Iman Taha

Modeling of strength and stiffness of short randomly oriented glass fiber—polypropylene composites:

This study presents an approach toward better understanding of the mechanical behavior of short discontinuous randomly oriented fiber-reinforced composites. Due to their expanded use, the combination of polypropylene (PP) matrix and glass fibers (GFs) was chosen as an example of an injection-molded short fiber system to represent the complex class of materials. Based on the systematic evaluation of available mathematical models for the estimation of mechanical behavior, in addition to the analysis of microscopic observations, improved models for the prediction of composite stiffness and strength were developed. The models developed in this study, take into consideration several aspects that are found in a nonperfect composite, such as fiber length, preparation and orientation, fiber—matrix bonding, and processing conditions. The new models show a good description of the actual behavior, not only for the GF—PP system under consideration, but also for various other short-fiber polymer composites cited by the literature, such as carbon and natural fiber systems.

Comparison of picture frame and Bias-Extension tests for the characterization of shear behaviour in natural fibre woven fabrics

The investigation of the shear behaviour of technical natural fibres is vital for the insurance of aesthetics and performance of light weight, high strength, and eco-friendly composites. In this study, Egyptian jute fibre plain weave fabrics of various areal densities were investigated to describe their shear behaviour in terms of shear forces, shear angles and shear lock angles, using the Bias-Extension and the Picture Frame test methods. Results show that both methods are valid for natural fibres and produce comparable results. Whereas the Bias-Extension test presents a fast and simple test procedure, the analysis of the results is more complex due to the interaction of non-shear components. On the other hand, the Picture Frame test proves to be time consuming and in need of a more complex test rig, but results in pure shear deformations throughout the sample.

Modelling of Strength and Stiffness Behaviour of Natural Fibre Reinforced Polypropylene Composites

The mechanical behaviour (strength and stiffness) of natural fibre reinforced thermoplastics is investigated on the example of an injection moulded sisal-polypropylene system. An analytical model based on the rule of mixtures is developed to predict the mechanical behaviour of such composites. Considering interfacial characteristics this model accounts for the different modes of load transfer between matrix and fibre and their changeover. Close agreement between model and experimental results was achieved at low fibre contents (below 20 wt.%) as well as at higher contents (exceeding 40 wt.%). The model was finally verified against the experimental data and against available literature results.

Vibration Damping Behavior of Fiber Reinforced Composites: A Review

This paper gives a wide view over recent research in dynamic characteristics and vibration damping properties of fiber-reinforced, polymer-matrix composites, with emphasis on parameters governing damping, such as fiber volume fraction, fiber orientation, exciting frequency, aspect ratio and fiber-matrix interface, as well as stacking sequence for laminated composites. Both experimental and analytical models are discussed and parameters used to measure the amount of vibration damping are covered. Natural-fiber based composites are handled in detail in the last section of this paper.

Illumination of dense urban areas by light redirecting panels

With the high population growth rate, especially in developing countries, and the scarcity of land resources, buildings are becoming so close to each other, depriving the lower floors and the alleys from sunlight and consequently causing health problems. Therefore, there is an urgent need for cost-effective efficient light redirecting panels that guide sun rays into those dim places. In this paper, we address this problem. A novel sine wave based panel is presented to redirect/diverge light downward and enhance the illumination level in those dark places. Simulation results show that the proposed panel improves the illuminance values by more than 200% and 400% in autumn and winter respectively, operates over wide solar altitude ranges, and redirects light efficiently. Experimental and simulation results are in good agreement.

Potential of Sisal Reinforced Biodegradable Polylactic Acid and Polyvinyl Alcohol Composites

The application of natural fibres as polymer reinforcement is of extreme interest, especially in combination with biodegradable polymers. Such “green” composite represent a step forward to eco-design and environmentally friendly applications. The use of biodegradable polylactic acid (PLA) on the basis of renewable resources in addition to the biodegradable polyvinyl alcohol (PVA) on petrochemical basis is compared in this study with the application of polypropylene (PP) as a surrounding matrix for sisal fibres. According to the law of similarities, the chemically similar structure of natural fibres and PVA and PLA provides stronger fibre-matrix bonding characteristics compared to PP. This was experimentally validated applying single-fibre pull-out tests, where the effect of improved bonding is further investigated in terms of tensile and impact composite behaviour. SEM investigation was further applied to describe failure modes of natural fibre composites.

