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Abstract: This paper considers the electro-mechanical interaction between a fiber and a matrix material in a 1–3 piezocomposite due to an axial load and electric charge applied to the fiber. The fiber–matrix interface is assumed to be mechanically imperfect and is represented by a spring-factor model. The interface is either electrically open- or short-circuited. The analytical general solutions corresponding to an infinite piezoelectric fiber with a vertical body force and an electric body charge are derived by using Fourier integral transforms. These solutions together with the analytical general solutions for a transversely isotropic elastic medium are used to formulate the fiber–matrix interaction problem. Selected numerical results for the fiber axial force and vertical electric field, and interfacial stresses are presented for representative 1–3 piezocomposites. The influence of the interface stiffness on the electro-mechanical load diffusion is also examined. [Copyright &y& Elsevier]

Abstract: An analytical model for determining the strain energy release rate due to a prescribed crack in an adhesively-bonded, single-lap composite joint with thick bondlines and subjected to axial tension is presented. An existing analytical model for determining the adhesive stresses within the joint is used as the foundation for the strain energy release rate calculation. In the stress model, the governing equations of displacements within the adherends are formulated using the first-order laminated plate theory. In order to simulate the thick bondlines, the field equations of the adhesive are formulated using the linear elastic theory to allow non-uniform stress distributions through the thickness. Based on the adhesive stress distributions, the equivalent crack tip forces are obtained and the strain energy release rate due to the crack extension is determined by using the virtual crack closure technique (VCCT). The specimen geometry of ASTM D3165 standard test is followed in the derivation. The system of second-order differential equations is solved to provide the adherend and adhesive stresses using the symbolic computational tool, Maple 7. Finite element analyses using J-integral as well as VCCT are performed to verify the developed analytical model. Finite element analyses are conducted using the commercial finite element analysis software ABAQUS™. The strain energy release rates determined using the analytical method correlate well with the results from the finite element analyses. It can be seen that the same prescribed crack has a higher strain energy release rate for the joints with thicker bondlines. This explains the reason that joints with thick bondlines tend to have a lower load carrying capacity. [Copyright &y& Elsevier]

Abstract: This paper develops a comprehensive micromechanical model for the analysis of periodic thin composite shells with an embedded grid of generally orthotropic reinforcements. The use of generally orthotropic constituents renders the analysis more complicated than with simply isotropic reinforcements, but significantly enhances the applicability of the model. The model is derived on the basis of asymptotic homogenization and allows the determination of the effective elastic stiffnesses (coefficients) of the composite shells. These effective coefficients are only dependent on the structural make-up of the pertinent periodicity unit (referred to as unit cell) of the composite shell, and are completely independent of the global formulation of the problem. As such, they are universal in nature and can be used to study a wide variety of boundary-value problems. In the limiting case in which the shell reduces to a thin flat plate with periodicity in the two in-plane orthogonal directions, the derived model converges to that of previously obtained models. The model is illustrated by means of several examples of practical importance including cylindrical-reinforced shells, multi-layer shells, grid-reinforced plates and single-walled carbon nanotubes. [Copyright &y& Elsevier]

Abstract: Analytic solutions are presented for elastic fields induced by normal and shear eigenstrains in an elliptical region (inhomogeneity) embedded in orthotropic composite materials (matrix). Conformal transformation and complex function method are adopted to obtain exact stress distributions in the matrix at the interior boundary to calculate strain energy in the matrix. The stress fields in the elliptical inhomogeneity are derived analytically based on application of the principle of minimum strain energy of the elastic system to determine two fundamental variables characterizing the equilibrium boundary. The resulting solutions are verified with the continuity conditions for the normal and shear stresses along the interior boundary of the matrix. These reduce to known results for some special cases. Numerical examples are provided to illustrate the resulting solutions to the analysis of stress distribution pattern, strength-based failure and fracture behavior. The proposed model can be applied to evaluate volumetric expansion induced cracking and failure of polymers and polymer composites due to freezing of trapped moisture in the elliptical inhomogeneity region as well as fatigue strength of the materials under freeze–thaw conditions. [Copyright &y& Elsevier]

