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This research presents a investigation of long fiber-reinforced thermoplastics (LFT) with mixed fiber types, combining experimental analysis with numerical modeling techniques. By accurately predicting the stiffness of mixed fiber composites, the design margin between mono fiber reinforced materials can be effectively exploited, facilitating the use of such materials. For this purpose in particular, a novel application of the Mori–Tanaka approach with two different inclusions guaranteeing symmetric stiffnesses is presented. This is a method that has never been used before in field studies. In addition, the study integrates fourth-order plate-averaged orientation tensors measured and subsequently interpolated to improve the accuracy of the modeling. Consistency with the established shear-lag modified Halpin–Tsai method is demonstrated, confirming the suitability of both approaches for predicting the tensile modulus of GF LFT and CF+GF LFT. However, discrepancies between predictions and experiments for CF LFT are attributed to the complex microstructure of the material caused by bundling and poor dispersion of the CF. Furthermore, the study reveals remarkable hybridization effects within the mixed fiber LFT, particularly evident in the 22% increase in elongation at break observed in CF+GF LFT compared to CF LFT. Overall, this research significantly advances the understanding and predictive capabilities regarding mixed fiber LFTs, which opens up a new design space of specific properties. This provides valuable insight for future research and industrial applications. [Display omitted] • Novel Mori–Tanaka with two inclusions shows appropriate results. • Orientation-dependent modeling is validated with experimental studies. • Fiber orientation determination by μ CT and interpolation methods is validated. • Mixed fibers in LFT lead to positive hybridization effects. [ABSTRACT FROM AUTHOR]

Highlights • Effects of the mechanical properties of end anchorage on the bond behavior are investigated. • An analytical model is derived to predict the bond performance. • A design method of end anchored FRP strengthened concrete structures is proposed. Abstract This study presents a new design method of end anchored (EA) fiber reinforced polymers (FRP) strengthened concrete structures. A previously developed analytical model is modified to predict the performance of EA-strengthened concrete structures under direct pullout loading. The typical performance is composed of five stages, where excessive deformation occurs in the end anchorage during the last two stages. The ultimate loads under different failure modes are obtained, showing that low axial stiffness of the end anchorage results in low increase in the ultimate load and premature debonding failure (before ductility is developed in the end anchorage), whereas high axial stiffness significantly increases the ultimate load and yields brittle failure such as FRP rupture. Effects on the bond performance due to various axial stiffness and strength of the end anchorage are investigated in a sensitivity study. To achieve good ultimate load and ductility, critical strength and axial stiffness of end anchorage is derived. Finally, a design method is proposed for the EA-strengthened concrete structures. [ABSTRACT FROM AUTHOR]

The tensile behavior of non-laminated and laminated CFRP straps composed of up to 100 layers was numerically and analytically investigated. The failure mode in non-laminated straps changed at 20–30 layers from brittle and sudden rupture of the outermost layer to progressive rupture starting from the innermost layer, due to the different non-uniform strain distributions across the layers. Non-laminated straps showed a significantly higher load-bearing efficiency for layer numbers higher than 20 and exhibited lower sensitivity to tape anisotropy and friction at the strap/pin interface than laminated straps. An empirical model was established to estimate the ultimate load of non-laminated straps with up to 100 layers and an analytical model was derived to predict the load-bearing efficiency of laminated straps, taking into account the strap anisotropy and friction at the strap/pin interfaces. [ABSTRACT FROM AUTHOR]

A concept of equivalent inhomogeneity is adopted to facilitate analysis of effective properties of particulate composites with surface-varying interphases. The basic idea is to replace the inhomogeneity and its interphase by a single equivalent inhomogeneity, combining properties of both. It is illustrated considering spherical inhomogeneity with spring layer model of interphases. Due to surface-varying properties of the interphase the resulting equivalent inhomogeneity is anisotropic. Thus, the Method of Conditional Moment – developed for composites with anisotropic constituents – is applied in analysis of the effective properties of the composite. For particular case of homogeneous interphase, the results obtained here are compared with those available in the literature. [ABSTRACT FROM AUTHOR]

Carbon/Carbon composites used in rocket propulsion contain many process-related pores and have a porosity-dependent oxidation recession rate. A 1D analytical model has been developed to describe this behavior and assess the structure-reactivity relationship for the oxidation of such composites. The model has been compared to experiments for validation. Oxidation experiments have been carried out using samples featuring individually different matrix fractions in a thermogravimetric analysis apparatus under dry air. Post-test morphologies were characterized with X-ray micro-computerized tomography and a 3D-image correlation technique. Finally, guidelines are given for the design and optimization of porous C/C composites with respect to oxidation resistance. [Display omitted] • Analytical modeling of the oxidation behavior of a porous 3D C/C composite. • Oxidation of C/C composites creates a double affected zone (fiber, matrix). • Affected lengths and areas determined via μ CT images and 3D-correlation technique. • Identification of ex-PAN fibers and RL PyC matrix oxidation kinetics in dry air. • Parameters optima for effective reactivity and affected depths are neatly different. [ABSTRACT FROM AUTHOR]

A semi-analytical method is used to investigate the dispersion and damping characteristics for rectangular thin orthotropic composite plates in mid frequency analysis. A symplectic eigenproblem is formed whose solution gives analytically the dispersion equation and the wave shape for any combination of simple boundary conditions along the plate edges. The damping capacity of each wave component is obtained using the strain energy theory. In the numerical examples, the dispersion and damping characteristics are calculated and analyzed for orthotropic composite laminated plates with three different combinations of boundary conditions. Comparison of the present results with the Rayleigh-Ritz results and the finite element results validates the effectiveness of the present method. Based on the damping analysis in the wave domain, the thresholds of mid frequency and high frequency vibration characteristics of the composite plate are illustrated. The relationship between the wave components in the present method and the modal modes in the modal method is also explained. [ABSTRACT FROM AUTHOR]

