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Abstract In this paper, a general vibration analysis of functionally graded porous (FGP) structure elements of revolution with general elastic restraints is performed for the first time. Under the basic framework of the first order shear theory, the moderately thick and thin FGP structure elements of revolution are considered. The specific FGP structure elements include the cylindrical shell, conical shell, spherical shell, cylindrical panel, conical panel and spherical panel. In order to simulate general elastic restraints, the artificial spring boundary technique is adopted this paper. And the modified series solution composed of a standard cosine Fourier series and two auxiliary terms is introduced in the Rayleigh-Ritz method to express the admissible function. A series of numerical examples are conducted, which show that the current model has superior convergence characteristics, computational accuracy and stability. On this basis, a series of innovative results are also given in the paper, which may provide basic data for other algorithm research in the future. [ABSTRACT FROM AUTHOR]

Abstract The possibilities for detecting defects in multilayer carbon composites occurring as a combination of layers of carbon fiber fabric with thin layers of epoxy resin (CFRP) are presented in this paper. The most common defect in this type of structure is delamination. For non-destructive testing of CFRP samples with deliberately introduced defects, infrared thermography with laser thermal stimulation was used and both computer numerical simulations (using the ThermoCalc program) and experimental tests were carried out. In the experimental testing, a semiconductor laser with a wavelength of 808 nm and a maximum power of 32 W was used for thermal stimulation. Changes of temperature field on the surface of the test sample were recorded with a thermal camera, FLIR 7600 SC. Both pulsed and lock-in thermography methods were used, and this paper presents selected results, together with their analysis. The results presented in this paper show that it is possible to use a laser as a heating source in thermographic non-destructive testing of CFRP composite. [ABSTRACT FROM AUTHOR]

Abstract Thrust force is a remarkable intermediate variable in the drilling-countersinking process of carbon fiber reinforced plastic (CFRP) and aluminum (Al) stacks. Because of the poor machinability and extreme abrasiveness of CFRP, tool wear cannot be neglected. Focusing on the CFRP drilling and countersinking thrust force of stacks, this paper provided a novel insight into the modeling of the influence of tool wear on thrust force through both experiments and theoretical analysis. The experimental exploration is first presented in this study, and the flank wear was observed and it is the primary abrasion type. Then a method of infinitesimal elements with substitution has been used to develop the theoretical model of thrust force based on the mathematical abstraction of flank wear size and morphology, and the forces of the deformation region under the wear land in the element are the increscent component which contributes a lot to the variation of the total thrust force. Finally the theoretical model is verified by the multivariate experiments, and the results show that proposed model can work well. The work in this paper enables us to understand the influence of flank wear on thrust forces through the fundamental insight of CFRP cutting process. [ABSTRACT FROM AUTHOR]

Abstract Failure prediction for composite materials is still a major area of interest within both the academic literature and the composite industry. This paper presents a modelling and experimental framework which has been developed for the application of Strain Invariant Failure Theory (SIFT), but which can be adapted to other failure prediction methods if required. SIFT is set of physics-based failure criteria developed to predict the onset of irreversible deformation of glassy polymers. The paper provides an overview of the available evidence for SIFT and provides a complete methodology for applying SIFT to predict the onset of failure in a composite component. Fundamental to the method presented is a modular and hierarchical dehomogenisation procedure; allowing for the evaluation of stress and strain state variables within the constituent components of the composite. Due to the constant evolution of composite characterisation techniques, the method presented in this paper is designed to be extensible (i.e. accommodating of new materials and product forms) and modular (i.e. subsections of the method can be easily substituted or refined). Known limitations of the current method are clearly presented and discussed. A companion paper will present validation of the approach for simple uniaxial and biaxial coupon experiments and will discuss how the method can be applied to a range of existing composite characterisation testing standards. [ABSTRACT FROM AUTHOR]

Highlights • This paper deals with the mechanical response of glued in rods. • It takes into account the diameter of rods, the material of rods and the direction of the grain of the timber. • It gives an overview and presents known design models and technical approvals comparing the different approaches. • Comparison between the experimental results and the main equations of the literature review. • The authors propose one equation for the case where the bars are parallel to the timbers' grain. • In addition, another one for the case where the bars are perpendicular to the timbers' grain. Abstract We address the mechanical response of glued in rods, taking into account parameters such as rod diameter, the material properties of the rods (carbon or glass fibre-reinforced polymer), and the grain orientation of the timber (rods parallel and perpendicular to the timber grain). All the experimental setups employ pull-out tests, where rods are glued in only on one side of the specimen, and these tests are assessed at the premises of the Laboratory for Composite Materials and Composite Structures at the University Claude Bernard Lyon I. In addition, we give an overview and present known design models, technical approvals and regulations, national standards, and guidance papers, comparing the different approaches among them and with the experimental results. Good agreement was shown and further useful results were observed. [ABSTRACT FROM AUTHOR]

Abstract Consolidation of a prepreg layup to a target thickness is critical in order to achieve the required fibre volume fraction and dimensions in a composite part. Experiments show that different processing conditions lead to different levels of compaction and variability in the thickness. This paper presents an analysis of processing conditions and their effects on consolidation of thick composite components. A model that accounts for both percolation and squeezing flow is employed to study two toughened prepreg systems – IM7/8552 and IMA/M21. This paper analyses the significance of the process parameters on the thickness of prepregs and its variability. The analysis of different layups and processing conditions suggests several strategies to control target thickness and its variability. The IMA/M21 prepreg system was found to have lower variability due to its toughening mechanism. The presented results provide a better understanding of the composite manufacturing and can be used to provide an informed choice in design for manufacture of composite structures. [ABSTRACT FROM AUTHOR]

Abstract This paper presents in a unified and comparative manner, the formulation of two triangular plate bending composite elements, i.e. DKMT and MITC3 which are published in 1993 and 2004. Both elements have 3 nodes and 5 dof per node (three displacements and two rotations), taking into account transverse shear effects. There are valid for thin to thick composite plates, and give good results in classical benchmark and patch tests. The numerical results using DKMT element show the optimal and uniform convergence for thin and thick plates with an advantage for DKMT compare to MITC3 due to semi quadratic interpolation for the rotation variables The present paper contains new convergence analysis based on the s -norm tests for sandwich plates considering uniform and distorted meshes, and for symmetric and non symmetric composite plates with 3 and 9 layers. As the novelty and main contribution of this article, we propose the shear projection method in the element formulations to show the asymptotic equivalence of DKMT and the MITC3 for thick to thin composite plates. [ABSTRACT FROM AUTHOR]

