EFFECT OF THE LOW-TEMPERATURE RELAXATION ON TOUGHNESS OF CURED EPOXY-RESINS

The relation between the magnitude of low-temperature relaxation and toughness was investigated for epoxy resins cured with some position isomers of naphthalenediols. A well-defined relaxation was observed near room temperature for a system cured with 2,6-dihydroxynaphthalene. The relaxation was denoted here as the beta'-relaxation. The values of the stress intensity factor, K-C, in this system was considerably higher than those of the other cured systems in the temperature region over the beta'-relaxation temperature. This is explained by the increase in the plastic deformation region at the crack front with an increase in the temperature near the crack tip caused by the presence of the beta'-relaxation. (C) 1994 John Wiley and Sons, Inc.