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This study presents an investigation on the mechanical properties and failure mechanisms of composites made of plain woven fabrics reinforced with carbon fibers, aramid fibers, and their intralayer hybrids. The specimens were fabricated by hand lay-up method. Tension, compression, and shear tests were performed in accordance with the relevant standards to investigate the tensile, compression, and shear properties of carbon fiber, aramid fiber, and carbon/aramid fiber intralayer hybrid plain woven composites. Accurate strain field was obtained by digital image correlation (DIC) technology and compared with the results measured by the strain rosettes. Furthermore, a multi-scale modeling strategy was developed to predict the mechanical properties of the hybrid composites. The fiber monofilament model was used to calculate the effective properties of carbon and aramid yarns at the micro-scale level. Representative volume element (RVE) models of the hybrid composite were constructed considering the real fabric pattern at the meso-scale level. The predicted results agree well with the experimental data which validates the multi-scale modeling strategy. The presented information on the tensile, compressive, and shear properties and finite element simulation method of carbon/aramid intralayer hybrid composites should be useful in subsequent research as well as in designing new high-performance composites and structures. [ABSTRACT FROM AUTHOR]

Carbon fiber laminated composites are widely used in aerospace and high speed railways industries due to their high specific strength and stiffness, but the poor interlaminar properties affect their further applications. In order to solve the problem of poor interlayer performance of woven laminated composites, this paper proposes a new type of laminated composite, called single-sided-loop two-dimensional (2D) woven laminated composites (SWLC). By introducing loop warp yarns to the thickness of general 2D woven laminated composites (GWLC), the loop between its preform and resin can improve the way of the fibers attached to the substrate and increase the volume content of the fibers between the layers. The mechanical behavior of SWLC is investigated experimentally and numerically. For numerical simulations, a unit cell is established based on the fine periodic structure. A progressive damage model is established using the 3D Hashin and the von-Mises criteria. Numerical results are in good agreement with the experimental data. Results show that the looped fabric can improve interlayer properties at the expense of slight reduction of some in-plane properties. [ABSTRACT FROM AUTHOR]

In this paper, the effect of interlaminar properties and the type of delamination defects on the residual compression properties of carbon fiber laminates were experimentally investigated. A new method, which employed magnetic force to guide the arrangement direction of stainless steel particles between layers of laminates, was adopted to improve the interlayer toughness. The digital image correlation, C-scan, and micro-CT were used to measure and identify the compression failure damages. Test results showed that the compressive strength of the intact carbon fiber laminates was 299.37 MPa, and the one of specimens containing the deeply buried delamination, the through-width delamination, and the surface delamination decreased by 55.98 MPa, 58.69 MPa, and 60.23 MPa, respectively. The compressive strength of the specimens containing the deeply buried delamination only decreased by 14.01 MPa when the mode I toughness increased by 81.88%, and the specimen containing the surface delamination only decreased by 30.86 MPa when the mode II fracture toughness increased by 87.72%. However, improving the fracture toughness could not strengthen the specimens containing the through-width delamination. Moreover, a qualitative dynamic damage relationship, which described the relationship between delamination expansion and compression damage vividly, was proposed. The reason the increase of the toughness could improve the residual compression performance of the laminates containing delamination was that the higher fracture toughness hindered the secondary expansion of the delamination during the compression process so that the delamination area could almost remain unchanged. [ABSTRACT FROM AUTHOR]

Due to corner stress singularities, free vibration analysis of thin sectorial plates with arbitrary boundary supports including a free vertex is a rather challenging problem. In this paper, a novel rotation-free quadrature element formulation based on Kirchhoff plate theory is presented to solve the problem. Different from all existing quadrature thin plate element formulations, rotational degrees of freedom are not used. Instead, a boundary point is modeled by two nodes separated by a very small distance and thus the C 1 continuity is easily enforced. Explicit formulations with arbitrary number of nodes and nodes of any type are worked out to ease the p -refinement. Numerical results demonstrate that the proposed formulation is simple, straightforward and has excellent performance for solving thin sectorial plate with arbitrary combinations of boundary supports. Some tabulated data are believed new which may serve as a reference. [ABSTRACT FROM AUTHOR]

Mapping an irregular domain into a square one is a common technique in analyzing problems of plates and shells with irregular shapes. For the irregular shape without four corners such as the elliptical shape, the difficulty arises that the Jacobian determinant is zero at the corner points. An efficient quadrature method is presented to analyze the transverse vibration of thin plates with an elliptical shape. To circumvent the above-mentioned difficulty, Gauss quadrature is used in numerical integration. Besides, derivative degrees of freedom are not used, and a boundary point is modeled by two nodes separated by a very small distance. Since the nodes are not coinciding with integration points, a way indirectly using the differential quadrature law is employed to derive the explicit formulas to ease the programming. A convergence study is performed. Free vibration of elliptical plates with continuous and discontinuous edge conditions is analyzed to demonstrate the efficiency of the developed rotation-free weak-form quadrature method. [ABSTRACT FROM AUTHOR]

It is difficult for the existing Burgers model to accurately depict the off-axis cyclic drawing process of woven coatings. In this paper, the mechanical deformation of woven PVC (polyvinyl chloride)-coated film at different temperatures is investigated. One-dimensional (1D) and two-dimensional (2D) constitutive models were established to characterize cyclic deformation processes. The 1D model is an improved Burgers model. The effects of the time dependence of the viscosity coefficient and the ratio of elastic to viscous deformation are considered simultaneously. The accuracy of the 1D model for predicting the cyclic nonlinear deformation at different temperatures and loading rates is improved. The 2D model is a nonlinear orthotropic model using polynomials. On the basis of the single-objective genetic algorithm, the inverse algorithm is used to obtain the shear polynomial coefficients in the tension phase and the shear modulus in the unloading phase, which circumvents performing the difficult shear test. UMAT subroutines of off-axis stretching and off-axis cyclic stretching are written separately. The intelligent inverse algorithm program consists of a single-objective genetic algorithm program, a finite element parametric modelling program, and a UMAT subroutine. The simulation results are compared with the off-axis cyclic tensile test data to validate the effectiveness and accuracy of the proposed 2D model for the analysis of the woven PVC-coated films in the tension–shear coupling state. [ABSTRACT FROM AUTHOR]

