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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]

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]

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]

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]

In this study, static deformation for the thermo–magneto–electro–elastic (TMEE) laminates subjected to uniform mechanical load is implemented by considering all the coupled effects including elastic stresses, electric displacements, magnetic inductions, and thermal entropy. The conventional constitutive equations are recapped and converted into their corresponding alternative forms, von Karman nonlinear strains for large deflection are adopted in accordance with the kinematic of classical plate theory. Maxwell equations accounting for the relations between electric/magnetic fields and electric/magnetic potentials are introduced, in addition, Fourier's law for heat conduction is illustrated to present the relation between the thermal flux and the temperature change. In-plane electric fields and magnetic fields are assumed to be neglectable in comparison with the transverse ones, furthermore, the temperature field is deemed to be various along the thickness direction only. In such doing, the Gauss' laws and the heat equation will thus be reduced into three simplified partial differential equations with respect solely to the thickness variable. By solving these equations simultaneously along with appropriate boundary conditions, exact solutions for the electric/magnetic potentials as well as thermal entropy can be achieved analytically. After substituting these quantities into stress components, the stress resultants of the TMEE thin plate can be easily evaluated, and thus the equilibrium equation for the plate bending can be attained in a nonlinear form. By employing the Bubnov–Galerkin method, the nonlinear governing equation will be transformed into a cubic equation in terms of the maximum deflection for the rectangular TMEE plate with simply supported boundary conditions. Two kinds of composite laminates are demonstrated as examples of TMEE heterogeneous materials, one is a bi-layered BaTiO 3 – CoFe 2 O 4 composite, the other is a tri-layered laminate with CoFe 2 O 4 stacked upon BaTiO 3 on an Epoxy substrate. Numerical results are carried out, the validity of the proposed methodology is verified, the effect of volume fraction is discussed, and the deflection curve versus the magnitude of applied load is depicted, in addition, the nonlinear characteristic is explored. [ABSTRACT FROM AUTHOR]

The snap-through behaviors and nonlinear vibrations are investigated for a bistable composite laminated cantilever shell subjected to transversal foundation excitation based on experimental and theoretical approaches. An improved experimental specimen is designed in order to satisfy the cantilever support boundary condition, which is composed of an asymmetric region and a symmetric region. The symmetric region of the experimental specimen is entirely clamped, which is rigidly connected to an electromagnetic shaker, while the asymmetric region remains free of constraint. Different motion paths are realized for the bistable cantilever shell by changing the input signal levels of the electromagnetic shaker, and the displacement responses of the shell are collected by the laser displacement sensors. The numerical simulation is conducted based on the established theoretical model of the bistable composite laminated cantilever shell, and an off-axis three-dimensional dynamic snap-through domain is obtained. The numerical solutions are in good agreement with the experimental results. The nonlinear stiffness characteristics, dynamic snap-through domain, and chaos and bifurcation behaviors of the shell are quantitatively analyzed. Due to the asymmetry of the boundary condition and the shell, the upper stable-state of the shell exhibits an obvious soft spring stiffness characteristic, and the lower stable-state shows a linear stiffness characteristic of the shell. [ABSTRACT FROM AUTHOR]

A meshfree orthotropic laminated shell model for geometrically nonlinear static and dynamic analysis based on the reproducing kernel particle method (RKPM) and the Mindlin-Reissner shell theory is proposed for the first time, suitable for dealing with the finite deformation of composite shell structures of arbitrary geometry in engineering. The Mindlin-Reissner shell theory is adopted to describe the geometric configuration of the laminated shells via a single-layer particle. Then, the Galerkin weak form governing equations are established explicitly and discretized using RKPM and linear transformation in the thickness direction. Furthermore, a laminate stacking sequence that can eliminate the coupling terms of linear and angular acceleration is proposed for simplification. For considering the orthotropic materials, the stress–strain transformation between local and material coordinates is introduced. A stiffened laminated shell model is also presented for simulating complex composited structures. The accuracy and convergence of the proposed laminated shell model are verified through several static and dynamic benchmarks, demonstrating the ability of the presented model to solve the nonlinear response of composite structures. [ABSTRACT FROM AUTHOR]

The nonlinear buckling response of laminated composite cylindrical shells reinforced with graphene nanoplatelets (GNPs) is studied in this paper. The functionally graded (FG) shell reinforced by GNPs is analytically studied under external pressure and uniform temperature rise loadings. It is also assumed that the GNP-reinforced laminated composite shell is in contact with an elastic foundation. Various types of profiles are employed for the GNP distribution patterns in the shell thickness including 10 nanocomposite layers. The nonlinear strain-displacement relations of the shallow cylindrical panel are established utilizing the third-order shear deformation shell theory. Governing equilibrium equations of the laminated GNP-reinforced composite shell are formulated employing the principle of virtual displacement. The coupled system of nonlinear differential equations is solved analytically for the hinged–hinged and fixed–fixed boundaries of the shell using a perturbation-based technique. Correctness of presented formulations and obtained solutions is proved by comparisons with results from previous studies for an isotropic cylindrical shell. Novel numerical results reveal that the material properties, geometrical characteristics and load parameters significantly affect on the buckling behavior of laminated composite cylindrical shells. [ABSTRACT FROM AUTHOR]

