ISO 5629:2017

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
  • Select ≥10 specimens per ISO 186; condition specimens per ISO 187; determine grammage per ISO 536.
• 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.