Overview
EN ISO 7539-2:1995 (ISO 7539-2:1989) describes procedures for designing, preparing and using bent-beam specimens for stress corrosion testing of metals and alloys. The standard is part of the ISO 7539 series on corrosion of metals and alloys - stress corrosion testing and must be read with ISO 7539-1 for general test guidance. Bent-beam tests are especially suitable for multiple testing and atmospheric stress corrosion tests, typically conducted under nominally constant strain (or nominally constant load) conditions.
Key topics and technical requirements
- Specimen types and product forms: flat strips from sheet, plate or extruded sections; also wire, rod or machined circular-section specimens. Welded parts can be tested.
- Surface preparation: retain original surface where appropriate; remove surface layers (e.g., 0.25 mm) by machining/grinding to exclude surface-condition effects; degrease before testing and avoid contamination.
- Loading methods: constant-strain configurations including two-point, three-point, four-point, double-beam, lever-loaded and fully-supported specimens. The document provides:
- approximate specimen dimension ranges (typical widths 15–50 mm, lengths 110–255 mm; example thin-strip thickness 0.8–1.8 mm with holder spans 175–215 mm),
- formulae for calculating elastic surface tensile stress for each loading mode and guidance on applicability (small-deflection limits).
- Stress calculation and validation: empirical and theoretical relationships are given; for accurate stresses attach strain gauges to companion specimens.
- Safety and material considerations: explicit warning that high-strength materials may fracture rapidly and fragments can be dangerous; personnel must be protected. Chemical/electrochemical surface treatments that produce hydrogen must not be used for hydrogen-susceptible alloys.
- Test interpretation: time-to-crack, threshold stress, and replication requirements because wide result variability can occur.
Practical applications and users
Who uses EN ISO 7539-2:
- Corrosion and materials engineers evaluating stress corrosion susceptibility
- Metallurgical laboratories and QA departments performing routine or comparative testing
- Manufacturers in aerospace, automotive, marine, oil & gas and structural industries verifying alloy performance and welds
- R&D groups comparing coatings, surface treatments, or heat treatments
Why it’s used:
- To simulate service bending stresses in the lab and determine threshold stresses and time-to-failure
- For multiple-sample screening and atmospheric exposure tests
- For comparative studies of alloys, welds and protective coatings
Related standards
Keywords: EN ISO 7539-2, bent-beam specimen, stress corrosion testing, corrosion of metals, constant strain testing, bent-beam test, specimen preparation, surface finish, stress calculation.
