Slip lines in front of a round notch tip in a pressure-sensitive material

Plastic deformation in the form of slip lines is observed in front of notches in pure epoxy and robber-toughened epoxy specimens under four-point bending. In contrast to the case for pressure-insensitive materials, the angles between two families of slip lines emanating from notch surfaces are not 90°: they are smaller than 90 ° under tension, but they are larger than 90 ° under compression. For the pure epoxy specimen, the angles are almost constant throughout plastic zones, and the deviations of the angles from 90 ° are almost the same under both tension and compression. For the robber-toughened epoxy specimen, however, the angles are not constant throughout the plastic zone under tension although they are almost constant under compression. In addition, the angles for the robber-toughened specimen under tension are smaller than those for the pure epoxy specimen under tension, but the angles for the rubber-toughened specimen under compression are larger than those for the pure epoxy specimen under compression. Furthermore, theoretical slip lines are constructed around notches for pressure-sensitive perfectly plastic materials. These slip lines are in good agreement with the slip lines observed in the pure epoxy specimen.