Carbon fiber laminated composites are widely used in the aerospace industry due to their excellent lightweight and excellent mechanical properties. However, when subjected to external impact, delamination damage occurs between the layers of composite materials, and thus how to suppress delamination and improve the interlaminar strength of composite laminates has become the focus of the research field. Based on the idea of interlayer toughening, a new double-sided-loop two-dimensional (2D) woven laminated composites (DWLC) is designed, woven and laminated using the RTM molding process. DWLC is based on a 2D fabric with the introduction of loop warp yarns in thickness direction, which form Z-directional loops and thus form a synergistic toughening layer with the resin matrix between the layers after lamination during the forming process. In order to study the mechanical properties of DWLC, the tensile, compressive, interlaminar shear mechanical properties and damage behavior of DWLC are experimentally and numerically investigated. In addition, the internal damage and failure fracture are examined using micro computed tomography (Micro-CT). Strength prediction model of DWLC is established based on a representative volume element (RVE) with a mesoscopic geometric model. Three-dimensional (3D) Hashin and Von-Mises criteria are introduced as the failure criteria for the component materials. The results show that due to the existence of loops, the in-plane fiber volume content of DWLC decreases, resulting in a decrease of tensile and compressive strengths but an increase of interlaminar shear strength. [ABSTRACT FROM AUTHOR]

A three-dimensional explicit finite element method was presented to investigate the bearing failure of single- and double-shear composite bolted joints. To predict the various failure modes of composite laminates, three-dimensional solid elements accompanied by mixed-mode failure criteria considering nonlinear shear behavior were employed in the model. A linear damage propagation law based on the fracture energy and the characteristic length was adopted to alleviate the mesh dependency. In addition, reduced integration elements were used in the models of single- and double-shear joints to avoid the overstiffness. The simulated models were implemented in the Abaqus/Explicit solver with a user-defined material subroutine. The numerical analysis run successfully without any convergence issues. The predictions of mechanical behavior agreed well with the experimental results, with typical damages in the laminates including matrix crack and fiber failure. The effect of secondary bending in the single-shear bolted joint was also analyzed in the explicit modeling. [ABSTRACT FROM AUTHOR]

A comprehensive experimental study on the coupling coefficients of unidirectional (UD) and woven fabric glass/epoxy laminates under off-axis tensile loading was conducted in comparison with the theoretical prediction. The capability of the off-axis test to evaluate the elastic constants in the loading direction was reported. Four coupling coefficients were obtained from tests and discussed in comparison with the theoretical prediction. A further comparison of coupling compliance coefficients in compliance matrix was made in order to generalize the influence of off-axis angle on the compliance coefficients. The theoretical prediction agreed well with the experimental data. It is shown that non-monotonic and symmetry phenomena can be observed in the curves of the coupling and compliance coefficients. The results of this experimental study provide a data base of the coupling coefficients of glass/epoxy laminates for engineering application. [ABSTRACT FROM AUTHOR]

A transient-dynamics model based on the approximate Riemann algorithm is proposed for the failure analysis of a frangible composite canister cover. The frangible cover, manufactured with a traditional manual lay-up method, is designed to conduct a simulated missile launch test using a specially developed test device. Deformation of the cover’s centre is determined using a transient-dynamics finite element model; failure pressure for the frangible cover is obtained based on a failure criterion and compared with simulated experimental results. Weak-zone position of the frangible cover has a significant effect on failure pressure compared to that of deformation of the cover’s centre. With the same structure of the weak-zone, an increase in its height can first raise and then reduce the level of failure pressure of the frangible cover. Close agreements between the experimental and numerical results are observed. [ABSTRACT FROM AUTHOR]

An experimental study was focused on investigation of the failure properties of plain woven glass/epoxy composites under off-axis and biaxial tension loading conditions. Four fibre orientations (0°, 15°, 30° and 45° with respect to the load direction) were considered for off-axis tests and two biaxial load ratios for biaxial tests to study failure characteristics and mechanism. Four classical polynomial failure criteria - Tsai-Hill, Hoffman, Tsai-Wu and Yeh-Stratton - were analysed comparatively to predict off-axis and biaxial failure strength of the composites. For failure prediction of the plain woven composites under multiaxial tension loads, the Tsai-Wu criterion was modified by introducing an interaction coefficient F 12 obtained from 45° off-axis or biaxial tension tests and the Yeh-Stratton criterion was modified with the interaction coefficient B 12 = 0 or obtained from the biaxial tension test. The former criterion was found to have higher accuracy. Finally, according to macroscopic and microscopic studies, the failed specimens showed mostly distinct failure with a specific fracture orientation, mainly exhibiting fibre or fabric tensile fracture mode and a combination of matrix cracking and delamination, both in off-axis and cruciform samples. [ABSTRACT FROM AUTHOR]

