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Fibre-reinforced polymers (FRPs) are composite materials of plastics reinforced with fibres. Cars, sea, aeronautics, and foundation projects progressively utilize fibre-reinforced polymers. This study aims to study the effect of adding multiwalled nanotubes fillers into the hybridized jute-glass FRP composites and their relative properties. This study uses multiwalled nanotubes (MWCNTs), and particles-hybrid jute-glass composites containing jute fibre chopped layer mats, woven glass mats, epoxy resin, and multiwalled nanotubes fillers were created using the hand layup method. After adding multiwalled nanotubes fillers in various weight proportions, the mechanical behaviours of fibre-reinforced polymers were analysed. The mechanical behaviours of laminated composites were tested using the ASTM standard; the following properties are tensile, flexural, and impact strength. The multiwalled nanotubes with 6% wt. attained the maximum mechanical properties compared to the 2 and 4 wt. % of MWCNTs. The E-based specimen contributes the most to the different types of specimens, with a contribution of 24.21% for tensile, 25.03% for flexural, and 24.56% for impact. The microstructures of hybrid composites were studied using a scanning electron microscope. [ABSTRACT FROM AUTHOR]

Organic fiber-based biocomposites have gained prominence in a variety of sectors over the last four to five years due to their exceptional mechanical and physical properties. Natural fiber-based composites are increasingly being employed in autos, ships, airplanes, and infrastructure projects. The current study will look at the effect of nanotitanium oxide (TiO2) fillers on the properties of hybridised jute-hemp-based composites. In this work, TiO2-filled biocomposites were created using the hand layup method in hybrid jute-hemp composites containing jute fiber mats, woven hemp mats, and epoxy resin. After nanotitanium oxide fillers were injected in various weight proportions, the mechanical properties of fiber-reinforced polymers were investigated. The mechanical properties of laminated composites were tested using the ASTM standard. Compared to 2 and 4 wt.% of TiO2, the 6 wt.% was provided the highest mechanical strength. Among the different types of specimen, the E-type specimen (30 wt.% of hemp, 7 wt.% of jute, 57 wt.% of epoxy, and 6 wt.% of TiO2) gives their highest contribution, i.e., for tensile 24.21%, for flexural 25.03%, and for impact 24.56%. The scanning electron microscope was utilized to analyse the microstructures of nanocomposites. [ABSTRACT FROM AUTHOR]

This paper applies stacking sequence optimization for maximizing the buckling load of rotationally restrained laminated composite rectangular plates with different boundary conditions resting on an elastic Pasternak foundation subjected to uniaxial and biaxial in-plane static loads. The Mindlin Plate Theory (MPT), which considers the firstorder shear deformation effect, was used to extract the characteristic equations of the plates under in-plane loading, including plate-foundation interaction. The buckling problem of laminated plates was analyzed by the Rayleigh-Ritz method. The aim of optimization was to maximize the buckling load and post-buckling load capacities using Genetic Algorithm (GA) method, and the design variable was the ply orientation. The results showed that the optimal orientation, of the laminated square plate under biaxial in-plane loading in various conditions was 45°, approximately. The existence of a foundation, clamped boundary conditions, and high aspect ratio led to increase in the optimal orientation. [ABSTRACT FROM AUTHOR]

Ceramic laminates were produced by thermal pressing of pure alumina (Al2O3) and TiO2‐MnO‐doped alumina (d‐Al2O3) tapes and subsequently sintered at temperatures ranging from 1100 to 1250°C. The diffusion of dopants through the interface was investigated by optical (OM), scanning electron (SEM) microscopy, nanoindentation, and energy‐dispersive X‐ray spectroscopy (EDS) together with scanning transmission electron microscopy. Temperature‐dependent dopant diffusion and porosity profiles were, respectively, observed investigating the microstructure. For d‐Al2O3, the average grain size, hardness, and Young's modulus were higher when compared to pure alumina, while the dopants diffusion zone presented intermediate values of these properties. The increase in sintering temperature resulted in higher values of hardness and Young's modulus in both layers. A further investigation showed a gradual decrease in grain size, hardness, and Young's modulus from the doped to the pure alumina layer, corresponding to a decreasing gradient in the dopants concentration in the Al2O3 layer with increasing distance from the interface. High concentrations of Mn and Ti were observed at triple points and grain boundaries, as well as within alumina grains. [ABSTRACT FROM AUTHOR]

In modal testing, the quality of vibration signals and clarity of peak points to extract the natural frequencies, corresponding mode shapes and damping ratio depend on the number and location of the sensors. High measurement costs are required for structural identification and long-term structural health monitoring in large structures, which require a high number of sensors. Therefore, the minimum number of sensors should be placed at appropriate locations on the system during experimental measurements to ensure both information of sufficient quality and cost reductions. The aim of this study is to perform cost-efficient non-destructive modal tests for a laminated composite and steel cantilever beams using an optimal sensor placement approach. Finite element models of the sample beams are constituted in ANSYS® software to determine the initial candidate set of sensor locations. Then, ambient vibration tests are conducted. Based on the experimental modal amplitudes and mode shapes, optimal sensor locations are determined using the effective independence method, and measurements are repeated. The study shows that there is good agreement between the natural frequencies and mode shapes obtained from the initial measurements and those obtained using the limited number of sensors. [ABSTRACT FROM AUTHOR]

