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This study presents a procedure based on constant amplitude (CA) fatigue data to predict the statistical fatigue lifetime of glass/orthopolyester composites subjected to repeated ordered and random two, three, and six sequences of block loadings. A numerical routine was developed to detect cycle‐by‐cycle the statistical strength degradation progression until failure, assuming that the strength at the end of a block cycle equals the strength at the start of the successive one and that the individual samples' static strength, the amount of degraded strength, and fatigue life share the same rank in their respective cumulative distribution function. Predictions conform to the statistically undetectable loading sequence effects and lightly overestimate the lifetimes of random and ordered high‐to‐low (1/100 cycles) repeated two‐block loadings. The vanishing effect of the loading sequence when the block extents remain fixed, the block extent effects for a given three‐block sequence, and the lifetimes of three‐block loadings were fully predicted. The six‐block sequence's experimental lifetimes with different block loading orders and block extent fell within the predicted lifetimes' cumulative distribution function. A reliable damage rule based on residual strength was proposed and compared to the Miner's rule. [ABSTRACT FROM AUTHOR]

This paper had conducted tensile shear tests on single-lap joints (SLJs)bonded structures of carbon fiber reinforced resin matrix (CFRP) composite laminates with different overlap lengths, overlap widths, overlap model, adherend material, and adhesive layer thicknesses under two environments: room temperature dry state (RTD) and elevated temperature wet state (ETW). The failure modes were observed, and load–displacement curves were obtained. The microscopic morphology of the fracture surface was observed by scanning electron microscope (SEM). At the same time, a finite element simulation model was established to simulate the damage initiation and evolution process between layers and in the adhesive layer, and analyze the distribution laws of peel stress and shear stress in the adhesive layer. Through the combination of test data and simulation results, the influences of geometric parameters, material parameters and environmental parameters on the structure were explored, and the joint failure mechanism was revealed. Finally, the ACO-BP neural network was used to optimize the geometric parameters through test data. The research results showed that the geometric parameters of the structure mainly affect the bearing capacity and failure type. Reducing the overlap length and increasing the overlap width within a certain range can weaken the peeling phenomenon, so that a smaller overlap area has a higher shear strength. The material parameters of the adherend mainly affect the stress distribution law and stress transfer process of the adhesive layer in the overlap area. The joint mainly bore shear stress and peel stress, and shear stress is the main cause of damage initiation. When the types of adherend materials are different, the stress distribution law shows obvious asymmetric offset. The lap model mainly affects the location distribution of the failure area, and the environmental parameters mainly affect the area proportion relationship of various fracture forms in the mixed failure mode. [ABSTRACT FROM AUTHOR]

Abstract This paper had conducted tensile shear tests on single-lap joints (SLJs)bonded structures of carbon fiber reinforced resin matrix (CFRP) composite laminates with different overlap lengths, overlap widths, overlap model, adherend material, and adhesive layer thicknesses under two environments: room temperature dry state (RTD) and elevated temperature wet state (ETW). The failure modes were observed, and load–displacement curves were obtained. The microscopic morphology of the fracture surface was observed by scanning electron microscope (SEM). At the same time, a finite element simulation model was established to simulate the damage initiation and evolution process between layers and in the adhesive layer, and analyze the distribution laws of peel stress and shear stress in the adhesive layer. Through the combination of test data and simulation results, the influences of geometric parameters, material parameters and environmental parameters on the structure were explored, and the joint failure mechanism was revealed. Finally, the ACO-BP neural network was used to optimize the geometric parameters through test data. The research results showed that the geometric parameters of the structure mainly affect the bearing capacity and failure type. Reducing the overlap length and increasing the overlap width within a certain range can weaken the peeling phenomenon, so that a smaller overlap area has a higher shear strength. The material parameters of the adherend mainly affect the stress distribution law and stress transfer process of the adhesive layer in the overlap area. The joint mainly bore shear stress and peel stress, and shear stress is the main cause of damage initiation. When the types of adherend materials are different, the stress distribution law shows obvious asymmetric offset. The lap model mainly affects the location distribution of the failure area, and the environmental parameters mainly affect the area proportion relationship of various fracture forms in the mixed failure mode.

