Papers by Keyword: Short Fibre

Abstract: The material replacement of component is often used procedure, which helps to reduce production costs, simplify manufacturing, improve functional properties of component and bring another benefits. In the last years, more and more metal parts are converted to plastic, also in the cases of mechanically loaded parts. For these special applications, the fibre reinforced composite plastics are successfully used. However, the mechanical properties of composite plastic are strongly dependent on the fibres orientation and following anisotropic behaviour. Moreover, the orientation of fibres is influenced by the conditions of the part production. Due to the number of these dependencies, the material conversion becomes a complex task which cannot be solved with analytical approach. Especially in case of complicated part geometry. In this study, the connection of two different numerical solvers was used for material conversion of a part from automotive industry. First, the new geometry of analyzed part was designed in order to compensate lower mechanical properties of plastic in comparison to metal. Next, the new part manufacturing was simulated and this way obtained anisotropic properties of composite plastic were described. Finally, the structural analyses of original metal and new composite plastic part with real anisotropic properties were performed to verify achievement of material conversion. The aim of this study is to demonstrate, how numerical analyses can help to predict an unexpected result.

Abstract: This paper describes the experimental investigation of the tensile and flexural strength of untreated Napier grass fibre reinforced polyester composites. Napier grass fibres were extracted trough conventional water retting process and used as reinforcing materials in the polyester composite laminates. Tensile tests were then conducted for the composite specimens from the laminates at 25% fibre loading using the electronic extensometer setup to obtain the tensile properties. The results show significant differences in tensile strength between random short fibres laminates and random long fibrelaminates with the long fibres yield over 30 % higher in strength.Both the short and long fibre composites exhibits similar strength with short fibres having slightly higher flexural strength to long fibres The laminate also shows higher maximum strength compared to other commonly available natural fibre composites with almost 75 % improved in the maximum strength compared to the short kenaf fibre reinforced composites.

Abstract: This paper describes the experimental investigation of the tensile strength of untreated Napier grass fibre reinforced polyester composites. Napier grass fibres were extracted trough conventional water retting process and used as reinforcing materials in the polyester composite laminates. Tensile tests were then conducted for the composite specimens from the laminates at 25% fibre loading using the electronic extensometer setup to obtain the tensile properties. The results show significant differences in tensile strength between random short fibres laminates and random long fibre laminates with the long fibres yield almost 45 % higher in the strength. The laminates also show higher maximum strength compared to other commonly available natural fibre composites with over 70 % increase in the maximum strength compared to the short kenaf fibre reinforced composites.

Abstract: Polymeric material's extrusion is a very complex manufacturing process opened for new research. In this paper the authors use for extrusion polyamide 6.6 reinforced with 20% glass fibres. This material offers very good mechanical, thermal and frictional proprieties. The improvement of these proprieties can be realized through the optimization of the extrusion process. Temperature is a very important parameter for obtaining good quality products, so to choose the proper values of it, is an interesting challenge. It was proved that the main influence upon the product's quality have the temperatures from the metering zone and from the forming zone so the optimization of these is of maximum importance for the quality of the products. The Response Surface Method (RSM), based on ANOVA - Analysis of Variance model was used for optimization the temperatures from the metering zone and from the forming zone.

Abstract: The demand for lightweight structures in the automotive and aerospace industry increases permanently, and the importance of lightweight design principles is also increasing in other industrial branches, aiming towards improved energy efficiency and sustainability. Light metals are promising candidates to realize security relevant lightweight components because of their high specific strength; and amongst them, aluminum alloys are the most interesting materials due to their high plasticity and strain to failure, good processability, passivation in oxygen containing atmosphere, and low cost. However, for many applications, their stiffness as well as strength and fatigue behavior at elevated temperature are insufficient. Metal matrix composite (MMC) formation by integration of reinforcements in the form of continuous or discontinuous (short) fibers can yield a high increase in the alloys’ specific mechanical properties at room temperature and at elevated temperature. The integration of fibers with conventional manufacturing techniques like squeeze casting, hot pressing or diffusion bonding leads to restrictions in the component’s geometry. Moreover, these techniques result in elevated process costs mainly caused by long cycle times and the need of additional protective fiber coatings. In the present paper, an alternative method for the manufacturing of aluminum matrix composites is described, combining thermal spraying and semisolid forming (thixoforging) technologies for the formation of fiber prepregs and subsequent forming with simultaneous densification. Therefore, prepregs with the matrix alloy as a thick surface coating on the reinforcement fibers are manufactured in a fast, automated coating process, while reheating, densification and shaping are performed in a separate process, allowing an optimization of both processes towards cycle times and resulting material properties. Continuous fiber and short fiber reinforced aluminum matrix composites are manufactured using woven or parallel arranged continuous fibers, or short fibers as a fleece or fiber paper material. For the coating process, twin-wire electric arc spraying is applied as a well established, cost efficient thermal spray technology. The coating process is optimized towards microstructure of the matrix alloy prior to semisolid forming, which requires a globular alloy microstructure, and reduced fiber damage during the high-temperature liquid melt deposition. The thermally sprayed fine-grained matrix material enables semisolid forming at liquid contents of 40-60 vol% of the alloy, with short flow paths, reduced mechanical loads and short cycle times. Thus, limited fiber damage and residual stresses will occur, leading to good mechanical material properties. A production line for industrial-scale coating of fiber fabric coils in a continuous process is introduced in order to provide prepregs of various fiber-reinforcement materials and fiber architectures; moreover, a winding equipment for simultaneous fiber winding and coating is presented that enables local reinforcement for components with adapted, tailored composite material design.