Based on theory of piezo-elasticity, bending behavior of functionally graded carbon nanotube reinforced composite (FG-CNTRC) cylindrical panel attached to thin piezoelectric layers subjected to thermal, mechanical loads and or electric field is investigated. It is assumed that thermo-elastic constants of the structure are independent of temperature gradient. In this paper, uniformly and various cases of functionally graded CNT distribution along the radial direction of host layer are considered. Governing differential equations are solved analytically by using the Fourier series expansion along axial and circumferential direction and state-space technique across the radial direction. Temperature, stress and displacement fields as well as induced electric voltage in sensor layer are obtained and used to study the thermo-piezoelastic behavior of hybrid FG-CNTRC cylindrical panel. Accuracy of present approach is validated by comparing the numerical results with the available reported results in literatures. Parametric studies are carried out to assess the effects of CNT volume fraction, case of CNT distribution along the radial direction, surface thermal/mechanical surface boundary conditions, applied voltage on the bending behavior of FG-CNTRC hybrid cylindrical panel. [ABSTRACT FROM AUTHOR]

This paper presents a nonlinear vibration analysis of the tensioned nanobeams with simple–simple and clamped–clamped boundary conditions. The size dependent Euler–Bernoulli beam model is applied to tensioned nanobeam. Governing differential equation of motion of the system is obtain by using modified couple stress theory and Hamilton's principle. The small size effect can be obtained by a material length scale parameter. The nonlinear equations of motion including stretching of the neutral axis are derived. Damping and forcing effects are considered in the analysis. The closed form approximate solution of nonlinear equations is solved by using the multiple scale method, a perturbation technique. The frequency-response curves of the system are constructed. Moreover, the effect of different system parameters on the vibration of the system are determined and presented numerically and graphically. The size effect is significant for very thin beams whose height is at the nanoscale. The vibration frequency predicted by the modified couple stress theory is larger than that by the classical beam theory. Comparison studies are also performed to verify the present formulation and solutions. [ABSTRACT FROM AUTHOR]

Structural health monitoring (SHM) including the real-time cure monitoring and non-destructive evaluation (NDE) in-service has been highly demanded with respect to smart composite material for the safe working of civil structures. Carbon fiber–reinforced polymer (CFRP) material is extremely strong and light fiber-reinforced polymer which can be used as electrical resistors due to its obvious piezoresistivity. This study presents an experimental investigation into the piezoresistive effect of CFRP tendon prepared by PAN-based carbon fiber and resin matrix modified with different carbon powder contents (i.e. 0%, 2%, 4%, 6%, and 8% by weight). Tests results showed that the mean value of initial electric resistance exhibited a decrease trend with increasing carbon powder content until it becomes stable when the powder content is greater than 6%. Electric resistance rate (dR/R) versus strain (ε) for different CFRP tendon specimens shows similar three stages regardless the carbon powder contents. An approximate liner relationship between dR/R and ε can be observed in the first stage for all tested specimens. Tests results also indicated that the sensitivity ( K ) increased with the increasing carbon fiber content at the beginning and followed by a decrease. The change law of K and its mechanism were evaluated and discussed from the microscopic point of view. Based on the analysis and low-energy theory, a coupled mechanical and electrical model combined resistivity scalar field response and structural strain vector field was established. The model provided herein was thereafter assessed and verified by comparing with existing tensile testing results. The consistence of the growth trend between the model and test results indicates the feasibility and reliability of the coupled model. [ABSTRACT FROM AUTHOR]

In this paper, distributions of stress and displacement components of rotating truncated conical shells with varying thickness made of functionally graded materials (FGMs) subjected to thermo-mechanical loading are obtained. The materials are assumed to be perfectly elastic and isotropic which are assumed to vary according to the power law function in the axial direction of the conical shell. Based on steady-state heat conduction equation, the higher-order shear deformation theory (HSDT) is used to describe the nature of thermo-elastic behavior of the truncated conical shells. The system of partial differential equations is semi-analytically solved by using multi-layer method (MLM). Numerical results are presented to verify the accuracy of present theory and the influences played by many parameters are investigated. [ABSTRACT FROM AUTHOR]

Nonlocal formulations are currently adopted to assess size effects in nanostructures. The Eringen differential constitutive model, due to its simplicity, is widely used to investigate the size-dependent behavior of beams at nanoscale. Nevertheless this theory provides vanishing size effects in nanobeams under point loads and exhibits stiffening phenomena in nanocantilevers for increasing values of the nonlocal factor. Accordingly, the analysis of structures like nanoactuators is commonly carried out by using more complex constitutive approaches, such as gradient or integral models. A new strategy is outlined in the present paper as a possibly convenient alternative, by equipping the Eringen differential law with an additional term involving the derivative of the axial stress. Effectiveness of the new methodology is tested with reference to simple case studies. [ABSTRACT FROM AUTHOR]

A new hyperbolic shear and normal deformation plate theory, presented in this paper, is used to study the static, free vibration and buckling analysis of the simply supported functionally graded sandwich plates on elastic foundation. This theory accounts for the realistic variations of the displacements through the thickness. In the analysis, two common types of FGM sandwich plates, namely, homogeneous face sheets with FGM core and FGM face sheets with homogeneous core are considered. The elastic foundation is described by the Pasternak model. The equations of motion are derived from Hamilton's principle. The closed form solutions are obtained by using Navier technique. Numerical results of present theory are compared with three-dimensional elasticity solutions and other higher-order theories reported in the literature. It can be concluded that the proposed theory is simple and efficient in predicting the mechanical behavior of functionally graded sandwich plates. [ABSTRACT FROM AUTHOR]

