Showing papers in "Composites Part B-engineering in 2001"
TL;DR: In this paper, a notch was inserted into the culm and node specimens using a razor blade with a thickness of 0.4mm, and tensile tests were carried out to evaluate fracture toughness.
Abstract: Bamboo is a typical natural composite material, which is longitudinally reinforced by strong fibers. The fibers are distributed densely in the outer surface region, and sparsely in the inner surface region, and their volume fraction changes with respect to radius. The structure of bamboo has been characterized by tensile tests and its mechanical properties have been related to its structure. This paper presents the fracture toughness of bamboo culms and nodes. A notch is inserted into the culm and node specimens using a razor blade with a thickness of 0.4 mm. Tensile tests are carried out to evaluate fracture toughness. The average value obtained was 56.8 MPa m1/2, which is higher than that of Al-alloy. It was concluded that the fracture toughness of the bamboo culm depends on the volume fraction of fibers.
262 citations
TL;DR: In this article, closed-form solutions for stresses and displacements in functionally graded cylindrical and spherical vessels subjected to internal pressure alone are obtained using the infinitesimal theory of elasticity.
Abstract: Closed-form solutions for stresses and displacements in functionally graded cylindrical and spherical vessels subjected to internal pressure alone are obtained using the infinitesimal theory of elasticity. The material stiffness obeying a simple power law is assumed to vary through the wall thickness and Poisson's ratio is assumed constant. Stress distributions depending on an inhomogeneity constant are compared with those of the homogeneous case and presented in the form of graphs. The inhomogeneity constant, which includes continuously varying volume fraction of the constituents, is empirically determined. The values used in this study are arbitrarily chosen to demonstrate the effect of inhomogeneity on stress distribution.
231 citations
TL;DR: The impact behavior and post impact compressive characteristics of glass-carbon/epoxy hybrid composites with alternate stacking sequences have been investigated in this paper, where plain weave E-glass and twill weave T-300 carbon have been used as reinforcing materials.
Abstract: Impact behaviour and post impact compressive characteristics of glass–carbon/epoxy hybrid composites with alternate stacking sequences have been investigated. Plain weave E-glass and twill weave T-300 carbon have been used as reinforcing materials. For comparison, laminates containing only-carbon and only-glass reinforcements have also been studied. Experimental studies have been carried out on instrumented drop weight impact test apparatus. Post impact compressive strength has been obtained using NASA 1142 test fixture. It is observed that hybrid composites are less notch sensitive compared to only-carbon or only-glass composites. Further, carbon-outside/glass-inside clustered hybrid configuration gives lower notch sensitivity compared to the other hybrid configurations.
208 citations
TL;DR: In this paper, the feasibility of using carbon fiber reinforced polymer (CFRP) epoxy laminates to repair steel composite bridge members was evaluated and the results indicated significant ultimate strength gains but more modest improvement in the elastic response.
Abstract: This paper presents results from an experimental investigation to determine the feasibility of using carbon fiber reinforced polymer (CFRP) epoxy laminates to repair steel composite bridge members. Six specimens, each consisting of a 6.1 m long W8×24 wide flange A36 steel beam acting compositely with a 0.114 m thick by 0.71 m wide reinforced concrete slab, were first loaded past yield of the tension flange to simulate severe service distress. The damaged specimens were then repaired using 3.65 m lengths of 2 or 5 mm thick CFRP laminates bonded to the tension flange and tested to failure. The results indicated significant ultimate strength gains but more modest improvement in the elastic response. Non-linear finite element analyses were in good agreement with the experimental results. The study suggests that it is feasible to strengthen steel composite members using CFRP laminates.
206 citations
TL;DR: In this article, the effectiveness of stitching in increasing the damage resistance of polymer composites against ballistic projectiles and explosive blasts is determined, and the amount of delamination damage caused by a ballistic projectile was reduced slightly with stitching.
