Papers by Keyword: Unidirectional

Abstract: Research on composites reinforced with abaca fiber is still being carried out. Research about fiber treatment, research about mixing abaca fiber with other natural fibers, or mixing abaca fiber with synthetic fiber, as well as the types of matrices used and research on differences in fiber orientation to determine its strength still being conducted. This research aims to study the mechanical properties of abaca fiber orientation on abaca fiber reinforced composite. The fiber is abaca fiber (Musa Textiles Ne) and the matrix is epoxy resin. The abaca fiber is first soaked in alkaline NaOH solution with a ratio of 5wt % to water for 2 hours. After being washed thoroughly and dried, the abaca fiber is prepared in 3 orientations, the first is woven orientation, the second is unidirectional orientation and the last is random orientation, where the fiber were cut into 20 mm pieces and arranged randomly. The abaca fiber is then mixed with epoxy resin in a ratio of 40% abaca fiber and 60% epoxy resin and pressed to a thickness of 4 mm. According to ASTM D638 standard, tensile strength testing was conducted and flexural strength was conducted according to ASTM D790 standard. The results show that the tensile strength of woven orientation is 63.1156 MPa and fiber with a unidirectional orientation is 62.4829 MPa and fiber with a random orientation is 22.3517 MPa. The elastic modulus of woven, unidirectional and random orientations are 3.6425GPa, 3.9734 GPa, and 1.6449 GPa, respectively. Bending test results show that random orientation is more flexible than woven and unidirectional orientation, where the strain value is 0.0408 mm/mm, 0.0393 mm/mm, and 0.0369 mm/mm, respectively. The flexural modulus of the three different orientations is 0.8082 GPa for random orientation, 1.2176 GPa for woven orientation and 1.675 GPa for unidirectional orientation. It can be concluded that the tensile strength of woven orientation increases by 1% to unidirectional orientation and 182% to random orientation. Compared to the three different orientations, random orientation has higher bending properties than woven and unidirectional orientation, and woven orientation is still more flexible than unidirectional orientation.

Abstract: Reliable composite forming experiments are required to characterize composite formability, to aid material development, and to validate process simulations models. Due to practical reasons, however, typically a limited amount of forming configurations is studied. The objective of this study is, therefore, to develop a methodology for obtaining controlled forming results in a wide range of configurations. Press forming experiments using a dome geometry were used to explore the formability of two commercial unidirectional thermoplastic composite materials. A variety of forming configurations was employed by changing the blank dimensions and layup. The observation of wrinkling defects was simplified by leaving an additional 3 mm tool gap. Blank width and layup had the most influence on the wrinkling severity, followed by blank thickness and length. Quasi-isotropic layups were found to produce wrinkles in nearly all cases, confirming a difficulty in general to form double curved parts. The size and number of wrinkles in these layups were found to change with the stacking sequence. Cross-ply layups showed better formability, but significant wrinkles were still observed depending on the orientation of the blank relative to the layup. The formability experiments using a dome geometry provided a reliable methodology for controlled forming results in many configurations using a generic toolset. Additionally, a comprehensive comparison of formability for two commercial thermoplastic UD materials in a variety of scenarios was provided.

Abstract: When testing unidirectional reinforced composites with a fiber orientation of 90° in tensile tests with rectangular specimens, the influence of the clamping often causes a failure in their vicinity and therefore the test cannot be regarded as valid. In this paper, a test specimen design was determined which is well suited for testing the material properties transverse to the fiber direction by calculating the influence of geometric details of shoulder bar specimens with the help of finite element simulation. The particularly critical clamping and shoulder areas were examined more closely to ensure failure mainly in the test field. In the clamping area the design of the glued-on tabs was investigated and in the shoulder area an optimization of the shoulder geometry was done. Based on the two optimized design proposals, test specimens were produced and evaluated by monotonous tensile tests. Subsequently, Wöhler tests were carried out at different R-ratios and load levels and compared with results of rectangular specimens.

Abstract: The interest of using kenaf fibers in composite fabrication has grown due to renewable, sustainable and environmental issues. The applications of kenaf composite have been broadly exploited especially in automotive industry. In this research, unidirectional kenaf polypropylene (PP) composites were prepared using the hot pressing method. The processing parameter need to be optimized to ensure that the fabrication process will enhance the mechanical properties of the composite. Thus, a research on the optimization process on the processing parameter (temperature, pressure, pressing time and kenaf percentage) on the tensile properties was conducted by using a two-level full factorial design. The effect of the individual factors and their interaction were observed. From statistical analysis, the main effect of tensile strength and young modulus is the percentage of kenaf fibers with 21.67% contribution. The interaction between kenaf percentage and pressing time also contribute an effect on the tensile properties with 13.29% contribution. Finally, the result showed that at 190°C, pressure 5 MPa, 5 minutes pressing time and 50% fiber content will give the optimum tensile strength and young modulus which is 163.12 MPa and 11.17 GPa respectively with improvement of 486% tensile strength compared to pure PP.