This work shows that solid–solid interfaces in a non-porous stiff material can enhance the sound absorption and provides an analytical model for describing the effects of constituents and interfaces on the sound absorption. The sound absorption coefficient α , the propagation constant Γ and the reflectivity R were determined for cement-based materials. At 125–500 Hz, α ranges from 0.039 to 0.160; Γ ranges from 2.6 × 10 −4 /mm to 3.5 × 10 −4 /mm; R > 0.9. Silica fume (∼0.1 μm) provides interfaces, thereby enhancing α and Γ by 40% and 20% respectively for cement paste (125 Hz), but it does not affect R . [ABSTRACT FROM AUTHOR]

In this work we demonstrate that the specific (weight-normalized) mechanical properties of polylactic acid (PLA) can be enhanced by leveraging a combination of (a) additive manufacturing (3D printing) and (b) initial post-tensioning of continuous natural-fiber reinforcement. In this study both tensile and flexural PLA specimens with different cross-sectional geometries were 3D-printed with and without post-tensioning ducts. The mechanical properties of two continuous reinforcing fiber strands (i.e., jute, flax) were experimentally characterized prior to threading, post-tensioning to a prescribed level of stress, and securing in place with 3D-printed anchors. The effect of fiber type, matrix cross-sectional geometry, number of reinforcing strands, and degree of post-tensioning on the specific mechanical properties (i.e., strength-, stiffness-, rigidity-to-weight) of PLA were investigated using both tensile and flexural mechanical testing. Experimental results confirmed that additive manufacturing alone can improve the specific tensile and flexural mechanical properties of PLA and that these properties are further improved via initial mechanical prestressing of natural fiber reinforcement. Data indicate increases of 116% and 62% for tensile specific strength and stiffness and 14% and 10% for flexural specific strength and rigidity, respectively, compared to solid, unreinforced PLA. A theoretical model of the prestressed composite tensile response was employed and found to accurately predict (<10% error) improvements in mechanical behavior. [ABSTRACT FROM AUTHOR]

In this study, flexural behavior of nonwoven fabric reinforced sandwich composites from jute and polypropylene (PP) fibers was investigated. Jute/PP composite plates reinforced with jute/PP commingled nonwoven fabrics of different jute/PP fractions were used as facing materials in sandwich production. Balsa wood, polyester (PET) foam and PP honeycomb were used as core materials. Jute/PP nonwoven fabrics were treated with NaOH solution prior to sandwich production in an attempt to improve the fiber–matrix adhesion and the quality of facing-core bonding. The flexural behavior of the sandwiches was investigated experimentally as well as using Euler–Bernoulli and Timoshenko beam theories. The flexural properties of the sandwiches improved as the jute fiber content increases. Euler–Bernoulli model yielded smaller deflection values when compared to experimental results whereas Timoshenko model provided a good estimation of sandwich flexural properties. The effectiveness of fiber/matrix adhesion and facing/core bonding was determined by conducting scanning electron microscopy (SEM) analysis. [ABSTRACT FROM AUTHOR]

Composite lattice core sandwich structure is a novel type of effective load bearing structure. In this paper, one kind of bolted splice joint between two CFRP lattice core sandwich panels is proposed. The mechanical behavior of this joint structure is investigated through four-point bending. The main deformation pattern and failure mode of the lattice core sandwich bolted splice joint structure are demonstrated by both experimental test and FE simulation. The failure mode includes the successive events, namely yield of the lower metal plate and then debonding between the lattice core and sheets. A simplified theoretical model is also proposed for this joint which is capable of calculating the load–displacement curve before yield of the lower metal plate. By monitoring the stress in the lower metal plate not to exceed the yield strength, the present model can give a simple engineering design for this kind of joint structure. [ABSTRACT FROM AUTHOR]

The major goal of this research was to obtain a closed form of the solution for critical combined loads (combined effects of the axial load and l lateral pressure or the axial load and hydrostatic pressure) of functionally graded (FG) truncated conical shell in the framework of the shear deformation theory (SDT). The basic equations of FG truncated conical shell shells subjected to the combined loads are derived in the framework of the SDT. By using the Galerkin method to basic equations are obtained the expressions for critical combined loads of FG truncated conical shell in the framework of the SDT. In particular, similar expressions in the framework of the classical shell theory (CST) are obtained, also. Our numerical experiments reveal that the proposed solution may offer accurate critical combined loads for the FGM shells as compared with reference solutions available in the literature. Finally, the calculation and presentation of the effects of many parameters included in the analysis conclude the goals to be reached in the study. [ABSTRACT FROM AUTHOR]

Hybrid bio-composites are environmentally friendly and can provide a sustainable alternative to existing engineering materials in several applications. While these hybrid composites have relatively low modulus, their material consistency lend them to be used in many structural applications. Many low modulus natural fibers exhibit nonlinear axial stress strain relations. Orthotropic material nonlinearity is typically analyzed for composites in the transverse and shear directions, and very few computational models consider axial nonlinearity. In this manuscript two new macro and one micromechanical constitutive models are developed to characterize the nonlinear orthotropic behavior of these material systems in the axial, transverse and shear directions. These models are then implemented within finite element (FE) code. A hybrid bio-composite in the form of pultruded layers manufactured with jute bio-fibers, combined with unidirectional roving E-glass, and embedded in a polymeric matrix was chosen for this study. Stress strain curves are generated for these dually reinforced systems in transverse, axial and shear modes to calibrate the nonlinear parameters for computational models. Photomicroscopy was also used to characterize the microsctructure to calibrate the micromechanical constitutive model. All three models are then validated under a multi-axial state of stress by full-field stress/strain analysis via Digital Image Correlation (DIC) and Thermoelastic Stress Analysis (TSA) of open-hole specimens. The results show that all of the models match the full-field TSA and DIC results under a multi-axial state of stress; however, the Anisotropic Potential Theory (APT) model based on the work of Hahn Tsai showed more response at stress concentrations than the Anisotropic Deformation Theory (ADT) model based on the work of Hashin. Differences may have resulted from the correction scheme implemented in the APT model. Also the Nine-Cell micromechanical model in this study based on the work of Haj-Ali et al. was developed for comparison with the APT and ADT macromodels. The macromodels and micromodel presented here were implemented in ABAQUS user material subroutines, and are beneficial for analysis and design of structures with soft fiber constituents that have a nonlinear axial response. [ABSTRACT FROM AUTHOR]