Abstract The result of an experimental programme investigating a novel technique to strengthen web plates against breathing fatigue is presented in this paper; the programme was divided into five phases, including: (1) the development of a novel preformed corrugated FRP panel for strengthening thin-walled steel plate girder webs against buckling, (2) selecting the adequate adhesive and epoxy using double-lap shear and tension specimens, (3) producing the FRP panel, and (4, 5) testing its performance in two main experimental series; the initial (static) series and the final (cyclic) series. Only the initial series which involved tests on 13 steel plates strengthened with the proposed preformed corrugated FRP panel and subjected to in-plane shear will be reported in this paper. This series investigated the performance of different forms of strengthening under static load, in preparation for a subsequent series of cyclic tests to investigate their fatigue performance. Test results showed the efficiency of the technique at increasing the stiffness of the strengthened specimens in comparison to the unstrengthened ones and reducing the critical stresses which will serve as a precursor for the anticipated increase in the fatigue life of the girders. [ABSTRACT FROM AUTHOR]

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

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

Abstract Structural Health Monitoring (SHM) systems allow early detection of damage which allows maintenance planning and reduces the maintenance cost.Several researchers have proposed use of Neutral Axis (NA) location as a damage sensitive feature. It has been shown that through proper signal processing, NA location is insensitive to measurement noise and ambient temperature changes. This paper presents a methodology for successful NA tracking under changing axial loading conditions. The novel methodology is validated using numerical data as well as experimental results. This paper demonstrates the development of a Kalman Filter (KF) based NA tracking strategy under different loading conditions. The methodology was employed on a composite beam instrumented with fiber optic strain sensors. The stable NA tracking under changing loading conditions allows the application of the NA as a damage sensitive feature. The change in NA location is used to detect delamination in the beam. The method has been validated through a numerical model and experiments. The results show that the novel formulation of the KF for NA tracking allows more robust use of NA location as a damage sensitive feature in a wider range of applications. [ABSTRACT FROM AUTHOR]

Abstract The paper describes a numerical and experimental study investigating the load carrying capacity of thin-walled composite columns with a top-hat cross section under axial compression. The tested columns were made of carbon-epoxy laminate with symmetrical lay-up and ply orientation [0/90/0/90]s. The experiments were performed on a universal testing machine, Zwick Z100, under full load conditions until total failure of the structure. In the experiments, post-critical equilibrium paths of the structure were determined, defining the relationship between compressive force and deflection and enabling the validation of the numerical models. Based on the obtained post-critical equilibrium paths, the critical load of the structure was determined by approximation methods. Simultaneously, a numerical analysis was performed by the finite element method using the Abaqus® software. The critical state was determined via a linear eigenvalue analysis, and the critical load and a corresponding buckling mode were estimated. The next stage of the numerical analysis involved solving a nonlinear stability problem for a structure with initialized geometric imperfection reflecting the lowest buckling mode. The geometrically non-linear problem was solved by the Newton-Raphson method. The load carrying capacity of the composite structure in the post-buckling state was determined by the progressive failure criterion which estimates damage initiation in the composite material based on the Hashin criterion, while the progression of damage is described with the energy criterion describing the degradation of stiffness of finite elements. The numerical and experimental results show high agreement, which confirms the adequacy of the developed numerical models of composite structures. Results presented in the paper are part of a study conducted under the project no. UMO-2015/19/B/ST8/02800 financed by the National Science Centre Poland. [ABSTRACT FROM AUTHOR]

Abstract Micromechanics based models are used for predicting the effective mechanical properties of reinforced polymer matrix composites. This paper reviews micromechanics based models for fiber reinforced polymer composites starting with the bounds established by Voigt and Reuss models, Hashin-Shtrikman model and then on to well-known micromechanics based models like Mori-Tanaka model, Self-consistent model and Differential scheme based models. The main objective is to critically review the areas in which these micromechanics based models hold good and analyse the limitations of these models. One of the limitations of the above mentioned models is the assumption of dilute dispersion and this is overcome in this paper by revising the Mori-Tanaka model by combining the differential scheme with Eshelby's model to take into account the non-dilute dispersion effect. Numerical results are verified by finite element based simulation of the representative volume element (RVE). Experiments were carried out to estimate the effective elastic constants for different fiber volume fractions. Theoretical results are reviewed with reference to experimental measurements. [ABSTRACT FROM AUTHOR]

Abstract In this paper, exact solutions for the static bending response of laminated composite beams have been derived considering the effect of strain gradient elasticity. Separate solutions for the laminate comprising of isotropic and orthotropic laminae have been presented here. The sixth-order tensor for the higher order elastic coefficients has been evaluated using the generalized first strain gradient elasticity model with three independent material length constants. The significance of the gradient elasticity in low-dimensional structures has been established employing numerical examples of micro and nano-beams, and comparing the current results with the classical elasticity results. A parametric study over the variation of the axial, transverse Cauchy and physical stresses across the thickness of the beam has been conducted. Also, the discontinuity of the inter-laminar transverse Cauchy stresses and higher order stresses across the thickness has been studied in the current framework. The exact solutions developed in this paper may be used as benchmark results for validating further research involving the strain gradient elastic response of low-dimensional laminated composite beams. [ABSTRACT FROM AUTHOR]

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

Abstract Nowadays, with the development of demand for construction, the use of composite structures in architectures become more and more popularity. How to improve the intelligent level of deformation monitoring has become one of the key problems. A detailed understanding about deformation behavior is significant for better monitoring of structures, especially in terms of accuracy and detail. The innovation of this paper focuses on that terrestrial laser scanning (TLS) measurement is adopted to investigate deformation of the composite masonry structures. In this paper, deformation segmentation and analysis of the masonry structures are investigated and the deformation tendency is compared and analyzed, based on the intelligent data extraction by window selection method, where high precision 3D laser technology provides reliable experimental data for this research. The deformation of different surfaces of a composite arch is considered and the maximum displacement distribution is analyzed through partially comparing the deformation of different epoch data. [ABSTRACT FROM AUTHOR]

