ISO 18338:2021

Overview

ISO 18338:2021 - "Metallic materials - Torsion test at room temperature" specifies a standardized method for performing torsion tests on metallic materials at ambient conditions. The procedure measures torsional properties such as shear stress, shear strain, torsional proof strength (plastic torsion), torsional yield strengths (upper and lower), torsional strength, and maximum plastic shear strain. Tests are typically run by applying a continuously increasing angle of twist (generally to fracture) while recording torque and angular displacement.

Key topics and technical requirements

• Scope & principle: Room-temperature torsion testing to determine torsional properties by controlled twist and torque measurement.
• Test pieces: Two common specimen types - cylinder and tube. Recommended cylinder size: 10 mm diameter with 50 mm or 100 mm gauge length; parallel lengths (examples) 70 mm or 120 mm. Tube specimens must be straight, round and plugged at ends outside the parallel length.
• Dimensional measurement: External (and internal, for tubes) diameters measured at multiple sections; measurement error not to exceed ±0.5%. Average dimensions are used to compute the original polar section modulus Wp.
• Instrumentation & accuracy:
  • Torque systems must be calibrated periodically; permissible relative error ±1.0% for indicated torque values.
  • Torque calibration references: ASTM E2624 and DIN 51309.
  • Angle-of-twist measurement commonly via troptometer (extensometer-based); troptometers must be firmly clamped with no slip and provide equivalent accuracy if using other sensors.
• Calculations & outputs: Procedures for computing shear stress/strain, slope of the elastic portion (Gs), torsional proof strength (τp), upper/lower torsional yield strengths (τe,H / τe,L), torsional strength (τm), and γmax. Annex A covers reference values based on Nadai’s expressions.
• Reporting: Test report requirements and defined symbols/designations are provided to ensure consistent results and interpretation.

Applications

ISO 18338:2021 is used for:

• Material characterization in metallurgy and materials science (ductility and torsional performance).
• Quality control and acceptance testing for components subjected to torsion (shafts, fasteners, tubes, springs).
• Research & development when comparing alloy processing, heat treatments, or manufacturing routes.
• Comparative data generation for design input and failure analysis.

Who should use this standard

• Materials testing laboratories and calibration facilities
• Metallurgists and mechanical engineers
• Manufacturers of rotational components and tubular products
• Certification bodies and quality assurance teams

Related standards

• ISO 377 (sample location/preparation)
• ISO 9513 (extensometer calibration)
• ASTM E2624 (torque calibration practice)
• DIN 51309 (torque measuring device calibration)

Keywords: ISO 18338:2021, torsion test, metallic materials, room temperature, torsional strength, torsional proof strength, troptometer, shear stress, shear strain, torque calibration.