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Cutouts are widely used to accommodate windows, openings for access purposes, or fasteners in the primary structural parts of airplanes. The presence of cutouts in composite panels results in stres...

The objective of this work was to grow carbon nanocoils (CNCs) on the glass fiber (GF) surface by chemical vapor deposition (CVD) and to prepare laminated composites by hand lay-Up, where CNC-coate...

Purpose The purpose of this study is to obtain strong materials with multiwall carbon nanotubes (MWCNTs) doped and investigate laser cut of MWCNTs also find the effect of the laser cutting parameters on composite materials. Design/methodology/approach The laminated composite plates were manufactured by using a vacuum infusion process. The mechanical properties of the composite materials produced were determined according to American Society for Testing and Materials (ASTM) D3039M, ASTM D3171, ASTM D 792 and ASTM D2583. A 130 Watts carbondioxide (CO2) laser cutting machine was used for drilling the two different composite plates with a thickness of 1.6–1.5 mm. Three variables were considered as process parameters including laser power (in three levels of 84.50, 104.00 and 127.40 W), cutting speed (in three levels of 4, 6, 8 mm/s) and 14 mm fixed focal position. Findings The fibers could not be cut due to insufficient melting in the experiments performed using 84.50 and 104.00 W laser power but the cutting was successfully completed when the laser power was 127.40 W. However, as the cutting speed increased, the contact time of the laser beam with the material decreased, so the kerf decreased, but the increased laser power created a thermal effect, causing an increase in hardness around the cutting surface. This increase was lower in MWCNTs doped composites compared to pure composites. It has been found that the addition of nanoparticles to layered glass fiber composite materials played an effective role in the strength of the material and affected the CO2 laser cutting quality. Originality/value This study is a unique study in which the CO2 laser cutting method of MWCNT-doped composite materials was investigated and the machinability without cutting errors, such as delamination, splitting, distortion and burring using the most suitable laser cutting parameters was revealed.

The electric conductivity and surface potential distributions of carbon fiber laminated panels with different ply orientations have been investigated. We found that the unidirectional (UD) lamina has higher conductivity along the carbon fiber direction than the perpendicular direction, and equipotential contours also show different gradients along the two directions. The cross-ply (CP) and quasi-isotropic (QI) laminates have the mixed effects of the UD lamina electric conductivity and ply orientations, while the surface potential distributions mostly depend on the surface lamina direction. The conductivity along the thickness direction depends on each lamina and inter-laminar bonding. A finite element analysis model was also developed to show the effect of ply orientation on potential distribution. The CP and QI laminates with 0° surface ply have uniform potential distributions and isotropic electricity behaviors. The results could be used to monitor damage locations and design electric composite materials.

The structure, the strength at high temperatures, and the fracture toughness of the composites fabricated under various conditions of diffusion welding of stacks of Nb foils with coatings made of a mixture of Nb, Ti, Mo, Si, ZrH2, Cr, and Al powders are studied. The strength in the temperature range of 1100–1300°C changes from 490 to 350 MPa, the fracture toughness at room temperature is 15.6 MPa m1/2, and the creep resistance determined in 100-h tests at a residual strain tolerance of 1% at 1150°C is 90 MPa.

In this study, viscoelastic damped dynamic behaviors of laminated composite shells (LCS) under different dynamic loads were investigated. In order to obtain better numerical stability, the truncated series method was used in the formation of equations governing the system. While deriving the equations governing the system, the z/R terms are usually neglected, whereas only 3 and higher order terms are truncated here. The method of truncated equations has been used for the first time as suggested here to obtain viscoelastic damped behavior of dynamically loaded LCS. The governing equation of composite shells was obtained with the help of Hamilton's principle. Afterwards, time dependent partial differential equations were obtained by applying Navier solution method to these valid equations. These equations were transformed into Laplace space in order to solve time dependent partial differential equations. The transformation of the resulting calculations from Laplace domain into the time domain was conducted with the help of Modified Durbin algorithm. In addition, one of the goals of this research is to highlight the importance of including the (1+z/R) part in the equations to account for the curvature effect of the shells. The addition of these effects and truncated series method to the equations and the investigation of their effects are the originalities of the present study. The present work obtained values were compared with the results obtained with Newmark's approach and ANSYS finite element methods. The numerical results showed that the proposed approach is a highly effective and efficient solution that can be easily applied to laminated viscoelastic shell problems.