The development of aerospace manufacturing has promoted the application of lightweight composite materials into aerospace structures. Although the aerospace composite structures possess numerous advantages, invisible internal structural damage such as delaminations induced by various external factors can significantly reduce the mechanical affordability, safety, and life-cycle of the structure. Therefore, it is of great significance to monitor and assess the health state and predict accurately the lifetime of aerospace composite structures. An acousto-ultrasonics-based multi-damage index identification approach is thus proposed in this study to identify and quantify possible multiple damage in thin-walled aerospace composite structures. In this approach, two indices for damage quantification were proposed: the energy and phase divergence indices. The energy index defines the reflected energy resulting from damage, and the phase divergence index defines the instantaneous phase variation of propagating waves due to damage. The two damage indices are obtained through the developed mode decomposition and spectral element analysis using sensor response signals collected by a transducer array placed onto the examined structure. Through a series of relevant experimental tests on the fabricated laminated composite panels with/without damage, the proposed acousto-ultrasonics-based multi-damage index identification approach was validated. The developed damage indices are competent to evaluate a structural health state in terms of damage quantification, and all of the validation results fell well in the prospected ranges. Moreover, it shows a linear and consistent trend between the variation of two damage indices and damage extents. Based on the particular relation, the linear regressive prediction functions were established separately regarding the two damage indices. They can be used to assess a structural health state due to the damage growth in real time. The proposed multi-damage index identification approach demonstrates its potential to serve as an online assessment tool to be aware of the reliability condition of a composite structure. [ABSTRACT FROM AUTHOR]

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Automotive and aerospace industries require new lightweight materials that enhance payload and improve efficiency via vehicle weight reduction. Employing composites, such as fiber-reinforced polymers, is a common approach to reducing vehicle component weight. In this work, we examine the use of atomic layer deposition (ALD) to alter the interfacial chemistry in cellulose-reinforced epoxy composites. As produced, most cellulosics are hydrophilic and immiscible in industrially relevant hydrophobic polymers. In this study, a variety of ALD-derived surface modification schemes are explored to improve resin permeation within a fibrous, cellulose-based paper preform and to increase interfacial adhesion between the epoxy and the cellulose preform. Specifically, we consider surface modification of the cellulose paper with the ALD precursors trimethylaluminum (TMA) and titanium tetrachloride (TiCl4) with a water oxidant to form aluminum oxide and titanium oxide-based surface chemistries. Few cycle ALD treatments (2-cycles) combined with an additional post-deposition heating step are found to make the cellulose preforms more hydrophobic. X-ray photoelectron spectroscopy verifies the presence of the metal oxide surface treatments and points towards high concentration of adsorbed adventitious carbon as the source for surface hydrophobicity. Tensile testing of laminated epoxy composites made from these cellulosic preforms indicates two mechanical property regimes depending on surface treatment: (1) high toughness and high strain for preforms that underwent only an ALD coating and (2) high modulus and high strength for preforms ALD coated and then heated at 120 °C in air. ALD treatments resulted in an 80% increase in toughness and a 47% increase in strain at break. ALD treatments with post-deposition heating resulted in a 16% increase in the elastic modulus and a 27% increase in the ultimate tensile strength. Here we propose a combination of cellulose/epoxy mechanical interlocking and interfacial adhesion as mechanisms to explain the difference in mechanical properties of the explored composites. [ABSTRACT FROM AUTHOR]

Aim: Mouthguard thickness influences the preventive effects against dental and oral injury. The aim of this study was to examine the difference in pressure-formed mouthguard thickness according to the laminate procedure used.Materials and Methods: The materials used were mouthguard sheets of 2.0-mm and 3.0-mm ethylene vinyl acetate, and pressure formed using a pressure former. Two forming conditions for laminated mouthguards were examined: the condition 23P used the 2.0-mm sheet as the first layer and 3.0-mm sheet as the second layer. The condition 32P used the 3.0-mm sheet as the first layer and 2.0-mm sheet as the second layer. The first layer was trimmed to cover only the anterior region; then, the second layer was formed over the first layer. Mouthguard thickness was measured at the labial surface of the central incisor, buccal surface of the first molar, and occlusal surface of the first molar. Statistical analysis was performed by two-way analysis of variance and Bonferroni method to analyze the differences in thickness by measurement region of mouthguards and forming conditions.Results: Mouthguard thickness differed in different regions of the central incisors and the first molars (P < .01). The thickness at the labial surface of the central incisor became statistically significantly larger on the 32P condition than that on the 23P condition (P < .01). The thickness at the buccal surface and the occlusal surface of the first molar became statistically significantly larger on the 23P condition than that on the 32P condition (P < .01).Conclusions: The thicknesses of the labial surface of the central incisor became larger when the sheet thickness of the first layer was larger. [ABSTRACT FROM AUTHOR]

