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Natural fibers are gaining much interest in composite materials because of their potential to replace conventional glass fibers. In particular, unidirectional flax fiber composites have shown excellent mechanical properties with different thermoset matrices. However, few data are available when they are made with a biodegradable thermoplastic matrix. This paper compares the mechanical properties of two types of unidirectional flax composites using polylactic acid as the matrix: one made with layers of aligned flax rovings alone and the other containing an additional paper layer fabricated using paper making techniques. The results show that specific tensile properties of the flax/PLA (252 MPa·cm 3 ·g −1 ) and flax-paper/PLA (217 MPa·cm 3 ·g −1 ) composites are similar to those made using woven glass fabrics impregnated with epoxy (227–278 MPa·cm 3 ·g −1 ). Very high impact strength (600 J/m) was also obtained for UD flax-paper composites compared to unreinforced resin (15 J/m). Together these mechanical properties are promising for industrial applications of this new reinforcement. [ABSTRACT FROM AUTHOR]

Abstract: Natural continuous bast fibres (hemp, flax, etc.) are gaining popularity in composite materials because they can advantageously replace glass fibres. It is found that intrinsic properties of unidirectional (UD) composites are almost equivalent to those of unidirectional glass fibre composites. Unfortunately it is difficult to get repeatable results because of the inherent variability in the properties of bast fibres compared to glass fibres. Their quality is largely affected by the weather conditions, the extraction location along the plant and the techniques used to extract them (retting, bleaching, etc.). In this work, unidirectional hemp/paper/epoxy and flax/paper/epoxy composites are manufactured by adding one or two sheets of paper at the surface of a unidirectional layer of hemp or flax fibres before molding. The composites are tested under tensile loads and the results compared with those obtained for UD composites made without paper. The results show a significant increase in strength and modulus repeatability when the paper layer is present. A significant increase in strength and modulus was also obtained compared to the base epoxy properties. The resin permeability of the flax–paper reinforcement has also been evaluated and compared to that of a standard glass fabric. Globally, the results suggest that adding thin sheets of paper at the surface of reinforcement layers stabilizes and increases the composite strength but slightly reduces the Young’s modulus. However the permeability of the flax–paper reinforcement was much lower than that of the glass fabric. Modifications to the paper architecture will be required to improve this aspect. [Copyright &y& Elsevier]

Abstract The use of Glass Fiber Reinforced Polymers (GFRP) can delay or prevent tension failure in timber beams under loading and highly reduce tensile stresses. In this paper, the problem of reversibility, compatibility, and poor performance at high temperatures, of "traditional" organic adhesives was mitigated through the use of metal connectors. The flexural behaviour of hardwood and softwood beams reinforced by mechanically connected GFRP plates, has been studied through series of experimental investigations and numerical modelling. The experimental program included strengthening and testing of a total of 91 beams (50 hardwood and 41 softwood). Each beam was loaded above its service load until complete failure. Different strengthening layouts and quantity of metal connectors were used. The increment in capacity and stiffness is the main focus of this paper and effects of strengthening on deflection, failure load and failure mode, strain, and beam ductility were discussed in details. The combination of different GFRP configurations with appropriate amount of metal connectors, led to the doubling of the maximum load carrying capacity of the beams. [ABSTRACT FROM AUTHOR]

Abstract The bending strength and the tensile strength are the important mechanical properties of T-shaped hooking composite structures, which are one of the connection structures in aero-engine. In this paper, a kind of 2.5D woven T-shaped hooking composite structure, which consists of a groove structure and a T-shaped structure, was designed and used for bending test and tensile test, respectively. Experimental results showed that the initial damages both occur at the root-edge of web, and then the damages extend to the root-middle in bending test or extend perpendicular to the root-edge to the edge of the flange in tensile test. Then, a strength prediction method of progressive damage for 2.5D woven T-shaped hooking composite structure based on three-unit-cell model was proposed and used to describe the mechanical behaviors and damage processes of the connecting structure under bending/tensile loads, respectively. The comparisons between the simulation results and tests showed that the maximum error of the bending/tensile strengths is less than 15% and the damage modes between tests and simulations are similar. Therefore, the predicted strengths are accurate and the strength prediction method of progressive damage proposed in this paper is effective. [ABSTRACT FROM AUTHOR]

Abstract This paper presents the determination of the crack resistance curve of the unidirectional carbon-epoxy composite material IM7-8552 for intralaminar fiber tensile failure under dynamic loading. The methodology, proposed by Catalanotti et al. (2014) for quasi-static loading conditions, was enhanced to high rate loading in the order of about 60 s−1. Dynamic tests were performed using a split-Hopkinson tension bar, while quasi-static reference tests were conducted on a standard electromechanical testing machine. Double-edge notched tension specimens of different sizes were tested to obtain the size effect law, which in combination with the concepts of the energy release rate is used to measure the entire crack resistance curve for the fiber tensile failure mode. Digital image correlation is applied to further verify the validity of the experiments performed at both static and dynamic loading. The data reduction methodology applied in this paper is suitable for intralaminar fiber failure modes without significant delamination. Sufficient proof is given that quasi-static fracture mechanics theory can also be used for the data reduction of the dynamic tests. It is shown, that the intralaminar fracture toughness for fiber tensile failure of UD IM7-8552 increases with increasing rate of loading. [ABSTRACT FROM AUTHOR]

Nomex honeycomb cores have been widely used in composite sandwich panels. To accomplish meso-scale finite element modeling of these cores, cell wall mechanical properties are required, for which limited data are available. In this work, tensile testing was performed on Nomex paper, phenolic resin, and Nomex paper coated with phenolic resin. Flatwise tension and compression tests were also performed on two types of Nomex honeycomb cores. Test results were calibrated in finite element modeling to account for strain gage local stiffening effects and thickness normalization. Identified cell wall material properties were implemented in a honeycomb core finite element model and further calibrated by matching simulation results to manufacturer test data. The cells' double-wall thickness was also adjusted. These calibrations and adjustments led to an exact simulation match with test data. Numerically matching cell wall material properties depends on modeling sophistication and is subject to core test result variability and core construction differences among manufacturers. [ABSTRACT FROM AUTHOR]

