ISO 15653:2018

Overview - ISO 15653:2018 (Metallic materials - quasistatic fracture toughness of welds)

ISO 15653:2018 specifies laboratory methods for determining the quasistatic fracture toughness of welds in metallic materials. It defines procedures to obtain point values of fracture toughness expressed as the stress intensity factor (K), crack tip opening displacement (CTOD, δ), and the experimental equivalent of the J‑integral (J) for welded joints. The standard uses fatigue precracked specimens that are notched after welding to target specific weld regions (weld metal or heat‑affected zone, HAZ). ISO 15653 is intended to be used together with ISO 12135 and complements parent‑metal fracture toughness testing standards.

Key technical topics and requirements

• Fracture parameters covered: stress intensity factor (K), CTOD (δ), and J‑integral (J) single‑point determinations.
• Specimen strategy: fatigue precracking, notch placement in a defined target area (weld metal or HAZ), and options for through‑thickness and surface‑notched specimens.
• Specimen preparation: machining tolerances, notch machining, side‑grooving and pre‑test metallography to confirm target microstructure and notch position.
• Precracking and crack sampling: methods to ensure the fatigue crack samples the intended weld zone and to evaluate crack front straightness and weld suitability for notching.
• Test apparatus and procedure: quasistatic loading arrangements, displacement measurement (e.g., clip gauges), and test control consistent with fracture toughness measurement.
• Post‑test analysis and reporting: metallographic sectioning and assessment, determination of K, δ and J values, handling of phenomena such as pop‑in, and standardized test report requirements.
• Limitations: describes point measurements only - it is not a method for producing valid R‑curves, though specimen prep methods may be reused when determining resistance curves.

Practical applications

• Assessing weld integrity and fracture resistance for pressure vessels, pipelines, structural steel, and heavy engineering components.
• Supporting welding procedure qualification, failure investigation, and fracture‑mechanics assessments in design and safety cases.
• Informing material selection and weld process optimization where weld metal or HAZ toughness is critical.
• Generating defensible fracture toughness data for fitness‑for‑service evaluations, certification, and regulatory compliance.

Who should use ISO 15653:2018

• Materials and welding engineers
• Fracture mechanics and metallography laboratories
• Quality assurance/quality control (QA/QC) teams in fabrication and construction
• Research organizations evaluating weld performance
• Certification bodies and regulators specifying fracture toughness criteria

Related standards

• ISO 12135:2016 - Unified method of test for quasistatic fracture toughness of parent metal (to be used in conjunction with ISO 15653).
• Other national/industry standards on fracture testing and weld qualification that reference CTOD, J‑integral, or K‑based assessment methods.

Keywords: ISO 15653:2018, fracture toughness of welds, quasistatic fracture toughness, CTOD, J‑integral, stress intensity factor, fatigue precracked specimens, HAZ, weld testing, specimen preparation, pop‑in.