Overview
ISO 5629:2017 - "Paper and board - Determination of bending stiffness - Resonance method" specifies a dynamic, vibration-based test for measuring bending stiffness of papers and boards. The method determines a single bending-stiffness value per test piece by measuring the material’s vibrational resonant length (at a fixed frequency) and its grammage. ISO 5629:2017 is the second edition (2017) and replaces the 1983 edition with minor revisions (added precision data and bibliography).
Key topics and requirements
- Scope and limitations
- Applies to a wide range of papers and boards but is not applicable to corrugated board.
- Values may not strictly represent bending stiffness for multi-ply materials whose plies can move, papers with appreciable curl (especially when curl axis is along the test piece), or very soft papers with grammage below ~40 g/m².
- Principle
- Measure the resonant length of a cantilevered test piece vibrating at a set frequency; calculate bending stiffness from resonant length and grammage.
- Bending stiffness (S) is related to Young’s modulus (E) and second moment of area (I) by S = EI / b (moment per unit width).
- Apparatus and test conditions
- Clamp (parallel metal plates), vibrator producing 25.0 Hz ± 0.1 Hz with amplitude ≤ 0.2 mm, stroboscopic lamp synchronized to the vibrator, and means to measure resonant length.
- Optional magnifier and movable lower clamp with scale.
- Measurement accuracy: resonant length to ±0.25 mm or ±0.5%, whichever is greater.
- Sampling and conditioning
- Procedures
- Two procedures: Procedure A (more accurate; individual grammage and length measurement per test piece) and Procedure B (faster; uses mean grammage).
- Results & reporting
- Calculation of bending stiffness from measured resonant length and grammage; reporting requirements and precision (repeatability) are specified.
Applications and who uses it
- Quality control in paper and board manufacturing to monitor stiffness properties linked to printability, convertibility, and product performance.
- R&D and material development for comparing stiffness across formulations, coatings, or ply structures.
- Packaging and converting engineers assessing flatness, folding behaviour, or stiffness-related performance for films, labels, cartons (excluding corrugated board).
- Independent test laboratories providing certified material property data.
Related standards
- ISO 186 - Sampling to determine average quality
- ISO 187 - Standard atmosphere for conditioning and testing
- ISO 536 - Determination of grammage
Keywords: ISO 5629:2017, bending stiffness, resonance method, paper and board testing, resonant length, grammage, clamp, 25 Hz vibration, test procedure, quality control.