Gradin, P.A., Graham, D., Nygård, P. and Vallen, H. (2007) The use of acoustic emission monitoring to rank paper materials with respect to their fracture toughness. Experimental Mechanics, 48 (1). pp. 133-137. ISSN 0014-4851 (Print), 1741-2765 (Online) (doi:10.1007/s11340-007-9055-7)

Gradin, P., Vallen, H., Graham, D., Nygard, P. and Gregersen, Ø.W. (2004) Acoustic emission testing of paper. In: Proceedings of the 2004 Progress in Paper Physics Seminar. NTNU (Norwegian University of Science and Technology) and PFI (Paper and Fibre Research Institute), Trondheim, Norway, p. 155. (Unpublished)