Improved mechanical properties of an epoxy glass–fiber composite reinforced with surface organomodified nanoclays

An organomodified surface nanoclay reinforced epoxy glass-fiber composite is evaluated for properties of mechanical strength, stiffness, ductility and fatigue life, and compared with the pristine or epoxy glass-fiber composite material not reinforced with nanoclays. The results from monotonic tensile tests of the nanoclay reinforced composite material at 60 °C in air showed an average 11.7% improvement in the ultimate tensile strength, 10.6% improvement in tensile modulus, and 10.5% improvement in tensile ductility vs. these mechanical properties obtained for the pristine material. From tension–tension fatigue tests at a stress-ratio = +0.9 and at 60 °C in air, the nanoclay reinforced composite had a 7.9% greater fatigue strength and a fatigue life over a decade longer or 1000% greater than the pristine composite when extrapolated to 10⁹ cycles or a simulated 10-year cyclic life. Electron microscopy and Raman spectroscopy of the fracture and failure modes of the test specimens were used to support the results and conclusions. This nanocomposite could be used as a new and improved material for repair or rehabilitation of external surface wall corrosion or physical damage on piping and vessels found in petrochemical process plants and facilities to extend their operational life.     

Seismic behavior of hybrid fiber reinforced cementitious composite beam–column joints

This paper presents the experimental results of six exterior beam–column joints with different concrete composites under cyclic loading. Engineered cementitious composite with polypropylene fiber and hybrid cementitious composites (HCC) using three different types of fiber namely hooked end steel fiber; brass coated steel fiber and polypropylene fiber are explored in this study. The hysteresis behavior, ductility response, energy dissipation with damping characteristics, crack patterns and damage index of all tested specimens are analyzed and compared with the cyclic response of conventional specimens. The test results indicate that HCC increases load carrying capacity and enhances energy dissipation with increased stiffness retention over conventional specimens. At higher rotation, joint specimens with HCC manifest better damage tolerance capacity over conventional specimens. This investigation implies that the use of HCC in the joint region may be an alternative solution to significantly increase the shear capacity, damage tolerance capacity and member ductility.     

Effects of environmental aging on the mechanical properties of bamboo–glass fiber reinforced polymer matrix hybrid composites

Short bamboo fiber reinforced polypropylene composites (BFRP) and short bamboo–glass fiber reinforced polypropylene hybrid composites (BGRP) were fabricated using a compression molding method. Maleic anhydride polypropylene (MAPP) was used as a compatibilizer to improve the adhesion between the reinforcements and the matrix material. By incorporating up to 20% (by mass) glass fiber, the tensile and flexural modulus of BGRP were increased by 12.5 and 10%, respectively; and the tensile and flexural strength were increased by 7 and 25%, respectively, compared to those of BFRP. Sorption behavior and effects of environmental aging on tensile properties of both BFRP and BGRP systems were studied by immersing samples in water for up to 1200 h at 25°C. Compared to BFRP, a 4% drop in saturated moisture level is seen in BGRP. After aging in water for 1200 h, reduction in tensile strength and modulus for BGRP is nearly two times less than that of BFRP. Use of MAPP as coupling agent in the polypropylene matrix results in decreased saturated moisture absorption level and enhanced mechanical properties for both BFRP and BGRP systems. Thus it is shown that the durability of bamboo fiber reinforced polypropylene can be enhanced by hybridization with small amount of glass fibers.     

Crashworthiness characteristics of a carbon fiber reinforced dual-phase epoxy–polyurea hybrid matrix composite

