Composite Sandwich Panels Research Articles

Experimental and numerical investigation of damage in multilayer sandwich panels with square and trapezoidal corrugated cores under quasi-static three-point bending

Multilayer composite sandwich panels with corrugated cores have the potential for structural applications requiring high stiffness and strength-to-weight ratios. This study aims to experimentally and numerically investigate the bending response of sandwich panels with novel square and trapezoidal corrugated core configurations fabricated from E-glass fiber-reinforced epoxy composites, both with and without polyurethane foam filling. Quasi-static three-point bending tests were conducted to evaluate and compare the flexural stiffness and maximum load capacity of the panel designs. The cores were manufactured using vacuum-assisted resin transfer molding. Key results showed that changing the core geometry from square to trapezoidal improved the bending stiffness by up to 26 %. Incorporating polyurethane foam further increased the bending stiffness by up to 41 % and maximum load by up to 47 % compared to solid cores. Failure initiation and progression were governed by matrix cracking in the face sheets and cores, followed by core cell wall buckling and delamination. Finite element modeling using ABAQUS captured the progressive damage behavior, exhibiting good agreement with experimental force-displacement responses. Failure modes included matrix cracks, fiber fractures, core buckling and delamination. This study provides valuable insights into the mechanical performance of innovative corrugated core sandwich panel designs under quasi-static bending loads. The validated FE approach also enables virtual testing and optimization of composite sandwich structures.

Buckling analysis of hybrid fiber‐reinforced composite sandwich panels with varying numbers of polyurethane cores

AbstractHybrid fiber‐reinforced composite sandwich panels with multi‐layer polyurethane cores are widely applied in aerospace, automotive, construction, and shipbuilding industries. This study aims to investigate the buckling performance of composite structures with varying numbers of polyurethane cores. To achieve this, the buckling loads of these structures are determined using an energy method, microscopic mechanics method, and the first‐order zigzag kinematic model. The accuracy of the equation employed in the algorithm is validated using the finite element method. Additionally, we conduct a parametric analysis to examine the influence of various parameters on the buckling performance of the structures. The results indicate that an effective strategy for improving the critical buckling loads of the hybrid fiber‐reinforced composite sandwich plate involves strategically placing fibers and matrix materials with higher elastic modulus on the skin layer. Moreover, the critical buckling load is notably influenced by the number and positioning of polyurethane layers, as well as the fiber content.Highlights An analytical model is established to predict the buckling behavior. The correctness of the model was verified using the finite element method. Effects of structural parameters on buckling performance were investigated.

Experimental study on composite spherical-roof contoured-core (SRCC) sandwich panels under the V-shaped quasi-static indentation loading

The paper investigated the experimental study of composite spherical-roof contoured-core (SRCC) sandwich panels under a V-shaped quasi-static indentation (QSI) test. The carbon fiber, glass fiber, aramid fiber, hybrid carbon/aramid, and glass fiber chopped strand mat sheets were used to manufacture the composite cores, which used the hand layup and hot compression techniques. The polylactide (PLA) core was fabricated using fused deposition modelling (FDM). The V-shaped indenter had a 65° angle and was set at 1 mm/min as indentation speed in the experimental test. It was found that the maximum indentation deflection was 35.49 mm on the SRCC sandwich panel with a hybrid carbon/aramid core compared to other composite cores. Furthermore, it was localized fiber fracture, matrix damage, delamination, inwards fronds, and debonding damage mode on composite SRCC sandwich panels, which was visually shown at the central SRCC core unit cell. It is highlighted that aramid fiber and hybrid carbon/aramid materials can provide outstanding impact characteristics, which have great potential to be used as impact-resistant sandwich structures.

Effect of Kevlar and Carbon Fiber Face Sheet on the Deformation Behavior of Aluminum Hybrid Composite Foam Core Sandwich Panel under Flexural Loading

Effect of Kevlar and Carbon Fiber Face Sheet on the Deformation Behavior of Aluminum Hybrid Composite Foam Core Sandwich Panel under Flexural Loading

CF/PEEK skins assembly by induction welding for thermoplastic composite sandwich panels

A method to assemble sandwich panels made of carbon fibre reinforced poly-ether-ether-ketone (CF/PEEK) facesheets and 3D-printed poly-ether-imide (PEI) honeycomb cores using induction welding is presented. Induction heating patterns inside CF/PEEK laminates of variable dimensions are first evaluated with a thermal camera and compared to a COMSOL Multiphysics model. Sandwich samples are then prepared by vacuum-assisted continuous induction welding under parameters selected from the modelling effort. Joining of sandwich panels made of CF/PEEK facesheets by induction welding under vacuum is demonstrated. Facesheets do not deconsolidate in the process and core crushing is avoided. Flatwise skin/core strength of the welded samples reaches up to 7 MPa, above reported performance for thermoset or thermoplastic composite sandwich panels.

