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In this study, the tensile and flexural properties of skin-core-skin woven glass fiber/epoxy laminated composites were conducted. Six plies (laminae) for the skins and twenty-four plies for the core were hand-laid up. All plies used had the same dimensions and the same elastic strength where the skins’ plies kept in flatwise direction while the core’s plies oriented in edgewise and flatwise to study the effect of plies alignments and hence loading direction i.e., edgewise (in-plane) and flatwise (out-of-plane) on the materials characteristics. It was observed that the composites oriented in edgewise position had the highest strength of 186 MPa (enhancement 59%) and deformed at higher loads with minor displacements compared to the flatwise strength of 117 MPa. The SEM analysis of the tensile’s fracture surface showed two dominant toughening mechanisms are debonding (fiber pullout) and fiber breakage, while interlaminar/intralaminar delaminated yarns was observed in the flexural fracture surface.

The dynamic mechanical behaviors of the [ 0 2 ° / 90 2 ° ] 4 s fiber-reinforced composite laminates subjected to double-position low-velocity impacts are investigated by finite element method. Two impact positions symmetrical about the center of the laminates are impacted sequentially with three impact distances (10 mm, 20 mm, and 40 mm) under three impact energies (5 J, 10 J, and 20 J) to study the interference effect of impact damage. For comparison, plastic damage model (PDM) and elastic damage model (EDM) are established to describe the intra-laminar constitutive, respectively. Compared with available experimental data, the mechanical responses calculated by PDM are more accurate, especially at high energies. Affected by the impact interference, the oscillation of force-time curve for the second impact rather than the first impact is relatively weaker, while the severity of impact damage is reversed. The results show that the maximum displacement is more suitable for characterizing the degree of damage interference than bending stiffness, peak force, and energy dissipation. [ABSTRACT FROM AUTHOR]

Auxetic laminates are part of a fascinating branch of materials denominated as auxetics, which display a NPR (Negative Poisson's Ratio), an uncommon property in the engineering world. Auxeticity is at the root of enhancements in shear and indentation resistance, fracture toughness and energy absorption, making the design of NPR a desirable feat in structural engineering. In composite laminates made of conventional, i.e. positive Poissons ratio, materials, auxeticity is a result of the combination between particular angular configurations and anisotropic materials. Such laminates can be used in a wide array of engineering applications, especially those which require high energy absorption capacity, including aerospace, personal defense and sports industries. This review focuses on particular property enhancements reported in the scientific world brought about by the design and application of IP (In-plane) and TTT (Through-the-thickness) NPR fibre-reinforced polymer laminates under QSI (Quasi-static indentation), LVI (Low-velocity impact) and fatigue solicitations. Furthermore, some insight is given on some possible future paths for further investigation of this topic. [ABSTRACT FROM AUTHOR]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Experimental methodologies for fatigue lifetime prediction are time-intensive and susceptible to environmental variables. Although the cohesive zone model is popular for predicting adhesive fatigue lifetime, entropy-based methods have also displayed potential. This study aims to (1) provide an understanding of the durability characteristics of carbon fiber-reinforced plastic (CFRP) adhesive joints by incorporating an entropy damage model within the context of the finite element method and (2) examine the effects of different adhesive layer thicknesses on single-lap shear models. As the thickness of the adhesive layer increases, damage variables initially increase and then decrease. These peak at 0.3 mm. This observation provides a crucial understanding of the stress behavior at the resin–CFRP interface and the fatigue mechanisms of the resin. [ABSTRACT FROM AUTHOR]

In this paper, the free-edge effects which play an important role in the failure analysis of composite laminates are studied. Pure temperature change and its combination with biaxial tension are investigated for a composite plate with a centric circular hole that is adequately small in comparison to the dimension of the plate. Moreover, the laminate is assumed to be thin, the temperature change of all points of the plate is identical and the biaxial tensile load is applied far from the center of the hole. For this purpose, a semi-analytical method based on a two-dimensional thermoelastic boundary layer theory and a minimum potential energy principle is proposed. It is shown that the present method predicts the interlaminar peeling and shear stresses surrounding the hole with good agreement compared to the results obtained by FEM analysis. [ABSTRACT FROM AUTHOR]

