Composite Sandwich Research Articles

Dynamic Behavior Modeling of Natural-Rubber/Polybutadiene-Rubber-Based Hybrid Magnetorheological Elastomer Sandwich Composite Structures.

This study investigates the dynamic characteristics of natural rubber (NR)/polybutadiene rubber (PBR)-based hybrid magnetorheological elastomer (MRE) sandwich composite beams through numerical simulations and finite element analysis, employing Reddy's third-order shear deformation theory. Four distinct hybrid MRE sandwich configurations were examined. The validity of finite element simulations was confirmed by comparing them with results from magnetorheological (MR)-fluid-based composites. Further, parametric analysis explored the influence of magnetic field intensity, boundary conditions, ply orientation, and core thickness on beam vibration responses. The results reveal a notable 10.4% enhancement in natural frequencies in SC4-based beams under a 600 mT magnetic field with clamped-free boundary conditions, attributed to the increased PBR content in MR elastomer cores. However, higher magnetic field intensities result in slight frequency decrements due to filler particle agglomeration. Additionally, augmenting magnetic field intensity and magnetorheological content under clamped-free conditions improves the loss factor by from 66% to 136%, presenting promising prospects for advanced applications. This research contributes to a comprehensive understanding of dynamic behavior and performance enhancement in hybrid MRE sandwich composites, with significant implications for engineering applications. Furthermore, this investigation provides valuable insights into the intricate interplay between magnetic field effects, composite architecture, and vibration response.

Experimental Investigations of Failure Behavior for Aerogel-Cored Stitched Sandwich Composites Under Vibration Conditions

Aerogel-cored stitched sandwich composites (ACSSCs), which possess numerous desirable properties, are anticipated to become the preferred choice for next-generation integrated thermal protection systems (ITPSs) in high-speed vehicles. Despite the reinforcement provided by stitching, the ACSSC structures on vehicles’ outer surfaces remain vulnerable to damage resulting from the excessively high deformation and vibration that occur during high-speed flight. Accordingly, experimental tests were conducted to investigate the failure characteristics of ACSSCs under bending vibration conditions. The tests demonstrated that the ACSSC structures were prone to fatigue failure caused by vibration, which resulted in significant shear damage in the aerogel core. Furthermore, the study introduced a new method for indirectly characterizing the fatigue life of shear damage in the core. Finite element analysis was undertaken to elucidate the cause of the cracking near the bottom layer of the core. The results indicated that the crack location of the aerogel core was littered with the high stiffness and deformation of internal stitches.

Graphite Nanoplatelets Nanostructured Films as Multifunctional Protective Layer in Kevlar/Nomex Sandwich Composites

In the aerospace sector, structural and non-structural composite components are usually subjected to a wide range of environmental conditions. Among all, moisture can seriously damage these materials’ performance, reducing their mechanical, thermal, electrical, and physical properties as well as their service time. Lightweight protective barrier coatings capable of reducing the diffusion of gases and/or liquids in a material can improve the material’s resistance in humid environments. In this work, nanolamellar nanocomposites characterized by a high in-plane orientation of nanoplatelets have been employed as protective coatings for Kevlar sandwich panels, reproducing the construction of a nacelle engine. The effectiveness of the protection against water uptake of nanocomposites reinforced with graphite nanoplatelets (GNPs) at high filler contents (70, 80 and 90 wt%) has been investigated using moisture uptake and Ground-Air-Ground (GAG) tests in an environmental chamber. GNP coatings effectively work as barrier by generating highly tortuous paths for molecule diffusion. Results showed a dependence of the absorption on the coating composition and inner structure. Films @70 wt% GNPs showed the best protection against moisture uptake by delaying the phenomenon and reducing the absorption by −80% after 3 days and −35% after 41 days.

