Carbon Fiber Composite Sandwich Panels Research Articles

Investigation of carbon nanotube reinforcement to polyurethane adhesive for improving impact performance of carbon fiber composite sandwich panels

In this study, the development of a polyurethane adhesive by using carbon nanotubes (CNT) to enhance the low-velocity impact behavior of aluminum honeycomb sandwich composite structures was investigated. The interaction of CNT and polyurethane for the impact behavior of sandwich composite panels is the main originality of this paper. The fabrication of carbon fiber reinforced composite (CFRC) sandwich structures was conducted using different polyurethane (PU) adhesives and different honeycomb cell sizes. CFRC sandwich structures were fabricated with multi-walled carbon nanotube (MWCNT) added and neat PU adhesives, 6.78 and 10.39 mm honeycomb cell sizes, and carbon fiber prepregs. Neat and nanotube added PU adhesives with MWCNT at reinforcement of 0.1% and 0.2% by weight percent were prepared. Sandwich composite panels were manufactured using the hot pressing method. Specimens of 100 × 100 mm were cut from the sandwich panels, and low-velocity impact tests were conducted at 100 J initial impact energy according to ASTM D7136 standard. After experiments, load-deflection curves, load-time, and energy-time histories were acquired. The absorbed energy values at maximum load were evaluated as a function of MWCNT content and honeycomb cell size. Specimens were sectioned from the impacted region and scanned using scanning electron and optical microscopes to analyze the damaged area. Specimens with MWCNT reinforced adhesives carried higher maximum loads compared to neat ones. CFRC sandwich structures with MWCNT added PU adhesives exhibited a 6% higher impact resistance at 100 J energy levels. Experimental results demonstrated that an increase in MWCNT loading and a decrease in PU adhesive cell size increased the maximum load values in CFRC sandwich panels. Among the nanotube added adhesives, 0.1 wt percent showed the best impact performance.

Preparation and sound transmission loss analysis of carbon fiber composite sandwich panel

Preparation and sound transmission loss analysis of carbon fiber composite sandwich panel

High-force dynamic mechanical analysis of composite sandwich panels for aerospace structures

High-force dynamic mechanical analysis (DMA) has enabled the non-destructive evaluation of thermo-mechanical properties for highly stiff structures over a range of loading frequencies, allowing for additional insight not provided by commonly used static and impact test procedures. In this study, carbon fiber composite sandwich panels with both aluminum and aramid honeycomb cores are characterized based on application conditions in the airframe structure of a high-performance two passenger aircraft. The relative stiffness and damping ability across critical flight frequencies (1 – 100 Hz) for different panel cores are compared. It is found that the damping of the composite sandwich panels is dependent on the applied static load as well as the core material used. Temperature sweeps are also conducted and found to be capable of detecting differences in the glass transition temperature of the composite face sheet matrix material based on post-curing procedures of the manufactured panels.

Investigation on the shear behaviors of carbon fiber composite sandwich panels with the X-core

In-plane shear response of an all-composite X-core sandwich panel was investigated experimentally, numerically and analytically in this paper. The shear experiments of the X-core sandwich panels with three different relative densities were performed and the delamination on the joint and web was the dominant failure mode. Finite element analysis were conducted to further investigate the large deformation and progressive failure of the X-core sandwich panels under in-plane shear loading. The numerical models can correctly simulate the initiation and extension of the delamination and the predictions for the shear response were in good agreement with experiments. A theoretical model based on a modified Reddy zig-zag laminated beams theory and a spring model for the joint were employed to forecast the shear mechanical properties. The analytical results indicated the member shear deformation and joint stiffness had significant effects on the shear modulus and had a reasonable agreement with the experimental results.

Temperature effects on the compressive properties and failure mechanisms of composite sandwich panel with Y-shaped cores

The effects of temperature on the mechanical properties and failure mechanisms of composite sandwich panel with Y-shaped cores under out-of-plane compression have been studied in this paper. The carbon fiber composite sandwich panel with Y-shaped cores was manufactured by a hot-press method using unidirectional carbon/epoxy prepregs. The out-of-plane compression tests of composite sandwich panels were conducted at temperatures ranging from 20 °C to 200 °C. Then the stress-strain curves, failure modes, compressive stiffness and strength of composite sandwich panel at high temperatures were analyzed and compared with those ones at room temperature. The results have shown that temperature had a significant effect on mechanical properties and failure behaviors of composite sandwich panel. And high temperature resulted in the decreasing of compressive stiffness and strength. Finally, the analytical expressions were presented to predict the compressive stiffness and strength of composite sandwich panel and compared with experimental results at different temperatures.