The present study investigates the flexural failure properties of a hybrid laminate beam subjected to three-point bending. A symmetrically laminated hybrid beam is constructed using high-strain and inexpensive glass fibre on the top layers and low-strain and expensive carbon fiber on the middle layers. Classical lamination plate theory is used to find the stress and strain distribution that occurs due to the bending moment on the compressive side. The theoretical failure limits of the laminated hybrid beam are analyzed considering the targeted span-to-depth ratios, volume fractions of the fibers and hybrid ratios using the Tsai-Wu failure criterion and Matlab codes. Using the graph of failure index versus hybrid ratios, the minimum thickness of carbon fiber needed for the delay of failure and cost efficiency of the laminated hybrid beam is identified by applying the linear interpolation method. The numerical results indicate that the failure index increases with the increasing loading span and decreases when the volume fraction of fiber increases. In particular, the placement of glass fiber on the top layer of the laminated hybrid beam might have contributed to obtaining higher strains and curvatures before the catastrophic failure properties of carbon fiber. The flexural stiffness of the laminates is found to increase when the hybrid ratio increases. Overall, it is noted that the theoretical analysis is one method that is less time-consuming and cost-effective than other alternative approaches, such as finite element methods and experimental tests to estimate the minimum thickness of high-stiffness and the expensive material needed to maintain the strength and stiffness of the hybrid composite structures over long periods. [ABSTRACT FROM AUTHOR]

This paper studies the mechanical properties of the 2-D tri-axial braided composite. A volume element is established, so that the classical laminate plate theory and the series-parallel model can be adopted to study a bi-directional stress--strain response. Failure criteria are given and the failure strength is determined. The finite element simulation is used to verify the reliability of the present theoretical model. [ABSTRACT FROM AUTHOR]

In order to investigate the durability of fiber-reinforced polymer composites in hygrothermal environments, hygrothermal accelerate aging tests, for 360 days at 70 °C, RH70%; 70 °C, RH85%; 85 °C, RH70%; and 85 °C, RH85% and natural storage for 2 years in Guangzhou, China, were carried out for composite laminates. Then, the moisture absorption and interlaminar shear strength were measured. The hygrothermal damage mechanism of the composite was studied by Fourier transform infrared (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and field emission scanning electron microscopy (FSEM). A dual stress storage life prediction model and the equivalent relationship between natural storage and hygrothermal acceleration were established. The results show that the order of moisture absorption rates, moisture absorption contents, and the severity effect order on the interlaminar shear strength is RH85%; 85 °C > 70 °C; RH85% > 85 °C; RH70% > 70 °C; and RH70%. The time to achieve an effective moisture absorption balance is opposite to this. The moisture absorption rate meets Fick's law before the effective moisture absorption balance, and then shows a linear trend. The interlayer shear strength still decreases exponentially with aging, which is mainly caused by the resin plasticization and interface weakening. Hygrothermal accelerated aging for 13.4831 days at 85 °C; RH85% is equivalent to that for one-year actual storage in Guangzhou. According to the failure criterion of shear strength decreasing to 77%, the storage life of T700/epoxy in Guangzhou is 14.4661 years. [ABSTRACT FROM AUTHOR]

The aim of this research is to investigate basalt as a natural mineral-based fibre together with a vitrimeric resin as a sustainable alternative to standard composite materials. Vitrimers combine the properties of thermoset and thermoplastic polymers, enabling the repair of specimens and hence prolonging the lifetime of the composite material. The micro-mechanical characteristics between the basalt fibres and the vitrimer resin are reported and shown to match those of a standard Skyflex K51 epoxy resin. Discontinuous (4 mm) basalt fibres were employed to produce aligned discontinuous fibre-reinforced composites (ADFRCs) using the high-performance discontinuous fibre (HiPerDiF) technology. The mechanical characteristics of the laminates were investigated through tensile testing and the fracture zones were analysed under a scanning electron microscope. By normalising the results by their respective fibre volume fraction, it was discovered that the vitrimer–basalt ADFRCs exhibited, on average, a 4% higher strength and a 25% higher stiffness compared to their basalt epoxy counterparts. The repair potential of the vitrimer ADFRC specimens was explored during low-temperature compression repair. Two approaches were tested using double-sided local- and full-patch repair. Both successfully recovered a significant amount of their prime strength. In conclusion, the potential of the sustainable vitrimer–basalt composite is shown by its competitive mechanical performance. Combining this with the manufacturing flexibility, repair potential, and recyclability of the material, the vitrimer–basalt composite seems to be a competitive alternative to standard glass epoxies. [ABSTRACT FROM AUTHOR]

