ISO 22889:2013

Overview - What ISO 22889:2013 covers

ISO 22889:2013 defines laboratory methods for measuring the resistance of homogeneous metallic materials to stable crack extension using low-constraint specimen geometries. The standard specifies quasistatic, displacement-controlled tests on fatigue-precracked, notched compact and middle-cracked tension specimens to produce crack extension resistance data in two complementary forms:

• Crack opening displacement (δ5) - COD measured over a 5 mm gauge length at the fatigue precrack tip.
• Crack tip opening angle (CTOA, ψ) - angle measured (or calculated) at 1 mm from the current crack tip; a critical CTOA (ψc) is defined as the steady-state value after sufficient crack extension.

ISO 22889 describes both multiple‑specimen and single‑specimen test techniques (single‑specimen methods may use unloading‑compliance or potential‑drop measurements) and procedures for constructing an R‑curve (δ vs. Δa) and determining fracture toughness point values where applicable.

Key technical topics and requirements

• Specimen types: compact specimens and middle‑cracked tension specimens in relatively thin gauges (low constraint to plastic deformation).
• Precracking: fatigue precrack following machining of a starter notch.
• Test control: quasistatic, slowly increasing displacement; measurement of force, δ5 and ψ during testing.
• Measurement methods:
  • Multiple‑specimen: each specimen loaded to different displacements, crack extension measured post‑test.
  • Single‑specimen: unloading‑compliance or potential‑drop techniques (must meet specified accuracy).
• Data outputs: δ5 R‑curve, critical CTOA (ψc), and point fracture toughness values (compact specimens per ISO 12135; methods for M(T) specimens in Annex D).
• Behavioral notes: δ5 R‑curves are unique only within specified crack extension limits-beyond that, compact specimen δ5 R‑curves can depend strongly on specimen width while M(T) curves are less width‑sensitive. CTOA is more experimentally demanding but can apply over larger crack extensions.
• Structural application: δ5 enables simpler assessments using established crack‑driving formulae; CTOA generally requires numerical methods (finite element analysis) for structural predictions.

Practical applications and who uses ISO 22889

ISO 22889 is used for:

• Characterizing material resistance to ductile crack growth in thin components or tension‑dominated loading.
• Producing R‑curves and fracture parameters for structural integrity assessments, material qualification, research and development, and fracture mechanics validation.
  Typical users include materials/test laboratories, fracture‑mechanics engineers, R&D groups, and structural integrity assessors who require accurate crack growth resistance data for numerical modelling or design assessments.

Related standards

• ISO 12135 - unified method for quasistatic fracture toughness (point values).
• ISO 3785, ISO 7500‑1, ISO 9513 - referenced for specimen axis designation, testing machine verification, and extensometer calibration.

Keywords: ISO 22889, crack opening displacement δ5, CTOA, crack tip opening angle, R‑curve, fracture toughness, low constraint specimens, compact specimen, middle‑cracked tension, single‑specimen, multiple‑specimen, unloading compliance, potential drop, finite element analysis.