Abstract A numerical study is performed which analyzes the effect of mesh parameter settings on the prediction accuracy of the P-approach, a simulation concept which has been proposed earlier by the author for predicting process-induced distortion of composite structures. A parameterized solid-element finite element (FE) ABAQUS model of a composite L-profile is used as the reference geometry, while numerically predicted distortions are compared with nominal values. This paper shows that significant, unacceptable mesh-related deviations occur for some mesh-parameter configurations. The paper also shows that the main drivers of these deviations are related to the effective geometry of the finite elements at the L-profile’s bend. Based on this finding, the P-approach has been extended with a novel model formulation, which helps to minimize mesh-related deviations, especially for coarse meshes. The validity of the proposed model is verified by a re-execution of the full study, which shows a remarkable reduction of mesh-related deviations. The paper provides general mesh-parameter guidelines for the P-approach application in ABAQUS as well as measures to apply coarser meshes without losing prediction accuracy. [ABSTRACT FROM AUTHOR]

Abstract Requiring probability density distribution functions of uncertain variables, it is difficult for conventional structural reliability analysis methods to calculate the reliability of composite laminates with both random and interval variables. To evaluate the safety of composite laminated structures under this circumstance, this paper is aimed at developing a precise and efficient univariate method for the reliability assessment of composite laminates taking use of Legendre orthogonal polynomials and Monte Carlo Simulation. In this paper, based on the Tsai-Wu failure criterion and first-ply failure assumption, the failure criterion of composite laminate is constructed firstly. Then the performance function of each lamina is approximately expressed as the sum of univariate contributions of all uncertain variables on the basis of the univariate method. Taking use of Legendre orthogonal polynomials, the univariate functions of random and interval variables are constructed by the least square fitting method and the univariate contribution bounds of interval variables are derived afterwards. Furthermore, the interval of failure probability can be calculated by substituting contribution bounds of interval variables and sample points of random variables into univariate function. At last, two examples and an engineering application are provided to demonstrate the efficiency and accuracy of the proposed method. [ABSTRACT FROM AUTHOR]

Abstract In this paper, a shell based finite element (FE) model previously introduced for capturing the face-on impact and compressive strength after impact (CSAI) response of composite laminated structures is evaluated for predicting the dynamic response and damage due to edge-on impact and the resulting CSAI. The model utilizes an in-plane progressive damage and failure material model, Enhanced Schapery Theory (EST), for modeling the full field damage and failure of a single lamina in the 1–2 plane. The material model captures the pre-peak matrix non-linearity due to micro cracking using Schapery Theory (ST). The Bažant-Oh Crack Band (CB) model is utilized for matrix cracking and fiber rupture at the lamina level. Discrete cohesive elements are used for delamination initiation and propagation. Edge-on impact data for a range of impact energies is used for evaluating the models capability. The predicted impact damage state of the laminate is used for acquiring predictions of the CSAI of the laminate. The model predictions show promising results for the impact and CSAI response of an edge-on impacted coupon. The paper discusses the strengths of the model, the issues encountered, as well as topics for future study. [ABSTRACT FROM AUTHOR]

Abstract The work provides an analysis of paperboard tubes subjected to transversal compression force. The investigations were performed for 8 tubes of different radii and different wall thicknesses. The number of layers for detailed pipe ranged from 4 up to 13. The each layer of the paper was modelled with orthotropic material properties. To compare the obtained results of experimental tests, numerical simulations of considered tubes in Ansys 16.2® software were conducted. The calculations were carried out for total failure of pipes using the anisotropic Hill potential theory to implement progressive phase of damage. The scores of investigations were compared with each other and discussed. [ABSTRACT FROM AUTHOR]

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

In the field of external strengthening and repairing of existing reinforced concrete structures, steel reinforced polymers (SRP) systems have emerged as a competitive alternative to the use of the more common carbon and glass fiber reinforced polymer (FRP) composites. Experimental investigations have frequently shown the potentials of these innovative composite systems in improving the performance of deficient structural members. At the same time, additional studies are needed to expand the existing knowledge and either to provide design recommendations or to develop specific guidelines. The paper fills some of the foregoing knowledge gaps by presenting an analytical investigation on the bond behaviour between SRP and concrete in which closed-form solutions are derived to predict the entire debonding propagation process. In particular, accurate and simplified local shear stress-slip (τ-s) laws are employed in the proposed modelling from which different expressions for the interfacial shear stress distribution, the axial stress profile and the concrete-SRP relative displacement (slip) are developed and commented in the paper; analytical estimates of the SRP effective bonded length are provided as well as relationships for calculating the maximum axial stress (or peak force) at SRP laminate debonding. The analytical procedure was, firstly, applied to simulate some single-lap shear tests performed in a previous experimental program with the purpose to investigate the influence on the debonding propagation process of the following main parameters: a) concrete strength, b) concrete surface finish and c) steel tape density. Then, the comparisons between the numerical simulations and the experimental results available for some bond tests have allowed for verifying the accuracy of the proposed modelling. [ABSTRACT FROM AUTHOR]

Composite materials have been widely used in the field of pressure shells for underwater vehicles due to their great potential. This paper presents an experimental study of composite cylindrical shells with and without the circular hole subjected to external hydrostatic pressure. The mechanical response of the composite cylindrical shells under external hydrostatic pressure is recorded by the strain acquisition system, and the buckling deformation process of the shells is also captured by the high-speed camera system. According to the experimental results, the entire compression process of the shell can be divided into three stages based on variations in strain. Based on the findings that buckling starts very early and accounts for about 35 % of the entire process, the concept of initial buckling pressure is proposed to distinguish the critical point of the shell transition from a stable state to an unstable state. It is found that the damage positions of the three shells all correspond to the troughs in the buckling waveform, and the final fiber breakage of the perforated shells with the reinforcements both occur near the reinforcement component. Finally, a comparative analysis of the strain response of the shell with the hole and the complete shell is carried out to explore their similarities and differences. The experimental results in this paper provide valuable information for the design of perforated composite pressure shells for underwater vehicles. [ABSTRACT FROM AUTHOR]

