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 rubber-toughened epoxy specimens under four- point bending. In contrast to the case for pressure-insensitive materi als, the angles between two families of slip lines emanating from notc h surfaces are not 90-degrees: they are smaller than 90-degrees under tension, but they are larger than 90-degrees under compression. For th e pure epoxy specimen, the angles are almost constant throughout plast ic zones, and the deviations of the angles from 90-degrees are almost the same under both tension and compression. For the rubber-toughened epoxy specimen, however, the angles are not constant throughout the pl astic zone under tension although they are almost constant under compr ession. In addition, the angles for the rubber-toughened specimen unde r tension are smaller than those for the pure epoxy specimen under ten sion, but the angles for the rubber-toughened specimen under compressi on are larger than those for the pure epoxy specimen under compression . Furthermore, theoretical slip lines are constructed around notches f or pressure-sensitive perfectly plastic materials. These slip lines ar e in good agreement with the slip lines observed in the pure epoxy spe cimen.