Delamination occurred due to poor manufacturing process or in-service actions significantly affects the mechanical and failure behavior of laminated composite structures. In this study, the buckling and post-buckling delamination behavior of laminated composite with an embedded initial delamination under in-plane compression was studied experimentally and numerically. First, compression tests for laminated composite specimens with embeded initial delamination were performed and the buckling and delamination responses were obtained. Then the experimental test was numerically simulated using finite element methods with the progressive failure accounted for by using cohesive zone modeling. The load-displacement curve, strain behavior and delamination shapes of experimental specimens obtained from load cells, strain gages installed at different locations, and C scan images, respectively, were compared with the FEM results, and good agreements were attained. The effect of the buckling modes, laminate stacking sequence and shape of initial delamination on the buckling load and propagation behavior was studied by considering different ply stacking and shapes of initial delaminations. It was found that the buckling mode determined the growth direction of the delamination propagation, and the stacking sequence influenced the extent of the propagation area, while the orientation of the delamination affected the buckling loads. [ABSTRACT FROM AUTHOR]

Considering the promotion effect of interlaminar normal tensile stress and the inhibition effect of interlaminar normal compressive stress-two kinds of elimination initial criteria were proposed in this paper. Based on these two delamination initial criteria-a modified cohesive zone model (CZM) was established to simulate the delamination behavior in laminated composites. Numerical simulations of double cantilever beam (DCB)-mixed, mode bending(MMB)and end notched flexure(ENF)tests were conducted. The results show that the proposed model can do a better job than common ones when it is used to predict laminates'delamination under interlaminar compression stress. Moreover-a factor r-named cohesive strength coefficient-was defined in this paper on account of the difference between cohesive strength and interlaminar fracture strength. With changing factor r-it shows that a moderate variation of cohesive strength will not cause significant influences on global load, displacement responses. Besides-in order to obtain a good balance between prediction accuracy and computational efficiency-there shall be two or three numerical elements within the cohesive zone. [ABSTRACT FROM AUTHOR]

Abstract Estimation of the remaining useful life (RUL) based on the elastic strain energy density using the non-contacting and full-field capabilities of Thermoelastic Stress Analysis (TSA) was applied to E-glass fiber-reinforced polymers (GFRPs) subjected to high-cycle fatigue loading conditions. A quantitative prediction was successfully attained during the material's intermediate and final fatigue life phases. The initial state of the specimen was used as the reference data for defining a damage parameter that enabled the detection of visually imperceptible subsurface cracks. [ABSTRACT FROM AUTHOR]

In addition to many advantages, composite materials constitute a new challenge in many industrial fields and applications. Vibration Based Methods (VBM) are relatively simple and at low cost to detect damage and fails in composite structures, but they are sensitive to variations in geometry and material properties. Recently, the main challenge in VBM is to establish a robust process to be applied on an industrial environment. In this work, a methodology to identify the effect of design parameters on the dynamic response of laminated composite plates is presented. For the case of composite materials, the production process plays an important role. Numerical dynamic analyses are run using the Finite Element code ABAQUS™ which is complemented with user subroutines written in Fortran and Python. A Design of Experiments (DoE) strategy is developed to reduce the number of experiments and to evaluate the effect of the design parameters. Two sets of composite plates were evaluated, [0] 8 and [0/−15/15/0/−15/15] s , with natural frequencies used as response quantities. In addition, Frequency Response Functions are analyzed, as they are obtained by a full factorial design. Afterwards, the results are discussed with proper attention for the potential and for the limitations of the proposed methodology from the perspective of usage to detect damage and failure in composite structures. [ABSTRACT FROM AUTHOR]

Abstract Composites are known to be vulnerable to out-of-plane loading such as impact. Investigating the residual properties of the laminate as a function of damage detection is the main purpose of impact damage tolerance design in aeronautics. As a good alternative to experimental campaigns, numerical approaches would lead to saving of time. The model developed in Institut Clément Ader over the last years enables representation of behavior of composite laminates subjected to low velocity/low energy impact – including permanent indentation – and Compression After Impact. Damage such as permanent indentation, fiber failures, matrix cracks and delamination are taken into consideration at each step thanks to a discrete ply modelling. The work presented here deals with the use of this model to make a composite laminate design optimization according to impact damage tolerance design. A method to improve optimization by reducing computation time is also proposed, based on a "best candidates" selection. [ABSTRACT FROM AUTHOR]

Abstract The snapthrough and free vibration response of bistable cross-ply [ 90 n / 0 n ] composite laminates is investigated. Thin unsymmetric composite laminates possess more than one equilibrium position when cooled to room temperature due to the difference in thermal expansion of the plies. Bistable cross-ply laminates have cylindrical shapes at room temperature provided appropriate side-length-to-thickness ratio is used. The laminate is modelled according to the classical lamination plate theory taking into account the von Karman geometric nonlinearity. The strains and displacements are approximated via a simplified Rayleigh-Ritz model that depends on only four time-dependent parameters for the general dynamic response. The simplified model is validated against experimental and finite element results and an acceptable agreement is obtained. The laminate's length-to-thickness ratio is key to assess the existence of bistability. The model is used to investigate the snapthrough response of an 8-ply [ 90 4 / 0 4 ] laminate that is subjected to three loading schemes: concentrated moments, normal forces, and tangential forces. The variations of the principal curvatures and the lateral displacement of the laminate with the applied forces are shown. The significance of the force location is also found a crucial element in finding the snapthrough force. The free vibration that takes place in the vicinity of a stable equilibrium position is studied and the variation of the fundamental frequency with the laminate size is presented. [ABSTRACT FROM AUTHOR]