This paper presents the theoretical investigations on the free and forced vibration behaviours of carbon/glass hybrid composite laminated plates with arbitrary boundary conditions. The unknown allowable displacement functions of the physical middle surface are expressed in terms of standard cosine Fourier series and sinusoidal auxiliary functions to ensure the continuity of the displacement functions and their derivatives at the structural boundaries. Arbitrary boundary conditions are achieved through the introduction of an artificial spring technique. The first shear deformation theory and Lagrange equations are utilized to derive the energy expression, and the eigenvalue equations associated with free and forced vibration are obtained by Rayleigh-Ritz variational operations. Subsequently, these equations are then solved to determine the natural frequency, mode of vibration, and the steady-state displacement response under forced excitation. The new results are compared with those from references and finite element methods to verify the convergence, accuracy and efficiency of the analytical method. The effects of hybrid ratios, stacking sequences, lamination schemes, fibre orientation, boundary conditions and excitation force on the free and forced vibration behaviours of the carbon/glass hybrid composite laminated plates are analyzed in detail. [ABSTRACT FROM AUTHOR]

This research focuses on investigating the buckling strength of thin-walled composite structures featuring various shapes of holes, laminates, and composite materials. A parametric study is conducted to optimize and identify the most suitable combination of material and structural parameters, ensuring the resilience of structure under both mechanical and thermal loads. Initially, a numerical approach employing the finite element method is used to design the C-section thin-walled composite structure. Later, various structural and material parameters like spacing ratio, opening ratio, hole shape, fiber orientation, and laminate sequence are systematically varied. Subsequently, simulation data from numerous cases are utilized to identify the best parameter combination using machine learning algorithms. Various ML techniques such as linear regression, lasso regression, decision tree, random forest, and gradient boosting are employed to assess their accuracy in comparison with finite element results. As a result, the simulation model showcases the variation in critical buckling load when altering the structural and material properties. Additionally, the machine learning models successfully predict the optimal critical buckling load under mechanical and thermal loading conditions. In summary, this paper delves into the study of the stability of C-section thin-walled composite structures with holes under mechanical and thermal loading conditions using finite element analysis and machine learning studies. [ABSTRACT FROM AUTHOR]

Ultrasonic testing (UT) is a commonly used method to detect internal damage in composite materials, and the test data are commonly analyzed by manual determination, relying on a priori knowledge to assess the status of the specimen. In this work, A method for the automatic detection of delamination defects based on improved EfficientDet was proposed. The Swin Transformer block was adopted in the Backbone part of the network to capture the global information of the feature map and improve the feature extraction capability of the whole model. Meanwhile, a custom block was added to prompt the model to extract object features from different receptive fields, which enriches the feature information. In the Neck part of the network, the adaptive weighting was used to keep the features that were more conductive to the prediction object, and desert or give smaller weights to those features that were not desirable for the prediction object. Two kinds of specimens were prepared with embedded artificial delamination defects and delamination damage caused by low-velocity impacts. Ultrasonic phased array technology was employed to investigate the specimens and the amount of data was increased by the sliding window approach. The object detection model proposed in this work was evaluated on the obtained dataset and delamination in the composites was effectively detected. The proposed model achieved 98.97% of mean average precision, which is more accurate compared to ultrasonic testing methods. [ABSTRACT FROM AUTHOR]

