Morphology and micromechanics of liquid rubber toughened epoxies

In the present work, a diglycidyl ether of bisphenol A (DGEBA)-based epoxy resin was modified with the help of a liquid rubber (I,R) obtained from the pyrolysis of rubber. Tensile tests on samples of rubber modified epoxy resins (REs) containing varying rubber volume fractions (RVF) were conducted to obtain their tensile properties. Fractographic analysis of fractured samples using field emission scanning electron microscopy (FESEM) revealed the presence of phase separated rubber zones characterized by microvoids, distributed uniformly in the epoxy domain. Young's modulus and yield strength of REs were observed to drop with RVF. A three-dimensional (3D) finite element model was employed to predict the elastic properties and stress distributions in REs. Various stress distributions and their dependence on the properties of rubber were examined in detail through the model. The effect of rubber properties on bulk elastic properties of the REs were also studied. Lastly, the effective stress-strain relationship was predicted with the help of an elastic-plastic analysis. Predicted results showed coherence with experimental results.