Study on the post-fire axial compressive performance of the lightweight ceramsite foamed concrete sandwich composite shear wall

This study is carried out to develop a new lightweight ceramsite foamed concrete sandwich composite shear wall, which is a new and affordable building system. The shear wall consists of two ordinary concrete wythes and a ceramsite foamed concrete intermediate sandwich layer between the wythes. Experimental investigation on five shear wall specimens is conducted by varying the parameters such as thickness of the ordinary concrete wythes and the insulation layer, reinforcement pattern and constrained component. Besides, by conducting fire test and axial compressive load test, the results are obtained, including the apparent phenomenon after fire, crack pattern and failure modes, load capacity, load-out of plane curve, strain distribution of the composite sandwich shear wall. The results show that sandwich ceramsite foamed concrete has good thermal insulation performance, and the compositeness of wythes and sandwich layer has reached in a certain degree. However, the compositeness of specimen using truss bars is weaken in the late loading stage and truss bars are advised to be used with the horizontal tie bars in practical engineering application. Compared with other specimens, the experiment ultimate strength has been increased by approximately 75 % by arranging the constrained component on the wall. Finite Element (FE) analysis is also conducted by ABAQUS and the results shows good agreement with experiment results, indicating that the FE model can be used to predict the behavior of the sandwich composite shear wall. Based on the existing methods, a modified method to calculate ultimate compressive bearing capacity after fire is proposed, with the maximum calculation error of 19 %, which shows that all methods can be applied to the practical engineering design.

On Impact Damage and Repair of Composite Honeycomb Sandwich Structures

This study is conducted on glass fiber-reinforced composite honeycomb sandwich structures by introducing delamination damage through low-velocity impact tests, establishing a three-dimensional progressive damage analysis model, and evaluating the delamination damage characteristics and laws of honeycomb sandwich structures under different impact energies through experiments. Repair techniques and process parameters for delamination damage are explored. It is found that as the impact energy increases, the damage area of honeycomb sandwich panels also increases, and the delamination damage extends from the impact center to the surrounding areas, accompanied by damage such as fiber fracture and matrix cracking. The strength recovery rates of sandwich panels at impact energies of 5 J, 15 J, and 25 J after repair are 71.90%, 65.89%, and 67.10%, respectively, which has a considerable repair effect. In addition, a progressive damage model for low-velocity impact on the composite honeycomb sandwich structure is established, and its accuracy and reliability are verified.

Optimal design of composite sandwich panel with auxetic reentrant honeycomb using asymptotic equivalent model and PSO algorithm

The composite honeycomb sandwich with auxetic reentrant honeycomb (CSP-ARH) is a typical negative Poisson’s ratio structure, which has better mechanical properties than composite structure with positive Poisson’s ratio. In this study, a 2D asymptotic equivalent model (AEM) based on the variational asymptotic method (VAM) is proposed and used to analyze the vibration and buckling problems of CSP-ARH incorporating CFRP facesheets and an aluminum honeycomb core. After validation with 3D finite element results, a particle swarm optimization (PSO) algorithm is applied to optimize the mesoscopic size of composite facesheets and honeycomb core. The primary objectives of the optimization process involve maximizing the buckling load and natural frequency, minimizing the mass while satisfying specific mechanical properties requirements. Moreover, a few additional optimization iterations are performed to find the optimal shape coefficients of the curved fibers in the CFRP facesheets for variable stiffness composite sandwich panels. The shape of the curved fiber is defined using a cubic polynomial function f(x,y) and is described by a 20 × 20 grid of discrete elements. The results indicate that CSP-ARH with optimal curved fibers shapes exhibit superior performance compared to those with straight fibers, with buckling load and natural frequency increased by 8.18% and 7.09%, respectively.

Design guidelines for the morphing of stiff lattice materials

Materials and structures with shape morphing capabilities are attractive in aerospace, maritime vehicles and robotics: such systems offer lighter weight, better distributed stresses, simpler kinematics, smaller numbers of actuators and higher reliability. Current morphing materials are either very compliant to achieve large shape changes (metamaterials, compliant mechanisms, hydrogels), or very stiff but with infinitesimal shape changes that require large actuation forces (metallic or composite sandwich panels with piezoelectric actuation). Morphing efficiency and structural stiffness are therefore mutually exclusive properties in current engineering morphing materials, which limit the range of their application. Here we propose a design for a stiff morphing beam made of “meta-elements” with unusual combinations of elastic properties, and which can be actuated from a simple push/pull at the base. To capture the performance of the beam we propose and use three metrics: The “morphing amplitude”, the “morphing compliance” and “structural stiffness”. We develop nonlinear finite elements to explore a wide range of designs, and to show some inevitable tradeoffs of stiffness and morphing. To aid the design of the structure we propose ternary diagrams to select optimum combinations of properties for the meta-elements. Finally, we fabricated and tested three prototypes of stiff morphing beams to validate the approach.