Co-Curing of CFRP-Steel Hybrid Joints Using the Vacuum Assisted Resin Infusion Process

This study focuses on the one-step co-curing process of carbon fiber reinforced plastics (CFRP) joined with a steel plate to form a hybrid structure. In this process CFRP laminate and bond to the metal are realized simultaneously by resin infusion, such that the same resin serves for both infusion and adhesion. For comparison, the commonly applied two-step process of adhesive bonding is studied. In this case, the CFRP laminate is fabricated in a first stage through resin infusion of Non Crimp Fabric (NCF) and joined to the steel plate in a further step through adhesive bonding. For this purpose, the commercially available epoxy-based Betamate 1620 is applied. CFRP laminates were fabricated using two different resin systems, namely the epoxy (EP)-based RTM6 and a newly developed fast curing polyurethane (PU) resin. Results show comparable mechanical performance of the PU and EP based CFRP laminates. The strength of the bond of the co-cured samples was in the same order as the samples adhesively bonded with the PU resin and the structural adhesive. The assembly adhesive with higher ductility showed a weaker performance compared to the other tests. It could be shown that the surface roughness had the highest impact on the joint performance under the investigated conditions.

Light redirecting system using sine-wave based panels for dense urban areas

Cities and towns around the world are becoming more condensed due to the shrinking amount of buildable areas, which significantly reduces the amount of light that occupants have access to. This lack of natural lighting results in health, safety and quality of life degradation. This paper presents a new technique of transmitting sunlight downward into narrow alleys and streets, by using a daylighting guiding acrylic panel that is capable of changing the direction and distribution of the incident light. The core of the proposed daylight guidance system is made up of light transmission panels with high quality. The corrugations have sine wave shaped cross-section so that the panel functions as an optical diffuser perpendicular to the direction of sunlight propagation. The day lighting system consists of the corrugated panels and a lattice frame, which supports the panel. The proposed system is to be mounted on the building roof facing the sun so as to redirect the incident sunlight downward into the narrow alleys or streets. Since building sizes and orientations are different the frame is arranged such that substantially deep light penetration and high luminance level can be achieved. Simulation results show that the proposed panel improves the illuminance values by more than 200% and 400% in autumn and winter, respectively, provides fan-out angle that exceeds 80° for certain solar altitudes and the transmitted power percentage varies from 40% to 90% as the solar altitude varies from 10° to 80°. Experimental results are in a good agreement with the simulations.

Behaviour of Hybrid SiC/Jute Epoxy Composites Manufactured by Vacuum Assisted Resin Infusion

Natural fibre-reinforced polymer composites are standing in the limelight of investigations due to their light weight and availability from natural and renewable resources. Improved mechanical and physical behaviour is targeted through hybridisation with other reinforcing elements. This study investigates the potential of adding silicon carbide particles at volume contents ranging between 2 and 8% to jute fabric-reinforced epoxy composite to produce such hybrid composites. In contrast to the commonly applied processing technique of hand layup used to produce natural fibre-reinforced laminates, the vacuum-assisted resin infusion method was applied in this study to produce high quality laminates. Samples were tested for their mechanical behaviour through tensile, flexural and impact tests. Scanning electron microscopy was further performed to analyse the modes of failure of the composites. Finally, erosion tests were conducted, by directly sanding the hybrid composite samples to evaluate their erosion wear resistance. Results indicated that the addition of particles had a significant effect on the tensile, flexural, impact and erosion wear behaviour of the composites under investigation. Hybrid composites reinforced with 4 vol.% SiC exhibited acceptable mechanical properties. The behaviour was found to deteriorate at SiC contents beyond 4 vol.%.

In-situ pyrolysis: A novel technique for the dispersion of carbon particles in thermoplastics

An adequate dispersion of fine particles is essential for improved properties in particle-reinforced composites. State-of-the-art methods mainly rely on mechanical (shearing) dispersion methods that do not yield the requested homogeneity within the final composite. This leads to a deterioration and inhomogeneity of mechanical properties. Other non-conventional methods such as in-situ polymerisation or solution compounding are not yet applicable on an industrial scale. This study tackles these problems and provides a novel method for the fabrication of well-dispersed particle-reinforced polymer composites while making use of conventional machinery on the one hand and allowing industrial applicability on the other hand. The presented technique makes use of the pyrolysis of a low thermally stable polymer within a conventional melt compounding process to produce well dispersed carbon particles throughout a thermoplastic matrix in an in-situ process. For this purpose, Carboxymethylcellulose particles are used. The selection of decomposition parameters around the processing temperature of polypropylene yields well-dispersed carbon particles, as evidenced by scanning electron microscopy. This further interprets the resulting promising mechanical properties.