The surface roughness and wettability of wood are critical aspects to consider when producing laminated wood products with adhesive applications. This study aims to investigate the surface roughness and dynamic wettability of Jabon wood in the presence of melamine formaldehyde (MF)-based adhesives. Commercial MF adhesives (MF-0) and modified MF adhesives (MF-1) were applied to Jabon wood, which includes tangential (T), radial (R), and semi-radial (T/R) surfaces. The surface roughness of Jabon wood was assessed using a portable stylus-type profilometer. The low-bond axisymmetric drop shape analysis (LB-ADSA) method was employed to identify the contact angle (θ) of the MF-based adhesives on Jabon wood. The wettability was determined by evaluating the constant contact angle change rate (K value) using the Shi and Gardner (S/G) model. Dynamic mechanical analysis (DMA) was employed to investigate the viscoelastic characteristics of the interphase analysis of the wood and MF-based adhesives. The roughness level (Ra) of the Jabon board ranged from 5.62 to 6.94 µm, with the T/R having a higher level of roughness than the R and T. MF-0 exhibited a higher K value (0.262–0.331) than MF-1 (0.136–0.212), indicating that MF-0 wets the surface of Jabon wood more easily than MF-1. The wood–MF-0 interphase reached a maximum stiffness of 957 N/m at 123.0 °C, while the wood–MF-1 had a maximum stiffness of 2734 N/m at 110.5 °C. In addition, the wood–MF-0 had a maximum storage modulus of 12,650 MPa at a temperature of 128.9 °C, while the wood–MF-1 had a maximum storage modulus of 22,950 MPa at 113.5 °C. [ABSTRACT FROM AUTHOR]

The Diels–Alder equilibrium is a widely known process in chemistry that can be used to provide a thermoset structure with recyclability and reprocessability mechanisms. In this study, a commercial epoxy resin is modified through the integration of functional groups into the network structure to provide superior performance. The present study has demonstrated that it is possible to adapt the curing process to efficiently incorporate these moieties in the final structure of commercial epoxy-based resins. It also evaluates the impact that they have on the final properties of the cured composites. In addition, different approaches have been studied for the incorporation of the functional group, adjusting and adapting the stoichiometry of the system components due to the differences in reactivity caused by the presence of the incorporated reactive groups, with the objective of maintaining comparable ratios of epoxy/amine groups in the formulation. Finally, it has been demonstrated that although the Diels–Alder equilibrium responds under external conditions, such as temperature, different sets of parameters and behaviors are to be expected as the structures are integrated into the thermoset, generating new equilibrium temperatures. In this way, the present research has explored sustainable strategies to enable the recyclability of commercial thermoset systems through crosslinking control and its modification. [ABSTRACT FROM AUTHOR]

The corrosion behavior of a hybrid laminate consisting of laser-structured aluminum EN AW-6082 ∪ carbon fiber-reinforced polymer was investigated. Specimens were corroded in aqueous NaCl electrolyte (0.1 mol/L) over a period of up to 31 days and characterized continuously by means of scanning electron and light microscopy, supplemented by energy dispersive X-ray spectroscopy. Comparative linear sweep voltammetry was employed on the first and seventh day of the corrosion experiment. The influence of different laser morphologies and production process parameters on corrosion behavior was compared. The corrosion reaction mainly arises from the aluminum component and shows distinct differences in long-term corrosion morphology between pure EN AW-6082 and the hybrid laminate. Compared to short-term investigations, a strong influence of galvanic corrosion on the interface is assumed. No distinct influences of different laser structuring and process parameters on the corrosion behavior were detected. Weight measurements suggest a continuous loss of mass attributed to the detachment of corrosion products. [ABSTRACT FROM AUTHOR]

In this study, the frequency and deflection response analysis of basalt, soy, flax and hybrid pineapple and flax hybrid laminated skew plates are done. The conventional hand-layup method is used to fabricate the different bio-composites-based laminated structures. The uniaxial tension test is conducted in the INSTRON 5967 UTM to determine the elastic properties of the bio-composite laminated structure as per ISO 527-5 standards. The hybrid laminate skew plate is modeled using the first-order shear deformation theory (FSDT) and their elastic properties are obtained from the uniaxial tensile test from which the frequency and deflection of the skew laminated plates are calculated. The eight-noded shell elements (S8R5) with each node having five degrees-of-freedom are deputed in the commercial finite element method (FEM) package ABAQUS to beget the numerical solutions. The damping effect is neglected in the analysis. The accuracy of the proposed model is verified with available literature and found to be in good agreement. Later, the effect of different parameters such as boundary conditions, aspect ratio and skew angles on the natural frequency and deflection of the bio-composites hybrid laminated skew plates are investigated. The obtained results inferred the natural frequencies are decreasing with an increasing aspect ratio of skew plates. The skew angles help to increase the natural frequencies of skew plates. The central deflections are lower for high-skew angled laminated plates. [ABSTRACT FROM AUTHOR]