Timoshenko nanobeams are investigated by using a nonlocal Eringen-like constitutive law described by two material length-scale parameters. A nonlocal variational treatment, based on a new definition of the Helmholtz free energy is proposed. The ensuing system of ordinary differential equations of nonlocal elastic equilibrium is consistently obtained with the corresponding boundary conditions. New closed form solutions of nonlocal Timoshenko nanobeams are established and comparisons with gradient and local formulations are performed. Finally, two examples are illustrated to assess nonlocality effects. [ABSTRACT FROM AUTHOR]

This paper investigates the nonlinear bending in thermal environments and thermal postbuckling of hybrid laminated beams with piezoelectric fiber reinforced composite (PFRC) actuators resting on an elastic foundation. The beam is made of fiber-reinforced composites (FRCs) with the reinforcement being distributed either uniformly (UD) or functionally graded (FG) of piece-wise type along the thickness of the beam. The formulations are based on a higher order shear deformation theory and von Kármán strain displacement relationships. The beam–foundation interaction and thermo-piezoelectric effects are also included, and the material properties of both FRCs and PFRCs are estimated through a micromechanical model and are assumed to be temperature dependent. The nonlinear bending load-deflection curves and the thermal postbuckling equilibrium paths of hybrid laminated beams are determined by means of a two-step perturbation approach. The effects of the material property gradient, temperature variation, applied voltage, stacking sequence as well as the foundation stiffness on the nonlinear bending and thermal postbuckling behaviors of the hybrid laminated beams are investigated through a comprehensive parametric study. [ABSTRACT FROM AUTHOR]

Buckling behaviors of shear deformable grid-stiffened functionally graded cylindrical shells are investigated under the combined compressive and thermal loads. The governing equations are established on the basis of Reddy's higher-order shear deformation theory. For the perfect grid-stiffened cylindrical shells, separation of variables is employed to obtain the accurate buckling solutions. Then, according to the derived mode functions, Galerkin's solving procedure is conducted for shells including the initial geometric imperfection. The effects of geometric parameters, properties of FGMs and temperature fields on the anti-buckling performances of grid-stiffened shells are concerned under the clamped boundary condition. Besides, imperfection sensitivities for various reinforced grids are discussed in detail. [ABSTRACT FROM AUTHOR]

FRP reinforcement is well known as a possible alternative to steel bars in order to improve durability of reinforced concrete members. However, the intrinsic brittleness of concrete and FRP materials may induce problems at the ultimate conditions due to premature failure modes; the performance under service loads is a critical issue as well. To investigate response of concrete members reinforced with longitudinal glass or carbon FRP bars without shear reinforcement, an experimental program has been developed. The sixteen specimens designed and cast within this project were characterized by different study variables concerning cross section geometry, concrete grade and type of reinforcement. The results of tests performed on FRP-reinforced specimens are presented in this paper. In particular, different failure modes due to flexure and shear have been observed; response under load levels simulating service conditions has been also examined. Results of FRP-reinforced specimens have been compared with those given by control specimens provided with conventional steel bars. Finally, analytical procedures to evaluate immediate deflections of FRP-reinforced members have been assessed. [ABSTRACT FROM AUTHOR]

This paper presents a static analysis of functionally graded (FG) single and sandwich plates using Carrera Unified Formulation with five new displacement fields of the non-polynomial form. In particular, trigonometric, exponential and hyperbolic displacement fields are employed. The simply supported FG single and sandwich plates are subjected to a bi-sinusoidal load. The governing equations for the static bending analysis are obtained employing the Principal of Virtual Displacement (PVD) under CUF and solved using Navier type solutions. The results show that non-polynomial thickness functions are accurate although, in a few cases, the influence of some non-polynomial terms may be detrimental. [ABSTRACT FROM AUTHOR]

In this paper, the small-scale effects on the nonlinear dynamic mechanical and electromechanical behaviors of the carbon nanotubes and their applications as nano-resonators and electronic nano-filters are analyzed using the consistent couple stress theory. The dynamic formulations of the single-walled carbon nanotubes are developed using the Euler-Bernoulli beam model obtained by the consistent couple stress theory. The hypothesis considered for the applied theory is based on the recently developed technique to resolve the problem of indeterminacy in previous couple stress based-formulations. The results prove that this theory can be applied in analyzing the dynamic characteristics of the nanostructures in general and carbon nanotubes in particular and their possible applications in nano-electromechanical systems. According to the reported results, the developed formula can capture the small-scale effects increasing the stiffness, vibration frequency and dynamic pull-in voltages of the carbon nanotubes under electrostatic actuation. [ABSTRACT FROM AUTHOR]

Thermoelastic analysis of composite cylindrical panel reinforced by single walled carbon nanotube (SWCNT) with simply supported edges by using three-dimensional theory of elasticity. Thermoelastic constant of carbon nanotube (CNT) as well as polymer matrix are assumed to be temperature independent. The volume fractions of oriented, straight SWCNTs are assumed to be uniformly distributed (UD) and or graded in the thickness direction according to four kinds of CNT distributions. The effective material properties of the nanocomposite cylindrical panel are based on rule of mixture. At first temperature distribution in three dimensions is obtained by solving heat conduction differential equation with variable coefficient. By applying Fourier series expansion to the stress and displacement fields along the axial and circumferential direction and state space technique along the radial direction thermoelastic analysis is carried out. Moreover, effects of volume fraction of carbon nanotube, uniform distribution and functionally graded distribution of CNT, mid radius to thickness ratio, length to mid radius ratio, thermal and mechanical surface boundary conditions on bending behavior of FG-CNTRC cylindrical panel are also examined. [ABSTRACT FROM AUTHOR]

