ISO 5628:2012 pdf download.Paper and board – – – Determination of bending stiffness一General principles for two-point, three-point and four-point methods.
ISO 5628 specifies three test methods for determining the bending stiffness of paper and
paperboard. The test methods differ in the type of loading mode, thus giving rise to the two-point, three-point and four-point bending test methods.
For paper and paperboard in a low thickness range, the two-point bending method and the three-point bending method are suitable.
For corrugated fibreboard and board with a higher thickness, the four-point bending method is recommended.
The measurement conditions are defined in such a way that the test piece is not subjected to any significant permanent deformation during the test, nor is the range of validity of the equations for calculating the bending stiffness exceeded.
In these bending tests, the test pieces of paper and board are regarded as “beams” as defined by the science of the strength of materials, see Reference [1].
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 186, Paper and board — Sampling to determine average quality
ISO 187, Paper, board and puips — Standard atmosphere for conditioning and testing and procedure for monitoring the atmosphere and conditioning of samples
ISO 534, Paper and board — Determination of thickness, density and specific volume ISO 3034, Corrugated fibreboard — Determination of single sheet thickness
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
bending stiffness
Sb
resistance that a test piece offers to bending, in the region of elastic deformation
NOTE The theories used for the determination of bending stiffness are derived under the condition that the test piece is perfectly flat at the beginning of the test. In a real situation, the test piece always deviates from flatness. It is, however, not possible to give recommendations on the magnitude of such deviations (such as curl, twist, cockle or other deviations) that can be present and still produce a valid test.
4 Symbols and units
The following symbols are used for the equations in ISO 5628.
5 Theory
For a beam of a homogeneous material, with equal thickness and a constant modulus of elasticity in the plane of the paper or board, the bending stiffness Sb (per unit width I;) may be derived from the product of the modulus of elasticity, E, and the second moment of inertia, 1, of the test piece, divided by the width, b, of the test piece as shown in Equation.ISO 5628 pdf download.