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Abstract

A study of the influence of the state and mode of cure of an epoxy resin, diglycidyl ether of bisphenol A cured with 4,4′-diaminodiphenylmethane, has been made. The state of cure was assessed by differential scanning calorimetry as residual heat of reaction and a transition temperature T* corresponding to either the melting point or the glass transition temperature. The state of cure was varied by controlling both the time and temperature of cure. Bond strengths can be related to either Tg or residual heat of reaction, but the different cure schedules produce different relations; simultaneous measurement of both parameters is necessary to specify the state of cure. Some additional work has been carried out on the effect of delayed cure on bond performance and on the effect of varying the cure schedule for a phenol-formaldehyde adhesive. Both single- and double-overlap joints have been used and a constant single/double bond strength ratio has been found. This constant is different for the two adhesives, reflecting their different behavior in shear.