ISO 5628:2019 pdf free.Paper and board – Determination of bending stiffness – General principles
for two-point, three-point and four-point methods.
resistance that a test piece offers to bending, in the region of elastic deformation Note 1 to entry: 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.From a testing point of view, the bending stiffness, Sb, may be evaluated in three principally different ways:
a) From the maximum slope of the curve achieved from recording force versus linear deflection (F/fl, or force versus angular deflection (F/a), see Figure 112]. The rate of testing shall be reported.
b) Applying a linear deflection or angular deflection and recording the force after a specified timeLl. This document gives suggestions for maximum allowable deflections for the various beam-bending methods. The time of application shall be reported.
c) Applying a force and recording the linear deflection or angular deflection after a specified time (References [3], [4], [5]). This document gives suggestions for maximum allowable deflections for the various beam-bending methods. The time of application shall be reported.The two-point method is suitable for paper and low-thickness board. For corrugated board, the two- point method is not recommended. The bending according to the two-point bending method can be performed in two ways. In Figure 2, the beam-shaped test piece is clamped at one end and subjected to a force, F, acting perpendicular to the surface of the test piece at the start of the test, at a bending length, I, from the clamp. The linear deflection,J of the test piece is the shift in the point of application of the force in the direction in which it acts. In Figure 3, the beam-shaped test piece is clamped at one end in a clamp that rotates and is subjected to a force, F, acting perpendicular to the surface of the test piece at the start of the test, at a bending length, 1, from the clamp. The bending angle, a, is the angle through which the clamp is rotated during the test.The three-point method is suitable for paper and low-thickness board. For corrugated board, the three- point method is not recommended.
NOTE 1 It is possible to usc the three-point bending method for corrugated hoard, if very long test pieces arc used. The test method is not suitable for test pieces of recommended dimensions used for paper and hoard, due to the shear strain of the corrugated board1I. The suitable dimensions depend on the material to he tested and no absolute values can he stated in this document. The beam-shaped test piece is supported close to each end and is subjected to a force, 2F, in the centre perpendicular to the test-piece surface at the start of the test, see Figure 4. ISO 5628 pdf download.