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Acoustically actuated magnetoelectric (ME) antennas based on resonant magnetoelectric coupling within ferromagnetic/piezoelectric ME laminated composites have recently been considered as a promising solution for antenna miniaturization. However, its radiation performance has been theoretically overestimated, since the negative effects on performances due to the magnetization saturation and the nonlinear mechanical behavior that occur from high-field driving have not been paid enough attention. This work presents a unique equivalent-circuit-based numerical method to analyze the near-field resonance radiation performances of ME antennas driven by high electric fields. In this method, we establish an equivalent circuit of the converse magnetoelectric effect for a ME laminated composite to describe the operating principle of acoustically actuated electromagnetic radiation. The equivalent parameters related to resonance characteristics are determined by fitting the circuit model to the data from frequency response measurements of the near-field magnetic flux density. The validity of the model is verified by comparing the theoretical predictions with the experimental results, in the view of the volume fraction dependence of the mechanical resonance-related radiation characteristics of the fabricated ME composites. Based on the proposed model, the influence of driving voltage amplitude on near-field radiation performances is further analyzed by experimental fitting to the model, and the potential limiting factors of ME antennas are discussed according to the driving-amplitude dependence of parameters obtained from the fit. This work provides an effective and engineering-friendly approach to predict the evolution of ME antenna performances, leading a way to improve the performance limit for resonant magnetoelectric coupling. [ABSTRACT FROM AUTHOR]

This study presents photothermal imaging results of subsurface material defects within fiber metal laminates utilizing the virtual wave concept. Therefore, we theoretically analyze the propagation of the virtual wave signal in a hybrid composite laminate via the method of images. For provoking local material damage, the hybrid composite sample is subjected to a defined impact loading. The results obtained from photothermal defect imaging, utilizing rectangular laser pulse excitation, are compared with results obtained from 3D x-ray computed tomography. To sum up, we demonstrate a fast, non-invasive, and easily interpretable reconstruction of defects within macroscopic hybrid composite laminates based on the virtual wave concept. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) sheets are widely used as building blocks in flexible electronic devices, structural materials, and energy storage technology owing to physicochemical flexibility and remarkable mechanical properties. GO exists as lamellar structures in these applications and, thus, it urges to enhance interface interaction to prevent interfacial failure. This study explores the adhesion of GO with and without intercalated water utilizing steered molecular dynamics (SMD) simulations. We find the interfacial adhesion energy (γ) depends on the synergistic effect of the types of functional groups, the degree of oxidation (c), and water content (wt). The intercalated monolayer water confined within GO flakes can improve the γ by more than 50% whereas the interlayer spacing is enlarged. The enhancement of adhesion is from the cooperative hydrogen bonding bridges between confined water and functional group on GO. Furthermore, the optimal water content wt = 20% and oxidation degree c = 20% are obtained. Our findings provide an experimentally available way to improve interlayer adhesion through molecular intercalation, which opens the possibility of high-performance laminate nanomaterial-based films for versatile applications. [ABSTRACT FROM AUTHOR]

The magnetoelectric (ME) response of laminated composites consisting of BaFe12O19 and Pb(Zr,Ti)O3 ceramics is systematically investigated. A butterfly-shaped curve of a magnetoelectric coefficient emerges in both three-layer and multilayer composites. We show that the appearance of a 7 ppm residual strain in the BaFe12O19 layer after magnetization is the main reason for this special curve. We also observe the self-biasing effect of the composites and a maximum ME response from 0.6 to 5 mV/(Oe cm) in laminated composites with magnetic and ferroelectric layers of different thicknesses that can be measured at a zero-bias magnetic field. The repeatable and stable maximum and minimum values of the magnetoelectric coefficient can be obtained under periodically applied biasing magnetic fields, which is important for a practical device application. An electric-field control of ferromagnetism, evidenced by a 17%–19% enhancement in the magnetization of the BaFe12O19 layer after Pb(Zr,Ti)O3 is polarized, is observed in the composites, implying potential applications in memory devices for the composites. Our work indicates that both magnetic field-controlled polarization and electric-field-controlled magnetization exist in BaFe12O19/Pb(Zr,Ti)O3 laminated composites. [ABSTRACT FROM AUTHOR]

This study investigates the influence of a combined thermal heat flux (imposed by a cone calorimeter) and a compressive loading on the deformation and damage mechanisms within quasi-isotropic carbon fibers reinforced PolyEtherEther Ketone laminates. Thermogravimetric Analyses conducted at increasing heating rates under nitrogen (from 5 to 500°C/min) provide valuable information on the thermal decomposition of C/PEEK that ranges from 550°C to 627°C, with a corresponding mass loss ranging from 20 to 26%. From the thermo-mechanical coupling standpoint, the softening and the thermal decomposition of the PEEK matrix under a 50 kW/m2 heat flux result in the micro-buckling of fibers bundles in matrix-rich areas at the ply scale. Ultimately, it leads to the formation and propagation in the transverse direction of plastic kink bands at the laminates scale. Post-failure observations show that this macroscopic kinking propagates specifically according to the PEEK matrix pyrolysis. [ABSTRACT FROM AUTHOR]

This study presents an investigation into mechanical and thermal properties, as well as the microstructure of Automated Fiber Placement-manufactured laminates using a novel carbon fiber-reinforced low-melt polyaryl ether ketone polymer material. The material's lower melting temperature and lower melt viscosity as compared to established high-temperature thermoplastic materials as PEEK, promises favourable characteristics for the Automated Fiber Placement process. This work aims at in-situ consolidation and the influence of a heated tooling and a post process tempering step, which both turned out to be promising in previous investigations. Laminates were manufactured using a cold tooling, a heated tooling configuration, a cold tooling with a subsequent tempering process step and a hot-pressed reference laminate. Differential Scanning Calorimetry showed that crystallinity values more than doubled for the heated tooling and post process tempering configurations, compared to the cold tooling, reaching 24% and 30%, respectively. Mechanical strength values showed an increase in interlaminar shear strength and compression strength but did not increase to the same extent as was expected from the increase in crystallinity. With Scanning Electron Microscopy differences in the microscopic structure of the polymer matrix could be detected. While the post process tempering step leads to a mostly lamellar crystalline structure, the heated tooling configuration and the post process hot pressing induce a predominance of crystalline spherulites, which might positively affect the mechanical performance. Computed Tomography scans revealed a high amount of porosity in the in-situ-manufactured samples and unprocessed tape material, which likely mitigated the positive effect of increased crystallinity. [ABSTRACT FROM AUTHOR]

Compression-compression fatigue behavior of hybrid unidirectional/woven carbon-fiber reinforced composite laminates after low-velocity impact (LVI) was studied in this paper. The paper contains two parts. Firstly, different levels of impact energy were introduced on the specimens. Impact damage modes were obtained and characterized as fiber breakages, matrix cracks, indentation and delamination. The relationships between indentation depth/damage area and impact energy were established. Secondly, compression-compression fatigue tests were conducted on the impact damaged specimens. Fatigue life degradation trends were analyzed and fatigue limit for different types of specimens was determined. Delamination areas by depth mode and amplitude mode of C-scan showed an increasing trend with the fatigue life increasing. Stiffness decreased sharply in the early and ending stages of fatigue life. However, stiffness exhibited stable or slightly decreasing rates in the mid-stage of fatigue life. A line-shaped failure cracks going through the impact point were observed in the fatigue failure specimens. [ABSTRACT FROM AUTHOR]