Abstract: Piezoelectric fiber composites were developed to overcome drawbacks of typical monolithic piezoceramic (PZT) actuators. Although piezoelectric fiber composites had many improvements over the monolithic PZT, there are still improvements. Thus, the single crystal piezoelectric fiber composite actuator is proposed. Single crystal piezoelectric materials such as PMN-PT have larger piezoelectric strain constants, higher bandwidth and higher energy density than polycrystalline counterparts. Piezoelectric fiber composites can improve the performance of various structures, and can be subject to wide temperature range where the thermoelastic behavior is important. Therefore, this paper studies the coefficients of thermal expansion (CTE) for single crystal piezoelectric fiber composites. The Macro Fiber Composite (MFC) as the piezoelectric fiber composite is considered. To calculate the effective properties of two orthotropic layers of the MFC, PMN-PT(or PZT)/epoxy and copper/epoxy layers, the rule of mixture is adopted. With the effective properties known for each layers, the two CTE of the MFC actuator are obtained from the classical lamination theory considering thermal effects. The difference of the CTE between the single crystal MFC and the standard MFC is studied. [Copyright &y& Elsevier]

Abstract: The tensile strength of short natural fibre reinforced thermoplastics (NFRT) was modeled using a modified rule of mixtures (ROM) strength equation. A clustering parameter, requiring the maximum composite fibre volume fraction, forms the basis of the modification. The clustering parameter highlights that as fibre loading increases, the available fibre stress transfer area is decreased. Consequently, at high volume fractions this decrease in stress transfer area increases the brittleness of the short fibre composite and decreases the tensile strength of the material. A key parameter, the interfacial shear strength, was determined by fitting the micromechanical strength model to tensile strength data at low fibre loading (10wt%) where there is minimal fibre clustering. To test the modified ROM strength model, compression molded specimens of high-density polyethylene (HDPE) reinforced with hemp fibres, hardwood fibres, rice hulls, and E-glass fibres were created with fibre mass fractions of 10–60wt%. The modified ROM strength model was found to adequately predict the tensile strength of the various composite specimens. [Copyright &y& Elsevier]

Abstract: Large scale fiber reinforced polymer (FRP) composite structures have been used in highway bridge and building construction. Recent applications have demonstrated that FRP honeycomb sandwich panels can be effectively and economically applied for both new construction and rehabilitation and replacement of existing structures. This paper is concerned with impact analysis of an as-manufactured FRP honeycomb sandwich system with sinusoidal core geometry in the plane and extending vertically between face laminates. The analyses of the honeycomb structure and components including: (1) constituent materials and ply properties, (2) face laminates and core wall engineering properties, and (3) equivalent core material properties, are first introduced, and these properties for the face laminates and equivalent core are later used in dynamic analysis of sandwich beams. A higher-order impact sandwich beam theory by the authors [Yang MJ, Qiao P. Higher-order impact modeling of sandwich beams with flexible core. Int J Solids Struct 2005;42(20):5460–90] is adopted to carry out the free vibration and impact analyses of the FRP honeycomb sandwich system, from which the full elastic field (e.g., deformation and stress) under impact is predicted. The higher order vibration analysis of the FRP sandwich beams is conducted, and its accuracy is validated with the finite element Eigenvalue analysis using ABAQUS; while the predicted impact responses (e.g., contact force and central deflection) are compared with the finite element simulations by LS-DYNA. A parametric study with respect to projectile mass and velocity is performed, and the similar prediction trends with the linear solution are observed. Furthermore, the predicted stress fields are compared with the available strength data to predict the impact damage in the FRP sandwich system. The present impact analysis demonstrates the accuracy and capability of the higher order impact sandwich beam theory, and it can be used effectively in analysis, design applications and optimization of efficient FRP honeycomb composite sandwich structures for impact protection and mitigation. [Copyright &y& Elsevier]

Abstract: In this paper, a stress–strain model for concrete confined by fiber reinforced polymer (FRP) composites is developed. The model is based on the results of a comprehensive experimental program including large-scale circular, square and rectangular short columns confined by carbon/epoxy and E-glass/epoxy jackets providing a wide range of confinement ratios. Ultimate stress, rupture strain, jacket parameters, and cross-sectional geometry were found to be significant factors affecting the stress–strain behavior of FRP-confined concrete. Such parameters were analyzed statistically based on the experimental data, and equations to theoretically predict these parameters are presented. Experimental results from this study were compared to the proposed semi-empirical model as well as others from the literature. [Copyright &y& Elsevier]

