A typical diglycidyl ether of bisphenol-F (DGEBF)/diethyl toluene diamine (DETD) epoxy system modified by multiwalled carbon nanotubes (MWCNTs) and a reactive aliphatic diluent named n-butyl glycidyl ether (BGE) was used as the matrix for glass fiber composites. The glass fiber (GF) reinforced composites based on the unmodified and modified epoxy matrices were prepared by the hand lay-up hot-press process. Mode II interlaminar fracture toughness at both room temperature (RT) and cryogenic temperature (77 K) of the GF reinforced epoxy composites was investigated to examine the effect of the matrix modification. The result showed that the introduction of MWCNTs and BGE at their previously reported optimal contents led to the remarkable enhancement in mode II interlaminar fracture toughness of the composites. Namely, the 22.9% enhancement at RT and the 31.4% enhancement at 77 K were observed for mode II interlaminar fracture toughness of the fiber composite based on the optimally modified epoxy matrix by MWCNTs and BGE compared to the unmodified case.
It is well known that matrices play a very important role in load transfer and crack resistance and hence significantly affect the mechanical properties of fiber reinforced composites. Epoxy resins are most popular matrices for fiber reinforced composites. Due to their shortages such as high brittleness, they are often modified by toughening agents. In our previous work [
Delamination of the composite laminates would take place when shear and peeling stress concentrations were high. And the fracture toughness under shear loading (i.e., mode II interlaminar fracture toughness) is a critical property to evaluate the potential crack growth resistance [
In our previous work [
In this work, the diglycidyl ether of bisphenol F (DGEBF)/diethyl toluene diamine (DETD) epoxy system modified by multiwalled CNTs and BGE was prepared according to our previous works [
Woven E-glass fibers (GF) were purchased from Feihangtongda Co., Ltd., China. The average diameter of single GF was about 11
The preparation of the glass fiber reinforced epoxy composite has been given in detail in our previous works [
Interlaminar fracture toughness at RT and 77 K for the composites based on unmodified and modified epoxy resins.
Matrix | DGEBF (g) | DETD (g) | MWCNT (g) | BGE (g) |
|
|
---|---|---|---|---|---|---|
RT | 77 K | |||||
A | 100 | 25.8 | 1.40 ± 0.03 | 3.25 ± 0.25 | ||
B | 99.5 | 25.7 | 0.5 | 1.46 ± 0.08 | 3.63 ± 0.40 | |
C | 100 | 28.4 | 10 | 1.59 ± 0.04 | 3.99 ± 0.42 | |
D | 99.5 | 28.3 | 0.5 | 10 | 1.72 ± 0.07 | 4.27 ± 0.32 |
Temperature and pressure profiles for manufacturing glass fiber reinforced composites.
The dimensions of the samples for measurement of
In the end notched flexure (ENF) test, the critical energy release rate is determined by [
The fracture surfaces of the composites were evaluated by scanning electron microscopy (SEM, Hitachi S-4300) at an accelerating voltage of 10 kV. All specimens were coated with a thin layer of gold to eliminate charging effects.
Typical ENF load-displacement curves at room temperature (RT) and liquid nitrogen temperature (77 K) for the composites are shown in Figures
Typical ENF load-displacement curves at room temperature for (A) unmodified epoxy/glass fiber composite, (B) MWCNT modified epoxy/glass fiber composite, (C) BGE modified epoxy/glass fiber composite, and (D) both MWCNT and BGE modified epoxy/glass fiber composite.
Typical ENF load-displacement curves at 77 K for (A) unmodified epoxy/glass fiber composite, (B) MWCNT modified epoxy/glass fiber composite, (C) BGE modified epoxy/glass fiber composite, and (D) both MWCNT and BGE modified epoxy/glass fiber composite.
The results for the interlaminate fracture toughness at RT and 77 K are shown in Figures
The interlaminar fracture toughness at room temperature for (A) unmodified epoxy/glass fiber composite, (B) MWCNT modified epoxy/glass fiber composite, (C) BGE modified epoxy/glass fiber composite, and (D) both MWCNT and BGE modified epoxy/glass fiber composite.
The interlaminar fracture toughness at 77 K for (A) unmodified epoxy/glass fiber composite, (B) MWCNT modified epoxy/glass fiber composite, (C) BGE modified epoxy/glass fiber composite, and (D) both MWCNT and BGE modified epoxy/glass fiber composite.
The data for the interlaminar fracture toughness at RT and 77 K for the composites based on unmodified and modified epoxy matrices are given in Table
The SEM images are presented in Figure
SEM images for the fracture surfaces (crack growth from left to right) after testing at RT and 77 K of (A) unmodified epoxy/glass fiber composite, (B) MWCNT modified epoxy/glass fiber composites, (C) BGE modified epoxy/glass fiber composite, and (D) both MWCNT and BGE modified epoxy/glass fiber composites.
At 77 K, the decrease in temperature makes the epoxy more brittle and reduces its strain to failure. The hackle mark features are shown in Figure
In this work, glass fiber reinforced composites have been prepared by the hand lay-up hot press process based on unmodified and modified epoxy matrices by introducing MWCNTs and BGE into a pure epoxy resin in modifying the epoxy resins. Mode II interlaminar fracture toughness (
The authors declare that there is no conflict of interests regarding the publication of this paper.
This work was financially supported by the National Natural Science Foundation of China (nos. 51373187 and 11372312) and the Beijing Municipal Natural Science Foundation (no. 2122055).