The present paper focuses on studying the underwater electro-mechanical vibro-acoustic characteristics of functionally graded piezoelectric material (FGPM) plates with general boundary conditions. For this purpose, the collocation points method is firstly developed to handle vibro-acoustic coupling, which can directly calculate the virtual work of secondary sound pressure via an easy double integral, without pre-simplifying the complex quadruple integral. The proposed FGPM plate model is established in the framework of first-order shear deformation theory (FSDT) and second type constitutive equations of piezoelectric materials, and the macroscopically inhomogeneous electro-mechanical properties are considered by means of Voigt model. The multi-physical fields including electric, mechanical and acoustic fields are uniformly extended in Chebyshev polynomials. Meanwhile, penalty function method is introduced to satisfy the arbitrary mechanical and electric constraints. All energy formulations are processed by Rayleigh-Ritz procedure and a standard governing equation is finally derived. Based on the proposed unified model, the convergence and accuracy for solving vibration and acoustic radiation of FGPM plates are validated firstly. Additionally, the influence of some key parameters on underwater vibro-acoustic characteristics of FGPM plates is fully examined. The results of this paper may provide a reference for future application of FGPM-based smart structures. [ABSTRACT FROM AUTHOR]

• Bending strength and power output of curved PV-TE device are analyzed; • Thermal stress is much lower than bending stress in hybrid device; • Circumferential stress is key factor resulting in strength failure; • Safety region is identified to keep hybrid device from strength failure; • Optimal geometric dimension of TE leg for maximum output power is given. Curved photovoltaic-thermoelectric (PV-TE) hybrid devices have great potential applications in the fields of aerospace, navigation and daily life. During the application, the curvature radius of the PV-TE hybrid device needs to be altered to fit different curved surfaces. Naturally, the bending strength of the curved hybrid device is a very important issue. This paper evaluates the bending strength and optimizes the output power and energy conversion efficiency of the curved hybrid device. The stress solutions are obtained by means of the variational principle. The recovery of transverse shear stress is achieved by using the Cauchy's polar equilibrium equation. It is found that the thermal stress is much smaller than the bending stresses induced by the bending deformation of the hybrid device. The circumferential stress is the key factor that results in the failure of the hybrid device. The optimization of the curvature radius of the hybrid device is conducted and the safety region is identified to protect the hybrid device from strength failure. The ratio of thickness to cross-sectional area of the thermoelectric leg is optimized to obtain the optimum power generation performance of the hybrid device. This paper offers some favorable suggestions for structural design of the curved hybrid device. [ABSTRACT FROM AUTHOR]

In this paper, the process deformation of 2D SiC/SiC composite materials in the pyrolysis stage of precusor infiltration and pyrolysis process (PIP) is investigated experimentally and computationally through a multiscale study. The pyrolysis process of PCS was described by a kinetic model. The intrinsic properties and behaviors of pyrolysed PCS were characterized experimentally. The macroscopic properties and behaviors of 2D-SiC/SiC composite materials were obtained through the homogenization method. The proposed methodology can successfully predict the process deformation of an L-shaped 2D SiC/SiC composite structure in cyclic PIP process. It is revealed that the pyrolysis of precusor can generate significant chemical shrinkage and stiffness variation, leading to the process deformation of the entire composite structure. Unlike the precusor, the variation of properties and behaviors of composite materials are anisotropic. Furthermore, the cyclic process and the evolution of matrix composition complicate the process deformation. The behavior of composite material is dominated by pyrolysing PCS at first several cycles whereas by pyrolysed SiC at last several cycles. The fundamental understating on process deformation in this paper may benefit the design and the manufacture of SiC/SiC composite materials. [ABSTRACT FROM AUTHOR]

• Harmonic vibrations of VE laminate plates with exponential complex-conjugate solution form and harmonic balance method. • The use of refined zig-zag theory for the description of layered plate kinematics. • Application of fractional Zener material model with separation of volumetric and deviatoric strain. The paper is devoted to the theoretical formulation of the harmonic vibrations problem for laminate plates in the von Kàrmàn geometrically non-linear regime. The plate layers are modelled as viscoelastic using the fractional Zener material with the linear elastic material being a special case. The model of the material is formulated with the separation of the volumetric and deviatoric strain. The laminate plate kinematics is described using the refined zig-zag theory. The vibrations of the plate are formulated using the alternative exponential form with complex-conjugate amplitudes. The harmonic balance method and the time-averaging are applied to derive the amplitude equation of the problem in hand. The efficiency and correctness of the formulation is verified in the continuation paper Part 2 – numerical analysis. [ABSTRACT FROM AUTHOR]

• FE solution of harmonic vibrations for VE layered plates with exponential complex-conjugate form and refined zig-zag theory. • Effective application of the continuation method to solve the discretised amplitude equation. • Numerous analyses of the influence of various plate and formulation parameters on the resonance behaviour of laminate plates. The paper is devoted to the numerical analysis of the harmonic vibrations of laminate plates with viscoelastic layers in the von Kàrmàn geometrically non-linear regime. The amplitude equation derived in the prequel paper Part 1 – theoretical background is discretized using the 8-noded bi-quadratic plate finite elements. The response curves are obtained using the continuation method to solve the discretised amplitude equation treated as the equation with the frequency of vibrations as a parameter. The proposed method of solution is verified by comparing the results with those from available literature. Furthermore, several numerical analyses are performed, including testing of FE mesh density, plate aspect ratio, various VE materials, support conditions and layers layout as well as the possibility of simplification of the complex-valued zig-zag function used in the description of plate kinematics. Several results of practical importance are found and discussed in the conclusions. [ABSTRACT FROM AUTHOR]

The combination of geopolymer sea-sand concrete (GSSC) and basalt fiber reinforced polymer (BFRP) reinforcement has the potential to optimally exploit the advantages of both materials, resulting in superior structural durability and environmental friendliness. The resulting structure is called a BFRP-reinforced GSSC structure, which has broad application prospects in marine engineering construction. This paper presents a recent experimental and analytical investigation into the flexural and compressive performance of BFRP-reinforced GSSC structures to verify the expected benefits of such a material combination. In particular, a type of GSSC that uses MgO as an expansion agent to reduce concrete shrinkage was used in this study. The results of four-point bending tests on nine rectangular beams, where longitudinal reinforcement ratios and reinforcement types were key parameters, and monotonic axial compression tests on seven columns, where concrete types and transverse reinforcement ratios were key parameters, are reported in this paper. The test results initially confirmed the advantages of using GSSC in combination with BFRP reinforcement and showed that: (1) the ultimate carrying capacity of BFRP-reinforced GSSC beams and columns was higher than that of conventional steel-reinforced counterparts for the same reinforcement configurations; (2) the flexural and compressive capacity of BFRP-reinforced concrete beams and columns could be enhanced by an appropriate increase in reinforcement ratio and the addition of expansion agents. Finally, this paper presents design equations for the flexural and compressive capacity of BFRP-reinforced GSSC structures. [ABSTRACT FROM AUTHOR]

