Lay-up Configurations Research Articles

Effective performance analysis of stiffened honeycomb sandwich panels using VAM-based equivalent model

The stiffened honeycomb sandwich panel (stiffened HSP) is an improved honeycomb structure by adding the stiffeners into the traditional honeycomb core to enhance the structural performance. The novelty of this work is that the constitutive parameters of the panel are obtained by asymptotical analysis of the strain energy stored in the periodic unit cell, and a 2D dimensional reduced model (2D-DRM) is constructed on this basis. The efficiency and accuracy of 2D-DRM are verified by comparing with the results of 3D direct numerical simulations (3D-DNS) under different working conditions (including static displacement, local field distribution, free vibration and global buckling). In addition, the effects of the structural parameters of the stiffened HSP and the layup configuration of the facesheet on the equivalent stiffness, specific stiffness as well as static and dynamic performance are systematically studied. The results reveal that the facesheet thickness-to-core height ratio had the greatest influence on the buckling load, while the side length-to-height ratio of core cell had the greatest influence on the fundamental frequency. Compare with the traditional and vertical stiffened HSPs, the horizontal stiffened HSP has larger buckling load and lower natural frequency.

Acoustic insulation characteristics improvement of a thick CNT-reinforced doubly-curved shell by using GPLRC and MEE composite layers

Noise reduction in structures and human living environments is one of the most important issues in engineering that is always given special attention. Sound insulation has always been improved using different methods, one of which is to use the properties of materials. Herewith, the aim of this paper is to take advantage of graphene-platelet reinforced composites and magneto-electro-elastic (MEE) material properties for sound attenuation. The present paper deals with the analysis of sound transmission loss (STL) through a three-layer sandwich doubly-curved shell where an MEE sheet is integrated with two nanocomposite sheets. In addition, these two nanocomposite sheets are reinforced by functionally graded (FG) distributions of CNT and graphene platelet (GPL)-reinforced composites, respectively. Firstly, the three-dimensional elasticity theory is employed to derive the governing equations of motion. Then, the vibroacoustic analysis for the resultant equations is completed according to the state space and transfer matrix method. Comparing the obtained results with the available literature discloses that the offered procedure has a high precision for structural acoustic problems. In the next step, in addition to inspecting two kinds of MEE composites, the effective parameters, such as layup configuration, FG distribution, volume fraction, weight fraction, radii of curvature, electromagnetic boundary conditions, and interphase thickness, are assessed on the STL. This assessment shows that the parameters involved in this paper are highly interdependent. Accordingly, the analysis of these parameters is done simultaneously with the aid of three- and four-dimensional plots in order that the optimal value for each parameter can be realized. As seen clearly in the outcomes, the electromagnetic boundary conditions parameters, compared to the other parameters, can much more alter the STL trend, so that a slight change in electric potential results in great change in the STL.

Influence of variable‐stiffness layup configuration on curing deformation of curved‐surface structures

AbstractAccurate prediction the curing‐induced deformation is the key to the fabrication of high‐quality composite structures. Aiming at controlling shape distortion of curved‐surface parts during curing process, a layup optimization strategy is proposed based on a variable stiffness (VS) placement method, which uses geodesic curves as fiber‐tow paths. Taking an offset parabolic antenna reflector (PAR) for example, chemical shrinkage and thermal deformation of curved‐surface composites during the curing process and after demolding are modeled. By combining Fourier heat conduction theory, curing kinetics, and generalized Maxwell viscoelastic model, the interactions between chemical cross‐link reaction, heat transfer, and mechanical deformation are taken into account. By comparing the deformation characteristics of VS and traditional constant stiffness structures, the proposed simulation strategy of curing process for composites can predict the factors that influence the curing deformation of VS structures are analyzed. The results show that the maximum of VS PAR decreases by 11.02%, and the average magnitude decreases by 32.35%.