Damage identification in sandwich structures using Convolutional Neural Networks

The increasing complexity of structures and materials, coupled with ever more stringent demands for safety and cost reduction in maintenance operations, has driven the need to develop advanced techniques for structural integrity monitoring, known as Structural Health Monitoring (SHM). In this context, this study investigates the use of image processing techniques of mode shapes in a composite sandwich panel, employing various Convolutional Neural Network (CNN) models, with the purpose of identifying damage. The main objective is to classify the type of damage, whether it is in the core, at the interface, or in the laminate, followed by the precise location of the flaw and determination of damage dimensions in terms of length and width. To achieve these goals, the finite element method was used to create a representative database, and subsequently, an efficient data management system and model implementation were established to optimize computational costs. The results obtained show that, in the classification task, a high accuracy in damage type identification (99%) was achieved, even when images had high levels of noise. Regarding the regression task for damage localization, satisfactory results were obtained, while the dimensioning of damage length proved acceptable, albeit with some limitations, and inclination identification presented challenges. This study represents a significant advancement in the field of SHM and explores both the advantages and limitations of using Convolutional Neural Networks for this purpose. The results obtained provide valuable insights for the practical application of these techniques in the detection and assessment of damage in sandwich structures, thus contributing to enhancing the safety and efficiency of maintaining such structures.

Energy efficiency in modular emergency shelters: Impact of envelope finishings and shadowing

In emergencies, ensuring rapid access to temporary housing for displaced individuals is a cornerstone of effective disaster response. Managing the issue time-effectively is crucial for addressing the immediate physical needs of the population and fostering a sense of stability. Unfortunately, given the vast scale of emergency camps, the number of shelters to be installed is often very high, requiring rapid transport and assembly for the success of settlement procedures. Furthermore, emergencies frequently occur in environments with extreme outdoor climates, heightening the challenge of maintaining indoor comfort within shelters. The present study considers a modular shelter based on composite sandwich panels made of glass-fibre reinforced polymer (GFRP) filled with a polyurethane (PUR) foam thermal insulation core. Experimental tests and numerical analyses are used to quantify the thermal conductivity of the panels and the heat losses through the panels' connections, respectively. Dynamic energy simulations are implemented accounting for the aforementioned data and used to quantify the energy required to ensure users' thermal comfort via active heating and cooling systems. Further, the model is applied to evaluate the influence of envelope finishes and shading devices in reducing the shelter's energy demands in three extreme climates. Results indicate that the combination of shading and reflective finishes can lead to significant energy demand reductions, decreasing the need for thermal insulation and, therefore, reducing the overall weight of the shelter. Finally, it is observed that in climates where cooling demands are dominant, passive strategies can achieve energy savings that thermal insulation alone cannot attain.

Non-destructive evaluation of a composite honeycomb sandwich panel with in-plane waviness damage using ultrasonic guided waves

ABSTRACT Composite honeycomb sandwich structures (CHSS) are often manufactured using an autoclave co-cure process, which can introduce in-plane waviness (IW) damage due to fibre misalignment. Such fibre waviness, whether in-plane or out-of-plane, significantly weakens the strength of these structures. Therefore, developing reliable non-destructive evaluation (NDE) techniques is essential for detecting IW. This study presents an NDE technique utilising ultrasonic guided waves (GW) to identify IW damage in CHSS panels. A numerical model was created using COMSOL Multiphysics, where IW damage is simulated through curvilinear coordinate physics, followed by a time-dependent study of GW propagation. This model simulates local fibre orientation changes due to IW damage, enhancing our understanding of GW interaction with IW. Experimental investigations are performed using contact-type transducers to corroborate the numerical observations. The presence of in-plane waviness causes a reduction in the group velocity of the A0 mode, a characteristic that can be exploited for detecting in-plane fibre waviness in CHSS. Also, parametric studies were performed to examine the effects of IW severity (aspect ratio) and increased IW area on GW characteristics. Finally, a technique for IW damage localisation is demonstrated using a convex hull algorithm based on changes in correlation coefficient values of the A0 mode.

