Anisotropy of fatigue breakdown of filled amorphous polymers

Abstract

1. The periodical expanding stressing of filled amorphous polymers leads to the accumulation of oriented defects over the whole bulk of the material. 2. In the case of the PNM-2 resin with PVC the difference between the elasticity modulus in the direction of the preliminary periodical stressing and perpendicularly to this direction reaches 8%; the difference between the ultrasound propagation velocities, 11.2%. The concentration of defects after periodical stressing varies from N=0.2 · 105 cm−3 to N=0.54 · 105 cm−3 and the dimensions of the cracks from 100 to 150μm. This dimension is slightly larger than the particle size of the filler. Short cyclic stressing at a temperature close to the vitrification temperature can lead, in addition to an accumulation of defects, to an orientation of the material and to an increase in the elasticity modulus in comparison with the undamaged material. 3. The influence of defects on the mechanical characteristics of filled amorphous polymers becomes more evident as the temperature of brittleness of the materials tested is approached. In order to eliminate unwanted effects of viscosity and plasticity in the study of the effect of damages it is recommended to test the materials at T ≪ Tv. 4. The anisotropy of the fatigue damages can be established on the basis of the propagation of ultrasound in the cases where the wavelength of the ultrasonic oscillations is of the same order as the dimensions of the defects. 5. The elastic characteristics of the damaged material, calculated from theory with account of the concrete character of the structure of the defects, are in good agreement with the experimental data.