Rule of mixtures (RoMs) of composite materials is continuously modified according to different component materials and their composition forms to play the role of theoretical verification and evaluation. This paper studied the regular relationship between the bonding surface and mechanical performance of the composites. The three bonding surface designs were made into PLA/EP test samples by 3D printing technology. The tensile and bending properties of the composite materials were proved to be stronger than the average of those of their component materials. The mechanical properties show regular changes with the bonding surface and structural design. The bonding surface between components is an important reference information that cannot be ignored for the performance prediction and adjustment of laminated composite materials.

I-fiber implantation is a new stitching technology that can effectively enhance the interlayer performance of laminated composites. This paper presents and evaluates the design and implementation of the I-fiber robot implantation system integrated for producing high-performance fiber preforms for advanced composites. The system was constructed and validated through I-fiber robot implantation experimentation. It was demonstrated that automated I-fiber implantation could be achieved by use of an industrial robot. The programming method and computer-aided manufacturing software of the I-fiber implantation robot were feasible and effective. The double-cantilever-beam (DCB) experiments showed that the implantation of I-fiber significantly improved the interlaminar fracture toughness of the laminated composite, where the maximum load value increased by up to 106%. The DCB load–displacement curve presented a zigzag shape, where the peaks and valleys were the location points of the I-fiber break. It was also found that for the reinforced laminated composite without an I-fiber head, the delamination failure was manifested as resin cracking and I-fiber pullout, while for the I-fiber with a certain head length, the I-fiber failure mechanism was brittle fracture. I-fiber with a certain head length could significantly improve the interlayer performance of the composite. In addition, DCB experiments also revealed that the implantation matrix had little effect on the interlayer performance of I-fiber reinforced composites, and the failure load value and the I-fiber implantation volume showed an obvious proportional relationship.

This article presents a type of plate Finite Element (FE) models with adaptive mathematical refinement capabilities for modeling laminated smart structures with piezoelectric layers or distributed patches. The p-version shape functions are used in combination with the higher-order Layer-Wise (LW) kinematics adopting hierarchical Legendre polynomials. Node-Dependent Kinematics (NDK) is employed to implement local LW models in the regions with piezoelectric components and simulate the global substrate structure with the Equivalent Single-Layer (ESL) approach. Through the proposed NDK FE models, the electro-mechanical behavior of smart structures can be predicted with high fidelity and numerical efficiency, and various patch configurations can be conveniently modeled through one set of mesh grids. Moreover, the effectiveness and efficiency of the NDK FE approach are assessed through numerical examples and its application is demonstrated.

The effective piezoelectric and flexoelectric properties of heterogeneous solid bodies with constituents obeying a piezoelectric behavior are evaluated in full generality, based on the asymptotic expansion method. The successive situations of materials obeying a piezoelectric and flexoelectric behavior at the macroscale is envisaged in the present work. Closed-form expressions for the effective flexoelectric properties are obtained for stratified materials. A general theory for laminated piezoelectric plates is formulated on the basis of the formulated asymptotic models, and the response of the homogeneous substitution plate is evaluated for a loading consisting of a pure bending moment, triggering electric fields and strain and electric fields gradients within the plate thickness. The local mechanical and electric fields at the microscopic level within the initial heterogeneous stratified domain are evaluated by solving unit cell boundary value problems for the localization operators. An effective flexoelectric plate model for a stratified composite is constructed, showing the generation of the gradient of an electric field under application of a pure bending moment.

Delamination represents one of the most severe failure modes in composite laminates, especially when they are subjected to uniaxial compression loads. The evaluation of the delamination damage has always been an essential issue of composite laminates for durability and damage tolerance in engineering practice. Focusing on the most typical and representative elliptical delamination issue, an analytical model simultaneously considering the conservative buckling process and non-conservative delamination propagation process is implemented. Various computational cases considering different delamination depths, directions, aspect ratios, and areas are established, and the predicted results based on the analytical model are carefully compared. Effects of these geometrical delamination parameters on the buckling, delamination propagation, and failure behaviors of composite laminates are thoroughly analyzed, and innovative evaluation principles of the delamination damage have been concluded. It is found that the delamination area is the key factor that truly affecting the failure behaviors of delaminated composites, and the local / global buckling and failure loads show clear linearity with the delamination area, whilst the delamination depth and direction only have slight effects.

