locking torque.
• Data Recording and Reporting: The process requires capturing torque-angle data and creating torque-angle curves to determine locking torque values accurately. Test reports must include detailed information such as part numbers, calibration dates, and measured locking torque results.

Applications

ISO 23887:2021 serves as a critical guideline for aerospace manufacturers, quality assurance teams, and testing laboratories involved in the production and inspection of blind fasteners. Its practical applications include:

• Quality Control: Ensuring that blind fasteners used in aerospace components meet locking torque specifications for safety and durability.
• Product Development and Certification: Verifying mechanical properties during fastener design and certification processes.
• Maintenance and Repair: Assessing fastening integrity in aerospace maintenance operations where self-locking fasteners are used.
• Supplier Compliance: Standardizing acceptance testing for suppliers and subcontractors manufacturing blind fasteners.

Adhering to ISO 23887:2021 helps reduce fastener failure risks, enhance structural integrity, and maintain compliance with aerospace industry requirements.

Related Standards

• ISO 286-2: Geometrical product specifications for tolerances on linear sizes, used here for specifying hole and shaft dimensions in test coupons.
• ASME B107.300: Specifications for mechanical torque measurement instruments that ensure calibration and accuracy of torque wrenches used in testing.
• Aerospace Fastener Standards (ISO/TC 20/SC 4): Complementary standards for aerospace fasteners that cover installation, materials, and performance testing.

By integrating ISO 23887:2021 with these related standards, aerospace engineers and technicians can establish comprehensive testing protocols that align with internationally recognized quality benchmarks.

Adopting ISO 23887:2021 promotes consistency, safety, and reliability in the testing of threaded blind fasteners-components pivotal to aerospace assembly and maintenance. This standard optimizes the accuracy of locking torque measurement, safeguarding structural integrity across aerospace applications.