BS ISO 5628:2019 pdf free.Paper and board – Determination of bending stiffness一General principles for two-point, three-point and four-point methods.
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, f, 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, I, 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 use the three-point bending method for corrugated board, if very long test pieces are used. The test method is not suitable for test pieces of recommended dimensions used for paper and board, due to the shear strain of the corrugated board[5], The suitable dimensions depend on the material to be tested and no absolute values can be 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.It is assumed in Formulae (2) and (3) that the bending occurs with negligible influence of inter-laminar shear strain. This strain depends theoretically on the ratio of inter-laminar shear stiffness to tensile stiffness and the ratio of the thickness to the bending length. In order to minimize the impact of inter-laminar shear strain on the result, the length I shall not be less than approximately 40 times the thickness of the test piece for paper and board, see Reference [5]. In this document, no particular requirement is stipulated for the width of the test piece. The choice of width has to be selected by the user and be suited for a particular testing equipment. The width shall be reported.BS ISO 5628 pdf download.