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In the field of high-frequency communications devices, there is an urgent need to develop high-performance copper clad laminates (CCLs) with low dielectric loss (Df) plus good flame retardancy and thermal stability. The hydrocarbon resin styrene-butadiene block copolymer (PSB) was modified with the flame-retardant 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide/polyhedral oligomeric silsesquioxanes (DOPO-POSS) to meet the demands of high-frequency and high-speed applications. The resulting DOPO-POSS-modified PSB was used as the resin matrix along with other additives to fabricate PSB/DOPO-POSS laminates. At a high-frequency of 10 GHz, the laminates containing 20 wt.% of DOPO-POSS and with a thickness of 0.09 mm exhibited a Df of 0.00328, which is much lower compared with the commercial PSB/PX-200 composite (Df: 0.00498) and the PSB without flame retardancy (Df: 0.00453). Afterwards, glass fiber cloth (GF) was used as a reinforcing material to manufacture GF-PSB/DOPO-POSS composite laminates with a thickness of 0.25 mm. The flame retardancy of GF-PSB/DOPO-POSS composite laminate reached vertical burning (UL-94) V-1 grade, and GF-PSB/DOPO-POSS exhibited higher thermal and dynamic mechanical properties than GF-PSB/PX-200. The results of a limited oxygen index (LOI) and self-extinguishing time tests also demonstrated the superior flame-retardant performance of DOPO-POSS compared with PX-200. The investigation indicates that GF-PSB/DOPO-POSS composite laminates have significant potential for use in fabricating a printed circuit board (PCB) for high-frequency and high-speed applications. [ABSTRACT FROM AUTHOR]

Industries such as aerospace, robotics, defence, light aircraft, and transportation are increasingly in need of lightweight and strong materials. Aluminium-magnesium alloys are the preferred choice due to their high strength and stiffness-to-weight ratios compared to traditional materials. This study utilized an innovative technique called friction stir additive manufacturing (FSAM) to develop a laminated sheet of Al5083-AZ31B alloys for multipurpose applications. The effect of the rotational speed of the tool is examined over the microstructural features and bonding strength of the lamination. The study examined the macrostructural and grain refinement results at the interfacial layer through light microscopy, FESEM and EBSD analysis. XRD test has been conducted and discussed in terms of crystallographic planes and chemical compounds at the interfacial layer. To validate the specimen's bonding strength, tensile tests and Brinell hardness tests are conducted. The result reveals a higher ultimate strength of 297.25 MPa at 2000 rpm while lower strength is observed at 234.47 MPa for rotational speed at 1000 rpm. The maximum BHN of 71.1 is recorded at a rotational speed of 2000 rpm The strong interfacial compounds such as Al4Fe, and Mg2Al3 are supports the bonding strength and increase hardness. [ABSTRACT FROM AUTHOR]

The progressive fatigue damage (PFD) model is a well-known approach for simulating the fatigue behavior of laminated composites. In the PFD model, stress-based failure criteria detect failure modes in a unidirectional (UD) ply of laminated composites. Using stress-based failure criteria requires performing numerous UD ply characterization tests. The present research presents a series of strain-based failure criteria for the unidirectional ply under fatigue loading conditions. Using the current criteria, the need for strength degradation tests was eliminated, and the number of characterization tests was reduced drastically. Using a user-defined material behavior (UMAT) subroutine code, stress-based failure criteria were replaced by the present strain-based failure criteria in the PFD model. To evaluate the results of the model, a comprehensive experimental program was conducted to characterize the mechanical properties of UD ply and laminated composites (with/without hole) under static and fatigue loading conditions. Moreover, the PFD model was also evaluated by the available experimental data of pin-loaded composites under fatigue-loading conditions. Compared to the stress-based criteria, the present criteria improved the accuracy of the predicted fatigue life by up to 63% and reduced the cost of testing by about 50%. [ABSTRACT FROM AUTHOR]

Orienting or placing the yarns at the third direction of three dimensional (3D) textiles may improve or degrade the in- plane mechanical properties of 3D composites. In the previous study, the bending and out- of- plane mechanical properties of 3D composites were comprehensively investigated. As the controversial results can be clarified in the literature, the study was extended to investigate the in and off- axes mechanical properties of 3D composites. The tensile and in- plane shear properties of 3D carbon woven, 3D carbon multi- axis warp knitted, and 3D carbon stitched fabrics were comparatively examined from dry structure to the composite. In addition, a carbon traditional laminated composite was produced and tested to make a comparison. According to the load bearing capacity of 3D textiles from dry structure to the composite, the 3D woven fabric shown the worst performance. [ABSTRACT FROM AUTHOR]

This study focused on assessing the morphological, anatomical, and physico-mechanical properties of fishpole bamboo [Phyllostachys aurea (André) Rivière and C.Rivière] grown in Baguio City, the Philippines. The aim of this study was to establish baseline information about these properties and recommend potential applications beyond ornamental use. The results showed that the relative density, modulus of rupture, and stress at the proportional limit of the fishpole bamboo were higher than those of commercial bamboo species. In terms of morphological properties, the culm diameter and culm wall thickness tended to decrease significantly by 64.0 and 39.96%, respectively, toward the top portion. In contrast, the internode length increased significantly from bottom to middle by 41.57%. With respect to anatomical properties, the fiber length, fiber and lumen diameter, and cell wall thickness significantly decreased from bottom to top by 14.89, 13.63, 23.32, and 10.67%, respectively. Conversely, its relative density and radial shrinkage significantly increased by 23.06% and 26.77%, respectively, toward the top. Regarding the mechanical properties, the modulus of rupture, stress at the proportional limit, and modulus of elasticity increased significantly by 62.41, 88.25, and 45.51% from the bottom of the culm to the top, respectively. However, the compressive strength (29.40 MPa) and shear strength (2.83 MPa) deviated from this trend. Fishpole bamboo can be employed as a raw material for furniture, window frames, and handicrafts, wherein a large diameter is not required. Additionally, it can be used for canes, walking sticks, umbrella and fan handles, and souvenir materials. Notably, culms with diameters exceeding 5.0 cm can be used as raw materials for laminated and engineered bamboo. They can also be used as raw materials for preparing pellets and briquettes. [ABSTRACT FROM AUTHOR]

This study embedded graphene nanoplatelet (GNP), nano-sized aluminum and copper in epoxy-reinforced woven glass fiber. The 0.5 wt% nanofillers were incorporated into epoxy resin. Nanofilled glass fiber/epoxy hybrid composite laminates were fabricated using the hand layup technique. Fillers were dispersed in an epoxy matrix via the ultrasonic processor. The influence of the inclusion of these nanofillers on the physical and mechanical performance of glass fiber/epoxy composites was studied. The resulting hybrid nanocomposites illustrated good characteristics when compared to control specimens. The graphene nanophased glass fiber/epoxy composite achieved the maximum improvement of 59.2%, 91.5%, 74.7%, and 100% in in-plane shear, fracture toughness, impact, and interlaminar shear strength, respectively. Additionally, glass fiber/epoxy filled with GNP behaved as the lowest seawater absorption. Control filled with 0.5 wt% GNP showed strong fiber/matrix interfacial bonding in scanning electron microscopy images after being subjected to a fracture toughness test. [ABSTRACT FROM AUTHOR]