A VAM-based reduced-order model for M-shaped folded core sandwich plates

The added bonding platform of the M-shaped folded core is expected to address the issue of facesheet-core interface debonding in sandwich plates. A two-dimensional reduced-order plate model based on variational asymptotic method is proposed to investigate the effective performance of the original composite sandwich plate with an M-shaped folded core (CSP-MFC). The effective plate properties of CSP-MFC are obtained by constitutive modeling over the unit cell, and inputted into the two-dimensional reduced-order plate model (2D-REM) for global and local analysis. The novelties of cell tailoring and local field recovery within the unit cell are very important features compared to traditional finite element models and significantly facilitate the engineering analysis of CSP-MFC. By comparing the global and local responses of the 2D-REM with those of the three-dimensional refined plate model (3D-RPM) under various boundary conditions, the accuracy and efficacy of the 2D-REM were validated. In addition, a comprehensive investigation of the structural responses to various parameters, including the layup configuration and core geometric parameters (e.g., opening angle, core height, side length, wall thickness, and form of the folded core), was also performed. It was determined that the CSP-MFC with a layup of ± 45 ° / 0 ° / 90 ° s , a larger opening angle and width of the bonding platform, as well as a smaller side length and core height had the most balanced performance. • The effective properties of CSP-MFC can be easily obtained without imposing BCs on the unit cell. • Local field distributions, which cannot be predicted by conventional models, are well captured. • Both linear buckling and nonlinear post-buckling behaviors are accurately predicted by 2D-REM. • The core height has a greater influence on the static displacement and buckling load of CSP-MFC. • The bonding platform reduces the stress concentration between the facesheet and the core layer.

The effect of load eccentricity on the compressed CFRP Z-shaped columns in the weak post-critical state

The study investigated short, thin-walled Z-shaped carbon-epoxy laminate columns. Two multi-layer composite lay-up configurations were tested [0/45/-45/90]s and [90/-45/45/0]s, each consisting of eight symmetric laminate layers. The Z-columns were loaded in compression, and the loading mode included the scenario of force application eccentric to the center of gravity of the column’s cross-section. The modeled boundary conditions corresponded to the ball-jointed support at the end sections of the column. The study set out to determine the effect of loading eccentricity on the buckling mode, the values of the buckling load (the perfect structure), and the critical force (the structure with initial imperfections). The critical force of the real structure was established using the approximation method, based on experimentally determined post-critical equilibrium paths of the structure. For the numerical finite element analysis (FEM), Abaqus software was employed. In the first step, the FEM solved the eigenvalue problem, which lead to establishing the mode of stability loss and the determination of the corresponding bifurcation load for the Z-column subjected to axial and eccentric loading. The second stage of analysis focused on the nonlinear behavior of the structure with initial imperfections. The critical force was derived from the results of approximation based on the numerical post-critical equilibrium paths. The experimental data then served as the base for the validation of the developed numerical models. The findings enabled determining the effect of the compressive load eccentricity on the buckling mode and the critical force values. The project/research was financed in the framework of the project Lublin University of Technology-Regional Excellence Initiative, funded by the Polish Ministry of Science and Higher Education (contract no. 030/RID/2018/19).

Optimization of Composite Cylindrical Shell Structures for Hydrostatic Pressure Loading

Abstract Deep-sea structures will collapse/implode under hydrostatic pressure when the structure dives below an instability threshold, leading to catastrophic failure. To better understand how the layup angle of composite cylindrical shells influences this instability threshold, this work explores how composite cylinders can achieve the highest (optimum) critical collapse pressure under hydrostatic loading conditions. To perform this analysis, a closed-form analytical cylinder buckling solution developed by previous work is used in conjunction with different cylindrical geometrical configurations and composite properties for glass, carbon, and intraply hybrid composite properties for woven and unidirectional structures. The results show that a composite structure's optimum layup configuration is unique to the structure's geometry and material system. However, general trends are observed for these different systems, such as how symmetric and asymmetric constructions place the axial-resistant layers near the neutral plane of the composite system. In addition, both constructions need an increase in shear-resistance layers as the L/D ratio decreases regardless of the material system. Lastly, the analytical approach presented in this work can be used to accurately determine the optimum layup angle for thin composite cylindrical structures that are subjected to external hydrostatic pressure.