This study analyzed the effect of incorporating graphene nanoplatelets in the fiber-matrix interphase on the behavior of a multiscale composite laminate based on carbon fibers and epoxy resin subjected to contact loads. The selected loading mode was the contact between an elastic surface and a cylinder. The multiscale composite material used was a quasi-isotropic laminate with graphene nanoplatelets (GnPs) added at the fiber-matrix interface. The specimens were prepared with 0.0%, 0.1%, and 0.25% by-weight GnPs. Laminate beams were used according to the ASTM D7264 standard, and contact was studied in two configurations, applying the load at the edge of the laminate and in the other, in the plane of the test pieces. The normal strains in the contact region were determined experimentally using the interferometric Moiré technique. These results were compared with estimations using the Hertz contact theory and the finite element method (FEM). The normal strains in the contact area of specimens with fibers modified with 0.1% GnPs were lower than those with 0.25% or fibers without surface modification. Excellent agreement between the experimental results along lines in the contact zone with those estimated with the FEM. The normal strains in a direction perpendicular to the applied load obtained by the Hertz theory for the maximum deformation were slightly higher than those obtained by FEM. Except for those calculated for the normal strain in εy for the load in the direction of the thickness, although the distribution was very similar to those obtained by FEM as well as the experimental one. [ABSTRACT FROM AUTHOR]

The difficulties in establishing an analytical model for plain woven fabric composites (PWFC) and its implementation are well-accepted due to the complexity of yarn architecture, approximations assumed, and lack of experimental validations. In this paper, a practical engineering approach is proposed to predict the tensile properties of PWFC. The approach assumes PWFC as cross-ply, the undulation angle an elliptical shape. The approach tremendously simplifies the calculation keeping a close agreement with the tensile experimental results of PWFC. The approach is remarkably compatible with other theoretical models and experiments that existed in the literature. [ABSTRACT FROM AUTHOR]

A dynamic model built theoretically and simulated numerically for an unsymmetric bistable laminate is elucidated, elaborating the dynamic regimes. Peak-to-peak amplitude diagrams being amplitude-frequency and amplitude-force response curves are derived. The single-well vibrations, the limit-cycle oscillations, the multiple-period dynamic snap-through, the chaotic dynamic snap-through and the intermittency dynamic snap-through can be detected. The amplitude-frequency response curves exhibit the softening stiffness effect. The dynamic regimes are correlated with the excitation amplitude and the modal frequencies. Deploying the high-level excitation amplitude and the low-level modal frequency leads to the limit-cycle oscillations. Besides, the single-well vibrations are characterized by the period-doubling bifurcation. [ABSTRACT FROM AUTHOR]

This study analyzes the behavior of CFRP tape laminates under high-velocity impact when they are subjected to in-plane tensile preload. Experimental tests were carried out using a gas-gun setup in non-loaded and preloaded laminates. Impact and residual velocities were measured, the ballistic limit and damage area were estimated, and it was observed that the ballistic limit was lower in preloaded specimens. An analytical model was developed and validated. Some differences were observed in terms of energy absorption mechanism distribution between preloaded and non-loaded laminates for impact velocities close to the ballistic limit. The influence on the ballistic limit with the preload level was studied. [ABSTRACT FROM AUTHOR]

In the current report, wave propagation analysis of a sandwich doubly curved nanopanel considering a laminated composite core and a couple of face sheets of magneto-electro-elastic (MEE) in the framework of nonlocal strain gradient theory (NSGT) is investigated. The higher-order-shear-deformable (HSD) model is employed to obtain the formulation of strain–stress equations. Maxwell equations are employed for modeling the behaviors of MEE materials. By considering Hamiltonian, the current model's governing equations have been extracted. Afterward, in order to analyze the influence of wavenumber, inserted ampere, inserted voltage, the laminated structure's geometry, nano-sized mechanics impact on the smart sandwich nano-scaled panel's phase velocity, a parametric study has been considered. It is also observed that by raising the electric potential, the number of critical waves could be likely to be increased. A useful suggestion of this study is that the influence of the magnetic field on the phase velocity is more than the influence of the electric field of the MEE panel on the wave propagation of the smart panel. Besides, the nonlocal parameter and phase velocity have an exponential negative relation, while the length scale parameter and phase velocity have a linear direct relation. [ABSTRACT FROM AUTHOR]

This article proposes a framework for the damage assessment of and effect of temperature variations in laminated composites using Lamb waves and unsupervised autonomous features. A network of piezoelectric transducers is employed to generate data for 18 health states of a laminated composite plate. The data is processed with sparse autoencoder (SAE) for unsupervised autonomous features. The discriminative capabilities of the extracted features are confirmed by processing the feature space in the supervised and unsupervised frameworks of machine learning. The confusion matrices of supervised learning provided physical insights into the problem. The feature space was also visualized in two dimensions in an unsupervised manner through principal component analysis (PCA), which revealed physically consistent results for the effect of temperature variations, damage of different severity levels, and the undamaged paths between the actuator and sensors. The healthy state data and information on the paths between the actuator and sensors was processed via SAE for damage localization. The proposed approach can be employed for the autonomous assessment of composite structures for the presence of damage and variations of operating temperatures while using both supervised and unsupervised machine learning algorithms. [ABSTRACT FROM AUTHOR]

Autoclave curing is a manufacturing process for high-performance parts based on carbon fiber–reinforced polymers (CFRPs) used for large aircraft parts. Today, this manufacturing process is the reference in terms of quality and, therefore, the manufactured parts' mechanical performance and robustness. However, several parameters can impact the quality of the parts resulting from this process, which requires optimizing key manufacturing parameters. In this study, the effect of autoclave process parameters (i.e., temperature, pressure, and vacuum-pressure) on the glass transition temperature (Tg), laminate compressive modulus (LCM), laminate compressive strength (LCS), and interlaminar shear strength (ILSS) was investigated using three factors, three-level Box–Behnken design (BBD) and response surface methodology (RSM). In addition, the interactions of processing parameters with Tg, LCM, LCS, and ILSS were investigated, making this study an essential investigation for accurately selecting processing parameters. Thus, there is a functionally non-linear relationship between the interaction of the autoclave process parameters. Therefore, these parameters were optimized using RSM with the maximum Tg, LCM, LCS, and ILSS. The optimization and validation of the obtained models were carried out with an average relative error below 3% for all thermomechanical and mechanical properties, indicating that the BBD and optimization were correct. Because of this, the established regression models can accurately predict the Tg, LCM, LCS, and ILSS in autoclaved epoxy/carbon composite laminates. [ABSTRACT FROM AUTHOR]

