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An instrument was developed for the rapid measurement of local mass density (formation) in fibrous networks and films using electron beam transmission (EBT) imaging. A transmission electron microscope (80 keV) was modified for use as a beam source for irradiating 5 cm×5 cm samples of paper or other fibrous webs. Local transmission of electrons through paper (directly proportional to the mass) was measured indirectly by video imaging of the pattern emitted by a Ca(Eu)F2 cathodoluminescing window supporting the specimen. The local optical density was also determined using a diffused electroluminescent lamp. A single CCD imaging system, with a spatial resolution of 0.1 mm, was used for both the electron and light transmission methods. EBT results were calibrated using mylar samples of known grammage. The irradiation sources and the detection system were characterized to establish the limits of operation and measurement capabilities. Electron beam flux was measured directly, and the attenuation curve for mylar correlated well with Monte Carlo estimation with an upper limit of ∼85 g/m2. For EBT imaging, procedures were established to prevent disruption of images by electrostatic discharging. Correction also was made for the back-reflected light that was a function of the reflectivity, R0, of the sample. A group of samples prepared from different pulps was imaged, and the actual grammages were compared with those determined from the instrument. The results demonstrated that, with few exceptions, good correlation existed.

Measured local paper structure—i.e. local basis weight, local thickness, local density and local fiber orientation—has been linked to local strain and local material failure (local temperature increase due to energy dissipation upon fiber–fiber bond failure) measured during tensile testing. The data has been spatially linked through data map registration delivering several thousand $$1\times 1\,\hbox{mm}^2$$ 1 × 1 mm 2 paper regions, each containing all measured properties. The relation between local paper structure and resulting local deformation and failure is studied with regression models. Multiple linear regression modeling was used to identify the paper structure related drivers for local concentrations of strain under load and local concentrations of material failure, which are both starting to occur considerably before rupture of the paper. Analyzing the development of local strain in paper we found that regions with higher basis weight and higher fiber orientation in load direction tend to exhibit considerably lower strain during tensile testing. Furthermore, the relation between local strain and local grammage can be predicted with the statistical theory of elasticity. Also regions with higher density have lower local strain, but not as pronounced. The findings for local fiber–fiber bond failure of paper are similar but not equivalent. The strongest correlation exists with local grammage. Local density and local fiber orientation show in turn weaker correlation with local bond failure. Local variations in paper thickness were not relevant in any case. These findings are highlighting the relevance of local fiber orientation and local density variations as structural mechanisms governing paper failure. In the past the focus has been mostly on paper formation. Together with local grammage (formation) they are responsible for the weak spots in paper, and thus cause local concentrations of paper strain and the initiation of failure under tensile load.