Abstract: The reinforced concrete spans of a bridge subjected to extreme vehicular loads are investigated and retrofitted with carbon fiber reinforced polymer (CFRP) laminates. A finite element model of the bridge superstructure was created to determine the forces resulting from extreme loads. A moment–curvature analysis was subsequently carried out to investigate the flexural characteristics of the reinforced concrete sections prior to and after strengthening with CFRP laminates. The analytical modeling concluded that significant strength can be gained at the ultimate limit state, while relatively small increase in strength is observed at service load levels. The increase in flexural resistance at ultimate does provide an adequate margin of safety against further overloading. The analytical investigation and the retrofitting work are presented herein. [Copyright &y& Elsevier]

Abstract: This paper presents the experimental and analytical results of the study carried out to investigate the influence of the radius of the cross-sectional corners (edges) on the strength of small scale square concrete column specimens confined with FRP composite laminates. The experimental part of the study was achieved by testing 20 specimens under uniaxial compression. Depending on the selected radius of the edges, the section varied from square to circular. Intermediate radii were about 1/6, 1/4, and 1/3 of the side dimension. The sharpest square specimens had a corner radius of 5mm to make composite application easier and to avoid a premature rupture of the composite. The results show that smoothening the edges of square cross-section plays a significant role in delaying the rupture of the FRP composite at these edges, and the efficiency of FRP confinement is directly related to the radius of the cross-section edges. A modified analytical model is presented to predict the strength of FRP-confined square as well as circular sections. The predicted results are found to be in excellent agreement with the measured ones. [Copyright &y& Elsevier]

Abstract: This paper examines the feasibility of using innovative composite materials to improve the blast resistance capacity of one-way reinforced concrete slabs. In order to achieve this objective, five slabs were tested under real blast loads. One of the slabs was used as the control unit to establish a baseline for comparison of the other four slabs. These four slabs were strengthened with carbon fiber and steel fiber reinforced polymers, comprising of two slabs retrofitted on a single side and two slabs retrofitted on both sides. Test results indicate that there was no significant increase in blast resistance when the slabs were retrofitted on a single side; however, slabs retrofitted on both sides displayed a significant increase in blast resistance. This result can be attributed to the negative moments that develop under the dynamics of blast loads. Another objective of this research program was to study the feasibility of using a modified displacement based methodology to predict the explosive charges weight and standoff distances required to impose a given damage level. Test results showed that for the most part the blast loads were effectively estimated using this method and the damage levels observed from the field tests correlated well with the predicted levels. This paper discusses the analytical steps used to predict the charges weight and standoff distances along with the relevant experimental results. [Copyright &y& Elsevier]

Abstract: Near-surface mounted (NSM) fiber-reinforced polymer (FRP) reinforcement is one of the latest and most promising strengthening techniques for reinforced concrete (RC) structures. Research on this topic started only a few years ago but has by now attracted worldwide attention. Issues raised by the use of NSM FRP reinforcement include the optimization of construction details, models for the bond behaviour between NSM FRP and concrete, reliable design methods for flexural and shear strengthening, and the maximization of the advantages of this technique. This paper provides a critical review of existing research in this area, identifies gaps of knowledge, and outlines directions for further research. [Copyright &y& Elsevier]

Abstract: The strain rate-dependence of the stress–strain curve and flow stress at 1873K of the directionally solidified eutectic alumina/YAG composite under applied compressivse stress parallel (0°) and perpendicular (90°) to the solidification direction were analyzed by a finite element model and by the isostrain and isostress models based the rule of mixtures. The experimentally measured stress–strain curve and flow stress in the steady state plastic deformation region of the composite was described by a finite element model for both 0° and 90° compression directions. The influence of the microstructural deviation of alumina and YAG from the theoretical isostrain and isostress models on the overall flow stress was discussed for both 0° and 90° compression directions, based on the calculated spatial distribution of the equivalent strain rate. [Copyright &y& Elsevier]