Sizing is the surface treatment of glass fibres (GFs) to protect them from wear, handle with ease and to create a good interface with the polymer matrix. This paper reports on the discernible procedure for the synthesis of epoxy-compatible amino silane sizing formulation for E-GF and its efficacy based on inter-laminar shear strength (ILSS) and flexural strength of in-house sized GF (SGF) woven roven mat (WRM) reinforced epoxy composites and compared to commercially available sized WRM [0°/90°]. The formulations of sizing were prepared by varying the proportions of aminopropyltriethoxy silane (APS, coupling agent) and polydimethylsiloxane (PDMS, anti-foam agent), for a fixed proportion of film former, surfactant and lubricant. Commercially available sized GF WRM were heat cleaned prior to sizing with prepared formulations. Interestingly, sizing with formulation of 0.65 wt% APS and 0.35 wt% of PDMS, coded as S6, showed homogeneous coating morphology and the loss on ignition (LOI) is comparable to commercially available SGF. Also, Fourier transform-infrared spectroscopy of SGF6 indicated the formation of silanol interphase by the presence of bands corresponding to Si–O–Si and Si–OH functional groups. The contact angle with epoxy hardener solvent by sessile drop method demonstrated good wetting favourable for better interphase with epoxy matrix. Thermogravimetric analysis indicated that sizing pick up and thermal stability were best for S6 formulation SGF. The mechanical testing shows that S6-sized WRM composite (SWC) yielded the best ILSS and flexural strength due to the effect of better wetting and good interfacial adhesion between SGF and matrix as revealed from fractography. The discernible recipe formulation and the better mechanical properties exhibited by SWC-reinforced SGF WRM sized with S6 comparable to that of commercial GF WRM epoxy composite indicate plausible industrial applications. [ABSTRACT FROM AUTHOR]

Due to their excellent strength-to-weight ratio, composite laminates are gradually being substituted for traditional metallic materials in a variety of industries. However, due to their orthotropic nature, composite laminates are prone to several different types of damage, with delamination being the most prevalent and serious. Therefore, deep learning-based methods that use sensor data to conduct autonomous health monitoring have drawn much interest in structural health monitoring (SHM). However, the direct application of these models is restricted by a lack of training data, necessitating the use of transfer learning. The commonly used transfer learning models are computationally expensive; therefore, the present research proposes lightweight transfer learning (LTL) models for the SHM of composites. The use of an EfficientNet–based LTL model only requires the fine-tuning of target vibration data rather than training from scratch. Wavelet-transformed vibrational data from various classes of composite laminates are utilized to confirm the effectiveness of the proposed method. Moreover, various assessment measures are applied to assess model performance on unseen test datasets. The outcomes of the validation show that the pre-trained EfficientNet–based LTL model could successfully perform the SHM of composite laminates, achieving high values regarding accuracy, precision, recall, and F1-score. [ABSTRACT FROM AUTHOR]

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]

Mode II (in-plane-shear) delamination tests are more complex than mode I (opening) due to the presence of a contact force between the two arms. This force is essential for the calculation of the energy release rate (ERR) and is closely linked to friction effects. A novel formulation is presented in this article to estimate the contact force analytically. Specifically, the contact force is derived within the context of the rigid, semi-rigid, and flexible joint models. The analytical solutions consider the case of a generally layered composite laminate with residual hygrothermal stresses and are used to evaluate the ERR. The new formulation is compared with numerical models created using the Virtual Crack Closure Technique (VCCT) and the Cohesive Zone Method (CZM) for a fiber–metal laminate. The results show that the new formulation provides nearly identical ERR predictions to those of the VCCT and CZM models. Additionally, it is demonstrated that the effect of friction on the ERR is less than 1%. [ABSTRACT FROM AUTHOR]

