Description of 'Hot Spots' Associated with Localized Shear Zones in Impact Tests

摘要

A heat sensitive film technique has been employed to give spatial resolution to the observation of 'hot spots' in the impact deformation of soft ionic or molecular crystals and in crystal-filled polymer composites. The temperature of these 'hot spots' is estimated to exceed 250 C for even modest impact loads. The heating is interpreted to depend on local shear deformation. The rise in temperature associated with the movement of a number of equally-spaced dislocations is reexamined. An additional multiplicative effect for the temperature rise due to the dislocation number is obtained if the dislocations are released as a pile-up avalanche from an internal obstacle. This rise in temperature carries over to the association of localized heating of 'hot spots' with cracking within polymers because of the equivalence in the continuum approximation of a dislocation pile-up and a physical crack. Two reasons for the heating effect being especially important at cracking sites are that they are typified by the largest internal concentrations of stress which the material can bear before local fracture occurs, and, in so doing, the new crack surfaces supply a ready 'sink' for the dissipation of the internal energies at the tips of shear zones.