Abstract: Asymptotic homogenization models for prismatic smart composite structures are derived and the effective elastic, piezoelectric, and thermal expansion coefficients are obtained. The actuation coefficients characterize the intrinsic transducer nature of active smart materials that can be used to induce strains and stresses in a coordinated fashion. Examples of such actuators employed with smart composite material systems are derived from piezoelectric, magnetostrictive and some other materials. The constituents of the smart structures are assumed to exhibit orthotropic characteristics. The original problem for the regularly non-homogeneous smart composite structure reduces to a system of three simpler types of problem, called unit cell problems. It is precisely these unit cell problems that enable the determination of the aforementioned coefficients. These effective coefficients are universal in nature and can be used to study a wide variety of boundary value problems associated with a smart structure of a given geometry. [Copyright &y& Elsevier]

Abstract: In this paper, the problem of interfacial shear stresses in beams strengthened with bonded prestressed composite laminates is analyzed using linear elastic theory. The analysis provided a closed-form formula for calculating the critical maximum shear stress at the end of the laminate for a beam with arbitrary cross-section and material. A demonstration study on strengthening an existing steel bridge using this technique has also been conducted using FE-analysis. The results from both analyses agreed very well. Also, a parametric study is performed in order to identify the effects of various geometrical and material properties on the magnitude of interfacial shear stresses. The results show that there exists a high concentration of shear stresses at the ends of the laminate, which might result in a premature failure of the strengthening scheme at these locations. Material properties such as laminate and adhesive stiffness and the dimensions of the laminate were all found to have a marked effect on the magnitude of maximum shear stress in the composite member. [Copyright &y& Elsevier]

Abstract: This paper presents the manufacturing process and testing of large scale hybrid composite girders. The evaluation of the girders was a part of the European funded ASSET project. The bridge project, started in 1998 and finished in the autumn of 2002. The ASSET project has in brief covered the design, manufacture and construction of a fully polymer composite traffic bridge. The longitudinal girders are the most important part for the load carrying system of the bridge. Different types of girders were discussed, i.e. steel, concrete or FRP girders. Due to the advantages of FRP girders, for example; light weight, easy installation, superb durability and less maintenance compared to traditional materials it was decided to use FRP in the girders. However, before this could be carried out, tests were needed to verify theoretical calculations. Also a FE-analysis has been carried out, and this analysis is compared with an engineering analytical solution and tests. Both the numerical and the analytical theory correspond quite well with obtained test results. [Copyright &y& Elsevier]

Abstract: Effects of specimen width on the bending strength of textile composites were investigated. 4 points bending tests were conducted on the 8-harness satin Nicalon/SiC (NICAROCERAM) composites. The width of the specimen was varied. Experimental results indicated that the bending strength increases with increasing width and drops at the multiples of the unit cell size. Analytical approach based on Curtin''s model was conducted to characterize the experimental results. The analytical prediction was compared with the experimental results. [Copyright &y& Elsevier]

The paper considers local bending effects induced in the vicinity of inserts in sandwich panels. Such local bending effects are associated with an increase of bending stresses in the sandwich faces and normal and shear stresses in the sandwich core. An earlier developed analytic model [Proceedings of the Sixth International Conference on Sandwich Structures (ICSS-6) (2002) 551] is adapted for the case of a sandwich panel with circular insert, with elastic properties differing from those of the core. The locally induced stresses in the faces and core due to presence of the insert are expressed via simple analytic relations (and charts) enabling an estimation of these local stresses. Finite element analysis is employed to demonstrate the applicability of the analytic model, and a good correspondence between the numerical and the analytical data is found. A study case related to marine applications, namely a circular insert in a sandwich deck panel used for mounting of a rigging fixture, is considered, and optimization of an existing design is carried out. [Copyright &y& Elsevier]