AbstractAdvancements in technology and the compulsion to use environment-friendly materials have been challenging tasks for researchers for the past two decades. Researchers have been focusing on the utilization of plant fibers to produce good quality fiber-reinforced polymer/polyester composites for automobile, structural, and building applications. Researchers have been looking for high-quality and cost-effective drilling processes. The primary goal of this study is to identify optimal drilling conditions for CCFRP composite laminates, affecting thrust force and torque. This is achieved by manipulating drilling process variables using Taguchi’s Design of Experiments (TDOE), Analysis of variance (ANOVA), Response Surface Methodology (RSM), Desirability Function Analysis (DFA) and Artificial Neural Network (ANN). From the results, it was observed that the spindle speed of 2000 rpm, feed of 15 mm/min, point angle of 90°, fiber length of 6 mm, fiber volume of 30%, and fiber diameter of 7 microns gave the optimum results for obtaining minimum thrust force and torque. Further RSM revealed that an increase in fiber vol % and a decrease in spindle speed resulted in an increase in thrust force and torque. From DFA optimization results, the minimum thrust force of 24.0042 N and minimum torque of 0.8001 N-m was obtained. Finally, the experimental values of thrust force and torque were compared with the corresponding values predicted by the MLP-ANN model. The average error percentage for thrust force and torque was 1.75% and 6.56% respectively.

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. [ABSTRACT FROM AUTHOR]

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 FROM AUTHOR]

Auxetic composite laminates, i.e. laminates with a NPR (Negative Poisson’s Ratio), are regarded as a promising solution to combat LVI (Low-velocity impact) delamination BVID (Barely visible internal damage) and ensuing property degradation, a cause for concern in aerospace components, mainly inflicted by fortuitous accidents during handling operations. In order to potentiate the auxetic effect through the minimization of the Poisson’s ratio, a thorough analysis of material properties and stacking sequences is required, as only a restricted domain of combinations can generate the desired effect, either in an IP (In-plane) or TTT (Through-the-thickness) configuration. This paper focuses on a MATLAB program developed for IP and TTT auxetic laminate design, based on the CLT (Classical Lamination Theory). Cases studies on NPR domain definition of C/E (Carbon/epoxy), G/E (Glass/epoxy) and hybrid C-G/E (Carbon-Glass/epoxy) laminates are presented. Moreover, the influence of fibre volume fraction on C/E and G/E laminates is analysed.

A computational framework combined with the commercial finite element software Abaqus and Bayesian optimization algorithm is proposed. The proposed computational framework leverages the Gaussian process based-probabilistic capability in Bayesian optimization as a surrogate model for minimizing the computational cost of objective function evaluations in the finite element analysis. The optimization problem in this work is to enhance the maximum fundamental frequency of the composite laminates, which is one of the critical parameters in the design for composite structures. The optimization of stacking sequence selection is investigated and validated by the results obtained from literatures. The effectiveness and efficiency of the proposed Bayesian optimization computational framework in maximizing the fundamental frequency of composite laminates are demonstrated by comparing the optimized results from different optimization techniques through a series of cases including the 8-layer rectangular plates with 11 different boundary conditions and the 10 to 20-layer trapezoidal plates with the same boundary condition. The proposed framework developed in this work has highly potential as an engineering tool to address a broader range of structural optimization in vibration problems.

Aiming at the high-speed impact problem of laminates, a three-dimensional finite element impact model consisting of 8 node cohesive element and 8 node solid element is established based on continuous damage mechanies. Based on the Hashin criterion, fiber damage can be well predicted, and puck criterion can well predict matrix damage, therefore. the criterion formed by the mixture of Hashin and puck is compared with the single Hashin failure criterion. It is found that the prediction result of the mixed criterion is closer to the test value. On this basis, the effects of ply angle and impact angle on the impact resistance of laminates are analyzed. The results show that the greater the angle difference between adjacent plies, the greater the incident angle, the stronger the impact resistance of laminates.

Copyright of Journal of Mechanical Strength / Jixie Qiangdu is the property of Zhengzhou Research Institute of Mechanical Engineering 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.)