The investigation of fatigue behavior typically involves time‐consuming tests, leading some researchers to explore methodologies based on self‐heating tests to reduce the process. For composite materials, the conventional approach involves piecewise linear approximations of the self‐heating curve and the stress transition between the first and second regimes is arbitrarily associated with a fatigue lifetime equal to 106 cycles. This paper proposes a novel methodology to address these simplifications. First, a non‐linear viscoelastic model is used to describe the self‐heating curve. Based on the mechanisms established in the literature, a link is proposed between the dissipation and the fatigue limit. The load leading to a significant contribution of non‐linear mechanisms is associated with an infinite life time. It allows the identification of an S– N curve and prediction of fatigue behavior through a minimal number of tests. The comparison with fatigue results is satisfactory. Highlights: A link is proposed between dissipation and fatigue.Modeling of the dissipation in laminated composites subjected to cyclic loadings.A criterion is proposed to identify the fatigue limit based on the dissipation.A S– N curve is identified and extrapolated up to high cycles fatigue. [ABSTRACT FROM AUTHOR]

In the present research, glass and basalt fiber-reinforced polypropylene composites' behaviour in quasi-static and dynamic conditions is studied. Composites were fabricated by vacuum assisted Compression molding method. Composites failure under quasi-static tension and compressive conditions was studied along with its failure behaviour under low-velocity impact and super-sonic shock loading under dynamic conditions. The study results showed that basalt fiber-reinforced polypropylene (Basalt/PP) composite's tensile and compressive strength is higher than glass fiber-reinforced polypropylene (Glass/PP). The Basalt/PP showed no penetration against low velocity impact (LVI) with negligible deformations till 50 J. However, the Glass/PP perforated at 50 J with various failure patterns occurring at back side. The fiber-matrix interface adhesion plays an important role in super-sonic shock loading by absorbing shock wave energy due to ductile nature of polypropylene and the two composites absorbed energy via matrix and fibers failure, no brittle failure of laminates occurred under shock loading. [ABSTRACT FROM AUTHOR]

This paper presents an investigation into prepreg tape composition and its impact on the consolidation quality of in‐situ Automated Fiber Placement-manufactured laminates. Three different prepreg tape materials were investigated in terms of fiber distribution, porosity and surface roughness. Laminates were manufactured using the in-situ Automated Fiber Placement process and subsequently tested using microanalysis and mechanical testing methods. Higher quality prepreg tape material yielded lower porosity laminates and increased mechanical strength results. The best in-situ Automated Fiber Placement-manufactured laminates achieved 82 % and 88 % of hot-pressed reference tensile- and compressive strength, respectively. Prepreg tape with disadvantageous composition for in‐situ consolidation yielded up to 74 % knockdown compared to the best in-situ consolidated laminates. A five-point bending test was successfully used to determine interlaminar shear strength with significant results relating to consolidation quality. A correlation was successfully established between prepreg composition, resulting laminate consolidation quality and mechanical properties. [ABSTRACT FROM AUTHOR]

The aim of the present study is to investigate the static and dynamic responses of damaged curved fiber laminated plates embedded with piezoelectric sensor/actuator. The damage characterized by anisotropic damage formulation is incorporated into the FE model to represent the damaged part of the structure. It is observed that continuous change of fiber orientation in lamina makes VSCL plates less affected by this type of damage and the reduction in natural frequencies can be minimized by adjustment of fiber orientation. Further, an active feedback control approach is adopted to damp out the vibration of the smart damaged VSCL plates. [ABSTRACT FROM AUTHOR]

Stability and vibration control are major challenges for applications in which laminated composite beams are being used. Using composite base materials with higher strength and/or using appropriate layout orientation are the two potential methods to improve the dynamic performance of laminated composite structures. However, using composite materials with higher strength significantly increases the manufacturing cost. Recently, layers/segments of Magnetorheological (MR) fluids have been added to the common laminated beams, the so-called MR-laminated beam, to improve the dynamic characteristics of such structures. The present work investigates the effect of base materials and applied magnetic field on the dynamic response of MR-laminated beams. Different composite materials, including E-glass, carbon fiber, and Kevlar, have been used as base materials to build the sandwich MR-laminated beam. The hollow spaces of the sandwich beam are filled with MR fluid to fabricate a testing sample for experimental purposes. A modified layerwise theory, N-layer, has been used to determine the vibration response of the structures. It is concluded that applying a magnetic field increases the natural frequency of the MR-laminated beam. In fact, applying 1400-Gauss magnetic fields to a low-cost material like E-glass provides the same natural frequency as that of the fiber-carbon without magnetic fields. [ABSTRACT FROM AUTHOR]

As a promising energy absorbing structure, reentrant honeycomb (RH) structures have been focus of interest in recent years. By reasonably adjusting the geometric configuration of the honeycomb cell, advanced structures with unique mechanical properties and deformation behaviors can be designed flexibly and novely. In this work, inspired by the composite laminates, a novel laminated reentrant honeycomb (LRH) structure is developed by controlling the orientations of RH layers for achieving excellent energy absorption capacity. Mechanical and deformation characteristics of the proposed structures under static and dynamic loadings are investigated experimentally and numerically. By comparing with single-layer RH structure with the same thickness, the results demonstrate that LRH structures have better energy absorption capacity. The deformation modes of RH and LRH structures are also discussed and it is noted that the LRH structure with ±30° honeycomb sublayers shows zero Poisson's ratio effect. It is worth emphasizing that LRH with 0° and 90° sublayers presents similar negative Poisson's ratio effect with RH by analyzing the equivalent Poisson's ratio-strain curves. In addition, it is found that the latter structure has the best energy absorption capacity when the thickness of single-layer 0° RH structure equals to 5 mm. This work provides a new and reliable thought to design the advanced protective structures under compression and impact loadings. [ABSTRACT FROM AUTHOR]

A novel damage tolerance design method of discrete interleaved toughening for laminated composite was proposed. In this paper, discrete thermoplastic Polyamide-6,6 (PA 66) films were deployed at between the selected adjected layers, and three toughening dimensions were considered. Besides, three impact positions of specimens were tested under 5 J, 10 J, and 15 J, respectively. The impact behavior and compression after impact (CAI) of specimens were discussed and compared. Experimental results showed that delamination damage was suppressed in the process of propagation outwards across the toughened region, and the path of delamination crack propagation was changed and swerved. Therefore, the delamination damage projected area (DDPA) of all specimens were reduced by 21.09%–62.85%, compared with the non-toughened plate (base plate). In addition, the finding demonstrated that CAI strength is influenced by the delamination position and DDPA. The proposed method could improve the CAI strength by suppressing delamination and swerving the propagation path of delamination. Moreover, the CAI strength of all toughened plates were improved by 16.35%–61.94% in contrast to the related base plates. [ABSTRACT FROM AUTHOR]

