Bending stiffness and moment capacity of cardboard obtained from three-point and elastica bending tests

Abstract The bending properties of cardboard in the machine direction and cross direction were obtained via three-point bending and elastica bending tests using samples of various span lengths. The bending stiffness, moment at the proportional limit, and moment capacity per unit width were determined, and the effects of the testing method and span length were investigated. In the three-point bending test, the bending stiffness often decreased as the span length decreased because of the effect of the low interlaminar shear modulus of cardboard, and this tendency was more pronounced when the length direction of the sample coincided with the machine direction. Such dependence was less obvious in the moment at the proportional limit. In contrast, when the length coincided with the cross direction, the moment capacity of the cardboard often decreased as the span length increased because the large deflection prevented the accurate calculation of the moment capacity by using elementary beam theory. However, in the elastica bending test, both the bending stiffness and moment capacity could be obtained while reducing the effect of the span length. Therefore, to obtain the bending properties of cardboard, the elastica bending test was determined to be more advantageous than the three-point bending test.