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

The relation between the magnitude of low-temperature relaxation and t oughness was investigated for epoxy resins cured with some position is omers of naphthalenediols. A well-defined relaxation was observed near room temperature for a system cured with 2,6-dihydroxynaphthalene. Th e relaxation was denoted here as the beta'-relaxation. The values of t he stress intensity factor, K-C, in this system was considerably highe r than those of the other cured systems in the temperature region over the beta'-relaxation temperature. This is explained by the increase i n the plastic deformation region at the crack front with an increase i n the temperature near the crack tip caused by the presence of the bet a'-relaxation. (C) 1994 John Wiley and Sons, Inc.