Researchers: Mikko Korteoja, Petri Tonteri, Petri Hirvonen, and Kimmo Kaski
We have devised an experimental method to examine the correlation between the evolving strain field and the onset of local damage in paper tensile specimens. Local strains and damage are determined with the video image correlation technique and silicon impregnation method. The strain measurement is based on digital image acquisition and subsequent image analysis while the silicon impregnation method  relies on enhanced light scattering at the locations of structural damage. We used this method to study damage accumulation in a set of paper tensile specimens.
The results suggest that the local material laws - and particularly
the local rupture point - of the specimens were determined
primarily by the drying shrinkage . No universal
values were found for the local strain or damage at rupture.
formation, controlled the distribution of external strain within the
specimen. A non-uniform structure leads to an effective
concentration of strain and damage into low grammage areas so
that high grammage areas are left practically intact. As a result
the average external elongation at the point of final rupture is
much smaller than the local strain in the rupture zone. In more
uniform structures the difference between high and low grammage
areas is smaller and the external breaking strain is
|Figure 10: Snapshots of the cross section of the silicon impregnated paper before (on the left) and after (on the right) straining. Local ruptures between fibers are clearly visible.|