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Purpose: In comparison to traditional, constant stiffness laminates, variable stiffness composite laminates (VSCL) with curvilinear fibres represent an extra analysis effort. It is the purpose of this work to present and test a relatively simple optimisation procedure, in order to find the maximum fundamental frequency of vibration in bending and in in-plane vibrations. It is also intended to explain why certain fibre paths lead to higher frequencies. Methods: The optimisation is performed using a genetic algorithm (GA), which is described in detail. The bending and the in-plane plate models are based on the p-version Finite Element Method. Each model requires a small number of degrees of freedom, an important feature because applying the GA involves the solution of a large number of eigenvalue problems. In order to support the physical interpretation of the optimal designs, mode shapes and stress fields corresponding to some optimal solutions are illustrated. Results: Single- and multi-layer plates with different boundary conditions and fibre path types are studied. Fibre paths that lead to maximum fundamental frequencies are found and justified. The consequences that maximising the first frequency has on the higher-order modes of vibration are studied. Conclusion: The proposed optimisation and modelling methods are effective. Curvilinear fibres with the characteristics considered led to the maximum first natural frequency of vibration in a few cases, but not all. Particularly in in-plane vibrations, curvilinear fibres can provide major gains in comparison to straight fibres. The increase in the vibration frequency is accompanied by, overall, larger stresses. [ABSTRACT FROM AUTHOR]

An experimental analysis was conducted to investigate the use of external steel plates as tensile reinforcement in concrete beams with prefabricated cages and its failure pattern. A prefabricated cage with an external steel plate as tensile reinforcement and stirrups welded directly to the steel plate was used as the rebar cage for the reinforced concrete beam. This work aims to explore the feasibility of external steel plates as tension reinforcement in terms of their bending behavior and deformability till the failure stage. Twelve specimens with the same beam geometry and concrete grade were used. The ultimate load, load–deflection characteristics, and crack pattern have been studied with respect to the control beam. There are four sets of specimens, which are control beam, plate-reinforced concrete beam, control beam with bent-up bar, and plate-reinforced concrete beam with bent-up bar. Two approaches have been taken in this study: an in-house experimental investigation incorporating theoretical analysis and a numerical simulation utilizing finite element approach (FEA). The obtained experimental data indicated a firm agreement of around 94.7–100% with that of the reference beam with the reduction of crack width, number of cracks, and compressive strain on the steel plate-reinforced beams. [ABSTRACT FROM AUTHOR]

In this paper, the extended layerwise method (XLWM), which was developed for laminated composite beams with multiple delaminations and transverse cracks (Li et al. in Int J Numer Methods Eng 101:407-434, 2015), is extended to laminated composite plates. The strong and weak discontinuous functions along the thickness direction are adopted to simulate multiple delaminations and interlaminar interfaces, respectively, whilst transverse cracks are modeled by the extended finite element method (XFEM). The interaction integral method and maximum circumferential tensile criterion are used to calculate the stress intensity factor (SIF) and crack growth angle, respectively. The XLWM for laminated composite plates can accurately predicts the displacement and stress fields near the crack tips and delamination fronts. The thickness distribution of SIF and thus the crack growth angles in different layers can be obtained. These information cannot be predicted by using other existing shell elements enriched by XFEM. Several numerical examples are studied to demonstrate the capabilities of the XLWM in static response analyses, SIF calculations and crack growth predictions. [ABSTRACT FROM AUTHOR]

The plate resting on the elastic foundation is an issue of mutual action between two media. The elastic foundation has important impact on static response of composite plates, while accurate prediction on transverse shear stresses of laminated composite plates resting on elastic foundation and subjected to hygro-thermo-mechanical effects is scare in literature. To fill this gap, this paper proposes a higher-order global-local model (HGLM) satisfying the continuity conditions of transverse shear stresses at interfaces. Based on the model HGLM, analytical solution for the governing differential equations of the simply supported composite plate subjected to mechanical loading, temperature and moisture concentrations is developed by employing Navier's technique followed by the procedure of the separation of variables. Comparing the present results with the available elasticity solutions, it is found that the proposed model HGLM can produce promising transverse shear stresses directly from constitutive equations. Based on the model HGLM, the elastic foundation parameters, stacking sequence and thermal expansion coefficients did have significant effects on the hygro-thermo-elastic response of composite plates. However, the other models lose capacity to simulate the effects of the elastic foundation parameters on displacements and stresses for hygrothermal expansion of composite plates. [ABSTRACT FROM AUTHOR]

The response of multilayered plates with imperfectly bonded interfaces and delaminations to quasi static and dynamic loadings is conveniently studied by assuming the displacements as two length-scales fields, given by global displacements, which are continuous in the thickness, and local perturbations or enrichments, which account for the multilayered structure and the jumps at the interfaces. The a priori imposition of interfacial continuity conditions then leads to a homogenized field defined by the global variables only. The number of displacement unknowns is independent of the number of layers and is equal to five or six, for sliding or mixed mode interfaces, respectively. Dynamic equilibrium equations are derived using variational principles. This effective idea, which was originally proposed in the zigzag theories for fully bonded plates, was first applied to plates with imperfect interfaces by Cheng et al. (J Appl Mech, 63:1019-1026, ), Schmidt and Librescu (Nova J Math Game Theory Algebra, 5:131-147, ), and Di Sciuva (AIAA J, 35(11):1753-1759, ). These pioneering models, as all subsequent models which extend the theories to various problems, suffer from a common omission in the treatment of the interfacial energy in the derivation of the equilibrium equations, which leads to solutions which are accurate only for fully bonded/debonded plates. In this paper a linear, first order model which resolves the inaccuracy and extends the theories to more general interfacial traction laws is presented along with the corrected formulations of the original models. The formulations are validated using exact 2D elasticity solutions for multilayered plates in cylindrical bending. [ABSTRACT FROM AUTHOR]