Abstract The transverse electrical conductivity of thin-ply carbon fibre laminates, enhanced with carbon nanotubes (CNTs), was investigated experimentally. CNTs were directly synthesised on spread tow tapes of UTS50S carbon fibre through chemical vapour deposition (CVD). Unidirectional laminates were manufactured using both a thermosetting (epoxy) and a thermoplastic resin (polypropylene). A substantial increase in the electrical conductivity and a decrease in electrical anisotropy was observed for both the material systems investigated. Improvement in conductivity by a factor of 8 for the epoxy specimens, and 28 for the polypropylene specimens were reported. [ABSTRACT FROM AUTHOR]

Abstract In the present study, epistemic uncertainty is quantified for bending and buckling analysis of laminated composite plates using evidence theory. By employing vertex and uniform sampling methods the degree of confidence of the failure analysis is carried out in terms of belief and plausibility. Dempster's rule of combination is used when the analysis subjected to more number of experts under vertex and sampling methods. To proceed the uncertainty quantification for the composite plates a trigonometric higher order shear deformation theory is assessed by analytical and finite element formulation. Numerical examples are carried out to illustrate the effectiveness of the proposed methods for failure analysis based evidence theory of real engineering problems. Considering various parameters such as size of focal element, uncertain variables as material and geometric parameters, more number of uncertain variables and more number experts for each uncertain variable the quantification is executed. From the numerical examples, it is observed that for quantifying the epistemic uncertainty employing more experts for uncertain variables is the favorable choice. [ABSTRACT FROM AUTHOR]

Abstract The purpose of this paper was to investigate the failure behaviors of composite stiffened panels with skin low-velocity impact (LVI) damage under axial compression. Barely visible impact damage (BVID) was introduced into the L-shaped and T-shaped stiffened panels within the skin between stiffeners. Compression after impact (CAI) tests were performed and delamination growth of specimens was observed directly. The results show that there are two types of delamination growth processes, which are unstable and stable respectively. Due to the restriction effect of the stiffener, the delamination growth is easier to initiate in the outer sublaminates on the smooth side of the skin compared to the ones on the stiffener side. In addition, according to the thermal-deply result, adjacent impact delaminations can be connected by matrix cracks, which results in a larger area of the sublaminate. It is revealed that buckling of the sublaminates and subsequent transverse delamination propagation in large area are the triggers leading to the final failure of the stiffened panel. [ABSTRACT FROM AUTHOR]

Abstract The metaheuristic optimization methods have been widely used in complex composite material design. However, it is still difficult to apply these methods to complicated problems due to expensive cost of evaluations. Therefore, to reduce the expensive cost of finite element (FE) analysis in the composite laminate optimization problems, the surrogate assisted optimization (SAO) method has been well developed. However, considering the low accuracy of surrogate model for complicated cases, the SAO is always difficult to converge to the global optimum. In this study, a fast and accurate solver, the reanalysis algorithm is extended to vibration problem and integrated to improve the efficiency of metaheuristic optimization of composite laminates instead of surrogate model. In the proposed method, the shifting method is used in each iterative step. To validate the performance of suggested method, several numerical examples are presented. The results demonstrate that reanalysis assisted particle swarm optimization (RPSO) is much more efficient for free vibration problems of composite laminates than the PSO. Moreover, such strategy can be extended to other metaheuristic algorithms easily. [ABSTRACT FROM AUTHOR]

Abstract This paper proposes the synergetic integration of system identification and artificial intelligence for the detection and assessment of delamination damages in smart composite laminates. An electromechanically coupled mathematical model is developed for the healthy and delaminated smart composite laminates on the basis of improved layerwise theory, higher order electric potential field and finite element method. A discriminative feature space is constructed for the healthy and delaminated structures via system identification from their structural vibration responses. The discriminative features are used for the training and cross-validation of various supervised machine learning classifiers and an optimal classifier is identified. The optimal classifier is employed to make predictions on unseen test delamination cases, and its predictions are validated via a dimensionality reduction tool. The obtained results show that the proposed technique could be employed as a reliable tool for nondestructive evaluation of smart composite laminates. [ABSTRACT FROM AUTHOR]

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

Abstract Fiber patch placement (FPP) is a manufacturing technique for variable stiffness composites. In the FPP approach, a structural component is assembled from a multitude of discrete fiber patches, thus allowing for an easy tailoring of the layup to the local load state. However, due to the discontinuous fibers at the patch edges, complex stress distributions occur in patched laminates. To date, an efficient method for the analysis of patched laminates on macro-scale does not exist. This article introduces a 2D planar shear-lag model (SLM) based on thin-plate mechanics and a simplified interlaminar shear stress formulation. It is shown how the governing partial differential equation system is assembled and how boundary conditions are set. The model is solved numerically using the Finite Element Method. For verification the 2D SLM is compared to a full 3D linear-elastic solution. It can be shown that the SLM allows for accurate prediction of stress fields disturbed by interrupted fibers with considerably improved numerical efficiency. An application example shows that the SLM resolves the effects of discontinuities significantly better than a state-of-the-art shell element modeling approach. As a consequence, a substantial progress in the design of patch laminated structures is achieved. [ABSTRACT FROM AUTHOR]

