Fracture of High Polymers

Abstract

Abstract General considerations of the physics of failure of high polymeric substances were reviewed using the example of one dimensional testing. It is shown that classical failure theory can be applied only with difficulty to viscoelastic substances. Relations between macroscopic failure properties and the parameters of test are reviewed. Several recent investigations have shown a direct relation between relaxation time spectra of high polymers and breaking energy, tensile strength, and elongation at break through their dependence on time and temperature. Finally, the relation between microscopic failure properties and experimental parameters are discussed. The processes occurring at the tip of the failure are determined by relaxation mechanisms just as are the processes which lead to sites of failure in the macroscopic specimen. These are illustrated by recent work in which the specific tearing energy is determined as a function of time and temperature of tearing. From all of the work referred to here, it follows that the very complicated relations at fracture of high polymers are essentially determined by their mechanism of molecular motion in a way analogous to other mechanical properties and are therefore determined by their molecular structure.