Abstract: The effectiveness of stitching in increasing the damage resistance of polymer composites against ballistic projectiles and explosive blasts is determined. Glass-reinforced vinyl ester composites stitched in the through-thickness direction with thin Kevlar®-49 yarn were impacted with a bullet travelling at 0.9 km s−1 or an underwater explosive shock wave moving at 1.5 km s−1. The amount of delamination damage to the composite caused by a ballistic projectile was reduced slightly with stitching. Stitching was highly effective in increasing the damage resistance against explosive blast loading. The increased damage resistance was due to the stitching raising the Mode I interlaminar fracture toughness of the composite. While the stitched composites experienced slightly less damage, their flexural modulus and strength was similar to the properties of the unstitched composite after ballistic impact testing. The post-blast flexural properties of the stitched composites, on the other hand, were degraded less than the properties of the unstitched material.
138 citations
TL;DR: In this article, a comparison of processing requirements and mechanical properties of carbon/carbon composites, ceramic matrix composites made with silicon carbide, silicon nitride and alumina fibers and carbon/polysialate composites is presented.
Abstract: Two classes of composite made using either ceramic matrix with high temperature fibers or carbon/carbon have been used for various applications that require high temperature resistance, over three decades. However, their use has been limited to special applications because of the high costs associated with fabrication. Typically the composites are cured at more than 1000°C, and in most instances the heating has also to be carried out in controlled environments. In addition, because of the high processing temperature, only certain type of expensive fibers can be used with the ceramic matrices. A recently developed inorganic matrix, called polysialate can be cured at temperatures less than 150°C, making it possible to use carbon and glass fibers. Composites made using carbon, glass and combinations of carbon and glass fibers have been tested in bending and tension. This paper presents the comparison of processing requirements and mechanical properties of carbon/carbon composites, ceramic matrix composites made with silicon carbide, silicon nitride and alumina fibers and carbon/polysialate composites. The results indicate that carbon/polysialate composite has mechanical properties comparable to both carbon/carbon and ceramic matrix composites at room and high temperatures. Since the polysialate composites are much less expensive, the authors believe that it has excellent potential for more applications in aerospace, automobile and naval structures.
128 citations
TL;DR: In this paper, the effect of temperature variations (low and high temperatures) was studied experimentally on impact damage to CFRP laminates, where a steel ball launched by the air gun was used to generate the CFRP laminate impact damage.
Abstract: In this paper, the effect of temperature variations (low and high temperatures) was studied experimentally on impact damage to CFRP laminates. The composite laminates used in this experiment were CF/EPOXY orthotropic laminated plates with lay-up [06/906]s and [04/904]s, and CF/PEEK orthotropic laminated plates with a lay-up of [06/906]s. A steel ball launched by the air gun was used to generate the CFRP laminate impact damage. For impact-damaged specimens, nondestructive evaluation (NDE), such as a scanning acoustic microscopy (SAM) was performed on the delamination-damaged samples to characterize damage growth at different temperatures. Therefore, this study was undertaken to experimentally determine the interrelations between impact energy and impact damage (i.e. the delamination area and matrix) of CFRP laminates (CF/EPOXY and CF/PEEK) subjected to foreign object damages (FOD) at low and high temperatures.
123 citations
TL;DR: In this article, the authors examined the relationship between fiber volume fraction and fiber strain to failure and used a computer program that is based on the thermokinetics of the resin and processing conditions to calculate the volume fraction distribution in the filament wound vessel.