Inflatable gossamer space structures require structural rigidity after partial or complete out-gassing of the inflation gases. The current study focuses on the rigidity generation in a fully deployed, out-gassed Kapton laminated conical boom. A novel approach is applied to produce out-of-plane structural stiffness in the gossamer structure using the shape memory alloy (SMA) wires embedded between Kapton laminate membranes. The finite element analysis is performed to find the generated stiffness in the system and validated with the experimental results. To this end, an experimental set-up is developed to provide a stable and uniform thermal environment with the inflation facility. Additionally, different measuring devices are also employed in the test set-up to note the readings of pressure, temperature, and displacement sensors. Moreover, the Kapton and SMA material properties are found experimentally, and their material models are validated with published studies. Furthermore, constitutive equations of the SMA-Kapton composite are also included in the study. After that, a parametric study is done to know the effect of design and material parameters on the boom's stiffness. [ABSTRACT FROM AUTHOR]

"Interleaving" is widely used for interlaminar toughening of fiber-reinforced composites, and the structure of interleaving is one of the important factors affecting the toughening efficiency of laminates. Several experiments have demonstrated that compared to continuous and dense structures, toughening layers with structural heterogeneity can trigger multiple toughening mechanisms and have better toughening effects. On this basis, this work further investigates the application of heterogeneous toughening phases in interlaminar toughening of bidirectional GFRP. CNT was selected to construct toughening phases, which was introduced into the interlaminar of composites through efficient spraying methods. By controlling the amount of CNT, various structures of CNT toughening layers were obtained. The fracture toughness of modified laminates was tested, and their toughening mechanism was analyzed based on fracture surface observation. The results indicate that the optimal CNT usage (0.5 gsm) can increase the initial and extended values of interlayer fracture toughness by 136.0% and 82.0%, respectively. The solvent acetone sprayed with CNT can dissolve and re-precipitate a portion of the sizing agent on the surface of the fibers, which improves the bonding of the fibers to the resin. More importantly, larger discrete particles are formed between the layers, guiding the cracks to deflect in the orientation of the toughened layer. This generates additional energy dissipation and ultimately presents an optimal toughening effect. [ABSTRACT FROM AUTHOR]

Carbon-fiber-reinforced polymer (CFRP) composites are widely used in lightweight structures because of their high specific strength, specific modulus, and low coefficient of thermal expansion. Additionally, the unidirectionally arrayed chopped strand (UACS) laminates have excellent mechanical properties and flowability, making them suitable for fabricating structures with complex geometry. In this paper, the damage process of UACS quasi-isotropic laminates under tensile load was tested using acoustic emission detection technology. The mechanical properties and damage failure mechanism of UACS laminates were studied combined with finite element calculation. By comparing and analyzing the characteristic parameters of acoustic emission signals such as amplitude, relative energy, and impact event, it is found that acoustic emission behavior can accurately describe the damage evolution of specimens during loading. The results show that the high-amplitude signals representing fiber fracture in continuous fiber laminates are concentrated in the last 41%, while in UACS laminates they are concentrated in the last 30%. In UACS laminates, more of the damage is caused by matrix cracks and delamination with medium- and low-amplitude signals, which indicates that UACS laminates have a good suppression effect on damage propagation. The stress–strain curves obtained from finite element analysis agree well with the experiment results, showing the same damage sequence, which confirms that the model described in this research is reliable. [ABSTRACT FROM AUTHOR]

Low fiber-direction compressive strength is a well-recognized weakness of carbon fiber-reinforced polymer (CFRP) composites. When a CFRP is produced using 3D printing, the compressive strength is further degraded. To solve this issue, in this paper, a novel magnetic compaction force-assisted additive manufacturing (MCFA-AM) method is used to print CFRP laminates reinforced with carbon nanofiber (CNF) z-threads (i.e., ZT-CFRP). MCFA-AM utilizes a magnetic force to simultaneously levitate, deposit, and compact fast-curing CFRP prepregs in free space and quickly solidifies the CFRP laminate part without any mold nor supporting substrate plate; it effectively reduces the voids. The longitudinal compressive test was performed on five different sample types. ZT-CFRP/MCFA-AM samples were printed under two different magnetic compaction rolling pressures, i.e., 0.5 bar and 0.78 bar. Compared with the longitudinal compressive strength of a typical CFRP manufactured by the traditional out-of-autoclave–vacuum-bag-only (OOA-VBO) molding process at the steady-state pressure of 0.82 bar, the ZT-CFRP/MCFA-AM samples showed either comparable results (by −1.00% difference) or enhanced results (+7.42% improvement) by using 0.5 bar or 0.78 bar magnetic rolling pressures, respectively. [ABSTRACT FROM AUTHOR]