Experimental investigation on impact behavior of curved sandwich composites with chiral auxetic core

The purpose of this study is to evaluate and compare the capability of impact energy absorption of the sandwich panels with various chiral auxetic cores. To this end, flat and curved panels were subjected to impact testing at varying energy levels. Glass fiber-reinforced epoxy composites and PLA material were used as the skins and core of the examined sandwich panels, respectively. The face sheets were produced by the hand-layup method and the auxetic cores with tetrachiral, anti-tetrachiral, and hexachiral configurations were printed using a 3D printer. The wall thickness, node diameter, and ligament length of the cells, as well as the core thickness, were kept constant for all the studied core structures. Flat and curved sandwich panels were obtained by combining the skins and cores produced in flat, 100 mm, 125 mm, and 160 mm radii of curvature with the epoxy used in skin production. Drop weight tests were carried out at impact energies of 10, 25, and 80 J. The contribution of the auxetic core configuration and panel curvature to the impact behavior of the sandwich panel was evaluated by examining the relationships between contact forces and deflection and by the analysis of the energy absorption and failure mode. The comparative evaluations showed that the auxetic core structure and the curvature of the panel have a significant effect on the impact properties of the sandwich panels. It was also observed that the use of tetrachiral cores could be the ideal design option for flat panels loaded at the perforation energy level. For curved panels, it was determined that the use of a hexachiral core configuration was advantageous in terms of more energy absorption capability, while the use of an anti-tetrachiral core structure was more effective in terms of specific energy absorption.

Flexural behaviors and failure mechanisms of CFRP sandwich structures with enhanced dual-phase lattice cores

Inspired by bionic/metallurgical microstructures, novel dual-phase lattice/ Carbon Fiber Reinforced Polymer (CFRP) composite sandwich structures are proposed to improve the energy absorption (EA). The composite sandwich structures for different dual-phase strengthening strategies are designed, where the topology optimization is used to yield efficient lattice distribution configurations. The experimental samples are fabricated by 3D-printing and three-point bending tests are conducted. The flexural failure process and failure modes are observed and analyzed to reveal the failure mechanisms. Results show that DPL-1-CFRP and DPL-2-CFRP have higher peak load (+24.8 % and 18.0 %), post-peak average load (42.6 % and 20.8 %) and specific energy absorption (+7.8 % and + 21.1 %) compared to SPL-1-CFRP. It is indicated that the interactive failure mechanism of dual-phase lattice is effective in improving the mechanical properties of sandwich structure. It represents the occurrence of synergistic deformation between struts rather than a single brittle fracture. Finally, several potential failure mechanisms for the separation of the core and end faces are revealed. This novel concept and structural design greatly contribute to improve mechanical properties of sandwich structure.

Buckling behavior and energy absorption of grid‐stiffened composite cylinders under low‐velocity axial impact

AbstractGrid‐stiffened composite cylinders are widely used in a variety of applications and are subjected to static, dynamic, and impact loads. In terms of buckling strength, these structures outperform simple layered and sandwich composites of the same weight, and the presence of unidirectional fiber ribs contributes to their delamination resistance. The purpose of this research is to look into the buckling behavior of grid‐stiffened composite cylinders under low‐velocity and high‐energy axial impacts. The tests were carried out at room temperature using a 35 kg impactor with an impactor fall height of about 2.75 m. This study builds on previous research and considers the samples' thin skin, indicating that skin buckling is the primary buckling mode in such scenarios. According to static loading research, three types of buckling can occur in grid‐stiffened composite cylinders: local shell buckling, local rib buckling, and general buckling, and each of these can be controlled by adjusting the geometric properties. But, based on the loading speed in the weight‐drop test, controlling the specific type of buckling that occurs during impact loading is difficult. Examining residual structural effects can help determine the type of buckling and damage sustained during impact events. According to the results, the forces that cause buckling in grid‐stiffened composite structures under impact loads are 1.5–2 times greater than static loading conditions. Notably, once the forces are removed, these structures can return to their original positions, however with less stiffness. As a result, they absorb a significant amount of impact energy.Highlights Composite cylinders with spiral ribs have higher static compression resistance. Dynamic loading increases local buckling forces in grid‐stiffened structures. Despite being damaged, grid‐stiffened cylinders bounce back quickly after impact. Skin buckling is a common mode of failure for grid‐stiffened composite. The global buckling force is greater than the local buckling force.

