a b s t r a c tA specific device has been set up to test by vibration resonance the mode I fatigue delamination growth onset of composite laminates. This test system, based on the DCB test specimen, is a mass-spring-specimen dynamic system designed to resonate. The defined operating conditions allow performing delamination propagation tests under imposed load and stopping the test under reproducible conditions, identical to the ones recommended in the ASTM-D6115 standard. This system allows fatigue tests to be driven up to 100 Hz, reducing the time taken by a factor of ten without detrimental heat being generated in the material. The effect of frequency on the fatigue delamination growth on mode I has been investigated through a comparison with standard tests performed at 10 Hz. A decrease in resistance to the propagation of delamination is observed with the increase in frequency for the composite studied. This frequency effect seems to be a strain rate effect and was taken in consideration by using dynamical critical energy restitution rate for the G-N curve plotting.⇑ Corresponding author. Tel.: +33 (0) 561339195; fax: +33 (0) 561339095. ⇑⇑ Principal corresponding author. Tel.: +33 (0) 561339141; fax: +33 (0) 561339095.
Keywords:Fiber reinforced polymer matrix Delamination fatigue Mode II loading Frequency effect Vibratory fatigue a b s t r a c t A fatigue crack propagation test under mode II has been set up for unidirectional composite laminate characterization at high frequency. The specimen is clamped on a shaker and loaded on its first bending resonance mode. This dynamical test allows an accurate delamination extension monitoring based on the resonance frequency shift. Dynamical tests are conducted at 260 Hz and 400 Hz and their results are compared to those obtained with 10 Hz 3-ENF tests. Fatigue crack propagation results are presented taking into consideration the loading ratio difference between both test configurations. All results are collapsed in a unique propagation rate curve.
The study of fatigue delamination growth in composite materials aims to develop a slow-growth approach for composite materials that would provide conservative and reliable results. The present work focuses on the study of the load ratio effect on fatigue crack growth at constant amplitude and on the effect of variable amplitude loading on crack propagation. With this in mind, a Crack Driving Force (CDF) is chosen to attempt to overlap delamination growth curves obtained from different load ratio values for mode I and mode II. It is shown that the CDF collects the effect of the load ratio on the crack growth curves and allows to build a crack growth master curve for mode I and II. Variable amplitude loads are then considered for delamination propagation in mode I. However, variable amplitude loads bring to light a load history effect during fatigue crack growth that the CDF does not take into account.
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