Thick Composite Panels Research Articles

Low velocity impact and compression after impact of thin and thick laminated carbon fiber composite panels

This study explores the impact behavior of thin and thick composite panels, yielding insights into their behavior under increasing impact energies. Thin composite specimens demonstrated limited surface damage tolerance, while thicker panels remained visually intact but suffered internal damage, adversely affecting their compressive load capacity. The study shows a robust correlation between impact energy and key measurements, including dent depth, bottom surface matrix splitting, and internal delaminations. Moreover, the research identified a consistent pattern in damage initiation, showing that the onset of matrix splitting and delamination remained relatively constant regardless of increasing impact energy, emphasizing the predictability of damage initiation. Compression after impact study showed distinctive responses between thin and thick composites. Thin composites exhibited global buckling before final failure, with a gradual reduction in peak load-carrying capability as damage escalated. In contrast, thick composites suffered substantial damage and delamination at higher impact energies, leading to significant losses, up to 60%, in residual compressive load capacity. The study introduces a simplified quasi-static model to capture delamination effects on panel responses to low-velocity impacts. This study contributes significantly to understanding composite materials’ impact behavior, providing essential knowledge for practical applications and future research endeavors.

Vibrational behavior of a 3D printed biomimetic dual‐core composite sandwich beam: An experimental and numerical study

AbstractComposite sandwich structures have been used in various applications like aerospace, automotive, and maritime sectors. The process of identifying the core design and the selection of a prominent core is crucially important in sandwich structures. In this study, biomimetic core development and vibration responses of composite sandwich beams with a dual biomimetic honeycomb core are investigated. The composite face layers are fabricated by the hand lay‐up method, and the fused deposition modeling is used to 3D print the PLA honeycomb cores. Based on ASTM‐E1876 and the alternative dynamic approach, the face layer elastic properties and rigidity modulus of the cores are evaluated, respectively. The numerical simulation is used to predict the sandwich panels' natural frequencies and mode shapes and verified with experimental results. There was an excellent agreement between the calculated and experimental natural frequencies. Due to the presence of the core and enhanced rigidity modulus, the dual lamellar honeycomb core sandwich beam produces the highest natural frequencies among all‐composite sandwich beams, followed by the dual regular honeycomb, single lamellar honeycomb, and single regular honeycomb cores. The geometric parametric studies, including core thickness, length‐to‐breadth ratio, lamination schemes, support conditions, and transverse vibration responses were also analyzed for different sandwich patterns. As a result of this work, thick composite sandwich panels in aeronautical and marine structures can be replaced with dual biomimetic core structures. The study highlights the fact that the dual‐core sandwich beam provided greater modal frequency than the single‐core beam with the same weight proportions.Highlights Pistachio nut shell‐based biomimetic honeycomb core has been developed. Alternative dynamic approach is used to find sandwich‐core shear properties. Lamellar‐infused biomimetic model yields higher shear modulus and stiffness. Dual‐core beam having high flexural stiffness enhances the natural frequency. Various parametric studies were analyzed for different sandwich patterns.

On a hybrid updating method for modeling vibroacoustic behaviors of composite panels

Composite panels, by virtue of their outstanding mechanical properties, have found various applications in different sectors like aerospace and transportation. Under certain assumptions like Kirchhoff–Love and Mead–Markus hypotheses, certain high-order differential equations can be used for vibroacoustic modeling of composite panels. However, for accurate modeling, updating parameters is an essential stage. Herein, we aim to theoretically and experimentally review this stage. For this purpose, a hybrid updating method is proposed, incorporating hierarchical functions, inhomogeneous wave correlation approach, and least squares optimizations. Then various laboratory measurements, including Laser Doppler Vibrometry measurements as well as sound pressure levels, are analyzed. The measurements were performed for a thick composite (sandwich) panel, and a thin composite (laminate) one, along with two isotropic (steel and aluminum) plates for additional validation. The experiments indicate the ability of the hybrid approach to adjust parameters and precisely model vibroacoustic behaviors of the panels. Furthermore, the proposed hybrid method can be used in studies whose goal is accurate vibroacoustic modeling for psychoacoustic issues and perceptual validations, which is also one of the future targets of this research.