The paper presents an experimental study concerning the bond behaviour of Carbon Fiber Reinforced Polymers (CFRP) sheet reinforcements applied to curved masonry surfaces. Such strengthening technique is more and more used in structural rehabilitation and retrofitting of existing buildings. Its effectiveness has been demonstrated by several studies published in the literature, mostly devoted to flat bonded surfaces. Observing that CFRPs are extensively applied on arches and vaults but only few research activities concern curved bonded surfaces, the experimental study described in this paper is aimed to contribute to fill this gap. The experimental program was carried out on portions of masonry arches, reinforced by CFRP sheets bonded at extrados or intrados, tested by a single lap shear test. The experimental results allowed to analyse the effectiveness of such reinforcements, loaded by actions tangent to an end of the reinforcement itself, with respect to its position (intrados or extrados) and to the curvature of the bonding surface. As expected, the results highlight that the bond behaviour strongly depend on the position of the reinforcement. In particular, the capacity of reinforcements bonded at the extrados increases with the curvature, while decreases with the curvature for those bonded at intrados. [ABSTRACT FROM AUTHOR]

Two formulas which can predict the tensile strength of hybrid composite filled with short fibers and spherical particles are derived in this paper. One of them is suitable for predicting the tensile strength of hybrid composites in which there is no cluster. And another formula is suitable for predicting the tensile strength of hybrid composites in which clusters exist. There are two vital points in this paper. One is that the influence of fiber end on the tensile strength has been quantitatively studied, while most predictions of the tensile strength of the composite from other authors neglect it. Another one is that the influence of reinforcement aggregation on the tensile strength of the composite has been quantitatively studied. [ABSTRACT FROM AUTHOR]

This two-part paper presents a numerical study about the fire resistance behaviour of pultruded GFRP profiles with square tubular cross-section subjected to bending and the ISO 834 time-temperature curve. The first paper deals with the development of numerical and analytical models and the discussion of relevant kinematic issues, including the evolution of beam deflection and position of neutral axis with the fire exposure time. The second part [1] reports an in-depth investigation on the side of static issues, which include the evolution of stress distributions and failure initiation with the fire exposure time. In the present paper, three–dimensional finite element models were developed to simulate fire resistance tests previously conducted by the authors on GFRP beams, in which different degradation curves were considered for compressive, tensile and shear moduli, based on experimental data. In these numerical simulations, both effects of varying the assignment of material properties (depending on the position of neutral axis) and of considering different thermal expansion coefficients were taken into account, and some conclusions were drawn on their influence on mid-span deflection evolutions. Since no failure criterion was implemented, both models were not able to reproduce the failure of the beams, but the overall tendency of the numerical results was consistent with the experimental data. Alongside the numerical study, analytical models based on Timoshenko beam theory were also developed and allowed obtaining accurate predictions of the mid-span deflection evolution of the GFRP beams; the analytical results were in close agreement with the numerical ones and also with the experimental data. [ABSTRACT FROM AUTHOR]

Fabric-reinforced cementitious matrix (FRCM) are composite materials more and more used for the reinforcement of masonry structures. The combination of high tensile strength fabrics (or meshes) with cementitious matrices, having good thixotropic capabilities and vapour permeability, makes such composites suitable for reinforcing a large number of masonry structures, including the one belonging to the historic heritage. FRCMs are bonded to the outer surfaces of structural masonry elements and, thanks to their adhesive capacity, bear much of the tensile stresses that unreinforced masonry cannot withstand. The effectiveness of such reinforcements, which is highly dependent on their ability to adhere to the masonry substrate, is generally investigated throughout specific experimental investigations (shear tests). Almost all the papers in the literature devoted to bond-slip analysis refer to the case of flat bonding surfaces, although these reinforcements are also widely used on curved structural elements such as arches and vaults. Therefore, this paper reports and examines the results of an extensive experimental program concerning the behavior of FRCM systems applied on curved masonry specimens. The results point out the influence of both curvature and reinforcement position (intrados or extrados) on the response of specimens in terms of bearing capacity, failure mode and post-peak response. [ABSTRACT FROM AUTHOR]

Corrugated laminates have highly anisotropic stiffness properties. Therefore, they are interesting candidates for flexible skins. The geometrically non-linear stiffness response of corrugated sheets is crucial for applications with large deformations. The present paper analyzes the governing mechanisms that drive the non-linear tensile behavior and suggests a model to analyze corrugated structures. The mechanical response mainly depends on the geometry such as amplitude and thickness of the corrugation and the material properties. The proposed model calculates the mechanical response based on a simplified model consisting of rods and discrete torsional springs. It is verified by comparison with non-linear structural analysis with FEM and experimentally validated by using samples manufactured by 3D printing. The paper also presents a parametric study investigating the influence of the geometry on the non-linear behavior and we identify the limits of linear approximation of the structural response of corrugated laminates. [ABSTRACT FROM AUTHOR]

With the rising global demand for hydrocarbon fuels, there is a growing need for the oil and gas industry to operate in deeper offshore waters. In this context, the traditional metallic tensile armours in flexible risers pose certain limitations (e.g. weight, corrosion, fatigue damage) in demanding service environments. This paper presents a novel and proprietary hybrid composite wire as an alternative to metallic (carbon steel) wires. The hybrid composite wire consists of an over-braided (Dyneema® (Dyneema is a trademark of DSM) fibres) core, with the core consisting of hexagonally packed composite rods (pultruded carbon fibre and vinyl ester). These hybrid composite wires can provide high tensile strength and stiffness accompanied by low flexural and torsional rigidities, which can easily be tailored by varying geometrical and manufacturing parameters. This paper presents the manufacturing methods used, and the mechanical behaviour of the hybrid composite wires with various configurations. [ABSTRACT FROM AUTHOR]

• A method to characterize GFRP bars using a bending test is proposed. • The method accounts for bar large displacements and shear deformation. • The bar tensile strength and elastic modulus can be simply estimated. Fiber-reinforced polymer (FRP) composite bars have been increasingly employed to reinforce concrete members when the use of traditional steel bars would represent an issue for the durability of the structure. In fact, FRP bars have high strength-to-weight ratio, do not suffer of corrosion, and do not conduct electricity. Mechanical characterization of composite bars is complex due to the remarkable difference between bar properties in the direction parallel and orthogonal to the fiber. Therefore, direct tensile testing of FRP bars requires proper specimen preparation, which usually involves expensive bonding of metal pipes at the specimen ends. In this paper, a 3-point bending test is proposed as a possible alternative to the direct tensile test to obtain a quick and reliable estimate of the bar tensile strength and elastic modulus. An analytical model that accounts for bar shear deformation and large displacements is used to describe the specimen bending behavior. Forty bending tests of glass FRP (GFRP) bars with thermosetting or thermoplastic resin and four different diameters are presented and used to validate the test set-up and analytical model proposed. The results are compared with those of corresponding direct tensile tests showing the validity of the proposed bending test. [ABSTRACT FROM AUTHOR]

