Evaluation of biaxial stress failure surfaces for a glass fabric reinforced polyester resin under static and fatigue loading

In an attempt to evaluate failure theories for a glass fabric reinforced polyester resin over 370 tests have been conducted on thin-walled tubes under combined axial loading and internal pressure, both for static and fatigue loading. For plane stress the results are considered in relation to imaginary failure surfaces in ₁, ₂, ₆ space. A limited measure of agreement between theories and results can be obtained after highly subjective selection of data. Only those theories which involve complex stress properties provide a reasonable fit. The behaviour of tubular specimens is strongly influenced by the presence of joints in the reinforcements.Nomenclature _x , _y nominal hoop and axial (principal) stresses in a thin-walled tube - ₁, ₂, ₆ normal and shear stresses in the direction of the principal material axes - F ₁,F ₂,F ₆ strengths in the principal material directions and the in-plane shear strength - F _1t,F _2t tensile strengths in the principal material directions - F _1c,F _2c compressive strengths in the principal material directions - K ₂ a constant evaluated from a combined stress test - H ₁₂ normal stress interaction component of a strength tensor - off-axis angle - S-N curve conventional stress-log life fatigue curve - R principal stress ratio, _y /gs _x