Measuring the stress-strain properties of paperboard in the thickness direction

In this paper, a device for measuring stress-strain properties in the thickness direction of paperboard is presented. The device is used for out-of-plane tensile, compression and shear loading. In order to measure stress and strain accurately: the deformation of the test piece is restricted to two directions in the desired plane of deformation by means of an attached fixture. The paperboard is first glued io metal blocks with a high-viscosity adhesive and these blocks are then attached ro the device using a fast-curing epoxy adhesive. To find the true strain in the material, knowledge of the penetration nf the adhesive into the surface of the paper structure is important. A method for determining the penetration of the adhesive, based on a comparison of stress-deformation curves for glued and non-glued rest pieces, is presented, Finally: true stress-strain curves in tension, compression, and shear are presented together with an analysis of the accuracy of the method.