Composite structures suffer from material imperfections. Non-deterministic models at the micro- and mesoscale propagate this spatial variability. However, they become impractical when the structure size increases. This paper proposes a numerically efficient multiscale methodology that links structural behaviour with the spatial variability of material imperfections on smaller scales. Fibre strength variability is accounted for through a fibre break model. A mesoscale model considers fibre volume fraction and fibre misalignment variability using random fields. Measurements provide probabilistic data for these imperfections. Subsequent homogenisation results in intercorrelated material properties on the structural macroscale that are modelled effectively with vine copulas. The methodology is verified by predicting the failure load of a coupon model. Predictions are very similar to those obtained by directly modelling spatial variability on the structural scale. • Propagation of uncertainty of unidirectional carbon-fibre-reinforced composite plies. • Stochastic fibre misalignment, volume fraction and fibre strength from measurements. • Intercorrelated finite element homogenised properties using vine copula models. • Efficient multiscale methodology accurately predicts unidirectional failure load. • Stochastic fibre misalignment and volume fraction reduce tensile strength considerably. [ABSTRACT FROM AUTHOR]

Abstract Flexible pipelines must be designed considering the extreme situation for which additional components are needed against severe loading and environmental conditions. Tensile armor is employed in case of high tensile forces, which increase with water depth; and massive components used against high internal and external pressures. In this paper, the mechanical behavior of the pipe under pure tension is investigated by both theoretical and numerical analysis, then the contribution of the external pressure to the axial problem is examined using an analytical analysis. As the deformations along the longitudinal direction of the studied pipe highly depend on the radial stiffness of the cross section, the influence of the pressure armor is carefully evaluated in the inception phase, and its radial stiffness is verified by its own numerical results. The plastic behavior for both steel and polymer layers is taken into account by using the secant modulus method. Moreover, this work answers a question raised by producers that need to know when tensile armor is required to reinforce Metallic Strip Flexible Pipes (MSFP). The theoretical model is employed to carry out the comparison between pipes with different configurations, in order to investigate the influencing parameters of the tensile stiffness. The results obtained from the theoretical and the numerical simulations lead to a remarkable confidence in the analytical solution thanks to a relatively small difference between the outcomes. [ABSTRACT FROM AUTHOR]

Highlights • Tensile tests on glass FRCM systems with different fabrics' overlap lengths have been performed. • DIC has been successfully employed to provide the FRCM strain field. • A variational model has been numerically implemented to simulate the FRCM tensile behaviour. Abstract The use of Fabric Reinforced Cementitious Matrix (FRCM) systems to reinforce existing masonry and concrete structures is nowadays a well-established practice. The mechanical characterization of FRCM systems is of fundamental importance to define the correct parameters needed to design a strengthening intervention. However, some aspects regarding FRCM tensile behaviour need to be further investigated. The aim of this paper is to provide a detailed overview on the mechanical behaviour of FRCM specimens subjected to tensile tests. In this context, the effect of fabrics' overlapping on the global behaviour of the system is extensively analyzed. Different sample's configurations have been studied: one reinforced with a single layer of bidirectional glass fabric and three others with different fabrics' overlap lengths, varying between 100 and 200 mm. Digital Image Correlation (DIC) has been also used to measure displacements in experimental testing. A phase-field model, that accounts for brittle fracture of cementitious matrix and fabric reinforcement and possible slippage at the fabric-to-matrix interface, has been developed. The variational formulation has been implemented in a finite element code to simulate the tensile behaviour of FRCM systems and the effects of using different fabrics' overlap lengths. [ABSTRACT FROM AUTHOR]

Abstract Matrix behavior is expected to widely influence the impact response of composites, but detailed conclusions in the case of thermoplastic laminates are still needed. In this paper, we investigated the effect of using either ductile homopolymer PP or less-ductile impact copolymer PP matrices on the low-velocity impact responses of continuous glass fiber-reinforced polypropylene (PP) laminate. These PP types represent two variants in the same family of thermoplastic matrix. A thorough experimental campaign was first performed to provide the tensile properties (for PP and glass/PP) and fracture toughness (Mode-I and Mode-II, glass/PP only) of the employed materials. Then, low-velocity impact tests where the energy levels are ranging from 12 to 30 J were performed. Using ductile PP in glass/PP laminates reduces the energy dissipated during impact as well as the impact damage area. The effect of selected stacking sequences on the resistance to impact was also studied as a way to reveal the difference between ductile and less-ductile glass/PP. Stacking sequence with thin plies shows better impact properties than other sequences regardless of the matrix ductility, which can be explained by micromechanics for both grades of material. Finally, as quasi-static indentation (QSI) is usually used to quickly access the resistance of laminates towards out-of-plane impact, we systematically compared our impact results with QSI results. We found that the prospective use of QSI in forecasting impact properties and damage is very limited in glass/PP composite due to strain-rate sensitivity. [ABSTRACT FROM AUTHOR]

Abstract Currently bonded repairs can only be permitted on those aircraft primary structures suffering cracks/damages having a residual strength well exceeding the design limit load prior to application of the bonded repairs. This paper focuses on the approaches to meet the certification requirement by combining a bonded patch with other methods that enhance residual strength of the damaged structures. An overview of the recent research in this area conducted by Defence Science and Technology Group and its research partner organisations is presented. The outcomes from six individual research programs indicated the hybrid repair methods are promising for primary structure repair applications. Significant residual strength increases were achieved through optimum damage removal and/or inclusion of alternative load paths. These methods also provide significant additional fatigue life post premature bond failure that would allow any possible bond-line defect/damage to be identified by NDI means long before a catastrophic failure. The adhesive bond in the hybrid repairs was proven to provide significant benefit in enhancing the static strength and fatigue resistance. Key issues for the application of these hybrid repair methods and future research directions are also discussed. [ABSTRACT FROM AUTHOR]