The crashworthiness characteristics of rectangular tubes made from a Carbon-fiber reinforced Hybrid-Polymeric Matrix (CHMC) composite were investigated using quasi-static and impact crush tests. The hybrid matrix formulation of the CHMC was created by combining an epoxy-based thermosetting polymer with a lightly crosslinked polyurea elastomer at various cure-time intervals and volumetric ratios. The load–displacement responses of both CHMC and carbon-fiber reinforced epoxy (CF/epoxy) specimens were obtained under various crushing speeds; and crashworthiness parameters, such as the average crushing force and specific energy absorption (SEA), were calculated using subsequent load–displacement relationships. The CHMC maintained a high level of structural integrity and post-crush performance, relative to traditional CF/epoxy. The influence of the curing time and volumetric ratios of the polyurea/epoxy dual-hybridized matrix system on the crashworthiness parameters was also investigated. The results reveal that the load carrying capacity and total energy absorption tend to increase with greater polyurea thickness and lower elapsed reaction curing time of the epoxy although this is typically a function of the loading rate. Finally, the mechanism by which the CHMC provides increased damage tolerance was also investigated using scanning electron microscopy (SEM).     

Fatigue behaviour of composite–composite joints reinforced with cold metal transfer welded pins

In this paper the fatigue properties of through-the-thickness reinforced joints are studied in detail. Unreinforced specimens, specimens reinforced with cold metal transfer welded titanium and steel pins and specimens reinforced with titanium z-pins are investigated. Besides classical S–N diagrams, hysteresis curves and stiffness based approaches are applied to improve the understanding of the mechanical behaviour of the joints in the progress of their fatigue life. Furthermore full field strain analysis gives information about damage initiation and growth in the joint section.     

Meso-scale strain localization and failure response of an orthotropic woven glass–fiber reinforced composite

The present work focuses on studying the multi-scale deformation and failure mechanisms of an orthogonally woven glass fiber reinforced composite as a function of fiber orientation angle using digital image correlation. The full-field displacement and strain localization are effectively captured at meso-scale. At continuum scale, a remarkable change in mechanical response is observed when the loading axis diverges from principal axes. The variation in the global mechanical response is observed to be most prominent in the change of stiffness and strain at failure. At meso scale, a high degree of local deformation heterogeneity is observed and the level of inhomogeneity is found to be more prominent in case of the 45° off-axis specimens. While fiber-pull out is the major failure mode in the case of specimen loaded parallel to 0° and 90° fiber orientation, the localized shear strain developed in polymer-rich regions is the driving failure cause in the case of 45° off-axis specimen.     

Effect of colloidal silica on the mechanical properties of fiber–cement reinforced with cellulosic fibers

The effect of colloidal silica on the hydration reaction of the Portland cement system and its effect on the resulting mechanical properties are not completely understood. Silica nanoparticles can affect the behavior and performance of fiber–cement, such as the calcium–silicate–hydrate gel of the matrix and the fiber–matrix interface bonding. The main objective of this study is to evaluate the effects of various contents of colloidal silica (0, 1.5, 3, 5, and 10 % w/w) on the microstructure and mechanical performance of cement composites reinforced with cellulosic pulp. Fiber–cement composites with unbleached eucalyptus Kraft pulp as the micro-fiber reinforcement were produced by the slurry dewatering technique followed by pressing. The average values of the modulus of rupture of the fiber–cement decreased with increasing colloidal silica content. However, the pullout of the fibers increased significantly in the fiber–cement composites with additions between 3 and 10 % w/w of colloidal silica suspension, as indicated in the scanning electron microscopy images and by the improvement in the energy of fracture values.     

Effects of fiber–matrix interaction on multiple cracking performance of polymeric fiber reinforced cementitious composites

The effects of polymeric fiber addition on the multiple cracking performance of composites have been investigated. For this purpose, cement-based matrices incorporating fly ash and a latex emulsion have been designed. Prismatic samples have been prepared and subjected to four-point bending load. The load-midpoint deflection curves and crack patterns have been determined. Meanwhile, flexural strength and relative toughness values have been calculated. Finally, the number of visible cracks formed throughout the testing period has been analyzed.Test results showed that the toughening improvement mechanisms of PP and PVA fibers in a cement-based matrix are extremely different and matrix modifications significantly change the multiple cracking performance. The addition of a latex emulsion in a weak matrix decreased the multiple cracking tendency of PP fiber reinforced composites. However, the same modification attempt improved the multiple cracking capacity of weak matrix in case of PVA fiber reinforcement. The possible causes of this performance improvement have been discussed with the aid of microstructure investigations.     