An experimental study on the effects of braided processes on the torsional strength, torsional modulus and failure modes of the three-dimensional braided composite tubes are presented. Based on the movement of carries, the yarn traces of three-dimensional braided composite tubes are analyzed systematically. Four different three-dimensional braided composite tubes are formed by resin transfer molding, and a number of torsional tests are performed respectively using a special test device. It is found that the torsional strength of three-dimensional five-directional braided composite tubes is higher than others, while the torsional modulus of three-dimensional multi-layer wrapping braided composite tubes is the highest. Furthermore, the damage behaviors of 3D braided composite tubes are significantly influenced by braiding process. One focus is to evaluate the damage mechanism of three-dimensional braided composite tubes by cutting the specimens and using scanning electron microscopy. Under torsional load, three-dimensional five-directional braided composite tubes and three-dimensional surface-core five-directional braided composite tubes are fractured in compression and shear failure, while three-dimensional multi-layer wrapping braided composite tubes and three-dimensional seven-directional braided composite tubes are split open in tensile and shear failure. [ABSTRACT FROM AUTHOR]

Mechanical properties of unidirectional (UD) and woven fabric glass/epoxy composites under off-axis tensile loading were experimentally investigated. A number of off-axis tests considering different fibre orientations were performed to study the character and failure mechanisms of the composite laminates. The experimental results indicated that both off-axis elastic moduli and strength degrade with increasing off-axis angle in all cases, and the woven fabric composites present nonlinear stress-strain behaviour under off-axial tension loading. The Tsai-Wu criteria used for failure analysis of the UD and woven fabric composites were compared and discussed, especially considering different values of interaction coefficient F 12 . The prediction results demonstrated that the Tsai-Wu criterion can be used successfully to analyse failure properties of the woven fabric composites under multiaxial stress conditions, where the criterion with the modified coefficient F 12 obtained from the 45° off-axial tension tests is better and has higher accuracy. Finally, the specific failure modes were compared in the UD and woven fabric composites. The selected fracture surfaces were also observed by scanning electron microscopy (SEM), and the corresponding failure mechanisms of the woven fabric composites under off-axis tensile loading were identified. [ABSTRACT FROM AUTHOR]

To enhance the interlaminar shear strength of carbon fiber/epoxy resin laminate, stainless steel particles were filled between laminas and uniformly arranged along the thickness direction by the outside magnetic field during manufacturing the composites. Specimens with five particle densities of 15 g/m2, 30 g/m2, 45 g/m2, 60 g/m2, and 75 g/m2 were prepared for testing. The interlaminar shear strength was obtained by short beam shear test and compared with the one of specimens without particles and with the randomly distributed particles between layers. Both modified equivalent stiffness predicting model and bridging model were established. A segmented prediction model was proposed by combining the two models. The error between results obtained by the proposed model and test was less than 10%. Results showed that the interlaminar shear strength of all specimens filled with particles was improved except for the one with particle density of 15 g/m2. The interlaminar shear strength of the specimens with randomly distributed particles between layers increased by 6.12%, 7.29%, 7.43%, and 6.01% for specimens with particle densities of 30 g/m2, 45 g/m2, 60 g/m2, and 75 g/m2. The interlaminar shear strength of the specimens with magnetically guided particles aligned along the thickness direction increased by 9.78%, 14.39%, 17.93%, and 20.39% for the four particle densities. This indicated that the interlaminar shear strength of the carbon fiber/epoxy laminate could be effectively enhanced by aligning the particles between laminas along the thickness direction using the outside magnetic field guidance during manufacturing the composites. • The interlayer toughened carbon fiber/epoxy laminates with magnetically guided steel particles are manufactured. • The enhancement of interlaminar shear strength (ILSS) of the interlayer toughened composites is studied experimentally. • Two models are established to predict the ILSS of the interlayer toughened composites. • The vertically arranged particles can effectively reduce the delamination and affect the ILSS to a greater extent. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study on the mechanical response of 3D integrated woven spacer carbon fiber composites under quasi-static indentation (QSI) and the failure behavior under compression after indentation (CAI). The test specimens are divided into weft direction ones (X-type) and warp direction ones (Y-type). The quasi-static indentation process is conducted using four types of indenters: the hemispherical indenter, the flat indenter, the conical indenter, and the pyramid indenter. A C-scan ultrasonic imaging system and a digital microscope are used to evaluate the damage visibility and penetration resistance of 3D integrated woven spacer composites during the QSI test. The digital image correlation (DIC) is used to perform the CAI analysis. The results indicate that the flat indenter has the largest indentation damage area (395 mm2 for X-type specimens, 398 mm2 for Y-type specimens), and the average indentation damage area caused by the four indenters is less than twice of the maximum cross-sectional area of each indenter. The maximum absorbed energy of two types of 3D integrated woven spacer composites is very similar in QSI tests under the same indenter. It is found that the residual strength of the X-type specimen decreases by 51.7% and that of the Y-type specimen decreases by 35.8% after the flat indenter penetrates the specimen. • The QSI response of the carbon fiber 3D integrated woven spacer composites is experimentally investigated. • The residual properties and failure mechanism of 3D integrated woven spacer composite under weft and warp compression are experimentally investigated. • The 3D integrated woven spacer composite exhibits good interlayer performance and a high level of damage tolerance. • X-type specimen has higher compression stiffness and residual compressive strength than the Y-type specimens. [ABSTRACT FROM AUTHOR]

• Low-velocity impact behavior of a new sandwich composite structure with negative Poisson's ratio lattice cores is studied. • A finite element analysis strategy is employed to investigate the mechanical response and energy absorption efficiency. • The sandwich structure with negative Poisson's ratio lattice cores can better disperse the concentrated impact load. • The impact location has certain influences on the energy absorption performance in different impact energy zones. In order to investigate the low-velocity impact performance of a new type of sandwich composite structure with negative Poisson's ratio lattice cores, low-velocity impact tests were carried out using the sandwich composite specimens, which were prepared by 3D printing lattice cores and glass/epoxy composite sheets. A finite element dynamic analysis strategy was also employed to investigate the mechanical response, the total energy absorption, and energy absorptivity of the sandwich panel at impact energies of 5 J, 10 J, 15 J, 20 J, 30 J and 40 J, respectively. Results show that the new sandwich structure can better disperse the concentrated impact load received by the upper sheet and dissipate most of the impact energy in the process of transferring the loads during cushioning. The negative Poisson's ratio lattice structure can guide damages, and it is found that the position of the impact point will affect the impact mechanical response and energy absorption ability of the sandwich panel. [ABSTRACT FROM AUTHOR]