The flexural and compressive properties of sandwich composites with different 3D-printed core structures

In this study, different core structures are produced with polylactic acid (PLA) and carbon fiber reinforced PLA (CFR-PLA) filaments using a 3D printer with fused deposition modeling (FDM) technique. An alternative new core structure is proposed to the honeycomb and square core structures commonly used in the literature. Then, sandwich composites are produced by bonding carbon fiber-epoxy plates to the lower and upper surfaces of these core structures. The effect of carbon fiber reinforcement and core types on the mechanical properties of sandwich composites was investigated. The core structures produced with carbon fiber-reinforced PLA showed lower compressive strength but higher compressive modulus than those produced with pure PLA. Among the core structures, the designed structure showed the highest compressive strength with a value of 9.867 MPa, which is 32.18% and 54.36% higher than the honeycomb and square structure. While the flexural strength and flexural stiffness of the sandwich composites increased with carbon fiber reinforcement, the designed sandwich composite showed approximately 1.40 and 3.15 times the flexural strength of the honeycomb and square sandwich composites, respectively.

Metal-faced sandwich composite panels: A review

This review paper discusses the challenges in improving the mechanical and structural performance of metal-faced sandwich composite panels while reducing weight and cost. It focuses on the core and facesheet structural trends of metal-faced sandwich panels, highlighting innovative design concepts and mechanical performance with respect to failure modes. The paper categorizes recent core geometries used in metal-faced sandwich structures into three types: cellular foam cores, two-dimensional periodic cores, and three-dimensional periodic cores, each with unique characteristics and advantages. The performance of metal sandwich panels with different core structures in response to various mechanical tests is also summarized, including high and low-velocity impact, flexural, and blast and fire resistance. The review emphasizes that the core geometry, facesheet thickness, and core-face interfacial bonding of sandwich composites play a critical role in determining their structural performance and potential applications. Overall, this review paper provides valuable insights into the challenges of improving the mechanical and structural performance of metal-faced sandwich composite panels and highlights the importance of innovative design concepts for achieving optimal performance.

Experimental investigation on mechanical performance of PVC foam‐based E‐glass isophthalic polyester composites

AbstractThe present research paper investigates the chemical, thermal, mechanical, thermo‐mechanical properties, and fractography of sandwich composites made from E‐glass‐reinforced isophthalic polyester with Poly Vinyl Chloride (PVC) foam as a core by hand. These composites are commonly used in marine applications and manufactured by hand lay‐up method. A comparison is made between the properties of the PVC foam polyester sandwich composite with E‐glass layers on both sides (SC1) and the PVC foam isophthalic polyester sandwich composite with double layers of E‐glass on both sides (SC2) in relation to single‐layer E‐glass. Fourier transform infrared (FTIR) spectroscopy is employed to analyze the chemical composition of the composites. Various mechanical properties, including impact strength, flexural strength (FS), fracture toughness, and tensile strength (TS), are evaluated for the fabricated composites. Thermo‐mechanical and thermal properties are examined using dynamic mechanical analysis and thermogravimetric analysis (TGA), respectively. The chemical analysis identifies the unsaturation sites of (CH2)n, carbonyl group CO of the ester group, and the stretching of CH and CH3. The mechanical properties of SC2 composites are observed to be superior to those of SC1 composites. TGA revealed that both SC1 and SC2 composites showcased comparable temperature‐dependent weight loss patterns. Nonetheless, the SC2 composite displayed elevated glass transition temperature values and superior damping properties, as indicated by its higher Tanδ values. Examination of the fractured surfaces using a scanning electron microscopy (SEM) micrograph reveals a honeycomb structure, matrix cracking, and fiber pullout.Highlights Examination of the chemical, thermal, mechanical, and thermo‐mechanical attributes of sandwich composites made from E‐glass‐reinforced isophthalic polyester with PVC foam as the core. Evaluation of the impact of E‐glass layering on the thickness of the composite skin. Analysis of interfacial properties through FTIR techniques. Assessment of mechanical properties like impact strength, FS, fracture toughness, and TS. Investigation of fracture surfaces using SEM.

