Tensile fatigue response of a novel carbon/flax/epoxy hybrid composite under strain-controlled and stress-controlled amplitude

Abstract

This is the first study on the fatigue tensile performance of a novel hybrid composite made as Type A (i.e. woven carbon fibers plus unidirectional flax fibers [W_C2/0_F12/W_C2]) or Type B (i.e. woven carbon fibers plus oblique flax fibers [W_C2/(±45)_F6S/W_C2]) in epoxy resin. Composite plates were examined under constant strain amplitude using conventional fatigue tests and constant stress amplitude using thermographic stress analysis at 5 Hz cycling with a constant amplitude ratio of 0.1. For conventional fatigue, the max strain ε_max versus cycles to failure N_f curve for Type A was log (N_f) = 9.7–588.2ε_max, while for Type B it was log (N_f) = 14.9–1000ε_max; neither material had a true endurance limit since curves never became horizontal. For thermographic stress analysis, high-cycle fatigue strength for Type A was 231.7 MPa (i.e. 56% of ultimate tensile stress σ_ut), while for Type B it was 203.2 MPa (i.e. 60% of σ_ut).