Due to their superior overall properties, 3D integrated woven spacer composites overcome the weakness of traditional sandwich composites under low-velocity impact (LVI). The dynamic response of carbon fiber 3D integrated woven spacer composites under LVI and failure behavior under compression after impact (CAI) were experimentally investigated in this work. The impact damage patterns were analyzed using ultrasonic C-scan and micro-CT techniques at various energy, while digital image correlation (DIC) was used for CAI analysis. The results indicate that the impact damaged areas of X-type specimens is 365.1 mm2 under the impact energy of 7 J, while that of Y-type specimens is 371.4 mm2. The maximal absorbed energy is very close for two types of 3D integrated woven spacer composite specimens, which is about 6.99 J. The residual strength of X-type specimens decreases by 38.9% after the impact energy of 7 J, while that of Y-type specimens is reduced by 24.6%. The damage mechanism of the composites under LVI and CAI was obtained, which can provide some guidance for designing more suitable 3D integrated woven spacer composite structures in engineering practice. • The LVI response of the carbon fiber 3D integrated woven spacer composites is experimentally investigated. • The residual performances under the weft and warp direction compression are obtained and compared. • The 3D integrated woven spacer composite exhibits good interlayer performances and a high degree of damage tolerance. • X-type and Y-type specimens exhibit distinct buckling modes, residual strength and failure modes under compressive load. [ABSTRACT FROM AUTHOR]

The effect of through-thickness compression on in-plane tensile strength of glass/epoxy composites with random microstructure was investigated experimentally. The studied composite laminates were manufactured with a self-regulating Resin Transfer Moulding device. Their mechanical behaviour was assessed in pure in-plane tensile and through-thickness compressive tests, followed by biaxial tests combining both loading modes; indenters with a radius ranging from 5 to 25 mm were used to impose a compressive mode. The obtained results demonstrate a nonlinear decreasing trend for the in-plane tensile strength under the growing through-thickness compressive stress. All the failed specimens showed catastrophic brittle failure with a specific fracture orientation that mainly exhibited a tensile mode of fibre fracture for smaller radii of indenters and a combination of matrix crack, fibre fracture and typical shear failure for larger radii. [ABSTRACT FROM AUTHOR]

This study deals with numerical and experimental free vibration analysis of through-the-thickness cylindrical polymer pin-reinforced foam core sandwich composite panels of two different core thicknesses. Four different pin-reinforcement configurations with varying pin diameters and pin center distances were used. First five non-zero eigenfrequencies were retrieved along with their eigenmodes in the numerical analysis. Experimental modal analysis was done for the validation of the numerical analysis. The results revealed that the pin-configuration with the densest pin allocation and the biggest pin diameter provided the highest natural frequencies, and the non-reinforced composites had the lowest natural frequencies. The increase in the pin diameter had a slightly more pronounced effect on the increase of the eigenfrequencies than the increase in the pin's densities. This work also demonstrated the impact of the core thickness on the natural frequencies. [ABSTRACT FROM AUTHOR]

In structural analysis, the technique of mapping an irregular plate into a regular domain is commonly used. When the irregular plate does not have four corners, some important issues on the geometric mapping should be taken care of and are clearly pointed out herein for the first time. Besides, general shape functions of 12-node Serendipity finite element with nodes of any type are proposed to improve the accuracy of geometric mapping. [ABSTRACT FROM AUTHOR]

Thin triangular plate is one of the common structural members widely used in engineering structures. A weak form numerical method is presented for the static and free vibration analysis of thin arbitrary-shaped triangular plates under various boundary and internal supports. With the help of the sub-parametric technique, the triangular plate domain is first mapped into a regular one with bilinear shape functions and then the discretization is carried out in the regular domain. Gauss quadrature is used to avoid zero of Jacobian determinant at a plate corner. Explicit formulas are worked out for an arbitrary number of nodes. A number of numerical examples are studies. Comparisons show that the presented method is simple and highly accurate. Thus the method may also be used in the design stage for the optimization design of plate shapes as well as lamination sequences of laminated plates. • An accurate numerical method is presented for analysis of thin triangular plates. • Explicit formulas with an arbitrary number of nodes are presented. • Both boundary and internal supports are considered. • Static and vibration behavior of triangular plates with general shapes are studied. [ABSTRACT FROM AUTHOR]

An experimental and numerical study on mechanical properties and damage behavior of 3D multi-layer wrapping braided composite under axial tensile load is presented. The braiding process of this material is introduced and its tensile properties are obtained in tensile tests. Numerical simulations employ periodical boundary conditions, with interface elements between yarns and matrix added to improve the accuracy of prediction. 3D Hashin-type criteria and Von-Mises stress criterion are employed as damage initiation criteria for yarns and matrix, respectively. The obtained numerical results show a good agreement with the experimental data. The load-bearing capacity and failure mechanisms of 3D multi-layer wrapping braided composites under axial tensile loading are also discussed. A stress distribution shows that the axial yarns are the main load-bearing component of the composite. The main failure mode of the yarns is the yarn-matrix tensile cracking in the width direction, followed by the yarn-matrix tensile cracking in the thickness direction and fibre tensile failure. When the fibres in axial yarns begin to break, the material loses its load-bearing capacity. [ABSTRACT FROM AUTHOR]