Abstract: This paper is a continuation of previous research reported in Ref. [1]. The previous paper discussed the relationship between fiber volume fraction in filament wound composite vessels and failure pressure. This research included a design of experiment investigation of manufacturing and design variables that affect composite vessel quality and strength. Statistical analysis of the data shows that composite vessel strength was affected by the manufacturing and design variables. In general, it was found that the laminate stacking sequence, winding tension, winding-tension gradient, winding time, and the interaction between winding-tension gradient and winding time significantly affected composite strength. The mechanism responsible for increases in composite strength was related to the strong correlation between fiber volume fraction in the composite and vessel strength. Cylinders with high-fiber volume in the hoop layers tended to deliver high-fiber strength. This paper further examines the relationship between fiber volume fraction and fiber strain to failure. Data from unidirectional strand tests and additional vessel tests are presented. A computer program that is based on the thermokinetics of the resin and processing conditions is used to calculate the fiber volume fraction distribution in the filament wound vessel. The strand's strength-versus-fiber volume data together with the computer program are used to predict composite vessel burst pressure. In general, good agreement with experimental data is observed.
107 citations
TL;DR: In this article, the authors used the finite element method for nonlinear transient analysis of reinforced concrete (RC) two-way slabs subjected to blast loading and analyzed both as-built and retrofitted slabs with carbon fiber reinforced polymer composite strips.
Abstract: Computational models using the finite element method for nonlinear transient analysis of reinforced concrete (RC) two-way slabs subjected to blast loading are presented. Both as-built and retrofitted slabs with carbon fiber reinforced polymer (CFRP) composite strips are analyzed. The models are used to investigate different parameters including (a) loading duration, and (b) effect of CFRP retrofit on damage accumulation. In this study, damage is globally quantified by the amount of reduction of the first two vibrational frequencies of the slabs. Local representation of damage in terms of reinforcing steel strains is also discussed. The computational models for both the as-built and the retrofitted slabs are verified using experimental results. In these experiments, a slowly increasing uniform pressure is applied to the bottom surface of large-scale RC slab specimens using high-pressure water bag. Experimental results showed that an increase up to 200% in the load carrying capacity is achieved when using the CFRP composite retrofit system. Transient nonlinear analysis results proved the efficiency of the CFRP composite retrofit in improving the slab behavior under blast loading for different loading durations, i.e. for small, medium, and large charge weights at the same applied maximum pressure. In particular, less than 50% reduction of the fundamental frequency due to concrete damage is obtained for the retrofitted slab compared to more than 85% reduction for the as-built slab. Moreover, the maximum displacement is reduced by 40–70% with the CFRP retrofit compared to the as-built slab. As for reinforcing steel strains, the application of CFRP retrofit significantly limited the spread of yielding in time and space. The improved slab behavior with CFRP is best when retrofitting is applied to both sides of the slab.
104 citations
TL;DR: An active damage interrogation (ADI) method which uses an array of piezoelectric (PZT) transducers attached to a structure was used to detect and localize disbonds and delaminations of advanced composite reinforcement from concrete structures as discussed by the authors.
Abstract: An active damage interrogation (ADI) method which uses an array of piezoelectric (PZT) transducers attached to a structure was used to detect and localize disbonds and delaminations of advanced composite reinforcement from concrete structures. The ADI system provides the ability to detect, localize, and estimate the extent of the disbond by actively exciting the structure with PZT transducers and processing the structural response as measured by the PZT transducers. The ADI system makes use of both amplitude and phase information from various actuator/sensor transfer functions, and also provides a unique method for determining when the transducer/structure bond has degraded. This paper investigates the feasibility of using the ADI method for health monitoring of concrete structures repaired with composite materials, and the advantages and limitation of this method are discussed.
96 citations
TL;DR: In this paper, a modified Zig-Zag technical theory for the analysis of thick composite beams with rectangular cross section, general lay-up and in cylindrical bending is developed and tested.
Abstract: A modified zig-zag technical theory, suitable for the analysis of thick composite beams with rectangular cross section, general lay-up and in cylindrical bending is developed and tested. An equivalent single-layer model and a multiple-layer model are implemented. The displacement field of both these models is postulated as to allow for appropriate jumps in the strains, so that the transverse shear and the transverse normal stress and stress gradient continuity at the interfaces are met. A third-order piecewise approximation for the in-plane displacement and a fourth-order piecewise approximation for the transverse displacement are assumed in the two models. Their predictive capability is investigated in sample cases wherein the exact three-dimensional elasticity and other approximate solutions are available. On the basis of this numerical investigation, they appear to predict accurately and efficiently the displacement and stress fields of composite beams with layers of different materials.
