An experimental investigation of normal and shear stress interaction of anepoxy resin and model predictions

The axial-torsional inter-action of an epoxy resin was investigated by subj ecting thin-walled tubular specimens to combined normal and shear stress co mponents. It is shown that a superimposed normal stress (tensile or compres sive) or hydrostatic pressure will influence shear creep behavior. Similarl y, a superposed shear stress affects the normal stress response of the resi n. The axial-torsional stress interaction is also observed in transient str ess responses under different strain paths, and in the creep deformation wi th non-proportional stress histories. Linear viscoelastic constitutive mode ls are unable to predict the aforementioned behaviors. Two typical nonlinea r viscoelastic constitutive models are examined with respect to their capab ilities to predict the observed response. It is shown that the predictions of these two models agree only qualitatively but not quantitatively with th e experimental results.