Online optimisation and active control of the cure process of thick composite laminates

This paper addresses the development of an active control tool for the in-situ optimisation of the cure process of thick composite parts. The methodology integrates a cure process model with real time monitoring data exploring potential temperature dwells that accelerate the curing while avoiding undesirable thermal gradients. The cure process simulation is based on a Finite Element (FE) model solution validated in the curing of a thick composite flat panel with an average absolute error of about 1.8 °C. The active control tool interacts PID controller of an oven setting a new cure temperature periodically. The implementation of active control tool during the curing of a thick carbon fibre/epoxy cable has the capability to determine in real time optimal solutions minimising process duration whilst also satisfying constraints in temperature overshoot. A process duration reduction of about 70 % can be achieved compared to a nominal cure cycle with a maximum temperature overshoot lower than 9 °C. The active control tool can replace off-line optimisation tools exploiting in situ with real time monitoring to drive the process and minimise the effects of uncertainty.

Elucidating the Sound Absorption Characteristics of Foxtail Millet (Setariaitalica) Husk.

The current study deals with the analysis of sound absorption characteristics of foxtail millet husk powder. Noise is one the most persistent pollutants which has to be dealt seriously. Foxtail millet is a small seeded cereal cultivated across the world and its husk is less explored for its utilization in polymer composites. The husk is the outer protective covering of the seed, rich in silica and lingo-cellulose content making it suitable for sound insulation. The acoustic characterization is done for treated foxtail millet husk powder and polypropylene composite panels. The physical parameters like fiber mass content, density, and thickness of the composite panel were varied and their influence over sound absorption was mapped. The influence of porosity, airflow resistance, and tortuosity was also studied. The experimental result shows that 30-mm thick foxtail millet husk powder composite panel with 40% fiber mass content, 320 kg/m3 density showed promising sound absorption for sound frequency range above 1000 Hz. We achieved noise reduction coefficient (NRC) value of 0.54. In view to improve the performance of the panel in low-frequency range, we studied the efficiency of incorporating air gap and rigid backing material to the designed panel. We used foxtail millet husk powder panel of density 850 kg/m3 as rigid backing material with varying air gap thickness. Thus the composite of 320 kg/m3 density, 30-mm thick when provided with 35-mm air gap and backing material improved the composite’s performance in sound frequency range 250 Hz to 1000 Hz. The overall sound absorption performance was improved and the NRC value and average sound absorption coefficient (SAC) were increased to 0.7 and 0.63 respectively comparable with the commercial acoustic panels made out of the synthetic fibers. We have calculated the sound absorption coefficient values using Delany and Bezlay model (D&B model) and Johnson–Champoux–Allard model (JCA model) and compared them with the measured sound absorption values.

The Investigation of Hole Delamination in Drilling Kevlar Composite Panel Using HSS Drill Tool

The drilling process has been mostly used in composite panel machining to be a final product. It becomes a critical process when the composite product requires a high hole precision for the purpose of assembly and quality standard. Machining Kevlar composite is a difficult task due its hardness, fiber layer bounding and fiber orientation. The cutting condition needs to be controlled carefully to minimize the vibration, cutting temperature and hole delamination. This paper discusses the investigation of hole delamination in drilling Kevlar composite panel. The twist drill type of High-Speed Steel (HSS) drilling tool with 12 mm diameter was used to drill a 4 mm thick Kevlar composite panel. Three levels of spindle speed (1000 rpm, 1400 rpm and 2000 rpm) and three levels of feed rate (130 mm/min, 160 mm/min and 180 mm/min) were selected as the configuration of cutting condition. The hole diameter was measured and was compared to the drill tool diameter. The result of the experiment shows that the cutting condition gave significant effect to the drill hole delamination factor. The highest delamination factor was 1.36 and achieved by drilling condition with spindle speed of 1000 rpm and feed rate of 160 mm/min. The lowest delamination factor was 1.161 and achieved by drilling condition with spindle speed of 2000 rpm and feed rate of 130 mm/min.

