Environmental stress cracking in e-glass and aramid/glass epoxy composites
Krystyna Imielińska Politechnika Gdańska, Wydział Mechaniczny, Katedra Inżynierii Materiałowej, Narutowicza 11/12, 80-952 Gdańsk
Quarterly No. 4, 2006 pages 19-23
DOI:
keywords: laminates, polymer composites, environmental stress cracking
abstract Glass fibre reinforced polymer composites (GFRP) show relatively low degradation in various corrosive environments in the unstressed state, however, they are very susceptible to stress corrosion, especially in dilute mineral acid environment. The stress corrosion crack propagation characteristics in glass fibre/epoxy laminates have been studied by several investigators. However, there is no relevant data on the behaviour of hybrid aramid-glass fibre polymer laminates (A-GFRP), now employed in construction of special vessels for naval and sport use. Due to high water absorption in aramid/epoxy laminates (5÷6%) hybrid aramid-glass/epoxy composites may be susceptible to early cracking. Accordingly, in the present work environmental stress cracking characteristics of GFRP and (A-G)FRP were studied using CT (fracture mechanics) samples (Fig. 1) under constant tensile load and water environment. For GFRP the characteristics of crack length as a function of exposure time (up to 3 months) were obtained (Fig. 3). The threshold stress intensity factor for environmental crack growth was found KI = 15 MPa ⋅ m1/2 in water compared to 22 MPa ⋅ m1/2 in air (Fig. 4). In hybrid (A-G)FRE composite only surface resin crack was found (Fig. 5) accordingly compared to GFRP (A-G)FRE composite was found practically immune to the environmental stress cracking in the conditions used in this study. Ductile aramid fibres seemed to protect the glass fibre reinforcement from stress cracking due to higher chemical resistance and complex failure mechanisms (Fig. 6).