Abstract Composite thin-ply laminates have been reported to exhibit superior performance in various loading conditions than standard-ply laminates due to positive size effects. However, the ultimate tensile strength of the thin-ply (<0.125 mm) laminates containing circular hole was lower than that of the thick (>0.125 mm) or standard-ply (0.125 mm) laminates with same size of the hole. Besides, fracture morphologies showed a transition from a combined mode of matrix crack, delamination and pull-out at 45° and −45° ply in the thick and standard-ply laminates to a quasi-brittle fracture in the thin-ply laminates. In order to explain the experimental phenomena, acoustic emission was used in this paper to identify and distinguish the failure modes of laminate specimens containing circular hole with different ply thickness, and finite element simulation was adopted to investigate the cause of lower tensile strength in the thin-ply specimen. Carbon fiber reinforced polymer matrix composite laminate specimens were prepared using prepregs with different ply thicknesses (0.02 mm, 0.055 mm and 0.125 mm). In tensile test, higher initial stress of damage, lower ultimate strength and quasi-brittle fracture morphology could be observed in the thin-ply laminate specimens with an open hole. The results of acoustic emission analysis demonstrated that the matrix damage and delamination were suppressed in the thin-ply laminates, and superior damage suppression and crack-propagating resistance in the thin-ply laminates lead to quasi-brittle fracture morphology. Besides the more homogeneous micro-structure and isotropic behavior of the thin-ply laminates leaded to higher initial damage stress compared to the laminates with thick plies. However, according to finite element analysis, the thin-ply laminates exhibited much stronger stress concentration after initial damage until ultimate failure of the specimens, leading to lower ultimate strength under tensile loading. [ABSTRACT FROM AUTHOR]

Abstract In this paper, a multi-scale stochastic fracture model is presented to study the nonlinear mechanical behaviors of two-dimensional (2D) woven C/SiC composites under uniaxial tension. This model considers the randomly distributed intrinsic flaws and the complex braided structure of composites. In the model, the micro-scale representative volume element (RVE) is developed to compute the effective properties of yarns, which are then used in the meso-scale RVE to capture the macroscopic stress response of woven composites. Weibull distribution law is applied to the material elements to reflect the random flaws. The failure mechanism of composites is identified by analyzing the damage rates and the fracture morphologies of fiber, matrix, and interface. The effects of fiber volume fraction and temperature on fracture strength are predicted and the results demonstrate that the failure location varies as the temperature increase due to the relief of thermal residual stress. The presented model provides an efficient tool for evaluating the mechanical properties of textile composites. [ABSTRACT FROM AUTHOR]

Abstract For the past many decades' enormous research has been done on mechanical and moulding properties of 2D woven and non-woven fabrics. The current paper presents a comprehensive investigation of the tensile, bending and moulding behaviours of 3D orthogonal warp interlock fabrics with different fabric densities. Four 3D warp interlock fabrics with different areal density made from 168Tex linear density p-aramid Kevlar yarn were manufactured on dobby loom in GEMTEX laboratory. Based on the investigation both fabric density and yarn density shows a significant effect on bending and tensile properties of the fabrics. The bending rigidity in the warp and weft directions become higher in preforms with denser weft and warp yarn densities respectively. In general, as the yarn density in the respective warp or/and weft direction increases, the maximum tensile load with maximum strain increases. Moreover, the fabric and yarn density has also shown a great impact on various mouldability characteristics of 3D warp interlock preforms while deformation. The study finally elucidated that, like other parameters, fabric and the yarn density of 3D warp interlock influenced greatly the tensile, bending and moulding properties where those parameters should be considered carefully while applying in various technical textile applications i.e., soft body armour. [ABSTRACT FROM AUTHOR]

Abstract Shear properties of coated fabrics is poorly understood and the effects of shear stiffness on the behaviour of tensile fabric structures are usually ignored in the current design practice. The paper presents a new test method for the investigation of architectural coated fabric shear properties. The method relies on the biaxial pretension of cruciform specimens, where warp and weft yarns are oriented 45° with respect to the loading directions. Loading protocol is used to generate consecutive shear stress wave with specific biaxial tensile stress aligned with the yarns. An advanced biaxial tensile test system has been developed to implement biaxial loading by either displacement or force control strategy. Biaxial tensile shear tests of PVDF-coated polyester materials have been carried out to validate the new method. The implications of shear deformation, and material’s viscosity and plasticity from the experimental results are addressed. The determination of shear stiffness is described and a comparison of results derived from different methods has been made. The advantages of the new biaxial tensile shear test method and some experimental findings are concluded. [ABSTRACT FROM AUTHOR]

In the present study, a novel theoretical model is developed, based on the energy method, to predict the equivalent mechanical properties of a new morphing structure with zero Poisson's ratio, which is composed of continuous fiber reinforced composite struts. Due to the employing glass fiber in fabricating the proposed cruciform honeycomb, higher strength than the structures made of pure isotropic materials is obtained. The use of cells with a zero Poisson's ratio also increases the flexural strength of the structure. In the continuation of the paper, by examining the geometric effects on the equivalent properties, a parametric study is performed. Then, using the appropriate failure criterion, the tensile and compressive strength of this network is obtained. The extracted properties are used in nonlinear analysis of the response of morphing structures and to improve the performance of these structures under different loads. It should be noted that in order to validate the relationships developed in this paper, the experimental tests and finite element methods are employed. [ABSTRACT FROM AUTHOR]

This paper focuses on revealing the evolution mechanism of micro curing residual stress and its impacts on the mechanical responses of medium-temperature cured composites (T700/7901) under out-of-plane tension. An integrated multi-scale framework is established, the macro-scale thermal-chemical and micro-scale stress–strain models are set up to predict the development of the micro residual stress during curing, and the obtained stress field is further employed as the initial boundary conditions in the micromechanical analysis to explore its effect qualitatively and quantitatively. Experimental and analytical methods are taken to verify and validate the current model. Besides, the impacts of different curing cycles on the micro residual stress and out-of-plane tensile strength are also discussed. The evolution of the micro curing residual stress in T700/7901 composites is intuitively revealed, and the results of the micromechanical model show that the out-of-plane tensile strength increases by nearly 14.4% due to the occurrence of the process-induced stress. Both the interfacial damage and matrix plastic deformation are delayed owing to the residual stress. The work builds the connection between the curing process and mechanical responses of unidirectional composites and demonstrates the necessity of considering curing residual stress in designing and evaluating composites. [ABSTRACT FROM AUTHOR]

