Failure modes of CFRP pre-tightened single tooth joints under axial cyclic tensile loading

Abstract

The fatigue behavior of a pre-tightened single tooth (PTST) joint composed of pultruded carbon fiber-reinforced polymer (CFRP) composite lamina and subjected to axial tensile loading was investigated experimentally by conducting fatigue tests and numerically by implementing finite element analysis. The pultruded CFRP composite laminae, however, are prone to interlaminar failure, thus necessitating understanding of the failure mechanism of such joints under a constant amplitude cyclic tensile load. In this work, the fatigue life of joints was obtained, and the failure mechanism was determined. Crack initiation and propagation were described, although the failure was always sudden and brittle. The dominant failure mode for all types of joints was a tooth-shear-off failure that occurred along the tooth root of the CFRP laminae. Independent of the failure mode, similar crack development was observed, characterized by initial and final regions of accelerated instability propagation and a middle interval of linear and slower crack propagation. The ratios of these three stages had significant correlations with the pre-tightening stress level especially at high pre-tightening stress, the middle stage became significantly longer, and the final stage became shorter. Considerable differences were observed for fatigue failure modes under different tooth lengths and pre-tightening stress levels.