The modal testing and numerical results on free vibration behavior of completely free woven fiber glass/epoxy-laminated composite shallow shell panels are presented in this investigation. The finite element numerical model is established by a doubly curved shell model on the basic of first-order shear deformation theory (FSDT). Vibration study of the composite shell panels is carried out using a quadratic eight-noded isoparametric element. The modal testing experiments are carried out using FFT analyzer with PULSE software to determine natural frequencies of woven fabric glass/epoxy composite cylindrical shell panels under free–free boundary condition. The first four natural frequencies of completely free woven fabric glass/epoxy laminated cylindrical shell panels are obtained for different curvature ratios, sequences of lamination and number of laminate layers. The modal test values illustrate an excellent concurrence with the numerical values and will serve as bench mark for future investigators in the present area. [ABSTRACT FROM AUTHOR]

Purpose: The current analytical study is devoted to examining the nonlinear free vibration behavior of the laminated nanocomposite cylindrical shells containing multi-scale hybrid reinforcements once a nonlinear three-parameter substrate surrounds the structures. The multi-phase material of the structures includes polymeric matrix, nano-scale GOPs, which are uniformly distributed through the thickness of each layer and macro-scale carbon fibers with various orientation angles. Methods: The effective material properties of each multi-phase nanocomposite layer are calculated by implementing the modified Halpin–Tsai micromechanical scheme together with the extended rule of the mixture in a hierarchy. After that, with an incorporation of the improved Donnell's shell theory and Hamilton's principle, the governing equations are derived. Then by adopting a two-step solution technique, these nonlinear equations are transferred to one ordinary differential equation via Galerkins' method, and in the next step, the nonlinear frequencies of the structure are obtained by employing the multiple scale technique. Results: In the framework of various graphical results, a parametric analysis is conducted in detail to reveal the influences of the different parameters such as nonlinear foundation parameters, carbon fibers' orientation angles, GOPs' weight, and carbon fibers' volume fractions and length-to-radius ratios on the nonlinear vibration characteristics of the multi-phase laminated nanocomposite cylindrical shell. Conclusions: The results declare that the addition of the GO nanofillers along with the CFs and also embedding the structure on the nonlinear substrate can significantly enhance the vibrational behavior of the multi-phase laminated nanocomposite cylindrical shell. [ABSTRACT FROM AUTHOR]

This study aims to investigate the tensile strength of the polypropylene-based bio-composites reinforced with natural kenaf fibers, basalt fiber, and nanographenes. The response surface methodology was used to investigate the behavior of the bio-composites based on the weight percentage of basalt and kenaf fibers and nanographenes. The behavior of the samples was analyzed using the tensile test, and the results were interpreted using field emission scanning electron microscope images. The fracture surface of the samples indicated the fibers' breakage and their separation as well as the pullout of the fibers from the substrate as the main mechanisms in improving the behavior of the bio-composite under study. Then, the multi-objective optimization was performed by increasing the tensile strength and elastic modulus and reducing the weight of the samples, and a Pareto diagram was drawn according to the design objectives. The results showed that the bio-composite sample in the optimal status with the maximum tensile strength of 30.9481 MPa and the lowest weight includes 15% kenaf fibers and 0.862% graphene nanoparticles. Moreover, the optimal sample of the bio-composite with the highest elastic modulus of 3.5126 GPa and the minimum weight of 1.626 g consists of 15% of kenaf fiber and 1.5% of graphene nanoparticles. Twenty-seven percent reduction in composite weight by optimizing the amount of reinforcements causes the weight of the final structure to be significantly reduced in the use of these composite plates in high volumes. [ABSTRACT FROM AUTHOR]

This research investigates the nonlinear thermal stability responses of functionally graded graphene-reinforced composite (FG-GRC) laminated plates with embedded circular and elliptical delamination as well as edge delamination, subjected to a uniform temperature rise and a variety of mechanical boundary conditions. The thermomechanical properties of the GRCs are estimated using the extended Halpin–Tsai micromechanical model that incorporates efficiency parameters to take into account nanoscale size and surface effects of the graphene reinforcement. The von Karman geometrical nonlinearity is adopted in a solution based on the third-order shear deformation theory. The nonlinear equilibrium equations derived by the minimum total potential energy principle are solved using the Ritz method in conjunction with the Newton–Raphson iterative procedure. Parametric studies reveal that the types of graphene distribution pattern and geometry of delamination zones have a substantial effect on the thermal equilibrium paths and buckling temperature of the GRC delaminated plates. FG-X graphene sheet pattern raises the critical buckling temperature and compressive strength of the baselaminate and reduces the nonlinear thermal postbuckling deflection; however, it causes a significant increase in normal stress distribution at the top and the bottom surfaces of the delaminated plates. [ABSTRACT FROM AUTHOR]

This study presents the vibroacoustic analysis of a hybrid epoxy composite panel reinforced with advanced multi-walled carbon nanotubes (MW-CNTs) and luffa fibre. The vibroacoustic responses were obtained numerically, and the model validity was verified with experimental values. The responses were analysed under the stimulus of harmonic point excitation, considering ambient conditions, using a coupled finite element–boundary element (FE–BE) model. To ensure the accuracy and stability of the numerical model, the different structural responses, including natural and thermal frequency, of hybrid composite plates, were evaluated and compared with data from published literature. In addition, experimentation was conducted, and the results were compared with the numerically derived model to demonstrate the model's effectiveness. Furthermore, several numerical examples were solved using the numerical model to illustrate its applicability and enhance understanding. The results obtained from the experimental investigation showed that adding luffa fibre and MW-CNTs to the composite panel improved its sound transmission loss and absorption coefficient. Overall, the results suggest that the hybrid composite panel has excellent vibroacoustic performance and can be used in various engineering applications that require lightweight, high-strength materials with good damping and noise reduction properties. [ABSTRACT FROM AUTHOR]

Already in the early 1980's, it has been conjectured that the pulsed ultrasonic polar scan (P-UPS) provides a unique fingerprint of the underlying mechanical elasticity tensor at the insonified material spot. Until now, that premise has not been thoroughly investigated, nor validated, despite the opportunities this would create for NDT and materials science in general. In this paper, we report on the first-ever implementation of an inverse modeling technique on the basis of a genetic optimization scheme in order to extract quantitative information from a P-UPS. We validate the optimization approach for synthetic data, and apply it to experimentally obtained polar scans for annealed aluminum, cold rolled DC-06 steel as well as for carbon fiber reinforced plastics. The investigated samples are plate-like and do not require specific preparation. The inverted material characteristics show good agreement with literature, micro-mechanical models as well as with results obtained through conventional testing procedures. [ABSTRACT FROM AUTHOR]