TL;DR: In this article, a simple theoretical model to estimate shear and peel-off stresses is proposed, including the variation in FRP plate fiber orientation, and the theoretical predictions are compared with solutions from an experimentally validated finite element model.
Abstract: Fibre-reinforced plastic (FRP) materials have been recognised as new innovative materials for concrete rehabilitation and retrofit. Since concrete is poor in tension, a beam without any form of reinforcement will fail when subjected to a relatively small tensile load. Therefore, the use of the FRP to strengthen the concrete is an effective solution to increase the overall strength of the structure. The attractive benefits of using FRP in real-life civil concrete applications include its high strength to weight ratio, its resistance to corrosion, and its ease of moulding into complex shapes without increasing manufacturing costs. The speed of application minimises the time of closure of a structure compared to other strengthening methods. In this paper, a simple theoretical model to estimate shear and peel-off stresses is proposed. Axial stresses in an FRP-strengthened concrete beam are considered, including the variation in FRP plate fibre orientation. The theoretical predictions are compared with solutions from an experimentally validated finite element model. The results from the theory show that maximum shear and peel-off stresses are located in the end region of the FRP plate. The magnitude of the maximum shear stress increases with increases in the amount of fibres aligned in the beam's longitudinal axis, the modulus of an adhesive material and the number of laminate layers. However, the maximum peel-off stress decreases with increasing thickness of the adhesive layer.
TL;DR: In this article, a finite element approach is proposed to deal with two conflicting demands: (i) due to the gradual stiffness degradation of a fibre-reinforced composite material under fatigue, stresses are continuously redistributed across the structure and as a consequence the simulation should follow the complete path of successive damage states; (ii) the finite element simulation should be fast and computationally efficient to meet the economic needs.
Abstract: Today, a lot of research is dedicated to the fatigue behaviour of fibre-reinforced composite materials, due to their increasing use in all sorts of applications. These materials have a quite good rating as regards to life time in fatigue, but the same does not apply to the number of cycles to initial damage nor to the evolution of damage. Composite materials are inhomogeneous and anisotropic, and their behaviour is more complicated than that of homogeneous and isotropic materials such as metals. A new finite element approach is proposed in order to deal with two conflicting demands: (i) due to the gradual stiffness degradation of a fibre-reinforced composite material under fatigue, stresses are continuously redistributed across the structure and as a consequence the simulation should follow the complete path of successive damage states; (ii) the finite element simulation should be fast and computationally efficient to meet the economic needs. The authors have adopted a cycle jump approach which allows to calculate a set of fatigue loading cycles at deliberately chosen intervals and to account for the effect of the fatigue loading cycles in between in an accurate manner. The finite element simulations are compared against the results of fatigue experiments on plain woven glass/epoxy specimens with a [#45°]8 stacking sequence.
TL;DR: In this article, a few guidelines for the design of tapered laminated composites are developed by studying the effect of important parameters that determine the strength of the laminate and some of the thumb rules used at present are rather conservative and may be relaxed to an extent.
Abstract: The present investigation aims at developing a few guidelines for the design of tapered laminated composites. The tapering in laminated composites is introduced by terminating (dropping-off) plies at different locations. The main objective in designing a drop-off is to reduce stress concentration. At present some thumb rules are used to design the drop-off. In this paper, guidelines have been developed by studying the effect of important parameters that determine the strength of the laminate. The numerical study shows that some of the thumb rules used at present are rather conservative and may be relaxed to an extent.
