Overview
EN ISO 11782-2:2008 (identical to ISO 11782-2:1998) specifies a fracture‑mechanics method for corrosion fatigue crack propagation testing using precracked specimens. The standard describes how to produce a fatigue pre‑crack, conduct cyclic crack‑growth tests in controlled aqueous or gaseous environments, monitor crack length versus cycles, and derive crack growth rates (da/dN) as a function of the stress intensity factor range (ΔK). It is part of the ISO 11782 series on corrosion fatigue testing (Part 1 covers cycles to failure).
Key topics and technical requirements
- Test principle: induce a fatigue pre‑crack in a notched specimen, then determine da/dN vs ΔK under environmental and loading conditions representative of service.
- Data produced: crack growth rate curves (da/dN versus ΔK) and the threshold stress intensity factor range (ΔKth) below which growth is insignificant for the application.
- Specimen types: commonly used geometries include SENB3 (three‑point bend), SENB4 (four‑point bend), CT (compact tension) and CCT (centre cracked tension). Pin‑loaded CT specimens are unsuitable when R ≤ 0 because of backlash.
- Fracture‑mechanics sizing and constraint: specimen dimensions must provide predominantly plane‑strain (triaxial) crack‑tip conditions; follow established fracture‑toughness size criteria to avoid geometry artifacts.
- Precracking and loading: procedures for fatigue precracking, selection of waveform, stress ratio (R), frequency and environmental control are described to ensure reproducible ΔK and crack‑growth measurements.
- Environmental and artefact considerations: guidance on aqueous vs gaseous environments, effects of residual stresses, hydrogen charging, through‑thickness fluid transport and frequency‑dependent/time‑dependent cracking modes.
- Measurements and reporting: continuous crack‑length monitoring methods (see informative Annex A), numerical analysis to convert load/crack length to ΔK and reporting requirements.
Practical applications
- Provides quantitative inputs for lifecycle, fracture‑mechanics assessments and damage tolerance design where corrosion fatigue crack growth controls component life.
- Used for material selection, qualification and comparison of metals and alloys in marine, oil & gas, power generation, aerospace, automotive and infrastructure applications.
- Useful to corrosion/materials engineers, failure analysts, test laboratories, R&D teams and standards bodies conducting environmental fatigue testing and producing design data (da/dN and ΔKth).
Related standards
- EN ISO 11782-1 / ISO 11782-1 (corrosion fatigue - cycles to failure)
- ISO 7539-1 (stress corrosion testing - general guidance)
- National and international fracture‑mechanics specimen standards and test method documents referenced within EN ISO 11782-2
Keywords: EN ISO 11782-2:2008, corrosion fatigue, crack propagation testing, precracked specimens, ΔK, da/dN, fracture mechanics, CT specimen, SENB, corrosion testing.
