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Statistical variation of paper strength (FORMA)

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 [14] 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.

 
Figure 9:   The evolution of the local strains in paper under tensile elongation determined with the video image correlation technique and silicon impregnation method.
Figure 9

The results suggest that the local material laws - and particularly the local rupture point - of the specimens were determined primarily by the drying shrinkage [15]. No universal values were found for the local strain or damage at rupture. Structural non-uniformity, 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 proportionately higher.

Figure 10 Figure 10
  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.


next up previous contents
Next: Dynamic fracture of disordered Up: Computational Physics Previous: MATRA- and FORMA- projects
Juha Merimaa
1/2/1998