Flutter is a typical dynamic instability phenomenon of the wing or rudder structure. Besides, the phenomenon of aerodynamic heating will be quite significant and temperature can rise rapidly with the increase of the flight speed, thermal flutter characteristics should be taken into consideration for the rudder structure of supersonic vehicle. To improve the thermal flutter characteristics of the rudder structure and meet the design requirements of a lightweight structure, this article optimizes the variable stiffness laminates of the skin on the premise of keeping the thickness of the skin unchanged, so as to improve the critical flutter speed of the rudder. A novel intelligent optimization algorithm named BJASCA, which is a hybrid algorithm coupling of Backtracking Search Algorithm, Sine Cosine Algorithm, and JAYA Algorithms is proposed in this article to improve the efficiency of structural optimization and this algorithm shows obvious advantages in searching global optima compared with several other algorithms. The finite element model and aerodynamic model of the rudder are established to calculate the critical flutter speed. The results represent that the rudder structure optimized by the BJASCA algorithm shows better flutter characteristics and the critical flutter speed can be increased by 76.4% compared with the un-optimized structure. [ABSTRACT FROM AUTHOR]

This paper presents a multiscale progressive fatigue damage model to predict the fatigue life of composite laminates. The multi-level damage model was employed considering the interfacial debonding effect, and effective material properties were calculated through homogenization. Damage variables and damage slopes were defined at the constituent level, and fatigue damage parameters were obtained using the residual stiffness data with the chaotic firefly algorithm. The model was implemented into ABAQUS, then validated with flat-bar and pin-loaded specimens of AS4/3501-6 composite. The numerical results corresponded well with the experimental data and showed the ability to capture the failure propagation of composite laminates. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study on the compressive behavior of concrete cylinders confined with fiber metal laminate (FML) composites. This research was motivated by the need to address limitations of traditional fiber-reinforced polymer (FRP) composites used for civil infrastructure applications, which demonstrate linear elastic and brittle behavior in tension. FMLs are composed of thin metal sheets bonded to E-glass fiber-epoxy composites, resulting in a pseudoductile stress-strain response characterized by strain hardening after yielding of the metal layers. A total of 38 cylindrical concrete specimens were prepared, of which 10 were unconfined, eight were confined by three FRP layups, and 20 were confined by six FML layups. The FML layups comprised of thin 2024-T3 aluminum layers bonded to 400 g/m2 E-glass fiber fabrics, with variations in the number of metal layers, fiber orientation, and fabric architecture. The specimens were tested under uniaxial cyclic compression to investigate the strength and deformation capacity as a function of the degree of pseudoductility exhibited by the FML jackets. The results showed that the strength and ductility enhancement provided by the FML jackets was dependent on the stress-strain characteristics of the jacket material. Jackets characterized by strain-hardening tensile behavior, such as those with unidirectional fabric layers, showed substantial increases in confined strength but reduced ductility and energy dissipation. Conversely, jackets with pseudoductile tensile response, such as those using bidirectional off-axis fabric, were the most ductile, exhibiting stable strain softening behavior. Further, for the same level of confining pressure, FML-confined concrete demonstrated improved postpeak response and gradual strength degradation compared with FRP jacketed concrete. This suggests redistribution of hoop stresses within the FML jacket after initial yielding. [ABSTRACT FROM AUTHOR]

• Analyzed the stochastic resonance and stochastic P-bifurcation of an axially moving shape-memory alloy laminate. • A change in the volume fraction of the SMA shifted the formant of the SNR (signal-to-noise ratio) curve up and down. • Variation in axial velocity, temperature, and stochastic intensity induced stochastic P-bifurcation. This paper investigates the transverse vibration of an axially moving shape-memory alloy (SMA) fiber hybrid laminations under the combined action of transverse harmonic excitation and stochastic disturbance. Considering the shape memory alloy (SMA) fiber volume fraction random field, the kinetic energy and strain potential energy of SMA laminates are solved, and the axial motion equation of SMA laminates is derived according to Hamilton principle, a non-dimensional differential equation of the transverse vibration of the axially moving SMA laminated plates is obtained by adopting the Galerkin integral method. Considering the volume-fraction stochastic field, the stochastic natural vibration of a SMA laminate is analyzed. Considering the stochastic resonance of the SMA laminate under the action of Gaussian white noise and harmonic excitation, the effects of geometric parameters, physical parameters of materials, and temperature on the stochastic resonance behavior of the SMA laminate is analyzed. Finally, the effect of the stochastic P-bifurcation phenomenon of the parameters on the steady-state response of the SMA laminate is analyzed. [ABSTRACT FROM AUTHOR]

• The elastic instability phenomenon in hyperelastic layered materials with the phases exhibiting stiffening behavior is studied • A closed-form expression for the critical stretch of macroscopic instability is derived • An analytical prediction based on Bloch-Floquet analysis for the microscopic instability is exhibited • The critical parameters and transition of instability modes are found to be highly tunable with phase stiffening This paper investigates the elastic instability behavior in soft periodic laminates subjected to finite strains, with a focus on both macroscopic and microscopic instabilities. Considering the deformation-induced phase stiffening, the Gent model with a high bulk-to-shear modulus ratio describes the behavior of incompressible phases. This non-Gaussian statistics-based model captures the non-linear constitutive results from the limited extensibility of polymeric molecular chains. This paper derives an analytical prediction for the onset of macroscopic (or longwave) instability and microscopic instability as functions of material parameters. Moreover, a numerical Bloch-Floquet analysis is imposed on identifying the instability behavior under compression. We consider a wide range of phase combinations and find that the relatively rapid stiffening of the matrix compared to the stiff layer increases the stability of laminates by decreasing the critical stretch ratio. Essentially, properly manipulating the stiffening parameters can produce an absolutely stable region without observed instability. This paper also systematically illustrates the changes in instability and the transition between macro and micro instability in fully Gent laminates, which show higher stability than fully neo-Hookean laminates with larger critical stretch ratios. The critical characteristics of instabilities, such as critical stretch ratios and critical wavenumbers, can be controlled by the choice of stiffening parameters and other material properties, enlarging the tuning of soft laminates for desired buckling patterns in practical applications. [ABSTRACT FROM AUTHOR]

• The flutter behavior of variable angle tow composite laminated plates in supersonic flow is theoretically studied. • Finite element simulations are conducted and successfully validate the developed theoretical model. • The effect of elastic foundations and laminate layouts on the flutter behavior of the composite plate are revealed. • This work can provide a reference for the dynamic design of the VAT composite laminates in the aerospace engineering. A theoretical model is developed to investigate the aerothermoelastic flutter behavior of variable angle tow (VAT) composite laminated plates on elastic foundation in supersonic flow with general boundary conditions. The equations of motion of the VAT composite laminated plate are established by adopting the first-order shear deformation theory and the supersonic piston theory. The composite laminated plate is considered to be lying on an elastic foundation (such as a thermal protection shield) on one side and exposed to supersonic airflow on the other side. The displacement components of the structure are expanded into Chebyshev polynomials multiplied by the boundary characteristic functions to satisfy the geometric or natural boundary conditions. To validate the proposed theoretical model, a finite element (FE) model is also established by ABAQUS, and the numerical results fit well with that of the developed theoretical model. The effects of the boundary conditions, thermal loads, elastic foundations and laminate layouts on the flutter characteristics of the VAT composite plate are revealed and discussed in detail. This work can provide a reference for the dynamic design of the VAT composite laminates in the aerospace engineering. [ABSTRACT FROM AUTHOR]