This work proposes a stochastic multiscale computational framework for damage modelling in 3D woven composite laminates, by considering the random distribution of manufacturing-induced imperfections. The proposed method is demonstrated to be accurate, while being simple to implement and requiring modest computational resources. In this approach, a limited number of cross-sectional views obtained from micro-computed tomography (µCT) are used to obtain the stochastic distribution of two key manufacturing-induced defects, namely waviness and voids. This distribution is fed into a multiscale progressive damage model to predict the damage response of three-dimensional (3D) orthogonal woven composites. The accuracy of the proposed model was demonstrated by performing a series of finite element simulations of the un-notched and notched tensile tests (having two different hole sizes) for resin-infused thermoplastic (Elium®) 3D woven composites. Excellent correlation was achieved between experiments and the stochastic finite element simulations. This demonstrates the effectiveness of the proposed stochastic multiscale model. The model successfully captured the stochastic nature of tensile responses (ultimate tensile strength and stiffness), damage modes (matrix damage and fibre failure), and initiation and propagation of transverse cracks in thermoplastic 3D woven composites, consistent with experimental observation. The stochastic computational framework presented in this paper can be used to guide the design and optimization of 3D textile composite structures. [ABSTRACT FROM AUTHOR]

This paper presented 180 specimens to investigate mechanical properties of steel fiber reinforced Nano-concrete (SFRNC) after elevated temperature through the method of compression test, splitting tension test and flexure test. The test parameters effects of different elevated temperature and different content of steel fiber on mechanical properties including compressive strength, splitting tensile strength and flexural strength of SFRNC were analyzed in this paper. The integrity of Nano-concrete after elevated temperature could be improved because of the mixing of steel fiber, which could be observed from the failure process of SFRNC. Furthermore, mixing of steel fiber can change failure mode of Nano-concrete and improve the ductility of concrete greatly. It could be summarized that the elevated temperature had negative effects on compressive strength, splitting tensile strength and flexural strength of SFRNC. And it also could be found that Nano-concrete mixed with steel fiber can improve residual compressive strength, splitting tensile strength and flexural strength of these specimens after high temperature. [ABSTRACT FROM AUTHOR]

This paper presents a numerical and experimental study on the intralaminar tensile fracture toughness of carbon fiber reinforced composite subjected to high strain rates. As there is no standardized testing procedures for intralaminar fracture toughness characterization of composites at high strain rates, there is a clear need to design specimen geometries, testing apparatus and data reduction schemes that allows the characterization of the fracture toughness of composites in the dynamic regime. Initially numerical studies were performed based on finite element simulations in order to investigate the viability of its construction for different testing configurations to characterize the intralaminar toughness of composite laminates. A comparative study is presented showing the advantages and disadvantages of each testing configuration. A new data reduction scheme based on modifications in the ASTM standard, accounting for material anisotropy and specimen finite geometry effects is suggested. Experimental tests were carried out, using the proposed specimen configuration at different strain rates in order to investigate the strain rate effects using a modified version of the Split Hopkinson Pressure Bar. Fractography analyses using Scanning Electron Microscopy(SEM) have been also performed in order to investigate the strain rate effects on the failures mechanisms of the composite material studied herein. [ABSTRACT FROM AUTHOR]

Woven structure is an essential component widely used in composite materials, bio-materials and mechanical metamaterials. The mechanical response of the dry woven fabric, which is widely used as reinforcement in composite materials is studied in the present paper. Typically, for the dry woven fabric, the warp and weft yarns are weaved with each other. Each warp or weft yarn also consists of large amounts of small filaments. Because of this multiscale nature, a model that can predict the material response as a function of the underlying structure is important for the design of the dry woven fabric. Hence, a computationally efficient model to simulate the uniaxial tensile loading response for dry woven fabrics is proposed. The proposed model is able to predict the macroscopic loading-deformation response, the effective in-plane Poisson’s effect and the deformation of the thickness by taking into account the influence of the filaments, the weaving pattern and the surface contact at the crossover of the yarns. The accuracy of the model is validated by a digital image correlation (DIC) experiment. For the weaved yarns, complex yarn geometries can be easily modelled and different yarn curve assumptions can be conveniently incorporated in the proposed model. The high computational efficiency of the model makes it potentially helpful for designing woven materials with high mechanical performance. [ABSTRACT FROM AUTHOR]

This paper provides critical data regarding the post-fire residual strength of Glass Fibre Reinforced Polymer (GFRP) reinforced concrete slabs. The residual tensile and bond strength of three types of GFRP reinforcing bars and the post-fire residual strength of a GFRP reinforced concrete slab are examined. For residual tensile strength, GFRP bars with a nominal diameter of 16 mm are exposed to temperatures up to 450 °C and tested after 24 h at room temperature. After 24 h, the specimens are loaded to failure at room temperature. For residual bond strength, pullout specimens are heated under various sustained load values. Finally, a full-scale GFRP reinforced concrete slab is tested at room temperature to evaluate the post-fire residual capacity after exposure to three hours of a standard fire. The residual tensile test results show that the bars that were exposed to 400 °C recovered at least 45% of the original strength while the residual bond strength is approximately 40% for pullout specimens that had experienced 300 °C. The post-fire residual strength of the slab is 68% of its room temperature flexural design strength with the bond loss at the ends of the slab being the governing mode of failure. [ABSTRACT FROM AUTHOR]

Fiber-reinforced polymer (FRP) wrapping has become an attractive strengthening technique for concrete columns. Within this strengthening technique, FRP jackets are wrapped around the concrete column with the fibers in the jacket being oriented in the hoop direction. In practice, the FRP jackets can be either continuous or discontinuous along the column height and thus the resulting column is referred to as FRP fully or partially wrapped concrete columns. Existing research has demonstrated that the FRP partial wrapping strengthening technique by discrete FRP strips (rings) is a promising and economic alternative to the FRP full wrapping strengthening technique. Although a number of experimental investigations have been conducted on FRP partially wrapped concrete columns, the stress-strain behavior of FRP-confined concrete in partially wrapped concrete columns is not yet completely understood. This paper presents an experimental program to investigate the axial compressive behavior of circular concrete columns partially wrapped with FRP strips. The test results are presented and compared with five existing representative stress-strain models to examine the reliability and accuracy of each model. It has been demonstrated that the Teng et al.’s (2007) model is superior to the other four representative models and it provides reasonably accurate predictions of the ultimate axial stress of FRP partially wrapped concrete while it usually underestimates the ultimate axial strain. [ABSTRACT FROM AUTHOR]