Deicing composite laminates often undergo functional and structural fatigue during long-term electro-thermal deicing process, posing a potential threat to their safe service. The article conducted the internal thermal and compression fatigue tests studies on deicing composite laminates embedding sprayable metal circuit. The internal thermal fatigue test refers to the specimen being subjected to 1000 cycles of temperature from -55 °C to 80 °C and then back to -55 °C. The compression fatigue test refers to the specimen being subjected to 30,000 cyclic loads and 4 static compressive loads. The results indicate that the deterioration of the electro-thermal function of the specimen precedes the damage of the structure. After 1000 thermal cycles, the electrical resistance has been increased by 20.46%, and heating power has been reduced by 17.02%. The compression fatigue effect of low load has a relatively small impact on the increase of resistance value, but the resistance value cannot be restored to its initial state. The compressive residual strength of the specimen after 30,000 compression cycles is about 50 MPa. The fatigue life of the structure was lower than that of the electro-thermal function. [ABSTRACT FROM AUTHOR]

Due to the excellent mechanical properties and strong design flexibility, the 3D woven composite engine casing shows great potential in high performance fields. This article adopted the method of double-layer weaving and adding yarn to achieve the variable thickness of the 3D woven composite engine casing. The purpose of this article is to study the compression performance and failure mechanism of this variable thickness casing in different thickness zones through experiments and numerical simulations to lay a foundation for future optimization and inclusiveness research on this casing with complex thickness changes. Three types of representative volume cells are established for progressive damage analysis. 3D-Hashin criteria and von-Mises stress criterion are used as damage criteria for yarns and matrix. The progressive damage process and the proportion of damage in the inner and outer layers of three types of 3D woven tubes under axial compression load are analyzed. Results show that the main failure modes of the three types of tubes are yarn-matrix compressive cracking along direction 3 and matrix failure. The damages are mostly concentrated in the warp bending area. The proportions of warp yarn damage in the inner and outer layers of three tubes are different. [ABSTRACT FROM AUTHOR]

Sandwich structures with an asymmetric configuration are employed to introduce in-plane loads as well as to connect them with other structural components. Understanding their failure mechanism is crucial to ensure the safety design of aircraft. This paper investigates experimentally and numerically the mechanical behavior of asymmetric sandwich panels (ASPs) under compression. Quasi-static tests are conducted to obtain the buckling loads, post-buckling behavior, and load-bearing capacity of ASPs. A non-linear finite element (FE) model is developed to elucidate their damage behavior and failure mechanism. Numerical predictions are compared with test results to validate the FE model and failure analysis. The results demonstrate that the presence of a tapered region significantly influences stress distribution and failure initiations. A parametric study is also conducted to investigate the effects of the tapered angle on the compression response of ASPs. The reported results can provide a reference for the optimal design of ASPs. [ABSTRACT FROM AUTHOR]

This study is conducted on glass fiber-reinforced composite honeycomb sandwich structures by introducing delamination damage through low-velocity impact tests, establishing a three-dimensional progressive damage analysis model, and evaluating the delamination damage characteristics and laws of honeycomb sandwich structures under different impact energies through experiments. Repair techniques and process parameters for delamination damage are explored. It is found that as the impact energy increases, the damage area of honeycomb sandwich panels also increases, and the delamination damage extends from the impact center to the surrounding areas, accompanied by damage such as fiber fracture and matrix cracking. The strength recovery rates of sandwich panels at impact energies of 5 J, 15 J, and 25 J after repair are 71.90%, 65.89%, and 67.10%, respectively, which has a considerable repair effect. In addition, a progressive damage model for low-velocity impact on the composite honeycomb sandwich structure is established, and its accuracy and reliability are verified. [ABSTRACT FROM AUTHOR]

To improve the simulation accuracy and evaluate the potential failure regions, this study proposes two finite element model correction methods based on surface manufacturing error: the direct numerical correction method and the deformation coordination correction method. Their methods aim to accurately describe the profile state of the composite antenna panel. The initial finite element model of prototype panel (Model IN) is respectively corrected by the direct numerical correction method (Model DN) and the deformation coordination correction method (Model DC). The prototype panel is then subjected to temperature difference testing. A comparison between the simulations and the test results reveals that Model DN and Model DC can predict the surface error distribution (SED) that Model IN lacks. The simulation results from Model DN and Model DC are overall consistent with the actual measurements obtained from the prototype panel tests. The average deviation of the simulated surface accuracy root mean square (rms) by Model DC from the test rms is only 1.66%, whereas that by Model DN is 19.44%. This demonstrates that the deformation coordination correction method effectively maintains simulation reliability in predicting antenna panel surface accuracy. Consequently, finite element model corrected by this method can provide valuable data support for evaluating the influence of potential failure regions and mitigating the impact on antenna surface accuracy. [ABSTRACT FROM AUTHOR]

In this paper, a new multi-part composite frangible cover (MCFC) was designed and fabricated. The frangible cover, manufactured with a traditional manual lay-up method, is designed to conduct a simulated missile launch test using a specially developed test device. A weak zone structure of the composite multi-part frangible cover was designed, and the separation process of the cover was studied by numerical simulation. Based on the strength envelope of the weak zone and the equal-strength design principle, a design method for the weak zone structure of the composite multi-part frangible cover was proposed. A finite element model of the composite multi-part frangible cover was established, and the separation process was numerically simulated and analyzed. Afterward, the verification experiments were carried out. Close agreements between the numerical and experimental results are observed. [ABSTRACT FROM AUTHOR]

