A Thermographic Observation of the Out-of-Plane Tearing Process of Paper

Infrared thermography was employed to investigate the tearing process of paper. The development of stress concentration was observed as a local temperature change using thermal images. With increased beating for a sheet made from longer fibres (NBKP), the size of the area where heat was generated during the tearing process decreased— i.e. the degree of stress concentration increased. The ratio of heat generation to tear work was ~10%, which is smaller than the corresponding ratio for the in-plane tensile test. The contribution of bending energy partly explains this difference. The tear energy of NBKP sheets correlated well with the heat from pull out or failure of fibres, except for heavily beaten sheets.