TL;DR: In this paper, the effects of the particle volume fraction and the three kinds of temperature conditions on the stresses in the matrix, stresses in particle and macroscopic stress are discussed, and the analysis of the thermal stress constitutive equation of a particle reinforced composite taking temperature change and damage process into consideration is used.
Abstract: Functionally graded materials (FGMs) have recently been received with considerable interest, primarily as high temperature resistant materials for space vehicles subjected to high temperature environment. FGMs are one of the composite materials and consist of continuous change of composition of different material components from one surface to the other. FGMs usually fabricated at high temperature at which the FGMs have stress free condition. After the FGMs cooled from the fabrication temperature to the room temperature residual thermal stresses produced. In this paper, elasto-plastic thermal stresses in a rectangular plate (FGP) of a particle reinforced composite FGM are treated by finite element method due to the microscopic combination law when the FGP is subjected to three kinds of temperature conditions, first is cooling from the fabricated temperature to the room temperature, second is heating and last is heating after cooling from the fabricated temperature. In the analysis, the thermal stress constitutive equation of a particle-reinforced composite taking temperature change and damage process into consideration is used. The effects of the particle volume fraction and the three kinds of temperature conditions on the stresses in the matrix, stresses in the particle and macroscopic stress are discussed.
TL;DR: In this article, an accurate higher-order theory employing finite element procedure for the free vibration analysis of multi-layered thick composite plates is presented, which accounts for the realistic variation of in-plane and transverse displacements through the thickness.
Abstract: This paper deals with an accurate higher-order theory employing finite element procedure for the free vibration analysis of multi-layered thick composite plates. The theory accounts for the realistic variation of in-plane and transverse displacements through the thickness. The accuracy of the present model is verified by comparison with three-dimensional elasticity solutions for the vibration study of the composite laminates. The performance and the applicability of the proposed discrete model are also discussed among developed elements and alternate models, considering different parameters such as ply-angle, degree of orthotropicity, aspect ratio and boundary conditions.
TL;DR: In this paper, an experimental investigation on the composite-strengthened concrete structures with the embedment of fibre-optic Bragg grating (FBG) sensors is presented.
Abstract: In this paper, the mechanical behaviour of the composite-strengthened concrete structures is addressed. Optical fibre sensor presents a great deal of potential in monitoring the structural health condition of civil infrastructure elements after strengthening by externally bonded composite materials. The use of embedded optical fibre sensor for strain and temperature monitoring enables to reveal the status of the composite-strengthened structure in real-time remotely. In this paper, an experimental investigation on the composite-strengthened concrete structures with the embedment of fibre-optic Bragg grating (FBG) sensors is presented. Single- and multiplexed-point strain measuring techniques were used to measure strains of the structures. Frequency modulated continuous wave (FMCW) method was used to measure strains in different points of the structure with using only one single optical fibre. All strains measured from the sensors were compared to conventional surface mounted strain gauges. Experimental results show that the use of the embedded FBG sensor can measure strain accurately and provide information to the operator that the structure is subjected to debond or micro-crack failure. Multiplexed FBG strain sensors enable to measure strain in different locations by occupying only one tiny optical fibre. Reduction of strength in composite laminate is resulted if the embedded optical fibre is aligned perpendicular to the load-bearing direction of the structure.
TL;DR: In this article, an experimental investigation has been carried out to estimate the static and fatigue behaviour of specimens made up of steel plates and sandwich composite panels joined together by either blind or mechanical lock fasteners.
Abstract: An experimental investigation has been carried out to estimate the static and fatigue behaviour of specimens made up of steel plates and sandwich composite panels joined together by either blind or mechanical lock fasteners. A preliminary study was carried out in order to analyse the drilling operation of sandwich panels to determine the best values of parameters to use for fastener installation. A first set of pull-out and shear static tests was performed in 1992, using sandwich panels composed of a nomex honeycomb core between two laminates of glass/graphite/kevlar fibres in epoxy matrix. The investigation was completed in 1998. It consisted of performing a set of pull-out and shear fatigue tests on joints with blind fasteners, and of performing a new set of static tests on identical specimens with the same loading conditions as in 1992 so as to evaluate the possible ageing effect on mechanical proprieties of sandwich panels tested.
