Seawater immersion ageing of glass-fibre reinforced polymer laminates for marine applications

Four glass-fibre reinforced polymer (GRP) materials along with castings of their matrix resins have been aged in seawater in the laboratory, some loaded under set-strain. Water uptake behaviour has been compared for the polyester, phenolic and vinylester GRPs and neat resin castings, and losses in mechanical properties determined for the GRPs. The phenolic GRP displayed anomalous uptake behaviour considered to relate to both interface and matrix absorption. Water uptake by the polyester and vinylester laminates appeared to be affected initially by suppression from fibre barrier effects then later by enhancement from interface effects. Flexural strength fell by 15–21% for the water saturated polyester and vinylester GRPs, and by 25% for the phenolic GRP. Loading at 20% of ultimate strain while under immersion exacerbated only the phenolic laminate degradation, advancing the loss in strength to 36%. Interlaminar shear strengths fell by between 12 and 21% for the GRPs at close to saturation.     

Mechanical behaviour of SMC composites with toughening and low density additives

A new type of SMC material (Flex-SMC) developed for automotive exterior body panels has been investigated. Flex-SMC contains hollow glass micro-spheres and thermoplastic toughening additives. A conventional SMC (Std-SMC) was used as a reference material. Materials were tested in monotonic tension and compression. Stiffness degradation with strain as well as fracture toughness was determined. In situ SEM was used to study failure mechanisms. Flex-SMC has a density almost 20% lower than Std-SMC and has higher impact resistance. The damage threshold strain of the Flex-SMCs is higher than for Std-SMC. Flex-SMCs have more than twice the fracture toughness of Std-SMC. The major reason identified is that Flex-SMCs shows extensive fibre pullout.     

Development of coir pith/nylon fabric/epoxy hybrid composites: Mechanical and ageing studies

The coir pith epoxy composites were hybridized with nylon fabric/epoxy resin by hand lay up technique followed by compression moulding. A set of composites of same composition having chemically treated coir pith was also prepared. Mechanical properties of composites such as tensile strength, flexural strength, impact strength and hardness were evaluated. Though coir pith acts as a good reinforcement in epoxy resin, the incorporation of nylon fabric and the chemical treatment of coir pith were found to enhance the properties of the composites further. Chemical resistance and flame resistance of composite systems were also found to be improved with hybrid composites. Since water uptake and retentions property of coir pith is a major drawback when it comes to its application in composites, the ageing of composite panels in moist environment was investigated. The results suggested that the presence of nylon fabric and chemically treated pith can contribute to longer durability of the panels in moist conditions.     

Fracture behaviour of hybrid glass matrix composites: thermal ageing effects

The thermal aging of a glass matrix composite reinforced by short carbon fibres as well as by ZrO₂ particles (hybrid composite) was investigated at temperatures in the range 500–700 °C for exposure durations of 24 h in air. The mechanical properties of as-received and aged samples were evaluated at room temperature by using the three-point flexure chevron notch technique. The fracture toughness values of as-received specimens were in the range 2.6–6.4 MPa m^1/2. Fracture toughness was affected by the thermal aging conditions. For thermal aging at temperatures <700 °C, degradation of fibre–matrix interfaces occurred and therefore the apparent fracture toughness and flaw tolerant resistance decreased. For the most severe ageing conditions tested (700 °C/24 h), fracture toughness values dropped to 0.4 MPa m^1/2. Significant degradation of the material was detected for this aging condition, mainly characterised by porosity formation in the matrix as a result of softening of the glass and oxidation of the carbon fibres.     

Mechanical behaviour of ferrocement composites: an experimental investigation

In-plane tension, compression and bending tests were conducted on plain mortar and ferrocement specimens with woven and welded meshes. Tension tests were also carried out on meshes. Bending tests were conducted using specimens with centre point loading. The objective of the study was to investigate the behaviour of material reinforced with varying number of mesh layers and orientations and to evolve a set of elastic and inelastic material properties. It is observed that the conventional empirical relations based on mortar crushing strength overestimate the mortar modulus. The elastic moduli obtained using the rule of mixtures compares well with the values evaluated from the tests on ferrocement specimens. The 45° orientation emerges as the weakest configuration both in terms of the Young's modulus and ultimate stress because of the lowest volume fraction of wire mesh in the direction of loading at this orientation.     

