Investigation of the effect of hygrothermal conditions on epoxy system by fractography and computer simulation

Epoxy resins are attractive materials for many engineering applications, as they are low in density, have excellent mechanical properties and are easily fabricated by processes such as injection molding, extrusion and vacuum forming. However, the hostile humid environment can degrade the epoxy system because most epoxies absorb moisture. In this paper, the tensile fracture surfaces have been analyzed by a scanning electron microscopy (SEM) for the initial dry, moisture-saturated (preconditioned under hygrothermal conditions, 85 degrees C/85%RH) and completely desorbed (dry under thermal conditions, 85 degrees C) specimens, respectively. Furthermore, fracture surface patterns are simulated by computer, based on the theory that the conic-shaped pattern is due to the intersection between a moving planar crack front and a radically growing circular craze or secondary crack front. From the fractographic analysis and computer simulation results, it can be concluded that there is a close relationship between the velocity ratios u / v and the effect of hygrothermal conditions. Additionally, the transition of brittle/ductile appeared because of the effect of hygrothermal conditions. (C) 2005 Elsevier B.V. All rights reserved.