ISO 7539-2:1989

Overview

ISO 7539-2:1989 specifies procedures for the design, preparation and use of bent-beam specimens for stress corrosion testing of metals and alloys. The standard covers specimen forms drawn from common product types (sheet, plate, flat extrusions, wire, rod) and is intended for evaluating susceptibility to stress corrosion cracking (SCC) under nominally constant strain or constant load. It is part of the ISO 7539 series and is normally read together with ISO 7539‑1 (general guidance).

Key topics and technical requirements

• Specimen types and dimensions: Bent-beam specimens are normally rectangular strips or circular-section wire/rod; typical widths and lengths are given (e.g., widths ~15–50 mm, lengths ~110–250 mm). For high‑strength materials recommended thickness ranges and span values are provided (examples in the standard: thickness ~0.8–1.8 mm with spans ~175–215 mm).
• Loading modes: Detailed guidance on two‑point, three‑point and four‑point bending, lever loading and full‑length loading. The standard provides formulas and empirical factors to calculate maximum tensile stress and bending deflection for the convex surface.
• Surface preparation and marking: Requirements for identification marks (at specimen ends), degreasing before testing, and recommendations to machine or grind away surface layers (typically ~0.25 mm) when comparing alloys to remove surface condition effects.
• Restrictions on treatments: Warnings against chemical/electrochemical treatments that can produce hydrogen or selectively attack phases; advice on avoiding residual machining effects and controlling surface condition.
• Test conditions and variability: Bent‑beam testing is suitable for multiple and atmospheric stress corrosion tests; the standard notes large data scatter is possible and recommends repetition. It also addresses possible relaxation during elevated‑temperature exposures and how to assess it.
• Safety: High‑strength materials may fracture rapidly and eject fragments - personnel protection and handling precautions are explicitly required.

Applications and users

ISO 7539‑2 is used to:

• Evaluate SCC susceptibility of sheets, plates, extrusions, wires, rods and welded assemblies.
• Support materials selection, quality control and failure analysis for industries such as aerospace, automotive, oil & gas, and corrosion testing laboratories.
• Assess coating or weld protection performance using bent‑beam arrangements.

Primary users:

• Corrosion/materials engineers, test laboratories, R&D teams, QA engineers, and failure investigation specialists.

Related standards

• ISO 7539‑1 (general guidance for stress corrosion testing)
• Other parts of the ISO 7539 series (Parts 3–8) covering U‑bend, tensile, C‑ring, pre‑cracked, slow strain rate and welded specimen methods.

Keywords: ISO 7539-2, bent-beam specimens, stress corrosion testing, stress corrosion cracking, SCC testing, specimen preparation, bending load methods, surface finish, corrosion test standard.