Mechanical behaviour of cadmium-boron and cadmium-tungsten particulate composites

Mechanical behaviour of particulate composites of cadmium containing 0.6 to 3 m size particles of boron and tungsten (up to 30 vol %) were studied from –196 to 260° C (0.13 to 0.9T _m). The marked strengthening of cadmium by the presence of fine particles is attributed to significant grain size and texture strengthening effects as well as to dispersion hardening effects.     

Mechanical behaviour of Textile Concrete under accelerated ageing conditions

The mechanisms of ageing and environmental degradation involving exposure to cyclic hot/cold temperatures, wetting/drying movements as well as exposure to a carbon dioxide (CO₂)-rich environment, have different effects on the microstructure of interfaces within cementitious composites. This paper presents results of an investigation into changes occurring in fibre pull-out and composite tensile behaviour in Textile Concrete (TC) after exposure to accelerated ageing conditions. The microstructure of the matrix at the fibre/matrix interface, and fibre properties, were found directly to affect the mechanical behaviour at the macro-level. The study illustrated that exposure of TC to a CO₂-rich environment improves the fibre/matrix bond significantly; no major changes were observed in the mechanical behaviour of the composites after exposure to hot/cold and wetting/drying environments.     

Acoustic emission for monitoring the mechanical behaviour of natural fibre composites: A literature review

In recent years, natural fibres are increasingly used as reinforcements for the production of low-cost and lightweight polymer composites: other advantages include non-abrasive nature, high specific properties, and biodegradability. However, their limitations, including moisture absorption, poor wettability and large scattering in mechanical properties, and the not sufficient understanding of mechanisms controlling their mechanical behaviour and failure modes, still confine the use of natural fibre reinforced composites in non-structural applications. Acoustic emission (AE) proved useful for its capability of real-time monitoring over the whole material volume and high sensitivity to any process generating stress waves.This paper presents a literature review of AE applications in studies on natural fibre composites. The following fields of application are covered: (1) interface studies in single fibre composite (SFC) tests, (2) damage evolution and failure mechanisms detection and (3) crack propagation, including also current limitations of existing literature and future work.     

Mechanical properties and styrene emission levels of a UV-cured glass-fibre/vinylester composite

The mechanical performance of a UV-cured glass-fibre/vinylester composite was compared with conventional room temperature cured and thermally post-cured counterparts. The UV-cured composite was exposed to UV light for 10 min, whereas the room temperature and post-cured composites required several hours of processing. The fibre-dominated tensile and flexural properties were comparable for each composite. The resin-sensitive interlaminar shear strength was highest for the UV-cured and post-cured composites and, within scatter, the performance of the UV-cured composite was comparable to its post-cured counterpart. In addition, the UV-cured composite emitted approximately four times less styrene during lamination and cure in an open mould than the conventional room temperature cured composite. The results highlight the potential for UV-curing composites to provide excellent mechanical performance while reducing manufacturing times and improving the manufacturing environment.     

Mechanical behaviour of circular and triangular glass fibres and their composites

Single fibre testing of circular (CircGF) and triangular (TriGF) glass fibres of equivalent cross-section has shown the TriGF to have a 25% higher average tensile strength compared to CircGF. Micro-composite compression testing (using resin bonded tows of 12–15 filaments) has revealed the TriGF to have a compression strength 60% greater than CircGF. Some of the increase can be attributed to an effective increase in second moment of area for the TriGF specimens due to imperfect packing. However, allowing for this effect there still appears to be an underlying significant improvement in compressive strength performance attributable to the inherent fibre shape. Mechanical testing under tensile load has shown that the triangular glass fibre reinforced plastic (TriGFRP) performs marginally better (20%) than that manufactured using circular fibre (CircGFRP) for equivalent fibre volume fractions. Similarly, under compressive loading the TriGFRP outperforms CircGFRP by a significant margin of 40%. Interlaminar shear testing has also indicated that TriGFRP may offer a performance advantage of approximately 5%, although this needs further verification to be conclusive.     