It is known that many researchers of the mechanical properties of layered composites claim that in comparison with traditional structural metals and alloys, composites have serious advantages, mainly associated with high specific characteristics of static and fatigue strength. It should be noted that a well-founded idea of the advantages of composites strength characteristics is of particular importance for the elements of aircraft structures, taking into consideration an extremely important issue of operation safety. Unfortunately, at least, such a reasonable conception with respect to fatigue resistance characteristics has not been formed yet, consequently, a number of points concerning application of laminated composites in aircraft structures remain unanswered. The article presents a method and an example of comparing the fatigue life of the specimens with the open hole made of modern aluminum aviation alloy 1163T7 and carbon laminate AS4-PW. An obvious advantage of fatigue life of carbon composite materials compared to aluminum alloy at room temperature is noted. On the basis of a number of significant factors to be considered, the specified advantage can be largely diminished. First of all, these factors include the following: effect of temperature and humidity and degradation of the resistance characteristics of layered composites after impact damage. Taking into account the effect of the listed factors, the results of the comparison for the fatigue resistance characteristics of the specimens under consideration are presented. It is noted that the mentioned comparison was carried out using experimental data for the specimens considered under cyclic loading with constant amplitudes as well as under irregular loading, therefore, the comparison results may be slightly different. Nevertheless, it is obvious that the similar comparison presents relevant interest and should be considered when drawing final conclusions about the advantages (or their absence) of the fatigue resistance characteristics of carbon laminates over aluminum alloys.

Through-thickness reinforcement is a promising solution to the problem of delamination susceptibility in laminated composites. Modeling Z-pin–prepreg interaction is essential for accurate robotics-assisted Z-pin insertion. In this paper, a novel Z-pin insertion force model combining the classical cohesive finite element (FE) method with a dynamic analytical fracture mechanics model is proposed. The velocity-dependent cohesive elements, in which the fracture toughness is provided by the analytical model, are implemented in Z-pin insertion FE model to predict the crack initiation and propagation. Then Z-pin insertion experiments are performed on prepreg sample with metallic Z-pins at different velocities to identify the analytical model parameters and validate the simulation predictions offered by the model. Dynamics of Z-pin interaction with inhomogeneous prepreg is described and the effects of insertion velocity on prepreg contact force are studied. Results show that the force model agrees well with experiments and the fracture toughness rises with the increasing Z-pin insertion velocity.

Purpose The purpose of the study is to machine the composites at lower machining time with higher accuracy without causing delamination. Design/methodology/approach Abrasive jet machining is the technology appropriate for machining composite materials to obtain good dimensional accuracy without causing de-lamination. The central composite design was followed in deciding the number of experiments to be carried out. Findings The influence of abrasive jet machining process parameters on machining time, material removal rate (MRR) and kerf characteristics were investigated. The experimental results proved the newly designed internal threaded nozzle increased MRR, thereby reducing the machining time. Originality/value Machining of glass fibre reinforced polymer (GFRP) is one of the challenging tasks given its non-linear and in-homogeneous properties. In this investigation, newly developed threaded and unthreaded nozzles in machining were used for making holes on the GFRP composites.

In this study, pin-loading behavior of laminated composites reinforced with three-dimensional (3D) spacer fabric was investigated, experimentally. Failure loads and modes of 3D-woven glass fiber epoxy composites, which are mostly preferred in automotive, machinery, and building production, are determined and compared with the mechanical properties of two-dimensional (2D)-woven fabric-reinforced composite materials. For this purpose, 2D plane and 3D spacer fabric composite plates were produced using the vacuum infusion method. The effect of pin geometry on joint strength and failure mechanism of composite was determined by tensile tests using test apparatus of single and two serial pin joint. In addition, low velocity impact tests of 2D and 3D plates were performed to explain the failure behavior. For mono-layer 3D-woven fabrics, the existence of out-of-plane fiber increases failure strength up to 50% compared to 2D fabrics. On the other hand, the use of multi-layer 3D fabric does not affect changes-specific failure load according to 2D fabrics significantly. Increasing in the specific load is only 9% for two-layers 3D. This situation has also been observed in impact tests.

