Damage characterisation of fibre polymer composites for high-pressure retaining structures

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Pressure-retaining tubular structures such as pressure vessels, shell structures in e.g. aerospace applications, and pipe systems could be advantageously produced from fibre-reinforced polymer composites. These structures frequently outperform traditional metallic components, owing to favourable properties including high specific strength, material anisotropy and superior resistance against degradation in harsh environments. Modern fabrication equipment such as filament-winding or braiding machines allow for the automated and efficient production of tubular shapes. As a consequence, improvements in performance, safety and economy may be obtained. However, despite these advantages, a limited understanding of the complex and interacting damage mechanisms and ensuing inadequate failure predictability, have hampered the extensive usage of fibre composites in high-pressure applications. This research work aims at providing a better understanding and predictability of the involved damage events. Micro-damage events such as the cracking of the polymer matrix may cause a loss in stiffness and strength as well as lead to a fluid permeation of the structure causing leakage and secondary damage events. It is anticipated to relate information about micro-damage events, such as type, extent, sequence, interaction and interconnectivity, to macroscopic characteristics, i.e. the evolution of stiffness, strength and permeability properties. To investigate the damage behaviour, advanced mechanical testing under multiaxial loading conditions must be conducted. Ensuing experimental data are essential to enable and verify further analyses using modelling techniques based on strength-of-materials, fracture mechanics and fluid mechanics theories.