Layered double hydroxides (LDH) have attracted much attention in the gas sensing field due to their unique laminate structure and flexible chemical composition. In this work, the single crystalline nanosheet-assembled ZnCo-LDHs are synthesized by a facile one-pot hydrothermal route. We find that the Zn addition amount plays a vital role in tuning the Co2+/Co3+ ratio distributed in the laminate structure of LDH, further modulating the amount of oxygen defects. When the Zn/Co addition ratio is 1.8 in the synthetic system, the obtained ZnCo-LDH exhibits abundant exposed active sites due to its orderly arranged nanosheet structure. It also shows a favorable oxygen adsorption capability resulting from more oxygen defects in the laminate structure. The hierarchical structure facilitates gas diffusion and catalysis in sensing the redox process by cooperation of Zn2+ and Co3+. The obtained flower like ZnCo-LDH exhibits a high response of 19.19 to 200 ppm ethanol at working temperature as low as 80 °C. It also shows good selectivity and stability. The hierarchical ZnCo-LDHs provide a new chemiresistive sensing material with low energy consumption and high sensitivity. [ABSTRACT FROM AUTHOR]

This study explores the impact of incorporating Halloysite Nanotubes (HNTs) nanoparticles on the low-velocity impact (LVI) behavior of carbon fiber (CF) laminate epoxy nanocomposites. The objective of this investigation was to observe the effects of different nanotube loadings (0.5 wt.% and 0.7 wt.%) on CF composites and assess their impact resistance. To achieve this, the CF was subjected to Electrophoretic Deposition (EPD) process to introduce the HNTs. Vacuum-assisted Resin Transfer Molding (VaRTM) was employed to fabricate the CF-reinforced epoxy-based laminated nanocomposites with incorporated HNTs. LVI tests were conducted following the ASTM-D-7136 standard, utilizing impact energies of 10 J and 15 J. Subsequently, the damaged areas within the composites were examined using optical microscopy (OM) and scanning electron microscope (SEM). The findings of this investigation revealed a significant enhancement in impact damage resistance with the addition of HNTs. The highest damage resistance and minimal energy absorption were observed at a loading of 0.7 wt.% HNTs. The results reveal that incorporating 0.7 wt.% HNTs substantially reduces delamination damage, influenced by absorbed impact energy. As well it composite underscores enhanced interlaminar bonding through 0.5 wt.% and 0.7 wt.% HNTs modification. Hence, we confidently assert that the addition of HNTs nanoparticles to CF/epoxy composites has considerably influenced the impact response of the nanocomposites. [ABSTRACT FROM AUTHOR]

The use of thin-ply composite materials has rapidly increased due to their tailorable mechanical properties and design flexibility. Considering an adhesively bonded composite joint, peel stress stands out as a key contributor leading to failure among other primary stress factors. Therefore, the reinforcement of carbon fiber-reinforced polymer (CFRP) laminates throughout the thickness could be considered as an approach to improve the joint strength. Using thin plies locally between the conventional CFRP layers in a laminate can enhance the strength, as the sudden change in stiffness means that the load transfer is not monotonous. Consequently, the following study examined the effect of altering thin plies gradually throughout the thickness on the behaviour of the CFRP laminates when subjected to transverse tensile loading. To achieve this goal, the CFRP laminates were gradually modified by using different commercially accessible prepreg thin plies, leading to an improved overall structural performance by reducing stress concentrations. Besides conducting an experimental study, a numerical assessment was also carried out utilizing Abaqus software with a Representative Volume Element (RVE) at the micro scale. The comparison of reference configurations, which involved various thin plies with different thicknesses and traditional CFRP laminates, with the suggested gradual configuration, demonstrated a notable enhancement in both strength and material cost. Furthermore, the proposed RVE model showed promising capability in accurately forecasting the strength of fabricated laminates. [ABSTRACT FROM AUTHOR]

Carbon fiber laminates have become popular in the manufacturing industry for their many desirable properties, like good vibration damping, high strength-to-weight ratio, toughness, high dimensional stability, and low coefficient of thermal expansion. During the manufacturing process, undesirable foreign objects, such as peel-ply strips, gloving material, and Kapton film, can be introduced into the part which can lead to a localized weakness. These manufacturing defects can function as stress concentration points and oftentimes cause a premature catastrophic failure. In this study, a method using high-resolution pulse-echo ultrasound testing is employed for the detection and quantification of the dimensions of foreign object debris (FOD) embedded within carbon fiber laminates. This research presents a method to create high-resolution C-scans using an out of immersion tank portable housing ultrasound scanning system, with similar capabilities to that of a full immersion system. From the full-waveform dataset, we extract the FOD depth and planar dimensions with an automatic edge detection technique. Results from several carbon fiber laminates are investigated with embedded foreign objects that are often considered undetectable. Results are presented for FOD identification for two different shapes: circles with diameters ranging from 7.62 mm to 12.7 mm, and 3-4-5 triangles with hypotenuses ranging from 7.6 mm to 12.7 mm. CT imaging is used to confirm proper FOD placement and that the FOD was not damaged or altered during manufacturing. Of importance for the ultrasound inspection results, in every single case studied, the FOD is detected, the layer depth is properly identified, and the typical error is less than 1.5 mm for the primary dimension. [ABSTRACT FROM AUTHOR]

Bending analysis was carried out for a laminated composite porous plate due to sinusoidal loading with various boundary conditions using improved third-order theory. Zero transverse shear stress provided a free surface at the top and bottom of the plate. Also, the authors developed a finite element formulation based on improved third-order shear deformation theory. To circumvent the C1 continuity requirement associated with improved third-order shear deformation theory, a C0 FE formulation was developed by replacing the out-of-plane derivatives with independent field variables. An in-house FORTRAN code was developed for the bending analysis of the laminated porous plate considering a 2D finite element model. The complete thickness of the plate was covered with different porosity patterns. The impacts of various modulus ratios, boundary conditions, thickness ratios, fiber orientation angles, and material parameters were examined for laminated porous plates. There was an 18.8% reduction in deflection in the case of the square plate as compared to rectangular plates, with a porosity value of 0.1, a thickness ratio of 10, and an orientation angle of 0°/90°/0°. According to the current research, adding porosities causes a relatively greater change in deflection rather than stress, thereby aiding in the development of a lightweight structure. [ABSTRACT FROM AUTHOR]

Magnesium (Mg)-matrix composites have excellent damping and electromagnetic shielding properties. However, the mismatch between their strength and toughness limits their wide application. The aim of this work is to overcome the strength-toughness mismatch by constructing micro- and nanostructures while maintaining the good functional properties of Mg-matrix composites. Electrophoretic deposition (EPD) was used to spread carbon nanotubes (CNTs) out evenly on a Mg foil matrix. After spark plasma sintering (SPS), the grain organisation was refined, and the interlayer bonding was strengthened by hot rolling deformation. Finally, the microstructure, mechanical properties, damping properties, and electromagnetic shielding properties of the composites were analysed. Compared with the pure Mg laminates, the tensile strength and elongation of the CNT/Mg laminates were increased by 6.4% and 108.4%, respectively, with the significant improvement in toughness resulting from the increase in energy required for crack propagation due to the laminate structure. When the total rolling deflection reaches 80%, the interlayer bond strength of the material is significantly increased, the grain is further refined, and the strength and elongation of the composite material reaches the optimum, with the tensile strength reaching 241.70 MPa and the elongation reaching 6.90%. The interlayer interface and grain refinement also affected the damping Mg and electromagnetic shielding effect of the composites. This work provides an experimental idea for the preparation of high-performance structure-function integrated Mg-based materials. [ABSTRACT FROM AUTHOR]