Compression and shear response of carbon fiber composite sandwich panels with pyramidal truss cores after thermal exposure

ABSTRACTThe composite pyramidal truss core sandwich panels with reinforced joints are manufactured by the water jet cutting and interlocking assembly method. The effect of thermal exposure on the out-of-plane compression and shear performances of composite sandwich panels is investigated experimentally. In particular, the out-of-plane compression and shear moduli and strengths of the structures after thermal exposure are predicted theoretically. Experimental results show that the out-of-plane compression and shear performances of composite pyramidal truss core sandwich panels first increase and then decrease with thermal exposure temperature at the thermal exposure of 6 h. The failure modes depend on the particular temperature and time of the applied thermal exposure. As well, the compression and shear performances first increase and then decease with thermal exposure time at 150°C. However, their compression and shear performances have a decreasing tendency with time for a given 230°C exposure temperature. In addition, the destruction responses of composite sandwich panels are also investigated and their possible failure modes (including the crushing, delamination and local buckling of struts) are complemented with the analytic results.

Experimental and numerical study of flatwise compression behavior of carbon fiber composite sandwich panels with new lattice cores

In this experiment, improvement of mechanical strength peak of fiber/epoxy sandwich panels with lattice cores in combination with their lightweight was investigated. In this regards, the method of VARTM (Vacuum Assisted Resin Transfer Molding) was used in order to achieve a laminate without any fault. Then, a unique design was presented to sandwich panel cores. The study of force curves against extension obtained from sandwich panel compression tests, showed that an optimum mechanical strength with a considerable lightweight. The accuracy of experimental data was evaluated by modeling of samples in ABAQUS software at the end of this study. The comparison between the results of experimental and finite element indicated that there was a good agreement between those which implies that the FE simulation can be used instead of time-consuming experimental procedures to study the effect of different parameters on the mechanical properties of lattice sandwich composites in the elastic range.

Effects of thermal exposure on mechanical behavior of carbon fiber composite pyramidal truss core sandwich panel

An experimental study was performed to investigate the effect of high temperature exposure on mechanical properties of carbon fiber composite sandwich panel with pyramidal truss core. For this purpose, sandwich panels were exposed to different temperatures for different times. Then sandwich panels were tested under out-of-plane compression till failure after thermal exposure. Our results indicated that both the thermal exposure temperature and time were the important factors affecting the failure of sandwich panels. Severe reductions in residual compressive modulus and strength were observed when sandwich panels were exposed to 300°C for 6h. The effect of high temperature exposure on failure mode of sandwich panel was revealed as well. Delamination and low fiber to matrix adhesion caused by the degradation of the matrix properties were found for the specimens exposed to 300°C. The modulus and strength of sandwich panels at different thermal exposure temperatures and times were predicted with proposed method and compared with measured results. Experimental results showed that the predicted values were close to experimental values.

Hybrid core carbon fiber composite sandwich panels: Fabrication and mechanical response

Carbon fiber reinforced polymer (CFRP) composite sandwich panels with hybrid foam filled CFRP pyramidal lattice cores have been assembled from a carbon fiber braided net, 3D woven face sheets and various polymeric foams, and infused with an epoxy resin using a vacuum assisted resin transfer process. Sandwich panels with a fixed CFRP truss mass have been fabricated using a variety of closed cell polymer and syntactic foams, resulting in core densities ranging from 44–482kgm−3. The through thickness and in-plane shear modulus and strength of the cores increased with increasing foam density. The use of low compressive strength foams within the core was found to result in a significant reduction in the compressive strength contributed by the CFRP trusses. X-ray tomography led to the discovery that the trusses develop an elliptical cross-section shape during pressure assisted resin transfer. The ellipticity of the truss cross-sections increased, and the lattice contribution to the core strength decreased as the foam density was reduced. Micromechanical modeling was used to investigate the relationships between the mechanical properties and volume fractions of the core materials and truss topology of the hybrid core. The specific strength and moduli of the hybrid cores lay between those of the CFRP lattices and foams used to fabricate them. However, their volumetric and gravimetric energy absorptions significantly exceeded those of the materials from which they were fabricated. They compare favorably with other lightweight energy absorbing materials and structures.