The buckling of a sandwich cylindrical shell under uniform external hydrostatic pressure is studied in three ways. The simplifying assumption of a long shell is made (or, equivalently, ‘ring’ assumption), in which the buckling modes are assumed to be two-dimensional, i.e. no axial component of the displacement field, and no axial dependence of the radial and hoop displacement components. All constituent phases of the sandwich structure, i.e. the facings and the core, are assumed to be orthotropic. First, the structure is considered a three-dimensional (3D) elastic body, the corresponding problem is formulated and the solution is derived by solving a set of two linear homogeneous ordinary differential equations of the second-order in r (the radial coordinate), i.e. an eigenvalue problem for differential equations, with the external pressure, p the parameter/eigenvalue. A complication in the sandwich construction is due to the fact that the displacement field is continuous but has a slope discontinuity at the face-sheet/core interfaces, which necessitates imposing ‘internal’ boundary conditions at the face-sheet/core interfaces, as opposed to the traditional two-end-point boundary value problems. Second, the structure is considered a shell and shell theory results are generated with and without accounting for the transverse shear effect. Two transverse shear correction approaches are employed, one based only on the core, and the other based on an effective shear modulus that includes the face-sheets. Third, finite element results are generated by use of the ABAQUS finite element code. In this part, two types of elements are used: a shear deformable shell element and a solid 3D (brick) element. The results from all these three different approaches are compared. [Copyright &y& Elsevier]

The effective stiffness of multi-walled carbon nanotubes (CNTs) in the radial direction is derived. A nonlinear pullout model for CNT-reinforced composites is presented in which thermal residual stress, Poisson''s contract effect, as well as nonlinear elastic behavior of nanotubes are considered. In the model, the CNT in the matrix is envisaged as an anisotropic cylinder shell submitted to axial tensile load and radial pressure, considering nonlinear in-plane stiffness in the axial direction and the effective stiffness in the circumferential direction. Based on the model, analytical solutions of axial membrane force of the nanotube and the nanotube–matrix interfacial shear stress are obtained. Results of sample calculations suggest that the distribution of interfacial shear stress along the nanotube length is sensitive to its elastic nonlinearity. [Copyright &y& Elsevier]

This study deals with the modeling of a magnetostrictive strain sensor. The sensor comprised of a conducting wire of copper covered with a strain-sensitive magnetic film of Permalloy (80% Ni–20% Fe by weight) that was deposited electrochemically. The voltage response of the sensor as a function of applied stress, thickness and length of the film, amplitude and frequency of the input current was characterized. The sensor was modeled as an electrical circuit having resistive and inductive components and was in good agreement with experimental response. [Copyright &y& Elsevier]

The bending mechanical property of carbon nanotubes are numerically investigated in this paper. An advanced finite element analysis package, ABAQUS, is used to simulate the formation of rippling which is the appearance of wavelike distortion on the inner arc of the bent nanotubes, caused by the severe anisotropy of carbon nanotubes and a relatively large deformation. A non-linear bending moment–curvature relationship is obtained, which shows the tangential stiffness greatly decreases when rippling appears. This result can be used to explain the phenomenon and conclusion of the resonant experiment measuring the Young''s modulus of carbon nanotubes, in which the Young''s modulus calculated using linear theory is found to sharply decrease as the diameter increases [Science 283 (1999) 1513]. Here an analytical method is adopted to conduct a vibration analysis using a bi-linear bending constitution simplifying from the non-linear bending moment–curvature relationship, and the effective Young''s modulus have been calculated for multi-walled carbon nanotubes of various sizes. The result carried out in the paper is similar to the measuring result is given by Poncharal et al. [Science 283 (1999) 1513]. [Copyright &y& Elsevier]

This paper deals with strengthening, upgrading, and rehabilitation of existing reinforced concrete structures using externally bonded composite materials. Five strengthened, retrofitted, or rehabilitated reinforced concrete beams are experimentally and analytically investigated. Emphasis in placed on the stress concentration that arises near the edge of the fiber reinforced plastic strip, the failure modes triggered by these edge effects, and the means for the prevention of such modes of failure. Three beams are tested with various edge configurations that include wrapping the edge region with vertical composite straps and special forms of the adhesive layer at its edge. The last two beams are preloaded up to failure before strengthening and the ability to rehabilitate members that endured progressive or even total damage is examined. The results reveal a significant improvement in the serviceability and strength of the tested beams and demonstrate that the method is suitable for the rehabilitation of severely damaged structural members. They also reveal the efficiency of the various edge designs and their ability to control the characteristic brittle failure modes. The analytical results are obtained through the Closed-Form High-Order model and are in good agreement with the experiment ones. The analytical and experimental results are also used for a preliminary quantitative evaluation of a fracture mechanics based failure criterion for the strengthened beam. [Copyright &y& Elsevier]