[Display omitted] 2.5D woven composites are ideal candidate materials for deep-sea pressure tubes owing to their excellent out-of-plane properties. This paper presents the damage evolution and failure mechanism of 2.5D woven composite tubes under quasi-static lateral compression. To conduct this study, 2.5D woven composite tubes with different thickness-to-diameter ratios, 0.04, 0.07 and 0.10, were designed and prepared. The quasi-static lateral compression tests were carried out in order to evaluate the progressive damage analysis, combining high speed photographic image with acoustic emission technologies. The results show that the increase of the ratio of thickness-to-diameter, the deformation and shear failure of the sample can be inhibited obviously. Due to the enhanced interlayer interaction, the lateral stiffness of the sample is obviously improved, so the lateral bearing stability of the sample is improved. When the peak load of samples with the thickness-to-diameter ratio of 0.1 reached 11.51 kN, it exceeded that of samples with thickness-to-diameter ratios of 0.04 and 0.07 by 450% and 82%, respectively. Furthermore, the failure mechanisms of samples with the thickness-to-diameter ratio of 0.1 were controlled by delamination fracture, whereas that of 0.04 and 0.07 were mainly influenced by shear failure and delamination failure, respectively. [ABSTRACT FROM AUTHOR]

[Display omitted] • Efficient, accurate multi-scale advanced FE2 method for MPH interfaces developed. • Revealed how interface micro-geometry affects failure modes and crack propagation. • Unveiled multi-scale propagation mechanisms of micro-geometric uncertainties in MPH structures. • Proposed high-adhesion design region and parameter matching for mixed failure mode. Metal/polymer-based composites hybrid (MPH) structures combine the high strength of metals with the low density of polymer-based composites, making them widely used in automotive applications. However, the random characteristics of the microgeometry at the pretreated MPH interface have made it challenging to predict its interface bonding failure probability accurately and quickly. This paper presents an advanced FE2 prediction method for bonding performance of MPH interface based on multi-fidelity regression and artificial neural networks (ANNs). When compared to experimental fracture mechanics results for failure mode I and II, the prediction errors for peak loads are 3.9 % and 5.6 %, respectively. At same time, the computational efficiency is over 6 times higher than that of traditional FE2 methods. Additionally, how interface microstructure parameters affect the tensile/shear performance, crack initiation, and propagation directions are investigated at the micro-scale. Under combined tensile/shear loads, the propagation mechanisms of interface microgeometry uncertainties in MPH are revealed theoretically. An interface design method with a high adhesion probability is proposed, identifying high load-bearing areas within the feasible design domain under bending loads for MPH structures. This provides a quickly accessible parameter matching scheme during conceptual design, offering a theoretical foundation for the application of MPH structures in engineering fields. [ABSTRACT FROM AUTHOR]

Modified (MOD) cure cycles that deviate from the manufacturer's recommended cure profile can reduce the inherent thermally induced residual stresses (TRS) in fiber metal laminates (FML). Literature shows that MOD cycles do not adversely affect the material properties but enhance the quasi-static material strength. However, the literature does not comprehensively discuss the impact of MOD cycles on material performance during cyclic fatigue loading. This paper, therefore, investigates how MOD cycles influence the fatigue characteristics of different FML layups made of carbon fiber-reinforced polymer (CFRP) and steel. The experimental results confirm that the quasi-static material strength and the modulus of the FML are increased when using MOD cure cycles. The evaluation of fatigue tests with digital image correlation, thermography, and electrical resistance measurements of notched specimens shows that a reduction of TRS delays damage initiation in the metal facesheets and decreases the crack growth rate until facesheet failure. The results further show that layup-dependent parameters, the maximum stress in the metal sheets, and metal sheet thickness significantly govern the evolution of fatigue damage. In summary, modified cure cycles are an efficient tool to enhance the quasi-static and fatigue performance of CFRP-steel hybrid laminates. [ABSTRACT FROM AUTHOR]

This paper investigated experimentally the shear performance of ultra-high-performance concrete (UHPC) deep beams reinforced longitudinally with glass fiber reinforced polymer (GFRP) bars without web reinforcements. Ten beams were cast, in which seven were longitudinally reinforced with GFRP bars, while the remaining three were reinforced with steel bars for comparison. All beams had similar lengths and widths of 2000 mm and 150 mm, respectively, while the depths varied. The test parameters included the effective depth (d), shear span-to-depth ratio (a/d), number of longitudinal bars, and longitudinal reinforcement ratio (ρ). All the GFRP reinforced beams had higher shear capacities and lower post cracking stiffness than their steel counterparts. The experimental results show that varying the test parameters have a significant impact on the shear capacity of the beams. For instance, decreasing the a/d ratio for the GFRP reinforced beams from 1.8 to 1.5 and from 1.8 to 1.1 increased the load carrying capacity by 33 % and 95 %, respectively. The experimental results for the shear capacity were compared against the predictions obtained using the strut and tie method as per the ACI-318–19 and CSA-S806-12 codes. The failure load predictions by the ACI and CSA code showed the same trends as those shown in the experimental results. Moreover, both codes were conservative in predicting the shear capacities. [ABSTRACT FROM AUTHOR]

Laminated composite honeycomb cellular core sandwich panels are widely utilized in various industries due to their exceptional stiffness-to-weight ratio and strength characteristics. Current analytical models often simplify honeycomb cores as homogenized continua, effectively predicting stiffness but falling short in capturing crucial failure modes, particularly shear buckling of honeycomb core walls. Existing theoretical studies on shear buckling are limited to isotropic materials and specific honeycomb geometries. While numerical models can simulate cell wall buckling, their computational demands render them impractical for large structures employing sandwich panels. This paper introduces a novel, simplified semi-analytical approach that accurately predicts the shear buckling load of laminated composite honeycomb cellular cores. The model accounts for bend-twist coupling effects and rotational restraints at laminate wall boundaries. To validate the proposed approach, predictions are compared with finite element analysis results for hexagonal honeycomb cores and cores of varying shapes, incorporating diverse fibre lay-up configurations. The findings demonstrate excellent agreement between the proposed approach and finite element analysis, indicating its reliability in predicting shear buckling. This research addresses the gap in existing methodologies by offering a practical and efficient tool for predicting shear buckling in laminated composite honeycomb cores, extending applicability beyond isotropic materials and specific honeycomb geometries. The proposed approach holds promise for optimizing the design and structural integrity of sandwich panels, impacting industries relying on these lightweight and high-performance structures. [ABSTRACT FROM AUTHOR]