TL;DR: In this article, a geometrically non-linear FEM code based on the total Lagrangian formulation has been used for crack growth analysis on composite panels containing embedded delaminations, which has been improved with an effective virtual crack closure technique to evaluate energy release rate and with penalty method to evaluate contact forces.
Abstract: In this paper, crack growth analyses on composite panels containing embedded delaminations has been performed using a geometrically non linear FEM code, based on the total Lagrangian formulation. The code has been improved with an effective virtual crack closure technique to evaluate energy release rate and with penalty method to evaluate contact forces. Validation of the proposed tool has been performed with experimental and numerical data available in the literature for double cantilever beam (DCB) specimens. Finally, the influence of the geometrical parameters of the delamination (size and location along the thickness) on the energy release rate distribution and delamination growth stability in composite panels under compression has been analyzed.
TL;DR: In this paper, the deformation of a composite cantilever beam actuated by shape memory alloy (SMA) wires is modeled, numerical simulation and experimental validation are presented and discussed.
Abstract: In this paper, the modeling, numerical simulation and experimental validation of the deformation of a composite cantilever beam actuated by shape memory alloy (SMA) wires are presented and discussed. The structural model incorporates a number of non-classical features such as laminated construction and anisotropy of constituent material layers, transverse shear deformability, distortion of the normals, and fulfillment of interfacial shear traction continuity requirement. Suitable for use in standard finite element codes, a numerical procedure is developed for solving the geometric non-linearity of the host structure and the hysteretic non-linearity of SMA wires, which is based upon the updated Lagrangian formulation. The application concerns an elastomeric beam with embedded and pre-stressed SMA wires at an offset from the neutral axis, which act as large bending actuators resulting from the thermally induced reversible transformation strains. The experiments and numerical simulation demonstrate the good predictive capability of the model proposed and the powerful role played by SMAs as large bending actuators.
TL;DR: In this article, a simple and efficient computational analysis to predict the nominal moment capacity of RC beams strengthened with external FRP laminates is presented, which considers the determination of the limits on the laminate thickness in order to assure tensile failure due to steel yielding and to avoid tensile failures due to FRP laminate rupture.
Abstract: A simple and efficient computational analysis to predict the nominal moment capacity of RC beams strengthened with external FRP laminates is presented. It considers the determination of the limits on the laminate thickness in order to assure tensile failure due to steel yielding and to avoid tensile failure due to FRP laminate rupture. The study presents the design of laminate thickness to attain a specified moment capacity in a given beam. Furthermore, the study affords the approach to determine the laminate thickness of any type of composite material available that is equivalent to FRP laminate required to achieve the desired moment capacity. This approach helps in studying comparative costs of rehabilitation using different FRP materials. The analytical and experimental results of series of beams strengthened with different number of layers of glass/epoxy or carbon/epoxy FRP laminates are presented. The results show that the design guidelines presented in this study performed well in prediction of experimental results.
TL;DR: In this paper, the structural response of a composite shell structure intended as a model of an under-water vehicle for service in sea environment was investigated using both analytical expressions and non-linear numerical analysis.