Polimer matrisli tabakalı kompozit malzemelerin bileşenlerinin dayanım yönünden çok farklı olması bu malzeme grubunun hasar analizlerini zorlaştırmaktadır. Tabakalı kompozitlerin hasar analizleri için önerilen birçok hasar ölçütü bulunmaktadır. Bu çalışmada iki yönde düzlemsel yayılı yüke ve bir yönde yayılı yük ile kayma yüküne maruz S-cam lifi/epoksi ve karbon lifi/epoksi tabakalı kompozit malzemelerin Tsai-Wu ve Puck ölçütüne göre hasarı araştırılmıştır. Birçok yükleme halinde Puck ölçütü daha güvenli hasar zarfları göstermektedir. Ancak hangi hasar ölçütünün daha güvenli olduğu tabakalı kompozit malzemelerin türüne, çevresel şartlara, takviye lif açılarına ve yüklemenin işaretine göre farklılıklar göstermektedir. Her iki malzeme türünün hem açılı hem de çapraz katlı tasarımları için tüm iki eksenli yüklemelerde malzeme dayanımını en çok düşüren etken ortam nemidir. S-cam lifi/epoksi tabakalı kompozitlerde Puck ölçütü ile oluşturulan hasar zarfları ortam sıcaklığından daha fazla etkilenirken, karbon lifi/epoksi tabakalı kompozit malzemelerde Tsai-Wu ölçütü ortam sıcaklığı değişimine karşı daha duyarlı davranış göstermiştir., The fact that the components of the polymer matrix laminated composite materials are very different in terms of strength makes the damage analysis of the materials difficult. There are many damage criteria recommended for damage analysis of laminated composites. In the present study, the damage of S-glass fiber/epoxy and carbon fiber/epoxy laminated composite materials subjected to planar distributed loads in two directions and also a planar distributed load with shear load was investigated according to Tsai-Wu criterion and Puck criterion. Puck criterion indicates more conservative damage envelopes in many loading cases. However, which of the criterions is more conservative varies according to the type of laminated composite materials, environmental conditions, orientation of fiber reinforcements and the sign of loading. For both the angle-ply and cross-ply stacking of both the laminated composite materials, it is the ambient humidity that decreases the material strength the most in all biaxial loadings. For the S-glass fiber/epoxy laminated composites, failure envelopes created by the Puck criterion were affected more by ambient temperature, while for the carbon fiber/epoxy layered composites Tsai-Wu criterion showed more sensitive behavior due to ambient temperature changes.

The present study investigates buckling characteristics of cut-out borne stiffened hyperbolic paraboloid shell panel made of laminated composites using finite element analysis to evaluate the governing differential equations of global buckling of the structure. The finite element code is validated by solving benchmark problems from literature. Different parametric variations are studied to find the optimum panel buckling load. Laminations, boundary conditions, depth of stiffener and arrangement of stiffeners are found to influence the panel buckling load. Effect of different parameters like cut-out size, shell width to thickness ratio, degree of orthotropy and fiber orientation angle of the composite layers on buckling load are also studied. Parametric and comparative studies are conducted to analyze the buckling strength of composite hyperbolic paraboloid shell panel with cut-out.

In this study, the effect of adding nanosize additive to glass fiber reinforced composite plates on mechanical properties and surface milling was investigated. In the light of the investigations, with the addition of MWCNTs additive in the composite production, the strength of the material has been changed and the more durable composite materials have been obtained. Slots were opened with different cutting speed and feed rate parameters to the composite layers. Surface roughness of the composite layers and slot size were examined and also abrasions of cutting tools used in cutting process were determined. It was observed that the addition of nanoparticles to the laminated glass fiber composite materials played an effective role in the strength of the material and caused cutting tool wear.

Aircraft designers are legally required to treat manufacturing variability so as to minimize the probability of structural failure, pursuant to Code of Federal Regulations (CFR) 25.613. The usual d...

Three types of representative unit cell (RUC) of [±θ/904]S composite laminates and cracked plies were created to obtain the constitutive model of the cracked plies and to compare their accuracy of ...

