Materials Science Forum Vols. 654-656

Abstract: Three-dimensional (3-D) spacer fabric composite is a novel lightweight sandwich structure, the reinforcement of which is integrally woven with two facesheets connected by continuous fibers (named piles) in the core. Usually the 3-D spacer fabric composite without extra reinforcement is called mono-spacer fabric composite, which provides outstanding facesheet / core debonding resistance. However, its mechanical properties cannot meet the demand of structure application because of the thin facesheet and low load-bearing capacity of high piles. Hence, two reinforcement methods were developed by laminating additional weaves at the facesheet and filling foam materials in the core to strengthen the facesheet and piles, respectively. This paper aims to investigate the influences of reinforcement methods on the mechanical behaviors and damage modes of 3-D spacer fabric composites under flatwise compressive, shear, edgewise compressive and three-point bending loads, by comparing with mono-spacer fabric composites. The results indicate that additional weaves reinforcement can enhance edgewise compressive and flexural properties effectively. Foam filling is one of the best options to improve the flatwise compressive and shear properties, and especially, there are synergistic effects between piles and foam under flatwise compressive load. Besides, the failure modes of reinforced and mono-spacer fabric composites are different.

Abstract: Interfaces are important for many properties and applications of multiphase materials. This is particular true for particle-reinforced polymer composites, where the interfacial characteristics between particle and polymer play a crucial role in load transfer and mechanical properties. In polymer nanocomposites, the adhesion strength between particle and polymer matrix is a major factor in determining their mechanical properties. In this work, we present our recent study towards the quantification of the interaction strength at the interface of clay-based polymer nanocomposites by molecular dynamics simulation.

Abstract: In recent years considerable attention has been dedicated to renewal power sources, such as wind power. This work was carried out in order to develop a small wind turbine of 1-10kW power generation capability. This wind turbine is designed to be energetically more efficient by 30-50% and having a lesser specific cost (by 25-30%). This work focused on the development of composite materials for application on the blades in the wind generator. In this paper we present the results of the research work done on the development of flexible technology for the fabrication matrix-epoxy resin based hybrid composites, reinforced with carbon, basalt and glass fibers. These new composite and hybrid materials were fabricated using epoxy matrixes. These matrices were reinforced with basalt and carbon fibers of different content and strengthened by mullite-like crystals. The basalt fibers for composite reinforcing were prepared from raw materials, with chemical composition: SiO2-15.3%; CaO-10.8%; Na2O-4.2%; MgO-8.8%; Fe2O3-12.1%; MnO-0.7%; TiO2-0.7%. The properties of new composites developed depend on the content and architecture of reinforcing components and are: tensile strength-(0.012-1.590)GPa; compression strength-(0.078-0.656)GPa; modulus of elasticity-(8.4-162.9)GPa; Poisson ratio-(0.015-0.559). The variation of strength and elastic characteristics under tension and compression of the new composites are presented.

Abstract: Metallic tubes have been extensively studied for their crashworthiness as they closely resemble automotive crash rails. Recently, the demand to produce lighter weight, yet safer vehicles has led to the need to understand the crash behaviour of novel materials, such as fibre reinforced polymer composites, metallic foams and sandwich structures. This paper discusses the static indentation response of Carbon Fibre Reinforced Polymer (CFRP) tubes. The side impact on a CFRP tube involves various failure mechanisms. This paper highlights these mechanisms and compares the energy absorption of CFRP tubes with similar Aluminium tubes. The response of the CFRP tubes during bending was modelled using ABAQUS finite element software with a composite fabric material model. The material inputs were given based on standard tension and compression test results and the in-plane damage was defined based on cyclic shear tests. The failure modes and energy absorption observed during the tests were well represented by the finite element model.

Abstract: The polyacrylonitrile (PAN)-based and pitch-based carbon fiber-reinforced nanoparticle filled polyimide based multiscale hybrid composites have been fabricated using vacuum assisted resin transfer molding (VaRTM) and autoclave curing. The carbon fibers used in this study were high tensile strength PAN-based (T1000GB) and high modulus pitch-based (K13D) carbon fibers. Fiber orientations of the T1000GB/K13D hybrid composites were set to [0(T1000GB)/0(K13D)]2S (T1000GB and K13D unidirectional layers were alternately and symmetrically laminated). The fiber volume fraction was 50 vol% (T1000GB: 24.9 vol%, K13D: 25.1 vol%). Polyimide used in this study was a commercially available polyimide precursor solution (Skybond 703). Four different types of nanoparticle (25nm-C, 20-30nm-β-SiC, 130nm-β-SiC and 80nm-SiO2) and particle volume fraction was 5.0 vol% used for the inclusion. The tensile properties and fracture behavior of T1000GB/K13D nanoparticle filled and unfilled hybrid composites have been investigated. For 25nm-C, 20-30nm-β-SiC and 80nm-SiO2 nanoparticle filled and unfilled hybrid composites, the tensile stress-strain curves show a complicated shape. By the high modulus pitch-based carbon fiber, the hybrid composites show the high modulus in the initial stage of loading. Subsequently, when the high modulus carbon fiber begin to fail, the high strength fiber would hold the load (strength) and the material continues to endure high load without instantaneous failure.