Failure behavior of laminated composite plates under anticlastic bending

In this study, the failure behavior of laminated composite plates subjected to anticlastic bending is investigated. Anticlastic bending is a special case of bi-axial out-of-plane loading that produces predominantly twisting moment. A test fixture is designed to actualize anticlastic loading condition. Carbon-fiber-reinforced epoxy composite is selected as the material of the specimens. Totally nine different layup configurations are chosen and at least four specimens are tested for each configuration. Acoustic emission monitoring (AEM) is utilized to detect the first-ply-failure load and the accumulation of damage in the laminates. In this method, elastic waves resulting from initiation and progression of damage are detected, and then AE signals are processed to identify the failure modes and determine the first-ply-failure load. A finite element model is developed to simulate the anticlastic bending test. A code is developed using ANSYS parametric design language to predict the first-ply-failure loads using various failure criteria like Tsai–Wu, Hashin, and Puck. The experimental and numerical results are then compared. Relative strengths and weaknesses of the failure criteria in estimating failure of laminated composite plates under anticlastic bending are discussed.

On the use of Brazilian disk specimen for measuring mixed-mode I/II translaminar fracture toughness of notched glass/epoxy composite laminates: A comprehensive study

In this work, a comprehensive experimental and theoretical study is performed on laminated composites containing V- and U-notch to evaluate the last-ply-failure (LPF) load in mixed-mode I/II loading conditions. Numerous tests are conducted on the composite laminates using the Brazilian disk specimen for the first time. The samples are fabricated of E-glass/epoxy in three different lay-up configurations, namely unidirectional, cross-ply, and quasi-isotropic. Three notch opening angles of 2α = 30°, 60°, and 90° are considered for the V-notched samples, while for both V- and U-notches three notch tip radii of ρ= 1, 2, and 4 mm are taken into account. Four mixed-mode I/II loading angles of β = {0°, 10°, 20°, mode II} and three repetitions for each notch opening angle and composite lay-up configuration lead to an overall of 432 fracture tests in the experimental section of the paper, which can provide a good amount of experimental data set for other researchers. Subsequently, in the analytical section, two stress-based fracture criteria accompanied by the virtual isotropic material concept (VIMC) are employed to estimate the fracture loads theoretically. It is demonstrated that using the VIMC approach can yield accurate predictions, while it has much less computational costs compared to the traditional approaches in the literature.

Tool wear prediction in edge trimming of carbon fiber reinforced polymer using machine learning with instantaneous parameters

Rapid tool wear occurs during the edge trimming of CFRP components due to the high strength and abrasive nature of the carbon fibers, leading to potential surface damage and delamination. This paper presents a hybrid approach by combining the machine learning technique and the physics-based kinematics model for tool wear prediction in edge trimming of CFRP. For edge trimming of unidirectional (UD) CFRP, the feature parameters of the machine learning models consist of the instantaneous fiber cutting angle, uncut chip thickness, and instantaneous radial force instead of the average force of a certain cutting period. The training data from UD CFRP is used to predict the overall radial force in edge trimming of multidirectional (MD) CFRP considering the nonuniform wear length distribution along the tool edge due to different fiber orientation angles of the UD layers. The machined surface, tool edge profile, and chip morphology were examined to demonstrate the nonuniform tool wear length and its effect on surface quality in edge trimming of MD CFRP. The tool wear monitoring in edge trimming of MD CFRPs with various lay-up configurations is achieved without the need for data training experiments on MD CFRP. The predictions from the machine learning methods are compared with experimental results in edge trimming of UD and MD CFRPs. As a result, the proposed method is able to reduce the experimental cost, considering the increased dimensionality if experimental data training of various fiber orientations of UD CFRP and various fiber lay-up configurations of MD CFRP is required.

