A Study of the Interlaminar Fracture Toughness of Unidirectional Flax/Epoxy Composites

Abstract

Having environmental and economic advantages, flax fibers have been recognized as a potential replacement for glass fibers as reinforcement in epoxy composites for various applications. Its widening applications require employing failure criteria and analysis methods for engineering design, analysis, and optimization of this material. Among different failure modes, delamination is known as one of the earliest ones in laminated composites and needs to be studied in detail. However, the delamination characteristics of unidirectional (UD) flax/epoxy composites in pure Mode I has rarely been addressed, while Mode II and Mixed-mode I/II have never been addressed before. This work studies and evaluates the interlaminar fracture toughness and delamination behavior of UD flax/epoxy composite under Mode I, Mode II, and Mixed-mode I/II loading. The composites were tested following corresponding ASTM standards and fulfilled all the requirements. The interlaminar fracture toughness of the composite were determined and validated based on the specific characteristics of natural fibers. Considering the variation in the composite structure configuration and its effects, the results of interlaminar fracture toughness fit in the range of those reported for similar composites in the literature and provide a basis for the material properties of this composite.

Fabrication and Thermo-Electro and Mechanical Properties Evaluation of Helical Multiwall Carbon Nanotube-Carbon Fiber/Epoxy Composite Laminates

“…The fracture toughness in the 0.2 wt.% HMWCNT was increased to about 50.88%, while the higher amount of HMWCNT content 0.4 wt.% showed a significant improvement of 190%. The presented results for G IC and G IIC are in complete agreement that the addition of HMWCNT in CF/E composite laminates further promotes the interlaminar fracture toughness of modes I and II [71]. A comparison of the increased interlaminar fracture toughness for the modes I and II values obtained for the 0.2 wt.% and 0.4 wt.% HMWCNT composite laminates with the control sample are presented in Table 4.…”

Flexural Properties and Low-Velocity Impact Behavior of Polyamide 11/Basalt Fiber Fabric Laminates

“…Given that the onset and propagation of delamination is strictly related to the interfacial fiber-matrix interaction [36], these observations confirm a greater fiber-matrix interaction in twill laminates compared to plain weave ones. Moreover, for systems containing twill basalt fabric layers, the plasticized matrix ensures that the failure of the matrix remains limited to the compressed region of the specimen, due to its expected ductility manifested mainly in the region of the specimen subject to tensile stresses.…”

“…Clearly, for systems with plain reinforcement, the maximum shape assumes a higher average value in the presence of the non-plasticized matrix, while the opposite occurs for laminates with reinforcement that have a twill architecture. This effect, taking into account the scarce chemical interaction between matrix and reinforcement, can be explained by assuming, in the first case, the influence of the greater rigidity of the PA11_TL matrix, and, in the second case, the greater capacity of the plasticized matrix to wrap on a reinforce- Given that the onset and propagation of delamination is strictly related to the interfacial fiber-matrix interaction [36], these observations confirm a greater fiber-matrix interaction in twill laminates compared to plain weave ones. Moreover, for systems containing twill basalt fabric layers, the plasticized matrix ensures that the failure of the matrix remains limited to the compressed region of the specimen, due to its expected ductility manifested mainly in the region of the specimen subject to tensile stresses.…”

Ultrafast carbon nanotubes growth on recycled carbon fibers and their evaluation on interfacial shear strength in reinforced composites

“…The damage that usually occurs in laminated composite materials is the separation of two adjacent sheets (plies), this is commonly known in fracture mechanics as interlaminar failure or delamination. There are three fracture modes for interlaminar failures, which depend on the displacement of the crack surfaces: Mode I (opening or tensile mode), Mode II (in-plane shear or sliding mode) and Mode III (out-of-plane shear or tearing mode) 38 . Mode I is used to measure interlaminar fracture toughness in composite materials.…”