PSI - Issue 82

Igor Guz et al. / Procedia Structural Integrity 82 (2026) 239–245 I. Guz et al./ Structural Integrity Procedia 00 (2026) 000–000

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gradients that can significantly influence the material failure response of pressurised FRP tubulars as demonstrated by Hastie et al. (2019a, 2019b, 2021, 2022), Cox et al. (2019), Wang et al. (2023). Analytical solutions for stresses and deformations in thick FW sandwich pipes subjected to internal pressure and pure bending were presented by Xia et al. (2000, 2002). A solution for FW sandwich pipes under internal pressure combined with uniform temperature change was also developed by Xia et al. (2001a, 2001b). Bakaiyan and Ameri (2012) presented a solution for the case of combined internal pressure and through-wall thermal gradient based on three-dimensional (3D) anisotropic elasticity, accounting for shear-extension coupling in the skins. The authors of this paper previously performed failure analysis of FW sandwich pipe under combined internal pressure and thermal loading by 3D finite element (FE) modelling (Hastie et al., 2021). Numerical models, e.g. developed in commercial FE packages, afford a number of advantages over analytical methods, such as the ability to introduce defects that would otherwise prove complex or unfeasible. In this paper, suitability of FE modelling for analysing stresses in thick-walled FW sandwich pipe subjected to surface pressures and thermal loading is verified by comparison with the analytical results presented by Bakaiyan and Ameri (2012) based on 3D anisotropic elasticity theory. As a numerical example, stresses in sandwich pipe with FW skins and homogeneous or graded-density core under pressure and thermal load combinations illustrative of offshore operation are analysed by finite element analysis (FEA). 2. Analytical formulation The problem of FW sandwich pipe subjected to pressure and radial temperature profile is formulated in line with 3D elasticity theory. Let us consider a section of pipe in cylindrical coordinates as illustrated in Fig. 1. The skins are made up of orthotropic plies; φ is the fibre orientation angle. The core is a single isotropic layer or can be made up of multiple isotropic layers with different properties (graded). The detailed analytical formulation is given by Hastie et al. (2019a, 2019b, 2021).

Fig. 1. Sandwich pipe in cylindrical coordinates and sandwich pipe FE model.

3. Model validation In this work a section of sandwich pipe was modelled in Abaqus/CAE. The model and mechanical loads are shown in Fig. 1 (F z is the equivalent end force). The mechanical loads are applied simultaneously with temperature boundary conditions in a coupled temperature-displacement analysis step. A starting temperature is defined over the entire section prior to the analysis. The model is meshed using the quadratic, thermally coupled element type C3D20RT available in the Abaqus element library. Suitability of the FE model for analysing thermomechanical stresses in the pipe is verified by comparing computed stress distributions for a carbon/epoxy system with those solved according to elasticity theory by Bakaiyan and Ameri (2012). The pipe comprises T300/LY5052 carbon/epoxy skins and LY5052 epoxy core. Pipe dimensions are chosen to be of practical interest e.g. for oil and gas gathering flowlines (Kennedy, 1993): inner radius 50mm, inner skin thickness 1mm, core thickness 10mm, outer skin thickness 1mm, outer radius 62mm. Inner and outer skins are comprised of two unidirectional plies orientated at angle ±φ (from the pipe longitudinal axis) and