Impact locations play a critical role in determining the residual performance of the composite stiffened panel, since the local damage behavior at different locations is not identical. The objective of this paper is to systematically investigate the influence of impact locations on damage behavior, stability and residual compression strength of T-shaped stiffened CFRP panels. Low-velocity impact tests are carried out by impacting at the skin center or the flange tip. The damage patterns and post-buckling behavior are monitored by ultrasonic C-scan and digital image correlation. An effective computational framework with explicit formulations considering complicated damage mechanisms is proposed to investigate the details of damage behavior. The skin center impact causes severe fiber breakage and matrix squeezing, while the flange tip impact induces complex damage patterns including ply splitting, fiber breakage, matrix cracks, as well as extensive skin–rib interfacial delamination. Compression after impact results indicate that impact damage at the skin center has little effect on the residual performance of the structure, and the compression failure load is only reduced by 2.02%, from 276.8 kN to 271.2 kN. However, impact damage at the flange tip weakens the supporting effect of the stiffener, leading to early buckling of the local skin. The propagation of the interfacial delamination at the damaged flange tip directly triggers the premature compression failure, resulting in an 18.79% decrease in the failure load, 224.8 kN. Numerical predictions correlate well with experimental data. The reported results may be useful in structural design and maintenance. • The effect of impact locations on compression after impact (CAI) performance of the composite T-shaped stiffened panel is experimentally and numerically investigated. • The damage mechanism and stability of specimens are obtained and compared using ultrasonic C-scan, DIC, and numerical prediction. • The impact damage at the flange tip weakens the supporting effect of the stiffener and causes early buckling of the local skin. • The propagation of the interfacial delamination at the impacted flange tip directly triggers premature compression failure. [ABSTRACT FROM AUTHOR]

In this paper, a new kind composite, called the magnetically guided stainless steel particle toughened composite, is manufactured and its I/II fracture toughness is then experimentally investigated. The stainless steel particles can be arranged either vertically under the outside magnetic guidance during manufacturing process or randomly. Comparisons with the one without stainless steel particles, the G I C and G I I C can increase by 81.88% and 87.72%. Numerical simulations are also carried out. A theoretical prediction model is proposed for the interface parameters of mode I fracture toughness and verified by comparing simulation results with experimental ones. The trial-and-error inversion method is used to effectively simulate the mode II fracture toughness. Different interlaminar interface parameters are tried to determine the interface parameters which can yield mode II fracture toughness closest to the experimental one. A relational equation is fitted using the particle volume content and interlaminar interface parameters. Additional experiment and simulation for specimen with a different particle density are performed to demonstrate the accuracy of interface parameters obtained by the trial-and-error inversion method. • A new magnetically guided stainless steel particle toughened composite is manufactured and experimentally investigated. • The G I C and G I I C of the magnetically guided particle toughened carbon/epoxy composites can increase by 81.88% and 87.72%. • A theoretical prediction model is proposed and verified for the interface parameters of mode I fracture toughness. • Different interlaminar interface parameters are tried to determine the interface parameters of mode II fracture toughness. [ABSTRACT FROM AUTHOR]

• High-cycle random vibration fatigue performance of CFRP thin plates was studied. • Proposing entire high-cycle vibration fatigue experimental process and method. • The fatigue failure mechanisms is only partially similar to traditional fatigue tests. • Established and validated random vibration fatigue S-N curves. • FEM and experiment investigated the mechanisms of fatigue failure under vibration. This study presents an in-depth investigation into the fatigue performance of carbon fiber-reinforced polymer (CFRP) thin plate subjected to high-cycle random vibration loading. The cantilever beam method is employed to simulate vibration loads encountered in engineering applications. The experimental processes include exploratory experiment, pre-experiment, and formal experiment to ensure the accuracy and reliability of the test results. Findings indicate that the conventional S-N curve models are not well-suited for directly predicting fatigue in composite materials under random vibrational loading. In the case of narrow-band distribution, the Rayleigh distribution exhibits superior predictive accuracy compared to the Dirlik model. Moreover, scanning electron microscopy (SEM) was employed for a comprehensive morphological analysis of surface and lateral damage zones within the specimens. The investigation unveils that lower strain levels lead to minor fiber or interface movements and adjustments on the specimen surface, while higher strain levels result in visible surface cracks and interface delamination. Matrix cracking and delamination are also observed along the lateral sides of the specimens. The damage analysis provides insights into the progression of damage and failure mechanisms at varying strain levels. [ABSTRACT FROM AUTHOR]

• Effect of thermal cycling on the mechanical properties of carbon fiber/epoxy laminated composites was investigated. • The residual tensile and in-plane shear moduli decrease rapidly during the initial thermal cycles. • The reduction ratio of the residual in-plane shear modulus is larger than that of the residual tensile modulus. • Different fiber materials affect the residual tensile and in-plane shear moduli of the laminates exposed to thermal cycling. Carbon fiber reinforced polymer (CFRP) composites are commonly used for reflectors of artificial satellites operating in low earth orbit (LEO). The decay of the modulus of the CFRP composite varies under different thermal cycling environments, which can lead to a reduction in the accuracy of the reflector panels, affecting the transmission of signals. This paper investigates the impact of different thermal cycling conditions on the mechanical behavior of carbon fiber/epoxy laminated composites experimentally. Three kinds of thermal cycling conditions involving continuous temperature changes are employed to explore the influence of temperature range on the residual tensile and in-plane shear moduli of the laminates. Test results indicate that the upper temperature limit and the temperature span of the thermal cycling conditions jointly affect the mechanical properties of CFRP composite laminates, but the responses of the residual tensile and in-plane shear moduli are different under the variation of each temperature parameter alone. The residual tensile and in-plane shear moduli of the laminates under thermal cycling decrease with an expansion of the temperature span having the same upper limit. If the temperature span remains constant, an increase in the upper temperature limit leads to an increase in the residual tensile modulus, but a decrease in the residual in-plane shear modulus. The main damages causing the decay of residual tensile and in-plane shear moduli of unidirectional laminates were investigated by scanning electron microscopy (SEM) technology. Observations of the microscopic fracture of the material show that the post-curing reaction factor predominantly influences the residual tensile modulus of unidirectional laminates, while the fiber/matrix interface damage factor dominates the residual in-plane shear modulus of the unidirectional laminates. Furthermore, an increase in the fiber tensile modulus decreases both residual tensile and residual in-plane shear moduli. Notably, the residual in-plane shear modulus exhibits greater sensitivity to thermal cycling compared to the residual tensile modulus. The findings reported in this paper would provide valuable insights and guidance for the design and application of carbon fiber/epoxy composites subjected to thermal cycling conditions. [ABSTRACT FROM AUTHOR]

