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 crack propagation rate of interface bond of red maple wood bonded to phenolic FRP composite. Three groups of tests are conducted: (1) for three waveforms of sinusoidal, triangular and square shapes at a constant frequency of 1 Hz and load ratio of 0.5; (2) for three frequencies of 0.1, 1.0 and 10 Hz at a constant load ratio of 0.5 and sinusoidal waveform; and (3) for three load ratios of 0.1, 0.3 and 0.5 at constant frequency of 1 Hz and sinusoidal waveform. Also included in this study is the effect of load ratio 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 of crack extension, is used for opening mode fatigue tests under constant cyclic loading. The crack growth rate is established by means of the compliance method. The different waveforms considered are found to have negligible effect on crack propagation rate of bonded interface. However, both load ratio and frequency are shown to have significant effect on crack propagation rate of the FRP-wood bonded interfaces. The load ratio R, frequency f, and several strain energy release rate, G, parameters, including G{sub}(min), G{sub}(mean) and G, are used to explain loading variable effects; the mean value of strain energy release rate is the best parameter to fit the experimental data for phenolic FRP-red maple wood bonded interface. A modified Paris Law equation including load ratio and frequency effects is proposed in this study.