Abstract: The temperature-dependent tensile strength is an important indicator used to evaluate combination property of short-fiber-reinforced elastomer matrix composite. Some short-fiber-reinforced elastomer matrix composites are manufactured in the molding preparation process, and the tensile tests of fiber, matrix and the composites are carried out at different temperatures. The fiber length and orientation distributions are statistically analyzed. The influence of temperature on the micromechanical stress distribution and transfer in the composite is investigated, and the thermal stresses in the fiber, matrix and fiber-matrix interface are obtained. Based on the theory of micromechanical stress distribution and transfer of the fibrous composite, the mixture law is modified, and a model for predicting the temperature-dependent tensile strength of this kind of composite is developed. Moreover, the mechanism of the tensile fracture of the composite at various temperatures is discussed. Research indicates that the tensile strength is largely related to the temperature, mechanical performances of the main components of the composite and some microstructural parameters, such as short fiber aspect ratio, volume fraction and orientation distribution. The tensile strength of SFRE decreases with increasing temperature. The tensile strength increases with the increase of fiber length when the fiber length is no larger than critical fiber length. There exists a critical fiber volume fraction where the tensile strength of SFRE reaches the maximum. The tensile fracture of the composite depends largely on the temperature, the bond strength of fiber-matrix interface and the average length of reinforcing short fibers. The temperature-dependent tensile strengths predicted by the presented model are in good agreement with experimental data.

Abstract: This work presents the investigation of the mechanical behavior of composite materials strengthened with short fibers and particles. A simple model is presented, with the purpose of predicting the fracture strength of this class of composite material. The model consists of the modification of the rule of mixtures, by the introduction of a correction factor, which corresponds to the adhesion of the resin to the fiber and the particles. The experiments were performed on three different composite materials having the same raw material but different mixture ratios. The composite materials produced were tested by the three-point flexural method, according to ASTM standard, in order to determine their mechanical properties. The comparison between theoretical and experimental results were also performed and found to be in reasonable agreement. Other relevant parameters will also be discussed.

Abstract: A new type of porous composite with a porous framework was prepared using a mixture of hydroxyapatite whiskers (W-HA) and poly(L-lactic acid) short fibers (F-PLLA) by a particle-leaching technique. The material, composed of a porous framework with interconnecting pore of >1 µm, has large-sized pores of about 200 µm. The large-sized pores were formed by leaching sucrose granules. The porosity can be controlled in the range from 60 to 85 % by the sucrose content. The small-sized pores in the framework formed due to the poor densification of the W-HAs / F-PLLAs mixture. The pore distribution in the framework can be controlled by the compressing pressure without change in the distribution of large-sized pores.

Abstract: The reinforcing mechanism of novel aramid pulp (AP) short fibre in CR matrix has been discussed in this paper, and it has been shown that the reinforcing effects of AP depend mainly on the dispersing uniformity and openness of those ultra-fine short fibres of AP in CR matrix.By proper pretreating method, the dispersing uniformity and openness of ultra-fine AP short fibres with high specific area can be improved markedly, so the large reinforcing potential can bring into play adequately.

Abstract: First, the characteristics of thermal residual stress in randomly oriented short δ-Al2O3 fiber reinforced aluminum alloy composites were analyzed by an elasto-plastic finite element method regarding the effect of the variation in short fiber orientation. Then, the effective moduli and initial tensile stress-strain curves of the composites were simulated by finite element method with the thermal residual stress taken into account. It is concluded that the simulated results obtained with thermal residual stress contained agree with corresponding experimental results better than those obtained in thermal residual stress-free cases.