The strengthening of steel structures in situ with externally bonded fiber-reinforced plastic (FRP) composite sheets is increasingly being used for the repair and rehabilitation of existing structures. The previous researchers have developed several analytical methods to predict the interface performance of bonded repairs. An important feature of a reinforced steel beam is the significant stress concentration in the adhesive at the ends of the FRP plate. In this paper, a closed-form solution for the interfacial shear and normal stresses in simply supported steel beams strengthened with a bonded FRP plate and subjected to thermomechanical loadings is presented. The shear strains of the adherends are included in the present theoretical analysis by assuming a parabolic distribution of shear stress across their thickness. Contrary to some existing studies, the assumption that both adherends have the same curvature is not used in the present study. The results of this numerical study are beneficial for understanding the mechanical behavior of material interfaces and for the design of hybrid FRP-reinforced steel structures. [ABSTRACT FROM AUTHOR]

Results related to the buckling delamination of elastic and viscoelastic composite plates are reviewed and analyzed. They have been obtained during the last fifteen years by the author and his students. The plates contain cracks whose faces have initial infinitesimal imperfections. The evolution of the imperfections under compression of the plates is studied, and the values of critical parameters are determined from a criterion of initial imperfection. The study is performed with the use of 3D geometrically nonlinear field equations. In the present paper, the historical background of the problems is outlined considered, general remarks about the field equations and solution method are made, and problems related to the plane strain state are reviewed. [ABSTRACT FROM AUTHOR]

In the present paper, fundamental frequency optimization of symmetrically laminated composite plates is studied using the combination of Elitist-Genetic algorithm (E-GA) and finite strip method (FSM). The design variables are the number of layers, the fiber orientation angles, edge conditions and plate length/width ratios. The classical laminated plate theory is used to calculate the natural frequencies and the fitness function is computed with a semi-analytical finite strip method which has been developed on the basis of full energy methods. To improve the speed of the optimization process, the elitist strategy is used in the Genetic algorithm. The performance of the E-GA is also compared with the simple genetic algorithm and shows the good efficiency of the E-GA algorithm. A multi-objective optimization strategy for optimal stacking sequence of laminated box structure is also presented, with respect to the first natural frequency and critical buckling load, using the weighted summation method to demonstrate the effectiveness of the E-GA. Results are corroborated by comparing with other optimum solutions available in the literature, wherever possible. [ABSTRACT FROM AUTHOR]

This paper presented a systematic approach toward localized failure inspection of internally pressurized laminated ellipsoidal woven composite domes. The domes were made of thin glass fiber reinforced polymer (GFRP) woven composite layups [0,0,0], [0,30,0], [0,45,0], and [0,75,0]. The analytical results demonstrated that the circumferential regions near meridian φ = 45° in prolate ellipsoidal domes and near meridian φ = 90° in oblate ellipsoidal domes sustain the highest deformation under internal pressure. This observation was then confirmed by the numerical and experimental results. In addition, the numerical and experimental results showed localized rather than uniform failure in those regions, irrespective of changes in laminate stacking sequence. It was observed that localized failure occurs since the woven fibers configuration in some areas of woven remains in initial geometry (square shape), while the rests are deformed into the rhombic shape. In other words, by moving along the circumferential direction from the area close to θ = 0° to θ = 45° and θ = 45° to θ = 90°, the shape of woven fibers gradually changes from square (strong area) to rhombic (weak area), and rhombic to square, respectively. Thus, to minimize failure pressure, the meridian region vulnerable to failure must initially be identified. Afterwards, the rhombic regions in the circumference corresponding to that meridian must be strengthened. [ABSTRACT FROM AUTHOR]

This paper presents the nonlinear free vibration analysis of laminated composite plates resting on elastic foundation with random system properties in thermal environments. System parameters are modeled as basic random variables for accurate prediction of system behavior. A C0 nonlinear finite element based on HSDT in von Karman sense is used to descretize the laminate. A direct iterative method in conjunction with first-order perturbation technique is outlined and applied to solve the stochastic nonlinear generalized eigenvalue problem. The developed stochastic procedure is successfully used for thermally induced nonlinear free vibration problem with a reasonable accuracy. Numerical results for various combinations of boundary conditions, geometric parameters, amplitude ratios, foundation parameters and thermal loading have been compared with those available in literature and an independent MCS. Some new results are also presented which clearly demonstrate the importance of the randomness in the system parameters on the response of the structures. [ABSTRACT FROM AUTHOR]

In this paper, the third-order shear deformation theory is employed to study static and dynamic deflection control of laminated composite plates. The effects of shear deformation and geometric nonlinearity (in the von Kármán sense) on the bending and transient response are investigated using the finite element method. Magnetostrictive material, Terfenol-D, layers are used to actively control the deflection via simple negative velocity feedback control in a closed loop. The effects of the lamination scheme, types of load, and boundary conditions on the deflection are investigated. [ABSTRACT FROM AUTHOR]

Laminated plates with holes are often used in industrial applications such as aeronautics, automobiles, and marine. It is necessary to present a study of the combined effect of deformation theories and thickness variation for the laminated plate with a hole. This manuscript considers analysis theories named: Kirchhoff, layer-wise, and Reissner-Mindlin, to study their validity for different thickness aspect ratios under transverse compression loading. Studies are conducted on CFRP laminate (symmetric cross-ply and quasi-isotropic), and the performed numerical (FEM) analysis processes are validated through existing literature. Transverse shear, circumferential, radial, and radial-hoop stress variations with stress concentration factors are presented along the thickness and around the hole configurations (18 cases are covered) of the plate. Also, the resultant effects are discussed on in-plane, and out-of-plane stresses for laminates to specify the selection of design conditions (theory, thickness, model, and laminates). This research may provide engineers and researchers with various assessments and design insight for laminate structures with a hole. [ABSTRACT FROM AUTHOR]