Abstract: In this paper, epoxy eco-composites reinforced with recycled cellulose fiber (RCF) and nano-fillers such as nano-clay platelets (30B) and halloysite nanotubes (HNTs), have been fabricated and investigated. The influences of RCF/nano-filler dispersion on the microstructure, physical and mechanical characteristics have been characterized. Results indicate that flexural strength decreased for the majority of study samples due to the poor dispersion of nano-fillers and the existence of voids within the samples. In contrast, impact toughness and fracture toughness were improved for all reinforced samples. The effect of water absorption was positive in terms of enhancing the impact toughness of the composites. Addition of nanoclay was found to increase the porosities of all nanocomposites.

Abstract: Metallic closed cellular materials containing polymer were fabricated by the penetrating polymer into metal foam. The aluminum and stainless steel foams were selected for the metal foam and epoxy resin and polyurethane resin were selected for the penetrated polymer. The many kinds of mechanical properties of this material were measured. The results of the compressive tests show that these materials have different stress-strain curves among the specimens that containing different materials in the cells. Also, this metallic closed cellular materials containing polymer have higher compressive strength, higher Young’s modules, higher energy absorption and higher internal friction than that of metallic closed cellular material without any polymer.

Abstract: In this study, the crystallization behaviors of the poly (ethylene terephthalate) oligomer/bisphenol-A polycarbonate (PETO/BAPC) blends were investigated under high pressure, and the recovered PETO/BAPC samples were characterized using XRD, DSC, SEM and AFM. The results showed that high-quality extended-chain single crystals with large c-axis thickness were formed in the multi-phase system within a relative short time, and the inner defects of the disclosed crystals could be removed by a self-healing process through high-temperature and high-pressure annealing. Morphologies of extended-chain crystals with different characteristics were also revealed with SEM and AFM. Wedge-shaped and bent extended-chain morphologies suggested that sliding diffusion and transesterification occurred simultaneously in the system, and the crystallization of the large crystals was a self-assembling process induced by chemical reactions at high pressure. This process provides a new route to grow large polymer extended-chain crystals and suggests self-assembly under high pressure is a promising method to create materials with new structures and properties.

Abstract: Due to the water absorption of wood fillers and poor adhesion between wood fillers and polymer matrix, the loosen material structure always appears in wood/polymer composites after injection molding process, which results in reduced composites mechanical properties. In this study, two kinds of wood particles with different sizes and properties were compounded with Polypropylene (PP) in highly filled level (by 50% and 60% weight concentration). The experimental tensile test samples were prepared by one double-gate injection mould integrated an ultrasonic generator unit. The experiments were carried out for studying how the ultrasonic output power and the oscillation inducing time affect the injection molded wood/PP composites mechanical properties. 3 output power levels (400W, 600W and 800W) and 2 inducing mode were set (Mode1. the oscillation is induced from injecting moment to ejection moment; Mode2. the oscillation is induced from injecting moment to packing procedure finishing). The results show that the E module, tensile strength and density of the test parts are obviously changed with various ultrasonic output power and inducing time. Comparing the mechanical properties of parts with and without ultrasonic assistant indicates that the ultrasonic oscillation is a practical method to improve mechanical properties of injection molded wood/PP composites parts.

Abstract: Fiber reinforced plastic structural shapes are readily available in civil engineering applications. Especially, pultruded fiber reinforced plastic is an attractive construction material for structural applications because it can be produced in mass production, and it has good mechanical and chemical properties compared with existing conventional structural materials. To be used in the construction field, connection of the pultruded structural member is unavoidable. Bolted connections may be the most suitable option for civil engineering applications compared with bonded connection. However, bolted connection has disadvantages such as reduction of strength due to bolt holes in the connection. Experimental and analytical studies on the bolted connection of PFRP plated member have been carried out. Four different types of connection distinguished by number and arrangement of bolt holes are investigated. Geometrical test parameters are edge distance, width, and longitudinal and transverse spacing. The effects of the parameters are evaluated and quantified based on the observations, such as failure load and failure mode, obtained from the experiment. In addition to the experimental investigation, analytical study is also conducted to predict the failure load of the member with bolted connection.