Abstract: The current trend particularly in industrial and commercial sectors is to search for alternatives to the current structural materials made from new lightweight materials. One option is to use unconventional material composite structures which have a combined fibre/matrix. Analysis of UD prepregs with unidirectional carbon fibres was performed. These special unconventional materials can be used for both flat and shaped structural products. The extent and quality of the saturation of the fibre layers in the resulting composite are important features for the whole complex of its parameters and influence its quality and mechanical properties. The experimental study also included an exploration of the inner structure and interactions of the individual components and detection of internal defects in the carbon UD prepreg composite using an X-ray microtomograph. The results illustrated the detection of microcracks, which significantly influence the resulting synergy of the composite and which were previously undetected.

Abstract: Optimizing the mechanical properties of composites is very important for light low energy constructions. Unidirectional prepreg (UD prepreg) is an intermediate product synthesizing a unidirectional layer of carbon fibres with a matrix. This can be used in the production of continuous fibres of reinforced composites. The individual layers can be stacked on top of each other to precisely orientate the layers and attain the maximum properties in a given direction. The resulting composite is ultra thin with the highest possible fraction of fibres. Prepreg composites are very high quality and have very good mechanical properties. They can be applied in sectors where the requirements for mechanical resistance are very high. This paper presents an experimental and numerical analysis of the surface of a composite and the changes that may occur to it under the influence of loading. The Ball Drop Test (ASTM D6024-07 / DIN 52306) was used as a stress test. Test samples scanned by image analysis showed that the surface properties of the UD prepreg were not disrupted, while scanning with AXIO IMAGER M2 showed apparent surface disruptions. From the numerical simulations it was determined that a directional orientation of the fibres of +45°/0°/-45° significantly affects their elastic properties.

Abstract: This paper presents an example of optimization of an automated manufacturing system comprising a transport subsystem based on the automated guided vehicles (AGV). Number of resources in the manufacturing system and the number and location of the AGVs were subject of optimization. Profit maximization was assumed as an objective function. Arena and OptQuest software were used to build the simulation model and perform the optimization. The article describes an original solution for optimizing the number and cost of AGVs.

Abstract: Scaffolds have to meet exacting physical, chemical, and biological criteria to function successfully, and those criteria vary with the type of tissue being repaired. In the present work, slurry with different initial content of 7.5-22.5 vol% HA prepared from calcinated hydroxyapatite. The prepared slurries freeze casted unidirectionally with the different cooling rate of 2-14°C/min with intervals of 3°C/min from the ambient temperature. Then, green bodies freeze-dried for 72h following with sintering at temperatures of 1350°C. The results showed that compressive strength goes up with cooling rate and initial content. Total porosity has a range of 66-88% while has a compressive strength of ~0.4-18 MPa. Porosity size has a value of 20-200 μm by initial content and cooling rate. Based on strength and porosity, the specimen with initial content and cooling rate of 15 vol% and 5°C/min, respectively, chose to be the optimum. This specimen has a compressive strength and porosity size of 5.26 MPa and 88 μm, respectively. The compressive strength value of the mentioned lamellar HA scaffolds was in the range of the values reported for human proximal tibia.

Abstract: The most important characteristic of biomaterial as bone-repairing material, in addition to biocompatibility and appropriate porosity, is providing mechanical strength complying with injured tissue. In the present work, slurry with 15 vol% HA prepared from calcinated hydroxyapatite. The prepared slurry freeze casted unidirectionally with the cooling rate of 8°C/min from the ambient temperature. Then, green bodies freeze-dried for 72h following with sintering at different temperatures of 1250-1350°C with intervals of 25°C. The results showed that lamella space and porosity decreases with temperature while compressive strength and shrinkage goes up. Total porosity has a range of 75-83% while has a compressive strength of ~2-8 MPa. The sintered sample at 1350°C, with 75% porosity, which has a ~ 8 MPa compressive strength, chose to be the optimum. Also, some dendritic branch like structure and bridges can be seen on the internal walls of lamellae which can improve mechanical properties. These features may improve adhesion and growth of osseous cells.

Abstract: The micromechanical approach of Simplified Unit Cell Method (SUCM) in closed-form three dimensional solutions is used for predicting creep response of unidirectional fiber reinforced composites. The composite consist of elastic fibers reinforcing nonlinear viscoelastic resin. The nonlinear viscoelastic matrix behavior is modeled by using Schapery single integral viscoelastic constitutive equation. Off-axis specimens of graphite/epoxy with 45 and 90 fiber orientations were subjected to 480 minutes creep tests and the results is compared with experimental data and MOC results available in the literature. There is good agreement with experimental results due to using SUCM.