Recently, the demand for lightweight multilayered parts in electronics and biomedical fields has been accelerated and shown great interest in understanding the combined effect of multilayered materials. However, these industries are still facing the challenge of developing dissimilar multilayered materials that can be suitable for biomedical applications. In this context, magnesium emerges as a promising biocompatible material used for several biomedical applications. However, the issues related to joining magnesium alloys with other similar materials still need to be solved. Moreover, friction stir additive manufacturing (FSAM) occupies a niche domain for developing or joining biocompatible materials such as magnesium alloys with low weight and high strength. Therefore, the present work highlights the development of a multipurpose three-layered multifunctional laminated composite plate of magnesium-based AZ31B–Zn–Al 1100 through the FSAM route. Microstructural and morphological examinations were carried out by light microscopy and FESEM equipped with EDS analysis and line mapping. Moreover, the grain refinement at the interfaces during the FSAM was also addressed using the electron backscattered diffraction (EBSD) study. Further, investigation on mechanical properties such as tensile test with fractography analysis and microhardness variation at the cross-section of the built-up section has been investigated. Furthermore, the corrosion and tribological analysis was also performed, and a 3D profilometer was used to visualize the corroded and worn-out surfaces. The microstructural results revealed that the average grain size of 6.29 μm at interface AZ31B–Zn and 1.21 μm at interface Zn–Al 1100 occurred, improving the bonding strength and overall properties. The tensile strength has occurred as 171.5 MPa at 15.5% elongation, whereas maximum microhardness is reported as 105 HV at the interface of AZ31B–Zn and 84.6 HV at the interface of Zn–Al 1100. The corrosion rate was calculated as 0.00244 mm/day, and the average coefficients of friction (COF) for both the interfaces, such as AZ31B–Zn and Zn–Al 1100, are 0.309 and 0.212, respectively. [ABSTRACT FROM AUTHOR]

Mg/Al composites were successfully fabricated by the differential temperature + asymmetrical rolling (DTAR) and the isothermal + symmetrical rolling (ISR), respectively. The effects of DTAR and ISR on the tensile properties, bonding strength, interface morphology, and microstructure of composite plates were investigated. The results indicated that grains near the Mg layer of the Mg/Al interface were fine and equiaxed because of the occurrence of dynamic recrystallization on the Mg layer. In contrast, the grains at the center and near the Al side interface were elongated. DTAR enhanced the recrystallization degree of Mg side grains. The tensile properties and bonding strength of the composite plates increased gradually with increase in reduction rate, while the interface morphology was gradually flat with increase in reduction rate. The ultimate tensile strength of DTAR sample reaches 205 MPa, which is 25% higher than that of ISR sample. [ABSTRACT FROM AUTHOR]

The stability behaviour of unsymmetrical laminated structures made of fibre-reinforced plastics is significantly influenced by bending–extension coupling and the comparatively low transverse shear stiffnesses. The aim of this work is to improve the analytical stability analysis of unsymmetrically laminated structures. With the discrete plate theory, the stability of laminated structures can be reduced to single laminated plates. The structure is divided into individual segments, and the surrounding structure is modelled by rotational elastic restraints. The governing equations for single plates under specific boundary conditions can be solved exactly with Lévy-type solutions. In this study, Lévy-type solutions for the mentioned boundary conditions under biaxial compressive load is described for the classical laminated plate theory, the first-order shear deformation theory and the third-order shear deformation theory (TSDT). In addition to transverse shear, bending–extension couplings of unsymmetrical cross-ply and antisymmetrical angle-ply laminates are considered. For the implementation of boundary conditions for the rotational restraints in the context of TSDT, a new set of conditions is formulated. The investigation shows very good agreement of the buckling load with comparative finite element analyses for different layups. [ABSTRACT FROM AUTHOR]

In this work, the nonlinear post-buckling of an advanced porous nanocomposite plate with and without imperfection subjected to a hygro-thermo-mechanical load and lying on elastic foundation is carried out using third-order shear deformation theory (TSDT). Also, a modified form of a Halpin-Tsai (M-H-T) micromechanical model is proposed to characterize the mechanical properties of graphene oxide powder (GOP)-reinforced polymer nanocomposite. To this aim, the influence on random distribution, non-straight shape and agglomerated state of the GOPs is adequately incorporated into the M-H-T model. Also, two porosity distributions including symmetric and asymmetric are considered. Both the linear and nonlinear influence of temperature and moisture concentration on the bending response are probed. Large deflection theory is considered to extract the stress field and displacement field for the perfect and imperfect nanocomposite plate. Navier solution is used to solve the large deflection nonlinear equations. Numerical results are validated by existing results in the literature. A parametric investigation is established to discuss the effects of the temperature rise and moisture concentration, elastic foundation coefficients, nanoparticle geometry, aspect ratio, porosity distributions, and geometry imperfection on the GOP-reinforced polymer composite post-buckling behaviors. [ABSTRACT FROM AUTHOR]

A graphene-reinforced composite plate (GRCP) with a sandwich-like structure is proposed. The nonlinear mechanical characteristics of the sandwich-like GRCP are investigated and compared to those of functionally graded and uniform GRCPs. The modified Halpin-Tsai model is employed to estimate the material parameters, and the Hamilton principle is used to derive the governing equation for the composite plates. The effects of the graphene nanoplatelet (GPL) distribution patterns, weight fraction, and the number of layers on the static and dynamic nonlinear responses of the plates are investigated. The results show that the various GPL distribution patterns have different enhancement effects on plates. Compared with the graded and uniform distribution patterns, the sandwich-like distribution pattern has significant advantages in terms of anti-vibration and anti-bending properties. Furthermore, it is found that the stresses of the sandwich-like GRCPs are discontinuous, there exist stress mutation phenomena between the surface layers and the pure matrix layer. [ABSTRACT FROM AUTHOR]

Background: In order to design thin-walled components it is necessary to consider the presence of holes and their effects. For high performance composite structures, this is still an issue, since usually only coupons are used in experimental observations and the influence of free edges and the hole affects the fatigue behavior mutually. Objective: This work aims to find, through experimental trials, an empirical model that can be used to describe and predict the damage propagation, originating from a circular hole. Methods: A fatigue test series is performed and the damage initiation and propagation is monitored with three-dimensional digital image correlation, with which the occurring damage can be measured. Validation of the experimentally induced damage size measured with digital image correlation is performed intermediate with an in-situ measurement with active thermography and phased array ultrasonic. The novelty of this approach is that wide specimens are used, where the influence of the free edges on the hole does not occur. Results: The progression of the detected damage over the test reflects the applied loads, where higher loads cause larger damage. For all defined load levels a similar damage propagation is identified, allowing to establish an empirical model and fit it to the test data. Conclusion: The proposed empirical model provides a novel approach to describe and predict damage propagation originating from a circular hole in thin-walled composite plates. In addition, it is shown that the damage propagation ceases for the selected plate configuration and thus does not lead to a complete failure. [ABSTRACT FROM AUTHOR]