Mode II (in-plane-shear) delamination tests are more complex than mode I (opening) due to the presence of a contact force between the two arms. This force is essential for the calculation of the energy release rate (ERR) and is closely linked to friction effects. A novel formulation is presented in this article to estimate the contact force analytically. Specifically, the contact force is derived within the context of the rigid, semi-rigid, and flexible joint models. The analytical solutions consider the case of a generally layered composite laminate with residual hygrothermal stresses and are used to evaluate the ERR. The new formulation is compared with numerical models created using the Virtual Crack Closure Technique (VCCT) and the Cohesive Zone Method (CZM) for a fiber–metal laminate. The results show that the new formulation provides nearly identical ERR predictions to those of the VCCT and CZM models. Additionally, it is demonstrated that the effect of friction on the ERR is less than 1%.

Due to their excellent strength-to-weight ratio, composite laminates are gradually being substituted for traditional metallic materials in a variety of industries. However, due to their orthotropic nature, composite laminates are prone to several different types of damage, with delamination being the most prevalent and serious. Therefore, deep learning-based methods that use sensor data to conduct autonomous health monitoring have drawn much interest in structural health monitoring (SHM). However, the direct application of these models is restricted by a lack of training data, necessitating the use of transfer learning. The commonly used transfer learning models are computationally expensive; therefore, the present research proposes lightweight transfer learning (LTL) models for the SHM of composites. The use of an EfficientNet–based LTL model only requires the fine-tuning of target vibration data rather than training from scratch. Wavelet-transformed vibrational data from various classes of composite laminates are utilized to confirm the effectiveness of the proposed method. Moreover, various assessment measures are applied to assess model performance on unseen test datasets. The outcomes of the validation show that the pre-trained EfficientNet–based LTL model could successfully perform the SHM of composite laminates, achieving high values regarding accuracy, precision, recall, and F1-score.

Scarf repair is a widely used repair method for damaged composite structures, which can be divided into two categories: dry (precured-patch) repair and wet (wet-layup) repair. The ultimate strength, failure mode and patch debonding of scarf repaired composite laminates were studied by static tensile test. The specimens with different damage sizes were repaired by dry repair and wet repair method. The experimental results show that the higher recovery of failure strength and the lower probability of patch debonding can be obtained by using precured-patch repair method. Based on the experimental investigation, finite element analysis was carried out to accurately predict the ultimate strength, stress-strain distribution and damage evolution process of scarf repaired laminates. The simulation results show that the use of precured-patch repair can improve the mechanical performance of the repaired laminates compared to that using wet-layup repair. The stress distribution of the bondline is more uniform, the stress level and stress concentration are lower, and the load of interface failure and cohesive failure are higher.

Advancements in technology and the compulsion to use environment-friendly materials have been challenging tasks for researchers for the past two decades. Researchers have been focusing on the utilization of plant fibers to produce good quality fiber-reinforced polymer/polyester composites for automobile, structural, and building applications. Researchers have been looking for high-quality and cost-effective drilling processes. The primary goal of this study is to identify optimal drilling conditions for CCFRP composite laminates, affecting thrust force and torque. This is achieved by manipulating drilling process variables using Taguchi's Design of Experiments (TDOE), Analysis of variance (ANOVA), Response Surface Methodology (RSM), Desirability Function Analysis (DFA) and Artificial Neural Network (ANN). From the results, it was observed that the spindle speed of 2000 rpm, feed of 15 mm/min, point angle of 90°, fiber length of 6 mm, fiber volume of 30%, and fiber diameter of 7 microns gave the optimum results for obtaining minimum thrust force and torque. Further RSM revealed that an increase in fiber vol % and a decrease in spindle speed resulted in an increase in thrust force and torque. From DFA optimization results, the minimum thrust force of 24.0042 N and minimum torque of 0.8001 N-m was obtained. Finally, the experimental values of thrust force and torque were compared with the corresponding values predicted by the MLP-ANN model. The average error percentage for thrust force and torque was 1.75% and 6.56% respectively. [ABSTRACT FROM AUTHOR]

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 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.

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]

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]

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]

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.

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.