This paper studies failure behaviors of glass fiber/PC resin thermoplastic composites under transverse tension and shear loads using explicit finite element method. Microscopic long fiber/matrix composite representative volume elements with randomly distributed fibers and periodic boundary conditions are established by ABAQUS-PYTHON script language. The finite-deformation viscoplastic Gurson model is used for predicting the plastic deformation and void growth of thermoplastic glassy polymer matrix, which is implemented using ABAQUS-VUMAT explicit subroutine. The bilinear cohesive model with finite-thickness interface element is used to simulate the fiber/matrix debonding. Three important issues are explored: first, effects of the cohesive interface strength on the plastic deformation and void growth of composites are studied using three mesh models and three fiber distributions. Second, failure surface under different tensile and shear displacement ratios is obtained, compared with the predictions using the Hashin and Puck failure criteria developed mainly for thermoset composites. Finally, the influence of the plastic softening effect of matrix on the strain concentration or localization behaviors is discussed. Results show the tension/shear load ratio and the cohesive interface strength produce large effects on the void growth and failure surface of composites, but fiber distribution shows a small effect on transverse load-bearing ability of composites. [ABSTRACT FROM AUTHOR]

This paper presents an study on the rupture strain of cylindrical fiber-reinforced polymer (FRP) jackets under internal ice pressure. A total of 45 cylindrical FRP jackets were prepared using three unidirectional carbon, glass, and basalt fabrics in three different internal diameters, namely 60, 114, and 216 mm, and one-, two-, and three-plies. Three jackets for each combination were typically tested and the average hoop rupture strains were obtained and compared to the rupture strain of flat coupons in the form of a strain efficiency factor. It was found that the strain efficiency factor ranged from 0.53 to 1.05 with an average of 0.77. A new analytical model was also developed based on the bi-axial state of stress in a cylindrical FRP jacket to obtain the rupture strain and strain efficiency factor of the FRP jacket using a closed-form solution. The model engaged four major parameters, namely: diameter, thickness, axial/transverse strength ratio, and Poisson’s ratio of the FRP jacket. The two latter parameters were eliminated after a parametric study to propose a simplified formula. The analytical and simplified models predicted the experimental strain efficiency factors with an average error of −3.4% and −4.6%, respectively. [ABSTRACT FROM AUTHOR]

The increasing use of adhesive joints in dynamic applications require reliable measurements of the rate-dependent stress-displacement behaviour. The direct measurement of the stress-displacement curve is necessary when using cohesive models in discretised solutions of boundary value problems in solid mechanics. This paper aims to investigate the rate-dependent tensile failure of adhesive joints by using a new experimental methodology – it relies upon the combination of the stress wave propagation theory and digital image correlation methods on high speed footage to quantify the tensile stress and the dissipated energy respectively. For this purpose, the Split Hopkinson Bar methodology was employed – the experimental configuration was optimised using numerical modelling. To prove the sensitivity of our framework, two different adhesives are characterised at different loading rates: the adhesive failure strength was found to increase considerably with the strain rate, while the plastic deformation of these adhesives was reduced. The film adhesive showed superior performance over the particle toughened one. In the final part, a rate-dependent cohesive zone model is proposed, one which captures the measured behaviour and which has the potential to be used in industrial applications. [ABSTRACT FROM AUTHOR]

During operational conditions, extreme environments combined with unexpected high loading rates can induce severe damages or, inclusively, premature fails. Therefore, this paper intends to study the effect of different hostile solutions on the longitudinal impact strength in order to establish design criterions. For this purpose, samples of GFRP composites were immersed into alkaline and acid solutions as well as distilled water. Variables like exposure time, temperature and concentration of the solution were analysed in detail. The effect of pre-damages was also studied for different pre-loads, where the severity of the damages introduced was quantified by acoustic emission. It was possible to conclude that, independently of the solution, the exposure time and temperature were determinant to decrease the tensile impact strength. Finally, the magnitude of the initial damage has a significant influence on the impact resistance. [ABSTRACT FROM AUTHOR]

Fiber metal laminates (FMLs) are usually more complicated in the failure aspect as compared to their constituents, especially when complex load is applied. In this paper, notched FMLs and the constituents, i.e., the aluminum and glass fiber reinforced plastic (GFRP) were subjected to off-axis tensile loading to evaluate the failure mechanism. Initial attention was paid on the off-axis dependence of mechanical responses, especially on its relation to the notch size. As expected, off-axis dependence of notched strength and notch sensitivity were closely related to the notch size, but different for GFRP laminates and FMLs due to their different damage behavior. Finite element model was employed to predict accurately the mechanical responses of FMLs, particularly for elucidating the damage mechanism. Failure of notched FMLs under off-axis loading was a combined transverse fracture and shear-off, while it was shear-dominated in notched GFRP laminates. Transverse fracture in aluminum appeared first, followed by the fiber breakage, which was postponed by the extensive subcritical damage. Thereafter, shear-failure in fiber and aluminum layers were encountered instantaneously at the descending part. Thus, the critical failure of off-axis notched FMLs was still tension-dominated as that in the on-axis case, but aluminum played the critical role. [ABSTRACT FROM AUTHOR]

A new strengthening composite system, namely Basalt Fiber Reinforced Polymer (BFRP) grid – Ultra-High Toughness Cementitious Composite (UHTCC) for Reinforced Concrete (RC) structures is explored in this paper. Thirty UHTCC specimens internally strengthened with BFRP grid and six similar reference specimens without strengthening were tested to investigate the tensile mechanical behavior. The reinforcement ratio of the BFRP grid (0.17%, 0.68%, and 1.16%) and the mix proportion of the UHTCC were the two main test parameters. The experimental results highlighted two failure modes: 1) rupture or slip off failure of chopped PolyVinyl Alcohol (PVA) fibers at the critical crack sections in the reference specimens, and 2) partial rupture failure of BFRP grid within the UHTCC in all strengthened specimens. Moreover, the relative slip at the interface between the BFRP grid and the UHTCC substrate was not observed during testing. The tensile force capacity of the strengthened BFRP–UHTCC specimens increased by 42% to 172% compared to the reference specimens depending on the reinforcement ratio of the BFRP grid. On the other hand, the tensile force capacity of BFRP–UHTCC specimens slightly decreased by 1% to 14% with the increase of the water-to-cement material ratio of the UHTCC layer from 24% to 38%. Additionally, a stress–strain relationship and strength models of the strengthened specimens are proposed and verified with the test results to predict the tensile mechanical behavior. [ABSTRACT FROM AUTHOR]

The behavior of composite laminates subject to notch based stress concentrations is difficult to apprehend, especially the mechanisms of damage progression leading to total failure. Numerical and experimental investigations were carried out on three different stacking sequences of notched, thin ply carbon/epoxy laminates. This paper presents a computational study of notched tensile tests (U-notch) using the Discrete Ply Modeling (DPM) method, which has already proved efficient on both in-plane and out-of-plane loading cases, such as pull through, low velocity impact and compression after impact. The specificities of this finite element model are its discrete nature (interface elements to model delamination and matrix cracks), the small number of parameters required, and its robustness. This work follows on from the study of open-hole tensile tests (same three layups) by the same authors [1] and analyzes the influence of layup and notch shape. Comparisons with experiments (using infrared technology) demonstrate that tensile strengths, and failure scenarios and patterns are predicted with acceptable accuracy. [ABSTRACT FROM AUTHOR]