This study investigated the manufacturability of ultra-strength steel-Al plate composite, the punch-cutting performance of these composites and base materials, and the cutting surface properties. Therefore, experimental studies included explosive welding, punching process, and materials characterisations (microstructure and sheared surface image analyses via SEM, hardness and tensile test). In the punching process, five different types of punches were used. Additionally, the load cell was mounted on the punch and connected to the computer by an amplifier and a data acquisition card; the force values corresponding to the processing times were directly monitored, and the data were obtained. Shear process analyses were performed using finite elements. Microstructure and mechanical test results show that the DP1200 steel-Al 1100 aluminium laminated bimetal composite was produced by explosive welding of acceptable quality. The flat punch showed the highest shearing force, and other punches (angled and concave ends) reduced the shearing forces P R2, P V16, P R1, and P 16, respectively. Punches with different cutting-edge forms reduced the shearing force by up to 75%. The sheared surfaces were investigated in detail. Shearing marks were observed on both sides of the bimetal similarly. The punching process force vs time results showed good agreement between modelling and experimental punching values. [ABSTRACT FROM AUTHOR]

The interface thermoelastic behavior of multi-layered structures under severe loads is a particularly important issue. Different from the previous generalized thermoelastic model, the Dual-Phase-Lag generalized thermoelastic model considering interface conditions is reestablished based on peridynamics in this manuscript. The model inherits the nonlocality of peridynamics, captures the thermal barrier at the interface, and can better deal with the discontinuous behavior at the interface. The monolithic algorithm is used for numerical model validation that is a sandwich plate subjected to thermal shock and subsequent calculation. On this basis, the influence of parameters, such as the horizon size, temperature gradient relaxation time, on the thermoelastic response behavior is studied. The thermoelastic responses with cracks and crack propagation at the interface were also carried out. It helps to better understand the effect of interfacial cracks in laminated plate subjected to thermal shocks. Finally, the analysis results are summarized. [ABSTRACT FROM AUTHOR]

The optimal design of multilayer substrates containing the cutout under compressive loads is fundamental to achieving maximum buckling resistance compared to structural weight, especially in aerospace structures. In this study, buckling and post-buckling behavior of composite laminated plates with orthogonal and symmetrical lay-up containing cutouts with different diameters have been investigated experimentally, semi-analytically, and numerically. Based on the first-order shear deformation theory, a finite strip method is developed to study the buckling of the composite laminates with cutout semi-analytically. A finite element method was used for numerical analysis. The required mechanical properties were obtained from standard tests. The current study results show that the size of the cutout diameter doesn't have a considerable effect on the elastic rigidity of the plate. Still, the buckling load decreases significantly by increasing the cutout diameter. Also, the plate's buckling load and elastic rigidity are increased considerably by increasing the number of composite layers. The thickness of the plate has more effect on the buckling load than the diameter of the cutout. The present study shows a good correlation between the results of buckling behavior derived from semi-analytical and finite element methods with experimental results. [ABSTRACT FROM AUTHOR]

The subject of this paper are thin composite rectangular plate. The plates are made of two families of ribs and homogeneous material of a matrix. The main feature of the considered plates is, that a distance between the ribs is comparable to the thickness of the plate. The widths of the ribs can vary slowly in the midplane of the plate. This allows you to get a desirable frequency of natural vibrations of the plate. The formulation of averaged model equations is based on the tolerance averaging approach (Wozniak et al. 2008, 2010). The general results of the contribution are illustrated using the analysis of natural vibrations of the plates under consideration. It will be carried out validation of the obtained mathematical model by comparison of results from obtained model equations with results from finite elements method (Abaqus program). [ABSTRACT FROM AUTHOR]

To investigate the dynamic response of circular and ellipse sandwich plates, a higher-order model with five displacement parameters has been proposed, which can fulfill compatible conditions of transverse shear stresses at the interfaces. Based on the proposed model, the finite element formulation has been developed, where the refined-element method is utilized to solve the compatible relation of first derivatives of transverse displacement on the common edges of adjacent elements. By analyzing free vibration of sandwich plates made up of aluminum/composite face sheets and polymethacrylimide core, the performance of the proposed model has been verified. In addition, influence of material properties and geometric parameters on natural frequencies has been also investigated. Results show that displacement modes in the ellipse plate differ from those of the circular plate attributing to different stiffness along x and y directions. Moreover, the ratios of major axis to minor axis have a severe impact on natural frequencies of ellipse sandwich plates. Stiffness of sandwich plates can be explicitly improved by applying the composite face sheets. Furthermore, the relative stiffness of sandwich circular plate can be further improved by changing the lamination configuration, which can demonstrate good designability of sandwich plates with composite face sheets. [ABSTRACT FROM AUTHOR]

Uncertainties caused by the deviation of functionally graded reinforcements from the ideal linear distribution form are unavoidable during the manufacturing process, and this can significantly influence the vibrational behavior of carbon-based nanocomposite plates. In this context, this work aims to carry out a detailed parametric study on the free vibration response of laminated composite plates made of multi-layer carbon-based nanocomposite plies, considering both linear and nonlinear distribution forms of the nano-reinforcements. Materials constituting the plies are nano-reinforcement-based carbon nanotubes (CNTs) embedded in a polymer matrix. The CNTs are assumed to be either uniformly distributed (UD) or functionally graded (FG) across the ply thickness. Two types of laminated plate arrangements are comparatively investigated. The effective material properties such as elastic modulus and mass density are derived using the extended rule of mixture, whereas the governing equations are obtained through the combination of the Lagrange equation of motion and the first-order shear deformation theory (FSDT). The natural frequencies of the carbon nanotube-reinforced composite (CNTRC) laminated plates are obtained using the finite element method. The accuracy of the present numerical model is validated by comparing our results with those published in the open literature. The obtained numerical results show that both the plate layout arrangement and how the CNT fillers are dispersed along the ply thickness have a remarkable influence on the CNTRC laminated plates. [ABSTRACT FROM AUTHOR]