The effect of low-velocity impact loading and seawater aging on the residual bending properties of glass fiber reinforced polymers (GFRPs) was evaluated. The self-sensing capability of the composite laminates provided by a hybrid combination of multiwall carbon nanotubes (MWCNTs) and graphene nanoplatelets (GNPs) was also examined. The composite laminates were fabricated by RTM with the incorporation of different contents of MWCNTs and GNPs onto the glass fiber surface using the spray coating technique. Impact tests were performed on specimens with and without seawater (SW) aging and then bending specimens were taken to evaluate the after-impact bending behavior. An important reduction in mechanical properties of composite laminates produced by SW aging, caused by plasticization and swelling effects of the polymer matrix, was confirmed. Despite this physical degradation in the mechanical behavior of GFRP composites, a positive synergistic effect of the carbon nanostructures (CNSs) in the composite laminates was observed. Carbon nanofillers cause the maximum force during the impact test increase in comparison with neat specimens; this effect was exhibited by both samples, with and without seawater aging. Previous impact damage reduced flexural strength and flexural modulus of dry (14% and 43%, respectively) and wet samples (15% and 26%, respectively); however, the reduction in flexural strength is slightly smaller in a certain hybrid combination of CNSs. Another important finding was that the self-sensing capability of GFRPs with CNSs was preserved, even after the impact loading and even after the seawater aging, making this technique suitable for structural health monitoring of marine components. [ABSTRACT FROM AUTHOR]

Background: Interlaminar delamination is a common damage mechanism in composite laminates that can lead to structural failure. Assessment using contemporary numerical modeling techniques requires delamination behavior as a traction–separation response. However, existing experimental characterization approaches are not well suited to support these modeling techniques as specimens were developed to assess single delamination parameters, not a full traction–separation response, or utilize analysis schemes that require knowledge of material properties. Objective: To develop a test specimen and data analysis methodology to directly measure the traction–separation response of Mode I delamination in a laminated fiber-reinforced polymer (FRP) composite, including strength, toughness, and damage response. Methods: The proposed composite Rigid Double Cantilever Beam (cRDCB) specimen is comprised of a [0]_4 unidirectional E-glass/epoxy laminate co-cured to rigid metallic adherends. Traction–separation response was assessed directly from measured force and displacement behavior using a closed-form analysis scheme that does not require a priori knowledge of composite material properties. Standard double cantilever beam (DCB) tests were performed for comparison. Results: The cRDCB specimen captured early damage initiation and progression in greater detail than the DCB, with measured strain energy release rates agreeing well between the two approaches. The cRDCB also captured the effects of large-scale damage mechanisms such as fiber bridging. The measured traction–separation responses are suitable for scenarios where prediction of the initiation and early damage response of delamination is important. Conclusions: Combined with a data processing technique, a single cRDCB test enabled measurement of the full Mode I traction–separation response. In addition, the cRDCB provided high-resolution and could detect early-stage Mode I delamination damage in FRP laminates. The measured traction–separation responses can be directly inputted into cohesive zone models to predict the initiation and progression of Mode I delamination. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Materials Engineering / Cailiao Gongcheng is the property of Journal of Materials Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this study, the effect of fiber angle on the tensile load-bearing performance and damage failure characteristics of glass composite laminates was investigated experimentally, analytically, and numerically. The glass fabric in the laminate was perfectly aligned along the load direction (i.e., at 0°), offset at angles of 30° and 45°, or mixed in different directions (i.e., 0°/30° or 0°/45°). The composite laminates were fabricated using vacuum-assisted resin molding. The influence of fiber orientation angle on the mechanical properties and stiffness degradation of the laminates was studied via cyclic tensile strength tests. Furthermore, simulations have been conducted using finite element analysis and analytical approaches to evaluate the influence of fiber orientation on the mechanical performance of glass laminates. Experimental testing revealed that, although the composite laminates laid along the 0° direction exhibited the highest stiffness and strength, their structural performance deteriorated rapidly. We also determined that increasing the fiber offset angle (i.e., 30°) could optimize the mechanical properties and damage failure characteristics of glass laminates. The results of the numerical and analytical approaches demonstrated their ability to capture the mechanical behavior and damage failure modes of composite laminates with different fiber orientations, which may be used to prevent the catastrophic failures that occur in composite laminates. [ABSTRACT FROM AUTHOR]

This paper aims at numerical finite element (FEM) research of guided Lamb waves propagation in multidirectional composite plates. All simulations were conducted in the Abaqus/CAE software by using the dynamic/explicit solver. The material considered in this work was carbon/epoxy composite laminate with [90⁰/θ/θ/θ/-θ/-θ/-θ/90⁰] stacking sequence where θ set was equal 0⁰, 30⁰, 45⁰, 60⁰ and 90⁰. The main goal of the analysis was to evaluate the influence of fiber orientation angles θ on propagation behavior of the separate symmetric S0 and asymmetric A0 Lamb wave modes. Numerical model was created by using the C3D8R brick element. The Lamb waves were generated by using concentrated force with 200 kHz frequency. The acoustic signal generated by travelling wave was registered at two nodes that representthe acoustic emission sensors. Obtained results were presented in tabular form where separate mode velocities were collected and on the normalized displacement versus time plots depicted registered wave signals. In addition, the contour diagrams and through-thickness deformations plots were created to present behavior of the extensional and the flexural modes. The greatest value of the S0 mode velocity was obtained for unidirectional laminates whereas the lowest for composite plate with 45⁰ fiber orientation angle. The asymmetric mode found to generate slightly greater deformation of plate in XZ plane than the symmetric. Recognition of the Lamb wave behavior in multidirectional laminates will allow to better planning the experimental acoustic emission tests. [ABSTRACT FROM AUTHOR]

