ISO 22088-3:2006

Overview

ISO 22088-3:2006 - Plastics: Determination of resistance to environmental stress cracking (ESC) - Part 3: Bent strip method specifies a laboratory procedure to rank the resistance of thermoplastics to environmental stress cracking when subjected to a fixed flexural strain in contact with chemical agents. The bent strip method detects ESC by monitoring a chosen indicative property (visual cracks, mechanical property loss, etc.) of flat or sheet specimens that are clamped over forms of defined radius and exposed to liquids, gases or migrating solids (e.g., adhesives or plasticizers). This is a ranking test and is not intended for design or quantitative performance prediction.

Key topics and technical requirements

• Test principle: Specimens are bent over a circular form (constant radius) to impose a nominal flexural strain in the tensile surface; a series of decreasing radii produces increasing strain levels. After defined exposure, specimens are examined and tested for failure according to selected criteria.
• Indicative properties & failure criteria: Visual cracking/crazing on the tensile surface; or mechanical reductions such as:
  • Tensile stress at break / stress at yield - failure when ≤ 80% of unexposed value
  • Flexural stress at maximum load - failure when ≤ 80% of unexposed value
  • Strain at break / yield - failure when ≤ 50% of unexposed value
  • Charpy unnotched impact - failure when ≤ 50% of unexposed value
• ESC index: Ratio of failure strain in test medium to failure strain in reference medium (usually air).
• Apparatus & specimens: Forms (chemical-resistant, perforated optional), light clamps, vessels for test medium, micrometer, and apparatus for indicative-property testing. For 2–4 mm specimen thickness, recommended form radii are ~30 mm to 500 mm.
• Conditions & procedure:
  • Specimen conditioning: typically 48 h at (23 ± 2) °C and (50 ± 10)% RH unless otherwise agreed.
  • Test temperature: normally (23 ± 2) °C; other temperatures (40 °C or 55 °C) by agreement.
  • Minimum of three specimens per strain level (including zero strain).
  • Maximum applied strain must be less than the strain at yield.

Applications

• Ranking material sensitivity to environmental stress cracking for sheeted thermoplastics and flat components.
• Screening materials when selecting polymers, additives or adhesives where contact with chemicals or plasticizers is expected.
• Quality control, comparative R&D, supplier qualification, and failure-analysis investigations focused on surface-localized ESC phenomena.

Who uses this standard

• Materials engineers, polymer formulators, R&D laboratories, quality assurance teams, failure analysts, and manufacturers of plastic sheets and components.

Related standards

• ISO 22088-1:2006 - General guidance on ESC testing
• ISO 22088-2: Constant tensile load method
• ISO 22088-5: Constant strain method
• ISO 22088-4 and -6 - other ESC methods
• Reference mechanical test standards: ISO 178, ISO 527-2, ISO 179-1

Keywords: ISO 22088-3, environmental stress cracking, ESC, bent strip method, thermoplastics, flexural strain, ESC index, indicative property.