Stress relaxation processes survey in strain composite with an epoxy matrix

Abstract

The present paper gives results from a study of the relaxation of internal stresses in a granular composite with an epoxy matrix. We studied samples of ED-20 epoxy resins cured by polyethylene polyamine. As the filler we used powdered copper oxide with a volumetric concentration 0.064–0.35. The samples had the shape of cylinders of diameter 8 mm and height 30 mm. The experiments are performed with the use of nuclear quadrupole resonance (NQR). Measurements are made of the 63-Cu NQR-frequencies in samples as of epoxy resin containing cuprous oxide powder as control sample – pure cuprous oxide powder. In the description of the results of the NQR experiments, the value of internal stresses is given in frequency units. We held experimental research on cylindrical samples of granular composite with epoxy matrix hardened at high temperature. These samples were subjected to uniaxial compression at room temperature. Deformation of the samples led to an increase NQR frequency of the filler. The change in the value of internal stresses during heating of deformed samples of a granular composite was experimentally investigated. Measurements were made of the frequency difference for copper oxide in the polymer and control samples in the temperature range 393–293 K at 10 K intervals. Stresses in the matrix and the frequency difference decreases with increasing temperature. The observed nonlinearity of the temperature dependences of the NQR frequencies for the filler indicates the presence of relaxation processes in the stressed matrix of the samples at temperatures below the glass transition temperature. It is shown that the process of relaxation of stresses caused by the deformation of the sample is well described by an exponential dependence. The activation energy of this process was 105 kJ / mol. Comparison of the calculation results with the experimental data has shown their satisfactory comparability. Similar experiments were conducted with samples having an epoxy matrix cured at room temperature. It was found that stress relaxation occurs at temperatures well below the glass-transition temperatures.