Achieving methods to improve the failure behavior of composite multilayer plates has always been of interest to researchers. In this article, in order to delay the collapse of composite multilayers in a brittle and sudden manner, a layer of elastomeric foam is inserted between glass-vinyl ester composite plates and the change of the failure pattern and ultimate strength of sandwiched plates with different layering of fibers, compared to single composite plates, is observed. In the examined layers, firstly, the failure pattern was observed in different types of multilayers with different layering including a stronger alignment, orthogonal layering and woven layers under concentrated loading, and the effect of interlayer foam in changing the pattern of rupture hinges in the plates and parameters of bearing capacity and the amount of absorbed energy was observed. Then, a layer of elastomeric foam was placed between the composite plates, which was able to absorb significant energy in the panels before the final collapse by distributing the stress from the upper plate to the lower plate, and delayed the moment of complete rupture. The results showed that the use of interlayer elastomeric foams causes a change in the formation pattern of rupture hinges in the composite panel and significant softening before the final collapse. This increases energy absorption, especially in the case of panels with lower bending stiffness, up to about 115%, which is a satisfactory result.The objective for application of an elastomeric foam was omission of disadvantage by inflexible crushable foams. Although, the elastomeric foam supplied aa lower flexural modulus for the sandwich composite panels due to its lower shear rigidity, it could distribute stress concentration areas from the top to the bottom composite panels, to create a considerable fuselage to reach the ultimate strength via absorption of considerable energy. The results showed promising performance for failure response of elastomeric foam cored sandwich panels. Application of the interlayer elastomeric foam in the case of composite panels with lower stiffness showed larger enhancing effect.

ObjectivesThe addition of thermoplastic phase materials between the layers of traditional marine composite laminates can effectively improve the impact resistance properties of marine composites. This study carries out experiments to explore the impact damage characteristics of such materials. MethodsThe thermoplastic/thermoset interface of laminates is observed with an optical microscope, and the bonding mode of the two-phase materials is analyzed. Composite laminates with different structures are impacted at low velocity with three different energies. The damage morphology of each specimen is observed via ultrasonic C-scan and electron microscopy to obtain the impact response and damage mechanism of each specimen. ResultsThe results show that marine composite laminates embedded with PEI film have better damage resistance than carbon fiber laminates. Under 8 J and 12 J of impact energy , the delamination damage is reduced by 19% and 39% respectively, and they showed better integrity after 12 J impact. ConclusionsEmbedding PEI thermoplastic film inside laminates can improve their toughness and significantly reduce internal delamination damage. Compared with carbon fiber laminates and double-sided coated laminates, PEI thermoplastic film can significantly improve the impact resistance of internal film embedded laminates.

ObjectivesIn order to investigate the influence of joints in composite laminate plates on the vibration transfer characteristics of structures, this study uses power flow based on the finite element method (FEM) and a related visualization technique.MethodsFirst, a method that describes plate vibration by power flow in solid elements is proven to be feasible, then power flow transmission efficiency is introduced and a method of calculating it in a finite element model is proposed and verified by the admittance power flow method. Finally, two joint simulations of embedded joints and screw joints are obtained, as well as the power flow transmission efficiency curve and typical power flow vector diagram.ResultsThe results show significant differences in vibration transmission and power flow transmission efficiency between the two models. ConclusionsPower flow based on FEM can directly reflect the vibration energy transmission path of a connected structure, which can provide useful references for the design of composite structures.

The time difference of arrival (TDOA) method has traditionally proven effective for locating acoustic emission (AE) sources and detecting structural defects. Nevertheless, its applicability is constrained when applied to anisotropic materials, particularly in the context of fiber-reinforced composite structures. In response, this paper introduces a novel COmposite LOcalization using Response Surface (COLORS) algorithm based on a two-step approach for precise AE source localization suitable for laminated composite structures. Leveraging a response surface developed from critical parameters, including AE velocity profiles, attenuation rates, distances, and orientations, the proposed method offers precise AE source predictions. The incorporation of updated velocity data into the algorithm yields superior localization accuracy compared to the conventional TDOA approach relying on the theoretical AE propagation velocity. The mean absolute error (MAE) for COLORS and TDOA were found to be 6.97 mm and 8.69 mm, respectively. Similarly, the root mean square error (RMSE) for COLORS and TODA methods were found to be 9.24 mm and 12.06 mm, respectively, indicating better performance of the COLORS algorithm in the context of source location accuracy. The finding underscores the significance of AE signal attenuation in minimizing AE wave velocity discrepancies and enhancing AE localization precision. The outcome of this investigation represents a substantial advancement in AE localization within laminated composite structures, holding potential implications for improved damage detection and structural health monitoring of composite structures.