Quantitative structural uncertainty analysis of composite honeycomb sandwich using a feedback neural network

The quantification of margins and uncertainty (QMU) method was applied using a neural network to inversely determine the strength boundary of a composite honeycomb sandwich structure considering the random uncertainty of its elastic modulus, shear modulus, tensile strength, compressive strength, and shear strength in the warp and fill directions, and panel thickness. An application framework for the deterministic quantitative analysis of strength was proposed based on margin design theory, combining the strength problem with the quantitative analysis of uncertainty. First, the failure criterion of the structure was modeled based on the progressive damage principle using ABAQUS. Next, Latin hypercube sampling was applied to simulate the stochastic uncertainty of the structural parameters, and the resulting sample sets were input into ABAQUS to calculate the corresponding structure lateral bearing capacities. These results were considered to collectively represent the actual strength boundary of the composite structure. A feedback neural network was subsequently trained on these ABAQUS data to obtain the functional mapping relationship between the parameters and capacity. The capacity obtained using this relationship was multiplied by an empirical safety factor to serve as the theoretical strength boundary. Finally, the QMU method was applied using cumulative distribution functions of the theoretical and actual strength boundaries to calculate the confidence factor and thereby evaluate the reliability of the composite honeycomb sandwich structure.

Free vibration characteristics of integrated fluted-core composite sandwich cylinders

Due to their excellent mechanical properties and inherent design versatility, fluted-core composite sandwich structures have gained substantial attention in aerospace and rail transit applications. This study investigated the free-vibration characteristics of composite fluted-core sandwich cylinders. Theoretical models were established following the Rayleigh-Ritz method to predict the natural frequencies of sandwich cylinders under free vibration. The representative cylindrical specimens were prepared using carbon fiber-reinforced plastics (CFRP) and integrated forming co-cured method. To analyze the additional effects of cutouts on vibration performance, specimens with circular cutouts were also fabricated. The vibration tests were performed to determine the natural frequencies and modal shapes under free-free boundary conditions. Validated finite element simulations were employed to assess the accuracy of theoretical results and investigate the influences of geometric parameters on the structural vibration behavior. The results indicated that circumferential lobar modes characterized the first five mode shapes. Significant enhancements were attained by increasing the structural stiffness through adjustments in the circumferential cell number, core-ribs thickness, or size of cutouts. However, when the structural stiffness increases beyond a certain threshold, it has limited effect on the vibration frequencies. The findings provided a comprehensive understanding of the vibration characteristics and optimized design of fluted-core sandwich cylinders.

A dovetail core design for joints in composite sandwich structures

The increase in the size of composite sandwich structures requires the introduction of core splices to join various segments. In this study, a novel core splice joint configuration is studied and proposed for composite sandwich structures of thick aluminum-based honeycomb core and facesheets made from carbon fibers and epoxy matrix. Experimental and numerical efforts investigate the impact of dovetail joints with different tenon angles on the auxiliary behavior of composite sandwich structures. The results are compared to conventional or straight-core splices without dovetail features. The core-splice interaction with the complete mechanical behavior of the system was assessed by subjecting the fabricated specimens to combinations of bending and shear forces. Additionally, 3D-finite element models compared normal and shear stresses in the splice material and the core/splice interface among the dovetail configurations considered. The study shows that depending on the dovetail joint detail, an ultimate strength increase between 13 and 51% is achieved compared to the strength from currently used straight joints. In terms of toughness, the dovetail specimens show a 2% to 35% higher toughness compared to the standard straight joints.