FRP external strengthening has proven its success in structural rehabilitation and upgrade. Researchers and practicing engineers are working towards introducing its design procedures to standard codes of practice. The current state of the art flexural design process suggests an iterative approach, which may lead to tedious calculations. This paper provides a direct approach furnishing calculation simplicity and design efficiency. It also proposes equations to design doubly strengthened sections for the first time. The expressions derived for doubly reinforced rectangular and Tee sections are written in a compact form based on those formulated for singly reinforced rectangular sections. Verifications against experimental results are performed. The solution, using the closed form equations, is compared to that of other procedures available in the literature through design examples. Tee section design is also presented and illustrated through a comparison with an analysis example. A doubly strengthened beam design example is also solved. The prevention of premature FRP plate separation using U-wraps to develop the full flexural capacity is also discussed. [Copyright &y& Elsevier]

The temperature distribution along a high thermal conductivity bar (fiber) embedded in a low thermal conductivity half-space (matrix) subjected to an axial differential of temperature is studied. It is assumed that the fiber and matrix are perfectly bonded along the entire interface between them. The system is assumed to be in steady state condition and no heat is generated internally. An approximated analytical solution to the problem based on the heat conduction equation, the principle of conservation of energy and the idea of boundary layer is presented. The problem is also solved numerically by means of the finite element method using commercial software. The results obtained by both approaches, analytical and numerical, are compared. The discrepancy between the two approaches appears very small in most of the cases although substantial relative error can be found at specific points in specific cases. [Copyright &y& Elsevier]

In this study, the buckling of an orthotropic composite truncated conical shell with continuously varying thickness, subject to a uniform external pressure which is a power function of time, has been considered. At first, the fundamental relations and the Donnell type stability equations of an orthotropic composite truncated conical shell, subject to an external pressure, have been obtained. Then, employing Galerkin method, those equations have been reduced of time dependent differential equation with variable coefficients. Finally, applying the variational method of Ritz method type, the critical static and dynamic loads, the corresponding wave numbers and the dynamic factor have been found analytically. Using those results, the effects of the variations of the power in the thickness expression, the semi-vertex angle, the power of time in the external pressure expression and the ratio of the Young''s moduli on the critical parameters are studied numerically, for the case when the thickness of the conical shell varies as a power and exponential function. It is observed, from the computations carried out, that these factors have appreciable effects on the critical parameters of the problem in the heading. [Copyright &y& Elsevier]

Motivated by the emerging concept of including metal phases within piezoelectric and other smart structures and materials, this paper presents a micro/macro theory for determining the coupled thermo-electro-magneto-elasto-plastic behavior of arbitrary composite laminates. The approach involves two models capable of analyzing geometries that include inelastic materials. The first is the electro-magnetic generalized method of cells (EMGMC) (Micromechanical Prediction of the Effective Behavior of Fully Coupled Electro-Magneto-Thermo-Elastic Multiphase Composites, 2000. [1]) micromechanics model. EMGMC has been reformulated to improve its computational efficiency and has been extended to admit arbitrary anisotropic local material behavior (in terms of the thermal response, mechanical response, electric response, magnetic response, as well as the coupling behavior) and inelasticity. The second model is classical lamination theory, which has also been extended for arbitrary anisotropic material behavior and electro-magnetic and inelastic effects. The end result is a coupled theory that employs EMGMC to provide the homogenized behavior of the composite plies that constitute the thermo-electro-magneto-elasto-plastic laminate. Sample results, which address the inelastic response of a hybrid smart/metal matrix composite laminate, are presented. [Copyright &y& Elsevier]

Stiffened cylindrical shells are the major components of aerospace structures. In this study global buckling load for a generally cross and horizontal grid stiffened composite cylinder was determined. This was accomplished by developing an analytical model for determination of the equivalent stiffness parameters of a grid stiffened composite cylindrical shell. This was performed by taking out a unit cell and smearing the forces and moments due to the stiffeners onto the shell. Based on this analysis the extensional, coupling and bending matrices (A, B and D matrices, respectively) associated with the stiffeners were determined. This stiffness contribution of the stiffeners was superimposed with the stiffness contribution of the shell to obtain the equivalent stiffness parameters of the whole panel. Making use of the energy method the buckling load was solved for a particular stiffener configuration. Buckling test was also performed on a stiffened composite cylinder and compared with analytical results. Finally, using the analytical model developed, parametric analysis of some of the important design variables was performed and based on these results conclusions were drawn. [Copyright &y& Elsevier]