Steel Reinforced Polymer (SRP) systems have recently emerged as an attractive solution for the external strengthening of reinforced concrete structures. They entail unidirectional fabrics made out of high tensile strength steel cords that can be externally bonded to the substrate via wet lay-up, using either epoxy or polyester resin. Currently, research about the behavior of SRP strengthening systems for concrete structures is evolving but further systematic and comprehensive studies are still needed to ensure the consistency and reliability of the studies performed to date. The present paper contributes to expanding the existing knowledge by presenting the results of an extensive experimental program devoted to investigate the bond behaviour between SRP and concrete substrate. To this purpose, a number of SRP strips were bonded to concrete blocks by a thixotropic organic matrix and the lap joint was subsequently subjected to direct shear tests performed in displacement control. Besides the concrete strength, the following study parameters were considered: (a) the concrete surface roughness in the bonded region, (b) the density of the steel fabric, (c) the ratio of the epoxy covered concrete surface width to the SRP strip width, and (d) the bonded interface length. [ABSTRACT FROM AUTHOR]

One of the important issues in the certification of composite aeronautical structures is large notches. In this paper, tests are carried out on technological specimens under tensile, shear and combined loadings using the VERTEX test rig presented in the first part of this publication. Strong interactions between postbuckling and propagation of cuts are observed. The specifically developed FE-SDIC methodology presented allows a first dialog between calculation and testing. The Discrete Ply Modeling method is able to compute the onset of failure in such complex tests. New test responses called “envelope curves” are proposed and are obtained by following a load path that allows the behavior of the notched structure to be validated for certification purposes. This methodology should eventually lead to a new vision of the test pyramid with the help of “Predictive Virtual Testing” procedures. [ABSTRACT FROM AUTHOR]

This paper presents the results of experimental investigations of the tensile properties of different types of CFRP plates. Coupon specimens of low, normal and ultra-high modulus CFRP plates were prepared and tested under tensile loading. Four different strain rates were used, including one low strain rate and three high strain rates. Two methods of capturing strain were used: image correlation photogrammetry and foil strain gauges. The results showed a significant increase in the tensile strength, ultimate strain and elastic modulus for coupons under high strain rates. The CFRP coupons were prepared and tested in accordance with the ASTM3039-08 standards. Finite element analysis was performed and the results agreed very well with the experimental results. [ABSTRACT FROM AUTHOR]

This paper presents the results of an experimental investigation into the durability behaviour of textile-reinforced concrete (TRC) subjected to both tensile and bending loads to compare its macroscale characterization. Composites are produced as a laminate material using 2 and 6 layers of glass fibre mat as reinforcements. The instantaneous and long-term (durability) properties of composite TRC are identified by tensile and flexural testing with specimens made from the same fresh mortar. The long-term tests are conducted in two ageing environments: natural ageing, which was conducted under the laboratory atmosphere (20 °C and 50% RH), and accelerated ageing, which consisted of immersion of the specimens in hot water at 50 °C. The durability performance of TRC is evaluated by the reduced macroscale performance and damage mechanisms. The effects of the reinforcement ratio, testing conditions, and thermal conditions on the long-term response of TRC are investigated, and the microstructure of both matrix and fibre is observed and discussed after the tests with observations via scanning electron microscopy (SEM). The addition of layers of glass fibre (reinforcement ratio) increased the strength capacity and the first macro-crack strength of TRC in both tensile and bending tests. The ultimate strength value of the TRC composites obtained from the tensile test is lower than that from the bending test over the same tested days as a result of the different redistribution mechanisms; however, the difference between tensile and flexural stress remains approximately equal with similar deviations. An increase in the tensile and flexural strength capacity over the ageing time is observed before 90 days of ageing. However, after 90 days, the test results showed a loss of ductility of the accelerated aged specimens. [ABSTRACT FROM AUTHOR]

The effect of ply thickness on the onset of intralaminar and interlaminar damage is extremely important for the structural response of laminated composite structures. This subject has gained particular interest in recent years due to the introduction in the market of spread-tow, ultra-thin carbon-fibre reinforcements with different configurations. In the present paper, an experimental test campaign was carried out to study the structural response of aerospace-grade plain weave spread-tow fabrics (STFs) of different areal weights. The results showed that, in spite of an apparent superior longitudinal tensile strength of the thick STF, the multidirectional thin-STF laminate exhibited an improved tensile unnotched strength over the thick-STF laminate, attributed to its damage suppression capability. However, damage suppression was also responsible for similar tensile notched strengths. In compression, the thin-STF laminate performed substantially better than the thick-STF laminate in both unnotched and notched configurations. Finally, a similar bearing response was obtained in both STF laminates, in spite of a slightly higher resistance of the thin-STF laminate to the propagation of subcritical damage mechanisms. [ABSTRACT FROM AUTHOR]

The gap is one of the most common defects during the AFP process, which has a nonnegligible impact on the mechanical properties of laminates. This paper proposes a novel three-dimension reconstructive gap model based on the in-process serial layer scanned point clouds, which can characterizes the gap features inside the laminate and pre-determine the mechanical performance before the subsequent procedures. The measured point cloud will be transformed into eligible and processible formats and then be used to generate a finite element grid using the element-based material property assignment method. The local material properties and fiber orientation are defined by previously assigned classes and grid geometries respectively. The effect of gap size on the in-plane tensile strength and damage evolution of laminates is investigated and both the experimental and simulation results find that the ultimate strength and stiffness show a significant decrease with the increase of gap size. [ABSTRACT FROM AUTHOR]

Carbon-fiber-reinforced polymer (CFRP) grids or textiles for concrete have high application potential in thin planar members such as bridge deck slabs or façade plates. With the high tensile strength of CFRP, shear failure governs design in wider regions, which calls for optimized shear models incorporating all relevant load-transfer mechanisms. The contribution of dowel action to shear resistance is often neglected in shear models derived specifically for FRP reinforcement. As reasons, the low transverse modulus of the anisotropic material and the small cross-sectional areas per reinforcement element and thus small cross-sectional stiffness are mentioned. Yet fundamental research on this mechanism for CFRP grids is amiss. This paper presents a new test setup for characterizing the dowel action of CFRP grids that are pre-strained, similar as in real applications where the reinforcement in the shear crack is stressed in flexural tension. The influence of (pre-) crack width, pre-strain and concrete cover is discussed. By comparison to results from flexural shear-tests it can be shown that, depending on the effective depth, the contribution to shear resistance can be significant. Furthermore, the important role of dowel cracking in the shear-compression failure mechanism could be analyzed using the results of the new dowel test. [ABSTRACT FROM AUTHOR]