Bio-inspired helicoidal carbon fiber reinforced polymer composite (CFRPC) laminates stacked with Bouligand configurations are considered to own great potential in engineering fields. The optimization design of helicoidal layups with single-form and combination-form of linear and nonlinear helicoidal arrangements is carried out using ABAQUS and Isight. Two single-objective optimizations and one multi-objective optimization of maximum fundamental frequency and the difference among the first four adjacent vibration frequencies of helicoidal CFRPC laminated plates are performed and the nonlinear free vibration characteristics of optimal ones are investigated for the first time. Numerical studies are carried out for 16-ply symmetrical rectangular helicoidal laminated plates under two different boundary conditions compared with quasi-isotropic counterparts. The results show that the combination-form helicoidal layup sequences can improve the linear vibration characteristics of CFRPC laminated plates. The plates stacked with the combination form of nonlinear Fibonacci and linear patterns are expected to provide better vibration characteristics. [ABSTRACT FROM AUTHOR]

Piezoelectric quasicrystals have attracted the tremendous attention of researchers for their unique properties. In this paper, the semi-analysis solutions of the functionally graded multilayered two-dimensional decagonal piezoelectric quasicrystal plates are investigated for mixed boundary-value problems. Based on the quasicrystal linear elastic theory, the state-space method is employed to derive the state equations composed of partial differential along the thickness direction. The differential quadrature method is utilized to discretize state variables to satisfy the mixed boundary conditions in the horizontal plane. Different from the conventional propagator matrix, a new propagator relationship is proposed to study numerical instability caused by extensive discrete points. Comprehensive numerical results are shown for the sandwich quasicrystal plate with four different stacking sequences. The numerical results reveal the effect of the functional gradient index factors, and boundary conditions on the electric potential, electric displacements, stresses, and displacements under the mechanical/electric loadings. [ABSTRACT FROM AUTHOR]

Composite laminates are prone to occur delamination. Currently, there is still lacking research on the temperature effect on mode II delamination of laminates, especially the multidirectional ones. Systematically experimental and numerical studies are conducted here. Delamination tests are performed at four temperatures (−50 °C, 23 °C, 80 °C and 130 °C) on aerospace-grade T800/epoxy multidirectional laminates using an end-notched flexure set-up. Pre-cracked and non pre-cracked fracture toughness, and R-curves are measured. The non pre-cracked fracture toughness is affected by temperature. Their values at −50 °C, 23 °C and 80 °C are relatively close to each other while the value at 130 °C is 34.14% lower than that at 23 °C. The pre-cracked fracture toughness exhibits negligible dependence on temperature and is significantly higher than the non pre-cracked one. R-curve phenomena are observed in specimens evaluated at different temperatures, which exhibit a good linear increase with the increase in delamination length. The R-curves measured at −50 °C∼80 °C are similar while significantly higher than that at 130 °C. In addition, the bridging stress is lower when the temperature is between −50 °C and 23 °C, compared to those at high temperatures of 80 °C and 130 °C. Numerical framework for simulating the mode II delamination growth behavior is established based on the cohesive zone model. Predicted results show that the reasonable interfacial strength of cohesive elements first increases and then decreases with the increase in temperature. Temperature effect on the damage area around crack tip is also revealed. [ABSTRACT FROM AUTHOR]

Thermoplastic carbon fiber-reinforced plastics (CFRPs) are increasingly utilized in the aerospace industry owing to their beneficial properties and enhanced formability relative to thermoset CFRPs. Despite the extensive use of these materials, studies focusing on compression after impact (CAI) tests with impact energies exceeding 20 J for thermoplastic CFRPs remain scarce. This study examines CAI tests on quasi-isotropic laminates of thermoplastic CFRP, subjected to a low-velocity impact energy of 27.04 J. For comparison, quasi-isotropic laminates of thermoset CFRP were subjected to a low-velocity impact energy of 36.5 J. These tests reveal that the CAI strength of both materials is comparable, notwithstanding the lower fiber volume fraction in the thermoplastic CFRP. Further, this research incorporates a finite element (FE) analysis to investigate the damage mechanisms in thermoplastic CFRP. The FE model, integrating interlaminar damage observed during the impact tests, accurately predicted the relationship between compressive stress and strain, correlating closely with the experimental outcomes. It was observed that both interlaminar and intralaminar damage propagation were constrained until the point of maximum compressive stress. Prior to reaching this maximum, a region of elevated compressive stress in the fiber direction was noted in the 0° layer near the non-impacted side. These findings indicate that the compressive stress in the fiber direction in the 0° layer adjacent to the non-impacted side is pivotal in dictating the final failure, which determines the CAI strength of thermoplastic CFRP laminates. [ABSTRACT FROM AUTHOR]

To solve the problem of the wall panel of high‐performance shelters protecting against the oblique penetration of projectiles, ballistic experiments were carried out with ultra‐high molecular weight polyethylene (UHMWPE) laminates subjected to normal penetration by high‐velocity projectiles, and the deformation and failure characteristics of UHMWPE laminates were analyzed. The numerical model of the resistance of UHMWPE laminates against penetration of projectiles was established by using the finite element program LS‐DYNA. The validity of the numerical model was verified by the experimental results of damage morphology and the depth of depression of the target plate and the deformation of the warhead. On this basis, the ricochet angle and failure mode of the UHMWPE target plate against projectile penetration were studied numerically, and the impact of the angle of incidence on the residual kinetic energy and normal penetration displacement of the bullet, as well as the damage morphology of the UHMWPE target plate, was revealed by using simulation. The results showed that the ricochet angle of the bullet obliquely penetrating into the UHMWPE target plate was in the range of 45° to 50°; at the initial stage of projectile penetration, the shear fracture failure of the fiber layer mainly occurred at the striking face of the UHMWPE target plate. Under the impact of the warhead deformation, with the reduction of the residual velocity of the bullet, the failure mode gradually changed to the tensile and interlaminar cohesion failure of the fiber layer near the back face; When the angle of incidence was greater than the ricochet angle, the residual kinetic energy of the projectile increased slowly with the increase of the angle of incidence of the bullet and then went up approximately linearly; the normal displacement of the bullet obliquely penetrating into the UHMWPE target plate decreased slowly after reaching the peak, and the peak value of the normal penetration displacement decreased gradually with the increase of the angle of incidence, and the time to peak of the displacement shortened gradually. The damage area of the bulge on the back surface of the UHMWPE target plate after penetration decreased gradually with the increase of the angle of incidence. The research results can provide a theoretical reference for the application of UHMWPE laminates in the design of military bulletproof shelters and armor. [ABSTRACT FROM AUTHOR]

