Kenaf

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Kenaf composites experience a number of damage modes under dynamic compression loading. Therefore, in order to understand the overall behavior of the Kenaf composite, it is necessary to identify the different types of impact damage that occurred. Damage of composites such as cracking constituents usually occur and are not totally visible.

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To understand it, examination and analysis of specimens are needed. Microscope observation was used to observe the morphology of fractures of tested samples.

This technique has been largely considered in various investigations of composites. The observed images of the fractured specimens under dynamic compressive test are shown in figure 9. On the top surface, it can be seen that the impact damage spreads throughout the specimen. These damage modes include degradation of the fiber/matrix bond strength and eventual debonding, matrix cracks, and fiber splitting, resulting in overall stiffness and strength degradation of the composite.

This failure of the matrix material can originate from various loading conditions. In all cases, cracks initiate or propagate within the matrix or at the interface between fiber and matrix, if the respective loading condition of normal stresses or shear stresses exceeds the local strength of the matrix or interface, respectively. While bulk of the failure involves cracking of matrix, or interface debonding, fiber splitting may occur especially if fiber itself is weak in transverse direction, and the unidirectional composite is highly aligned in transverse direction.

Referring to Fig. 7, longitudinal ply splitting or matrix fractures parallel to the fibre direction occurs and extends from the top and to the bottom surfaces. So, at the moment of impact, stress concentration is generated at the contact point where the matrix cracks and fiber bundles split. On the one hand, the stress wave propagates along the fiber direction, the fiber bundles act as the main load-bearing object, and fewer cracks can be seen along the longitudinal direction.

Moreover, Figs. 9 shows a higher extent of fiber splitting and bending, which confirmed lower fiber-matrix adhesion, also indicates fibers were carrying higher load share than matrix (Ku et al. 2011).Based on the results of the experimental investigation, bonding at the fiber-matrix interface is identified as the dominant compressive failure mechanism in Kenaf composites which controlling the mechanical performance.

Previous study have also shown that debonding of the fiber/matrix interface has caused substantial degradation in the transverse response of a composite, resulting in an early degradation in the stress-strain curve [33]. Besides, multiaxial tests conducted by Lissenden, et al. [34] on SiCTi tubular specimens revealed that fiber/matrix interfacial debonding plays an important role in the axial shear response.

The mechanical properties of natural fibre reinforced composites highly depend on the interface adhesion property between the fibres and the polymer matrix as have been reported by many researchers [5–8]