Damage localization on CFRP composites by electrical impedance tomography

This work exploited the use of electrical impedance tomography (EIT) with one-step difference Gaussian-Newton (GN) algorithm to detect different types of damage on unidirectional carbon fibre/epoxy composite laminates. The major challenge concerning the implementation of EIT on composite materials has to do with their anisotropy. To assess this issue, this study was conducted on carbon fibre composites having different layup configurations with different degrees of anisotropy: a quasi-isotropic layup, to approximate as much as possible these layered materials to an isotropic material, and an unbalanced layup, with further degree of anisotropy. Damage detection in the highly anisotropic unbalanced laminates is a major challenge for EIT technique, which has not been assessed before in the literature. Severe damage, in the form of through-thickness holes, was created in the laminates with different diameters and at two locations of the specimen to evaluate the sensitivity of this technique to damage size and its capacity to detect multiple damages. EIT showed progressive decrease of electrical conductivity as the diameter of through-thickness holes increased. Impact damages of different severities were also created. The EIT technique was able to distinguish different damage shapes in the laminates with different anisotropy. EIT identified elongated shaped damages, produced by impact events of different impact energies, on unbalanced laminates. However, the EIT images overestimate the damaged area, as compared to non-destructive ultrasonic inspections. The EIT images of the quasi-isotropic laminates revealed damage in the central area of the specimens, but a well-defined damage shape could not be distinguished.

Effect of lamina fiber orientation interfaced with semi-flexible adhesive layer on strength and failure mode of composite single-lap joints

Various geometric and material parameters such as adhesive thickness, adhesive overlap, adherend thickness, and composite layup may affect the strength of the joint under quasi-static loading and failure mode of bonded composite-to-composite single-lap joints (SLJs) and are investigated by previous studies. The study herein broadens these findings by looking into the effect of lamina fiber angle adjacent to the adhesive layer on the damage initiation and evolution in detail. In this regard, a composite-to-composite adhesively bonded SLJ with adherends made of E-glass/epoxy composites and [04//θ/03] (where//shows the adhesive location) layups are manufactured and tested under quasi-static tensile loading. The adhesive type is semi-flexible Araldite 2015. Experimental results show that by increasing the fiber angle from 0° to 90°, the shear stress in the adhesive layer is decreased while the peel stress is increased. In examining typical fracture interfaces for each layup configuration, a full description of failure mode assessment is obtained. In particular, the SLJ is modeled in Abaqus using cohesive elements with bilinear traction-separation law. Numerical results indicate that the bilinear cohesive law cannot model the exact load-displacement curve due to semi-flexible behavior of the epoxy adhesive, but it can predict maximum strength precisely. The failure of composite joints is significantly influenced by shear stress.

Composite lay-up configuration effect on double and single sided bonded patch repairs

Understanding the failure modes of damaged or cracked structures and repaired by bonding a composite patch is an essential point to improve its resistance to failure and subsequently extend its service life. In the present study, a 3D finite element analysis using ANSYS software was performed to elucidate the failure modes of the repaired structures by double and single sided bonded composite. The plate is represented by an aluminum plate (Al2024 T3), cracked at the edge and repaired by three types of laminates, with different fiber orientation in order to determine its effect on the repair. The contact interfaces patch-adhesive and aluminum-adhesive were modeled by cohesive zone modeling (CZM) using bilinear interface of delamination (BID) method to determine the failure at the adhesive layer. The obtained results show the importance of the impact of the composite patch fiber orientation on the structure design for suitable repair.

Leakage performance of CFRP laminate under cryogenic temperature: Experimental and simulation study

Leakage rate prediction of carbon fiber reinforced polymer (CFRP) composites for cryogenic propellant tanks has been a challenge for the research community. In this paper, the leakage properties of CFRP laminates with various lay-up configurations are experimentally assessed by measuring their leakage rates under different loads and temperatures. The effects of temperature, cooling conditions and loading on the leakage rates of the above laminate composites are discussed. Meanwhile, in-situ micro X-ray computed tomography (μCT) testing is performed to characterize the internal microstructure evolution of the composites under tension. The geometric morphology and parameters of defects are investigated as well. The propagation of internal cracks in the composites under loading is carefully monitored. A novel 3D image-based model is developed using μCT scans to predict the leakage properties of the composites under various loads. The initiation and propagation leakage rates of laminates, whose values are found to be within the same order of magnitude as experimental ones. The proposed simulation method allows one to quickly calculate the image-based leakage model suitable for the prediction of leakage performance and the lay-up design of composite cryogenic propellant tanks under cryogenic temperatures.