Reinforced concrete beam–column joint strengthened with carbon fiber reinforced polymer

An effective rehabilitation strategy is proposed to enhance the strength and stiffness of the beam–column joint in this study. An analytical model is proposed to predict the column shear of the joints strengthened with carbon fiber reinforced polymer (CFRP). Three full scale interior beam–column joints, including two specimens strengthened with CFRP and one prototype specimen, are tested in this study. The specimens are designed to represent the pre-seismic code design construction in which there is no transverse reinforcement. A new optical non-contact technique, digital image correlation (DIC), which can measure the full strain field of specimen, is used to measure and observe the full strain field of the joint. The experimental results show that the beam–column joints strengthened with CFRP can increase their structural stiffness, strength, and energy dissipation capacity. The rehabilitation strategy is effective to increase the ductility of the joint and transform the failure mode to beam or delay the shear failure mode. By observing the measured results, it is found that the mechanical anchorages can prevent the debonding of CFRP. Comparing the analytical and experimental results, the proposed model can accurately predict the column shear and shear strength of the joints strengthened with CFRP.     

Investigation of freeze–thaw effects on mechanical properties of fiber reinforced cement mortars

Fibers are used for improving some properties of conventional concrete (which is a brittle material) such as tensile strength, abrasion resistance, absorption and crack control. This study investigates the usability of fibers against the harmful effects of freeze–thaw cycles on cement mortars. For this objective, five different types of fibers, i.e., Polypropylene (PP), Carbon (CF), Aramid (AR), Glass (GF) and Poly vinyl alcohol (PVA) in four different ratios (0.0%, 0.4%, 0.8% and 1.2%) were added to cement mortars along with an amount of air agent. These samples were then subjected to five different freeze–thaw cycles (0, 25, 50, 75 and 100). Thus, mechanical behaviors were investigated under freeze–thaw effects.The most important results of the study are summarized; the fibers increase flexural strength and deflection ability of the samples while decreasing compressive strength, dynamic modulus of elasticity and specific mass. The highest flexural strength was obtained with a 1.2% addition of CF fiber for the samples in normal conditions. The mechanical properties of the samples subjected to repetitive freeze–thaw cycles were also investigated; the best flexural strength was provided with 1.2% CF addition, while the highest dynamic modulus of elasticity was obtained with a 1.2% PP addition.     

An analytical model for predicting the freeze–thaw durability of wood–fiber composites

The development and validation of an analytical model that predicts the onset of frost-induced damage in wood–plastic composites (WPCs) is presented in this work. The mathematical model is based on the mechanics of a hollow cylinder subjected to an internal pressure caused by the expansion of freezing moisture bound in the wood–fiber reinforcement. The model is substantiated using experimental data from several published studies. Using a stochastic approach, the model is implemented to analyze the effect of wood fiber specie, fiber volume fraction, and matrix material properties on the frost resistance of fully and partially saturated WPCs. Results show that WPCs with high fiber contents, high moisture contents, and low polymer tensile strengths are most susceptible to frost-induced damage. Data also suggest that the use of softwood fibers (e.g., pine, spruce) and polymers with low moduli and high tensile strengths enhances the frost-resistance of WPCs.     

Manufacture of photovoltaic cells with hybrid organic–inorganic bulk heterojunction

The aim of this paper is to present the influences of material composition and production conditions of the photovoltaic cells on its parameters as well as the active layer properties. The layers were made of organic compounds: metal phthalocyanine/perylene derivatives. In addition, the effects of TiO₂ and SiO₂ nanoadditives were investigated. The materials used are selected so as to allow P–N junction creation. Deposition technique allows at simultaneous applying the materials leads to obtaining homogeneous dispersion of one material in the other, which determines the formation of bulk P–N junctions. Research includes the estimate of share of individual components in the active layer, then determination of the morphology of surface and optical properties of the same layer and its implementation in photovoltaic structures. The structural researches and morphology of surface investigation were made using transmission electron microscopy (TEM), atomic force microscopy (AFM), and scanning electron microscopy (SEM). The optical properties were researched with the use of UV–Visible spectroscope. The parameters of cells have been determined on the basis of current–voltage characteristics. The work undertaken within the framework of article allowed to linking properties of active layers with the parameters of the same cells.     