Three-dimensional Composite Lattice Structures Fabricated by Electrical Discharge Machining

We present a novel method for fabricating carbon fiber composite sandwich panels with lattice core construction by means of electrical discharge machining (EDM). First, flat-top corrugated carbon fiber composite cores were fabricated by a hot press molding method. Then, two composite face sheets were bonded to each corrugated core to create precursor sandwich panels. These panels were transformed into sandwich panels with near-pyramidal truss cores by EDM plunge-cutting the corrugated core between the face sheets with a shaped cuprite electrode. The flat top corrugation permits adhesive to be applied consistently, and the selected dimensions leave a substantial bond area after cutting, resulting in a strong core-to-sheet bond. The crushing behavior of this novel construction was investigated in flatwise compression, and the results were compared to analytical expressions for strength and stiffness.

High Velocity Impact Response of Composite Lattice Core Sandwich Structures

In this research, carbon fiber reinforced polymer (CFRP) composite sandwich structures with pyramidal lattice core subjected to high velocity impact ranging from 180 to 2,000 m/s have been investigated by experimental and numerical methods. Experiments using a two-stage light gas gun are conducted to investigate the impact process and to validate the finite element (FE) model. The energy absorption efficiency (EAE) in carbon fiber composite sandwich panels is compared with that of 304 stainless-steel and aluminum alloy lattice core sandwich structures. In a specific impact energy range, energy absorption efficiency in carbon fiber composite sandwich panels is higher than that of 304 stainless-steel sandwich panels and aluminum alloy sandwich panels owing to the big density of metal materials. Therefore, in addition to the multi-functional applications, carbon fiber composite sandwich panels have a potential advantage to substitute the metal sandwich panels as high velocity impact resistance structures under a specific impact energy range.

Mechanical Behavior and Failure Mechanisms of Carbon Fiber Composite Pyramidal Core Sandwich Panel after Thermal Exposure

An attempt has been made here to evaluate the effect of thermal exposure on the mechanical behavior and failure mechanisms of carbon fiber composite sandwich panel with pyramidal truss core under axial compression. Analytical formulae for the collapse strength of composite sandwich panel after thermal exposure were derived. Axial compression tests of composite laminates and sandwich panels after thermal exposure were conducted at room temperature to assess the degradation caused by the thermal exposure. Experimental results showed that the failure of sandwich panel are not only temperature dependent, but are time dependent as well. The decrease in residual compressive strength is mainly attributed to the degradation of the matrix and the degradation of fiber–matrix interface, as well as the formation of cracks and pores when specimens are exposed to high temperature. The measured failure loads obtained in the experiments showed reasonable agreement with the analytical predictions.

Mechanical response of carbon fiber composite sandwich panels with pyramidal truss cores

The combination of light carbon fiber reinforced polymer (CFRP) composite materials with structurally efficient sandwich panel designs offers novel opportunities for ultralight structures. Here, pyramidal truss sandwich cores with relative densities ρ¯ in the range 1–10% have been manufactured from carbon fiber reinforced polymer laminates by employing a snap-fitting method. The measured quasi-static shear strength varied between 0.8 and 7.5MPa. Two failure modes were observed: (i) Euler buckling of the struts and (ii) delamination failure of the laminates. Micro-buckling failure of the struts was not observed in the experiments reported here while Euler buckling and delamination failures occurred for the low (ρ¯⩽1%) and high (ρ¯>1%) relative density cores, respectively. Analytical models for the collapse of the composite cores by these failure modes are presented. Good agreement between the measurements and predictions based on the Euler buckling and delamination failure of the struts is observed while the micro-buckling analysis over-predicts the measurements. The CFRP pyramidal cores investigated here have a similar mechanical performance to CFRP honeycombs. Thus, for a range of multi-functional applications that require an “open-celled” architecture (e.g. so that cooling fluid can pass through a sandwich core), the CFRP pyramidal cores offer an attractive alternative to honeycombs.

