Investigation of the deleterious effects of low-temperature and hygrothermal aging conditions on the mixed-mode fracture resistance of epoxy resin using a short-beam bend specimen

The effect of different environmental aging conditions on the mixed-mode fracture behavior of epoxy resins was investigated using a sub-size specimen. The short-beam bend (SBB) specimens with different crack inclination angles were manufactured and subjected to low-temperature (-71 degrees C), hygrothermal (immersion in deionized water at 60 degrees C) and room-temperature conditions. The deleterious effect of low-temperature and hygrothermal aging conditions on the mode-I, mode-II and mixed-mode I/II fracture responses of the epoxy resin was studied by testing the aged and unaged SBB specimens under three-point bend loading. The experimental results indi-cated that the hygrothermal aging condition, with a reduction of 49% in the effective fracture toughness, imposed a more severe deleterious effect on the fracture response of the specimens in comparison with the low -temperature condition with a decrease of 35% in the effective fracture toughness. The generalized maximum tangential stress criterion was used to predict the fracture loads of the aged and unaged specimens. Moreover, optical microscopy and scanning electron microscopy techniques were employed to assess the fracture surfaces of the specimens aged under different conditions.