PROGRESSIVE DAMAGE IN PAPER

The local strain field and debonding of fibers (''damage'') were measu red simultaneously during the tensile testing of paper specimens. The results suggest that the local material laws - and particularly the fi nal rupture point - of the papers studied in CD were determined primar ily by the drying shrinkage. No universal values were found for the lo cal strain or damage at ruptures. Structural non-uniformity of the ent ire specimen controlled the distribution of external strain within it. A non-uniform structure leads to an effective concentration of strain and damage in low grammage areas so that high grammage areas are left practically intact. As a result the average age external elongation a t the point of final rupture is much smaller than the local strain int he rupture zone. In more uniform structures the difference between hi gh and low grammage areas is smaller and the external breaking strain is higher.