An experimental study of the mechanical properties of seamless and overlapped stitched composite tubes under hydrostatic pressure, lateral compression, and impact

Mechanical properties and damage mechanisms of closed circular preforms and overlapped stitched composite tubes under lateral compression, impact, and hydrostatic pressure were studied. The functional failure pressures of the tubes with different boundary conditions were determined and compared. Stitch at the overlapped zone creates stress risers that lead to premature functional failure at a hydrostatic pressure at ∼1/3 of the theoretical maximum pressure of the tube as delamination occurs at the overlapping region. Seamless tubes reached values close to theoretical operating hydrostatic pressures before leakage was observed at the tube ends. The deflection of the overlapped stitched tube due to lateral compression is less than the deflection in the seamless tube, and it is limited to 5% of the inner diameter using the Spangler equation. Brittle kinks, cracks, and delamination occur in overlapped stitched tubes while seamless tubes regain the shape with limited localized cracks after unloading. The fabric architecture of a seamless tube allows for the reorientation of fiber tows as cracks develop in the matrix, thus resulting in a lesser extent of damage when the tube is subject to impact.