Waveform, Load Ratio and Frequency Effects on Fatigue Crack Propagation Rate of FRP-Wood Bonded Interfaces

摘要

In this paper, we investigate the waveform, frequency and load ratio effects on fatigue crackpropagation rate of interface bond of red maple wood bonded to phenolic FRP composite. Threegroups of tests are conducted: (1) for three waveforms of sinusoidal, triangular and square shapes ata constant frequency of 1 Hz and load ratio of 0.5; (2) for three frequencies of 0.1, 1.0 and 10 Hz at aconstant load ratio of 0.5 and sinusoidal waveform; and (3) for three load ratios of 0.1, 0.3 and 0.5 atconstant frequency of 1 Hz and sinusoidal waveform. Also included in this study is the effect of loadratio on threshold strain energy release rate range. A Contoured Double Cantilever Beam (CDCB)specimen, for which the fracture toughness is independent of the crack length for a certain range ofcrack extension, is used for opening mode fatigue tests under constant cyclic loading. The crackgrowth rate is established by means of the compliance method. The different waveforms consideredare found to have negligible effect on crack propagation rate of bonded interface. However, both loadratio and frequency are shown to have significant effect on crack propagation rate of the FRP-woodbonded interfaces. The load ratio R, frequency f, and several strain energy release rate,G,parameters, including Gmin, Gmean and ΔG, are used to explain loading variable effects; the meanvalue of strain energy release rate is the best parameter to fit the experimental data for phenolicFRP-red maple wood bonded interface. A modified Paris Law equation including load ratio andfrequency effects is proposed in this study.