The effect of cylindrical defects on the tensile strength of glass fiber/vinyl-ester matrix reinforced composite pipes

The influence of cylindrical defects on the tensile strength of glass fiber/vinyl-ester composite pipes was evaluated. The properties were determined using the ring test. The radius and depth of the defects were varied, and the significance of their effect on the results obtained was verified using the analysis of variance between groups (ANOVA). The analysis showed that the depth of the defects has a stronger influence than the radius, and that the interaction of these parameters is not relevant. The fractographic analysis showed delamination and clusters of pulled-out fibers as the main fracture characteristics, and that the fracture initiates at the internal surface of the rings. The distribution of the circumferential stress, calculated through finite element analysis, validates the fractographic analysis. The finite element analysis showed a significant stress and strain increase at the internal surface of the rings, close to the edge of the internal steel disks of the grips of the fixture equipment. The variation of both stress and strain is due to the presence of bending at this position.