ISO/TR 13086-3:2018 PDF

Overview

ISO/TR 13086-3:2018 provides guidance for calculating stress ratios when analyzing filament-wound composite gas cylinders. Applicable to cylinder Types 2, 3 and 4, the technical report supports design, verification and the development or revision of standards for fibre-reinforced composite pressurized cylinders. The document explains how to determine the ratio of reinforcing-fibre stress at burst conditions relative to stress at working pressure - a key metric for assessing stress rupture (static fatigue) risk.

Key technical topics and requirements

• Definition of stress ratio: the maximum fibre stress at burst divided by the maximum fibre stress at working (rated) pressure. Stress ratio is used in stress-rupture predictions similar to how stress range is used in cyclic fatigue analysis.
• Burst ratio vs stress ratio: For Type 4 cylinders with a single structural fibre, burst ratio (burst pressure / working pressure) equals stress ratio. For Type 2 and 3 cylinders, autofrettage and liner interaction can make burst ratio conservative or non-representative.
• Hybrid (multi‑fibre) Type 4 evaluation: Hybrids (e.g., carbon + glass) require per-fibre stress checks. The report describes using a reinforcement stiffness/load‑share factor based on fibre cross-sectional area and elastic moduli to adjust required burst demonstration. Example: if the primary fibre carries 90% of the structural load, a minimum demonstrated burst ratio of 2.475 was used in the guidance.
• Analysis methods: Numerical methods (e.g., finite element analysis) are encouraged for Type 2/3 designs to capture liner–composite interaction and nonlinear liner behaviour. Models must be validated against measurements.
• Measurement and validation: Stress ratios may be confirmed by strain or deflection measurements. Validity of analysis or measurements must be demonstrated, and burst-location (cylinder vs dome) should be verified.
• Required data for accurate analysis: composite elastic moduli and strength, layer thicknesses, liner stress–strain behaviour and thickness, inner diameter, autofrettage/test/working/minimum burst pressures, and significant pre-stresses from winding.

Practical applications and users

Who benefits from ISO/TR 13086-3:2018:

• Composite pressure-vessel designers and mechanical engineers
• Manufacturers of filament-wound gas cylinders (Types 2–4)
• Test laboratories and failure‑analysis teams performing burst and strain testing
• Standards developers and regulatory bodies assessing safety criteria
• Structural analysts performing FEA of liner–composite interaction

Practical uses:

• Establishing stress-rupture margins and safe working parameters
• Validating design via analysis and measurement before production
• Evaluating hybrid winding strategies and material selection
• Supporting standard development and certification evidence

Related standards

• Part of the ISO 13086 series on composite cylinder design and testing (see ISO website for the complete series and related technical reports).