Experimental investigation of failure mechanisms and evaluation of physical/mechanical properties of unidirectional flax–epoxy composites

Abstract

Using natural fibers as reinforcement in polymer matrix composites necessitates evaluating the latter under different modes of solicitation. This allows extracting its material properties for engineering design and research purposes. The main objective of the study is preparing a consistent set of material properties for unidirectional flax fiber-reinforced epoxy composite with defined composition and basic configuration. These data are prerequisites for growing researches on flax fiber-reinforced epoxy composites, especially for numerical analysis purposes using the finite element method. In this work, partially green unidirectional-flax fiber-reinforced epoxy composites are tested for physical and mechanical properties and studied for their failure modes. Tension, compression, flexion, and shear properties, as well as physical properties like density, specific heat capacity and thermal diffusivity, are evaluated according to ASTM standard test methods. Flax fibers, which are composites by themselves, come in bundles in the composites and demonstrate a complex behavior. Therefore, a fractographic analysis has been conducted to understand the macro and microscale failure mechanisms to correlate them with the material properties. The results are in good agreement with those of the literature, when available, but they mainly show the specific behavior of unidirectional-flax composites subject to different solicitation modes, especially compression and direct shear modes evaluated this way for the first time for unidirectional-flax fiber-reinforced epoxy composite. They cover most of the data required for engineering design and numerical analysis by methods like finite element method, particularly for simulating the machining process of flax fiber-reinforced epoxy composite in the ongoing works.

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

“…According to the standard, the non-pre-cracked (NPC) and pre-cracked (PC) CC tests, at a i = 20 and 40 mm, and fracture tests, at a 0 = 30 mm, were carried out on the same specimen to obtain the compliance plots as well as the maximum loads (P Max ), to be used for determination of G IIC . The initial CC forces (P i ) were approximated using the flexural modulus (E f ) of the same material [77] and G IIC of a similar material [66], then, the result of ENF tests with accepted G IIC was used to update the P C and P i . The calculated crack length after NPC tests (a calc ) was calculated using unloading data of the NPC fracture test, as mentioned in the test procedure.…”

“…The loading of the specimen was continued until the delamination extended past 25 mm. The required elastic and shear properties were used from our previous work [77], and the out-of-plane shear modulus G 13 was assumed to be equal to G 12 . Also, for the calculations of the estimated force and deflection, the estimated Mixed-mode IFT, G est (I/II)C , was considered as the average values of the G IC and G IIC of the composite measured in this present study.…”

In-plane shear and tensile behavior of two-pass injection-molded glass fiber reinforced polypropylene composites with different fiber lengths

“…Khashaba 36 noticed that, the maximum in-plane shear strength for glass fiber reinforced epoxy cross-ply laminate composite was for composite with 45° and 60° off-axis angles and the minimum in-plane shear strength for 0° and 90°. Saadati et al 37 examine longitudinal and transversely aligned unidirectional flax/epoxy composites finding that the former has a ductile shear failure at low strains and the latter has a brittle shear failure.…”

Development and application of nonwovens based on palm fiber as reinforcements of unsaturated polyester

“…[18][19][20] The mechanical properties of composites are generally defined as the degree of fiber/matrix adhesion and durability. 21 Moisture diffusion in a composite can impair fiber/matrix adhesion and reduce composite mechanical performance. 21 Furthermore, the mechanical properties of composites can be affected further factors such as fiber volume, fiber orientations, fiber distribution, void content and humidity.…”