A study on mechanical behavior of the carbon fiber composite sandwich panel with pyramidal truss cores at different temperatures

A series of compression tests were conducted to investigate the mechanical properties and failure mechanisms of carbon fiber composite sandwich panels using pyramidal truss cores subjected to temperatures ranging from −100°C to 350°C. The compressive strength and stiffness of sandwich panels decreased as temperature increased. Cryogenic temperatures caused an increase in strength and stiffness, while elevated temperatures resulted in a reduction of strength and stiffness. The effect of temperature on the failure mode of the sandwich panel was revealed as well. The interface between the fiber and matrix was examined by a scanning electron microscope (SEM) in order to study the effect of temperature on strengthening the mechanism and good bonding conditions within the fiber-matrix interface was observed at cryogenic temperatures. The comparison of the predicted and experimental data indicated that the stiffness and strength of the composite sandwich panels for temperature variation was consistent.

Shear response of carbon fiber composite pyramidal truss structures after high-temperature exposure

Shear behavior and residual strength at room temperature of carbon fiber composite sandwich panel with pyramidal truss cores exposed to different temperatures for different time were studied experimentally and analytically. Experimental results showed that the residual shear modulus and strength of composite sandwich panels decreased with increasing exposure temperature and time. The decreasing of shear modulus and strength after thermal exposure was mainly attributed to the degradation of the matrix property and fiber-matrix interface property. The effect of high-temperature exposure on failure mode was revealed as well. The failure was characterized by node rupture when sandwich panels were exposed to temperature in a range of 20–250°C, while node rupture and face sheet delamination were observed when specimens were exposed to 280°C. The analytical formulae were also presented to describe residual shear modulus and strength after thermal exposure.

High Temperature Residual Properties of Carbon Fiber Composite Sandwich Panel with Pyramidal Truss Cores

A study on the mechanical property degradation of carbon fiber composite sandwich panel with pyramidal truss cores by high temperature exposure is performed. Analytical formulae for the residual bending strength of composite sandwich panel after thermal exposure are presented for possible competing failure modes. The composite sandwich panels were fabricated from unidirectional carbon/epoxy prepreg, and were exposed to different temperatures for different time. The bending properties of the exposed specimens were measured by three-point bending tests. Then the effect of high temperature exposure on the bending properties and damage mechanism were analyzed. The results have shown that the residual bending strength of composite sandwich panels decreased with increasing exposure temperature and time, which was caused by the degradation of the matrix property and fiber-matrix interface property at high temperature. The effect of thermal exposure on failure mode of composite sandwich panel was observed as well. The measured failure loads showed good agreement with the analytical predictions. It is expected that this study can provide useful information on the design and application of carbon fiber composite sandwich panel at high temperature.

Shear and bending performance of carbon fiber composite sandwich panels with pyramidal truss cores

Structural performance in direct (pure) shear and three-point bending was investigated for sandwich panels with a carbon fiber pyramidal truss core. Analytical estimates for sandwich panel strength for each loading condition were presented for possible competing failure modes. In the experimental part of the study, pyramidal truss cores were made using the hot press molding technique and then attached to flat carbon fiber composite face sheets to build all-composite sandwich panels. Panels with different configurations (e.g., core relative density and face sheet thickness) were tested to probe different failure modes and investigate the mechanical properties. In general, measured failure loads showed good agreement with the analytical predictions. Failure mechanism maps illustrate the controlling failure mechanisms in various regions of parameter space.

Compression and impact testing of two-layer composite pyramidal-core sandwich panels

Quasi-static uniform compression tests and low-velocity concentrated impact tests were conducted to reveal the failure mechanisms and energy absorption capacity of two-layer carbon fiber composite sandwich panels with pyramidal truss cores. Three different volume-fraction cores (i.e., with different relative densities) were fabricated: 1.25%, 1.81%, and 2.27%. Two-layer sandwich panels with identical volume-fraction cores (either 1.25% or 2.27%), and also stepwise graded panels consisting of one light and one heavy core, were investigated under uniform quasi-static compression. Under quasi-static compression, load peaks were identified with complete failure of individual truss layers due to strut buckling or strut crushing, and specific energy absorption was estimated for different core configurations. In the impact test, the damage resulting from low-velocity concentrated impact was investigated. Our results show that compared with glass fiber woven textile truss cores, two-layer carbon fiber composite pyramidal truss cores have comparable specific energy absorptions, and thus could be used in the development of novel light-weight multifunctional structures.