Abstract It has recently been proved that interleaving electrospun nanofibers between composite layers has a significant effect on their fracture toughness. In this study, a non-destructive method, Acoustic Emission (AE) technique, was applied to evaluate the effect of nylon 66 nanofibers on failure modes such as matrix cracking and fiber breakage. For this aim, mode-I and mode-II fracture tests were conducted on the non-modified and modified samples. Two various methods (peak frequency based method and wavelet transform) were utilized to analyze AE signals, and at last, their results were compared. According to the outcome of fracture tests, by applying nylon 66, mode-I and mode-II fracture toughness enhanced 46% and 65%, respectively. On the other hand, AE analysis showed that damages decreased significantly in the nanomodified laminates. For instance, matrix cracking, fiber/matrix debonding, and fiber breakage decreased 82%, 53%, and 64% by the wavelet transform method. SEM images were also provided to investigate the failure modes occurred during fracture tests. Highlights • Nylon 66 nanofibers were used in glass/epoxy laminate to increase mode-I and mode-II fracture toughness. • AE technique was also used to consider the effect of nanofibers on different failure modes during fracture test. • Nylon 66 could decrease matrix cracking, matrix/fiber debonding, and fiber breakage, significantly. [ABSTRACT FROM AUTHOR]

Abstract The deflection of the composite laminates and their maximum tensile strain in bending conditions are investigated in this study. For this purpose, different equivalent single layer and layerwise theories based on polynomial shape functions are used. Then Rayleigh–Ritz approximation technique and principle of minimum potential energy are applied to obtain the unknown coefficients of the displacement fields. The results are compared with the three dimensional finite element analysis and the experimental investigation. Also the process of obtaining material properties in tensile condition is explained completely. Regarding to the computational costs and agreement of the analytical and numerical results with the experimental ones, for both CCFF and SSFF boundary conditions the deflection prediction by layerwise HSDT is in a good consistency with the experimental results than the other plate theories and FEM method in this study. Although for obtaining strains in SSFF boundary conditions precisely FEM is more applicable. Highlights • The deflection of laminates and their maximum tensile strain in bending conditions are studied. • Different equivalent single layer and layerwise theories based on polynomial shape functions are used. • The results are compared with the 3D finite element analysis and the experimental investigation. • The deflection prediction by layerwise HSDT is in a good consistency with the experimental results. [ABSTRACT FROM AUTHOR]

In this work, the hybridization effects of hydrazine reduced graphene oxide (rGO) on the inter-laminar shear strength (ILSS), impact strength, and in-plane fracture toughness of symmetric type carbon fiber/epoxy composite (CF/epoxy) laminates were investigated. The composite laminates were fabricated through the vacuum-assisted resin transfer molding (VARTM) process. At 0.2 wt% of rGO loading, the CF/epoxy composites showed the best load carrying capacity among the developed laminates. ILSS, impact strength, and critical stress intensity factor ( K IC ) were enhanced by ∼ (84, 100, and 33) %, respectively, in the case of rGO (0.2 wt%) filled CF/epoxy composite specimens, as compared to CF/epoxy composite. The consumed fracture energy of rGO (0.2 wt%)/CF/epoxy increased, as compared to the rGO (0.4 wt%)/CF/epoxy composite. The fracture surfaces obtained from field emission scanning electron microscopy of the developed composites showed compatible dispersion of rGO in the epoxy matrix, and branched fracture of the specimens. This study suggests that the rGO nanofiller might be used as a matrix modifier to resist matrix fracture, as well as fiber fracture. [ABSTRACT FROM AUTHOR]

This paper aims to study dynamic structural responses and failure mechanisms of composite pressure vessels subjected to low velocity impact. First, a three-dimensional laminated media model based on sub-laminate theory is introduced for intralaminar damage, where Puck's failure criteria and strain based damage evolution laws for fiber and matrix are used. The impact responses of composite pressure vessels can be calculated based on sub-laminates and the fiber and matrix damage are predicted based on each ply by using this approach. Second, the proposed laminated media model is implemented using ABAQUS/Explicit user-defined material subroutine VUMAT by the time stepping algorithm and the bilinear cohesive model is employed to simulate interlaminar delamination. Finally, numerical simulations are performed to study the impact force-time/central displacement curves and intralaminar damage and interlaminar delamination features for composite pressure vessels at three different impact energy. Detailed energy dissipation mechanisms due to intralaminar dynamic progressive failure, interlaminar delamination and deformation of liner are also discussed. By comparison, relatively good agreement is achieved between the experimental and numerical results by using the three-dimensional laminated media model. [ABSTRACT FROM AUTHOR]