The formulation of the nth-order shear deformation theory was modified to discuss the hygrothermal response of free vibration of laminated composite plates. Current theory has four unknown variables. Besides, this theory does not require a shear correction factor and gives a parabolic distribution of shear stresses across the thickness of the plate. The properties of the plate are affected by temperature and humidity. The equations of motion are established from Hamilton's principle. The Navier-type solution procedure is applied to determine analytical solutions for free vibration of simply-supported laminated plates. The numerical results obtained by the present analysis of the free vibrations of composite plates are discussed to present the influence of the temperature, humidity, proportion of the aspect, and the orientation of the fiber orient on the characteristics of the vibration of the laminated plate. [ABSTRACT FROM AUTHOR]

In this paper, dispersion properties of guided waves in multilayer composite cylindrical shells are studied, which is composed of the inner and outer hybrid nanocomposite (MHC) layers and the middle composite core layer reinforced with shape memory alloy (SMA) fibers. According to the Hamiltonian principle and the thermoelastic theory, wave equations of the composite structure at different ambient temperatures are derived and discretized with spectral elements. By combing the thermal effects and the acoustoelastic effects, the modified semi-analytical finite element method is proposed here for the thermo-acoustoelastic effects of wave characteristics in laminated composite shells. The influence of important parameters on the dispersion characteristics of the structure is explored. The results show that the coupling of SMA fiber reinforced composite layer and MHC layers can significantly improve wave propagation characteristics of the composite cylindrical shells. The frequency of modal conversion increases with the increase of CNT volume fraction. Smaller radius-to-thickness ratios are favorable for internal wave propagation in the structure. This work is of great significance for the regulation of elastic wave propagation in multilayered cylindrical shell structures, and provides a valuable guide for the design and optimization of shell structures in engineering applications. [ABSTRACT FROM AUTHOR]

Background: The unit pulse integral method is used extensively with the incremental hole-drilling residual stress measurement technique. The ASTM E837 standard, which applies only to isotropic materials, recommends the use of Tikhonov regularization to reduce instability when many depth increments are used. In its current formulation, Tikhonov regularization requires the decoupling of stress, as is possible for isotropic materials. The fully coupled integral method is needed for residual stress determination in layered composite laminates and is currently employed without Tikhonov regularization. This causes greater sensitivity to measurement errors and consequently large stress uncertainties. An approximate method of applying Tikhonov regularization exists for biaxial composites, but is not applicable to more complex laminates. Objective: Extend Tikhonov regularization to the fully coupled integral method to improve residual stress determination in composite laminates. Methods: This work investigates the use of the approximate and fully coupled regularization approaches in an angle ply composite laminate of [+45/-45/0/90]s construction. Experimental validation in a [0/+45/90/-45]s laminate is also presented where the regularized fully coupled integral method is compared to the series expansion method that includes all in-plane stress and strain directions simultaneously in a least-squares solution. Results: The regularized integral method produces comparable results to those of series expansion while requiring twelve times less FE computation to calculate the compliances. The optimal degree of regularization is also more convenient to determine than the optimal combination of series order required by series expansion. Conclusions: The new method is easily applied and should find wide application in the measurement of residual stresses in composite laminates. [ABSTRACT FROM AUTHOR]

This study explores the impact of resin-missing defects on the mechanical properties of composite laminates through experimental and finite element methods. Specimens with varying defect contents (5.3%, 8.0%, 10.7%, 13.3%, and 16.7%) were prepared via Vacuum Assistant Resin Infusion process. Experimental tests were conducted with the assistance of Digital Image Correlation measurements to illustrate the impact of resin-missing defects on failure characteristics. The experimental results indicate that the existence of resin-missing defects altered the stress distribution, increased the local stress, and reduced the tensile strength of the composite laminate. The DIC results indicate that the presence of defects weakens the matrix, leading to premature damage and deterioration. Numerical modeling with a progressive damage analysis method was developed to simulate the failure process and the influence of the resin-missing defects. The simulation results agree well with the experimental results, and the maximum error was 3.06%. The failure modes obtained from finite elements are consistent with the experimental and DIC results. Furthermore, a study was conducted on how the location of resin-missing defects affects the mechanical properties of composite laminates. The findings suggest that defects situated at the edges or on the surface of the material have a more significant impact on the tensile strength. [ABSTRACT FROM AUTHOR]

In this study, AA1050/AA6061 laminated composites were prepared by three-cycle accumulative roll bonding (ARB) and subsequent rolling. The effects of the rolling process on the microstructure evolution and mechanical properties of AA1050/AA6061 laminated composites were systematically investigated. The results indicate that the mechanical properties of the laminated composites can be effectively improved by cryorolling compared with room-temperature rolling. The microstructure analysis reveals that cryorolling can suppress the necking of the hard layer to obtain a flat lamellar structure. Moreover, the microstructure characterized by transmission electron microscopy shows that cryorolling can inhibit the dynamic recovery and significantly refine the grain size of the constituent layers. Meanwhile, the tensile fracture surface illustrates that AA1050/AA6061 laminated composites have the optimal interfacial bonding quality after cryorolling. Therefore, the laminated composites obtain excellent mechanical properties with the contribution of these factors. [ABSTRACT FROM AUTHOR]

The mechanical property of the thin-ply composite are improved, which has more uniform microstructure and fewer manufacturing defects compared with the standard ply composite. Based on the micromechanics theory, an RVE analysis method is proposed considering the interlaminar resin region in this paper. The influence of the interlaminar resin region on the RVE model of thin-ply composites is studied. The initiation and propagation of cracks are discussed in the thin-ply laminate under transverse tensile, and the in-situ transverse strength of 90° ply is predicted with different thicknesses. The results show that considering the interlaminar resin region has a great influence on the in-situ strength prediction results. Reducing the ply thickness can change the fracture mechanism and improve the transverse in-situ strength of the material. [ABSTRACT FROM AUTHOR]

A method for detecting low-velocity impact damage in carbon fiber reinforced polymer (CFRP) is presented. It involves the use of the Impulse Excitation Technique (IET) and hysteresis loops to calculate the damping parameter of T700/NCT304-1 carbon/epoxy samples subjected to various low-velocity impact energies. The value of the coefficient of restitution (COR) is determined for each impact, ranging between 0.62 for the lowest impact energy to 0.48 for the highest one. The results reveal that a three-step increase in the damping parameter exists in all cases as the impact energy on the specimen increases. An abrupt jump in the damping parameter value is observed for impact energies exceeding ∼0.9 of the material's maximum capacity. Overall, at the highest impact energy equal to 3.65 J, the damping parameter increased by 43.3% compared to the pristine specimen. Additionally, two cases of cyclic tension-tension loading were applied to the specimens, with maximum stresses set at 150 MPa and 200 MPa. The measured values of plastic and elastic strain energy were used to determine the damping ratios. For both cases, the damping of the specimen subjected to the highest impact energy was ∼1.2 times greater than that of an intact specimen, with an increase pattern similar to the findings of the IET method. Optical microscope images of the specimens are provided to illustrate various damage modes observed in the composite materials. [ABSTRACT FROM AUTHOR]

