The aim of the present work is to study the effect of fiber loading and fiber length on the mechanical behavior of bamboo fiber reinforced epoxy composites. Properties of fiber reinforced polymer composites are determined by many factors such as properties of the fibers, fiber length, concentration of the fibers, orientation of the fibers, fiber-matrix interfacial strength, properties of the matrix etc. The hardness of the bamboo column mainly depends on the number of fiber bundles and the method of scattering.
Therefore, both the matrix and fiber properties are important to improve the mechanical properties of the composites. The structural properties and mechanical properties of coir fiber reinforced polyester composites were evaluated and the effect of molding pressure on the flexural strength of the composites was investigated [29]. 34] investigated the effect of fiber length on the mechanical behavior of coir fiber reinforced epoxy composites.
36] studied the effect of fiber length and fiber content on the fracture behavior of short bamboo fiber reinforced polyester composites. The effect of fiber mass fraction and coupling agent on dynamic thermal mechanical properties of bamboo fiber/Polylactic acid (PLA) composites were studied by dynamic thermal mechanical analyzer [38]. The effect of fiber content on the mechanical behavior of bamboo fiber reinforced epoxy composite was evaluated by Bahrom et al.
41] evaluated the effect of fiber length on bamboo fiber strength and mechanical properties of green fiber-reinforced composites.
Objectives of the present research work
Preparation of composites
Mechanical testing of composites
The most commonly used specimen geometries are dogbone specimens and straight specimens with end tabs. The ASTM standard test recommends that specimens with fibers parallel to the direction of loading should be 11.5 mm wide. The test used here was of the dog-bone type and sized according to standards.
The tension test was performed on all three samples according to ASTM D3039-76 test standards. A three-point bend test is performed to determine the flexural strength of composites using Instron 1195. The strength of a material during bending is expressed as the stress on the outer fibers of a bent test specimen, at the point of failure.
The pendulum impact testing machine determines the notch impact strength of the material by crushing the V-notch specimen with a pendulum hammer, measuring the energy expended and relating it to the cross section of the specimen.
Scanning electron microscopy (SEM)
MECHANICAL CHRACTERISTICS OF COMPOSITES
RESULTS & DISCUSSION
Mechanical characteristics of composites
The test results show that with the increase in fiber loading hardness (Hv) value of the short bamboo-epoxy composites is improved [Figure 4.1]. The effect of weight fraction of fiber in the composite on the tensile strength is shown in Figure 4.2. From the figure, it is clear that the flexural strength of composites increases significantly with the increase in fiber loading up to 30wt%, but further increase in fiber loading flexural strength decreases.
In contrast, as shown in Figure 4.3, the flexural strength increased with increasing fiber loading up to 30 wt%. Figure 4.3 also shows that the linearly increasing trend up to a certain value of fiber load (30 wt.%) and the sudden drop due to the failure of the samples and retention points correspond to the breakage and extraction of individual fibers from the resin matrix. The impact strength of composites first increases by a small degree, i.e. up to 15% by mass, and with a further increase in fiber loading, the strength increases drastically.
The Rockwell hardness test results are shown in Figure 4.5 as a function of bamboo fiber (weight. It is clear from the figure that the hardness of composites increases significantly with the increase in fiber length up to 1.5 cm, however with further increase in fiber length up to 2 cm the hardness decreases gradually Therefore, the void content in the composites automatically increases with the increase in the fiber loading.
The figure shows that with a fiber length of 2 cm the composite shows a higher tensile strength than that of a fiber length of 1 cm with a comparable weight fraction (45 wt%). With a fiber length of 1.2 cm, the tensile strength is slightly higher than that of the composite with a fiber length of 1 cm, namely 45 wt.%. When the fiber length is increased to 2 cm, the yield point is found to be consistently higher than 1 cm and 1.5 cm fiber length.
In this work, the flexural strength values of the bamboo-epoxy composites are increased with the increase in fiber length under constant fiber loading, i.e., 45 wt%. However, in the previous case, as the fiber load increases, the flexural strength increases to 30 wt% and then decreases to 45 wt%, with the fiber length remaining constant (1.2 mm), as shown in Figure 4.3. For this study, the best result was obtained at a fiber load of 30% by weight with a fiber length of 1.2 cm.
But with the increase in fiber length, the maximum bending increases as shown in Figure 4.7. It is clear from the figure that the impact strength of composites increases significantly with the increase in fiber length.
Surface morphology of the composites
It is observed from the figure that the surface looks very smooth and less void content as shown on the top surface of the composite sample. When applying tensile load to the 45 wt% bamboo fiber reinforced epoxy composite, the fractured surface of composite shows fracture of matrix material under initial loading condition (Figure 4.9(b)). This is because without fibers to slow the crack growth during external loading, the crack will propagate in an unstable manner.
In addition, it is also observed that there is matrix plastic deformation near the crack tip, which contributes to the formation of a plastic zone in the material. However, by increasing the tensile load up to the yield strength, relatively long extruded fibers can be observed, as shown by fiber pull-out as shown in Fig. 4.9(c). This is a sign of crack bending, where the fiber changes the path of the crack and directs it along the surface of the fiber.
This leads to fiber debonding, which is an indication of matrix separation around the fibers as the crack front intersects it. Furthermore, fiber edge damage and fiber splitting are observed, when the fiber length increases up to 2 cm, the highest fracture toughness is achieved at the highest fiber weight fraction. At higher fiber loading, there is more fiber surface area that contributes to energy dissipation, thus further improving fracture resistance.
It has also been reported that long continuous sisal composites have consistently higher fracture toughness than short sisal composites at similar fiber volume fraction [61].
CONCLUSIONS
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![Table 1.1 Composition of few Natural Fibers [7, 8]](https://thumb-ap.123doks.com/thumbv2/azpdfnet/10557847.0/13.918.132.786.142.453/table-1-1-composition-of-few-natural-fibers.webp)
![Table 1.2 Average chemical composition (g kg-1) dry matter [DM]) of Bamboo leaves (n = 3) [12]](https://thumb-ap.123doks.com/thumbv2/azpdfnet/10557847.0/15.918.141.799.174.744/table-average-chemical-composition-dry-matter-bamboo-leaves.webp)