In this paper, the debonding of adhesive double-lap joints between FRP adherents is analyzed with regard to the influence of an initial adhesion defect on their ultimate capacity. The analysis is carried out by using the interface cohesive models proposed by Hutchinson & Suo, Xu & Needleman, and Camacho & Ortiz. The mechanical model utilized takes into account the shear deformability of the adherents and the coupling effects between axial and shear/flexure behavior. The model is non-linear due to the hypothesis of a cohesive interface adopted for the adhesive layer. The numerical results, obtained via finite element analysis, have highlighted that the model of Hutchinson and Suo is less conservative than the other two and that joints subjected to axial forces are less sensitive to initial adhesion defects than ones loaded by both axial and shear forces. [ABSTRACT FROM AUTHOR]

The analytical approach is presented to investigate non-linear buckling analysis and post-buckling behavior of FGM toroidal shell segments filled inside by an elastic medium under external pressure loads including temperature effects. The governing equations of non-linear buckling of FGM toroidal shell segments are derived based on the classical thin shell theory with the geometrical nonlinearity in von Karman–Donnell sense, Stein and McElman assumption and elastic medium modeled by Pasternak's two-parameter elastic foundation. The static critical buckling loads and the post-buckling pressure–deflection curves in two cases: movable and immovable boundary conditions including temperature effects are obtained by using the Galerkin's method. In the paper, the results are also compared with the solutions published in the literature for the specific cases. Effects of geometrical and material parameters, elastic foundation and temperature on the nonlinear buckling behavior of shells are shown in obtained results. [ABSTRACT FROM AUTHOR]

To evaluate the risk of complex structures such as a 2.5D/SiC composites turbine blade, Response Surface Methodology is applied to investigate the reliability due to its high efficiency. In this paper, the Response Surface is based on Support Vector Machines (SVM), and new sample strategies are proposed to assess the failure domain and probability as well as reliability index with less computational cost and higher accuracy. 2.5D/SiC composites are defined by 5 geometric parameters to represent their architecture. Using the finite element method, we establish the structure of 2.5D/SiC composites and predict the mechanical properties with double scale models. The stochastic behaviors of load, material strength and microstructure of 2.5D/SiC composites are considered to analyze the reliability of a turbine blade in an aircraft engine. The methodology in this paper provides an accurate and effective way to value the risk of turbine blade design. [ABSTRACT FROM AUTHOR]

This paper concerns the shear behavior of reinforced concrete beams externally strengthened with composite materials. The study gathers numerous experiments on concrete beams, strengthened in shear with FRPs, from the international literature and develops an experimental database. The database is utilized to assess the predictive accuracy of significant existing design recommendations, with respect to the vertical load capacity of the tested beams. The crucial parameters for predicting the shear capacity of FRP strengthened beams are identified. Some of these parameters are disregarded in the reported results of several experimental programs or are difficult to measure. The research utilizes the available full load-deformation curves for numerous tests as well as the predictive accuracy and easy to apply modified compression field theory (MCFT). Reverse MCFT analysis of beams may provide significant information concerning the angle of main shear crack, the average crack width of concrete and the average effective deformation of the FRP and of internal steel, given the failure load. Thus, a hybrid approach is followed to enrich the experimental database with analytically derived significant parameters towards an advanced database. The hybrid experimental–analytical database is further elaborated and recent studies on shear behavior of concrete members are taken into account. The study explores the influence of different crucial parameters and proposes suitable modifications of existing design equations towards remarkably improved shear force resistance predictions. [ABSTRACT FROM AUTHOR]

The dynamic behavior of gradient cellular solids subjected to high velocity impact is investigated, with shock theory and rigid-perfectly-plastic-locking idealization. The impact is induced by the fragments of a cased charge explosion in near field, sufficiently high to progressively crush the cellular solids from the loading part, regardless of the density variation of the cellular solids. The dynamic response and energy absorption are examined for different gradient cellular solid layers with the same mass and thickness, but different density variation. The cellular solids with larger density gradient lead to smaller crushed distance and higher energy absorption compared to those with smaller density gradients, when subjected to the same impact, provided that the cellular solid is not fully densified. However, when the cellular layer is fully crushed, the effect of density variation on energy absorption vanishes. [ABSTRACT FROM AUTHOR]

In the present paper free vibrations of embedded single-walled carbon nanotubes based on local Euler–Bernoulli beam theory are investigated. The surrounding elastic medium is described as the Winkler and Pasternak models, defined by the k w and k p coefficients. The Hamilton principle is applied to derive the governing equations and boundary conditions, which are solved by using the well-known Differential Quadrature Method (DQM). The influence of the elastic medium coefficients, nonlocal parameter and end supports on the free vibrations characteristics of the single-walled carbon nanotube (SWCNT) is described. Numerical examples are performed to show the accuracy of the proposed method. [ABSTRACT FROM AUTHOR]

The closed-form solution of a generalized hybrid type quasi-3D higher order shear deformation theory (HSDT) for the bending analysis of functionally graded shells is presented. From the generalized quasi-3D HSDT (which involves the shear strain functions “ f ( ζ )” and “ g ( ζ )” and therefore their parameters to be selected “ m ” and “ n ”, respectively), infinite six unknowns' hybrid shear deformation theories with thickness stretching effect included, can be derived and solved in a closed-from. The generalized governing equations are also “ m ” and “ n ” parameter dependent. Navier-type closed-form solution is obtained for functionally graded shells subjected to transverse load for simply supported boundary conditions. Numerical results of new optimized hybrid type quasi-3D HSDTs are compared with the first order shear deformation theory (FSDT), and other quasi-3D HSDTs. The key conclusions that emerge from the present numerical results suggest that: (a) all non-polynomial HSDTs should be optimized in order to improve the accuracy of those theories; (b) the optimization procedure in all the cases is, in general, beneficial in terms of accuracy of the non-polynomial hybrid type quasi-3D HSDT; (c) it is possible to gain accuracy by keeping the unknowns constant; (d) there is not unique quasi-3D HSDT which performs well in any particular example problems, i.e. there exists a problem dependency matter. [ABSTRACT FROM AUTHOR]