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]

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]

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]

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]

Manufacturing processes of composites involve a margin of parameter variability (e.g., geometric, mechanical, loading) which results in an inaccurate prediction of their dynamics when considered with exact assumptions. Real-time calculation of such structures confronts engineers with several challenges (e.g., dimension of finite element model, size of parameter space, uncertainty level, nonlinearity). To guarantee accuracy while saving computing time, a double-process Reduced Order Model (ROM) is proposed. It allows reducing both offline data acquisition and online data interpolation for real-time calculation. The learning phase is gradually becoming one of the most critical part of data-driven models. To overcome this problem, a set of reduced bases are built using the Proper Orthogonal Decomposition (POD) from a set of solutions computed using a regression-based Polynomial Chaos Expansion for a properly chosen Design of Experiments. In the online phase, the POD bases are interpolated on a Grassmann manifold using the Inverse Distance Weighting at a non-sampled set of the uncertain parameters' values. The proposed double-process ROM allows to accurately approximate the nonlinear dynamics of a laminate plate with uncertain thickness and fiber orientation of two layers, with a drastically reduced computing time compared to a Full Order Model solving based on classical statistical data-sampling and postprocessing. • Double-process online and offline reduction of a non-intrusive data-driven model. • Nonlinear dynamics of laminate structures with multiparametric uncertainties. • Polynomial Chaos Expansion with Grassmann interpolation of Proper Orthogonal Modes. • A powerful decision-making tool for real-time simulations. [ABSTRACT FROM AUTHOR]

• The proposed FE modeling methodology can accurately predict the impact response of composite laminates. • Fiber breakage, pull-out, splitting, kinking, crushing, and matrix cracking are predicted using the enhanced LaRC05 criteria. • Delamination and intralaminar matrix cracking interactions are modeled. • The matrix fracture plane and the fiber kink band angle can be found 48 % faster using the SRGSS algorithm. • The detailed sequence of impact damage occurrence is predicted by analyzing the histories of dissipated energies. A finite element model was developed using both continuum and discrete damage modeling techniques to provide detailed predictions for ply-by-ply damage progression in composite laminates during low-velocity impact (LVI) events. A new fiber failure model was incorporated into the LaRC05 failure criteria to predict fiber pull-out and fiber crushing during the fiber damage evolution. In addition, the selective range golden section search (SRGSS) algorithm was implemented to efficiently predict fiber breakage, pull-out, splitting, kinking and crushing, and matrix cracking. The delamination was captured by cohesive element layers embedded between every adjacent composite ply. The interactions of intralaminar matrix cracking and delamination were modeled by deploying cohesive elements within each composite ply. The prediction results were validated by 30 J and 75 J drop-weight tests with different-sized impactors, as well as X-Ray CT inspections on 254 mm by 304.8 mm [0/45/90/-45] 4 s IM7/977–3 laminates. The model predicted the maximum deflection and contact duration with <2 % error, and the peak load, damaged areas, and absorbed energy with <8 % error. The matrix fracture plane and the fiber kink band angle were found with 1° precision 48 % faster via the SRGSS algorithm. The detailed sequences of damage occurrence were predicted by analyzing the energy dissipation histories through various damage modes. Although this modeling methodology was developed for LVI scenarios, it has broad applications for predicting failures in composites. [ABSTRACT FROM AUTHOR]

This work utilizes the Immersed Boundary Conformal Method (IBCM) to analyze linear elastic Kirchhoff–Love and Reissner–Mindlin shell structures within an immersed domain framework. Immersed boundary methods involve embedding complex geometries within a background grid, which allows for great flexibility in modeling intricate shapes and features despite the simplicity of the approach. The IBCM method introduces additional layers conformal to the boundaries, allowing for the strong imposition of Dirichlet boundary conditions and facilitating local refinement. In this study, the construction of boundary layers is combined with high-degree spline-based approximation spaces to further increase efficiency. The Nitsche method, employing non-symmetric average operators, is used to couple the boundary layers with the inner patch, while stabilizing the formulation with minimal penalty parameters. High-order quadrature rules are applied for integration over cut elements and patch interfaces. Numerical experiments demonstrate the efficiency and accuracy of the proposed formulation, highlighting its potential for complex shell structures modeled through Kirchhoff–Love and Reissner–Mindlin theories. These tests include the generation of conformal interfaces, the coupling of Kirchhoff–Love and Reissner–Mindlin theories, and the simulation of a cylindrical shell with a through-the-thickness crack. [ABSTRACT FROM AUTHOR]

