Effective adhesive modulus approach for evaluation of curing stresses

A study was performed to measure the curing stresses of several epoxy systems using the bimaterial beam approach. In addition, the stress relaxation profile of the adhesive bonded to the metallic strip (bimaterial strip) was compared to the relaxation profile of the bulk adhesive. It was found that the shape of the relaxation curves was consistent for both samples, but that the magnitude of the two curves differed. It is argued that the difference between the curves is a result of curing stress and that the long-term effective modulus as measured from the bonded adhesive should be used to establish the curing stress. Use of an improper modulus is one possible cause of confusion regarding the determination of curing stresses as reported in the literature.