Out-Of-Plane Permeability Evaluation of Carbon Fiber Preforms by Ultrasonic Wave Propagation.

Out-of-plane permeability of reinforcement preforms is of crucial importance in the infusion of large and thick composite panels, but so far, there are no standard experimental methods for its determination. In this work, an experimental set-up for the measurement of unsaturated through thickness permeability based on the ultrasonic wave propagation in pulse echo mode is presented. A single ultrasonic transducer, working both as emitter and receiver of ultrasonic waves, was used to monitor the through thickness flow front during a vacuum assisted resin infusion experiment. The set-up was tested on three thick carbon fiber preforms, obtained by stacking thermal bonding of balanced or unidirectional plies either by automated fiber placement either by hand lay-up of unidirectional plies. The ultrasonic data were used to calculate unsaturated out-of-plane permeability using Darcy’s law. The permeability results were compared with saturated out-of-plane permeability, determined by a traditional gravimetric method, and validated by some analytical models. The results demonstrated the feasibility and potential of the proposed set-up for permeability measurements thanks to its noninvasive character and the one-side access.

Nonlinear Dynamic Responses of Shear-Deformable Composite Panels under Combined Supersonic Aerodynamic, Thermal, and Random Acoustic Loads

The skin panel structures of vehicles in supersonic flights are subjected to combined thermal, acoustic, and aerodynamic loads. These combined loads may cause a nonlinear dynamic response of the high-speed flight vehicle’s panel structures. Among these nonlinear dynamic responses, the snapthrough and limit cycle oscillation response seriously affect the fatigue failure of the panel structures. This work investigates the nonlinear dynamic responses using the numerical method, when combined supersonic aerodynamic, thermal, and random acoustic loads are applied to the panel structures simultaneously. To consider the thin and thick composite panels, the first-order shear deformation plate theory (FSDT) and the von Karman nonlinear displacement–strain relationship are applied. The aerodynamic load in the supersonic flow is modeled using the first-order piston theory. The thermal load distribution is assumed constant in the thickness direction of the composite panel. The random acoustic load is represented as stationary white-Gaussian random pressure with zero mean and uniform magnitude over the panels. The nonlinear equations of motion of the composite panel under combined loads are derived using the principle of virtual work and the finite element method. The static displacement, which is the solution of the nonlinear static equation, is calculated using the Newton–Raphson method, and the nonlinear dynamic equation is solved using the Newmark-β time integration method. Using these numerical methods, the nonlinear dynamic analyses are conducted under various loading conditions such as thermal–random acoustic loads, thermal–supersonic aerodynamic loads, and supersonic aerodynamic–thermal–random acoustic loads. Numerical results show the nonlinear dynamic response of the composite thin and thick panels such as snapthrough and limit cycle oscillation responses. Particularly, the snapthrough response is caused when the random acoustic load is applied appropriately to the thermally buckled composite plate when the aerodynamic load is not applied or applied with the relatively small magnitude of the dynamic pressure.

Simulating the sound transmission loss of complex curved panels with attached noise control materials using periodic cell wavemodes

The sound transmission loss of complex curved aircraft panels under diffuse acoustic field excitation is experimentally and numerically studied. Two different aircraft sidewall panels are considered: a thick composite sandwich panel and a thin aluminium panel with stiffening elements (stringers and frames). Both bare configuration and with attached soundproofing material are tested in laboratory conditions in coupled rooms. The numerical approach relies on a wave finite element method including modal order reduction at cell scale and an extension based on the transfer matrix method, for the inclusion of poroelastic treatments. The results obtained show that the proposed numerical scheme is efficient for predicting the sound transmission loss of such complex structures.