As a crossover frontier of physics and mechanics, quantum computing is showing its great potential in computational mechanics. However, quantum hardware noise remains a critical barrier to achieving accurate simulation results due to the limitation of the current hardware. In this paper, we integrate error-mitigated quantum computing in data-driven computational homogenization, where the zero-noise extrapolation (ZNE) technique is employed to improve the reliability of quantum computing. Specifically, ZNE is utilized to mitigate the quantum hardware noise in two quantum algorithms for distance calculation, namely a Swap-based algorithm and an H-based algorithm, thereby improving the overall accuracy of data-driven computational homogenization. Multiscale simulations of a 2D composite L-shaped beam and a 3D composite cylindrical shell are conducted with the quantum computer simulator Qiskit, and the results validate the effectiveness of the proposed method. We believe this work presents a promising step towards using quantum computing in computational mechanics. [ABSTRACT FROM AUTHOR]

Sandwich structures are commonly used in a wide range of industrial sectors, due to their very good compromise between strength and lightness. However, owing to the presence of thin/slender parts, they are prone to buckling under global or local compression, which becomes primarily responsible for the collapse of such sandwiches. This paper thus focuses on the elastic buckling/wrinkling behavior of sandwich columns under overall axial compression. This work follows on from a previous analysis restricted to homogeneous and isotropic skin and core materials. In the present study, the more general case of laminated composite faces is investigated, and anisotropic core materials are also considered. It allows one to deal with heterogeneous core structures in an homogenized way. The modeling approach is based on the use of a laminated beam model for the faces whereas the core layer is represented as a 2D equivalent continuous solid. With such a formulation, analytical solutions can be obtained for the critical loadings and the associated buckling modes, by means of a bifurcation analysis. These solutions are finally confronted to the numerical results derived from 2D linearized buckling finite element computations, for validation purposes, and the particular case of a honeycomb sandwich is addressed. [ABSTRACT FROM AUTHOR]

• FMC is used for translaminar fracture toughness characterisation. • Glass fibre/PA6 laminated composites by varying the thickness are considered. • The experimental campaign is numerically simulated. • Considerations on fracture toughness dependence on specimen sizes are provided. This paper proposes a novel approach for the characterisation of the material fracture toughness associated with translaminar tensile failure, consisting in the application of the Fictitious Material Concept (FMC) by using the testing configuration of the Modified Two Parameter Model (MTPM). The main advantage of such an approach is to avoid the use of nonlinear fracture mechanics for material fracture toughness characterisation. The novel approach is applied to compute the translaminar fracture toughness of a unidirectional glass fibre (GF)/polyamide 6 (PA6) laminated composite. Moreover, the experimental campaign carried out is numerically simulated by means of a micromechanical finite element model, and the fracture toughness is computed by employing two different approaches, that is, the novel one and the MTPM. The present study proves, for the first time, that the Fictitious Material Concept can be applied by considering both experimental and numerical structural responses since it provides, in both cases, quite satisfactory accuracy in term of laminated composite fracture toughness. Therefore, the great advantage is that, when a validated numerical model is available, experimental campaigns may be avoided, saving time and money. Moreover, it is proved that the FMC can be used to investigate specimen size effect on fracture toughness. [ABSTRACT FROM AUTHOR]

Automated Fiber Placement (AFP) is a manufacturing technique widely used for the serial production of aerospace parts. A deep understanding of the effect of lay-up defects is crucial for part and lay-up design. Currently, numerical models for structural simulation lack a precise representation of the internal structure of AFP laminates, which is crucial for understanding the impact of defects on mechanical properties. This paper presents a novel approach based on high-resolution micro-computed tomography (micro-CT) scans from specimens manufactured with AFP, which automatically creates a mesoscale numerical model incorporating as-fabricated defect morphologies. The hexahedral mesh, generated from the segmented plies of the micro-CT volume, accounts for ply thickness and out-of-plane fiber orientation. This approach is verified with mechanical testing and digital image correlation (DIC) under tensile loading. The simulation results align closely with experimental testing and accurately illustrate the influence of fiber waviness in various defect configurations, such as gaps and overlaps. The study shows that lay-up defects can lead to knockdown factors of up to 12% in tensile properties, with each defect creating a distinct pattern in the local strain. This model can serve as a benchmark for further numerical simulations and surrogate models of defect configurations under varying loading conditions. • Generation of a robust hexahedral mesh of AFP laminates with defects based on micro-CT. • Mapping of local out-of-plane fiber orientation. • Identification of distinct patterns in the elastic deformation. • Accurately capturing effective macromechanical behaviour. [ABSTRACT FROM AUTHOR]

Ply-drop (PD) is the termination of specific plies for laminated composite structures to obtain continuous thickness changes. It brings flexibility to the design of tapered composite laminates. However, as a structural defect, ply drops could have an impact on performance. Considering the impact of ply drop during stacking sequence design can provide more accurate performance analysis, but this will bring challenges in modeling and optimization. To consider the PD impact and achieve convenience in optimization, this paper proposes a high-fidelity finite element automatic modelling method of tapered laminates and corresponding optimization framework. By parameterizing the PD information and defining the basic elements and nodes of start stacking surface of the structure, the entire finite element model is layer-wisely constructed and controllable. Subsequently, based on the genetic algorithm framework, a repair strategy and its genetic operations are proposed to ensure that the design variables satisfy the ply-drop design guidelines. And a detailed optimization process is provided. Finally, the strength and deflection performance optimization problem of a tapered laminate with PD from 28 layers to 16 layers under three-point bending test is introduced for illustration of the proposed automatic modeling and optimization method. Comparisons between simulation results and experimental data of the obtained optimization solution verify the effectiveness of the proposed modeling and optimization method. [ABSTRACT FROM AUTHOR]

