Multiaxial Fatigue Behavior of CFRP Thin-Walled Tubes: An Experimental Study with Analysis of the Acoustic Signals.

The fatigue behavior of continuous fiber-reinforced composite materials is still not fully understood, particularly under multiaxial out-of-phase loading conditions. This study assesses the multiaxial fatigue behavior of thin-walled carbon fiber-reinforced polymer (CFRP) tubular specimens fabricated by filament winding (FW). A comprehensive experimental study is presented, investigating axial-torsion loads, phase shifts (0°, 45°, and 90°), and load ratios (-1, 0.05, and 0.5). Simultaneously, the acoustic emission (AE) method provides supplementary data for assessing fatigue damage accumulation. Consequently, a shear nonlinear material model and progressive damage in a shell-based finite element model were applied for stress analysis. The experimental results demonstrate the negative influence of a 90° out-of-phase load and the detrimental effect of mean stress for investigated positive load ratios. These findings offer valuable insights into the impact of phase shift (δ) and load ratio (R) in filament-wound carbon composites. These are essential for accurately modeling the fatigue behavior of composite materials under complex multiaxial loading.