The presence of temperature and crystallinity gradients in carbon fiber–reinforced PolyEtherEtherKetone (PEEK) composite laminates, produced via laser-assisted tape placement, is investigated in this paper. The manufacturing process takes place with high deposition speed and using localized laser source for heating, therefore enhancing the formation of temperature and crystallinity gradients through the laminate thickness. A previously validated thermal model coupled with a non-isothermal crystallinity model and a fusion model are used to simulate the temperature and crystallinity distributions through the laminate thickness. The results from the model are correlated with Dynamic Mechanical Analysis (DMA) tests and Differential Scanning Calorimetry (DSC) tests since a crystallinity gradient is difficult to monitor experimentally. The simulated gradients suggested the presence of an amorphous layer between two consecutive plies and an increase in the crystallinity through the material's thickness. This observation is correlated with the behavior reported for the semi-crystalline laminates during the DMA test, where the modulus drops abruptly during the glass transition, a typical behavior for an amorphous material. [ABSTRACT FROM AUTHOR]

A novel intralaminar model has, for the first time, been applied and validated for the rate-dependent failure of multidirectional carbon/epoxy laminates. Quasi-static compressive failure is evaluated by the growth of intralaminar rate-dependent damage combined with the interaction of cohesive zones for interlaminar delamination. A special feature of the intralaminar model is the homogenised ply response, allowing simultaneous damage-degradation of the polymer matrix combined with the fibres. To model the observed quasi-brittle failure response of the plies under finite deformation, we have used a viscoelastic-viscoplastic matrix combined with damage and isotropic hardening behaviour. Elastic transverse isotropy is used to model the fibre reinforcement of the plies. Standard cohesive surfaces are used to model the initiation and propagation of delamination. Numerical simulations using ABAQUS/Explicit are performed to predict the growth and delamination of intralaminar damage under compression in different laminates with 56 plies of IM7/8552 carbon/epoxy. Predictions of stress versus strain and damage growth are shown to agree well with experimental results for a range of strain rates and stacking sequences. [ABSTRACT FROM AUTHOR]

Nano-batteries have been widely used in electric vehicles, new energy, and aerospace engineering since their high energy density, low manufacturing cost, and long cycle life. In recent years, there have been many papers that contributed to investigate the diffusion-mechanical coupling problems under non-uniform molar concentration environments (e.g., rapid charging, etc.). Nevertheless, the memory dependence of strain relaxation and mass transfer has not been considered yet. This paper aims to construct a unified fractional-order non-Fick mechanical-diffusion coupling model by introducing the fractional derivatives of the Caputo (C), Caputo–Fabrizio (CF), Atangana–Baleanu (AB), and Tempered-Caputo (TC) types. The proposed theoretical model is applied to investigate structural transient dynamic responses of multilayered composite laminates with imperfect interfacial conditions by Laplace transformation approach. The influences of different fractional derivatives, imperfect interfacial conditions, and materials constants ratios on the wave propagations and dynamic mechanical-diffusion responses are evaluated and discussed in detail. [ABSTRACT FROM AUTHOR]

In order to investigate the effects of the charges of Eu3+-doped layered double hydroxide laminates on the drug loading capacity and drug release, anticancer drug methotrexate was loaded into a series of Eu3+-doped MgAl-layered double hydroxides with different layer charges. X-ray diffraction results suggested that the methotrexate was successfully loaded into the interlayer of the Eu3+-doped MgAl-layered double hydroxides. Zeta potential test revealed that the positive charges on the laminates of the Eu3+-doped MgAl-layered double hydroxides gradually increased when the Mg2+/(Al3+ + Eu3+) molar ratio varied from 3.0, 2.0, 1.5, to 1.3. After the negatively charged methotrexate was loaded into the Eu3+-doped MgAl-LDHs, the positive charges of laminates obviously decreased. The loading capacity of the Eu3+-doped LDH for methotrexate gradually increased with the increasing positive charges of the laminates. However, the drug release exhibited similar kinetic behavior despite the different charge numbers of laminates. Fluorescent spectra indicated that all the Eu3+-doped MgAl-layered double hydroxides showed fluorescent changes during drug delivery and release. In vitro cytotoxicity experiment through CCK-8 assay suggested that the intercalated methotrexate could be successfully controlled-released from drug delivery system and exhibited anticancer effects against HepG2 cancer cells. [ABSTRACT FROM AUTHOR]

This paper explores the aero-thermo-elastic properties of variable stiffness composite laminates (VSCLs) with fibers steered along curved trajectories using a refined 1 D model. High-order solutions are generated by the p-version finite element method in conjunction with the Carrera Unified Formulation (CUF), which is applied to structural modeling by employing the improved hierarchical Legendre expansion (IHLE) in particular. The merit of using such a kind of expansion lies in that both the Equivalent Single Layer (ESL) and Layer-Wise (LW) theories can be formulated in a compact and straightforward manner. The linear piston theory is utilized to model the aerodynamic force, whereas the steady-state temperature field is applied during the flutter analysis. The weak-form governing equations are derived by taking a perturbation of the equilibrium configuration, and divergence and flutter instabilities are determined by solving the related eigenvalue problem. The accuracy of the proposed model has been verified through several test cases involving flutter, thermal buckling, and vibration of symmetric and antisymmetric VSCLs. The obtained results were compared to those obtained using the ABAQUS software and the available literature. Finally, the effect of the kinematic order, shear coefficient, and temperature variation on the critical dynamic pressure of VSCLs is thoroughly investigated. [ABSTRACT FROM AUTHOR]

Jute fibers are commonly used as reinforcement in composite materials manufacture due to its excellent mechanical properties. In this study, alkali (NaOH) and silane coupling agent KH570 treatment were conducted on component jute nonwovens to improve the bonding strength of jute/PLA composite interface. The jute/PLA composites were prepared from treated jute nonwovens and PLA films by molding method. The results show that alkali treatment can significantly improve the tensile, flexural and dynamic thermomechanical properties of jute/PLA composites. The composites treated with 1% NaOH exhibits the maximum tensile strength while the composites treated with 5% NaOH presents the maximum flexural strength and the minimum loss in the dynamic thermo-mechanical process. Moreover, the tensile and flexural strength of the composite treated with the combination of 5% NaOH-5% KH570 is significantly stronger than that when they act alone. This research can provide an optimal treatment strategy for the jute/PLA degradable composites with higher mechanical and thermos-mechanical tolerance. [ABSTRACT FROM AUTHOR]