In this study, the continuum damage mechanics model for predicting the stiffness reduction of composite laminates including transverse cracks is formulated as a function of crack density. To formulate the model, first the damage variable in the direction normal to the fiber of a ply including transverse cracks is derived. The damage variable is derived by the model assuming a plane strain field in the isotropic plane and using the Gudmundson–Zang model for comparison. The effective compliance based on the strain equivalent principle proposed by Murakami et al. and classical laminate theory are then used to formulate the elastic moduli of laminates of arbitrary lay-up configurations as a function of the damage variable. Finally, the results obtained from this model are compared to the finite-element analysis reported in previous studies. The model proposed in this paper can predict the stiffness of laminates containing damage due to transverse cracks (or surface crack) from just the mechanical properties of a ply and the lay-up configurations. Furthermore, this model can precisely predict the finite-element analysis results and experiment results for the elastic moduli of the laminate of arbitrary lay-up configuration, such as cross-ply, angle ply, and quasi-isotropic, including transverse cracks. This model only considers the damage of the transverse crack; it does not consider damage such as delamination. However, this model seems to be effective in the early stage of damage formation when transverse cracking mainly occurs. The model assuming plane strain field in the isotropic plane which is proposed in this paper can calculate the local stress distribution in a ply including transverse cracks as a function of crack density. The damage evolution of transverse cracks can thus be simulated by determining the fracture criterion. [ABSTRACT FROM AUTHOR]

Due to the existence of large number of design variables for large-scale composite laminated structures, such as ply thicknesses and stacking sequence, etc., it has become one of most important concerns to build an efficient optimization design method for composites. In this paper, the purpose is to propose a novel reliability-based two-level optimization design method including thickness and stacking sequence optimizations, where uncertain parameters of composites are taken into account for reliability evaluation. Firstly, by characterizing existing uncertain parameters of composites as random or interval variables, one can carry out uncertainty analysis for structural responses. Then the evaluation models of probabilistic and non-probabilistic reliabilities are separately introduced when treating uncertainties as random and interval variables. Furthermore, by combining the reliabilities with the two-level optimization model, a novel reliability-based two-level optimization model is advanced and the detailed optimization procedures are listed for convenience of understanding. Lastly, two numerical examples including a simple-supported composite plate and a composite wingtip of aerospace plane are given out to demonstrate the validity and availability of the proposed method. The results show that the proposed method can be successfully and efficiently applied in the optimization design of composite structures. [ABSTRACT FROM AUTHOR]

The effective method of transformed differential quadrature (TDQ) is improved for the buckling design optimization of functionally graded (FG) carbon nanotube‐reinforced laminated composite quadrilateral (FG‐CNTRCQ) plates with arbitrary straight‐sided based on the first‐order shear deformation theory. The laminated plates with both uniformly and FG distributions of single‐walled carbon nanotubes varied along the thickness of layers are considered. The TDQ method is used to directly discretize the governing differential equations for an arbitrary straight‐sided physical domain without any need to transform the equations to the computational domain. In the presented genetic algorithm, the orientation of fibers is considered as the design parameter to obtain the optimum critical buckling loads in terms of different parameters including distributions of the fibers, number of layers, stacking sequence, CNTs volume fraction, geometrical parameters, and boundary conditions. The edges of the plates can take arbitrary end supports of simply and clamped boundary conditions. The formulation is developed based on the invariant terms to provide a systematic procedure with minimum computational cost. Some parametric studies are conducted to examine the effectiveness of the model for the design purpose of the FG‐CNTRCQ plates. POLYM. COMPOS., 39:E853–E868, 2018. © 2017 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

The effects of temperature on the static tensile behavior of continuous E-glass/polyamide laminates were studied in order to assess the feasibility of using the material system for structural applications. Uniaxial tensile tests were conducted on [0] 8 , [90] 8 , [0 2 /90 2 ] s and [0 4 /90 4 ] s laminates at multiple temperatures above and below the glass transition temperature, which was measured using different methods. Optical and scanning electron microscopy were performed on the tested samples, and the effects of temperature on failure modes were investigated. The [0] 8 and [90] 8 laminates displayed three reduction stages in modulus versus temperature, where the largest reduction was in the glass transition region as a result of notable softening of the polyamide matrix, as confirmed by fractographic analysis. However, the [0 2 /90 2 ] s and [0 4 /90 4 ] s laminates displayed the largest modulus reduction prior to the glass transition temperature with little reduction beyond, which was attributed to matrix softening coupled with in situ ply constraining effects. [ABSTRACT FROM AUTHOR]

Hybrid composites consist of two or more different fibres in a single matrix has become an interesting topic in the field of fibre reinforced polymers. In this study, woven kenaf and Kevlar fibre along with polypropylene were used to fabricate hybrid composites. Different fibre configurations of composite laminate materials were introduced to study its effects on the tensile, quasi-static indentation and lowvelocity impact characteristics of hybrid and non-hybrid composite materials. The composites were fabricated through a hot press compression moulding process. From the results, it was noticed that the hybrid kenaf / Kevlar fibre reinforced polypropylene composites showed a positive hybrid effect in which they demonstrated higher tensile and penetration resistance, compared to the non-hybrid kenaf fibre reinforced composites. Furthermore, partial incorporation of Kevlar fibre in the non-hybrid kenaf reinforced polypropylene composites also improved the low-velocity impact resistance of such materials. The findings revealed that a balance between the mechanical strength and the environmental friendliness could be achieved through hybridisation. [ABSTRACT FROM AUTHOR]

