Experimental investigation of single and butt-welded GFRP filament winding tubes bending behavior based on conventional and Digital Image Correlation method

Composite joints have become increasingly popular in pipeline assembly, replacing conventional fasteners. However, butt-welded joint composite techniques still need further structural study. This paper aims to study the flexural mechanical performance of the above mentioned composite joint method. Four-point bending tests were conducted on both unassembled (single) and two butt-welded tube types (based on NFT and DIN standard methods). In this context, the 2D digital image correlation (DIC) technique was applied during these tests to analyze the damage scenario based on full-field strain mapping. To further visualize the microscopic damage modes, X-ray tomography observations were conducted on both single and butt-welded specimens. The experimental results show that single tubes have the highest mechanical properties, with quasi-elastic behavior until the occurrence of fracture. The NFT butt-welded composite tubes present the maximum flexural stiffness and strength compared with the DIN tubes. It has also been shown that the strain distribution depends on the specimen configuration. The DIC analysis results show that the damage scenario is divided into two events: the onset of fracture and then the fracture propagation. These results were confirmed through microscopic inspections.