In this study, two dimensional (2D) and quasi three-dimensional (quasi-3D) shear deformation theories are presented for static and free vibration analysis of single-layer functionally graded (FG) plates using a new hyperbolic shape function. The material of the plate is inhomogeneous and the material properties assumed to vary continuously in the thickness direction by three different distributions; power-law, exponential and Mori–Tanaka model, in terms of the volume fractions of the constituents. The fundamental governing equations which take into account the effects of both transverse shear and normal stresses are derived through the Hamilton's principle. The closed form solutions are obtained by using Navier technique and then fundamental frequencies are found by solving the results of eigenvalue problems. In-plane stress components have been obtained by the constitutive equations of composite plates. The transverse stress components have been obtained by integrating the three-dimensional stress equilibrium equations in the thickness direction of the plate. The accuracy of the present method is demonstrated by comparisons with the different 2D, 3D and quasi-3D solutions available in the literature. [ABSTRACT FROM AUTHOR]

A new analytical model is presented to predict indentation behavior of the sandwich circular panel with gradient foam cores under a flat-end cylindrical indenter. In the model, a displacement field of the upper face sheet of the sandwich panel is assumed to be a cosine function and plateau stress of the gradient foam core varies with the mass density along the thickness direction of the sandwich panel. The sandwich panel is modeled as an infinite, isotropic, plastic membrane on a rigid-plastic foundation. The explicit solutions of the relation between the indentation force and maximum plastic regions of the upper face sheet are derived based on the principle of minimum work. The analytical results are validated using the finite element code ABAQUS ® . The influences of the gradient foam core on the maximum plastic region, the indentation force and the plastic strain energy of the sandwich panel are also investigated. [ABSTRACT FROM AUTHOR]

Axial buckling behavior of single-layered membranes from vertically aligned single-walled carbon nanotubes is studied in the context of the nonlocal continuum theory of Eringen. To this end, useful discrete models based on the nonlocal Rayleigh, Timoshenko, and higher-order beam theories are developed to evaluate critical buckling loads associated with both in-plane and out-of-plane buckling modes. In discrete models, the size of the eigenvalue equations to be solved drastically magnifies for highly populated membranes. Thereby, development of models whose computational efforts do not affected by the population of the membrane is of great advantageous. To bridge this scientific gap, appropriate nonlocal continuous models are established based on the developed discrete models. The accuracy of the proposed discrete and continuous models is checked and remarkable results are achieved. Subsequently, the roles of the influential factors on both in-plane and out-of-plane axial buckling loads are addressed. The obtained results can be regarded as a basic step in examining of axial buckling mechanisms of more complex systems consist of multi-layered membranes from parallel or even orthogonal single-walled carbon nanotubes. [ABSTRACT FROM AUTHOR]

The objective of this study was to evaluate three potential core alternatives for glass fiber reinforced polymer (GFRP) foam-core sandwich panels. The proposed system could reduce the initial production costs and the manufacturing difficulties while improving the system performance. Three different polyurethane foam configurations were considered for the inner core, and the most suitable system was recommended for further prototyping. These configurations consisted of high-density polyurethane foam (Type 1), a bidirectional gridwork of thin, interconnecting, GFRP webs that is in-filled with low-density polyurethane foam (Type 2), and trapezoidal-shaped, low-density polyurethane foam utilizing GFRP web layers (Type 3). The facings of the three cores consisted of three plies of bidirectional E-glass woven fabric within a compatible polyurethane resin. Several types of small-scale experimental investigations were conducted. The results from this study indicated that the Types 1 and 2 cores were very weak and flexible making their implementation in bridge deck panels less practical. The Type 3 core possessed a higher strength and stiffness than the other two types. Therefore, this type is recommended for the proposed sandwich system to serve as a candidate for further development. Additionally, a finite element model (FEM) was developed using software package ABAQUS for the Type 3 system to further investigate its structural behavior. This model was successfully compared to experimental data indicating its suitability for parametric analysis of panels and their design. [ABSTRACT FROM AUTHOR]

A model to predict time-dependent evolution of simultaneous transverse cracking developed in multiple plies during creep loading and its effects on creep of multidirectional polymer matrix composite laminates is presented. The stress states in the intact regions of the plies are determined using the lamination theory during an incremental change in time. The stored elastic energy, determined using this stress state, is compared with a critical stored elastic energy value for damage to determine if a ply would fracture after the increment. If fracture is predicted, variational analysis is used to determine the perturbation in ply stresses due to cracking. This procedure is repeated to determine the crack evolution and creep strain. Model predictions compared well with experimental results for a [± θ m /90 n ] s laminate. [ABSTRACT FROM AUTHOR]

This paper deals with the investigation of the effect of hygrothermal conditions on the bending of nanoplates using Levy type solution model employing the state-space concept. The nanoplates are assumed to be subjected to a hygrothermal environment. The two-unknown function plate theory is used to derive the governing differential equations on the basis of Eringen's nonlocal elasticity theory. The governing equations contain the small scale effect as well as hygrothermal and mechanical effects. These equations are converted into a set of first-order linear ordinary differential equations with constant coefficients. Analytical solution of bending response for nanoplates under combinations of simply supported, clamped and free boundary conditions is obtained. Comparison of the results with those being in the open literature is made. The influences played by small scale parameter, temperature rise, the degree of moisture concentration, boundary conditions, plate aspect ratio and side-to-thickness ratio are studied. [ABSTRACT FROM AUTHOR]

