ON CRACK STABILITY IN PAPER TOUGHNESS TESTING

The elastic energy stored in a double-edged notched tension specimen a t the moment of crack propagation initiation is analysed. The stored e nergy increases linearly with specimen length and, in the range of int erest, almost linearly with crack length. Experiments show somewhat su rprisingly that copy paper specimen dimensions contribute to the exter nal fracture work very much according to the linear elastic analysis. The specific essential fracture work of such a material cannot be dete rmined as proposed by Cotterell and Reddel, this obviously applying to most paper grades. The fracture work of extremely tough and ductile s ack paper appears to be independent of specimen dimensions as long as the sample is not longer than its width.