This article investigates the three-scale mechanical response and damage progression of woven composite laminates by probabilistic progressive damage analysis. Micro-scale, meso-scale, and macro-scale stochastic finite element models of woven composite laminates were established to consider the random fiber distribution in yarns and stochastic nature of material properties. Based on Monte-Carlo method, three-scale probabilistic progressive damage model was proposed to predict damage progression and probabilistic distribution of strengths for woven composite laminates. Good agreement between the predictions of elastic properties and strengths and experimental results has been achieved, demonstrating the validity of proposed three-scale probabilistic progressive damage model. [ABSTRACT FROM AUTHOR]

This work focuses on the effect of wrinkle defects within curved laminate composites under compressive load. In the study, 22 curved specimens with different levels of maximum misalignment angles – ranging from 1.5° to 17° – were manufactured. The specimens with embedded defects were tested under compression to assess the effect of defects on the compressive strength. Then, specimens were modeled using the Discrete Ply Model strategy and simulations were run. The numerical model showed a relevant correlation with the experimental results and was used to distinguish the influence of different failure mechanisms (matrix cracking, delamination and fiber failure) on the global failure of the specimen. Finally, a numerical sensitivity analysis of the compressive strength of curved specimens in relation with the misalignment angle was carried out. [ABSTRACT FROM AUTHOR]

An analysis is performed in the current investigation to study the vibrations of composite laminated plates integrated with piezoelectric layers. Composite laminated plate is reinforced with graphene platelets (GPLs). Also the amount of GPLs in the layers may be different which results in a piecewise functionally graded (FG) media. Elasticity modulus of the GPLRC media is obtained by means of the Halpin-Tsai rule which contains efficiency parameters to capture the size of reinforcements. First order shear deformation theory of plates and parabolic distribution of electric field through the piezoelectric layers are assumed as the basic assumption. For the piezoelectric layers, both the open circuit and closed circuit conditions are applied. The total strain and kinetic energies of the plate are obtained. After that by means of the general idea of the Ritz method and also Chebyshev polynomials as the basic shape functions, the matrix representation of the equations of motion dealing with free vibration of sandwich plate with piezoelectric face sheets are obtained. Results of this study are first compared with the available data in the open literature. After that novel results are given to explore the effects of different parameters such as the electrical and mechanical boundary conditions, plate geometry, GPL weight fraction and GPL distribution profile. It is shown that with introduction of GPLs, frequencies of the plate may be enhanced for both closed circuit and open circuit conditions. [ABSTRACT FROM AUTHOR]

Advances in today's technology have led to the use of composite materials with their advantages of significant high strength with lightweight structure in aircraft design worldwide. With the aid of simulation, ANSYS, two main common problems in designing the aircraft composite wing, which is the aerodynamic loading on the wing and composite modeling; whereby both can be coupled to solve the aforementioned problems. The paper addresses with the use of fluid Structure Interaction (FSI) simulation and developed a standard numerical approach by integrating the aerodynamic loading from fluid domain with Finite Element (FE) analysis from structural domain in the application of hybrid composite laminates of aircraft wing structure. In this study, the Computational Fluid Dynamics (CFD) is conducted on the selected wing model of Selig 1223 in order to obtain the pressure loading from fluid domain before transferring it as an input to FE composite of structural domain. The FSI simulation was performed for two parametric conditions, namely Composite Wing Skin without Honeycomb (CWS) and Composite Wing skin with Honeycomb (CWSwH). From the result, CWSwH has lower total deformation with 3.06% percentage difference compared to CWS. However, the shear stress and strain values of CWSwH showed higher value than those of CWS due to the effect of the elasticity of honeycomb core. Therefore, the numerical approach of FSI with the application composite material has proven to be feasible and significant of current research on the behavior of fluid flow and structural for the wing skin, which replicates the real conditions of the aircraft wing during take-off or cruise. [ABSTRACT FROM AUTHOR]

This work compares the low velocity impact (LVI) behavior of conventional fiber metal laminate (FML) with hybrid fiber metal laminates (H-FML) that include an elastomer layer. The aim is to demonstrate the potential of the proposed composite comprising metal, elastomer, and carbon-fiber-reinforced polymer (CFRP) to meet the high demands of emerging products that require lightweight materials. Experimental methodologies and finite element (FE) analysis are used to assess the impact behavior of FML and H-FML. The study evaluates various internal damage processes and the distribution of energy of each ingredient and interaction during the LVI to understand the behavior of the laminates. The results show that the inclusion of elastomer leads to a wider energy distribution and greater participation of the proposed H-FML composites in bearing the load rather than focusing only on the impact area. The materials are used more efficiently in energy absorption since a more extensive energy distribution inside the hybrid laminate takes place. The amount and proportion of energy absorption by each component in laminates are influenced by introduction of the elastomer. The study highlights the potential of using innovative hybrid laminates for energy absorption, and the placement of the elastomer in the laminates affects the extent of energy absorption by each component. [ABSTRACT FROM AUTHOR]

Tidal turbine infrastructure is currently in the large-scale prototype and short-term demonstration phase. However, the immediate requirement is to develop materials, processes and long-term life predictive facilities for tidal turbine plant that has decades of operational lifetime requirements. Computational modelling is a key tool to interpret the experimental data, understand the relevant mechanisms and provide a predictive capability for the performance of aged components for industries. The goal of this paper is a prediction of the long-term life of marine-based glass/epoxy and carbon/epoxy composite laminates aged in artificial seawater with 3.5% salinity based on Arrhenius degradation theory and tensile strength retention over 180 days ageing at room temperature and 60°C. Three different analytical models (linear and exponential) were implemented to calculate time shift factors and corresponding life in a real marine environment. Additionally, multi-scale modelling has been implemented via a representative volume element approach for square and hexagonal cells, and two-step homogenization of textile composites in accordance with nanoindentation testing for matrix/resin cells and fibre constraint cells after 90 days of immersion in saltwater. In general, the multi-scale modelling in ABAQUS and TexGen4SC was able to approximate (with about 10% difference) the mechanical properties of dry and aged composite laminates. [ABSTRACT FROM AUTHOR]

The accelerated testing methodology (ATM) for the statistical life prediction of carbon fiber reinforced plastics (CFRP) under creep and fatigue loads based on the viscoelasticity of matrix resin has been proposed by authors. This method has been successfully applied to the life predictions of unidirectional CFRP with thermosetting epoxy resin as the matrix under tensile and flexural loads. In this paper, this method was applied to the fatigue life prediction of unidirectional CFRP (CF/PP laminates) with thermoplastic polypropylene (PP) as the matrix under tensile and flexural loads, and the effect of matrix viscoelasticity and load cycles on the fatigue behavior of CF/PP laminates were discussed under tensile and flexural loads. First, the viscoelasticity of matrix PP was measured. Second, the static and fatigue strengths of CF/PP laminates were statistically measured at various temperatures and frequencies under tensile and flexural loads. Third, all of material parameters in the fatigue strength formulation in ATM were determined using measured data, and the statistical long-term fatigue strengths of CF/PP laminates were predicted under tensile and flexural loads. As results, comparison with tension and bending test results clarified that the long-term tensile fatigue strength of CF/PP laminates decreases at an accelerated rate as the number of cycles increases, and that the flexural fatigue strength is affected by temperature and frequency rather than by the number of cycles to failure. [ABSTRACT FROM AUTHOR]

