The evolution of the lateral contraction ratio of two commercial (high and low temperature cure) epoxy resins is studied in uniaxial tension using moire' interferometry. The ratio of transverse to axial strains evolves from an elastic value of about 0.40 to a rubbery plateau value of 0.49 at long times. Furthermore, the data indicate that the contraction ratio follows time- temperature superposition with a shift function indistinguishable from other axial viscoelastic functions. The lateral contraction behavior at several cure states past gelation was measured and a model is proposed to describe the cure dependence.
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