A new method for obtaining energy release rate by the Double Cantilever Beam test for angle-ply laminates is proposed. Two different sequences, symmetric and anti-symmetric, have been studied. The fact that the layers are oriented at different angles and the residual stresses, causes the existence of mixed mode fracture. The analytical model presented, based on the complementary energy of a laminated beam, is an extension of a previous model for unidirectional laminates and includes hygrothermal effects. Experimental results of the energy release rate obtained by means of the area method agree with those determined by the proposed approach. [ABSTRACT FROM AUTHOR]

Laminated bamboo in structural applications has the potential to change the way buildings are constructed. The fibrous microstructure of bamboo can be modelled as a fibre-reinforced composite. This study compares the results of a fibre volume fraction analysis with previous experimental beam bending results. The link between fibre volume fraction and bending stiffness shows that differences previously attributed to preservation treatment in fact arise due to strip thickness. Composite theory provides a basis for the development of future guidance for laminated bamboo, as validated here. Fibre volume fraction analysis is an effective method for non-destructive evaluation of bamboo beam stiffness. [ABSTRACT FROM AUTHOR]

ABSTRACT The aim of this study was to analyze how corona dosages above recommended levels affect film surface energy and hydrophobic recovery of such treated film surfaces as well as laminate bond strength of laminates made of these films. The adhesive for lamination was a polyurethane-adhesive with a dry film thickness of ∼5 µm. Polar and dispersive parts of the surface energy were measured frequently according to DIN 55660-2 (Owens-Wendt-Rabel-and-Kaelble method) for up to 140 days after corona treatment. The corona dosage had a value of up to 280 W min/m2. Laminate bond strength was measured according to DIN 55543-5. The effect of corona treatment was highest for low-density polyethylene (PE-LD) films, mean for biaxial-oriented polypropylene (PP-BO) films, and lowest for biaxial-oriented poly(ethylene terephthalate) (PET-BO) films. With increasing storage time, surface energy decreased, as expected. The higher the effect of corona treatment, the faster the polar part of surface energy decreased. At PE-LD, laminate bond strength increased with a higher corona dosage from 0.05 to 8.87 mN/15 mm, whereas at PET-BO and PP-BO laminate bond strength was so high that samples teared before delamination during bond strength testing. By our results is shown that corona dosages above recommended levels resulted in higher laminate bond strength. Only at PP-BO a reduction of laminate bond strength due to 'overtreatment' was be observed. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45842. [ABSTRACT FROM AUTHOR]

The energy-absorption (EA) of fibre metal laminate (FML) conical frusta under quasi-static compression loading is studied by performing virtual test. A progressive deterioration model combined with the conventional shell model is initially employed to simulate collapse behaviors of composite wrapped aluminium conical (CWAC) frusta. To sufficiently understand collapse behaviors, the stacked shell model is used to reproduce intralaminar damage and delamination. The numerical models are validated with available experimental results and the collapse behaviors of aluminium wrapped composite conical (AWCC) frusta are detailedly discussed. The effects of conical frusta with single and hybrid materials towards EA are investigated. The triggering mechanisms including inward and outward chamfer triggers, and convex and concave plug-type triggers are studied to better induce collapse modes of FML conical frusta. Results show that the stacked shell model has better predictive ability of collapse behaviors. The only difference between experiment and simulation is that the initial load is not perfectly captured due to specific conical profile, complex failure modes and hybrid fibre metal materials. The FML conical frusta with appropriate hybrid materials, such as AWCC frusta, present a higher EA capacity with an increase of 28.7% in SEA. The outward chamfer trigger and convex plug-type trigger can effectively improve EA of FML conical frusta. [ABSTRACT FROM AUTHOR]

Natural fiber-reinforced polymeric composites are gaining significant attention in engineering applications. The present investigation is an attempt to assess the hybridization effects of different laminate stacking sequence involving jute/kenaf/E-Glass woven fabric through study of physical and mechanical properties of nine different resulting composites. The composite laminates were fabricated using vacuum bagging method. The assessment of mechanical properties and study of fractured surfaces indicate significant improvement in tensile and flexural properties of jute/kenaf fabrics reinforced epoxy composites. [ABSTRACT FROM AUTHOR]

The aim of this paper is to assess the accuracy and reliability of a simple non-destructive sonic technique for evaluating the effective elastic and vibration properties (damping coefficient) of various isotropic and orthotropic materials--in particular, of a recently developed class of 3D fiber-metal laminates (FML). Aluminum, E-glass/epoxy composite, 3D-FML, and glass-reinforced aluminum FML (GLARE) materials were considered. It is exhibited that the 3D-FML offers the greatest damping characteristics in comparison to all the considered materials. Moreover, the sonic technique, facilitated through the use of a GrindoSonic equipment, proves to produce accurate and reliable results with minimal effort. Finite element analysis is also employed to further establish the accuracy of the properties evaluated by the experimental data. The utility of the established homogenized experimental properties within the finite element framework is also discussed. [ABSTRACT FROM AUTHOR]