In this paper, an enhanced VARTM process is proposed and its pressure effect on resin infusion behavior and composite material performance is studied to reveal the control mechanism of the fiber volume fraction and void content. The molding is vacuumized during the resin injection stage while it is pressurized during the mold filling and curing stages via a VARTM pressure control system designed in this paper. Theoretical calculations and simulation methods are used to reveal the resin’s in-plane, transverse, and three-dimensional flow patterns in multi-layer media. For typical thin-walled components, the infiltration behavior of resin in isotropic porous media is studied, elucidating the control mechanisms of fiber volume fraction and void content. The experiments demonstrate that the enhanced VARTM process significantly improves mold filling efficiency and composite’s performance. Compared to the regular VARTM process, the panel thickness is reduced by 4% from 1.7 mm, the average tensile strength is increased by 7.3% to 760 MPa, the average flexural strength remains at approximately 720 MPa, porosity is decreased from 1.5% to below 1%, and the fiber volume fraction is increased from 55% to 62%.

Abstract Matrix cracking of composite laminates leads to stiffness degradation and dominates the medium leakage of liner-less composite vessels. A stiffness degradation model can be established through the machine learning method, which provides only discrete form equivalent moduli data without explicit analytical results. This paper further explored the use of the discrete form data set of stiffness degradation in the crack density estimation for composite laminates by using an iterative process. Furthermore, different mixed-mode fracture criteria were discussed. The results showed that Benzeggagh-Kenane (B-K) criterion and the power law criterion are more appropriate in mixed-mode crack density analyses. [ABSTRACT FROM AUTHOR]

This article investigates the effect of alternating the sequence of variable‐energy repeated low‐velocity impact on the residual strength of carbon fiber reinforced polymer (CFRP) laminates. Quasi‐isotropic CFRP specimens were impacted using three impact energy levels, that is, Low (L), Medium (M), and High (H). Every group, out of three groups in total, was impacted consecutively using one of three sequences: LMH, HML, and MLH. Delamination and its growth after each impact was quantified using a phased‐array ultrasonic probe. The impacted specimens were then subjected to compression after impact loading with in situ acoustic emission (AE) and digital image correlation (DIC) measurement. Mechanical results showed that the residual strength of the specimens was not significantly affected by alternating the impacts sequence. However, the AE, sentry function and DIC results revealed that the impact‐induced damage in HML configuration was activated much earlier than MLH, and the damage induced in LMH configuration was activated later than both. [ABSTRACT FROM AUTHOR]

Composite laminates are widely used in various engineering applications due to their excellent mechanical properties and lightweight nature. However, predicting their behaviour and damage evolution remains a challenge due to the complexity of the inter/intralaminar failure modes. In this paper, we propose a new progressive damage model that takes into account both inter and intralaminar failure modes to accurately predict the flexural behaviour and damage evolution of composite laminates under three-point bending. The proposed model incorporates a progressive failure algorithm and gradual stiffness degradation rules through a user defined subroutine UMAT to predict further damage evolution following damage initiation, estimated by the combination of the three-dimensional Puck failure criteria and the cohesive zone model. One of the objectives of this research is to develop a finite element model (FEM) capable of simulating the behaviour of different composite laminates under three-point bending, to reduce effectively processing time and testing costs. As part of the investigations carried out in this study of two types of composite laminates IMS194/CYCOM977-2 and AS4/PEEK, we considered the prediction of ultimate load and stiffness. The results showed significant agreement with the experiments, as well as degradation trends in the load vs. deflection curves. In addition, the interaction between matrix cracking and delamination has been addressed, alongside the impact of cohesive zone elements on the strength of the material. Corrodingly, we found that the interface strength should be considered, to fully exploit the laminate features, and to reduce the effect of delamination which causes intra-laminar longitudinal cracks to appear under the effect of higher inter-laminar stresses. Furthermore, a mesh dependency of the model used has been conducted, to determine the optimal mesh size and shape required to accurately capture the behaviour of the composite laminates. The significance of our study lies in the development of a more accurate and reliable progressive damage model that can improve the design and engineering of composite laminate. [ABSTRACT FROM AUTHOR]