Emission modeling of styrene from vinyl ester resins with low hazardous air pollutant contents

Styrene is a commonly used co-monomer in vinyl ester (VE) resins, which acts as a reactive diluent and is required in most liquid molding fabrication methods to reduce viscosity and improve overall resin performance. Resins containing low hazardous air pollutant contents have been developed to reduce the styrene emissions during composite fabrication. VE monomers with a bimodal molecular weight distribution have been used to effectively decrease the amount of styrene in the system while maintaining low resin viscosities. Fatty acid vinyl ester (FAVE) resins partially replace styrene with non-volatile fatty acid monomers to reduce styrene emissions. The emissions from bimodal and FAVE resins were measured as a function of time and various parameters, including styrene content, VE molecular weight, and fatty acid monomer content and chain length. The initial emission rate from VE resins is only dependent on styrene content for constant evaporation geometry. Furthermore, the evaporation rate constant was the same regardless of VE molecular weight, styrene content, or the use of co-reactive diluent (MFA monomers). The diffusivity was not dependent on the styrene content in the resin, but decreased linearly as the VE molecular weight increased because of a corresponding increase in the resin viscosity. The diffusivity also increased as the content of MFA increased because of a decrease in the resin viscosity with high MFA content at high emission time. Furthermore, the emission profiles were accurately modeled using a modified version of 1D diffusion through a planar sheet that accounts for the depth change as a function of styrene evaporation. Overall, the model predicted emission profiles similar to the experimentally measured profiles as a function of time for various styrene contents, VE molecular weights, and fatty acid monomer contents.     

Mechanical behaviour of carbon and glass hybrid fibre reinforced polyester composites

Mechanical behaviour of carbon fibre/glass mat/polyester resin hybrid composites of sandwich construction is studied through tension, flexure, impact and post-impact tension tests. Tensile and flexural strength, modulus and failure strain values are compared to the calculated values. Total impact fracture energy and residual (after impact) tensile strength values of hybrid composites are analysed with regard to corresponding values of carbon/polyester composites. Failure of tested coupons was analysed by visual inspection and observation by scanning electron microscopy.     

Mechanical and structural studies of low density polyethylene

This paper is one of a series concerned with the complete characterisation of the creep behaviour of oriented polymers, the correlation of creep behaviour with other mechanical properties and the interpretation of such data in the light of present structural knowledge. Sheets of oriented low-density polyethylene were prepared from initially isotropic sheets by cold-drawing, cold-drawing followed by heat-treatment at 55° C, drawing at a temperature of 55° C and hot-drawing at temperatures in the range 90 to 100° C. At each draw ratio, specimens were cut at angles of 0°, 45° and 90° to the draw direction. For each specimen, the variation of longitudinal and lateral strain with time, during uniaxial tensile creep at 20° C, was measured simultaneously by direct extensometer methods, for a wide range of applied stresses. All the materials exhibited complex anisotropic non-linear viscoelastic behaviour. The methods of presenting such data are discussed and the results are presented in some detail. Many similarities in the creep behaviour of the cold- and hot-drawn materials are noted. However, marked differences are apparent in the non-linearity and creep rate of the 45° specimens from these two materials at high draw ratio. These, and other effects found at high draw ratio, are discussed with reference to the structural studies reported in part 1. At low draw ratio, it is shown that the anomalous behaviour of the modulus in the draw direction, reported previously for cold-drawn material, may also be found in the hot-drawn material, although at a different creep time. On the basis of obvious differences in wide-angle X-ray patterns other workers had previously predicted that the anomalous mechanical behaviour of cold-drawn LDPE was probably unique. The anomalous behaviour of the hot-drawn material is also explained in terms of the structures discussed in part 1.     

