Overview
ISO 28704:2011 specifies a standardized test method for cyclic four‑point bending fatigue of porous fine ceramics (advanced/technical ceramics) in air at room temperature. The standard defines specimen geometry, test-fixture and machine requirements, loading waveform and precision, environmental recording, data treatment (including S‑N plots) and reporting rules for fatigue life of porous ceramics (typical porosity 30–60 %, pore size 1–100 µm).
Key topics and technical requirements
- Test scope: Cyclic four‑point bending fatigue of porous ceramics at room temperature in air.
- Specimen geometry: Rectangular beam, standard dimensions 70 mm ±0.5 mm length, 8.0 mm ±0.1 mm width, 6.0 mm ±0.1 mm thickness; edges chamfered/rounded 0.1–0.3 mm.
- Fixture spans & rollers: Four‑point flexure fixture (outer span 60 mm ±0.5 mm, inner span 30 mm ±0.5 mm); roller diameter 4–6 mm; bearing tip radius 2.0–3.0 mm; bearing material elastic modulus ≥ 140 GPa; surface roughness Ra ≤ 0.40 µm.
- Loading waveform & frequency: Sinusoidal cyclic stress with minimum‑to‑maximum stress ratio R = 0.1. Frequency selected by agreement (20 Hz recommended).
- Loading precision & instrumentation: Maximum stress fluctuation within ±1 %; R within ±5 %. Machines must record max/min load and cycle count and prevent auto‑restart after interruption. Use micrometers (0.01 mm), dial gauges (0.01 mm) and vernier calipers (0.05 mm) per referenced GPS standards.
- Test procedure: Measure flexural strength (same specimen shape) at 0.5 mm/min crosshead speed to set fatigue stress levels. Test at least three specimens at each of at least three maximum stress levels; do not reuse specimens. A “run‑out” may be recorded if a specimen survives 10 loading cycles (unless otherwise specified).
- Data treatment: Calculate maximum stress using σmax = 3Pmax(L − l) / (2 b d^2) and round to three significant figures. Present fatigue data as S‑N plots (stress vs. cycles, commonly log‑log). Record environmental temperature and humidity at start/end or hourly for long tests.
Applications and users
ISO 28704:2011 is used to assess the fatigue performance of porous ceramics applied as filters, catalyst carriers, humidity sensors and molecular sieves, helping manufacturers, R&D labs, quality control teams and materials engineers:
- Compare fatigue life across formulations and processing routes
- Specify performance limits for components subject to cyclic bending
- Support material selection and reliability assessments in product development
Related standards
Keywords: ISO 28704:2011, cyclic bending fatigue, porous ceramics, four‑point bending, fatigue test, S‑N plot, flexural strength, test fixture.
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