In-plane shear performance and damage evolution of FRP connectors for composite sandwich panels

This study investigated the in-plane shear responses of four types of connectors (single-strand truss, double-strand truss, grid-type, and I-shaped) in precast concrete sandwich panels (PCSPs). The influence of connector type, connector arrangement, and wythe material on the shear performance was discussed through in-plane shear tests and finite element analysis. The failure modes and test results of the four types of connectors were closely related to their shear resistance mechanisms. Changing the connector arrangement method from continuous along the length to discrete arrangement improved connector damage extent and toughness index (TI). The substitution of ordinary concrete with ECC or UHPC in wythes can prevent the wythes failure and enhance peak load (Pm). The finite element (FE) model using the Hashin damage model and randomly generated fibers can accurately capture the shear response of the connectors within PCSP. The damage factor was introduced for quantitative analysis of the damage processes in connectors and wythes and corresponding damage evolution model was developed. Furthermore, the damage evolution model was applied to characterize the degradation of shear stiffness in the load-slip curve, and a load-slip theoretical model that accounted for the progressive development of damage was established.

Compression behavior of lightweight corrugated composite Sandwich panels with smart facesheets reinforced by shape memory alloy wires: an experimental study

AbstractThis paper presents an experimental examination of the compression demeanor of lightweight corrugated core composite (CCC) sandwich panel and corrugated core smart composites (CCSC) sandwich panels subjected to quasi‐static edgewise compression loading. The existence of shape memory alloy (SMA) wires and pre‐strain percentages of SMA are the indicators studied in this article. The fabrication procedure presented and the appraisement of the mechanical properties of the CCC and CCSC sandwich panels are expressed. The core geometry of samples is trapezoid corrugated made of aluminum. The facesheets are four layers of woven glass fiber/ epoxy laminated composite. For evaluation of the efficacy of the presence of SMA wires on mechanical specifications of sandwich panels, three SMA wires with various pre‐strain percentages (0%, 3%, and 6%) are embedded in each composite facesheet. Mechanical properties of all types of CCC and CCSC sandwich panels such as maximum force, critical damage force, specific strength, absorb energy, specific toughness, Young's modulus, and specific stiffness were evaluated. Results showed that the CCC sandwich panel has higher mechanical specifications than the CCSC sandwich panels with 0% and 3% pre‐strain. Also, increasing pre‐strained SMA wires improves all mechanical parameters of CCSC sandwich panels. CCSC sandwich panel with 6% pre‐strain has the highest compression properties than other sandwich panels. Maximum Force, Critical Damage Force, Specific Strength, Absorbed Energy, Specific Toughness, Young's Modulus, and Specific Stiffness of CCSC sandwich panel with 6% pre‐strain are 14.73 kN, 13.6 kN, 9.55 MPa/g, 26.61 kJ, 0.346 MJ/m3g, 4395 MPa and 0.61 kN/mm g, respectively.Highlights Lightweight CCC sandwich panel and CCSC sandwich panel manufactured. Compression behavior of CCC sandwich panel and CCSC sandwich panel evaluated. Pre‐strained SMA wires improves energy absorption of CCSC sandwich panels. Higher specific toughness was obtained with 6% pre‐strain SMA. Presence of SMA wires with no pre‐strain cannot improve the specific strength.

Study on manufacturing process and load-bearing capacity of innovative GFRP composite sandwich panels with connecting grooves

Composite sandwich panels have been widely utilized in various fields, including civil engineering, wind turbine blades, and transportation engineering, due to their lightweight, high strength, corrosion resistance, and exceptional thermal and damping properties. This paper introduces a novel wood-core composite sandwich panel produced through pultrusion. It features connection grooves designed to fulfill lateral connection requirements. The production of this innovative composite sandwich panel has been completed. The bending load-bearing capacity of this panel is comprehensively studied through theoretical analysis, and a modeling approach utilizing the general finite element software ANSYS is introduced. Ultimately, the efficacy of both theoretical methods and finite element simulations is verified through rigorous experiments. The research findings presented in this paper are highly significant for optimizing the design and manufacturing of composite sandwich panels, ultimately enhancing their utilization in rail transit vehicles and other industries.

Flexural Behavior of Composite Ultrahigh-Performance Concrete Sandwich Wall Panels

Flexural Behavior of Composite Ultrahigh-Performance Concrete Sandwich Wall Panels

An experimental study of multi-core composite aluminium honeycomb sandwich panels under low-velocity impacts

This paper aims to evaluate the impact response of the multi-core composite sandwich panels from low-velocity experiments. Geometrical parameters of sandwich panels like cell size, cell height, and facesheet thickness are varied and their effect on peak load, energy absorption, and efficiency is reported in this article. The effect of impact energy variation ongraded and non-graded types of sandwich panels is also studied. Based on these experiments suitable recommendations are given for impact energy absorber applications. From a crashworthiness point of view, graded multi-core composite sandwich panels are found to be more effective than non-graded ones.