In high-velocity projectile impacts, the contact duration is very short and the response of the target is governed by the local behavior of the material in the impact zone. On impact, a compressive stress wave is generated in the target, which travels in the thickness direction. This compressive stress wave plays a significant role in the failure of thick composite targets. In conventional laminates, the out-of-plane (transverse) compressive strength of composite resists the generated compressive stress wave which is not efficient since out-of-plane compressive strength is significantly lower than the fiber direction strength value. In the current numerical study, a non-conventional approach has been adopted by orienting the fibers in the impact direction to utilize the high compressive strength in the fiber direction to resist the projectile impact. In this regard, unidirectional composite rod segments are considered with fiber aligned in the projectile impact direction. The resulting effect on the impact energy absorption and the overall mechanical impact response is numerically studied and compared with conventional woven fabric laminates. Several configurations of these unidirectional fiber rod segments and the role of lateral confinement are also studied to understand their effect on the impact energy absorption. The numerical simulation results indicate an advantage for the proposed arrangement of composite (segments) rods with fiber in impact direction over the conventional woven fabric laminates. [ABSTRACT FROM AUTHOR]

The mechanical post-buckling behaviour of variable stiffness layered composite beams reinforced by curvilinear fibres subjected to compressive loads is investigated here using a sine function-based shear flexible beam model. The neutral axis stretching force stemming from the axial movement restraints is accounted for through von Karman's assumption based geometrical nonlinearity. Furthermore, the modified beam constitutive equation arising from the consideration of the Poisson's effect is introduced in the formulation for the laminated beam analysis with general lay-up or ply sequences. The governing equations incorporating the incremental stiffness matrices are formed through the minimization of total potential energy principle and are solved by numerical method. The solutions for the developed governing equations are evaluated iteratively based on eigenvalue analysis and the characteristics of post-buckling of laminated beams can be inferred through the relationship between the beam deflection level and post-buckling axial load. An in-depth analysis selecting many design parameters for instance lamina's curvilinear fibre angles, beam slenderness ratio, lay-up and edge conditions, load type and so on is dealt with in bringing out the behaviour of variable stiffness laminated beam in linear and post-buckling regions. Also, the influence of flexible end supports by restraining elastically against ends rotation is studied on the beam elastic stability behaviour. [ABSTRACT FROM AUTHOR]

In this investigation, three subjects are considered. First, the effect of the human factor is examined. In carrying out analyses of fatigue delamination propagation tests on laminate composites, the delamination length must be measured. The human effect on measurement of the delamination length a by different investigators is discussed. A limited influence of the human factor on the measurement of the delamination length a, as well as on delamination propagation rate da/dN, is observed in this study. Secondly, the paper proceeds to discuss the influence of the R‐ratio on the fatigue delamination growth rate. It is found that a higher rate of crack/delamination propagation is associated with lower R‐ratios which appears to contradict conventional wisdom. This behavior is confirmed in tests. Thirdly, a comparison between the fatigue propagation rates of two material systems is considered. It is concluded that the energy release rate used to assess these materials should not be normalized. Highlights: Impact of human factor on fatigue delamination tests in laminate composites.Limited influence of the human factor on delamination length and propagation rate.The lower the R‐ratio, the higher the delamination propagation rate.The crack driving force for laminates should be taken as GImax. [ABSTRACT FROM AUTHOR]

Novel Ti/Al laminated composite embedded with particles of the high entropy alloy Al0.5CoCrFeNi were produced by vacuum hot press sintering at 650°C. The microstructure of the laminated composite was investigated using XRD, SEM, EDS, TEM and EBSD techniques. It was found that a thin layer of Al3Ti was formed at the Ti/Al interface. There were no obvious defects between the Al0.5CoCrFeNi particles and Al matrix, achieving a good interfacial bond. The tensile properties of the material were tested at room temperature. The results of the tensile test indicated that the material exhibited an elongation to failure of 59% and an average tensile strength of 240 MPa, demonstrating excellent plastic deformation capability. During the tensile process, the expansion of fractures and cracks in Al0.5CoCrFeNi particles can consume energy, which helps to improve the material's ability to undergo plastic deformation. Based on the morphologies of tensile fracture, it has been observed that the fracture surface of high entropy alloys exhibits a mixed fracture mode consisting of both brittle and plastic fracture. The brittle BCC phase has been identified as the main cause of cracking in HEA. Ultimately, the material fractures due to necking. [ABSTRACT FROM AUTHOR]

This study concerns several possible ways of computing the J-integral in the cases of laminated composite plate structures containing delamination. On the one hand, two special types of plate finite element families are provided for advanced fracture mechanical analyses. On the other hand, a numerical algorithm is introduced also that utilizes results derived from solid element models built in commercial finite element software. In order to create plate elements, the first-order (FSDT) and the third-order shear deformation theories (TSDT) are applied with two equivalent single layers. A subparametric element family is created by using the Hermite interpolation with the FSDT that grants the continuity of the derivatives at the element borders. Besides, an isoparametric family is created also with the TSDT employing the Lagrange interpolation scheme. This paper aims to present the compact formulations of calculating the J-integral around the delamination fronts for both plate element families. The calculation of the J-integral is implemented as a matrix multiplication by taking advantage of the properties of plate transition elements. The models yield improved fracture mechanical analyses for delaminated composite plates with linear elastic material behaviour. In addition, computing the J-integral is not available in most commercial finite element software for laminated orthotropic materials, therefore, an appropriate algorithm is presented here for this purpose. To conclude, the models and algorithms are applied to two case studies and subjected to a comprehensive comparison with analytical and formerly used finite element solutions. • A subparametric FSDT plate element family with granted continuity of the derivatives for delaminated plates. • An isoparametric TSDT plate element family that is appropriate for modelling curved delamination fronts. • A robust algorithm for computing the J-integral numerically in solid element models. [ABSTRACT FROM AUTHOR]