• A quasi-fiber scale model of three-dimensional braided composite was constructed to investigate the compressive behavior. • The internal yarn primarily bears the stress of the composites with a braiding angle of 20°. • The surface yarn predominantly carries the stress of the composites with a braiding angle of 40°. • The deformation of yarn cross-section results in uneven distributions of stress and strain, leading to catastrophic failure. The three-dimensional braided composites (3DBCs) possess a complex spatial structure, which can lead to microscopic deformation of fibers under high-speed impact. This paper proposes a quasi-fiber scale model using virtual fiber-embedded (VFE) method to simulate the impact behavior and failure of 3DBCs. The results reveal that the maximum eccentricity of the VFE model yarn cross-section is 0.318, representing a 194% improvement compared to solid yarns. According to the characteristics of damage, it can be deduced that interactions among fibers play a pivotal role in determining the failure behavior of composites, particularly concerning non-linear changes. The modulus, strength and the time of initial damage rise with an increasing braiding angle, whereas the resin stress, yarn stress, and degree of damage exhibit opposite trends. The stress distribution over the braiding path shows that the main load-bearing component at 20° braiding angles is internal yarns, whereas the surface yarns take precedence at 40°. The maximum deformation of the yarn cross-section always occurs at the center of the shear band, with a maximum eccentricity of 0.456 at 20° braiding angles. The deformation in yarn flexing and cross-section flattening cause an uneven distribution of stress and strain, leading to localized damage and ultimately catastrophic destruction. [ABSTRACT FROM AUTHOR]

• For the first time, silicon carbide fiber (SiC f) was adopted as the main resonator to stimulate resonance, while SiC f and carbon fiber (C f) work together to support resonance modes and adjust energy dissipation. • Based on pure absorption mechanisms, the single layer structure realizes the efficient absorption with reflection loss less than −10 dB within the 10.6–18 GHz frequency band, and the double layer structure has an efficient absorption band of 11 GHz. • For the first time, the electromagnetic loss mechanism is illustrated by the phase time of the electromagnetic resonance excited by the material. Broadband and efficient electromagnetic wave absorbers have always been a hot research topic due to their wide application needs. Herein, silicon carbide fiber (SiC f) and carbon fiber (C f) were introduced to construct a composite fibers structure. The structure supports the resonant modes and regulates the electromagnetic energy dissipation through the coordination of SiC f and C f. Based on pure absorption mechanisms, the single layer structure realizes the efficient absorption with reflection loss less than −10 dB within the 10.6–18 GHz frequency band, and the double layer structure has an efficient absorption band of 11 GHz. Experimental and numerical analysis show that SiC f and C f generate different resonance modes and loss mechanisms respectively under the excitation of incident electromagnetic field, which can complement and enhance energy dissipation over a wide frequency range, ultimately achieving the broadband absorption performance of the structure. The composite fibers structure proposed in this paper has the advantages of simple structure, easy preparation, small outline, lightweight, and broadband efficient absorption. In addition, it provides a new idea for the design of composite fibers structure for electromagnetic wave absorption. [ABSTRACT FROM AUTHOR]

• General exact closed-form solution for rectangular FG beams are derived. • Application of closed-form solutions does not require reconsideration of load conditions. • Retaining the first few terms of the exact solution also achieves high accuracy. • A novel three-parameter power-law modulus is presented. • Explicit special solutions for four cases with quadratic loads are obtained. This paper derives the exact general elasticity solution for functionally graded rectangular beams subjected to arbitrary normal and tangential loads and with arbitrary end constraints. The general solution consists of bending moments and their integrals and derivatives, along with load-independent function sequences of the longitudinal coordinate. The method for determining function sequences has been established based on the stress function method. General solution formulas for stresses, strains and displacements have been derived and used to solve explicit special solutions for six cases involving concentrated forces, uniformly loads, and quadratically distributed loads with different displacement constraints scenarios. The results obtained are compared with existing exact solutions and those of Euler–Bernoulli and Timoshenko beams, and the errors of the latter two are analysed. [ABSTRACT FROM AUTHOR]

This paper introduces a novel approach to infer the material properties of multiscale material systems through a variety of experimental scenarios. We utilize the hierarchical Bayesian paradigm which enables us to integrate multiple experimental data at different length scales and/or different material compositions, in a systematic way. Specifically, a probabilistic model is constructed which implements the Transitional Markov Chain Monte Carlo method to extract samples from the posterior distributions of both the multiscale model parameters and the hierarchical hyperparameters. The posterior distribution of the hyperparameters encapsulates the information from all the different experiments and it is utilized to derive an informed set of physical parameters, which can be used for making predictions in future material models. Feed forward neural networks play a crucial role in mitigating the computational effort of implementing the hierarchical Bayesian analysis on top of multiscale nonlinear computational homogenization analyses. Their purpose is to learn and accurately emulate the nonlinear constitutive law across multiple length scales. The proposed methodology is demonstrated on a case study of carbon nanotube (CNT) reinforced cementitious material configurations through the investigation of the CNT interfacial mechanical behavior. The hierarchical Bayesian framework is applied on a set of measurements gathered from independent literature experiments performed on dissimilar material compositions on the macroscopic structural scale. [ABSTRACT FROM AUTHOR]

• Dielectric properties of GFRP are affected by tension–compression fatigue by changing the damage state inside the material. • Fatigue-induced structure change will decrease the PDIV and breakdown strength of GFRP by changing the charge transport and dielectric polarization behaviors. • The stiffness of GFRP after fatigue shows a significant positive linear relationship with conductivity, and a negative relationship with breakdown strength. However, the relationship with dielectric constant is not obvious. • The insulation performance changes caused by fatigue need to be carefully considered during material selection and design for electrical equipment subjected to dynamic loads. Glass fiber reinforced polymer (GFRP), used in insulating components like insulation rods, needs to withstand both high voltage and large dynamic mechanical fatigue during operation. In this paper, the effects of tension–compression fatigue loads on the dielectric properties of GFRP under various fatigue cycles and stress levels are investigated. The results show that DC conductivity has a strong negative correlation with stiffness, while breakdown strength is showing a positive correlation. Fatigue-induced internal damage could cause continuous charge accumulation and enhanced interfacial polarization, leading to the increase of dielectric constant by 46.89% and the reduction of breakdown strength by 15.05%, when the fatigue span ratio reaches 80% under 40% stress level. Understanding the evolution of dielectric properties of GFRP under dynamic mechanical fatigue conditions is helpful for ensuring the safe and stable operation of electrical power equipment subjected to both high voltage and fatigue loads. [ABSTRACT FROM AUTHOR]