Compressive failure analysis of composite honeycomb sandwich panels with impact damage and stepped-scarf repairs

Composite honeycomb sandwich panels (CHSPs) have been widely used in the aerospace industry owing to their lightweight and superior mechanical properties. However, these CHSPs are susceptible to impact damage, leading to a significant reduction in compressive strength and potentially jeopardize aircraft safety. It is crucial to investigate repair methods for CHSPs with impact damage. This paper aims to evaluate the repair performance of CHSPs with impact damage through an analysis of their compressive failure behaviors. To accomplish this, both experimental tests and advanced numerical models are employed. The numerical models for the intact, damaged and stepped-scarf repaired CHSPs are established using the progressive failure analysis model, cohesive zone model and sandwich plate theory. A good agreement is observed between the experimental results and numerical predictions of compressive failure behaviors. Moreover, the validated numerical models are successfully utilized for determining optimum repair parameters by parametric analysis of the repaired CHSPs. The establishment of these numerical models offers an accurate and cost-effective evaluation of repair performance for CHSPs with impact damage, highlighting the novelty and main contribution of this paper.

Effects of core geometry, silica nanoparticles, and polyurethane foam on the mechanical properties of a novel circular-shaped core sandwich panels under compression test: Experimental study

For the first time in this paper, a composite sandwich panel with a novel circular-shaped core reinforced with silica nanoparticles (SNPs) is designed and fabricated using the vacuum-assisted resin transfer molding (VARTM) method. Carbon fibers and epoxy resin are utilized to construct the composite sandwich panels, followed by polyurethane foam injection. After fabrication, the sandwich panels undergo uniform compression testing to examine their mechanical behavior and properties. In this study, the effects of various parameters, such as core length, core height, weight percentage (wt.%) of SNPs, and polyurethane foam, on the compressive strength of the structure are evaluated. To validate the results, a finite element simulation of the sandwich panel compression test is performed using ABAQUS software, and the results obtained are compared with experimental data, showing good agreement. The results of this research demonstrate that adding SNPs within a specific range results in a considerable enhancement of the structural strength. Adding SNPs up to 3% leads to approximately a 19% increase in the compressive strength of the structure. However, adding 4 wt.% SNPs results in a decrease of about 12% in the strength of the sandwich panel. Additionally, the core’s geometry significantly influences the control of compressive strength and rigidity of the sandwich panel. In other words, by increasing the core length, the compressive strength increases by 38%, while increasing the core height decreases compressive strength by about 30%. Also, it is found that adding polyurethane foam to the sandwich panel, despite a slight increase in weight, leads to a significant increase in compressive strength by about 32% and postpones its ultimate failure. Eventually, the hybrid specimen exhibits a strength approximately 57% greater than that of the pure foamless sandwich panel.

Curved Polymeric Sandwich Composites Subjected to Air Shock: An Experimental Investigation

BackgroundThe vulnerability of polymeric composite sandwich structures in marine applications to air explosions highlights a significant gap in our understanding of the dynamic behavior of the curved sandwich structures, which is essential for design improvements.ObjectiveThis study aims to explore the dynamic response and failure mechanisms of curved sandwich composite panels subjected to air-blast loading, providing insights into their structural integrity under such conditions.MethodsExperiments were performed using laboratory-simulated air shocks generated by a shock tube, employing high-speed photography and digital image correlation to measure deflections on the back surface of the panels. The panels, made with PVC closed-cell foam cores of two densities (H45 and H130), were tested across three curved geometries (radii of 112 mm, 305 mm, and infinity) under various boundary conditions.ResultsFindings indicate an increase in deformation with a decreased radius of curvature under simple support conditions, a trend that reverses under arrested displacement conditions. Moreover, a reduced radius significantly enhances panel strength and resistance to interfacial damage, with the primary failure mode transitioning from core shear cracking to interfacial debonding as core density increases.ConclusionsThe study reveals that the radius of curvature, boundary conditions, and core density significantly affect curved sandwich panels’ dynamic response and performance. Panels with smaller radii and higher core densities exhibit increased strength, though boundary conditions introduce variable effects on deformation behavior.