Effect of low temperature ageing on the transformation behaviour of near-equiatomic NiTi

A unique three-stage transformation behaviour on cooling has been observed in a Ti-50.2 at% Ni alloy after a low temperature ageing treatment. The cooling transformation in the aged alloy occurred as a three-stage process of austenite-to-R phase transition followed by two separate martensitic transformations. The R phase transition developed during ageing with a clear second order nature initially and gradually evolved into a predominantly first order process. The occurrence of the R transition is not associated with a decrease in the martensitic transformation temperature during ageing. The reverse transformation to austenite occurred in one step, regardless of the nature of the forward transformation on cooling. An all-round shape memory effect was observed in aged samples. These experimental observations suggest that precipitation induced by the ageing treatment is responsible for the unusual transformation behaviour. This revised version was published online in November 2006 with corrections to the Cover Date.     

Mechanical and structural studies of low density polyethylene

During uniaxial orientation of low density polyethylene (LDPE) at 90 to 95°C some unusual structural changes occur, as revealed by wide and low angle X-ray diffraction. Quantitative measurements of diffracted intensity distributions have been made. At low draw ratios a novel 6-point low angle pattern appears which persists to extensions of over 300%. Cone distributions are present in all the crystal axis orientations, and these are superimposed on transverse components to give complex wide angle diffracted intensity profiles. A spherulite deformation model is proposed to explain these observations. At high draw ratios uniaxial crystal alignment obtains, but we find that the lamellar orientations differ between specimens annealed after drawing at room temperature and those drawn directly at the higher temperature. The implications of this observation are considered.     

Mechanical behaviour of plain-knit reinforced injected composites: Effect of inlay yarns and fibre type

This paper investigates the effect of inlay yarns and fibre type (E-glass, basalt, carbon) to improve the mechanical behaviour of plain knit reinforced composites (epoxy matrix). The tensile behaviour of the dry reinforcement was investigated in the wale and course-directions and has shown that the course-wise deformation is drastically reduced whereas the strength is strongly increased when inlay yarns are included. Fibre type has a weak effect on deformation and strength. For the composite material, processed by Liquid Composite Moulding, the carbon fibre reinforcement gives always the best results whatever the testing direction. Inlay yarns decrease the 0° mechanical properties, whereas 45° and 90° are increased. Moreover a quasi-isotropic behaviour is obtained when using two inlay yarns, irrespective of the fibre types.     

Mechanical and tribological behaviour of nano scaled silicon carbide reinforced aluminium composites

ABSTRACT

This work assesses the impact of the presence of Nano scaled silicon carbide on the Mechanical & Tribological behavior of aluminium matrix composites. Aluminium matrix composites containing 0, 0.5, 1, 1.5, 2 and 2.5 wt.%-nano scaled silicon carbide was set up by a mechanical stirrer. The trial comes about to demonstrate that the inclusion of Nano silicon carbide brings about materials with progressively high elastic modulus and likewise brings about expanded brittle behavior, fundamentally lessening failure strain. Shear modulus and flexural shear modulus likewise increases with silicon carbide increase. The presence of Nano scaled silicon carbide in the aluminium matrix diminishes subsurface fatigue wear and increases wear resistance, because of silicon carbide lubricant activity. Wear testing, microstructure & morphological, density & void testing, hardness, flexural and tensile test of the readied composites were investigated and outcomes were analyzed which demonstrated that including nano-SiC in aluminum (Al) matrix increased wear resistance, tensile strength, and 2 wt. % of nano scaled SiC for Al MMC indicated maximum wear resistance, tensile strength, and an optimum balanced mix of both Tribological and Mechanical properties. Microstructural observation uncovered uniformand homogeneous distribution of SiC particles in the Al matrix.     

Mechanical and water absorption behaviour of banana/sisal reinforced hybrid composites

The tensile, flexural, impact and water absorption tests were carried out using banana/epoxy composite material. Initially, optimum fiber length and weight percentage were determined. To improve the mechanical properties, banana fiber was hybridised with sisal fiber. This study showed that addition of sisal fiber in banana/epoxy composites of up to 50% by weight results in increasing the mechanical properties and decreasing the moisture absorption property. Morphological analysis was carried out to observe fracture behaviour and fiber pull-out of the samples using scanning electron microscope.