Semi-aromatic poly (hexamethylene terephthalamide) (PA6T) oligomer (prePA6T) ultrafine powder, with a diameter of <5 μm, was prepared as an emulsion sizing agent to improve the impregnation performance of CF/PA6T composites. The prePA6T hyperfine powder was acquired via the dissolution and precipitation "phase conversion" method, and the prePA6T emulsion sizing agent was acquired to continuously coat the CF bundle. The sized CF unidirectional tape was knitted into a fabric using the plain weave method, while the CF/PA6T laminated composites were obtained by laminating the plain weave fabrics with PA6T films. The interfacial shear strength (IFSS), tensile strength (TS), and interlaminar shear strength (ILSS) of prePA6T-modified CF/PA6T composites improved by 54.9%, 125.3%, and 120.9%, respectively. Compared with the commercial polyamide sizing agent product PA845H, the prePA6T sizing agent showed better interfacial properties at elevated temperatures, especially no TS loss at 75 °C. The SEM observations also indicated that the prePA6T emulsion has an excellent impregnation effect on CF, and the fracture mechanism shifted from adhesive failure mode to cohesive failure mode. In summary, a facile, heat-resistant, undamaged-to-fiber environmental coating process is proposed to continuously manufacture high-performance thermoplastic composites, which is quite promising in mass production. [ABSTRACT FROM AUTHOR]

This paper proposes a simple yet accurate finite element (FE) formulation for the thermomechanical analysis of laminated composites and sandwich plates. To this end, an enhanced first-order shear deformation theory including the transverse normal effect based on the mixed variational theorem (EFSDTM_TN) was employed in the FE implementation. The primary objective of the FE formulation was to systematically interconnect the displacement and transverse stress fields using the mixed variational theorem (MVT). In the MVT, the transverse stress field is derived from the efficient higher-order plate theory including the transverse normal effect (EHOPT_TN), to enhance the solution accuracy, whereas the displacement field is defined by the first-order shear deformation theory including the transverse normal effect (FSDT_TN), to amplify the numerical efficiency. Furthermore, the transverse displacement field is modified by incorporating the components of the external temperature loading, enabling the consideration of the transverse normal strain effect without introducing additional unknown variables. Based on the predefined relationships, the proposed FE formulation can extract the C0-based computational benefits of FSDT_TN, while improving the solution accuracy for thermomechanical analysis. The numerical performance of the proposed FE formulation was demonstrated by comparing the obtained solutions with those available in the literature, including 3-D exact solutions. [ABSTRACT FROM AUTHOR]

Remarkable advances in the research and development of micro/mini Unmanned Aerial Vehicles (UAVs) seek thin, lightweight and strong materials for their structural applications. As these structures involve various loading conditions in both the in-plane and through-the-thickness directions during their life cycle, the assurance of the structural stability in each direction is deemed mandatory. The woven Aramid fibers as high strain materials (HSM) are known to improve the through-the-thickness impact strength. However, the addition of the HSM can affect the overall tensile behavior of composite laminates. This study investigates the effect of the woven Aramid fiber on the in-plane tensile behavior of Carbon/ epoxy laminates. Laminates are fabricated using an easy and cost-effective Vacuum Assisted Resin Infusion Molding (VARIM) setup. A uniaxial tensile test was conducted to analyze the tensile behavior of Carbon/Aramid hybrid composites. The effect of adding the woven Aramid layer and the Carbon fabric sequence on the tensile modulus, strain to failure and modulus of toughness are investigated in this study. The results revealed that the presence of Aramid has a positive hybrid effect on the failure strain, exhibiting pseudo-ductile behavior with a compromise in the tensile modulus of the virgin Carbon/epoxy laminate. [ABSTRACT FROM AUTHOR]

The dynamic model of a bistable laminated composite shell simply supported by four corners is further developed to investigate the resonance responses and chaotic behaviors. The existence of the 1:1 resonance relationship between two order vibration modes of the system is verified. The resonance response of this class of bistable structures in the dynamic snap-through mode is investigated, and the four-dimensional (4D) nonlinear modulation equations are derived based on the 1:1 internal resonance relationship by means of the multiple scales method. The Hopf bifurcation and instability interval of the amplitude frequency and force amplitude curves are analyzed. The discussion focuses on investigating the effects of key parameters, e.g., excitation amplitude, damping coefficient, and detuning parameters, on the resonance responses. The numerical simulations show that the foundation excitation and the degree of coupling between the vibration modes exert a substantial effect on the chaotic dynamics of the system. Furthermore, the significant motions under particular excitation conditions are visualized by bifurcation diagrams, time histories, phase portraits, three-dimensional (3D) phase portraits, and Poincare maps. Finally, the vibration experiment is carried out to study the amplitude frequency responses and bifurcation characteristics for the bistable laminated composite shell, yielding results that are qualitatively consistent with the theoretical results. [ABSTRACT FROM AUTHOR]

This document is a list of references for research articles related to the topic of interlaminar fracture toughness in composite materials. The articles cover various aspects of the subject, including the use of different materials and techniques to enhance fracture toughness, such as surface treatments, coatings, veils, and nanofibers. The articles also explore the effects of different factors, such as fiber type and length, on interlaminar fracture toughness. The references provide a comprehensive collection of research on this topic, which can be useful for library patrons conducting research in this area. [Extracted from the article]