An axially moving composite cylindrical shallow shell is presented in a wide class of engineering problem, such as the space sailors drag sail mechanism and the deployable antennas. It is very important to have a better understanding of the vibrational characteristics of an axially moving composite cylindrical shallow shell. Nonlinear forced vibrations of an axially moving thin laminated composite cylindrical shallow shell are investigated in the present work. The governing equation and the compatibility equation are derived based on the von Kármán plate theory and discretized by the Galerkin method in a system of ordinary differential equations. The ordinary differential equations are solved by employing the harmonic balance method to obtain the approximate analytical response. Moreover, the stability of the analytical response is also determined. The model is validated by comparing with the natural frequencies available in the literature and the dynamic response obtained through the Runge–Kutta method. Natural frequencies and frequency–response characteristics are discussed in detail. The effects of the movement speed, curvature radius on the natural frequencies are examined. The system has a strong hardening nonlinear behavior and complex dynamic behavior. The frequency–response curve possesses three peaks, due to the strong nonlinear modal coupling. It is further found that the effects of the movement speed, curvature radius, transverse excitation amplitude, damping coefficient and initial tension on the nonlinear dynamic response of an axially moving thin laminated composite cylindrical shallow shell are examined. [ABSTRACT FROM AUTHOR]

To investigate the influence thickness has on the impact resistance of glass fiber woven composite laminates, a series of impact tests on 1–5 mm‐thick laminates impacted by the hemispherical‐nosed projectile on a one‐stage gas gun are conducted. The influence thickness has on the ballistic limit, energy absorption, failure mode, and damage mechanism of laminates is analyzed. The results show the ballistic limit velocity of 1–5 mm thickness to increase in a linear manner. It is found that the ballistic limit velocity of laminate 5 mm in thickness is 2.8 times greater than that of a laminate that is 1 mm in thickness. As the impact velocity of the projectile increases, the energy absorption of a laminated plate decreases to approximately 10% before becoming stable. Fiber tensile tearing and matrix cracking occurs on the back of the laminate, while the domain failure mode changes from fiber tensile fracture to shear as the velocity of the projectile increases. [ABSTRACT FROM AUTHOR]

The first purpose of this study was, as the first time in the literature, to investigate usability of polylactide (PLA) biopolymer as the matrix of high-performance composite laminated structures having woven forms of glass and carbon fibers. For this purpose, 2-14 layers of 2 × 2 twill Carbon Fiber (CF) and 1 × 1 plain weave Glass Fiber (GF) forms were stacked by PLA powders followed by consolidation of these layers by compression molding technique. After conducting various tests and analysis it was observed that significant improvements in the mechanical and thermal properties could be obtained by laminating PLA with woven CF and GF layers. For instance, mechanical properties obtained for PLA/CF laminates with 14 layers were flexural strength of 641 MPa, flexural modulus of 34 GPa and interlaminar shear strength of 38 MPa. Another purpose of this study was to compare mechanical performance of the PLA matrix laminates with Epoxy matrix laminates having exactly the same type and number of GF and CF layers. It was revealed that mechanical properties of the PLA/CF laminates were approaching to the values of the Epoxy/CF laminates (e.g. flexural strength of 607 and 673 MPa, respectively); while due to poor adhesion between the PLA matrix and Glass Fiber surfaces, the properties were lower in the PLA/GF laminates (e.g. flexural strength of 302 and 553 MPa, respectively). Therefore, it could be generally concluded that, in terms of mechanical performance; traditional thermoset Epoxy matrix could be replaced with the renewable biopolymer PLA matrix in the Woven Carbon Fiber laminates. For the Woven Glass Fiber laminates, a proper sizing treatment with a PLA compatible silane coupling agent would be necessary. [ABSTRACT FROM AUTHOR]

Abstract Due to the high vibration sensitivity, the flexible composite structure is prone to vibration and structural deformation, thus it is necessary to study active vibration control to improve its performance. Based on the idea of the PID control and LQR control, a PID-LQR hybrid controller is proposed in this article. It is proved that the hybrid controller has better control performance by simulating the structural vibration response under various excitation conditions. Finally, the effectiveness of the hybrid controller is verified by the active control experiment, and the vibration response is reduced by about 31.55% after control. [ABSTRACT FROM AUTHOR]

This study aims to develop composite laminates for the manufacture of prosthesis socket with enhanced mechanical performance. Layered hybridisation of fabrics (i.e. glass, carbon, and Kevlar fabrics) is used to manufacture hybrid composite laminates by resin infusion via vacuum bagging method. The response of these materials to compression loading is investigated by using compression-loading testes and the load-bearing ability was examined by tensile strength tests. Moreover, finite element analysis has been carried out by using the Abaqus software to predict the compressive failure load and damage failure modes for all sockets samples. Experimental results revealed that the hybrid laminates exhibited more stability and higher absorbing energy compared to non-hybrid laminates during compressive loading tests. Furthermore, the hybridisation of fabrics layers can play key role for improving the tensile strength properties of hybrid composite laminates compared to composite laminates without hybridisation. The numerical simulation results of compressive failure load and damage failure modes are in accordance with experimental results qualitatively as well as quantitatively. [ABSTRACT FROM AUTHOR]

