Transverse Shear Measurement for Corrugated Board and Its Significance

When a corrugated box is placed under vertical load the panel walls will deform out of plane and the propensity of the liners to move with respect to one another in this and similar situations is described by the transverse shear rigidity of the corrugated board. This has been largely a neglected property in the corrugated industry and is never measured routinely in manufacturing environments. However, loss of stacking strength in corrugated containers can potentially be attributed to the loss of transverse shear rigidity which can easily occur through the unobserved and immeasurable crushing of board in board converting operations. This diminished transverse shear resistance cannot be measured through usual quality measurements such as board caliper or flexural rigidity (4 point bending stiffness). For example, a typical 10 % loss of caliper from board crushing results in a 20% reduction in flexural rigidity but a 300% loss in transverse shear rigidity which in turn can affect the stacking strength more so than is predicted from combined loss of flexural rigidity and ECT. A method of measuring the MD and CD transverse shear as well as the twisting stiffness using a mechanical method of a torsional pendulum is described and demonstrated on a selected variety of corrugated boards. The sensitivity of the measurement to board crushing is shown by corresponding flat crush hardness values.