The analysis of the mathematical and mechanical properties of thermoelastic coupling tensors in anisotropic laminates is the topic of this paper. Some theoretical results concerning the compliance tensors are shown and their mechanical consequences analyzed. Moreover, the case of thermally stable laminates, important for practical applications, is also considered. The study is carried out in the framework of the polar method, a mathematical formalism particularly well-suited for the analysis of planar anisotropic problems, introduced by Prof. G. Verchery in 1979. [ABSTRACT FROM AUTHOR]

A Kriging-based optimization method is proposed and applied to the design optimization of stacking sequence for quadrilateral laminated composite plates with curved edges. The vibration model for evaluating the fundamental frequency of plates is constructed using the first-order shear deformation theory (FSDT). Then a Kriging surrogate model is used to approximate the vibration model to improve design optimization efficiency. A starting strategy based on the fitting quality coefficient is proposed to determine when to use the expected improvement (EI) infill criterion during the sequential sampling process. Three widely used correlation functions are dynamically selected during the Kriging modeling process to improve the generalization ability of model. In addition, a hybrid whale optimization algorithm (HWOA) is employed to optimize the Kriging hyperparameters, maximize the mean squared error (MMSE), the Expected Improvement (EI) function, and the Kriging predictor. Finally, a comparison is made with the classical DACE toolbox, the optimization procedure using the MMSE criterion and the standard one-shot Kriging-based optimization procedure. Results have demonstrated the effectiveness of the proposed method and clearly indicate that the required number of samples for optimization can be effectively reduced when starting to use the EI infill criterion at the fitting quality coefficient larger than 0.85. [ABSTRACT FROM AUTHOR]

The Hyper Velocity Impact Experiments of prospective structural materials and shields are necessary to ensure the safety of satellites and spacecraft, particularly in lower earth orbits. The advancement of computational tools has made it simpler to reproduce the hyper velocity impact scenarios by facilitating the change in control parameters during simulations. Numerical models have been extensively used for the impact simulations of metallic target plates that possess isotropic behavior. However, due to the intricate nature of the material models, failure models, shock response, and fracture models, it is more challenging to simulate orthotropic target materials compared to isotropic materials. In this work, a numerical model has been adopted to predict the behavior of orthotropic materials during hyper velocity impact experiments involving spherical aluminum AA2017-T4 projectiles (1 mm in diameter). The orthotropic material comprises a 16-layered sequence of carbon fiber-reinforced epoxy plies in a quasi-isotropic arrangement. The numerical simulations were conducted on the ANSYS Autodyn® finite element software. On comparison of numerical and experimental results, it was observed that perforation diameter from the simulation was in close agreement with that of the experimental at both 2.5 km/s and 5.0 km/s. Additionally, the damage mechanisms (energy absorption) for different failure modes of the laminates were analyzed in detail. Fiber pullout and Fiber debonding were the dominant failure mechanisms contributing to more than 90% of the surface energy. • Multi-layered CFRP laminates subjected to hypervelocity impact (HVI). • Numerical model developed for orthotropic laminates. • HVI simulations at 2.5 km/s and 5 km/s with emphasis on debris propagation. • Katz model for identifying dominant energy absorption mechanism during HVI. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs) are added to the matrix according to proper distribution configurations by many researchers to improve the stiffness of laminated composites. However, the distribution configurations of CNTs may induce dramatic changes in displacements and stresses, which significantly affect structural safety. Moreover, such issues have received little attention at present because existing theoretical models encounter difficulties in accurately predicting dramatic changes in stresses of these structures. To accurately analyze the thermal expansion behaviors of laminated panels reinforced by CNTs, an equivalent single-layer higher-order model is proposed in which in-plane displacements are constructed by superimposing the second local displacements onto a smooth cubic varying field. Transverse normal deformation should be considered for the thermal expansion behavior of the laminated plate; therefore, a smooth cubic distribution along the thickness is adopted in the transverse displacement field. The layer-dependent displacement parameters can be expressed using global displacement variables by applying compatible conditions of displacements and stresses. Based on the proposed model, analytical solutions for laminated composites are obtained using Navier's technique. The capability of the proposed model is verified by comparing the results of the proposed model with the exact solutions and the three-dimensional finite element model. The effect of the distribution configuration and volume fraction of CNTs on the thermomechanical behavior of the composite panels is studied based on the present model. Numerical results show that the distribution configuration and volume fraction of the CNTs significantly influence the distributions and magnitudes of stresses. Practical Applications: In order to improve the stiffness of aircraft wings, stiffeners are typically used to enforce the skin of the wing. However, the aerodynamic shape of the wing cannot be changed, so that the stiffeners cannot be placed on external surface of the skin. As a result, the panel's bending stiffness relative to the midplane is not asymmetric, which affected its loading capability. To overcome such problems, previous studies have demonstrated that adding CNTs can improve the stiffness of panels, and it has been found that composite panels reinforced with X-X-distributing CNTs possess the best capability in preventing buckling deformation. However, the effect of the distribution profiles of CNTs on the thermomechanical behavior has been less studied in the existing literature. Therefore, this study proposes a higher-order model to accurately predict the thermomechanical behavior of CNT-reinforced composite panels and investigate the effect of CNT distribution profiles and volume fractions on the thermomechanical responses of composite panels. The present work can provide suggestions for the design of a reinforcing scheme for CNT-reinforced composite panels, so that the stiffness of wings can be enhanced. [ABSTRACT FROM AUTHOR]

