Short-beam shear fatigue behavior of round curved pultruded composite

Abstract

Short-beam shear test has been used to evaluate the fatigue strength of round curved pultruded carbon fiber – epoxy matrix composite specimens in three point bending test of a convex-beam. The specimens were cyclically loaded at peak stresses from 50 to 80% of the quasi-static short-beam strength, and load ratios of 0.1 to 0.5, and damage evolution was monitored using the apparent stiffness method. Basquins’ law was used to fit the experimental S-N data. The results showed that the fatigue strength of curved pultruded composites is lower than for conventional thin flat unidirectional laminates, and less sensitive to load-ratio effects. Residual strength of pre-fatigued specimens was determined by quasi-static short-beam tests, and it sometimes exceeded the pristine material performance due to fatigue-induced strengthening phenomenon. Stress redistribution and residual manufacturing-induced stress relief due to the previous cyclic loading were found the main responsible for mitigating damage growth under quasi-static loading. Fractographic survey indicated that stress redistribution and stress relief governed the strengthening process under high-cycle and low-cycle fatigue regime, respectively.

Keywords:

• Curved composite
• carbon fiber
• fatigue
• pultrusion
• residual strength
• short-beam test

Acknowledgments

The authors gratefully acknowledge Petrobras (contract number: 2000.0067652.11.9) for the financial support, and the Coordination for the Improvement of Higher Education Personnel (CAPES) and National Council for Scientific and Technological Development (CNPq) for the grants.

Author contributions

Tonatto M.L.P. was the main responsible for samples preparation, mechanical testing, data acquisition and interpretation; Tarpani J.R. performed the analysis and interpretation of data, besides substantial revision of the paper; Amico S.C. conceived, designed and coordinated the whole project, besides substantial revision of paper. All authors have read, revised, and agreed to the submitted version of the manuscript.

Conflicts of interest

The authors declare that they have no conflict of interest.