Enhanced mechanical properties at 400 °C of carbon fabric reinforced phthalonitrile composites by high temperature postcure

Phthalonitrile resins have received growing attention due to their superior thermal stability and good structural properties required for high temperature applications in aerospace industry etc. In this work, a newly developed phthalonitrile blend resin with an appropriate viscosity for autoclave processing is employed for manufacturing of high quality void-free thick composite panels using MT300 carbon fabrics. In particular, the effects of postcure temperature are systematically examined on their 400 °C mechanical properties required for high temperature structural applications. Dynamic mechanical analysis reveals that the composite postcured at the high temperature of 375 °C exhibits a high glass transition temperature over 450 °C. Mechanical testing results show that the flexural and compressive strengths at room temperature are lowered by the high temperature postcure, but their counterparts at 400 °C are obviously enhanced by the postcure. Moreover, the 400 °C interlaminar shear strength initially decreases but then increases with increasing the postcure temperature. The char retention in nitrogen at 1000 °C is 89% of its initial weight. Consequently, the newly developed phthalonitrile resin is highly promising for manufacturing of thermal resistant polymeric composites for high temperature application in aerospace industry etc. that need composites to have high temperature capabilities.

Design and Fabrication of Aluminum Cladding and Curtain Wall of a Sports Club

The paper discusses the design, fabrication and the execution of the cladding supported by steel trusses and curtain wall of a sports club. The cladding and the curtain walls were subjected to a wind load of 1.2 Kpa considering basic wind speed of 25 m/s as per the project specifications. The first part of the paper deals with the cladding work of the canopy that consist of a 4 mm thick aluminium composite panels supported by steel trusses extended from the main structure. Two types of steel trusses were provided, the main truss connected to the space truss, whereas the intermediate truss connected to channels. Both trusses were spaced at 2.5 m centre to centre. These trusses were fabricated at factory and transported to the site for installation. The second part of the paper is related to the curtain wall design having Maximum Mullion spacing of 2 m, considered as worst scenario for the design calculations. The maximum Mullion height was 5.55 m, adopted in the calculations with bottom and top pinned connection. The Technal system was adopted for the design of mullions and transoms. Design was carried out using numerical modeling with CSI SAP2000 for cladding and its supporting structures. The bracket was realized and checked for the corresponding induced forces. All the structural systems were found safe according to different acceptance criterion.

Free edge stress prediction in thick laminated cylindrical shell panel subjected to bending moment

• A Galerkin based Layer-wise formulation is presented for thick composite panel subjected to bending moment. • An analytical solution is presented for governing equations of the panel considering free edge conditions. • Free edge stresses in bending of thick panel with general layer stacking is studied for the first time. • The predictions satisfy the free edge and free surface conditions. • The effect of geometrical parameters and layer stacking are investigated. A thick composite cylindrical shell panel with general layer stacking is studied to investigate the free edge and 3D stresses in the panel which is subjected to pure bending moment. To this aim, a Galerkin based layerwise formulation is presented to discretize the governing equation of the panel to ordinary differential equations. Employing a reduced displacement field for the cylindrical panel, the governing equations for thick panel are developed in terms of displacements and a set of coupled ordinary differential equations is obtained. The governing equations are solved analytically for free edge boundary conditions and applied pure bending moment. The accuracy of numerical results is examined and the distribution of interlaminar and in-plane stresses is studied. The free edge stresses are studied and the effect of radius to thickness ratio, width to thickness ratio and layer stacking on the distribution of stresses is investigated. The focus of numerical results is on the prediction of boundary layer and free edge stress distribution.

