Anisotropy in Rupture Lines of Paper Sheets
  We have experimentally investigated the fracture process in paper samples submitted to a uniaxial force. Five types of paper sheets (newsprint, towel, sulfite, silk and couche papers) were fractured along two orthogonal orientations. In order to characterize the rupture lines of the paper sheets we utilized the Hurst exponent. Our results indicate a dependence of the Hurst exponent on the orientation of the paper sheets for samples of newsprint and, probably, towel and silk papers. For the other types of paper the Hurst exponent does not depend on the direction of crack propagation. 
I. L. Menezes-Sobrinho, M. S. Couto and I. R. B. Ribeiro