Effect of Tear Rotation on Ultimate Strength in Reinforced Natural Rubber

International audienceVulcanized natural rubber samples reinforced with carbon black or precipitated silica are studied. Single edge notched reinforced samples stretched at constant velocity exhibit an abrupt instability in the direction of propagation of the crack. This phenomenon has been known as tear rotation. We analyze the impact of tear rotation on the tensile strength of the samples. A mechanism is proposed to relate the presence of tear rotations observed in reinforced natural rubber to the tensile strength of the material. The measured apparent tensile strength (in terms of energy at break) may be increased by a factor of 6 to 8 in some cases. This large increase in tensile strength associated to the presence of tear rotations is analyzed semi-quantitatively, based on energetic arguments, without entering into a detailed description of the elastic strain field in the vicinity of the tear tip. We also show a correlation between the length of a rotation and the stress level at which it appears. The proposed interpretation is based on the idea that tear rotations relax the local strain (or stress) at the tear tip by creating a macroscopic tip radius. Materials reinforced with carbon black or precipitated silica aggregates show similar behavior