This paper presents the modelling of the stress strain response of glass fiber reinforced epoxy (GRE) composite pipes subjected to multiaxial loadings at room temperature (RT). This particular modeling work was developed to predict the non-linear stress strain response caused by the fatigue cyclic and static loading in the multiaxial ultimate elastic wall stress (UEWS) tests by considering the effects of matrix cracking within the laminates. The UEWS test, whilst not yet standardized, appears to offer an attractive alternative to existing procedures of qualifying GRE pipes. The ply properties initially expressed as a function of crack density were computed as a function of increasing stress and strain using shear lag approximation. The results show that the model developed from the classical laminate theory which takes into account whether the effects of transverse matrix micro-cracks on stiffness and strains is capable of predicting the resulted elastic properties. The predictions are found to be in good agreement with the data from multiaxial UEWS tests on ±55° filament wound glass-reinforced epoxy pipes.Keywords: Stress strain response; multiaxial loadings; composite pipes; cyclic and static loading; crack density.
INTRODUCTIONThe failure behavior of filament wound GRE pipes subjected to biaxial load has been the subject of numerous experimental and modelling investigations spanning decades, as demonstrated in the literature (Bachtiar, Sapuan, & Hamdan, 2010;Carvalho & Marques, 2007;Frost & Cervenka, 1994;Gibson, Saied, Evans, & Hale, 2003a, 2003bHale, Shaw, Speake, & Gibson, 2000;Hull, Legg, & Spencer, 1978;Jeffrey, Tarlochan, & Rahman, 2011;Meijer & Ellyin, 2008;Mertiny & Ellyin, 2006;Ravi Sankar, Srikant, Vamsi Krishna, Bhujanga Rao, & Bangaru Babu, 2013;Salleh, Yusop, & Rosdi, 2013;Tarakcioglu, Gemi, & Yapici, 2005). The majority of such investigations have emphasized failure envelopes, fatigue strength, leakage and the associated deformation of angle ply laminates similar to those used in GRE pipes. However, whilst most of these studies concentrated on structural failure in composite pipes, the more significant issue of micro structural progressive damage, which leads to the final failure, is less clear. Most of the literature has reported that filament wound composite pipes under fatigue biaxial load failed due to sequences of damage which