Degradation of polymer composites is a significant problem in many engineering aspects. Due to the interaction of various degradation factors during the exploitation of composites, a synergistic effect of destruction is observed. The article describes the phenomena occurring in glass fiber reinforced polyester laminates under the influence of ultraviolet radiation (UV) in an aquatic environment. The laminates were exposed to UV-A, UV-B and UV-C radiation for 1000 h in free-air and underwater conditions. During the test, the materials were immersed at stable depth of 1 mm and 10 mm, respectively. The three-point bending tests performed on the samples after being exposed to UV showed an increase in the flexural strength of the composites. Simultaneously, degradation of the outer surface layer was observed. The degradation removed the thin resin film from the surface which resulted in a direct exposure of the reinforcing fibers to the environment. The transformations taking place in the deeper layers of the composite increased the mechanical strength due to the additional cross-linking reactions excited by the energy arising from the radiation. Moreover, the formation of polymer structures from free styrene remaining after the technological process and the occurrence of free radical reactions as a result of the cage effect was also observed. [ABSTRACT FROM AUTHOR]

This work presents novel three-dimensional solutions for the multiphysics response of magneto-electro-elastic multilayered plates with interfacial imperfections in a thermal environment. The Stroh formalism is employed, incorporating thermal coupling with the Eringen nonlocal theory to capture small-scale effects. The laminated structures are simply supported and subjected to time-harmonic temperature distributions and extended tractions represented using Fourier series expansions. The dual variable and position technique is used to address the challenges posed by non-ideal thermal and mechanical bonded contacts between constituents, ensuring the consistency and stability of the recursive field relations. A wide range of application examples are analyzed, including the influence of material arrangements, aspect ratio and nonlocal length characteristics, elastically compliant and thermally/dielectrically weakly conducting interfaces, as well as forced vibrations in combined thermo-mechanical environments. The comprehensive results shed light on the intricate multiphysics response of multilayered structures and provide valuable insights into practical engineering implications for advanced materials and structures. [ABSTRACT FROM AUTHOR]

This article describes the application of the A-priori algorithm for defining the rule-based relationships between individual defects caused during the lamination process, affecting the deformation defect of the yacht shell. The data from 542 yachts were collected and evaluated. For the proper development of the algorithm, a technological process of the yacht lamination supported by expert decisions was described. The laminating technology is a complex process of a sequential application of individual laminates according to a special strategy. The A-priori algorithm allowed for obtaining the set of association rules defining the relationships between the defects resulting from the lamination process and influencing the deformation defect of the yacht shell, which is one of the most common errors in yacht production. The obtained aggregated rules were compared with the expert knowledge of the employees of the production, quality control, mould regeneration, and technology departments of the yacht yard. The use of the proposed A-priori algorithm allowed for the generation of relationship rules consistent with the general opinion of experts. Associative rules additionally took into account detailed causes of a specific error, which were not always noticed by employees of specific departments. The assessment of the lamination process using an artificial intelligence algorithm turned out to be more objective, which made it possible to gradually reduce the total number of errors occurring in the yacht shell lamination process, and thus shorten the time needed to repair errors and the total time of producing the yacht. [ABSTRACT FROM AUTHOR]

To detect the debonding defect of glass fiber reinforced polymer (GFRP) laminate, the lock-in infrared thermography non-destructive testing system is built and the systematic testing research are conducted, and the effect of different geometrical parameters of debonding defects on the testing results are analyzed. Algorithms such as inter frame differential-multi frame cumulative average method, polynomial fitting-correlation coefficient method, and time-difference contrast method are used to process the image sequence, and signal-to-noise ratio and information entropy are defined as the parameters for evaluating the performance of algorithms. [ABSTRACT FROM AUTHOR]

In the process of preparation and service, the carbon fiber reinforced polymer (CFRP) material is prone to defects such as delamination and inclusions, which seriously impact the normal use. In this paper, non-linear frequency-modulated (the logarithmic sweep) thermal excitation is used to carry out finite element simulation and experimental research. In order to investigate how different detection process parameters affect defects, the impact of different detection parameters on the surface temperature difference and contrast is analyzed, and the detection parameters that can quickly identify defects and have better recognition effect are obtained. [ABSTRACT FROM AUTHOR]