Abstract: The paper is concerned with the structural response of a composite shell structure intended as a model of an under-water vehicle for service in sea environment. The main objective of the research is the prediction of the collapse pressure using both analytical expressions and linear or non-linear numerical analysis and the following comparison with the experimental pressure obtained in off-shore tests. The structure is composed of three basic parts with regular geometry: a cylindrical part (with the following geometrical properties: R/t=30.5, L/R=2 being the internal radius 305 mm, the length 610 mm and the thickness 10 mm) and two conical and spherical end-closures with the same thickness. The cylindrical shell was made up of 7 plies of E-glass woven roving with polyester resin. Various structural analyses were conducted before performing the experiment in the sea to verify the reliability of the analytical and numerical tools. Firstly the entire model was analysed to predict the nature of the collapse (material failure or elastic buckling) and it was stated that the collapse was due to elastic buckling of the cylindrical part. Consequently, the attention was focused on this component and approximation formulae for the evaluation of the linear buckling pressure of isotropic and composite cylindrical shells were used together with finite element models. Afterward the study was enlarged to consider the effects of the recorded geometric imperfections into a non-linear buckling analysis. The collapse pressures were compared to the design values derived from the available recommendations and to the experimental result obtained in an off-shore test (1.3 MPa).
TL;DR: In this paper, a general procedure for the determination of the effective elastic properties of two-dimensional cellular sandwich cores with arbitrary cell topology and geometry is presented. But this procedure assumes that macroscopically equivalent strain states have to cause the same strain energy in a representative volume element whether the real microstructure or the effective homogenised medium is considered.
Abstract: The present study provides a general procedure for the determination of the effective elastic properties of two-dimensional cellular sandwich cores with arbitrary cell topology and geometry. The scheme uses a strain energy-based representative volume element procedure assuming that macroscopically equivalent strain states have to cause the same strain energy in a representative volume element whether the real microstructure or the “effective” homogenised medium is considered. The strain energy can be evaluated either by analytical or pure numerical methods. Both approaches agree well in a number of examples considering different sandwich core geometries.
TL;DR: In this paper, an unidirectional glass fiber reinforced and glass carbon fiber reinforced (glass to carbon fiber volume ratio 3:1) epoxy matrix composite samples were subjected to tension-tension fatigue in air and in distilled water at 25°C.
Abstract: Unidirectional glass fiber reinforced and glass–carbon fiber reinforced (glass to carbon fiber volume ratio 3:1) epoxy matrix composite samples were subjected to tension–tension fatigue in air and in distilled water at 25°C. While no significant change in fatigue life was observed for both types of samples tested in air and in water when cyclically tested at 85% of average ultimate tensile strength (UTS), the detrimental effect of water becomes apparent at lower stress levels of 65 and 45% UTS. Compared to samples tested in air, cyclic loading in water results in shorter fatigue lives for both glass and hybrid samples. While all of the glass fiber composite samples did not survive to 106 cycles when loaded in water, hybrid samples showed better retention in structural integrity under environmental fatigue for lives up to 107 cycles, a consequence of the corrosion resistant of carbon fiber. Thus, by incorporating appropriate amount of carbon fibers in glass fiber composite, a much better performance in fatigue can be achieved for glass–carbon hybrid composite.
TL;DR: In this article, the authors address the issue of micro-structural damage in the longitudinal direction of the woven during a deformation process, primarily in the tensile mode, and identify the physical characteristics which initiate the various damage modes, what these modes are and when they occur.
Abstract: This work addresses the issue of micro-structural damage in the longitudinal direction of the woven during a deformation process, primarily in the tensile mode. This paper extends the insight into self-inflicted damage in dimensional multilayer woven composites subjected to uniaxial tensile and shear loading. Two composites made of multilayer woven architectures, hereby named: orthogonal and normal layer interlock forms the basis of this study. It identifies the physical characteristics which initiate the various damage modes, what these modes are and when they occur. This work complements the work already reported on the transverse direction in woven composites.
TL;DR: In this article, the damping of multilayer beams was accurately modelled by calculating the distribution of strain energies in the structure with the help of finite elements and knowledge of the loss factors of the individual layers (as a function of frequency).