Fatigue life prediction and optimization of GFRP composites based on Failure Tensor Polynomial in Fatigue model with exponential fitting approach

In this study, a new fatigue life prediction and optimization strategy utilizing the Failure Tensor Polynomial in Fatigue (FTPF) model with exponential fitting and numerical bisection method for fiber reinforced polymer composites has been proposed. Within the experimental stage, glass/epoxy composite laminates with [Formula: see text], [Formula: see text], and [Formula: see text] lay-up configurations were fabricated, quasi-static and fatigue mechanical behavior of GFRP composites was characterized to be used in the FTPF model. The prediction capability of the FTPF model was tested based on the experimental data obtained for multidirectional laminates of various composite materials. Fatigue life prediction results of the glass/epoxy laminates were found to be better as compared to those for the linear fitting predictions. The results also indicated that the approach with exponential fitting provides better fatigue life predictions as compared to those obtained by linear fitting, especially for glass/epoxy laminates. Moreover, an optimization study using the proposed methodology for fatigue life advancement of the glass/epoxy laminates was performed by a powerful hybrid algorithm, PSA/GPSA. So, two optimization scenarios including various loading configurations were considered. The optimization results exhibited that the optimized stacking sequences having maximized fatigue life can be obtained in various loading cases. It was also revealed that the tension-compression loading and the loadings involving shear loads are critical for fatigue, and further improvement in fatigue life may be achieved by designing only symmetric lay-ups instead of symmetric-balanced and diversification of fiber angles to be used in the optimization.

Assessment of four-variable refined shear deformation theory for low-velocity impact analysis of curved sandwich beams

In this paper, the accuracy of the four-variable refined global-local (FRGL) shear deformation theory in the prediction of dynamic responses of curved sandwich beams under low-velocity impact has been investigated. The governing equations of motion of the curved sandwich beams are derived by employing a finite element (FE) model based on FRGL shear deformation theory. By using the method of truncated superimposition of modes, the size of the total dynamic system is firstly reduced. Then, the resulting dynamic system is solved via the state-space (SS) approach. For validation, curved sandwich beams with various deepness ratios and different boundary conditions are analyzed using the proposed model. Different materials and lay-up configurations were assumed for the face-sheets. The obtained results are validated through comparison with the results of ABAQUS simulations and other analytical and numerical results reported in the open literature. The comparisons show that the FRGL shear deformation theory in conjunction with the truncated reduced modal SS approach is a precise and computationally low-cost model for solving the dynamic problems of curved sandwich beams under impact loads.

Tailoring the Local Design of Deep Water Composite Risers to Minimise Structural Weight

Following the rising technological advancements on composite marine structures, there is a corresponding surge in the demand for its deployment as ocean engineering applications. The push for exploration activities in deep waters necessitates the need for composite marine structures to reduce structural payload and lessen weights/loads on platform decks. This gain is achieved by its high strength–stiffness modulus and light-in-weight attributes, enabling easier marine/offshore operations. Thus, the development of composite marine risers considers critical composite characteristics to optimize marine risers’ design. Hence, an in-depth study on composite production risers (CPR) is quite pertinent in applying composite materials to deep water applications. Two riser sections of 3 m and 5 m were investigated under a 2030 m water depth environment to minimise structural weight. ANSYS Composites ACP was utilized for the CPR’s finite element model (FEM) under different load conditions. The choice of the material, the fibre orientation, and the lay-up configurations utilised in the modelling technique have been reported. In addition, the behaviour of the composite risers’ layers under four loadings has been investigated under marine conditions. Recommendations were made for the composite tubular structure. Results on stresses and weight savings were obtained from different composite riser configurations. The recommended composite riser design that showed the best performance is AS4/PEEK utilising PEEK liner, however more work is suggested using global design loadings on the CPR.