In this paper, the repeated low velocity impact responses and compression‐after‐impact (CAI) behaviors of woven glass fiber‐reinforced composite laminates were studied at the same total impact energy. Three types of impact energies, 30, 40, and 60 J, were chosen for the repeated impact tests relative to the single 120 J impact event. The impact behaviors including impact contact force–displacement and energy–time curves during the impact testing were recorded. The variations of the impact mechanical characteristics such as peak impact force, maximum displacement, and energy absorption were evaluated. The methods of visual inspection and stereo microscope were applied to identify the damage morphology of the impacted laminates. The damage accumulation was evaluated employing the absorbed energy fraction and normalized maximum displacement. It was found that the influences of impact energy on the repeated impact mechanical response are more remarkable than that of the impact number, and the impact events with fewer impact numbers cause more damage to the laminates for the same accumulative impact energy. Furthermore, the load–displacement and the CAI strength versus impact number curves were compared for the CAI testing. The ultimate load and the resulted CAI strength decrease with the increase of impact number owing to the influence of damage accumulation in repeated impacts. Highlights: Repeated impact responses were studied at the same total impact energy.The impact energy makes significant influence on the impact dynamic responses.The impact events with fewer impact numbers cause more damage to the composites.The CAI behavior was explored considering the effect of damage accumulation.The CAI strength of damaged laminates decreases with impact number increasing. [ABSTRACT FROM AUTHOR]

Bistable reeled composite shells (BRCS) have been widely used in deployable space structures due to advanced properties of light weight and large volume reduction. A finite element simulation and experimental validation to study the transition of BRCS between their two stable states are performed. In this article, multiscale representative volume element (RVE) modeling is used to compute the equivalent mechanical properties of carbon/epoxy plain woven fabrics that were utilized to construct the deployable composite laminates, followed by experimental verification. The deformation characteristics and strain energy distribution of the deployable composite shell (DCS) during snap through and coiling up are investigated using finite element analysis (FEA) and verified by strain‐gauge and digital image correlation (DIC) tests. The results show that the strain energy distribution in the snap through and coiling up of the carbon/epoxy plain woven BRCS with laminate stacking sequence of [+45/−45] is approximately symmetric. Additionally, an offset phenomena is observed during the coiling up of the BRCS in the finite element modeling. A parametric analysis is complemented to investigate effects of fiber angles on the deformation characteristics and strain energy distribution of the shell structures during snap through and coiling up. Highlights: Shell deformation during snap through and coiling up was investigated.DIC test was performed to capture the shell deformation.Strain energy distribution of the deployable composite shell was discussed.Offset phenomena are observed during the coiling up. [ABSTRACT FROM AUTHOR]

The post‐buckling strength, which is simply called as crippling, is investigated for laminated composite structures in this study. L profiles that had various stacking sequences of carbon fiber reinforced epoxies were tested. Three different layups configurations were used by changing flange‐to‐thickness ratios. The main objective of this research was to show that flange‐to‐thickness ratio was not the only effecting parameter for crippling. Therefore, a new parameter, EGY number, was developed by considering the positions of 0° and 45° plies. Depending on EGY number, a new semi‐empirical formulation was presented to calculate crippling strength of the laminated composite structures. One of the test results was employed to verification of EGY number. In addition, the test results were validated with finite element analyses. Static, Riks and Dynamic, Explicit computational results were compared to simulate the experiments. Highlights: Determination of crippling strength both experimentally and theoretically.Comparison of numerical models: Static, Riks versus Dynamic, Explicit.Developing a new parameter called as EGY number.Developing of a new analytical semi‐empirical formula for crippling strength. [ABSTRACT FROM AUTHOR]

Compared to composite components prepared by traditional thermal process, microwave‐cured laminates exhibit superior mechanical properties under the same heating cycle, indicating a unique heating mode that differs from air circulation. To progressively replace the thermal curing process with microwave technology in the aerospace composites manufacturing field, it is crucial to elucidate the heating mechanism of microwave‐cured composite materials. In this study, the microwave absorbing performance of both carbon fibers and epoxy resins was systematically compared and revealed. Drawing upon principles of organic chemical reaction and Fourier transform infrared spectroscopy, the results demonstrated the swift response of carbon fibers to microwaves, which facilitated heightened functional group transformation and more complete curing reactions at the fiber‐matrix interface. Notably, as indicated by the results of the three‐point bending tests and fiber push‐in tests, microwave‐cured laminates displayed enhanced interlaminar and interfacial bonding properties in comparison to thermally cured counterparts, resulting in a 10.74% increase in interlaminar shear strength (ILSS) and a 20.23% rise in interfacial shear strength (IFSS). Highlights: Carbon fibers exhibits a more pronounced ability to absorb microwaves than resins.Microwave‐cured laminate achieves a higher degree of curing reaction.Microwave curing enhances the ILSS and IFSS of composite materials. [ABSTRACT FROM AUTHOR]

The working condition of the rail transit components such as bogies is complicated, so the high comprehensive performance of composite parts is desperately required. However, existing pure three‐dimensional braided or laminated composites have been unable to satisfy the cooperative demand of in‐plane and interlaminar properties. In this paper, a novel design of three‐dimensional braided/unidirectional (3D/UD) hybrid composite is proposed to balance the in‐plane (tensile, compression, bending), interlaminar (interlaminar shear, low‐speed impact) properties of the composite. The effects of different 3D/UD mixing ratio and layup sequence on the mechanical properties and damage mechanism of hybrid composites were studied by the parametric analysis of the experimental test results, and the comprehensive mechanical properties of the hybrid structure were optimized by COPRAS evaluation method. The results show that the larger the proportion of unidirectional layer, the better the mechanical property in‐plane, but the worse interlayer property. In addition, the change of layup sequence induces a complex nonlinear relationship between 3D/UD mixing ratio and mechanical properties. Combined with microscopic failure characterization results, it is found that the sandwich structure and the addition of uniformly distributed interfacial layer can improve the mechanical properties of the hybrid composite. The optimization results show that the sandwich structure hybrid composite UD6/3D/UD6 with the best balance between in‐plane and interlaminar properties was selected by COPRAS. Compared with pure 3D composites, the comprehensive mechanical properties of UD6/3D/UD6 are increased by 53.9%, which provides a reference for the structural design of hybrid composites in the future. Highlights: A novel design of 3D/UD hybrid composite is proposed to balance the in‐plane and interlaminar properties.The influence regularity of 3D/UD mixing ratio and layup sequence on properties of hybrid composites were obtained.The mixing failure mechanism of interlayer and in‐plane was revealed.The optimal structure UD6/3D/UD6 under complex working conditions was obtained by COPRAS. [ABSTRACT FROM AUTHOR]

This work reveals the synergistic effect of argon/nitrogen double plasma alteration on the mechanical properties of para‐aramid fiber/epoxy resin composites with various laminating sequences. Acoustic emission monitored interface failure during tensile, bending and fracture testing. A comparative analysis was conducted on the bending performance of the composites modified by argon/nitrogen double plasma and single plasma. The results showed that the synergistic effect of nitrogen and high‐energy molecule argon optimized the modifying effect of argon/nitrogen double plasma. The optimal modification parameters obtained through fiber extraction testing analysis are power 200 W, time 120 s, and Ar/N2 double gas flow rate of 12 sccm. After plasma treatment, twill weave modifies better than plain weave. The AE signal amplitude of PX1 is minimized during stretching. Due to the difference in internal bending stiffness of PX2, interface delamination failure is more likely to occur. The PX5 had greater fiber and matrix debonding failure between mode‐II fracture tests due to the weak modification effect of plain weave and its difficulty in deformation. In ballistic testing, PX1 blocks impact force through fiber bundle stretching deformation, while PX4 is more brittle. Highlights: Prepare para‐aramid/epoxy resin composites with various laminating sequences.Study on the interfacial properties of composites treated with double plasma.The composites with different gas sources treatment were analyzed.Acoustic emission analysis was used to identify interface failure modes.The bonding strength between plain and plain interfaces is the lowest. [ABSTRACT FROM AUTHOR]