We propose a modified Laurent series for investigating the elastic field around holes/inclusions under plane deformation by dividing the classical Laurent series over the first derivative of the conformal mapping, which is justified from a mathematical point of view. Through a group of numerical examples concerning the stress concentration around holes of common shapes, the accuracy of the modified Laurent series is verified. It is also demonstrated that the use of the modified Laurent series as compared with the classical one generally leads to significantly more accurate results with even much fewer terms of the series. Utilizing the modified Laurent series, we revisit the stress field around an irregularly shaped elastic inclusion embedded in an infinite matrix and effectively eliminate the severe interfacial stress fluctuation reported earlier in the literature. More importantly, the modified Laurent series may be very useful for a highly accurate prediction of the physical field in particulate composites with densely packed inclusions. [ABSTRACT FROM AUTHOR]

• Strain rate effects on the tensile and shear strength of carbon fibre composites were investigated. • The strain rate effect of the composite material was considered in VUMAT for simulations. • High-velocity impact responses with different impact velocities and angles were tested and simulated. • Failure behaviours and energy absorption mechanisms were analysed and discussed. In this paper, the tensile and in-plane shear behaviors of carbon fiber reinforced laminated composites (CFRLCs) under high strain rate loading were experimentally investigated. The strain and damage processes of the specimens were obtained using the Digital Image Correlation (DIC) method and a high-velocity camera. Quasi-static test results were used as the control group for obtaining the dynamic correction factors of the material system under high strain rate conditions. In addition, high-velocity impact (HVI) tests with different impact velocities and angles were conducted on CFRLCs. The dynamic correction factors were used in HVI simulations to consider the effect of strain rate. The energy absorption mechanisms and failure modes of laminates under different impact conditions were analyzed using testing and simulated results. It is found that during the HVI, matrix tension and fiber tension failures are the main failure modes. The energy absorbed by the laminate in oblique impact is larger than the one in normal impact. The possible reason is that the increase rate of the damage area with the four failure modes in oblique impact is larger than the one in normal impact. [ABSTRACT FROM AUTHOR]

• The impact resistance and damage tolerance of carbon fiber composite laminates were experimentally investigated. • In the process of high-velocity impact, the main failure modes are fiber shear and tension failure. • Compression after impact (CAI) were performed on laminates with different impacted positions. • The CAI damage of laminates impacted at the central position is main delamination buckling. In this paper, the impact resistance of carbon fiber/resin composite laminates with a thickness of 2.5 mm at different impact velocities, angles and positions was investigated experimentally. In the process of high-velocity impact, fiber shear failure and tension failure are the main failure modes. When the impact velocity is 300 m/s, the fiber tension failure and matrix compression failure under oblique impact are more than that under normal impact, and the energy absorption of laminates is also lager than that under normal impact. The ballistic limits, energy absorption and delamination area of the center and edge impact of laminate are similar. In addition, the CAI tests are conducted to study the influence of different positions on the residual compressive strength of laminates after high-velocity impact, and the fracture loads and failure modes of two impact positions are quite different. The failure modes of the center impact laminate are main buckling failure, and the failure modes of the edge impact laminate are compression failure near the bullet hole side of the fixture and buckling failure near the center of the laminate. The research results can provide a reference for the residual strength of laminates after impact at different locations in practical situations. [ABSTRACT FROM AUTHOR]

• A localized impact framework for full-scaled composite sandwich panel is developed and validated with test data. • The nonlinear shear response of CFRP woven fabric for simulation usage is calibrated by original cyclic shear test data to guarantee computational accuracy. • The damage and energy absorption mechanisms of different impact energy levels are comprehensively analyzed. • The effects of core height, facesheet stacking sequence and impact angle are explored regarding impact scenarios with perforation damage. Composite sandwich structure with large in-plane dimension is frequently used in high-performance fields. However, the behavior of such structure subjected to low-velocity impact possesses a localized damage characteristic. The objective of this paper is to systematically investigate the influence of impact energy and structural parameters on the damage behavior and failure mechanism of full-scaled composite sandwich panels under localized impact. Tests are carried out by impacting at the middle of the specimens with various energies. A finite element model with localized impact framework, considering complicated damage mechanisms, is developed to predict the impact responses, failure patterns, and energy absorption. The validation of the framework is achieved by comparing numerical results with experimental data. Moreover, a comprehensive parametric analysis is conducted with focus placed on the impact energy, foam-core height, stacking sequences of the laminated facesheets, and angle of impact trajectory. The results indicate that localized structural damage behavior varies with impact energy, foam-core height and impact angle, while stacking sequences of facesheet have little effect on the impact resistance of the sandwich panel. The foam core dominates the energy absorption especially in the case with perforation damage. The reported results may be useful in safety design and maintenance. [ABSTRACT FROM AUTHOR]