In the present study, the Gurtin-Murdoch elasticity theory, as a theory capable of capturing size effects, is implemented to predict the nonlinear buckling and postbuckling response of cylindrical nanoshells under combined axial and radial compressive loads in the presence of surface stress effects. For this purpose, a size-dependent shell mode containing geometric nonlinearity is proposed within the framework of the classical shell theory. Because it is necessary to satisfy balance conditions on the surfaces of nanoshell, it is assumed that the normal stress component of the bulk varies linearly through the shell thickness. On the basis of a variational formulation using the principle of virtual work, the non-classical governing differential equations are derived. Subsequently, a boundary layer theory is employed including the nonlinear prebuckling deformations and the large deflections in the postbuckling regime. Then a two-stepped perturbation methodology is utilized to obtain the size-dependent critical buckling loads and the postbuckling equilibrium paths of nanoshells corresponding to the axial dominated and radial dominated loading cases. It is revealed that in the radial dominated loading case, a positive value of surface elastic constants leads to increase the critical buckling load but decrease the critical end-shortening of nanoshell. However, in the axial dominated loading case, surface elastic constants with positive sign causes to increase the both critical buckling load and critical end-shortening of nanoshell. [ABSTRACT FROM AUTHOR]

In this paper, we develop a novel size-dependent plate model for the axisymmetric bending, buckling and free vibration analysis of functionally graded circular/annular microplates based on the strain gradient elasticity theory. The displacement field is chosen by using a refined third-order shear deformation theory which assumes that the in-plane and transverse displacements are partitioned into bending and shear components and satisfies the zero traction boundary conditions on the top and bottom surfaces of the microplate. Besides, the present model contains three material length scale parameters to capture the size effect. The material properties of the microplate are assumed to vary in the thickness direction and estimated through the classical rule of mixture. By using Hamilton's principle, the equations of motion and boundary conditions are obtained. Afterward, the differential quadrature method is adopted to discretise the governing differential equations along with various types of edge supports and therefore the deflection, critical buckling load and natural frequency can be determined. Convergence and comparison studies are carried out to establish the reliability and accuracy of the numerical results. Finally, a parametric study is conducted to investigate the influences of material length scale parameters, gradient index, thickness-to-outer radius ratio, outer-to-inner radius ratio and boundary conditions on the mechanical characteristics of the microplate. [ABSTRACT FROM AUTHOR]

The torsional design provisions of the Canadian standard S806 for fiber reinforced polymer (FRP) reinforced (RC) or prestressted (PC) concrete members are presented and their theoretical and empirical justifications are provided. The key parameters governing the nominal torsional strength are identified and their appropriate values for FRP-RC/PC members are specified. The accuracy of the method is evaluated by analyzing 27 FRP-RC/PC members tested under pure torsion by other investigators. The CSA method is able to reasonably predict the torsional strength of these beams. It is also shown that the cracking torque can be predicted using the formulas in the ACI and AASHTO LRFD codes without any modification. Some considerations with the statements of CNR-DT 203, fib 40, JSCE guidelines are also carried out. [ABSTRACT FROM AUTHOR]

The discussion about nonuniform stress distribution around interference-fit joint is particular significance in the design of composite laminates structures. In order to investigate the stress distribution of interference-fit area around composite laminates joint, an analytical model is developed for stress distribution based on the Lekhnitskii's complex potential theory. The normal and tangential stresses of contact are achieved by the relationship of deformation between pin and hole. The effects of ply orientation and interference percentage on stress components distributions of each individual layer around symmetrical laminates joint are discussed. In order to verify the validity of the analytical model, extensive 3D finite element models are established to simulate the stress components of laminates interference-fit joint. The results show that the analytical model is valid, and the laminate property and ply orientation have a significant effect on stress distribution trend while interference percentage mainly affects stress magnitude. [ABSTRACT FROM AUTHOR]

Based on nonlocal theory, this article discusses vibration of CDVGS 1 1 Coupled double viscoelastic graphene sheets. systems. The properties of each single layer graphene sheet (SLGS) are assumed to be orthotropic and viscoelastic. The two SLGSs are simply supported and coupled by an enclosing viscoelastic medium which is simulated as a Visco-Pasternak layer. This model is aimed at representing dynamic interactions in nanocomposite materials with dissipation effect. By considering the Kirchhoff plate theory and Kelvin–Voigt model, the governing equation is derived using Hamilton's principle. The equation is solved analytically to obtain the complex natural frequency. The parametric study is thoroughly performed, concentrating on the series effects of viscoelastic damping structure, aspect ratio, visco-Pasternak medium, and mode number. In this system, in-phase (IPV) and out-of-phase (OPV) vibrations are investigated. The numerical results of this article show a perfect correspondence with those of the previous researches. [ABSTRACT FROM AUTHOR]

A method of solution that extends to the case of curved laminated structures the traditional approach developed by Newmark et al. for straight beams is presented. The method is specialized to curved laminated glass, a composite formed by two external glass layers that sandwich a very thin polymeric interlayer. The effect of curvature on the shear coupling of glass plies through the interlayer is examined in the paradigmatic example of a laminated beam with constant moderate curvature under radial loading with different boundary conditions, varying the initial camber, the end constraints and the elastic properties of the polymer. Comparisons with numerical experiments confirm the accuracy of the proposed modeling. In general the response of a curved structure is greatly influenced by the axial force it undergoes, and such internal action is mainly governed, for fixed applied loads, by the boundary conditions at the extremities. The axial force produces the arch-response of the structure, which is not substantially affected by the shear coupling of glass through the interlayer. On the other hand, such coupling has major effects on the bending properties. [ABSTRACT FROM AUTHOR]

