Manufacturing and joining technology of fibre-reinforced composite materials for tubular components under biaxial loading conditions

Pressure-retaining tubular structures (e.g. pipes) could be advantageously produced from fibre-reinforced polymeric composites (FRPC). Due to favourable properties, e.g. material anisotropy and corrosion resistance, these structures frequently outperform traditional metallic components. The axisymmetric shape is suited for the efficient filament winding process, which facilitates automated and continuous production. Improvements in performance and economy may thus be realised. Despite these advantages a limited understanding of damage behaviour, deficient design methodologies, and a lack of economical joining techniques have hampered an extensive utilisation of FRPC in high-pressure applications.

A favourable design for all-composite piping ought to possess the following characteristics: (a) The pipe body possesses adequate strengths under biaxial loadings associated with installation and in-service conditions; (b) the structure exhibits leak-before-burst failure (i.e. fail-safe design); and (c) joining of pipe sections is field-friendly and economical. The current study investigates the feasibility of such structures. A unique approach encompassing the design, manufacturing and joining was employed. Firstly, the manufacturing process was studied to identify efficient winding conditions (such as fibre tensioning) for optimal pipe performance. Secondly, different fibre architectures were analysed with regards to strength and damage behaviour. Finally, a unique yet simple adhesive bonding technique was employed for the integration of subcomponents. Due to the lack of suitable criteria for leakage prediction (i.e. the predominant failure mode), here the emphasis is on experimental investigations under monotonic loading conditions. Glass-fibre and thermoset resin were utilised to fabricate small-scale model as well as large-scale prototype specimens. Using an innovative permeability-based method and conventional strength-of-material approaches an investigation on specimen scaling/size effects was conducted. Experiments were complemented using analytical methods for the determination of material and structural properties (e.g. pipe wall thickness); the joint geometry was optimised using finite element techniques.

Best overall prototype performance was achieved for a multi-angle lay-up with exterior filaments inclined to provide axial reinforcement. Namely, a [±60₃,±30]_T fibre architecture exhibited superior strengths under the applied loadings. Favourable winding conditions were identified producing intermediate fibre volume fractions (∼60%) and low void contents (∼1%). In conjunction with bonded overlap sleeve joints, which were employed for their field-friendliness and cost-effectiveness, prototype structures were able to satisfy the aforementioned design requirements.