Overview
ISO 18591:2015 defines a standardized testing method to determine the compressive strength of ceramic granules used in fine/advanced ceramics. The method measures granule behavior under uniaxial compressive loading in a confining die using a Universal Testing Machine (UTM), records the load‑displacement response, converts it to a pressure–density curve, and identifies the critical pressure (compressive strength) at the slope change.
Key topics and technical requirements
- Test principle: Compact granules in a cylindrical die, record load‑displacement, convert to pressure–density, determine compressive strength from intersection of two slope regions.
- Apparatus & accuracy:
- Cylindrical die (hard material; diameter 10–25 mm; height/diameter ratio 0.3–0.5).
- UTM capable of simultaneous load and displacement recording; accuracy per ISO 7500‑1, Grade 1 (±1%).
- Balance (≥10 g capacity, precision ±0.001 g) and micrometer (precision ±0.01 mm).
- Procedure essentials:
- Typical crosshead speed: 1 mm/min for compaction.
- Test performed on three independent test portions; report average densities.
- Optional granule drying: 110 °C ±5 °C for ≥24 h if required (do not dry granules containing volatile organics).
- Lubrication: die‑wall lubrication or powder lubricant (0.1–3.0 wt% solid lubricant) is allowed but must be reported - lubrication can significantly affect results.
- Data and results:
- Convert load‑displacement to pressure (load/area) and compact density; plot on a pressure (log scale) vs density curve.
- Compressive strength = intercept point of two linear regions of different slope.
- Reporting:
- Test report per ISO/IEC 17025 requirements, including material batch, test conditions (temperature/humidity), lubrication details, compact dimensions, pressure–density curve and comments.
Applications
ISO 18591 is used for:
- Quality control of ceramic granules and powder feedstocks.
- Process optimization for pressing and forming of advanced/technical ceramics (electronics, structural, biomedical ceramics).
- Predicting green density and compaction behavior for powder‑to‑component processes.
- Comparative testing between batches, suppliers, or formulation variants.
Who should use it
- Materials scientists and ceramic engineers
- Manufacturing and quality labs in advanced ceramics industry
- R&D teams developing powder formulations and granulation processes
- Accredited testing laboratories seeking reproducible compressive strength data
Related standards
- ISO 7500-1 (UTM calibration and accuracy)
- ISO/IEC 17025 (testing laboratory reporting and competence)
- EN 725‑10, JIS R1639‑5/6, KS L 1623 (related compaction/ceramic powder test methods)
Keywords: ISO 18591, compressive strength, ceramic granules, fine ceramics, advanced ceramics, pressure–density curve, uniaxial compressive loading, universal testing machine, powder compaction, test report.