Translaminar notch fracture toughness expressions for composite laminates

First, two different test specimens, namely the rectangular tension (RT) and semi-circular bend (SCB) specimens, weakened by U-notches of various notch tip radii and made of E-glass/epoxy composite laminates of different lay-up configurations, are considered for measuring experimentally the translaminar notch fracture toughness (TLNFT) of the composite material under pure mode I loading conditions. Then, two new closed-form expressions are proposed for the TLNFT, by taking advantages of the maximum tangential stress (MTS) and the mean stress (MS) criteria, as well as the recently proposed virtual isotropic material concept (VIMC), with the goal to estimate the experimental results. It is found that both criteria can well estimate the test results that locate always between the predictions of MTS and MS criteria. Taking into account that MTS criterion is more conservative and simpler than MS criterion, it is preferred in mechanical design of notched E-glass/epoxy composite structures.

U-notch fracture in additively manufactured ABS specimens under symmetric three-point bending

This paper aims to investigate the fracture behavior of U-notched semi-circular bend (USCB) specimens fabricated from the Acrylonitrile Butadiene Styrene (ABS) using the fused deposition modelling (FDM) method under opening-mode loading. The notched specimens are manufactured with different notch tip radii and various unidirectional layup configurations for which the fracture loads are experimentally acquired by conducting fracture tests under symmetric three-point bending. Some additional tests are also performed on cracked and plain tensile specimens to obtain the fracture toughness and tensile properties of the ABS material. With the goal of estimating the fracture loads theoretically, the recently proposed virtual isotropic material concept (VIMC) is linked to three different brittle fracture models, namely the point-stress (PS), mean-stress (MS), and averaged strain energy density (ASED) criteria. Comparing with the experimental results, it is shown that the VIMC-MS criterion is generally the best model among the three ones, while VIMC-PS criterion gives fair results and VIMC-ASED criterion is excellent only for larger notch tip radii. The crack growth path of the mentioned samples as well as their type of failure is also evaluated. It is revealed that the unidirectional USCB samples with 0, 30, and 45 degrees layup configurations experience inter/cross-laminar fracture, while those with 60 and 90 degrees layups experience inter-laminar fracture.

Experimental validation of inertial twist concept for rotor blade application

The present study performs a set of static tests to demonstrate a novel passive morphing concept. The concept introduces a bend–twist coupled composite spar to rotor blades, allowing for twist morphing to be achieved by imposing a lagwise bending moment using centrifugal forces produced by a movable mass at the blade tip. First, three composite spars are fabricated using a symmetric layup configuration with varied ply orientations. A set of static tests are designed to replicate the effect of the centrifugal forces during rotation, where the detailed distribution of twist, deflection and strain are measured on each spar with varied loading conditions. The experimental results suggest that the blade twist can be well controlled by the position of the tip mass and rotational speed. It was also found the distribution of the twist is linear when the spar deflection is small, whereas a quadratic twist distribution was observed for a large tip deflection due to the induced lateral restoring forces. Furthermore, the influence of the ply angle upon the coupled twist is demonstrated from the experimental and numerical results.

Experimental study of the effect of temperature and velocity in channel forming of polyvinyl chloride composite reinforced by 3D-fiberglass with an aluminum middle layer

In this paper, the stamp forming process of a U-shaped cross-section channel with sharp corners of composite laminates including aluminum sheet and polyvinyl chloride (PVC) reinforced with 3D-fiberglass was investigated. The laminates were produced by manual layup and arrangement of fibers with different angles of [0°/90°] and [± 45°] degrees using hot press. The process of forming composite samples was carried out at temperatures of 25, 80, 120, 160°C and different velocities of punch. The effect of parameters including layup configuration, temperature, and forming speed on the spring-back of the formed laminates and the required forming force were evaluated. The results showed that as the forming temperature increased, the forming force decreased sharply. The lowest forming force was obtained for the laminate with [± 45°, Al, ± 45°] layout at 160°C temperature which was equal to 0.7KN. Also, with the increase in temperature, the spring-back angle has been reduced, the lowest of which is obtained with the laminate with [0°/90°] 3 layout equal to 8 degrees. Finally, it was concluded that increasing the speed of the forming process results in a decrease in the spring-back angle and this effect is more pronounced at higher temperatures.Graphical abstract