The paper presents a theoretical prediction of the structural behavior of reinforced concrete (RC) beams externally strengthened to flexure by using a unidirectional ultra-high tensile strength steel (UHTSS) reinforcing mesh embedded in an inorganic matrix (Steel Reinforced Grout, SRG) or in an organic matrix (Steel Reinforced Polymer, SRP). For these innovative composite materials are not yet available in literature specific standard documents, guidelines or analytical models capable to predict the structural behavior of the strengthened elements. Therefore, in order to evaluate the flexural strength of the strengthened beams some analytical models to predict the maximum axial strain developed in Fiber Reinforced Polymer (FRP) systems at the onset of intermediate debonding failure, have been used. The goal is to assess the effectiveness of current analytical models used, up to day, to FRP strengthening systems to the SRG and SRP strengthening systems. For this aim, a database of experimental results on RC beams strengthened in bending by bonded SRG and SRP systems has been collected. The comparisons between the theoretical predictions and the experimental data, in terms of debonding strain values, load carrying capacity, load-midspan deflection curves, have highlighted the reliability and adaptability of the current analytical models. Finally, in order to evaluate the effectiveness of the SRG and SRP systems for strengthening RC beams a parametric study was also carried out. [ABSTRACT FROM AUTHOR]

Background/Purpose Numerous bridges of the Italian arterial road network were designed for live loads significantly lower than those produced by the current vehicular traffic. Many of them are masonry arch bridges whose load carrying capacity should be assessed for defining the necessary strengthening interventions. In the present paper the design criteria for strengthening masonry bridges with carbon fiber reinforced cementitious matrix (C-FRCM) materials are presented with reference to a masonry arch road bridge built right after the second world war. Methods The structure is analyzed both in its original and in its strengthened configuration following the approach of the collapse mechanisms. The considered approach allows to capture the strengthening effect of the C-FRCM material in terms of modification of the collapse mechanism and increase of the load collapse multiplier. Two different configurations of C-FRCM strengthening material applied at the extrados have been considered. In the first configuration the ends of the C-FRCM material are anchored at the vaults imposts, while in the second configuration they are not anchored at the imposts. Results To obtain load collapse multipliers greater than one three layers of C-FRCM strengthening material have to be applied at the extrados of all the three vaults in the case of end anchored strengthened material, while in the case of unanchored strengthening material four layers of C-FRCM strengthening material have to be applied at the extrados of all the three vaults. Conclusion The performed analyses show a lack of load carrying capacity of about 60% with respect to the load carrying capacity required by current codes. This lack can be filled up adopting the considered strengthening technique. [ABSTRACT FROM AUTHOR]

Background/purpose This paper deals with analysis of biaxial buckling behavior of double-orthotropic microplate system including in-plane magnetic field, using strain gradient theory. Methods Two Kirchhoff microplates are coupled by an internal elastic medium and also are limited to the external Pasternak elastic foundation. Utilizing the principle of total potential energy, the equilibrium equations of motion for three cases (out-of-phase buckling, in-phase buckling and buckling with a plate) are acquired. In this study, we assumed boundary conditions of all the edges are simply supported. In order to get exact solution for buckling load of system, Navier approach which satisfies the simply supported boundary conditions is applied. Results Variations of the buckling load of double-microplate system subjected to biaxial compression corresponding to various values of the thickness, length scale parameter, magnetic field, stiffness of internal and external elastic medium, aspect ratio, shear stiffness of the Pasternak foundation and biaxial compression ratio are investigated. Furthermore, influence of higher modes on buckling load is shown. By comparing the numerical results, it is found that dimensionless buckling load ratio for in-phase mode is more than those of out of phase and one microplate fixed. Also it is shown that the value of buckling load ratio reduces, when non-dimensional length scale parameter increases. Conclusion However, we found when properties of plate are orthotropic the buckling load ratio is more than isotropic state. Also, by considering the effect of magnetic field, non-dimensional buckling load ratio reduces. [ABSTRACT FROM AUTHOR]

In this paper, the predictions of elastic constants of 2.5D (three-dimension angle-interlock woven) continue carbon fiber reinforced silicon carbide (C/SiC) composites are studied by means of theoretical model and numerical simulation. A semi-analytical method expressing elastic constants in terms of microstructure geometrical parameters and constitute properties has been proposed. First, both the geometrical model of the 2.5D composite and the representative volume element (RVE) in both micro- and meso-scale are proposed. Second, the effective elastic properties of the RVE in 2.5D C/SiC composites are obtained using finite element method (FEM) simulation based on energy equivalent principle. Finally, the remedied spatial stiffness average ( RSSA ) method is proposed to obtain more accurate elastic constants using nine correction factor functions determined by FEM simulations, also the effects of geometrical variables on mechanical properties in 2.5D C/SiC composites are analyzed. These results will play an important role in designing advanced C/SiC composites. [ABSTRACT FROM AUTHOR]

This paper presents an efficient method for predicting the free and transient vibrations of multilayered composite structures with parallelepiped shapes including beams, plates and solids. The exact three-dimensional elasticity theory combined with a multilevel partitioning hierarchy, viz., multilayered parallelepiped, individual layer and layer segment, is employed in the analysis. The continuity constraints on common interfaces of adjacent layer segments are imposed by a modified variational principle, and the displacement components of each layer segment are assumed in the form of orthogonal polynomials and/or trigonometric functions. Numerical studies are given for free vibrations of composite laminated and sandwich beams, plates, and solids. Some in-plane shear vibration modes missed in previous elasticity solutions for multilayered plates are examined. The natural frequencies derived from Reddy’s high-order shear deformation theory and layerwise theory for soft-core sandwich plates show significant deviation from elasticity solutions. Transient displacement and stress responses for angle-ply laminated and sandwich plates under four types of impulsive loads (including rectangular, triangular, half-sine and exponential pulses) are obtained by the Newmark integration procedure. The present solutions may serve as benchmark data for assessing the accuracy of advanced structural theories and new developments in numerical methods. [ABSTRACT FROM AUTHOR]