Failure analysis of a woven composite under tension–compression very high cycle fatigue (VHCF)

In this work, the tension–compression response of a carbon fiber woven composite is investigated in the Very High Cycle Fatigue (VHCF) regime through axial ultrasonic testing. To enhance the stress-to-displacement ratio with respect to standard straight bars, hourglass-shaped specimen was proposed in a previous work, with, however, the failure influenced by shear stresses. To overcome this limitation, while maintaining high stress-to-displacement ratio, a straight-tabbed geometry is here proposed and tested. Several combinations of adhesives, tab materials and tab geometries are studied to identify a suitable configuration for ultrasonic testing. Results show comparable fatigue performance of the hourglass-shaped and tabbed specimens, with failure driven by stress concentrations at the tip of the tabbed region. Finite Element analyses of a microscale fiber–matrix model are performed to examine the multiaxial stress states in both geometries and evaluate the contribution of individual stress components to the matrix stress field.