Development of epoxy-based sandwich composite panel with hollow glass microspheres/clay hybrid core and banana fiber facesheet for structural applications

This study focuses on improving the mechanical properties of sandwich composites by developing epoxy-based sandwich composite panels with hollow glass microspheres/nanoclay hybrid core and banana fiber facesheets for structural applications. The mechanical performance of sandwich composite panels made with hollow glass microspheres (HGM)/nanoclay hybrid core with banana fibers face-sheet composites panel is investigated in this work. The HGM content of the core was varied from 1 wt% to 3 wt% in the sandwich composites panel, while the nanoclay content of the core was varied from 1 wt% to 5 wt% in each of the HGM-filled series of the sandwich composite panel, these sandwich composite panels were fabricated using a conventional resin casting method. In this investigation, the mechanical, water absorption, and buoyancy behavior are thoroughly studied and the findings revealed better improvement at the sandwich composites with hybrid core formulation with banana fiber facesheets than the sandwich composites without hybrid core formulation. This demonstrates that banana fiber with epoxy resin has a limited amount of strength when used without a hybrid core but delivers better performance when HGM and clay particles are mixed as the hybrid core because of excellent interfacial adhesion between the hybrid core and the matrix. The improved mechanical properties could suggest that this material may be suitable for application in industries where sandwich structures that are lightweight with good mechanical properties are required. This study showed a new area of sandwich structure development by enhancing mechanical properties using hybrid core and banana fibers.

Computational simulation of impact perforation of polymeric-foam core sandwiched composites with different skin–face configurations

The normal and oblique impact perforation responses of composite sandwich panels based on a Rohacell polymeric-foam core are numerically investigated at high impact energies (>60 J). A cylindrical form factor with a diameter of 140 mm and a thickness of 15 mm is selected for the sandwich specimens. Four different stacking sequences of 1 mm carbon/epoxy face sheets are considered (i.e., quasi-isotropic, cross-ply, angle-ply, and unidirectional stacking). A computational model was constructed using LS-DYNA finite element software and an inverse perforation testing scheme adapted with a split Hopkinson bar and confirmed by comparing these results with those obtained using the free shooting projectile-target testing schemes published in the literature. The effects of impact energy, failure modes, impact angles, and damage key parameters are analyzed. The results reveal the contact force versus displacement curves are highly influenced by the impact energy increases. The stacking sequence of the face sheets does not influence the energy absorption capacity. However, the maximum absorbed energy increases with an increasing impact angle up to 20°. Using Hopkinson bars in conjunction with the virtual inverse perforation testing approach is effective for examining the response of sandwich composites at high impact energies.

Manufacturing of thermoplastic composite sandwich panels using induction welding under vacuum

A new method to manufacture thermoplastic composite sandwich panels is presented, making use of the induction welding process in which a magnetic susceptor generates the heat at the core/facesheet interface. This technique proposes a fast way to assemble thermoplastic sandwich structures without risking the deconsolidation of the composites skin. The welding pressure is obtained by applying vacuum over the sandwich panel. This vacuum induction welding method (Vac-IW) allows joining thermoplastic composite facesheets to a thermoplastic polymer core in a clean and non-contact manner. The feasibility of the method is demonstrated by preparing sandwich samples made of glass fibre reinforced polyetheretherketone (PEEK) skins and a 3D-printed polyetherimide (PEI) honeycomb core. A susceptor made of PEI and µm-sized nickel (Ni) particles is used to generate heat by magnetic hysteresis losses. The strength of the sandwich samples assembled by the Vac-IW method is evaluated by flatwise tensile (FWT) tests.

Low-velocity impact damage of bionic turtle shell sandwich laminates with different suture shapes

Turtle shells have evolved over millions of years, developing exceptional mechanical properties such as high relative strength and toughness, rendering them highly effective in resisting impacts. This study delves into the impact resistance of bionic turtle shell structures with various suture shapes. This article analyzes the low-velocity impact of carbon fiber epoxy resin prepreg (CF/EP) composite sandwich panels with a suture interface by using the finite element simulation. The simulations encompass closed and unclosed models featuring bonded and unbonded tips, each with diverse trapezoidal geometries (triangular, trapezoidal, anti-trapezoidal, and rectangular). The findings reveal that sandwich structures with suture interfaces demonstrate significantly enhanced impact resistance compared to those lacking sutures, displaying 3–9 times greater deformation capacity and 20–30 times higher energy absorption capacity. The impact resistance of the triangular suture interface exceeded that of other bioinspired suture shapes, with trapezoidal and anti-trapezoidal sutures also enhancing stiffness, strength, and toughness. Additionally, a 6° bonded tip angle resulted in optimal performance for the triangular suture interface across all analyzed perspectives. The simulation study in this paper provides comprehensive and reliable data on low-velocity impact results, offering fundamental insights for researchers to design composite material structures that meet specific mechanical requirements effectively. Additionally, it offers novel ideas for the connection of protective structures, such as artificial armor.