Experimental Testing and Numerical Modeling of Ballistic Impact on S-2 Glass/SC15 Composites

The work presented in this paper details both an experimental program and an associated numerical modeling effort to characterize and predict the ballistic response of S-2 glass/SC15 epoxy composite panels. The experimental program consisted of ¼ inch diameter soft carbon steel spheres impacting ¼ and ½ inch thick flat composite panels at velocities ranging from 220 to 1570 m/s. High speed cameras were used to capture the impact event and resulting residual velocity of the spheres for each test configuration. After testing, each panel was inspected both visually and with ultrasonic C-scan techniques to determine the extent and depth of damage imparted on the panel by the impactor. The numerical modeling efforts utilized the anisotropic multi-constituent composite model (MCM) within the CTH shock physics hydrocode. The MCM model allows for evaluation of damage at the constituent level through continuum averaged stress and strain fields. The model also accounts for the inherent coupling of the equation of state and strength response that occurs in anisotropic composite materials. Finally, the simulation results are compared against the experimentally measured residual velocity as a quantitative metric and against the measured damage extent and patterns as a qualitative metric. The comparisons show good agreement in residual velocity and damage extent.

Combined experimental/numerical investigation of directional moisture diffusion in glass/epoxy composites

A combined experimental and numerical investigation is conducted on the anisotropic water diffusion behaviour of unidirectional glass/epoxy composites. Experimental diffusivity values are obtained by immersing thin material slices for each of its planes of orthotropy extracted from a thick composite panel and interphase measurements are performed using thermal analysis. In order to elucidate the observed anisotropy, the diffusion process is modelled at the microscale using a representative volume element (RVE) of the material with random fibre distribution. Water concentration gradients are applied to the micromodel and a homogenisation procedure is used to retrieve the macroscopic diffusivity coefficients. The influence of the interphase around the fibres on the diffusion process is modelled by making the matrix diffusivity a function of the distance to the nearest fibre using a level set field. The models are used to fit the experimental data and test a number of hypotheses that may explain the observed anisotropy. The effect of fibres acting as barriers for water movement is found to partially explain the observed transverse diffusivity. However, a fit is only obtained by allowing faster diffusivity at the interphase. In the longitudinal direction, a fit can only be found by allowing for orthotropic interphase diffusivity.

Evaluation of a hybrid TMM-SEA method for prediction of sound transmission loss through mechanically coupled aircraft double-walls

This paper presents a detailed experimental validation of a hybrid TMM (transfer matrix method)/SEA (statistical energy analysis) method to predict the sound transmission through mechanically coupled aircraft double-walls. The accuracy of the model is investigated using lightweight structures representative of a composite aircraft fuselage cross-section over a large frequency band. The studied structure is composed of a thick composite sandwich panel representative of primary structure, lined with an acoustic insulation layer (glass wool), and structurally connected via vibration isolators to a thin composite sandwich lining panel representative of an interior trim panel. Three types of vibration isolators are considered: a soft, stiff and rigid mechanical links. Results show that the transfer matrix model is able to predict changes in the overall transmission caused by different structural couplings. Modelling limitation is mainly traced to the uncertainties in the measurement of the dynamic stiffness of vibration isolators which are directly propagated to the coupling loss factor and, therefore, to the transmission loss.

Edge stresses analysis in thick composite panels subjected to axial loading using layerwise formulation

Based on a reduced displacement field, a layer-wise (LW) formulation is developed for analysis of thick shell panels which is subjected to axial tension. Employing the principle of minimum total potential energy, the local governing equations of thick panel which is subjected to axial extension are obtained. An analytical method is developed for solution of the governing equations for various edge conditions. The governing equations are solved for free and simply supported edge conditions. The interlaminar stresses in the panel are investigated by means of Hooke's law and also by means of integration of the equilibrium equations of elasticity. Dependency of the result upon the number of numerical layers in the layerwise theory (LWT) is studied. The accuracy of the numerical results is validated by comparison with the results of the finite element method and with other available results in the open literature and good agreement is seen between the results. Numerical results are then presented for the distribution of interlaminar normal and shear stresses within the symmetric and un-symmetric cross-ply thick panels with free and simply supported boundaries. The effects of the geometrical parameters such as radius to thickness and width to thickness ratio are investigated on the distribution of the interlaminar stresses in thick panels.