The complex nature of the anisotropic plate bending problems undergoing large deflection necessitates the need for an efficient approach. The generalized matrix-form formulation proposed herein is based on the Ritz method to handle bending of rectangular anisotropic thin plates undergoing large deflection. This matrix formulation is then encoded in a Mathematica program that provides an automated solution for the problem. The derived matrix-form formulation and the developed code are tested by two numerical examples of composite laminated plates involving different degrees of anisotropy. In both examples, the accuracy of the proposed method is demonstrated by comparing the present results with FEM and the available results from the literature. The results of the investigated plates showed the effect of extension–shear and bending–twisting couplings on the symmetry of the deflection, bending moments, and in-plane forces. [ABSTRACT FROM AUTHOR]

A laser processing technique is proposed for the processing of a 2.5 mm thick carbon nanotube (CNT) composite bipolar plate for proton exchange membrane fuel cells (PEMFCs). This study aims to understand laser interaction with the CNT composite plate experimentally using a pulsed nanosecond laser. Penetration depth, top width, spatter width, and overall physical morphologies are studied. Scanning electron microscope (SEM) and 3D Scanning Confocal Microscope were used for observation and measurements. Based on that, a parametric investigation is conducted and reported systematically. Most importantly, the pulse repetition rate presents a unique nature of interaction that resulted in a critical repetition rate distinguishing three operational regimes. The physical and chemical properties of the regimes are further analyzed by Vickers microhardness testing and energy dispersive X-ray (EDX) analyses performed on the surface and cross-section of each specimen. The results reveal that the pulse repetition rate introduces changes in mechanical properties and chemical compositions in the vicinity of the processed region. In conclusion, lower pulse repetition should be favored for less impact on mechanical properties, chemical composition, and morphological aspects. [ABSTRACT FROM AUTHOR]

This work initially aims to study the influence of temperature on the mechanical properties of composite materials and adhesive. With this purpose, the mechanical properties of the adhesive and composite were measured experimentally under different temperature to provide the requested information for finite element modeling, and then inserted in a numerical model of bonded composite patch on cracked laminate composite plate to evaluate the fracture energy variations at repaired crack tip for different temperatures. The main results obtained confirm the beneficial effects of the composite patch on the mechanical behavior of a cracked composite. Moreover, the reduction in the mechanical properties induced by temperature negatively affects the repair strength. On the other hand, the fracture energy is strongly related to crack length and temperature. [ABSTRACT FROM AUTHOR]

A numerical study on ceramic/thermoset (hybrid) composite bulletproof armour against AK-47 bullets was carried out to find a suitable hybrid composite to stop the projectile. The study was conducted in two phases. In the first phase, the ballistic impact performance of three different ceramics such as silicon carbide, boron carbide and aluminium nitride were analysed. In the second phase, a ceramic/thermoset (hybrid) composite was chosen by varying the thickness of the three thermoset (glass–epoxy, carbon–epoxy and kevlar–epoxy) composite back plate and by performing multi-bullet hits. This numerical study was done using the FE package Abaqus/Explicit by implementing the user-material subroutine VUMAT. Penetration depth and the absorption of kinetic energy were evaluated to find the suitable material for the armour. The residual velocity of individual bullets was assessed after the impact of multiple bullet hits. Silicon carbide as a face plate and carbon–epoxy as a back plate were found to be the best hybrid composition for the body armour. [ABSTRACT FROM AUTHOR]

In the present work, for the first time, a general analytical solution is developed and applied for functionally graded (FG) composite laminated plates with circular cutouts under various in-plane loading conditions. The stress resultants are expressed in a simple and elegant form. Firstly, the extension is achieved by first introducing arbitrarily oriented uniaxial, biaxial, and shear loading conditions into Greszczuk's solution. Then, the expressions of effective moduli of unsymmetrical laminated plates, obtained by the layer lumping method, are introduced in the present solution. The FG plate can be discretized into a large number of skinny orthotropic layers such that a continuous gradation of their mechanical properties can be obtained. The material properties of the FG plate are graded continuously through the thickness direction according to a power-law function. The robustness and accuracy of the proposed analytical solution are ascertained by comparing its results with analytical findings using the complex variable method and those predicted by the finite element method (FEM). This comparison demonstrates a good level of agreement between these results. Results also show the validity of the proposed solution for both symmetric and non-symmetric FG-laminated plates. Moreover, a comprehensive parametric study is examined and discussed in detail to show the effects of various parameters such as gradation of the material properties and applied loading on the orientation of material axes and the stress distribution around the cutout. The present analytical findings can serve as a benchmark for future research on the modeling of multilayered perforated FG plates. [ABSTRACT FROM AUTHOR]

Titanium polymer composites are evaluated concerning their suitability as bipolar plates in acid water electrolysis as a replacement of milled Titanium bipolar plates. It turns out that our highly filled polymer composites with 80 wt.-% Titanium powder meet all criteria given by US Department of Energy concerning electric conductivity and mechanical stability. Concerning the electrochemical corrosion test, an improved behavior is obtained by coating the composites by a 0.5 μ m thin Titanium layer. The coated Titanium composite bipolar plate has been successfully integrated in a PEM fuel cell. The polarization curves show good electrolysis performances for short time, but further improvements on the coating and the surface roughness need to be made for long-time stability. [ABSTRACT FROM AUTHOR]

We propose a novel recurrence plot-based approach, the difference recurrence plot (DRP), to detect small deviations between measurements. By using a prototypical model system, we demonstrate the potential of DRPs and the difference to alternative measures, such as Pearson correlation, spectral analysis, or cross and joint recurrence analysis. Real-world data comes from an application of guided ultrasonic waves for structural health monitoring to detect damages in a composite plate. The specific challenge for this damage detection is to differentiate between defects and the influence of temperature. We show that DRPs are suited in the following sense: DRPs of two time series that derive from measurements at different temperatures hold practically full recurrence, whereas DRPs of one time series from a measurement without and one time series with defect show a hugely reduced recurrence rate. [ABSTRACT FROM AUTHOR]