This paper aims at experimental research of the effect of hybrid interface (carbon/glass fibers) on delamination resistance in unidirectional fiber reinforced polymer (FRP) composite laminates under the mode I opening load conditions. Three group of laminates exhibiting different combinations of reinforcing materials at delamination plane were tested. Critical strain energy release rates were determined by using the double cantilever beam (DCB) tests in accordance with the ASTM D5528 Standard. Values of the GIC were calculated by using classical data reduction schemes and they were compared with values obtained by using an alternative compliance based beam method (CBBM). For precise detection of delamination onset all tests were additionally supported by registration of the acoustic emission (AE) signal. Contribution of mixed-modes were evaluated by using numerical finite element analysis. Obtained outcomes revealed, that differences in the mode I c-SERR values obtained by using four different methods were insignificant. Moreover, the greatest value of the GIC was determined for laminates with hybrid interface and it was equal 0.24 N/mm.

This paper presents a novel methodology to detect and isolate individual ply information contained within a relatively low-resolution cross-section image of thick composite laminate specimens. The proposed method can process laminate sample images and construct detailed geometric models in a fast and automated manner with minimal user interaction. The finite element models can be used directly for structural and strength simulations to analyse the effect of waviness defects. The algorithm processes the greyscale sample image and splits it into multiple slices. The initial starting points for each ply were identified by analysing the pixel brightness of the image. The pixel brightness variation was used to identify the different plies in all image slices and a list of possible ply centreline coordinate is generated. The ply centreline points are grouped and connected by selecting the points with minimal distance to the previous one in the ply. A finite element mesh is created for each ply by creating a boundary at the midpoint between two adjacent plies. The geometric information of the isolated plies is then used to create structured finite element models using an in-house meshing algorithm. [ABSTRACT FROM AUTHOR]

Orthogonal antisymmetric composite laminates embedded with shape memory alloys (SMAs) wires have the potential to improve the sound quality of vibro-acoustics by taking advantage of the special superelasticity, temperature phase transition, and pre-strain characteristics of SMAs. In this research, space discretion and mode decoupling were employed to establish a vibro-acoustic sound quality model of SMA composite laminates. The association between the structural material parameters of SMA composite laminates and the sound quality index is then approached through methodologies. Numerical analysis was implemented to discuss the effects of SMA tensile pre-strain, SMA volume fraction, and the ratio of resin-to-graphite in the matrix on the vibro-acoustic sound quality of SMA composite laminates within a temperature environment. Subsequently, the sound quality test for SMA composite laminates is thus completed. The theoretically predicted value appears to agree well with the experimental outcomes, which validates the accuracy and applicability of the dynamic modeling theory and method for the sound quality of SMA composite laminates. The results indicate that attempting to alter the SMA tensile pre-strain, SMA volume fraction, and matrix material ratio can be used to modify loudness, sharpness, and roughness, which provides new ideas and a theoretical foundation for the design of composite laminates with decent sound quality. [ABSTRACT FROM AUTHOR]

The fatigue behavior of composite materials is still a very challenging issue for the scientific community. So far, several numerical methodologies allow us to faithfully simulate the propagation of delamination due to fatigue. However, the reduction of material properties due to the applied cyclic load should be considered. The main objective of this work is to investigate the role of the material property degradation and the intralaminar damages on the propagation of delamination in composite laminates under fatigue loads. The numerical tool FT‐SMXB, based on the Paris Law and virtual crack closure technique, for the mimic of fatigue‐driven delamination, has been integrated with a user material subroutine, based on the generalized residual material property 7degradation model and the Hashin fatigue failure criteria. Typical aeronautical stiffened panel has been considered as test case. Matrix damages and strength degradation due to fatigue cycles have been found to influence the propagation of delamination. Highlights: Interaction between interlaminar/intralaminar damages on the fatigue behavior of laminates.Development of a UserMat to simulate the degradation of material properties.Assessment of the fatigue and post‐fatigue behavior of a composite stiffened panel.Study of the boundary conditions and crack length influence on the damage evolution. [ABSTRACT FROM AUTHOR]

Composite laminated bolted joints are increasingly used in the aerospace industry, and most researchers are involved in the study of the failure behavior of composite bolted joints' structures. Because of the complexity and stability of the structure, precisely predicting the damage evolution and failure behavior of the composite laminated bolted joint becomes rather difficult. In this paper, an asymptotic damage model is proposed to predict the failure behavior of the composite bolted joint structure. The model is based on the frame of mainstream criteria and some improvements are made to adapt to the particularity of composite laminated bolted joints. Combining the damage model with the finite element method, the failure behavior of single-lap and double-lap bolted joint structures are predicted and analyzed. In order to guarantee the reliability of the model, the corresponding experimental study is conducted, and the results show that the simulation curve and the experimental data are in good agreement. This damage model can further predict the failure behavior of various types of complex composite laminated bolted joints effectively. [ABSTRACT FROM AUTHOR]

