Loading rate effects on mode-I delamination in glass/epoxy and glass/CNF/epoxy laminated composites

Abstract

The main objective of the present study is to assess the loading rate effects on mode-I delamination growth in glass/epoxy laminated composites. Furthermore, hybrid reinforcement of these composites by incorporating carbon nanofibers (CNFs) was followed to enhance the interlaminar fracture resistance and affect its loading rate sensitivity. Experiments on DCB specimens made of glass/epoxy and glass/CNF/epoxy laminated composites were conducted by varying the loading rate from standard quasi-static testing up to 200 mm/sec crosshead speed in a servo-hydraulic test machine. More than 21% decrease was observed in the propagation fracture toughness of the glass/epoxy samples due to loading rate elevation in the studied range. Moreover, the results of the present study clearly show the benefits of CNF modification, not only in enhancing the fracture toughness but also in reducing the loading rate dependency. Adding CNFs to glass/epoxy composites caused 32.8% and 13.5% increase in the quasi-static values of the initiation-and propagation-interlaminar fracture toughness (G IC), respectively. Also, owing to CNF incorporation, the maximum drop in the propagation fracture toughness at elevated loading rates was decreased to 8%. Fractography inspections were performed to provide an in-depth explanation for the observed loading rate effects and the advantages of CNF reinforcement.

Loading rate dependency of strain energy release rate in mode I delamination of composite laminates

“…It can be concluded that the bridging length and the amount of energy dissipated within the pull-out or breakage of the bridged fibers decrease with increasing loading rate. A similar fiber bridging behavior and loading rate dependency of mode I delamination was previously observed in carbon/epoxy [21] and glass/epoxy composites [30].…”

“…The expression above shows that the crack tip opening rate decreases with increasing delamination length. This approach was applied in the present study to further clarify the rate sensitivity of the fracture toughness as previously done in [21,30].…”

Strain rate effects on the mechanical behavior of single-lap glass/carbon nanofiber/epoxy composite bolted joints

“…Shamaei-Kashani and Shokrieh 33 using the classical lamination theory 34 showed that adding CNF into the joint could improve the bearing chord stiffness of SLJ. Also, it was shown 23,35,36 that carbon nanofiber can improve the delamination toughness of laminated composite due to the modification of the fiber-matrix interface and reinforcement of the matrix phase. By improving the delamination toughness of laminated composite, the bearing strength and energy absorption of the single-lap composite bolted joint can be increased.…”

“…Ekhtiyari et al. 23 showed that by adding 0.25 wt.% CNF into the glass/epoxy laminated composite, the delamination toughness of laminated composite could be improved.…”

The Thickness Effect of PSF Nanofibrous Mat on Fracture Toughness of Carbon/Epoxy Laminates

“…Up until now, the abilities of some polymeric nanofibers, such as polyvinylidene fluoride (PVDF) [34][35][36][37], nylon [38][39][40][41][42][43], and carbon nanofibers [44,45], have been considered…”