Double-double (DD) laminates are promising replacements for conventional Quad laminates in aerospace applications because of their inherent design simplicity and, more importantly, the ease of tapering. However, the thickness thinning due to tapering will significantly increase the risk of buckling failure. In this paper, we proposed an implicit global & local model for thickness tapering optimization of DD laminates to maximize buckling resistance under the given weight constraint or weight reduction under buckling constraints. Firstly, a global model is established for buckling load calculation, with material properties calculated from homogenization of local laminates using the classical laminate theory. Then, nodal repeats of a four-plies DD sub-laminate are chosen as design variables to interpolate the tapered thickness profile. Sensitivities of structural responses are calculated semi-analytically to achieve efficient gradient-based optimization. Tapering spacing constraints between adjacent thicknesses are introduced to mitigate the potential delamination due to the stress concentrations caused by sharp thickness variation at the cost of a reduced optimization effect. Finally, typical numerical examples show that DD laminates with optimal gradual thickness tapering can remarkably increase the structural buckling resistance or the weight reduction. [ABSTRACT FROM AUTHOR]

Ballistic protection extensively employs curved ultra-high-molecular-weight polyethylene (UHMWPE) laminates to conform to protective targets. However, ballistic tests have indicated that the curvature of laminates increases back-face deformation, diminishing ballistic performance, while the mechanism behind this curvature effect on back-face deformation remains unclear. In this paper, the back-face deformation of curved UHMWPE laminates, including apex displacement and the boundary of the deformation region, are systematically studied through numerical simulation and theoretical analysis. Firstly, a numerical model of curved UHMWPE laminates under the high-speed impact is established. The numerical results indicate that as the curvature increases, the deformation region becomes more concentrated, resulting in a larger apex displacement. Secondly, as the curvature increases from zero, the deformation mode of curved laminates changes from membrane stretching dominated to a combination of membrane stretching and bending. Finally, considering the change in the deformation mode, a theoretical analysis for the propagation of bending waves in an orthotropic curved plate is conducted to reveal the relationship between curvature and back-face deformation. The theoretical analysis shows that increasing curvature slows bending wave speed, reducing in-plane deformation region movement, thus increasing apex displacement. This study is expected to help design curved UHMWPE laminates with better ballistic performance. [ABSTRACT FROM AUTHOR]

This paper addresses reduced order homogenization of composites with strength difference (SD) effects in elastoplasticity coupled to damage, while containing several well-known plasticity criteria as special cases. We extend two approaches for this purpose: 1. nonuniform transformation field analysis (NTFA by Michel and Suquet, 2003) and 2. a recent variant called cluster-based NTFA (CNTFA by Ri et al., 2021), and conduct a comparative study on them. For the NTFA approach, a space–time decomposition is done separately for volumetric and deviatoric inelastic strain fields. A coupled model is derived for the present case to govern the evolution of resulting reduced variables. For the CNTFA approach, a clustering analysis is additionally performed for a spatial decomposition of the micro-domain. Unlike the NTFA, the online analysis is formulated as a unified minimization problem, which does not require a major adaptation for the present case. For both approaches, localization rules are deduced from the superposition principle and then homogenized to obtain the effective responses. FE-based implementation is presented in detail for both approaches. Numerical results show that both approaches provide a striking acceleration rate against conventional FE computations. The CNTFA predictions are more accurate than the NTFA ones by involving clustered microscopic fields in the online analysis, thus resulting into a slightly increased memory requirement. [ABSTRACT FROM AUTHOR]

This paper presents a novel Finite Element (FE) simulation approach to examine the mode I fracture of thick adhesive joints used particularly in the trailing edge of the wind turbine blades. The approach involved FE models of the DCB specimens focusing on aspects overlooked in the existing literature. There has been limited investigation on residual stresses caused by thermal mismatch between composites and adhesives. Similarly, the impact of generating notches/pre-cracks in the adhesive layer during the preparation of Double Cantilever Beam (DCB) specimens on residual stresses has received minimal attention. Additionally, the Cohesive Zone Model, commonly used for simulating elastoplastic adhesives, may be inadequate due to its inability to account for the plastic deformation of the adhesive. In the present work, the pre-cracks were virtually generated in DCB FE models so that their effect on the stresses within the joint could be examined, making it a novel contribution to the field. The components were assigned with appropriate thermal expansion coefficients, and a simulation of the cool-down process was conducted to determine the thermal residual stresses. Furthermore, the Drucker-Prager plasticity criteria were used to capture the elastoplastic behaviour of adhesives in the FE simulations. Concurrently, the T-stresses were assessed through numerical investigations. For validation, experiments were conducted on DCB specimens made of two cross-ply composite laminates bonded with a ∼ 10 mm thick layer of an epoxy-based adhesive. A good agreement between computational and experimental results was observed, confirming the effectiveness and reliability of the proposed approach. [ABSTRACT FROM AUTHOR]

In this paper, a versatile compound strip method (CSM) with non-uniform spline functions is developed for buckling analysis of stiffened structures. The proposed method further extends the existing CSM by permitting the flexible modification of local knots to place the stiffeners along the strip arbitrarily. In addition, a reasonable knot arrangement can achieve an accurate solving procedure with improved convergence. The displacements of stiffeners are expressed compatibly by the fundamental parameters of skin according to the beam-plate model. Consequently, the reinforcement of stiffeners is naturally incorporated by adding the beam stiffness matrix to the corresponding strips. Based on the first-order shear deformation plate theory and non-uniform spline functions, the semi-analytical formulations of stiffened structures are established. The present method provides the possibility to achieve the local mesh refinement in the finite strip methods. The convergence and validation study is demonstrated through the comparisons with the results of the existing literature solution and finite element method. In conclusion, a more efficient and applicable CSM is proposed to analyze the buckling behaviors of stiffened structures. [ABSTRACT FROM AUTHOR]

Three-dimensional woven composites (3DWCs) have received widespread attention due to their advantages, such as integral near-net molding of complex components and high damage tolerance. However, 3DWCs exhibit significant variations in mechanical behavior under various influencing factors, which poses challenges in selecting appropriate application scenarios. In recent years, there has been rapid development in the performance analysis and modeling strategies for 3DWCs, leading to substantial results. This paper provides a comprehensive overview of the mechanical properties and damage mechanisms of 3DWCs under various influencing factors, aiming to facilitate the selection of 3DWCs for different engineering applications and to complement the existing database of mechanical properties. [ABSTRACT FROM AUTHOR]