Analysis of Surface Strains and Leakage Behavior in Composite Pipes and Vessels Using Digital Image Correlation Technique

Abstract

Pipe and vessel structures made from fiber-reinforced polymer composites are know to commonly outperform metallic structures in terms of corrosion resistance and strength-to-weight ratio. However, composite pressure piping and vessels without internal lining are prone to leakage failure caused by matrix cracking. Microscopic fractures in the often brittle matrix phase grow and coalesce under loading, forming a network of matrix cracks that facilitates fluid to permeate the pipe or vessel wall. Hence, liners are often incorporated into composite pressure containment structures. Leakage failures usually occur considerably below pressures causing rupture of composite pipes and vessels. Hence, more efficient designs may be obtained if liners could be avoided altogether. To achieve this goal a thorough understanding of the damage mechanisms leading to leakage failure is required. Composite pressure piping and vessels are generally manufactured using filament winding or similar techniques. Resulting interwoven fiber architectures are generally considered to influence strain patterns and leakage behavior. Classical experimental methods are usually unable to verify this hypothesis, and therefore modeling techniques have largely been employed. In the present study, the effect of fiber architecture on surface strain patterns and the initiation of leakage were investigated experimentally using digital image correlation technique. Surface strain maps were produced for tubular filament-wound composite specimens subjected to combined internal pressure and axial traction. The findings of this study indicate that no distinct correlation exists between surface strain patterns and leakage initiation points.