Carbon Fiber Reinforced Polymer (CFRP) laminates habitually experience either tensile or compressive prestressing loads and are simultaneously susceptible to external low-velocity impacts in genuine operating scenarios. The current study establishes a meticulous model to elucidate the low-speed impact behavior of prestressed CFRP laminates, substantiated by finite element simulations. Initial validation of the model is accomplished by comparing simulated low-velocity impact scenarios without prestress against experimental data. Subsequently, the validated model is employed to simulate the low-velocity impact process under varying impact velocities and under both tensile and compressive prestress loads. It is demonstratively shown that tensile prestressing accentuates the extent of damage incurred by the laminate, a phenomenon that amplifies concomitantly with increasing impact speed. In contrast, compressive prestress is found to mitigate the laminate damage to a particular degree, albeit this mitigative effect is observed to diminish with escalating impact velocities. The findings derived from the investigation furnish pivotal data concerning the impact resilience of composite materials under practical working conditions and yield substantial engineering applicability for optimizing the design of related structures. [ABSTRACT FROM AUTHOR]

The paper deals with bifurcation and/or non-bifurcation post-buckling curves of composite plates under biaxial compression. For different lay-up sequences, a coupling, i.e. extension-bending (EB) is considered. The current investigations present distinct equilibrium paths describing when they have bifurcation-type and/or non-bifurcation-type responses. The novel parameter (i.e. EB coupling imperfection) is calculated to show the amount of non-bifurcation in the equilibrium path as a quantitative parameter. For the case of non-square plates, a novel mixed-mode analysis is conducted. The effects of different characters in laminated composites such as layer arrangement, loading ratio, aspect ratio, and boundary conditions are investigated. A novel result concluded in the numerical examples where there are some possibilities to have different mode shapes in linear and non-linear buckling analysis. FEM results of ANSYS software verify the results of analytical equations. [ABSTRACT FROM AUTHOR]

Carbon fiber-reinforced composites are popular due to their high strength and light weight; thus, the structures demonstrate high performance and specific strength. However, these composites are susceptible to impact damage. The objective of this research was to study the behavior of carbon fiber-reinforced laminates based on a polyetheretherketone (PEEK) matrix with six stacking sequences under static and impact loading. Four-point bending, short-beam bending, drop weight impact, and compression after impact tests were carried out. The results were complemented with digital shearography to estimate the damaged areas. Finite element modeling served to assess the failure mechanisms, such as fiber and matrix failure, in different layers due to tension of compression. Three behavior pattern of layups under drop-weight impact were found: (i)—energy redistribution due to mostly linear behavior (like a trampoline) and thus lower kinetic energy absorption for damage initiation, (ii)—moderate absorption of energy with initiation and propagation of concentrated damage with depressed redistribution of energy in the material, (iii)—moderate energy absorption with good redistribution due to initiation of small, dispersed damage. The results can be used to predict the mechanical behavior of composites with different stacking sequences in materials for proper structural design. [ABSTRACT FROM AUTHOR]

Microvascular self-healing composite materials have significant potential for application and their mechanical properties need in-depth investigation. In this paper, the tensile and compressive properties of woven fabric carbon fiber-reinforced polymer (CFRP) laminates containing three-dimensional microvascular channels were investigated experimentally. Several detailed finite element (FE) models were established to simulate the mechanical behavior of the laminate and the effectiveness of different models was examined. The damage propagation process of the microvascular laminates and the influence of microvascular parameters were studied by the validated models. The results show that microvascular channels arranged along the thickness direction (z-direction) of the laminates are critical locations under the loads. The channels have minimal effect on the stiffness of the laminates but cause a certain reduction in strength, which varies approximately linearly with the z-direction channel diameter within its common design range of 0.1~1 mm. It is necessary to consider the resin-rich region formed around microvascular channels in the warp and weft fiber yarns of the woven fabric composite when establishing the FE model. The layers in the model should be assigned with equivalent unidirectional ply material in order to calculate the mechanical properties of laminates correctly. [ABSTRACT FROM AUTHOR]

It is commonly acknowledged that polymer composites in service are often subjected to not only intricate mechanical loads but also harsh environmental conditions. The mechanical and thermal properties of five particular composites are explored here. The composites are composed of laminates of glass cloth type "E" sheet infilled with a duroplastic matrix. This is a thermoset polymer—epoxy resin with different molecular weights. The composites were fabricated by IZOERG company, which is based in Poland. The final articles were 1.5 mm thick by 60 cm long and 30 cm wide, with the glass layers arranged parallel to the thickness. Young's modulus and tensile strength were measured at room temperature. Using the thermal analysis of dynamic mechanical properties (DMTA), the values of the storage modulus and the loss modulus were determined, and the damping factor was used to determine the glass transition temperature (Tg). It was revealed that the nature of changes in the storage modulus, loss modulus, and damping factor of composite materials depends on the type of epoxy resin used. Thermal expansion is a crucial parameter when choosing a material for application in cryogenic conditions. Thanks to the TMA method, thermal expansion coefficients for composite materials were determined. The results show that the highest value of the coefficient of thermal expansion leads the laminate EP_4_2 based on brominated epoxy resin cured with novolac P. Duroplastic composites were characterized at cryogenic temperatures, and the results are interesting for developing cryogenic applications, including electric motors, generators, magnets, and other devices. [ABSTRACT FROM AUTHOR]