Comparison of Thermal Maps with Damage Revealed by Silicone Impregnation

Two different techniques are used to detect local straining and failure in order to study the fracture process in paper. Thermography is used to measure the local temperature variations. Ebeling has found that during the apparent elastic straining heat is absorbed by the specimen and during destraining heat is correspondingly generated. During the apparent plastic straining heat is generated irreversibly. Another technique, a silicone impregnation, reveals bond ruptures. It has been used to measure the extent of bond ruptures from the crack line in paper.Two beating sets and two mixture sets of chemical and mechanical pulps were used to study fracture. In the in-plane tear test the shape of the FPZ measured by using the two detection techniques is similar. However, the area where temperature increases during the tear test is larger than the area of bond ruptures revealed by the silicone technique. This is consistent with Ebeling’s observation on heat generation during elastic destraining. The difference is used to evaluate the contribution of elastic recoil and plastic deformations on energy consumption in different samples.The local temperature profiles ahead the crack tip are compared with damage profiles measured by using the silicone impregnation to analyze the process of fiber debonding. In addition, thermography is used to compare tensile fracture in the short span test with tear fracture. After the crack nucleation, the tensile fracture resembles crack propagation in the tearing