Determination of local strains and breaking behaviour of wet paper using a high-speed camera

In this study, the digital image correlation (DIC) method was used to determine local strains in paper strips during a tensile test. The grammage of never-dried LWC paper from the pilot paper machine was 38 g/m² and the dryness ranged from 50 to 75%. The maximal straining speed in the single-phase tensile test was 100 mm/s and the corresponding image acquisition rate was 9000 frames/s. The local maximal strain ε_MAX in every paper strip that was analyzed was larger than the strain at the break value ε_Break of the strip, as determined from the tension-strain curve. The largest ε_MAX to ε_Break ratio was about 1.7. It was possible to estimate the starting region of the fracture based on the measured local strains. In the single-phase tensile test, the fracture started lengthways along the strip from the zone with the largest local difference between the strains on the left and right edges of the paper strip. At that zone the fracture usually started from the edge of the strip where the local strain was larger. In the three-phase tensile test, the fracture started lengthways along the strip from the zone with the largest local strain. In this case, the fracture usually also started from the edge of the strip with more local strain of the two. The relaxation phase seemed to have a significant effect on the breaking behavior of the wet paper strip.