RATE MECHANISM OF PLASTICITY IN THE CRYSTALLINE COMPONENT OF SEMICRYSTALLINE NYLON-6

The rate mechanism of crystal plasticity was studied in quasi-single crystalline (QSC) Nylon 6 prepared by plane strain compression in a channel die to equivalent extensional strains on the order of 1.39. Specimens of such highly oriented material were probed in simple shear experiments on the (001)[010] and (100)[010] monoclinic chain slip systems by means of strain rate change experiments in the temperature range of 255-366 K. These experiments demonstrated that while there is a well developed glass transition in the shear moduli of the material there is no corresponding transition in the plastic resistances, indicating that the plastic behavior of the QSC material is derived entirely from the crystalline component. Analysis of the experiments with reference to dislocation mechanics has disclosed that the plastic shear resistance for the chain slip systems is made up of several components. These include an athermal component due to random internal stresses of misfit, a lattice resistance, most probably affecting only the screw dislocations, and a terminal nonhardening flow resistance due to close range interaction of these dislocations with a family of small crystalline packing imperfections such as chain crossovers, slack pockets, etc. Activation analysis has indicated that the activation volumes Delta upsilon(*) governing this interaction are linearly dependent on stress, resulting at zero stress in Delta upsilon(*) = 6 x 10(-21) cm(3) for the (001)[010] chain slip system and 2.73 X 10(-21) cm(3) for the (100)[010] chain slip system. Moreover, from the stress level where the activation volume vanishes athermal overall shear resistances of 8.2 % and 14.2% of the respective shear moduli of the (001)[010] and (100)[010] slip systems are obtained respectively. Experiments were also carried out on untextured Nylon 6 for purposes of comparison. These gave results intermediate to those of the chain slip systems.