ISO 7961:2021

Overview

ISO 7961:2021 - "Aerospace - Bolts - Test methods" defines standardized test methods for bolts used in aerospace structures. The second edition (2021) replaces the 1994 version and provides detailed procedures, apparatus requirements and reporting rules to ensure consistent, reproducible assessment of bolt mechanical and environmental performance.

Key topics and technical requirements

• Scope and normative reference
  • Applies to test methods for aerospace bolts; it references ISO 7500‑1 for calibration and verification of tension/compression testing machines.
• Test types covered
  • Tensile tests at ambient and elevated temperatures (apparatus, fixtures, and controlled load application).
  • Double shear tests using guillotine-style fixtures.
  • Tension fatigue tests with automatic load maintenance and frequency/temperature limits.
  • Stress durability (ambient), stress relaxation (elevated temperature), stress corrosion, and stress rupture tests.
  • Inspection for grinding burns and general test validity checks.
• Apparatus and assembly requirements
  • Functional fixture details (cups, lower/upper blocks, spacers, washers) and guidance for ensuring axial loading and uniform stress (e.g., centering tolerances and stress uniformity limits).
  • Requirements that test nuts or threaded parts be of sufficient strength to ensure bolt failure, and limits on thread exposure during assembly.
  • Calibration requirements conforming to ISO 7500‑1 and additional requirements in Annex A.
• Procedure, loading and reporting
  • Controlled loading rates (specified in tables) and procedural steps for each test to ensure reproducibility.
  • Mandatory elements for test reports and recordkeeping described in Clause 6 and Annex B.
• Supporting material
  • Normative annexes for apparatus calibration and test-report formats, plus an informative annex with relevant formulae.

Applications and users

• Who uses ISO 7961
  • Aerospace fastener manufacturers, OEMs, component suppliers, independent test laboratories, quality assurance teams, and procurement/specification engineers.
• Practical uses
  • Qualification of bolt designs and materials for aircraft and spacecraft structures.
  • Incoming inspection and lot acceptance testing to meet procurement specifications.
  • Supplier and process audits, failure analysis, and certification evidence for regulatory compliance.
  • Establishing test plans and laboratory procedures consistent with international practice.

Related standards

• ISO 7500‑1 - Calibration and verification of static uniaxial testing machines (tension/compression) - directly referenced for force-measuring system calibration.

Keywords: ISO 7961, aerospace bolts, bolt test methods, tensile test, double shear test, fatigue testing, stress corrosion, ISO 7500-1, bolt qualification, aerospace fasteners.