ISO 22088-4:2006

Overview

ISO 22088-4:2006 specifies the ball or pin impression method for determining resistance to environmental stress cracking (ESC) of plastics by a constant‑strain test. The method applies to finished products and to specimens prepared by moulding or machining. Tests expose specimens with impressed balls or pins to chemical environments (or air) to assess ESC behaviour and to compare materials or environments. The standard is part of the ISO 22088 series on ESC testing.

Key topics and technical requirements

• Test principle: Drill and ream a hole, insert an oversize ball or pin to impose a constant local strain, expose the specimen to a test environment, then assess cracking visually or by mechanical testing.
• Specimen types:
  • Type A: Finished products - assessed visually for cracks (×5 magnification).
  • Type B: Moulded/machined specimens - evaluated by tensile or flexural testing to defined failure criteria.
• Failure criteria (Type B): reductions relative to deformation‑step zero, e.g. ~5% reduction in maximum tensile or flexural force, or ~20% reduction in tensile elongation at rupture (as specified).
• Deformation series: Successive “oversize” steps (ball/pin diameters progressively larger) beginning with a zero‑deformation baseline.
• Apparatus & dimensions: drills (≈2.8 mm), reamers (≈3.00 mm), polished balls/pins with tight diameter tolerances (±0.001 mm up to 4 mm), pin geometry and surface roughness requirements (pins with parallel section 10–50 mm, Ra preferably <0.02 µm).
• Material suitability: Well suited for amorphous plastics; less appropriate for materials with strong creep or stress relaxation (semi‑crystalline materials - pins preferred if tested).
• Test conditions: Conditioning per relevant ISO standards, controlled test temperature, compatible immersion vessels and chemical media; results may be compared with a reference environment (e.g., air).

Practical applications and users

• Use ISO 22088-4 to:
  • Screen materials for susceptibility to environmental stress cracking in specific chemicals.
  • Compare ESC resistance of different grades or production lots.
  • Evaluate finished parts (Type A) and standardized specimens (Type B) for quality control and failure analysis.
• Typical users:
  • Plastics manufacturers and compounders
  • Materials and polymer engineers
  • Independent testing laboratories and QA departments
  • Product designers concerned with chemical exposure and long‑term durability

Related standards

• ISO 22088 series: Part 1 (general), Part 2 (constant tensile load), Part 3 (bent strip), Part 5 (constant tensile deformation), Part 6 (slow strain rate).
• Other referenced standards for specimen prep and testing: ISO 178, ISO 291, ISO 293, ISO 294-1, ISO 527‑1/2, ISO 2818, ISO 3167, ISO 3290, ISO 4287.

Keywords: ISO 22088-4, environmental stress cracking, ESC testing, ball impression method, pin impression method, plastics testing, constant-strain test, test specimens.