Cu/Ni laminated composites with the same total thickness of 128 µm, but different modulation wavelength λ (the sum of monolayer thickness of constituent layers) of 32 µm and 3 µm, respectively were prepared using a dual-bath electrodeposition technique. The tensile testing results and the quantitative characterization of strain gradient in the post-necking region of the composites reveal that the λ = 3 µm composites have the higher tensile strength and the better strain hardening ability, as well as the stronger resistance to post-necking compared with the λ = 32 µm ones. A high density of layer interfaces in the ultrathin laminated composite may play a key role in delaying the development of unstable plastic deformation along the layer thickness direction through periodical strain gradient and a number of geometrically necessary dislocations near the interfaces. Thus, the fatal localized plastic deformation along the through thickness direction has to be spread over along the loading direction, leading to the large neck breadth in the ultrathin laminated composites. [ABSTRACT FROM AUTHOR]

Compared with homogenous monolithic structure, laminated structure was utilized to improve the fracture toughness of Ti/B 4 C composite in this work. Monolithic and laminated composite with Al doped as sintering aids were successfully prepared via vacuum hot-pressing sintering. Structurally, laminated composite was designed to stack periodically with Ti(Al) and B 4 C layers. The results of XRD and EDS suggested that laminated structure restrained the interfacial reaction between Ti and B 4 C phase by confining the contacting area between Ti and B 4 C layers on interface. As expected, the fracture toughness of the laminated composite reaches to 9.22 ± 1.12 MPa m 1/2 , which increased by approximately 201% compared with monolithic composite (4.58 ± 0.81 MPa m 1/2 ). This remarkable improvement of fracture toughness was attributed to multiple-layers structure, ductile Ti layers and crack deflection. Thus, laminated structure is a promising approach to produce high toughens metal/ceramic composites. [ABSTRACT FROM AUTHOR]

The results of a low-velocity impact programme on both carbon/epoxy and glass/polyamide-6 composite laminates are compared to the results of quasi-static indentation. Cross-ply and quasi-isotropic stacking sequences are impacted and quasi-static indentation tests are performed up to the same maximum displacement. The response of the laminates to both test methods is compared in terms of force-displacement behaviour, dissipated energy and resulting damage. Significant differences between low-velocity impact and quasi-static indentation are found for both material systems. It is therefore concluded that the test methods cannot be interchanged for material characterisation. [ABSTRACT FROM AUTHOR]

Transmitted light photography, microscopy and transmitted light scanning are well-established methods of optical damage characterization in glass fiber-reinforced composites. Subsequent damage evaluation such as determination of crack density and delaminated areas can either be done by hand or by means of image analysis software. Digital image analysis, however, is rather sensitive to damage illumination and contrast. Results tend to be inaccurate when damage states are complex, showing overlapping cracks and delamination. Therefore, a new laser-based illumination method capable of separately illuminating transverse cracks and interfacial delamination is presented. An exemplary [90/0] s cross-ply laminate tested in the very high cycle fatigue range was evaluated using transmitted light photography as well as the new method. [ABSTRACT FROM AUTHOR]

In order to study the delamination of thick composite laminates under low-energy impact, damage prediction and analysis were presented in this paper. The impact tests were carried out on specimens with three kinds of stacking sequence under three energy levels, and followed by the nondestructive tests to obtain the delamination region. Then numerical models were built to simulate the delamination behavior of composite laminates. The simulation results showed a good correlation to the experimental observations. Furthermore, delamination characteristics in plane and its extension through thickness direction were put forward. The delamination shape was found enclosed by Archimedes spiral and the fiber direction of the layer above and below. The delamination location was limited by the impact zone and the fiber distribution. In the thickness direction, the extension area was found decreased layer by layer. Moreover, the characteristics above were revealed through the analysis of damage mechanism. Finally, the verification of the predicted results was presented based on experiments. The realization of delamination prediction may contribute to evaluating residual strength and optimizing airplane structures. [ABSTRACT FROM AUTHOR]

Changes are reported in perpendicular and parallel glossiness, lightness (L*), red colour (a*) tone, and yellow colour (b*) tone due to thermal aging in beech (Fagus orientalis Lipsky), maple (Acer pseudoplatanus L.), northern red oak (Quercus rubra), American black walnut (Juglans nigra L.), and walnut (Juglans regia L.) wood coated with a UV system commonly used on laminated parquets. Coated samples were exposed to different thermal aging levels (30 °C for 30 days, 60 °C for 60 days, and 90 °C for 90 days). Colour and gloss were determined before and after the thermal aging processes. The L* decreased for all species with the thermal aging decreasing more for more intense processes. Variations of the a* and b* colour parameters depended on the species. The colour parameters changed for temperatures higher than 30 °C. In general, glossiness decreased proportionally to the severity of the thermal aging for all of the species studied. [ABSTRACT FROM AUTHOR]

Scaling effects in the perforation resistance of a carbon fibre-reinforced polymer (CFRP) composite have been investigated under quasi-static and low velocity impact loading conditions. The perforation data have been supplemented with results from additional flexural tests on scaled composite beams, which highlighted a decrease in both strength and failure strain as scale size increases. Strain-rate effects in this composite have been also identified, with the plates absorbing less energy as the loading-rate is increased. Tests on scaled plates have shown that the normalised perforation energy increases rapidly with scale size. An examination of the load-displacement response indicates that the elastic response obeys a simple scaling law, whereas that the damage does not. It was found that fibre damage was more severe in larger composite panels. It is argued that the energy absorbed in fibre fracture does not scale in the expected manner, leading to greater levels of fibre damage in the larger plates. [ABSTRACT FROM AUTHOR]