Tensile, Quasistatic and Dynamic Fracture Properties of Nano-Al₂O₃-Modified Epoxy Resin

Abstract

Epoxy resin, modified with different particle sizes (50 nm, 100 nm, 200 nm) and contents (1 wt %, 3 wt %, 5 wt %, 7 wt %) was manufactured. The mechanical behaviors of tensile, quasistatic fracture and dynamic fracture under SHPB (split Hopkinson pressure bar) loading were investigated. The dynamic fracture behaviors of the composites were evaluated by 2D-DIC (digital image correlation) and the strain gauge technique, and the fracture surface was examined by SEM (scanning electron microscope). According to the results, the tensile modulus and strength significantly increased for epoxy resin modified with 5 wt % Al₂O₃ of 50 nm. The quasistatic fracture toughness of modified epoxy resin increased with the particle content. However, the fracture toughness of epoxy resin modified with high content fillers decreased for particle agglomeration that existed in epoxy resin. The crack propagation velocity can be decreased for epoxy resin modified with particles under dynamic loading. The dynamic initiation fracture toughness of modified epoxy resin increases with both particle size and content, but when the fillers have a high content, the particle size effects are weak. For the composite under dynamic loading conditions, the toughening mechanism is also affected by particle size.

Keywords: 2D-DIC; SHPB; dynamic fracture; epoxy resin; nanoparticles.

Figure 1

The process of specimens manufacturing.

Figure 2

System of split Hopkinson pressure bar (SHPB) loading and data acquisition.

Figure 3

Geometric size of sample (L = 64 mm, S = 60 mm, W = 28 mm, B = 14 mm, a = 7 mm, l = 2 mm, h = 2 mm).

Figure 4

Maximum time of the crack tip strain gauge signal.

Figure 5

Crack velocity calculated via the DIC method.

Figure 6

Displacement contour of u_x for t = 0 µs, t = 24.98 µs, t = 49.96 µs, and t = 74.94 µs.

Figure 7

Loading-point displacement evaluated via DIC and Equation (4).

Figure 8

Tensile modulus and strength of epoxy modified with nano-Al₂O₃: (a) tensile modulus (E), (b) tensile strength (σ_m).

Figure 9

Mode-I fracture toughness of epoxy resin modified by nano-Al₂O₃.

Figure 10

Agglomeration on the fracture surface of epoxy resin modified with 7 wt % of 50 nm.

Figure 11

Dynamic stress intensity factor (DSIF) history of composites with different particle size and content: (a) epoxy resin modified with 50 nm particles; (b) epoxy resin modified with 100 nm particles; (c) epoxy resin modified with 200 nm particles.

Figure 12

Crack initiation toughness (K_Id) of particle modified epoxy resin.

Figure 13

Loading rate of unmodified and modified epoxy resin (${\dot{K}}_{Id}=d{K}_{Id}/dt$).

Figure 14

The mechanism of particle size effect on the dynamic fracture toughness: (a₁,a₂) neat epoxy; (b₁,b₂) 50 nm Al₂O₃-filled epoxy (1 wt %); (c₁,c₂) 100 nm Al₂O₃-filled epoxy (1 wt %); (d₁,d₂) 200 nm Al₂O₃-filled epoxy (1 wt %).

Figure 15

SEM micrographs of the dynamic fracture surface (a) neat epoxy; (b) 50 nm Al₂O₃-filled epoxy (3 wt %); (c) 100 nm Al₂O₃-filled epoxy (3 wt %); and (d) 200 nm Al₂O₃-filled epoxy (3 wt %).