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The influence of the variation in wall thickness of glass fibre reinforced plastic pipe bends subjected to in-plane bending

Abstract Glass reinforced plastic (GRP) pipe bends as used in the process plant industry are often made by hand lay-up and, because of overlapping of layers in the construction, are prone to thickness variations sometimes approaching ± 50 percent of the mean thickness. An existing Fourier series analysis for calculating flexibility factors and strain distributions in such components with constant thickness subjected to in-plane bending moments is extended to include typical thickness variations. Results are expressed in closed form, and their practical implications are discussed. The theoretical results are also discussed in relation to experiments on two GRP pipe bends having nominal inside pipe diameters of 250mm and mean pipe radii of 250mm where the resin was polyester and the E-glass reinforcement consisted of three layers of 0.6 kg m−2 chopped strand mat and one layer of 0.6kg m−2 woven rovings.