Mechanical properties of multidirectional fiber-reinforced composite laminates are dispersive and random, and these uncertainties cause difficulties in safety design of structures. So, it is necessary to analyze the sensitivity of uncertain material properties on failure of structures. In this paper, sensitivity analysis of uncertainties for composite laminates with different stacking sequences and under various loadings is performed by the improved Puck’s theory and the importance measurement analysis method. The improved Puck’s theory with the in situ strength effect which considers the influence of both the lamina itself and its neighboring laminae can predict the initial and final failure accurately. Three examples ([45°/0°/–45°/90°]2s laminates under uniaxial tension, [0°/90°2/0°]s laminates under uniaxial tension and biaxial tension) are examined, and results show that the failure loads obey normal or log-normal distribution when the distribution of uncertain material properties is log-normal. Results of sensitivity analysis show that the longitudinal tensile strength of a unidirectional lamina has the greatest influence on the final failure for laminated composites, and is positive relative to final failure loads. As for initial failure, the influence of each material property on failure is different because of different failure mechanisms of composite laminates with different stacking sequences and under various loadings. The results provide an in-depth understanding of the influence of material properties on failure of composite laminates for safety design.

The unique microstructure of biomaterials provides inspiration in materials structure design and performance breakthroughs. Here we prepared a MoAlB reinforced Al matrix composites with laminated structure and strong interfacial bonding. This work mainly focuses on the relationship between tribological properties of the MoAlB/Al laminated composites and the MoAlB layer orientation. The results show that the tribological properties of the composites deeply depend on the relation of sliding direction VS. the MoAlB layer orientation, while the dependency gradually decreases with the MoAlB content increasing. The friction coefficient and wear rate of the composites can be decreased by 55.5% and 95.1%, lower than those of pure Al, when 15 vol% MoAlB reinforcement is added. The friction and wear mechanisms of the MoAlB/Al laminated composites are proposed, and the outstanding tribological properties are ascribed to the formation of tribochemical worn film and different stress states caused by the laminated structure.

Ceramic composites are extremely sensitive to the surrounding environment. Their tribological performance may degrade drastically if they are polluted by some external agent. The present article was aimed to investigate the unidirectional sliding characteristics of brake oil treated woven carbon-carbon (C/C), and carbon-carbon-silicon carbide (C/C-SiC) composites. The laminate orientation, surface conformity, normal load, and sliding velocity were varied. It was depicted that the quantity of oil absorbed by the composites depends on the laminate orientation. The decay rate in friction coefficient revealed that C/C composites are more prone to brake oil in comparison to C/C-SiC composites. The results showed that it is difficult to make an assumption regarding the wear and friction behavior of laminated composites in low conformity contacts concerning normal load and sliding velocity. However, friction coefficient increased with increment in sliding velocity and normal load, for non-conformal Hertzian contacts. The generation of friction film was arduous in the presence of absorbed oil. SEM analysis of worn surfaces revealed different surface morphology for low, and non-conformal contacts which depicted distinct tribological mechanisms.

Laminated metal composites are composed of alternating layers of metals or alloys, bonding together at their interface, which have gained extensive attention because of their advantages such as improved fracture toughness, impact behavior, corrosion, wear and damping capacity. Roll bonding is the most widely used method to process many metallic composites. In this study, we fabricated some kinds of Al/Ti/Al sandwich-like laminated composites by cryogenic roll bonding. We find that cryogenic roll bonding techniques can improve the mechanical properties of laminated composites. Finally, we will discuss the mechanism of improvement in bonding strength and mechanical properties.

In this article, mode II fracture toughness ( G IIc {G}_{\text{IIc}} ) of unidirectional E-glass/vinyl ester composites subjected to sulfuric acid aging is studied at two different temperatures (25 and 90°C). Specimens were manufactured using the hand lay-up method with the [ 0 ] 20 {{[}0]}_{20} stacking sequence. To study the effects of environmental conditions, samples were exposed to 30 wt% sulfuric acid at room temperature (25°C) for 0, 1, 2, 4, and 8 weeks. Some samples were also placed in the same solution but at 90°C and for 3, 6, 9, and 12 days to determine the interlaminar fracture toughness at different aging conditions. Fracture tests were conducted using end notched flexure (ENF) specimens according to ASTM D7905. The results obtained at 25°C showed that mode II fracture toughness increases for the first 2 weeks of aging and then it decreases for the last 8 weeks. It was also found that the flexural modulus changes with the same trend. Based on the results of the specimens aged at 90°C, a sharp drop in fracture toughness and flexural modulus with a significant decrease in maximum load have been observed due to the aging. Finite element simulations were performed using the cohesive zone model (CZM) to predict the global response of the tested beams.

