Butt-Welded Composite Tubes Mechanical Behavior Under Flexural Loading

The structural integrity and the mechanical performance of the composite piping networks are highly dependent on the strength and stiffness of the junction zone between the tubes. Moreover, the increasing application of composite tubes in pipeline systems nowadays requires an accurate characterization of composite tubes’ mechanical properties and a thorough understanding of their damage mechanisms. Especially, bending strength remains a principal issue for the design of assembled tubular structures. One of the main requirements is to characterize the mechanical performance of the joints between two tubes. This paper aims to investigate the flexural mechanical behavior of two categories of butt-joined composite tubes. Three-point bending and four-point bending tests were carried out. During loading, an analysis of the initiation and growth of macroscopic damage was performed. The results of this study show that the joining method has a significant effect on the mechanical strength of composite joined tubes. The geometry of the joint influence significantly the strain distribution on the butt-welded tubular joint and the overlap joint. Also, regardless of the load type, the NFT butt-assembled composite tubes are more resistant than the DIN butt-welded tubes. The NFT butt joint provides improved load transfer between the different joint configurations. Finally, macroscopic observations show that the geometry and material combination leads to several failure modes.