Void fraction and fiber volume fraction (FVF) are among the most important parameters determining the quality of fiber‐reinforced plastic products. Most of the voids in liquid composite molding–manufactured composites are directly related to the viscous matrix (resin) flow through the porous medium (fiber) during impregnation. In this investigation, a different method, resin spray rather than injection was used to reduce the resin's flow path, which resulted in low void content and higher FVF. The resin was sprayed on the surface of the preform, and compaction was applied to infiltrate the resin towards the thickness. Sample laminates were manufactured, and computer tomography scanning was applied to diagnose void content and laminae quality. The images collected from the scanner were analyzed using ImageJ software. Effects of compaction pressure and compaction speed were characterized. According to the investigation, compaction speed was the key factor in determining a laminate's void content. Only 1.5% void fraction was integrated with a compaction speed of 1 mm/min and a compaction pressure of 100 KPa. On the other hand, compaction speed has less of an impact on a laminate's FVF. Highlights: The void fraction of a composite is reduced via the spray and compaction method.Fiber volume fraction is not much affected by compaction speed.Slow compaction speeds minimize void content.Spray compaction is a low‐cost manufacturing method. [ABSTRACT FROM AUTHOR]

The jointing problem has become increasingly prominent with the growing applications of composites in industrial fields. Besides, the hybrid bonded‐bolted (HBB) joint has aroused extensive attention for its excellent mechanical performance. In this study, numerous tests and simulations were conducted to investigate the load‐bearing performance of the plain‐woven carbon fiber‐reinforced plastic (CFRP) laminates HBB joints under quasi‐static uniaxial tensile conditions. The influence of HBB morphological parameters was systematically analyzed. The 3D Hashin failure criterion was successfully implemented in the finite element model for the failure analysis of a numerical equivalent cross‐ply laminate structure. Highlights: FEA‐based mechanical property analysis tool for CFRP bonded‐bolted joint.Quantitative influences of HBB morphological parameters are discussed.Failure modes of HBB with different characteristics are revealed. [ABSTRACT FROM AUTHOR]

This study aims to quantify impact damage in laminated composites using acoustic emission (AE) and to verify the AE results with finite element (FE) method. Carbon fiber reinforced polymer (CFRP) composite specimens were subjected to quasi‐static out‐of‐plane indentation loading. A procedure, including feature extraction, feature selection, data dimensionality reduction, and data clustering using an evolutionary algorithm, that is, differential evolution (DE) optimization algorithm, was proposed to identify and quantify different damage mechanisms using AE. The AE results showed that the dominant damages were matrix cracking and delamination. For the quantitative evaluation of the AE results, the indentation test was simulated using the FE method. A FE model based on cohesive zone modeling and continuum damage mechanics was implemented to predict interlaminar and intralaminar damages. The quantity of the damaged elements associated with the matrix cracking and delamination was consistent with the AE results. This study showed the applicability of the AE for impact damage identification and quantification in composite structures. Highlights: Indentation damage in CFRP is experimentally quantified using the AE method.The DE algorithm is used to cluster the AE data.CZM and CDM are used to numerically model the damage.The AE clustering results are compared with the numerical results. [ABSTRACT FROM AUTHOR]

The study assessed the tensile, flexural, and impact properties of composite materials reinforced with flax fibers, employing three distinct resin types. The composite laminates were fabricated using three commercial resins: a conventional epoxy resin, an epoxy resin with a 31% weight concentration of bio-renewable content, and a recyclable methyl methacrylate infusion resin. This aims to assess if there exists a commercially available alternative to the traditional epoxy resin that can reduce the overall carbon footprint of composite materials. To investigate the influence of humidity on the mechanical behavior of the flax layers, a drying treatment was applied to the fibers before the infusion process. Micro-computed tomography analysis revealed that heat treatment resulted in a reduction of porosity, although it did not affect the mechanical response of the composite laminates. Moreover, laminates produced with non-recyclable and sustainable resins exhibited no significant change in tensile and flexural modulus. In contrast, those produced with recyclable resin demonstrated a slight reduction in the strengths of the composite laminates. Conversely, out-of-plane impact tests and repeated impact tests indicated that composites prepared with recyclable and bio-epoxy resin formulations present superior damage resistance to repeated impact compared to traditional epoxy resin. [ABSTRACT FROM AUTHOR]

In this paper, the low-velocity impact behavior and damage modes of carbon/glass-hybrid fiber-reinforced magnesium alloy laminates (FMLs-H) and pure carbon-fiber-reinforced magnesium alloy laminates (FMLs-C) are investigated using experimental, theoretical modeling, and numerical simulation methods. Low-velocity impact tests were conducted at incident energies of 20 J, 40 J, and 60 J using a drop-weight impact tester, and the load–displacement curves and energy–time curves of the FMLs were recorded and plotted. The results showed that compared with FMLs-C, the stiffness of FMLs-H was slightly reduced, but the peak load and energy absorption were both greatly improved. Finally, a finite element model based on the Abaqus-VUMAT subroutine was developed to simulate the experimental results, and the damage modes of the metal layer, fiber layer, and interlayer were observed and analyzed. The experimental results are in good agreement with the finite element analysis results. The damage mechanisms of two kinds of FMLs under low-velocity impacts are discussed, providing a reference for the design and application of laminates. [ABSTRACT FROM AUTHOR]

This paper provides a brief review on modeling of composite structures. Composite structures in this paper refer to any structure featuring anisotropy and heterogeneity, including but not limited to their traditional meaning of composite laminates made of unidirectional fiber-reinforced composites. Common methods used in modeling of composite structures, including the axiomatic method, the formal asymptotic method, and the variational asymptotic method, are illustrated in deriving the classical lamination theory for the composite laminated plates. Future research directions for modeling composite structures are also pointed out. [ABSTRACT FROM AUTHOR]

This work aims to obtain recycled carbon fibre and develop an application for this new material. The carbon fibres were obtained by recycling aerospace prepreg waste via the pyrolysis process. The recycled fibres were combined with an Araldite LH5052/Aradur LY5053 epoxy resin/hardener system using manual lay-up and vacuum bagging processes. For comparison, the same resin/hardener system was used to produce a composite using commercial carbon fibre. The recycled and commercial composites were subjected to flexural, tensile and Mode I testing. Fracture aspects were analysed via scanning electron microscopy (SEM). The pyrolysis process did not affect the fibre surface as no degradation was observed. The fracture aspect showed a mixture of failure in the recycled composite laminate and interlaminar/translaminar failure near the surface of the commercial composite caused by flexural stress. Flexural and tensile tests showed a loss of mechanical strength due to the recycling process, but the tensile values were twice as high. The sand ladder platform was the project chosen for the development of a product made with recycled carbon fibres. The product was manufactured using the same manufacturing process as the specimens and tested with a 1243 kg car. The method chosen to design, manufacture and test the prototype sand ladder platform made of recycled carbon fibre was appropriate and gave satisfactory results in terms of high mechanical strength to bending and ease of use. [ABSTRACT FROM AUTHOR]

