Determination of the Mode I critical J-integral of copy paper

•Mode I critical J-integral of copy paper are investigated by two different methods.•The tests are conducted under varying the crack length.•The J-integral was measured effectively by considering the additional crack length.

Centre-notched tension and double-edge-notched tension tests were conducted using specimens of copy paper in order to determine the Mode I critical J-integral. The crack length was varied during the test, and the effects of the test method and crack length were examined. The critical J-integral obtained from the centre-notched tension test was significantly smaller than that obtained from the double-edge-notched tension test. In both tests, the critical stress intensity factor decreased as the initial crack length increased. When the crack length correction was performed, however, the Mode I critical J-integral could be accurately obtained while reducing the aforementioned dependencies.