Information criteria and selection of vibration models

This paper presents a method of determining an appropriate equation of motion of two-dimensional plane structures like membranes and plates from vibration response measurements. The local steady-state vibration field is used as input for the inverse problem that approximately determines the dispersion curve of the structure. This dispersion curve is then statistically treated with Akaike information criterion (AIC), which compares the experimentally measured curve to several candidate models (equations of motion). The model with the lowest AIC value is then chosen, and the utility of other models can also be assessed. This method is applied to three experimental case studies: A red cedar wood plate for musical instruments, a thick paper subjected to unknown membrane tension, and a thick composite sandwich panel. These three cases give three different situations of a model selection.

Visualization and simulation of a linear explosive-induced pyroshock wave using Q-switched laser and phased array transducers in a space launcher composite structure

During space flights, pyrotechnic devices are used for various purposes such as separation of boosters, satellites, fairings, and stages. In particular, the prediction of high shock structural response induced by linear explosives is important for safe operation of pyrotechnic devices. In general, repetitive explosive testing using distributed accelerometers is widely used, but multiple test structures are usually necessary because they are easily damaged and not reusable. This paper pertains to a nondestructive technology to replace the damage-causing, time-consuming, expensive, dangerous, and low-repeatability explosive test with a laser-induced shock test. The method proposed in this paper predicts nondestructively the linear explosive-induced pyroshock wave, visualizes its propagation, and allows the simulation of some detonation conditions. A ballistic test based on a linear explosive and noncontact laser Doppler vibrometer (LDV) as well as a nondestructive pyroshock test using laser-induced shock and PZT array sensors is performed in a 12.68-mm thick composite sandwich panel. The optimal laser-induced shock experimental conditions to predict real pyroshock response spectra (SRSs) are investigated by controlling the optical characteristics of the laser beam and adjusting the frequency bands in signal acquisition. The similarity of the SRS of the conditioned laser-induced shock to that of the real explosive pyroshock is evaluated with the mean acceleration difference. Next, the experimentally-determined optimal conditions are applied to arbitrary points in the laser-induced shock scanning area. Finally, it is shown that the proposed method will allow nondestructive and quantitative pyroshock testing, pyroshock wave propagation visualization showing the direction and magnitude of principal wave propagation, and detonation speed simulation depending on explosive type and detonation initiation point and direction.

Study into causes of damage to carbon epoxy composite material during the drilling process

There is increasing interest from industry in the machining of composite materials, especially the drilling of thick composite panels and of multi-material assemblies. Damage to laminates due to drilling has an influence on the resistance of plates to the various stresses applied to the structure. The present paper aims firstly to highlight the different defects generated by drilling thick carbon epoxy plates at the entry, on the wall and on the whole exit. Following this, the main aim of this work is the observation in the real time of the initiation and the propagation of such defects. This enables to understand and to show the causes of these defects and then allow operating procedures to be proposed that are likely to reduce such damage.

Enhancement of Ultrasonic C-Scan Images for Inspection of Multi-Layered Composite Panels

One of the serious problems that make the flaw identification in a multi-layered thick composite panel more difficult is the interference effect of the upper layer. To take care of such a problem, here we propose an image enhancement approach that can get rid of such an interference effect to ultrasonic C-scan images by a normalization of the acquired signals by a reference signals, and demonstrate its performance in the experiments. Specifically, three specimens with artificial flaws are prepared and ultrasonic C-scan images are acquired experimentally to eliminate the undesired interference effect. Great successes are observed in the present study demonstrating the high potential of the proposed algorithm as a practical image enhancement tool in many practical situations.