Instability Mode and Damage of Fiber-Reinforced Composite Pipes under Axial Compression Loading

Fiber-reinforced composite pipes represent a potential alternative to steel pipes. To elucidate the failure mechanism of fiber-reinforced composite pipes under axial loading, this study constructs a progressive failure model based on the Hashin failure criterion and cohesive interlaminar failure criterion under axial buckling. The effects of aspect ratio, thickness-to-diameter ratio, winding angle, and initial ovality on buckling load and damage patterns are investigated. The results showed that axial compression induces overall buckling with an outer tensile–inner compressive bending pattern, where midsection deformation triggers brittle fracture in the reinforcement layer. Increasing the length-to-diameter ratio reduces the critical buckling load, and increasing the diameter-to-thickness ratio enhances buckling resistance. Initial ovality induces local buckling in the composite tube. Increasing ovality amplitude reduces ultimate pressure and exacerbates local buckling, and extending the oval segment length alleviates stress concentration by broadening the axial range. Following local buckling, the composite tube’s reinforcement layer primarily fails through matrix compression, with damage exhibiting circumferential and axial symmetry. These findings provide theoretical foundations for the design, manufacturing, and evaluation of fiber-reinforced composite tubes.