دانلود رایگان مقاله اثر بریجینگ در فرسودگی بار لایه لایه نمونه کربن اپوکسی بدون جهت

Abstract

Fatigue delamination growth in composites is accompanied by large scale bridging (LSB) that yields important toughening effects. However, the extent of this mechanism depends on the laminate geometry rendering its modeling a challenging task. This work presents a combined experimental/numerical study on characterization of specimen thickness dependence of LSB in fatigue delamination. Double cantilever beam specimens of different thicknesses (h = 2, 4 and 8 mm), equipped with arrays of multiplexed fiber Bragg grating sensors, are subjected to mode I fatigue loads. Measured strain data with the sensors are employed to identify the bridging tractions and subsequently compute the energy release rate (ERR) due to the bridging as well as the ERR at the crack tip. The obtained results confirm that fatigue delamination growth strongly depends on the specimen geometry when LSB prevails. It is shown that both the extent of bridging and critical ERR at failure increase by increasing the specimen thickness while the maximum bridging traction at the crack tip is found independent of the specimen geometry. The identified traction-separation relations serve to establish a power correlation, between the crack growth rate and ERR at the crack tip which is independent of the specimen thickness.

4. Conclusions

1. Load controlled fatigue delamination is accompanied by LSB and significantly depends on the specimen thickness resulting in crack deceleration and eventual specimen fracture at a critical ERR almost equal to the corresponding steady state ERR under monotonic delamination. 2. The identified bridging tractions suggest that the maximum bridging traction at the crack tip is independent of the three tested specimens with thicknesses of 2, 4 and 8 mm. However, fatigue delamination in thicker specimens is accompanied by a longer bridging zone, in which the bridging tractions decay with a lower rate. 3. The scaling relationships between the specimen thickness and the bridging parameters, derived previously in the case of monotonic delamination [16,17], can be effectively used to predict thickness effects on bridging parameters in fatigue. 4. The identified values of ERR at the crack tip and the corresponding crack growth rate data suggest a power relation independent of the specimen thickness and crack length.