Natural fiber‐reinforced composites exhibit excellent mechanical properties. However, achieving a balance between excellent mechanical properties and optimal acoustic performance remains a challenge. In this study, four composite laminates with different stacking orders were fabricated using polyester fiber mats (WFs) and palm sheaths (WPs) through a hot‐press process. Moreover, the effects of different stacking orders on the mechanical and acoustic properties of the composite were investigated. The results revealed that the incorporation of polyester fiber felts and the modification of the layup sequence of WP and polyester fiber felts significantly improved the mechanical and acoustic properties of the composites. Scanning electron microscopy images revealed a strong bonding between palm fibers and polyester fibers at the epoxy resin interface. Compared with pure palm fiber composites, the alternately stacked palm fibers and polyester fibers (WP/WP/WF/WP/WF) exhibited the highest mechanical properties, with a significant enhancement of 142.67% and 16.90% in flexural and tensile strengths, respectively. Additionally, the peak absorption coefficient of polyester fiber felts, positioned in the surface layer of the composite material, within the 2580–3400 Hz frequency band significantly increased from 0.07 to 0.44. Therefore, this study indicates that modifying the stacking order improves the mechanical and acoustic properties of the composites, making them suitable for use in acoustic engineering materials for buildings and decorative panels for furniture, including perforated panels and acoustic screens. Highlights: The fabric‐like textured structure significantly enhanced the overall performance of the composites.The stacking order significantly influenced the overall properties of the composite.Alternately stacked polyester fiber felts and palm fibers exhibited excellent mechanical performance.The polyester fiber felts positioned on the surface layer of the composites exhibited superior mechanical performance.A laminate with "green" attributes and good acoustic properties was fabricated. [ABSTRACT FROM AUTHOR]

The finite element model of a 7.62 mm armor‐piercing incendiary bomb penetrating lightweight composite target is established. The structure of the target plate is composed of boron carbide ceramic/carbon fiber laminate/aramid fiber laminate/damping material. The reasonable distribution position of damping material is explored by designing the material structure and geometric parameters. Genetic algorithm is used to optimize the structure of the lightweight composite target plate, and the feasibility of the optimization results is verified through experiments. The results show that under the same surface density, the energy absorption value of the target plate with a certain thickness of back layer damping is 1.36% higher than that of the target plate without damping. And the damping material on the back layer can act as a buffer layer to reduce blunt trauma caused by bullets to the human body. The surface density of the optimized lightweight composite target plate is reduced by 21.6% under the same protection capability. This work provides a theoretical foundation for the impact resistance design and optimization of lightweight composite target plates. Highlights: Impact resistance performance of lightweight composite target plate is investigated.The impacting analytical model of the structure is established.The validity of the optimized impacting analytical model is verified by numerical simulation. [ABSTRACT FROM AUTHOR]

Elium® Acrylic/Glass Fiber thermoplastic laminate composites are liable to develop irreversible local defects under quasi‐static loading. To reinforce the damaged material, repair is a cost‐effective mechanical alternative. The present study investigates the tensile behavior of an Elium® glass‐fiber‐based acrylic laminate composite panel, repaired by vacuum bonding with Elium® repair resin and double overlap of external patches (DP). The results obtained for all repaired laminate composites E190/GF_D(10, 20, 30)R with diameters 10, 20, and 30 mm showed an improvement in the mechanical properties of the repaired panels, compared with the drilled and pristine samples. Average load recovery rates were significant for E190/GF_D10R (7.9%, 3.55%, 13%) E190/GF_D20R (23%, 18%, 3.32%), E190/GF_D30R (7.2%, 9.36%, 32.37%) at strain rates of 0.001, 0.01, and 0.05 s−1 respectively. Finite element (FE) models for the virgin, drilled, and repaired composite, performed by coupling the Hashin criteria with the cohesive zone model (CZM), provided a relevant prediction of intra‐ and interlaminar failures of these woven laminated composites. Highlights: The effect of vacuum bonding repair with Elium E351 EOT resin was studied.Symmetrical repair of acrylic laminate drilled by fiberglass patches.Tensile strength of the repaired laminates was investigated.Intra‐ and interlaminar damage was predicted by finite elements modeling. [ABSTRACT FROM AUTHOR]

This study proposes a process for the preparation of composite laminates using the shear thickening fluid (STF) impregnated aramid fabric and presents some fabric panel configuration strategies. Firstly, this study prepared two kinds of STF using 20 nm and 500 nm silica particles. Then, the STF‐impregnated Kevlar fabrics were laminated and hot‐pressed to form the fabric panels. After that, the ballistic performance of the fabric panels was evaluated by firing the 9 mm steel core projectile using a gas gun. The ballistic tests showed that the ballistic performance of the hybridized configuration panels using STF‐20 treated fabrics as the front panels and STF‐500 treated fabrics as the backing panels was superior, with a reduction of 36.1%–37.6% in the number of perforated layers (4.7–5 layers) compared to a single STF‐treated panel. This study provides a new idea and method for applying STF in protective equipment. Highlights: Shear thickening fluid (STF) and aramid fabric are better combined by hot pressing lamination process;The ballistic properties of fabric panels are significantly improved by hybrid configuration;The ballistic performance enhancement mechanism of composite bulletproof plate was revealed. [ABSTRACT FROM AUTHOR]

This research conducts a comprehensive experimental and numerical analysis of carbon fiber composite laminates under low‐velocity impact conditions. Split Hopkinson Pressure Bar (SHPB) was employed to conduct impact testing on laminates with two layup sequences (03/+45/−45s and 03/903s) under impacts ranging from 2 to 6 J. For assessing damage in laminates, a comprehensive progressive damage model and a simplified model were developed. The primary distinction between these models lies in the fact that the former incorporates the strengthening effect of compression on the delamination behavior, while the latter does not. Both models produce a good agreement with experimental results in terms of force–time, force–displacement curves, and absorbed energies. However, notable differences were noted in the predicted internal damage; the simplified model was underpredicted in terms of damage size and distribution compared to the comprehensive progressive damage model. Highlights: Impact tests were conducted on 03/+45/−45s and 03/903s composites.In order to simulate damage caused by impacts in laminates, an energy‐based damage model was created, and cohesive elements were utilized to model interlaminar delamination.The strengthening effect of compression was explored.Distinct damage criteria were established for two cases.Damage detection of composites by x‐rays. [ABSTRACT FROM AUTHOR]