Conventional near-surface mounted (NSM) FRP methods rely on expensive and less durable epoxy-filler bond to transfer tensile force from FRP reinforcements into concrete elements, generally failing to fully develop the tensile strength of FRP reinforcements. In this paper, cost-effective and potentially more durable fillers (e.g. cement-based paste and ceramic tile adhesive) combined with anchorages have been proposed to improve conventional NSM FRP methods. Experimental results demonstrate that the proposed NSM methods are able to make full use of FRP reinforcements, suggesting excellent compatibility between fillers and the proposed method. Further mechanical improvements can be achieved by evenly distributing the FRP material of one groove into multiple grooves. Moreover, the study tends to use high-viscosity cement filler for facilitating FRP installation especially on the bottom or side of concrete elements. The application of flexural reinforcement on the side of concrete elements have also been explored, aiming to deliver a much easier FRP installation. It is believed that the paper presents feasible improvements for NSM methods. Test results suggest that those improvements can achieve a stronger and potentially more durable NSM method with cost-effective fillers. [ABSTRACT FROM AUTHOR]

This paper deals with the study of the vibratory behaviour of rotating composite shafts and the effects of stacking sequences and shear-normal coupling on natural frequencies and critical speeds. Equivalent Single Layer Theory (ESLT) including shear deformation, rotary inertia and gyroscopic effects is introduced for the dynamic analysis. A finite element based on ESLT is developed to model the rotating composite shaft using Timoshenko beam theory. This finite element is developed to consider the effects of stacking sequences and shear-normal coupling on rotating composite shafts. Obtained results are compared with those available in the literature using different theories. The close agreement in the obtained results shows that the developed finite element based on ESLT can be effectively used for composite rotor dynamic analysis. Moreover, results revealed that shear-normal coupling, fiber orientations and stacking sequences have a great influence on the dynamic characteristics of rotating composite shafts. [ABSTRACT FROM AUTHOR]

Concrete canvas (CC) is a promising material in civil and military engineering due to its flexibility, fast construction with low labor cost, and rapid strength development. However, relatively lower tensile and flexural strength limit the application of CC products. This paper presents an experimental study of the improvement of the tensile and flexural strength of CC panels through the employment of external reinforcement by a fiber-reinforced polymer (FRP) sheet. The tensile and flexural behaviors of CC and FRP reinforced CC panels are investigated through uniaxial tensile and four-point bending tests in both warp and weft directions. The bond behavior between FRP sheets and CC is investigated through a single-shear pull-off test, by which both strain distribution and local bond stress-slip relationships are experimentally measured. Experimental results reveal that the tensile and flexural properties, especially the reinforcing efficiency of flexural strength, are significantly improved in the FRP reinforced CC samples. [ABSTRACT FROM AUTHOR]

In this paper, the tensile strength and failure modes of thin ply carbon fiber-reinforced polymer (CFRP) angle-ply laminates are investigated by experiments and predicted by Finite element method (FEM) and theoretical model. First, experiments are performed to evaluate the tensile behavior of thin ply CFRP angle-ply laminates fabricated with different fiber areal weights of prepreg (20,60,120 g/m 2 ) and ply angle (15°, 30°). Experimental results show that thin ply angle-ply laminates present different failure modes, and also the tensile strengths do not increase monotonically with the decrease in fiber areal weight. Second, both theoretical and FEM models are established to predict the strength and failure modes of thin ply CFRP angle-ply laminates with different ply thickness and fiber volume fraction, also two competing mechanisms finally cause the non-monotonic change of strengths of thin-ply laminates which has good agreement with experimental results. Finally, a failure diagram of thin ply angle-ply laminates under tensile load is given, which shows different failure modes (fiber breakage, delamination and transverse matrix failure) for fiber areal weight (0–240 g/m 2 ) and ply angle (0–90°). Also the delamination is suppressed and the fiber breakage is extended with the decrease of fiber areal weight in the ply angle range of 10°–25°. [ABSTRACT FROM AUTHOR]

Previous studies show that welded shear connectors in steel-ultra high performance concrete (UHPC) composite structures have poor ductility, which cannot satisfy the requirement of Eurocode 4 for ductile design. This paper presents a series of tests on demountable headed stud shear connectors in steel-UHPC composite structures, which can be employed in prefabricated building structures and bridge decks. This type of demountable stud shear connectors can make structural components recyclable and environment-friendly. The effects of the shank diameter and aspect ratio on failure modes, initial stiffness, ultimate strength and ductility of the shear connectors are investigated through push-out tests. Five groups of the connectors each with three specimens are tested considering deviations of the specimens due to material discreteness and manufacturing errors. Design formula for the shear strength of the demountable stud connectors is proposed, and design recommendations are also presented based on the experimental results. [ABSTRACT FROM AUTHOR]

Carbon fiber reinforced polymers (CFRP) laminates are extensively employed to manufacture the deployable composite thin-walled lenticular tubes (CTLTs). This paper presents a comparison of experimental and numerical and analytical results of compressive and tensile flattening types of deployable CTLTs. Firstly, a compressive flattening model created by ABAQUS was introduced to obtain its strain and stress of each ply of composite tube. Secondly, compressive flattening experiments were performed for CTLT specimens to explore compressive flattening mechanism of CTLTs. Then, the numerical simulation methods to simulate the compressive flattening of CTLTs were verified by comparing measurements and corresponding numerical results. Thirdly, analytical models are employed to predict the flattening process of CTLTs under compression. Lastly, for the tensile flattening process of CTLTs, the numerical simulation method and corresponding experiments and theoretical results are respectively also carried out with aim of revealing mechanical properties of CTLTs under tension. The flattening process of CTLTs can be considered to be a nonlinear deformation and small strain process. For the compressive flattening, the maximum compressive force, displacement and strain are 98N, 60mm and 0.29%, respectively. For the identical tensile flattening, the maximum tensile force, displacement and strain are 550N, 42.5mm, 0.53%. respectively. It is found that the compressive flattening way is a better choice in the design of the actuated mechanism. [ABSTRACT FROM AUTHOR]