The analysis of cumulative fatigue damage is an important factor in predicting the life of composite elements and structures that are exposed to field load histories. A method for predicting the fatigue life of composite laminates under varying loads is suggested in this paper. A new theory of cumulative fatigue damage is introduced grounded on the Continuum Damage Mechanics approach that links the damage rate to cyclic loading through the damage function. A new damage function is examined with respect to hyperbolic isodamage curves and remaining life characteristics. The nonlinear damage accumulation rule that is presented in this study utilizes only one material property and overcomes the limitations of other rules while maintaining implementation simplicity. The benefits of the proposed model and its correlation with other relevant techniques are demonstrated, and a broad range of independent fatigue data from the literature is used for comparison to investigate its performance and validate its reliability. [ABSTRACT FROM AUTHOR]

Bolted joints are often used in thin parts such as plates or shell-like components in lightweight structures, e.g. air- and spacecraft. This is also motivated by an inexpensive manufacturing and the ability to disassemble. To make these joints, holes need to be drilled and stress concentrations arise. Leading to the instantaneous destruction of the connection, attention should be drawn to fatal tension failure. The efficient and precise prediction of the corresponding failure stresses using analytical methods is the focus of this paper. Usually, rows of bolts are placed. Then, the load is partly introduced into one bolt while the rest stays in the plate. This setting is also referred to as bolted joint under combined bearing-bypass load, which shall be idealised as a linear 2D plate problem. The corresponding characteristic stresses are discussed for orthotropic laminates showing good agreement to Finite Element values. Then, failure analysis is conducted using Finite Fracture Mechanics. This part is dedicated to quasi-isotropic laminates. The size effect and in this context the failure stress reduction with increasing bolt diameter is analysed. Primary physical effects due to finite dimensions and the ratio of bearing and total load are identified. The higher this ratio and the larger the bolt diameter, the lower the sustained failure stress. Failure envelopes for the graphical determination of the critical bearing and bypass stresses are provided. All in all, a comprehensive and efficient framework for tension failure assessment of composite bolted joints under bearing-bypass load interaction is developed. [ABSTRACT FROM AUTHOR]

This paper proposes a data processing scheme for laser spot thermography (LST) applied for nondestructive testing (NDT) of composite laminates. The LST involves recording multiple thermographic sequences, resulting in large amounts of data that have to be processed cumulatively to evaluate the diagnostic information. This paper demonstrates a new data processing scheme based on parameterization and machine learning. The approach allows to overcome some of the major difficulties in LST signal processing and deliver valuable diagnostic information. The effectiveness of the proposed approach is demonstrated on an experimental dataset acquired for a laminated composite sample with multiple simulated delaminations. The paper discusses the theoretical aspects of the proposed signal processing and inference algorithms as well as the experimental arrangements necessary to collect the input data. [ABSTRACT FROM AUTHOR]

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The concentration of the present investigation is on the development of a quadrilateral shell element for the deformation analysis of composite laminates. For this purpose, a higher-order shell model with 12 parameters is adopted along with the three-dimensional state of stress. The principle of virtual work is implemented to derive the stiffness matrix and the load vector for the four-node shell element. In order to verify the performance of the higher-order shell element developed herein for the treatment of laminated composites, some benchmarks are solved and compared with solutions available in the literature. [ABSTRACT FROM AUTHOR]

In this work, the damage accumulation and failure mechanism of glass fiber-reinforced epoxy composite laminates under repeated low velocity impacts were studied considering the influence of stacking sequence. The typical sandwich-like [0°2/90°2]s, angle-ply [±45°]2s and quasi-isotropic [0°/−45°/45°/90°]s laminates were tested at 20 J impact energy. The impact responses including contact force–time/central displacement and energy–time curves were recorded. The tendencies of the peak contact force, maximum displacement, bending stiffness, and energy dissipation with the increase in impact number were analyzed. Damage induced in the laminates was further evaluated. The results show that the impact resistance of the sandwich-like laminate is the weakest with the lowest peak load and the highest energy dissipation. The impact resistance of the quasi-isotropic laminate is better relative to the angle-ply laminate before the occurrence of fiber breakage, whereas the damage tolerance of the angle-ply laminate is higher with relatively slower damage accumulation at subsequent impacts.