Most micromechanical models for stiffness prediction of woven composites assume independence of the Q-matrix on the number of fabric layers in the composite. For example, the moduli of single and 10 layer composites are assumed to be equal in the case when all layers have the same in-plane orientation. Although this statement is likely to be true for isotropic materials or even for unidirectional laminated composites, it may not be valid in some cases of woven composites.This paper contains experimental and theoretical investigations of plain weave carbon fiber/polyester composites. Specimens with one single and eight layers of fabrics are tested and observable differences of mechanical properties are obtained.The theoretical part of this article consists of derivation and application of several micromechanical models on these particular composites. The use of those simplified models finally allows us to find the main mechanisms which cause the observed effects. [Copyright &y& Elsevier]

The purpose of this paper is to determine the indentation produced by a rigid indentor falling on a sandwich plate with a height–density closed cellular foam core. Two different indentor shapes are considered: a rigid sphere and a cylindrical rigid punch. By assuming that the time of complete indentation of the indentors is much larger than the time required by the elastic waves to propagate from the point of first contact to the boundary of the plate, a static analysis is performed. A distribution of surface pressures reproducing the contact law of the rigid indentor on an elastic half-space is introduced and the sandwich plate theory proposed by Dundrova´, Kovarı´k and Slapa´k (1970) is adopted; the explicit solutions with pre-assigned surface pressures are obtained and the contact force–indentation relations, before the sandwich plate is damaged, are found. The contact laws are obtained for both a simply supported and a clamped circular sandwich plate and the relevant influence of boundary conditions on the elastic response of the sandwich plate is shown. [Copyright &y& Elsevier]

The aim of this work is to investigate the mechanical behavior of a soft matrix reinforced by a single family of parallel fibers subjected to simple shear. Specimens with fibers oriented at −45° with respect to the applied shear load were tested. The shear and normal stress components as well as the amount of shear were simultaneously measured. Due to the initial orientation, fibers were subjected to compressive loads, resulting in buckling. The positive Poynting effect was observed when soft materials were sheared. The off-axis stiffness theory and the Murphy model at small deformations were used to predict the mechanical behavior of the soft composites. In general, there is a reasonable correlation between model predictions and measured data by adjusting only one empirical parameter. However, the model based on the off-axis stiffness shows better prediction than the Murphy model for relatively higher fiber volume fractions. From universal relations for simple shear, the results indicate that the studied composites are of a coaxial type in a weak sense. • A new simple shear procedure to measure shear and normal stresses on soft composite. • Positive Poynting effect in composite for fibers under compression in simple shear. • The effect of fiber buckling was observed in the shear and normal stress responses. • Comparison between experimental data, off-axis stiffness theory and Murphy model. [ABSTRACT FROM AUTHOR]

Abstract: In the manufacture of the prepreg, the impregnation degree was a key factor to ensure the quality of the prepreg. In experiment, the impregnation degree of the prepreg was analyzed by developing the reference method. Near infrared (NIR) spectra were combined with partial least squares (PLS) to develop the calibration models of the impregnation degree of the prepreg. The determination coefficient (R 2) was 0.98 and root mean square error of calibration (RMSEC) was 4.24 for the calibration models. The regression coefficient of the actual values against NIR predicted values for calibration model was 0.989. With this rapid and noncontact analytical method, prepreg quality will be improved. [Copyright &y& Elsevier]

Fiber-reinforced polymer matrix composite materials can fail by kink-band propagation mechanism when subjected to in-plane compressive loading. This mode of failure is especially prevalent in compressive loading of laminates with holes, cut-outs, or impact damage. Most of the successful models for predicting compressive strength of such laminates require "fracture" toughness associated with kink-band propagation under in-plane compression. However, this property is difficult to measure experimentally, limiting the use of such models in design practice. In this paper an inverse method is proposed to estimate the kink-band toughness of the laminate from its open-hole compression strength data, which is an easier property to measure experimentally. Furthermore, a scaling relationship is proposed to estimate kink-band toughness for other laminate configurations of the same material.