This paper presents a novel investigation on the robustness of Acoustic Emission (AE) technique on the characterization of indentation-induced Damage Mechanisms (DMs) in scaled laminated composites. AE is used to monitor a comprehensive series of scaled Quasi-Static Indentation (QSI) tests performed on Quasi-Isotropic (QI) S-glass/8552 epoxy composite plates, with in-plane and intra-plane scaling. A detailed assessment of the damage evolution is carried out through\ud clustering of the monitored AE signals. The AE results indicated the existence of different DMs such as delamination, matrix\ud cracking and fiber breakage. Ultrasonic C-scan and visual observations were also used to verify the AE based results. It was\ud observed that both in-plane and intra-plane scaling alter the induced DMs, and the AE analysis was able to accurately identify\ud and quantify the DMs in each case. However, the AE features (frequency, energy and count) were found to be dependent on\ud different variables such as size, geometry and stacking sequence of the investigated samples. This research highlights the\ud potential and challenges to develop AE as a reliable structural health monitoring system for impact/indentation damage monitoring of composite plates over a range of sizes and complexities.

The main objective of this paper is to investigate the effects of distilled water on the flexural and impact properties of glass/aramid fibers reinforced epoxy resin hybrid laminated composites. Four different groups of composite samples ([G6]S, [A6]S, [G3A3]S, [A3G3]S) were produced by the vacuum infusion method (VARIM), and treated with the distilled water at a temperature of 25 and 70°C for 1000 h. Mechanical tests were carried out under three different conditions, dry, wet, and re-dried. The mass gain ratio of the samples was examined for different periods. The fracture surfaces of the samples were examined using SEM. Results indicated that water intake of all composite samples followed as Fickian-like behavior. The stacking sequence of hybrid composite showed a major effect on water absorption features. The distilled water treatment caused a significant decrease in flexural strength, impact strength of all groups. Reduction of flexural strength and impact strength were increased as the temperature was increased for both impact tests.

In this paper, the impact response of bi-directional corrugated core sandwich structures was investigated. The core and skins were made of E-glass/epoxy laminated composites. Additive manufacturing technology was used to print the molds applied to fabricate the cores. The influence of different periods, i.e. T = 30, 37.5, 50 and 75 mm, of the double-cosine corrugated core on the impact response of the panels was evaluated. In addition, some other panels with regular corrugated cores were manufactured to evaluate the impact response of the bi-directional corrugated core structures. A finite element modeling was also carried out to analyze the impact behavior of the samples. The empirical measurements and the numerical predictions showed that the panels with the bi-directional corrugated core have a significant improvement in the absorbed energy under impact loading at each given period. It was also manifested that the panel consisting of the bi-directional corrugated core with T = 37.5 mm has the highest specific energy absorption.

Based on a modified Hellinger–Reissner mixed variational principle and considering the displacements as known quantity, a simple and straightforward finite element linear system of equations for al...

In this article, the effects of damage (delamination) on the structural vibration characteristics of spar wingskin joints (SWJs) made with curved laminated composites are investigated. Three dimens...

The review of recent literature shows that the bending performances of transversely loaded laminated composite singly curved stiffened surfaces are not studied in detail using the geometrically nonlinear strains. The present paper aims to fill that void and proposes an isoparametric C° finite element formulation combining von-Karman nonlinearity and Sanders’ first approximation theory. The curved surfaces are simulated using nonlinear strains. The stiffeners are formulated using geometrically linear and nonlinear strains. The correctness of the proposed approach is confirmed through solution of benchmark problems. The relative performances of stiffened curved surfaces in terms of maximum transverse displacements are studied for industrially important parametric variations like boundary conditions, laminations, stacking sequences, and number, orientations, eccentricities, and depth of stiffeners. The results are critically discussed and it is concluded that the clamped 0°/90°/0° shell with curved stiffeners ( y-stiffener) located below the mid-surface shows the greatest bending stiffness. The nonlinear approach is essential for both shell and stiffener for correct prediction of the transverse displacements. The relatively simpler linear approach can be considered for single x-stiffener only.

