The local compressive properties of paper in the z-direction as related to paper friction

Investigation into the structural and z-direction mechanical properties that influence paper friction may provide insight into friction. This investigation focused on evaluating the z-direction compressive characteristics related to paper friction.; Storage phosphor β-radiography was used to determine the local mass density of the paper sheet. This technique provides a number of experimental simplifications. Through the use of a computational technique developed in this work, storage phosphor β-radiography was shown to provide similar information about the distribution of mass density compared to traditional β-radiography.; The local compressive properties of paper were evaluated using a continuous indentation technique. An apparatus capable of recording the load/displacement curves for single paper sheets was developed. A novel Thin Material Analysis that compensates for the effect of thickness was developed to analyze the continuous indentation data. A measurement of hardness was also described.; A model of the compression of an oriented fiber mass that predicts an increase in the tangent modulus with the apparent density was developed. This relationship was shown experimentally for bulk samples, and found to be relatively independent of the densification method (i.e. refining, wet pressing, or calendering) or fiber type (bleached hardwood or softwood kraft).; The local compressive properties were mapped over a 45 x 45 mm area to a spatial resolution of 1 mm. The local variation in the tangent modulus within a single sheet was linked to the local sheet surface structure. This was demonstrated by correlations of the local tangent modulus with the local thickness variation and formation. The local apparent density had little detectable effect on the variability in the local tangent modulus.; The local hardness of the material was also investigated. It was found for a thin material with uniform elastic modulus that as the thickness decreases the measured hardness increases. The indentation hysteresis was found to decrease as the material hardness increases.; The static coefficient of friction was related to the co-variance of the local tangent modulus of the sheet. The variability in the compressive characteristics may create an effective rough surface during normal loading. This leads to an increase in the static coefficient of friction.