The low-velocity impact response of the sandwich curved panels with functionally graded carbon-nanotube-reinforced composite (FG-CNTRC) surface and isotropic foam core is discussed in this paper. Five types of stacking arrangements including uniform distribution of FG-CNTRC considering thermal environment were analysed. Using the Hertz contact law and rule of mixture model as well as the Kármán-type equations, the nonlinear formulations were built and solved by the two-step perturbation method. The carbon nanotubes' volume fraction, the structure size, the original impact velocity, temperature, relative thickness and the influence of gradient forms on the panels' impact behaviours were analysed. The outcomes show that the stiffness of the non-contact surface has large influence on contact response and various types of FG-CNTRC can be used for different operating conditions providing stiffness or cushion performance. [ABSTRACT FROM AUTHOR]

Aluminum alloy (Al 5052) and magnesium alloy (AZ31B) plates were welded at different loading ratios (mass of explosive/mass of flyer plate, R = 0.7, 0.8, and 0.9) through explosive welding. The interface microstructure revealed a wavy interface for the attempted loading ratios, whereas, for a higher loading ratio (R = 0.9), cracks and pores were observed in the aluminum alloy (Al 5052). X-ray diffraction detected the presence of the Al12Mg17 compound at the interface for all the attempted conditions. The interface microhardness is directly proportional to the loading ratio. The maximum ram tensile strength (167 MPa) and shear strength (103 MPa) were obtained at a lower loading ratio (R = 0.7). Therefore, the satisfactory weld of the Al 5052/AZ31B composite plate was achieved at a lower loading ratio (R = 0.7). [ABSTRACT FROM AUTHOR]

This work intends to present a novel numerical approach for studying the vibration behaviours of variable angle tow (VAT) composite structures in their quasi-static nonlinear equilibrium states. This methodology is able to predict the buckling load, to investigate the natural frequencies variation for progressively higher loads, and to provide a means for verifying experimental Vibration Correlation Technique results. The use of VAT composites, in which the fibre orientations are allowed to vary along with a curvilinear pattern within each lamina, dramatically increases the design space and provides a significant improvement in buckling performance and benefits in the postbuckling regime. This study has been performed using an innovative methodology based on the well-established Carrera Unified Formulation able to describe several kinematic models for two-dimensional structures. In detail, layerwise theories are employed to characterize the complex phenomena that may appear in VAT composite structures. All Green-Lagrange strain components are employed because far nonlinear regimes are investigated. Furthermore, the geometrical nonlinear equations are written in a total Lagrangian framework and solved with an opportune Newton–Raphson method along with a path-following approach based on the arc-length constraint. Different VAT composite structures have been analyzed to validate the proposed approach and provide some benchmark solutions. The computed equilibrium paths are compared with results obtained using the commercial code ABAQUS. The results document the good accuracy and reliability of the presented methodology and show this numerical tool's potentialities. [ABSTRACT FROM AUTHOR]

Modeling and Methods: This work is devoted to the numerical dynamic bending characterization of delaminated multi-walled carbon nanotubes (MWCNTs) reinforced epoxy/glass fiber-based hybrid composite plate based on finite element method with displacement fields derived from classical laminated plate theory (CLPT). Verification: The accuracy and performance of the developed method were confirmed by a validation study with reference solutions available in the literature. Results: Various parametric studies were carried out to study the influence of MWCNTs content, delamination location, delamination interface, ply orientation, and end condition on the dynamic bending characteristics of the intact and delaminated hybrid laminated composite plate. Conclusion: The weight fraction of MWCNTs, delamination location, and clamping condition significantly influences the natural frequency. The natural frequencies also depended upon the ply configuration and delamination interface irrespective of the MWCNT loadings. However, anomalous trends were observed as far as the influence of end conditions is concerned. [ABSTRACT FROM AUTHOR]

We analyse the behaviour of thin composite plates whose material properties vary periodically in-plane and possess a high degree of contrast between the individual components. Starting from the equations of three-dimensional linear elasticity that describe soft inclusions embedded in a relatively stiff thin-plate matrix, we derive the corresponding asymptotically equivalent two-dimensional plate equations. Our approach is based on recent results concerning decomposition of deformations with bounded scaled symmetrised gradients. Using an operator-theoretic approach, we calculate the limit resolvent and analyse the associated limit spectrum and effective evolution equations. We obtain our results under various asymptotic relations between the size of the soft inclusions (equivalently, the period) and the plate thickness as well as under various scaling combinations between the contrast, spectrum, and time. In particular, we demonstrate significant qualitative differences between the asymptotic models obtained in different regimes. [ABSTRACT FROM AUTHOR]

The interface characteristics and microstructure formation of TA2-5083 composite plate after explosive welded were studied. Optical microscope and electron microscope were used to analyze the microstructure of intermetallic compounds. Furthermore, ANSYS/AUTODYN was adopted to calculate the characteristics of interface microstructure simulated by the smooth-particle hydrodynamics (SPH) method. The results show that most molten metal in the wave front stays in the wave-waist region. There was a relative velocity difference between the vortex of molten metal and the titanium tissue, resulting in that broken titanium particles being scoured by vortexes. Ti3Al was generated in the vortex, whose antioxidant capacity wound lead to the formation of cracks. Consider soldering in a vacuum environment or adding an intermediate layer to reduce interfacial defects. The temperature of the outer vortex was higher than that of inner vortex, and the vortex has a transition layer of 5 μm, which is thinner than the transition layer of 10 μm between the fly and base plate. The jet of molten metal was mostly composed of aluminum, with the jet velocity of interface reaching 3000 m·s−1 and the interface temperature rising up to 2100 K. Compared with the molten metal in the wave-back vortex, the jet temperature at the interface was higher, resulting in a thicker transition layer at the bonding surface. [ABSTRACT FROM AUTHOR]

The protective performance of a three-layer explosive welded composite plate consisting of steel and aluminum plates is studied in ballistic experiments and numerical simulations. The mechanism of target plate failure under the impact of spherical fragments is investigated. [ABSTRACT FROM AUTHOR]