As with many tasks in engineering, structural design frequently involves navigating complex and computationally expensive problems. A prime example is the weight optimization of laminated composite materials, which to this day remains a formidable task, due to an exponentially large configuration space and non-linear constraints. The rapidly developing field of quantum computation may offer novel approaches for addressing these intricate problems. However, before applying any quantum algorithm to a given problem, it must be translated into a form that is compatible with the underlying operations on a quantum computer. Our work specifically targets stacking sequence retrieval with lamination parameters, which is typically the second phase in a common bi-level optimization procedure for minimizing the weight of composite structures. To adapt stacking sequence retrieval for quantum computational methods, we map the possible stacking sequences onto a quantum state space. We further derive a linear operator, the Hamiltonian, within this state space that encapsulates the loss function inherent to the stacking sequence retrieval problem. Additionally, we demonstrate the incorporation of manufacturing constraints on stacking sequences as penalty terms in the Hamiltonian. This quantum representation is suitable for a variety of classical and quantum algorithms for finding the ground state of a quantum Hamiltonian. For a practical demonstration, we performed numerical state-vector simulations of two variational quantum algorithms and additionally chose a classical tensor network algorithm, the DMRG algorithm, to numerically validate our approach. For the DMRG algorithm, we derived a matrix product operator representation of the loss function Hamiltonian and the penalty terms. Although this work primarily concentrates on quantum computation, the application of tensor network algorithms presents a novel quantum-inspired approach for stacking sequence retrieval. [ABSTRACT FROM AUTHOR]

In this paper, a fatigue-creep damage model that can take into account the interaction of fatigue and creep damage is proposed under high temperature cyclic loading. In the proposed model, the effect of temperature on creep damage, the variation of creep damage under different high temperature cyclic loading conditions, and fatigue-creep interaction damage are considered. In addition, in order to accurately describe the creep behavior of unidirectional laminates with different orientations, the damage mechanism of unidirectional laminates was also analyzed. The creep and fatigue test results at different temperatures showed that the proposed creep rupture time model and the fatigue-creep damage model considering the damage mechanisms can successfully predict the creep and fatigue lives of unidirectional laminates at high temperature, and the prediction results are in good agreement with the experimental data. [Display omitted] [ABSTRACT FROM AUTHOR]

Under static loading, measuring experimentally the mode II and mixed mode fracture toughness of composite materials and adhesive joints is well standardised. However, under dynamic loading, no standard procedure has been defined yet. Therefore, this paper proposes an experimental methodology to measure the mode II and mixed mode interlaminar fracture toughness of composite materials and adhesive joints. The methodology is based on a modified split Hopkinson compression bar. Two different data reduction schemes are explored and compared, one based on measuring the crack length, and another based on measuring the force from the strains in the transmitted bar. The two data reduction methods provided considerably different results. By using the method based on measuring the force, the mode II and mixed mode fracture toughness for both interlaminar and adhesive joints decreased for higher strain rates, while the opposite was found with the other approach. The method based on the crack length measurement was deemed to be unreliable due to the difficulties in measuring it. • Experimental study of the mode II and mixed mode fracture toughness under dynamic loading. • Interlaminar fracture toughness of composite materials and adhesive joints is explored. • Two different data reduction methods are employed and compared. • Significant strain rate is found, but results are dependent on the data reduction method. • Advantages and limitations of the data reduction methods are discussed. [ABSTRACT FROM AUTHOR]