This study aims to investigate the thermo-mechanical coupling in carbon fibers reinforced Poly Phenylene Sulfide (PPS) laminates subjected to critical temperature conditions. In order to dissociate the physical phenomena (degradation/decomposition on the one hand and deformation/damage mechanisms on the other hand) at play in quasi-isotropic laminates (fiber-dominated mechanical behavior), homogenous and fire testing conditions (heterogenous) were considered with or without mechanical loading. X-Ray tomographic and fractographic analyses were conducted to identify the role played by porosities formation (resulting from thermally induced deformations and damages) on the structural bearing capabilities of C/PPS laminates to be used in high-temperature environments. Under high temperature conditions (homogenous temperature distribution), the retention of tensile properties is not well preserved as the axial stiffness and strength decrease of 50% and 75%, respectively. Under fire conditions (heterogenous temperature distribution), the degradation of tensile properties is more dramatic with an 80% decrease. [ABSTRACT FROM AUTHOR]

Composite laminates have become increasingly popular in industries like aerospace and shipbuilding. In practical applications, the creation of notches in composite laminates is often necessary to enable assembly and modifications. This rise in the use of notched composite laminates highlights the need for reliable methods to predict potential failures in these components. With these predictions, the safety and reliability of composite structures can be ensured by preventing catastrophic failures. The present paper investigates the use of the Virtual Isotropic Material Concept (VIMC) combined with the Finite Fracture Mechanics (FFM) criterion to predict the Last Ply Failure (LPF) load in keyhole notched composite laminates and under mode I loading conditions. Experimental tests were conducted to measure the LPF load of E-glass/Epoxy keyhole notched specimens, and the results were compared with the predicted results using the VIMC-FFM criterion. The paper also derives an expression for the Stress Intensity Factor (SIF) function for a crack that emanates from the keyhole notch tip under mode I loading conditions. The derived equation matches very well with numerical data and have a mean absolute error about 2% in the studied domain. The study shows that the VIMC-FFM criterion predicts the LPF load of keyhole notched composite laminates with acceptable accuracy and in a simple and low-cost manner. [ABSTRACT FROM AUTHOR]

The use of biocomposite materials in different fields requires enhanced knowledge of the nonlinear phenomena related to their complex mechanical behaviour. Namely, nonelastic mechanisms such as damage, plasticity, and rupture, potentially coupled with viscosity incidence, affect the structure's lifetime. In this context, the aim of this paper is to propose a simplified and accessible approach that leads to modelling the overall mechanical behaviour of the composite material. The studied laminate composites were made of thermoplastic Elium resin reinforced with flax plies. Experimental quasistatic and dynamic characterisations were conducted via tensile and cyclic tensile tests to investigate the structure's mechanical properties and corresponding failure mechanisms. The test results clearly demonstrated the presence of significant nonlinear specific coupling effects due to both flax fibre and Elium resin. The proposed multi-scale modelling analysis assumes two principal entities: the ply constituted by one or more layers of unidirectional fibres and the fibre-matrix interface considered as a surface layer of resin. Each entity was characterized by specific damage variables that were determined by mechanical tests. Model parameters were experimentally identified and expressed in the behaviour model to simulate the composite structure subjected to low-velocity impact using the Pam-Crash F.E. numerical code. [ABSTRACT FROM AUTHOR]

In this work two novel criteria for strength predictions of bearing failure on mechanically fastened composite joints are proposed for preliminary design. These criteria can estimate the bearing strength of hybrid laminates, which makes them innovative and applicable to a much wider range of aircraft structures that usually use this type of laminate in mechanical joints. The new approach uses characteristic lengths d 0 and a 0 to estimate the joint strength in bearing. Three surrogate models based on a linear regression of lamination parameters and AML (Angle Minus Load) parameter are proposed to provide accurate estimates for characteristic lengths d 0 and a 0 for a given set of these parameters. The regression models used three or two lamination parameters or a single parameter AML. They were applied to experimental results of six different laminate families including three hybrid laminates. The modified average bearing stress criterion (ABSC) outperformed the modified point bearing stress criterion (PBSC) in all cases. The results of the ABSC have a maximum discrepancy for the bearing strength of all laminate families of 2.77% and 1.91%, for the three and two parameters, respectively. The single parameter regression model using AML had a maximum discrepancy of 8.83%. All these results compare very favorably with the criteria proposed in the literature, including the AML regression that had the worst accuracy. Therefore, these criteria together with the proposed surrogate models can be used to minimize the number of tests required for the aircraft development, being a good candidate for preliminary design. [ABSTRACT FROM AUTHOR]

In this study, nonlinear buckling response of composite sandwich semi-ellipsoidal shell subjected to uniform hydrostatic external pressure is investigated numerically and experimentally. The face sheet of the sandwich shell is made up of laminated composite layers and the honeycomb core is considered as reinforced with and without strips. The various honeycomb core configurations with strip reinforcements are employed in the sandwich semi-ellipsoidal shell. The numerical buckling analysis of the sandwich shell is performed using the commercially available software ANSYS®. The geometric nonlinearity and material nonlinearity of the shell structures are included through the arc length method while solving the nonlinear differential equations and identifying the critical pressure of the structure. The efficacy of the numerical modeling and analysis are verified by comparing the critical pressure obtained through the experimental investigations performed on a composite semi-ellipsoidal sandwich shell and results available in the literature. The various parametric investigations are performed on the composite sandwich shell to study the effect of honeycomb configurations, ply orientation of face sheets, aspect ratio and slenderness of the structure, geometric imperfections on the critical pressure. It was seen that the semi-ellipsoidal sandwich shell having double strip reinforcement core yields higher critical pressure among the various configurations of honeycomb cores. However, the semi-ellipsoidal sandwich shell with the single strip reinforcement in between the core having [0°]6s face sheet composite ply configuration yields higher stiffness to weight ratio which leads to the highest critical pressure among the various configurations of sandwich shell. [ABSTRACT FROM AUTHOR]

In this study, 3D representative volume element models with microchannels were established based on measured data. And the periodic boundary conditions were moderately modified to adapt to the actual constraints of the studied object. The effects of different microvascular parameters on the tensile and compressive properties of composites were studied. And the damage pattern of carbon fiber as the main load-bearing phase under the force was analyzed. The models were verified by tensile testing and micromorphology experiments. The research results are of application to the design and analysis of CFRP laminates containing similar microchannel structures. [ABSTRACT FROM AUTHOR]