Composite plates are widely used in many engineering fields such as aerospace and automotive. An accurate and efficient multiscale modeling and simulation strategy is of paramount importance to improve design and manufacture. To this end, we propose an efficient data-driven computing scheme based on the classical plate theory for the multiscale analysis of composite plates. In order to accurately describe the relationship between the macroscopic mechanical properties and the microscopic architecture, the multiscale finite element method (FE 2 ) is adopted to compute the generalized strain and stress fields. These data are then used to construct a database for data-driven computing. Since the database is offline populated, the data-driven computing scheme allows for a reduced computational cost when compared to the traditional multiscale method, where the concurrent coupling of different scales is still a burden. And data are obtained from a reduced structural model for computational efficiency. The proposed scheme is therefore addressed as Structural-Genome-Driven (SGD) modeling of plates. Compared to the general data-driven computational mechanics modeling of plates, SGD is found to be more efficient since the number of integration points is significantly reduced. This scheme provides a robust alternative computational tool for composite plate structures analysis. [ABSTRACT FROM AUTHOR]

A modified zig-zag theory was used to investigate the bending behavior of composite plates and sandwich structures. The theory is based on the first-order shear-deformation theory on some piecewise linear functions for in-plane displacements. This theory does not depend on the shear correction factor and can be applied to various engineering problems associated with the structural dynamics. The nonlinear strain terms in the von Kármán compatibility equation were taken into account to calculate accurate results at large deformation. The governing equations and associated boundary conditions were derived using the principle of virtual work. The calculated numerical results are compared with those of other theories, and an excellent agreement between them was found. The figures and tables presented illustrate the superiority of the model considered in predicting the stress and displacement fields. The model proposed is applicable to nonlinear problems with large deflections. [ABSTRACT FROM AUTHOR]

The influence of temperature is regarded as particularly important for a structural health monitoring system based on ultrasonic guided waves. Since the temperature effect causes stronger signal changes than a typical defect, the former must be addressed and compensated for reliable damage assessment. Development of new temperature compensation techniques as well as the comparison of existing algorithms require high-quality benchmark measurements. This paper investigates a carbon fiber reinforced plastic (CFRP) plate that was fully characterized in previous research in terms of stiffness tensor and guided wave propagation. The same CFRP plate is used here for the analysis of the temperature effect for a wide range of ultrasound frequencies and temperatures. The measurement data are a contribution to the Open Guided Waves (OGW) platform: http://www.open-guided-waves.de. The technical validation includes initial results on the analysis of phase velocity variations with temperature and exemplary damage detection results using state-of-the-art signal processing methods that aim to suppress the temperature effect. Measurement(s) Guided ultrasound waves in a composite plate under temperature variations • temperature Technology Type(s) Piezoelectric transducers • Temperature Sensor Device Factor Type(s) excitation frequency • temperature Machine-accessible metadata file describing the reported data: 10.6084/m9.figshare.9863465 [ABSTRACT FROM AUTHOR]

Based on three-dimensional theory of elasticity, static bending, free vibration and buckling behaviors of functionally graded carbon nanotube-reinforced composite plates are investigated with the isogeometric analysis (IGA). The carbon nanotubes are supposed to be distributed uniformly and graded functionally along the plate thickness. The refined rule of mixtures is applied to predict the effective material properties. Based on the IGA, the displacement field of the plate is expressed by three-dimensional NURBS basis functions. The Hamilton's principle is used to obtain the formulations for the static bending, free vibration and buckling analysis. The convergence study is performed and the accuracy of the present approach is validated by comparing the numerical results with the published literature. In addition, the effects of CNTs volume fractions, CNTs distributions, geometrical parameters and boundary conditions on the static bending, free vibration and buckling analysis of the functionally graded carbon nanotube-reinforced composite plates are investigated. [ABSTRACT FROM AUTHOR]

The tight oil reservoir rocks in the Jidong Oilfield are generally characterized by high hardness, strong abrasiveness, and extremely unevenness, which seriously reduce the drilling efficiency. In view of this problem, the mineral composition, hardness, plasticity coefficient, and drillability of rocks were first determined. It was found that the rock integrity, compactness and high hardness are the main factors leading to the low rock breaking efficiency of PDC bits. Then, combined with logging data, the drilling resistance profile of the whole well section was established. According to the crushing mechanism of rocks under the action of a PDC bit, the mechanical model of a single composite plate under rock crushing conditions is established, and the influence of the back angle on the cutting force is analyzed. The flow field distribution of the drill bit surface under different nozzle combinations was calculated by finite element numerical simulation. Based on the experimental and simulation results, the optimal backward angle was 15°, and the optimal nozzle combination was two 16-mm central nozzles and five 14-mm peripheral nozzles. Finally, a personalized PDC bit design scheme for tight oil reservoirs in the Jidong Oilfield was proposed. The scheme includes the following: (1) a 5-blade straight-arc crown is profiled; (2) anti-impact cylindrical components are set; (3) the nozzle hydraulic structure adopts a bending type; and (4) the diameter-retaining teeth and diversion grooves are optimized. The optimized bit reduces stick–slip, improves stability, and has an obvious acceleration effect. [ABSTRACT FROM AUTHOR]

Considering the excellent physical properties, graphene can be regarded as an ideal reinforcing material for composite structures today. Nevertheless, the existing higher-order models neglecting the continuity conditions of interlaminar stresses may lose capability to analyze precisely the stability of functionally graded graphene-reinforced composite (FG-GRC) laminated thick plates. For FG-GRC laminated structures, the compatibility conditions of interlaminar stresses will directly affect the accuracy of critical loads. As a result, an appealing plate theory with only seven unknowns is suggested for buckling analysis of FG-GRC laminated thick plates. The compatibility requirements of interlaminar shear stresses between adjacent layers are satisfied in the proposed model. Improved transverse shear stresses are obtained using a preprocessing approach based on the three-dimensional (3D) equilibrium equation and Reissner's mixed variational theorem (RMVT). The performance of the suggested model is assessed by using the 3D elasticity solutions and the results obtained from some existing models. Numerical results indicate that the proposed model can reliably predict critical loads of laminated and sandwich plates. Additionally, the impact of the graphene distribution pattern, staking sequence, volume fraction, boundary conditions, thermal environment, and geometric parameters of the plate on the buckling behavior of FG-GRC laminated plates is explored. [ABSTRACT FROM AUTHOR]