The matrix cracking severely decreases the load-bearing performance of composite laminates even though its smaller degree in comparison with delamination, cut-out, and hole. The initial parameters in modal analysis, such as natural frequency, modal displacement, and modal curvature, can only detect a damage with large changes in geometric shape and elastic modulus. To solve this situation, a new Non-Destructive Testing (NDT) method using the power function of modal curvature difference is developed to identify the multi-point matrix damage. The Camanho damage criterion is adopted to construct the matrix compression failures in multiple locations, and the finite element models are established for undamaged and damaged laminates with different fiber angles. The force hammer excitation experiment is performed on undamaged carbon fiber laminates, and the modal displacements of measuring points, obtained by Dong-Hua Data Analysis System (DHDAS), are compared with numerical results. Considering the simulation provides enough measuring points to precisely characterize the abrupt characteristics of the curved surface, the numerical mode shape is adopted to calculate the Gaussian curvature. The square of Gaussian curvature difference between undamaged and damaged laminates is defined as the unevenness coefficient, and its variations with the location and number of matrix damage are studied for single- and multi- order modes. Simultaneous and high-accuracy detection of multi-point matrix failure is realized in this process, confirming that the presented method is a valuable tool for detecting the damage of composite laminates. [ABSTRACT FROM AUTHOR]

The mechanical response and damage accumulation of carbon-fiber-reinforced composite laminates subjected to repeated low-velocity impacts were experimentally investigated. The repeated impact tests were conducted on [902/−452/02/452]S quasi-isotropic and [902/02]2S cross-ply composite laminates under 16.8 J impact energy, respectively. For each impact, impact responses such as force-time, force-displacement and energy-time curves were recorded. The trends of peak force, maximum central displacement, energy absorption rate and bending stiffness with the increasing impact number were summarized, and the maximum number of repeated impacts corresponded to the occurrence of penetration events. The results showed that the delamination initiation, fiber breakage and penetration were the three typical characteristics describing the damage evolution of the repeated impacts. The damage accumulation of both the laminates was characterized by employing appropriate damage indices. By contrast, the quasi-isotropic laminates had higher impact resistance and damage tolerance, and their damage accumulation was relatively slower. [ABSTRACT FROM AUTHOR]

Carbon-aluminum bolted assemblies are difficult to simulate because of the complex phenomenology involved (contact, friction, preload and thermal expansion). Therefore, accurate but computationally feasible methodologies are necessary. We propose two simplified methodologies, one based on continuum shell elements and the other on conventional shells, and compare them with a full 3D solids model. The two cases explored are a single-lap shear coupon with one bolt, and a hybrid wingbox subcomponent with 46 bolts. The effect of temperature jumps on the bolt preloads are explored. Results show that the continuum shell model presents the best tradeoff between accuracy and computational cost. [ABSTRACT FROM AUTHOR]

Composite materials are gaining popularity as an alternative to classical materials in many different applications. Moreover, their design is even more flexible due to the potential of additive manufacturing. Thus, one can produce a tailored composite laminate with the optimal values of some design parameters providing the desired mechanical performance. In this context, having a parametric numerical model for the mechanical response of the composite laminate is essential to compute the optimal parameters. In the present paper, the design parameters under consideration are the angles describing the orientation of the reinforcement fibers in different layers or patches of the composite laminates. We obtain a generalized solution using Proper Generalized Decomposition (PGD) which is adopted to provide solutions with explicit parametric dependence. The Tsai-Wu failure criterion is used to estimate first ply failure. In this context, Tsai-Wu criterion is used as the objective function for the optimization of the fibre orientations in the laminate. The PGD solution provides also sensitivities for a gradient-based optimization algorithm. The potentiality and efficiency of the presented approach is demonstrated through some numerical tests. [ABSTRACT FROM AUTHOR]

The transverse cracking behavior of a carbon-fiber-reinforced plastic (CFRP) cross-ply laminate is investigated using a fatigue test and an entropy-based failure criterion in this study. The results of fatigue experiments show that the crack accumulation behavior depends on the cyclic number level and frequency, in which two obvious transverse cracks are observed after 104 cyclic loads and 37 transverse cracks occur after 105 cycles. The final numbers of transverse cracks decrease from 29 to 11 when the load frequency increases from 5 Hz to 10 Hz. An entropy-based failure criterion is proposed to predict the long-term lifetime of laminates under cyclic loadings. The transverse strength of 90° ply is approximated by the Weibull distribution for a realistic simulation. Progressive damage and transverse cracking behavior in CFRP ply can be reproduced due to entropy generation and strength degradation. The effects of stress level and load frequency on the transverse cracking behavior are investigated. It is discovered that, at the edge, the stress σ22 + σ33 that is a dominant factor for matrix tensile failure mode is greater than the interior at the first cycle load, and as stress levels rise, a transverse initial crack forms sooner. However, the initial transverse crack initiation is delayed as load frequencies increase. In addition, transverse crack density increases quickly after initial crack formation and then increases slowly with the number of load cycles. The proposed method's results agree well with those of the existing experimental method qualitatively. In addition, the proposed entropy-based failure criterion can account for the effect of load frequency on transverse crack growth rate, which cannot be addressed by the well-known Paris law. [ABSTRACT FROM AUTHOR]