Rate dependent deformation of carbon fibre reinforced Al–Li metal matrix composite

Abstract

The dynamic deformation characteristics and failure behaviour of laminated carbon fibre reinforced Al–Li metal matrix composite has been studied experimentally with the objective of investigating the dependence of mechanical properties on the applied strain rate and fibre volume fraction. A vacuum melting/casting process was used for manufacturing the tested composite. Impact testing was performed using a Saginomiya 100 metal forming machine and a compressive split Hopkinson bar over a strain rate range of 10^-1 s^-1 to 3×10³ s^-1. It is shown that the flow stress of the composite increases with strain rate and fibre volume fraction. The highest elongation to fracture values were found at low rate loading conditions, although a significant increase in ductility is obtained in the dynamic range. The composite appears to exhibit a lower rate of work hardening during dynamic deformation. Strain rate sensitivity and activation volume are strongly dependent on strain rate and fibre volume fraction. Fractographic analysis using scanning electron microscopy reveals that there is a distinct difference in the morphologies of the fractures, with corresponding different damage mechanisms, between specimens tested at low and high strain rates. Both strain rate and fibre volume fraction are important in controlling fibre fragment length and the density of the Al–Li debris. The relationships between mechanical response and fracture characteristics are also discussed.     

Effect of Mo on the VC–VB particles reinforced Fe-based composite coatings

VC–VB particles reinforced Fe-based composite coatings with different molybdenum contents were in-situ fabricated by laser cladding. The microstructure and properties of the coatings were systematically investigated by means of micro hardness tester, XRD, SEM, EDS, ring-block wear testing machine and box-type resistance furnace. The results showed that both hardness and wear resistance of the coatings were greatly improved. When the content of Mo exceeds 3%, anti-oxidation of the coating decreased. Through analysing of the oxidation kinetics curves at different temperatures of the samples, it can be found that the coating with 2.5% Mo has the preferable oxidation resistance at 600°C, and its antioxidant property is five times of the coating without Mo, two times of the substrate.     

Mechanical properties and oxidation resistance of C–B–Si coated silicon nitride fiber reinforced Si–N–C composites with cross-ply structure

To enhance the oxidation resistance of a ceramic matrix composite, a C–B–Si interface layer was applied between the fiber and the matrix. The layer was deposited on the fiber by chemical vapor deposition. Three types of coatings were prepared: A1, A2 (multilayers of graphite layer/B–C–Si crystalline layer/graphite layer) and B1 (monolayer of B and C containing graphite). The multilayer coated CMC retained 88–97% of the original strengths after oxidation at 1523 K for 36 ks. The monolayer coated CMC degraded to 55% of its original strength after oxidation, but had a high fracture toughness (28 MPa m^1/2) before oxidation. The differences of the oxidation resistance and fracture toughness were discussed in relation to the microstructure of the coatings.     

Active structural-acoustic control of laminated composite plates using vertically/obliquely reinforced 1–3 piezoelectric composite patch

This article deals with the active structural-acoustic control of thin laminated composite plates using vertically reinforced 1–3 piezoelectric fiber-reinforced composite (PFRC) material for constraining layer of active constrained layer damping (ACLD) treatment. A finite element model is developed for the laminated composite plates integrated with ACLD patches and coupled with acoustic cavity to describe the coupled structural-acoustic behavior of the plates enclosing the cavity. Both in-plane and out of plane actuation of the constraining layer of the ACLD treatment have been utilized for deriving the finite element model. The analysis revealed that the vertical actuation dominates over the in-plane actuation. The performance of PFRC layers of the patches has been investigated for active control of sound radiated from thin symmetric and antisymmetric cross-ply and antisymmetric angle-ply laminated composite plates into the acoustic cavity.