In recent years, the polymer industry has intensified its efforts to produce renewable material based polymer. Therefore, the use of natural fiber composites has been widely considered in various engineering sectors to replace conventional synthetic composite usage. This is because natural fiber composite properties are easily disposed and environmentally friendly in generating economic and sustainability societies. Vinyl polymer is a group of matrices comprising of thermosets and thermoplastics that are normally preferred as matrices with natural fibers. Both groups have their own unique features in benefiting their applications. The composite made of thermoset resin cannot be reprocessed or recycled. The composites of the thermoset matrix tend to provide good mechanical strength, are fragile and have low tensile effects. This is in contrast to the properties of the thermoplastic polymer that can be formed and diluted without changing its physical properties. Thermoplastic has excellent impact resistance and ductile. However, various approaches continue to be carried out by researchers to meet the requirements of natural fiber composites in different applications.

Nowadays, natural fibers getting attention from researchers and industries to optimize the use it, with combination of polymers as composite structure, due to environmental awareness. Furthermore, it show a few advantage, such as biodegradability, light in weight and non-toxic characteristic. In this study, kenaf natural fibers was used as reinforcement material, with combination of polyester as matrix material, known as polymer matrix composites. The main purpose of this study is to analysis the mechanical properties of kenaf natural fiber/polyester composite structure, in order to know the suitability of kenaf natural fibers as replacement material for table tennis blade structure, instead of using wood. The structural panel of composite laminates has been produced using hand lay-up technique. The experimental works are performed in tension, impact (Charpy) and shear condition. The characteristic of different condition on kenaf composite structure was studied. Based on the result, it found the properties of kenaf composite structure, and it will used as a benchmark, to compare with initial properties of table tennis blade made by wood. In addition, the strength and a weakness of that particular materials and lamination structure will be identified.

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This study aims to investigate the fatigue behaviour and determine the fatigue life prediction under biaxial loading. Fatigue tests were performed according to ASTM 2207-02 and the values of tensile stresses are selected from the ultimate tensile strength which is 0.5 Su, 0.6 Su, 0.7 Su, 0.8 Su and 0.9 Su, while the torsion angle representing the shear stresses acting was set at 15 degrees. The biaxial fatigue test was conducted using a combination of two types of stresses acting on the same frequency, namely 1 Hz, on smooth specimens made from medium carbon steel. The biaxial fatigue lives of the specimens are recorded when the specimen has completely fractured. The results indicate that the observed fatigue lives are in good agreement with the predicted lives by using the Coffin-Manson, Morrow, and Smith-Watson-Topper strain-based models. Mohr's circle approach was used to determine the maximum shear stress and principal normal stress. The maximum shear stress increased from 457 MPa to 486 MPa with the increment of principal normal stress from 612 MPa to 767 MPa. The principal stresses, maximum shear stresses, and energy dissipated were used to explain and describe the behaviour of biaxial fatigue. Both stresses are inversely proportional to the fatigue life. Meanwhile, the energy is linearly proportional to the stress applied, where the values increase in the range 500 kJ/m 3 to 605 kJ/m 3. Thus, the basic understanding of the material behaviour may be used in the processes of declaring component service lives and the fatigue life prediction of a particular automotive component. Therefore, the cost incurred can be reduced for the development process in material engineering.

Natural fibres have the potential aspect to replace glass fibre reinforced composites. One of these fibers is kenaf. It is also one of the selected natural fibres that have bio resource profit regarding on their capability to absorb energy absorption especially. In order to prove the application of this fiber for the load-bearing application, the fiber in the form of yarn is weaved into fiber mat and reinforced with the plastic resin. This study focused on the twill yarn kenaf woven composite structure. Composites were prepared using the hand lay-up method with different type of orientation where the orientation is designed using Taguchi method. The hardened composites were cured for 24 hours in an ambient temperature before it was shaped according to ASTM D3039. The samples were then stressed uni-axially to obtain the stress-strain curves. The result shows the fiber orientations were significant factor in determining the performance of tensile strength. In this work, fiber mats are then optimized and the results showed that the values of tensile and modulus strength were 55.738 MPa and 5761.704 Joule, which is increased 3.77% and 4.23% for tensile strength and Young modulus, respectively. By comparing fracture mechanism before and after optimizations, there was clear decreasing fracture surface. It indicated that, the mechanical behavior performances of the twill woven kenaf reinforced composites can be effectively improved by this method.

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In engineering applications, analysis of crack growth life is useful in situations where an unexpected crack has been found in a component of a machine, vehicle, or structure. The objective of this research is to investigate the correlation curve of magnetic flux leakage, Hp(y) signals by evaluating their critical value point with respect to step size. Moreover, the relation of fatigue crack growth rate, da/dN toward the stress intensity range, ΔK and Hp(y) in metal components is also discussed in this paper. The tension-tension fatigue test was conducted with the metal magnetic memory scanning device and crack opening displacement (COD) gauges in 10 Hz (testing frequency) by applying a load for 3.0-5.0 kN respectively. As a result, the correlation curve of Hp(y) was built with the R-Squared values in the range of 0.99 and one mathematical model has been developed for estimation analysis. The sigmoidal shape curve was plotted on the graph of da/dN versus ΔK and also with Hp(y). Thus, for validation, the linear relation is represented between ΔK and Hp(y) that present a good approach for magnetic parameter to be developed in the fatigue crack growth analysis. Therefore, the magnetic method has greater capability to analyze the fatigue crack propagation life in a real application.