Self‐resistance electric (SRE) heating for the curing of carbon fiber reinforced plastic (CFRP) offers the benefits of saving energy consumption and reducing investment in equipment. In this work, the investigation was carried out to illustrate the effect of carbon nanotubes (CNTs) addition (0.5, 1.0, and 1.5 wt%) on the thermoset curing and mechanical properties of carbon fiber‐reinforced epoxy laminates fabricated by SRE heating method. The results show that adding CNTs can improve the temperature uniformity and interlayer‐resin flow during the SRE heating process and have a limited influence on the curing degree of CFRP composites. The tensile strength in the longitudinal direction of the composites increased with the increase of CNT addition. Meanwhile, the flexural strength and interlaminar shear strength had the maximum value with the CNTs content of 0.5 wt% and decreased significantly at the CNTs content of 1.5 wt%. It concludes that the appropriate content of CNTs addition has the potential to improve the thermoset curing performance and mechanical properties of the CFRP laminate composites fabricated by SRE heating. Highlights: This study focuses on the effect of CNT addition on SRE heating for CFRP.The addition of CNTs improved the temperature uniformity during SRE heating.The addition of CNTs can reduce the voids of SRE‐cured CFRP composites.Threshold value of CNTs affected the mechanical performance of SRE‐cured CFRP. [ABSTRACT FROM AUTHOR]

One environment that hinders the performance of reinforced concrete is fire. In most cases, this results in the affected part or the entire structure being rendered useless or completely collapsing. When fire mishaps happen in structures, this is the case. This study reviews green structural retrofitting materials for reinforced concrete buildings in an effort to repair damaged structures in an environmentally friendly manner. The information gathered from earlier laboratory test results is assembled to comprehend the impact of room temperature strength properties and varied concrete mix material composition on the residual mechanical properties of concrete. The performance of various fibers, synthetic and natural, as laminate materials for concrete were evaluated, and the study showed that to a significant extent, distressed structural elements could be repaired with retrofits. However, provision of appropriate guidelines for using natural fibre laminates for retrofitting has not been overly explored. This review has highlighted areas that require further study in order to fully understand the residual strength characteristics of concrete exposed to high temperatures, particularly damaged concrete that have been retrofitted with fibers. Overall, the review's findings will be helpful to academics, professionals in the field of civil engineering, and those engaged in construction. [ABSTRACT FROM AUTHOR]

Hybrid bonded–bolted composite material interference connections significantly enhance the collaborative load-bearing capabilities of the adhesive layer and bolts, thus improving structural load-carrying capacity and fatigue life. So, these connections offer significant developmental potential and application prospects in aircraft structural assembly. However, interference causes damage to the adhesive layer and composite laminate around the holes, leading to issues with interface damage. In this study, we employed experimental and finite element methods. Initially, different interference-fit sizes were selected for bolt insertion to analyze the damage mechanism of the adhesive layer during interference-fit bolt installation. Subsequently, a finite element tensile model considering damage to the adhesive layer and composite laminate around the holes post-insertion was established. This study aimed to investigate damage in composite bonded–bolted hybrid joints, explore load-carrying rules and failure modes, and reveal the mechanisms of interference effects on structural damage and failure. The research results indicate that the finite element prediction model considering initial damage around the holes is more effective. As the interference-fit size increases, damage to the adhesive layer transitions from surface debonding to local cracking, while damage to the composite matrix shifts from slight compression failure to severe delamination and fiber-bending fracturing. The structural strength shows a trend of initially increasing and then decreasing, with the maximum strength observed at an interference-fit size of 1.1%. [ABSTRACT FROM AUTHOR]

To promote the development of the 'Bamboo as a Substitute for Steel' proposal, rotary cut bamboo veneers were applied to prepare a kind of high-strength laminated bamboo composite, which was achieved through the hot press molding method in this study. Orthogonal experiments of L9 (33) were performed, with hot-pressing temperature, pressure, and time considered as three influencing factors. Physical properties like density and moisture content, and mechanical properties like modulus of rupture (MOR), modulus of elasticity (MOE), shear strength, and compressive strength were tested for the samples. It can be obtained from the results of range analysis and ANOVA that higher density and lower moisture content were correlated with higher mechanical strength. Within the selected range of tested factors, a hot-pressing temperature and time of 150 °C and 10 min can contribute to higher density and lower moisture content, and the combination of 150 °C and 50 MPa can produce greater mechanical strength. In the thickness direction, the laminated bamboo composites displayed a notable compressed structure. [ABSTRACT FROM AUTHOR]

Carbon fiber reinforced polymer (CFRP) composites are popular materials in the aerospace and automotive industries because of their low weight, high strength, and corrosion resistance. However, wrinkles or geometric distortions in the composite layers significantly reduce their mechanical performance and structural integrity. This paper presents a method for non-destructively extracting the three-dimensional geometry, lamina by lamina, of a laminated composite. A method is introduced for fabricating consistent out-of-plane wrinkled CFRP laminate panels, simulating the in-service wrinkle observed in industries that utilize thick structure composites such as the vertical lift or wind power industries. The individual lamina geometries are extracted from the fabricated coupon with an embedded wrinkle from captured ultrasonic waveforms generated from single-element conventional ultrasonic (UT) scan data. From the extracted waveforms, a method is presented to characterize the wrinkle features within each individual lamina, specifically the spatially varying wrinkle height and intensity for the wrinkle. Parts were fabricated with visibly undetectable wrinkles using a wet layup process and a hot press for curing. Scans were performed in a conventional immersion tank scanning system, and the scan data were analyzed for wrinkle detection and characterization. Extraction of the layers was performed based on tracking the voltage peaks from A-scans in the time domain. Spatial Gaussian averaging was performed to smooth the A-scans, from which the surfaces were extracted for each individual lamina. The extracted winkle surface aligned with the anticipated wrinkle geometry, and a single parameter for quantification of the wrinkle intensity for each lamina is presented. [ABSTRACT FROM AUTHOR]

The damage stages of the ballistic impact effect on both thin and thick laminated composites were investigated. Thin and thick laminated composite plates were produced with unsymmetrical cross-ply [0/90], [–45/+45], and [30/60] layups consisting of 16 and 50 unidirectional layers, respectively. Ballistic tests of the composite plates were carried out by means of a single-stage gas gun system at different velocities in the range from 447 to 861 m/s. The thin composite plates were more damaged than the thick plates at ballistic tests with the same velocity. Relatively small strains were observed at low-velocity impact while the projectile rebounded in all thick specimens. All thick plate specimens, except the plates with [–45/+45] layup, were perforated at high velocity impacts. Tests showed an increase in the shear stress between layers with increasing projectile velocity. [ABSTRACT FROM AUTHOR]

The growing demand for unmanned aerial vehicles (UAVs) in the wide range of commercial applications has necessitated engineers to develop lightweight and economical models that are simple to manufacture. This study focuses on the analysis of UAV wing a unconventionally manufactured medium altitude long endurance (MALE) by performing transient and static fluid structure interaction analysis. The wing was made of an expanded polystyrene (EPS) foam core reinforced by a glass and carbon fiber-reinforced polymer composite. The current study utilizes the one-way fluid-structure interaction technique to obtain the pressure profile from a computational fluid dynamics study, which then is used as a load boundary condition for the static and dynamic structural analyses of an EPS-reinforced composite wing to observe its failure characteristics under loading conditions. Modeling the composite laminate was conducted in the ANSYS Composite PrePost module with varying ply orientations to obtain an optimum configuration. The topology optimization of the wing core led to a 30.5% reduction in its overall weight, offering an economical and feasible solution for manufacturing UAVs on small and medium scales. [ABSTRACT FROM AUTHOR]