The objectives of this article are to seek the opportunity to enhance the local Indonesia timber material physical performances (encompassing the low-class quality of III and IV timbers with the Modulus of Elasticity (MOE) = 5,000 - 9,000 MPa) utilizing laminated composite technology to become higher-class timber quality (class II) with the Modulus of Elasticity (MOE)> 15,000 MPa so that it can be used as an alternative material for constructing the bridge mainframe structures (girder beams) especially for the Indragiri Hilir regency, Riau Province, Indonesia. This regency needs several hundred small-medium bridges for connecting 20 districts, 39 wards, and 197 villages using local materials such as local timbers. This laminating technology is not a new technology but the utilization of this technology for constructing the main bridges structures is challenging and limited to the implementation in the civil construction industrial sector. This study composed 2 types of the low-class quality (lcq) of timber materials (such as Shorea sp and Shorea peltata Sym) and 2 types of medium class-quality (mcq) ones (Dipterocarpus and Calophyllum) for constructing the main bridge structures. Based on the laboratory test results utilizing 80% of lcq materials and 20% mcq ones, these composite timber materials may increase the timbers MOE by 145% to 166% from the existing MOE value of the mcq solid timbers. Based on the simulations these laminated composites wooden bridge girders 2 x (70x20) m2, these timber materials have passed all the tests and the application of this technology may improve the lcq timber values and it could be used for an alternative material of the bridge girder's main structures.

A manufacturing process hand layup technique was used to produce carbon fiber/epoxy laminates with the epoxy matrix with a variation of 0.5 wt % to 2 wt% carbon nanotubes (CNTs). Microstructural ob...

The problem of the effective elastic properties of a fiber-reinforced cross-ply composite material and imperfect contact between plies with orthogonal fiber directions is considered. The imperfect contact is modeled by a porous isotropic interlayer that is in perfect contacts with the plies. The stochastic equations of elasticity for unidirectional fibrous and laminated composites are used. The problem is solved in two stages: (i) prediction of the effective properties of a unidirectional fiber composite from the given properties of the fibers and matrix and (ii) prediction of the effective properties of the laminated composite from the known properties of the plies. The effect of interlayer defects on the effective elastic properties of a fiber-reinforced laminate is studied.

The composite materials exposed to dynamic loads may suffer damage at strength value, which is under own yield strengths. Also, improper environmental conditions accelerate the damage process. In this study, the effect of heavy chemical environments such as acid and alkaline and retaining time for these environments on flexural strength and fatigue behavior of E-glass/epoxy laminated composites was investigated. In this content, glass/epoxy (G8) having eight layers was produced by using the hand lay-up method. The produced composite materials were retained into acidic and alkali solution having 5%, 15%, and 25% concentration a period of 1, 2, 3, and 4 months. A computer-controlled fixed-end type fatigue test machine capable of tilting 10 test samples at the same time was designed and manufactured to determine the fatigue behavior of composite samples. Fatigue behavior of glass/epoxy was determined under dynamic flexural load which corresponds to 80%, 70%, 60%, 50%, and 40% of static three-point bending strength of the test sample. SEM image of damaged specimens was taken to describe the failure mechanism of damage which occurs after fatigue. Also, to better understand environmental condition on the fatigue life, results were compared with results of glass/epoxy laminated composites, which were not retained into any environments (0%).

Natural fiber reinforced composites are currently used in various fields such as automobile, building construction and furniture materials considering the increasing environment pollution caused by the extensive use of plastic products. In this study, jute fiber and polylactic acid (PLA) were combined to prepare jute PLA-based biodegradable composites. PLA is one of the most attractive research pursuits among thermoplastic composites due to its excellent biodegradability and the ultimate degradation products of PLA are carbon dioxide and water, which have no pollution to the environment. Basically, the mechanical and thermal performances of the jute/PLA laminated composites were characterized and analyzed in this work. The analytical results on jute/PLA sandwiches reveal that different ply counts and stacking sequences significantly influence the mechanical properties of the composites material. The study on jute/PLA composites will provide quantitative experimental data for potential applications with advantages of lightweight, cost effective, easy manufacture, biodegradable and excellent mechanical properties.

