Mode II fatigue delamination growth characterization of a carbon/epoxy laminate at high frequency under vibration loading

Abstract

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.

Prediction of mode II delamination propagation life under a standard spectrum loading in a carbon fiber composite

“…(c) The delamination driving force G eq for the rainflow counted cycles was calculated using the relation proposed by Maillet et al 18 based on Hojo et al 17 G eq ¼ ÁG where g is the best fit for the da/dN versus G eq curve and will be discussed in the subsequent section.…”

“…These results are in similar trend of reference stress-life curves for composites under spectrum loads. 18,28 Figure 5(b) shows a typical delamination growth behavior measured experimentally. Figure 5 also shows the predicted propagation life and behavior which will be discussed later in the Prediction of delamination propagation life section.…”

“…Maillet et al have reported a value of 4.6 for T700/M21 CFRP material with a normalized FDGR plot under mode II condition. 18 Typically, the value of k varies from 2 to 4 for metals while for the polymer composites the value is generally higher and could be as high as 10-15. 15 This apparent high value of k is generally observed in mode I conditions in the literature where crack tip shielding mechanism like fiber bridging is neglected.…”

“…This definition of DG is tantamount to G max (1ÀR) 2 used earlier by Matsubara et al 8 However, neither G max nor DG showed the similitude effect in the material that they investigated. 8 Maillet et al 18 used the DG eq concept in mode II studies, similar to DK eq developed by Hojo et al 17 for a mode I condition, to merge all the stress ratios into a single da/dN curve.…”

Cyclic fatigue fracture of composites: What has testing revealed about the physics of the processes so far?

“…If higher frequencies are used, the specimen temperature shall be monitored and, if exceeding a specified limit (e.g., +5°C above ambient) the test frequency shall be reduced to avoid effects from heating due to energy dissipation. Unless cyclic fatigue fracture tests are operated at resonance, e.g., in the kHz range [56], the cyclic frequency will remain below 100 Hz. Compared with this, the time-scale on which the microscopic damage mechanisms are active is at least four to five orders of magnitude lower.…”