• The deicing composite curved beam specimens were prepared and tested at two different temperature environments by means of a four-point bending. • In the experiments, the delamination properties of specimens were compared and analyzed. • A three-dimensional finite element model was created and analyzed with cohesive elements at the interfaces of adjacent plies. • Simulation results matched the experimental results well, and the model can predict delamination positions. • Internal heating has a significant effect on the failure behavior of deicing composite curved beams. The deicing composite curved beams can easily experience delamination under internal heating, but fewer studies have been found so far. In this study, the effect of internal heating on the delamination properties of deicing composite curved beams under four-point bending was investigated experimentally and numerically. The composite curved beam specimens were prepared according to the ASTM D6415 standard. A heating circuit in a heating layer was designed to generate heat and tested in compliance with the standard. A three-dimensional (3D) finite element (FE) model was established with cohesive elements for the interfaces of adjacent plies. In the experiments, the load–displacement curves, strain-load curves, and delamination properties of the curved beam specimens in two environments were compared and analyzed. The numerical results agreed well with the experimental data, and the FE model can predict the delamination precisely. The average curved beam failure load of internal heating was about 36% lower than the ones of other environments, and the internal heating can cause the position of delamination to change significantly. [ABSTRACT FROM AUTHOR]

In this paper, a new stitch-plain weave fabric composite (SPWF) by acupuncture technology is proposed. Two patterns are designed, one is a typical chessboard layout (SPWF-1), and the other is a layout optimized by a genetic algorithm (SPWF-2). Simulated and experimental results show that SPWF can disperse electromagnetic wave energy in all directions and effectively reduce the radar cross-section (RCS) in the frequency range of 12.5 GHz−26.5 GHz, and the maximum RCS reduction for SPWF reaches −40 dB. The tensile modulus and strength of SPWF-1 are predicted by finite element method, and the results are in good agreement with the experimental data. In addition, a new optimization objective function is proposed to design the patterns of SPWF-2. [ABSTRACT FROM AUTHOR]

A progressive damage model is proposed to predict buckling strengths and failure mechanisms for both symmetric and asymmetric patch repaired carbon-fibre reinforced laminates subjected to compression without lateral restrains. Solid and cohesive elements are employed to discretize composite and adhesive layers, respectively. Coupling with three dimensional strain failure criteria, an energy-based crack band model is applied to address the softening behaviour in composites with mesh dependency elimination. Both laminar and laminate scaled failure are addressed. Patch debonding is simulated by the cohesive zone model with a trapezoidal traction–separation law applied for the ductile adhesive. Geometric imperfection is introduced into the nonlinear analysis by the first-order linear buckling configuration. Regarding strengths and failure patterns, the simulation demonstrates an accurate and consistent prediction compared with experimental observations. Though shearing is the main contributor to damage initiation in adhesive, stress analysis shows that lateral deformation subsequently reverses the distribution of normal stresses which stimulates patch debonding at one of the repair sides. The influence of patch dimensions on strengths and failure mechanisms can be explained by stress distributions in adhesive and lateral deformation of repairs. Comparison between symmetric and asymmetric regarding strength and failure modes shows that structural asymmetry can intensify lateral flexibility. This resulted in earlier patch debonding and negative effects on strengths. [ABSTRACT FROM AUTHOR]

In this paper, a plain-woven metamaterial consisting of a ribbon-like blend of carbon fiber-glass fiber strips is proposed. The structure of the proposed hybrid material has a broadband filtering function of electromagnetic wave, can form beam reconstruction and selective wave transmission, and reduce radar scattering cross section (RCS) in the 9 GHz - 25 GHz frequency band. The macroscopic equivalent mechanical parameters are estimated by constructing the micro fine structure model and combining the periodic boundary conditions. The Hasin failure criterion is used to predict the progressive damage evolution of the proposed hybrid material under tensile loading. In addition, the plain-woven metamaterial has the advantages of simple structure and easy fabrication, which provides a new design idea for the metamaterial radome and important engineering guidance for its fabrication process. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) plain fabric is prone to delamination when subjected to bending, shear, impact loads. To enhance the interlayer properties of 2D plain fabrics, standing up loops is added. In this paper, specimens of the double-sided-loop 2D woven laminated composites (DWLC) and general 2D woven laminated composites (GWLC) are made for double cantilever beam (DCB) tests and end-notch flexure (ENF) tests to study their toughening mechanism. Test results show that the values of model I and mode II interlaminar fracture toughness are increased by 870% and 250% for the DWLC compared with the GWLC. Based on the three-linear cohesive zone model (CZM), finite element (FE) models of composite laminates specimens of DCB and ENF considering the phenomenon of interlaminar bridging are established, and numerical results are in good agreement with the experimental data, that verifies the accuracy of the FE models. Using the verified FE models, model I and mode II fracture properties of the DWLC specimens of DCB and ENF with different initial crack lengths are investigated, and the results show that the stress is redistributed and the load gradually decreases as the length of the prefabricated cracks increases. The obtained fracture toughness of the DWLC provides a reference for the toughening methods and the engineering applications of DWLC. [ABSTRACT FROM AUTHOR]

The electrothermal deicing composites usually experience flexural deformations, but fewer studies have been done on their flexural properties. In this study, specimens were manufactured by using the autoclave curing and spray metal multi-layer deposition technology. Three-point bending tests were conducted. A progressive damage model using user-defined material subroutine and cohesive elements was proposed to understand the damage evolution. A steady-state heat transfer model was established to obtain the temperature field. It is shown that the damage distributions obtained from the numerical modeling correlate well with experimental observations. • The L-shape shape, heating circuit and laying data of the specimens were designed. • The specimens were made using the autoclave curing and spray metal technology. • A progressive damage model using UMAT subroutine and cohesive elements was raised. • The load–displacement curves, the damage prediction and evolution were obtained. • The finite element model can predict the damage process. [ABSTRACT FROM AUTHOR]