A mixed mode crack density estimation method based on the finite element analysis (FEA) for laminated composites is proposed and verified in this paper. The damaged properties of cracked ply are obtained using semi-analytical micro-mechanical method for the first time. The piecewise functions of the mode I and mode II energy release rates involving crack density are given based on Griffith’s energy principle and discrete damage mechanics (DDM). Any mixed mode fracture criteria could be simply applied to the FEA of the structure to calculate the initiation and evolution of the micro-cracks in the laminate. Mode I criterion, power law and B-K criterion are applied in the numerical examples to compare their performances in the crack density estimation. It has been concluded that the accuracy of the fracture toughness is more important than the choice of fracture criterion in crack density estimation.

Damping characteristics of three-layered sandwich cylindrical shells with the focus on mode switching phenomenon are investigated in the present study. All layers of the sandwich cylinder are formu...

Addition of oxygen in the interface between Cu and Al2O3 can significantly improve the wettability. In the present work, Cu/Al2O3 laminated composites were fabricated by bonding Cu foils with CuO-coated Al2O3 plates. Before bonding, the coated Al2O3 plates were pretreated at different temperature in the air. The effect of pretreated temperature on the interfacial microstructure, wettability and bending property were investigated. Phase composition in the interface after wetting test was characterized according to the thermodynamics of Cu–O system. The wetting mechanism and bending failure mode of Cu/Al2O3 laminated composites were also analyzed. Pretreated temperature significantly influences the wettability and bending strength of the composites. The contact angle decreased to about 22° when the pretreated temperature equal to 1100 °C. Continuous CuAlO2 in the interlayer is beneficial to the wettability between Cu melt and Al2O3, while other phases such as Cu2O and CuAl2O4 would increase the contact angle. Crack formation and propagation are the main failure mode of Cu/Al2O3 laminated composites during bending test. Different from the wettability, Cu/Al2O3 laminated composites fabricated with pretreated temperature at 1050 °C show the highest bending strength, although the contact angle is not the lowest on this condition. The reason is illustrated through analyzing the bending failure mode.

Studying buckling behavior of large shell structures through full-scale test articles can be complex and expensive. Therefore, reduced-scale structures are often preferred for investigating bucklin...

For the high cost of aramid fibres and the necessity for finding alternatives which are environmentally friendly, a portion of aramid was substituted by woven kenaf at various sequences and thicknesses, to identify the proper arrangement for producing helmet shell. Drop-weight impact tests were conducted on different configurations of 19 layers of kenaf and aramid reinforced polyvinyl butyral film, which were fabricated by the hot press method. Effects of fibre content, layering sequence and energy absorption of the laminated composites were studied at three different impact energies 50, 75, 100 J. Results suggested that the behaviour of hybrid laminates has a positive effect in terms of energy absorbed and impact resistance, due to lower failure strain of kenaf fibres. Additionally, placing woven kenaf layers alternate with aramid layers provides higher impact loads and absorbed energy than placing woven kenaf and aramid separately, especially at impact level 100 J. For example, the absorbed energy of the 17 Aramid/2 Kenaf Alt. (H1A) is 72.99 J, while for 17 Aramid/2 Kenaf (H1) is 66.04 J. The closed curves indicated the success of the samples in absorbing the dissipated energy at various impact energies values. It could be deduced that it is possible to replace the aramid fibre in various composites industries by kenaf fibre, to minimize harmful environmental effects and cost of petroleum products.

Spatial heterogeneity of adhesion properties is known to result in bridging during debonding of secondary bonded composite joints. The ligaments that bridge both substrates have crack-arrest features and thus significantly enhance the fracture resistance of joints. We have investigated the effect of randomly distributed adhesion properties between the adhesive layer and each composite substrate in previous works; however, the spatial correlation of adhesion heterogeneity within or between the substrates and how it effects the failure of secondary bonded composites is still poorly understood. In this current work, we assume that the spatial heterogeneity of adhesion follows a log-normal distribution. The Napierian logarithm of interface toughness Gc and separating strength S can thus be described by a Gaussian Process. We investigate in detail the effect of spatial correlation both within each substrate and between opposite substrates. Finally, we predict the crack resistance of such joints with adhesives of different mechanical properties. We find that the failure strain of adhesives is important through varying the elongation of ligaments and thus the associated extra dissipated energy. This work represents the first critical step for designing tougher secondary bonded composite joints by triggering and controlling adhesive ligament bridging.