Abstract: Sandwich-fabric panels can provide for an alternative spacer material in a constrained layer damping configuration. Constraining layer configurations with sandwich-fabric spacers can be a weight efficient replacement for full composite constraining layers, if the shear stiffness of the rubber used is not too high. It seems that in any case the use of sandwich-fabric spacers can lead to a more cost-effective damping treatment. To predict the damping of multilayer materials a strain energy method was used. The damping of multilayer beams could be accurately modelled by calculating the distribution of strain energies in the structure with the help of finite elements and knowledge of the loss factors of the individual layers (as a function of frequency).
TL;DR: An approach to evaluate the impact damage initiation and propagation in composite plates is investigated in this paper, where the main characters of impact damage can be predicted by introducing both threshold strength and propagation strength for matrix cracking.
Abstract: An approach to evaluate the impact damage initiation and propagation in composite plates is investigated It is shown that the main characters of impact damage can be predicted by introducing both threshold strength and propagation strength for matrix cracking The threshold strength controls whether the damage occurs in the composite structures, whereas the propagation strength determines by which extent the damage develops Maximum stress and quadratic stress failure criteria were employed in three failure modes It has been revealed from both the simulation and the experiment that there is a small zone of no matrix failure at the centre of impact area in the core for 059 J impact It is shown that this approach has flexible applications at an appropriate stage in the design and research process
TL;DR: In this paper, the structural properties of composite strengthened reinforced concrete (RC) structures are discussed through experimental studies, and the authors show that the use of glass-fibre composite wrap can increase the load carrying capacity of plain concrete cylinders with and without notch formation.
Abstract: The interest of using fibre reinforced plastic (FRP) materials in rehabilitating damaged concrete structures respectively has been increased rapidly in recent years. In this paper, the structural behaviours of the glass–fibre composite strengthened concrete structures subjected to uni-axial compression and three point bending tests are discussed through experimental studies. Two types of concrete structure are used in present study, they are concrete cylinder and rectangular concrete beam. Discussion on the environmental effects of composite strengthened reinforced concrete (RC) structures is also addressed. Experimental results show that the use of glass–fibre composite wrap can increase the load carrying capacity of the plain concrete cylinders with and without notch formation. The flexural load capacity of the concrete beam increases to more than 50% by bonding 3 layers of glass–fibre composite laminate on the beam tension surface. Direct hand lay up method gives better strengthening characteristic in term of the ultimate flexural load compared with pre-cured plate bonding technique. The flexural strengths of composite strengthened RC beams submerged into different chemicals solution for six months are increased compared with the RC beams without strengthening. The strength of the concrete structure is seriously attacked by strong acids.
TL;DR: In this article, the bending, buckling and free vibration problems of non-homogeneous composite laminated cylindrical shells are considered and the influence of the nonhomogeneity and thickness ratio on the shell structural response is investigated.
Abstract: The bending, buckling and free vibration problems of non-homogeneous composite laminated cylindrical shells are considered. Hamilton–Reissner's mixed variational principle is used to deduce a consistent first-order theory of composite laminated cylindrical shells with non-homogeneous elastic properties. The governing equations with their required boundary conditions are derived without introducing any shear correction factors. Numerical results for the transverse deflections, stresses, natural frequencies and critical buckling loads are presented to show the advantages of this theory. The influences of the non-homogeneity and thickness ratio on the shell structural response are investigated. The study concludes that the inclusion of the non-homogeneity effect is required, even if it is weak, for predicting the actual structural response of the shells.
TL;DR: In this article, the effect of surface cracks on strength has been investigated theoretically and experimentally for glass/epoxy filament wound pipes, which are mainly used for bazooka launchers.
Abstract: In this work, the effect of surface cracks on strength has been investigated theoretically and experimentally for glass/epoxy filament wound pipes, which are mainly used for bazooka launchers. The pipes with surface crack which have several notch-aspect ratios a/c and notch-to-thickness ratios a/t in the axial direction were exposed to open-ended internal pressure. Critical stress intensity factors were determined experimentally for several winding angles by tensile tests with center notched ring specimens. The strength values of pipes with surface cracks are compared with internal pressure test results and theoretical results.