Fragments analysis of an hypervelocity impact experiment on a solar array

A large fraction of spacecraft external surfaces or appendages often consists of solar arrays, which can be subjected to space debris impacts as in the case of the Sentinel 1 A event of August 2016. Therefore, it is of interest to understand how solar arrays respond to hypervelocity impacts and to investigate the generated fragments population. In this context, the University of Padova performed an impact experiment on a solar array consisting in a composite sandwich panel, coated with a Kapton layer, and provided with solar cells: a nylon cylinder of 0.039 g collided with the solar panel at a velocity of 4.86 km/s with an impact angle of 45 deg, detaching a solar cell and damaging the panel structure. More than 4500 fragments larger than 0.2 mm were collected and classified after the impact.In this paper the impact experiment is described and the fragments analysis is presented in terms of size and shape distributions; a comparison with a test on a composite sandwich panel shows that the distributions are strongly affected by material and manufacturing choices, in particular regarding the fragments generated by delamination.

The relationship between the impact position interference and CAI strength of composite sandwich structures under double impacts

Sandwich structures are susceptible to multiple-impacts, and such multiple-impacts will typically occur at certain distances from each other. Therefore, the influence of five different distances between impact positions (DBIP) and three impact energies on compression after impact (CAI) strength are considered and discussed for honeycomb sandwich structure with composite face sheets in this paper. By comparing two typical impact characteristics, i.e., maximum impact force and displacement, the trend of CAI strength shows a turning-point, which is closely related to the size of the impactor. However, high impact energy (15 J) leads to damage in the bottom face sheet during the second impact, and the presence of damage in both top and bottom face sheet reduces CAI strength, resulting in the turning point of CAI strength not exist. It was observed that there is obvious buckling failure, and some cracks along the width direction from the impact point to the edge after CAI. To provide a more comprehensive understanding of double impacts and CAI behavior, a finite element (FE) model considering different DBIP is developed. In addition, the predicted fraction of energy absorbed by top face sheet, honeycomb core, and bottom face sheet is also obtained to reveal the relationship between the impact position interference and CAI strength.

The Effect of Reinforce Powder Size on The Properties of Pineapple Leaf Fiber – Bagasse Sandwich Composites

The growth of ship production in Indonesia encourages the shipping industry to utilize the composite material in order to be more efficient. Natural fibre-reinforced composite (NFRC) is one option that should be considered for use safer than fiberglass. The usage of fiberglass could trigger several health problems. Sugarcane and pineapples are one of the most common agricultural commodities, yet their waste has not been treated optimally. This research is going to analyse the effect of reinforcement powder size on its bending strength in pineapple leaf fibre – bagasse reinforced sandwich composites. Pineapple leaf fibre use as skin reinforcement whereas bagasse use as core reinforcement. Sandwich composites were reviewed for their bending strength on specimens on reinforcement powder size 40, 60, and 100 mesh. The composite was made using the hand lay-up method with skin composition is 20:80% and core composition is 25:75%, each layer of skin and core have 2 mm thickness. The highest bending strength for sandwich composite is 52,72±0,85 MPa as a result of the experiment using 100 mesh of reinforcement powder. The bending strength of sandwich composite increase as finer particle powder use for the reinforcement. The highest bending strength in this study can be used as bulkhead material for the interior of the ship’s accommodation space based on SNI 01-4449-2006.

Titanium/steel composites were prepared by composite interlayer and two pass laser welding

In this study, a composite sandwich was used as an intermediate layer and TC4/304 stainless steel was joined by explosion welding. First, intermetallic compounds with different butt joint sizes were added. When the length of the butt joint was kept at 4 mm, the mechanical properties of the joint increased with the extension length. The maximum tensile strength of the joint was 600 MPa when the extension length was varied between 1 and 2.5 mm. A "net basket organization" was formed in the titanium-side weld, and α → β and β → α ′ phase transitions occurred. Comparative microstructural analysis shows that the aspect ratio of the organization decreases with the increase of the length of the titanium side weld.