Performance Enhancement of Bonded Aluminum Composite Panels through Control of Polyethylene Core Thickness

Abstract

This study analyzes the global mechanical behavior and performance optimization of Aluminum Composite Panels (ACP) with a polyethylene (PE) core. Conventional multilayer ACP designs often lead to excessive material use and high weight. The effect of PE core thickness on mechanical performance was investigated to reduce the number of layers while maintaining structural integrity. Experimental tensile tests and finite element (FEM) simulations using ABAQUS/Explicit were conducted to evaluate the elastic and plastic deformation of ACP up to failure. The combined effects of core thickness and the number of sandwich layers were systematically analyzed. Results show that the apparent Young’s modulus (E _app) decreases with increasing core thickness and number of layers. Adjusting the PE core thickness allows a single ACP to replace multiple bonded panels while maintaining equivalent load-bearing capacity. A single ACP with a 10 mm PE core can replace three 4 mm bonded panels. This approach reduces aluminum consumption, structural weight, and material usage while promoting the use of recyclable polymer cores. The findings highlight the relevance of the apparent modulus as a key design parameter and confirm the potential of ACPs as lightweight, high-performance, and sustainable materials for industrial applications.

1. Introduction

Composite materials are extensively utilized to fulfill precise design and performance requirements, including weight reduction, energy absorption, impact resistance, and improved rigidity. Their exceptional specific stiffness and strength, combined with the capability to customize properties for particular applications, have positioned them at the forefront of research on laminated composites and sandwich structures. Selecting the appropriate composite materials is essential to achieving the intended performance and characteristics for each specific application. The growing adoption of these materials has driven the development of advanced theoretical models to analyze their behavior under various loading conditions, such as tension, compression, bending, buckling, and vibration. In particular, the design of aluminum composite panel (ACP) sandwich elements has played an important role in technological advancements and cost-effectiveness.

The growing demand for multifunctional and high-performance building materials has led to a shift from traditional single-material solutions to advanced composite structures, such as metal–polymer combinations. Among these, aluminum composite panels (ACPs) have gained widespread popularity in construction and architectural design due to their exceptional durability, lightweight properties, and versatile aesthetic potential. One of the most well-known ACP brands, Alucobond, was developed by 3A Composites and has become a standard in the industry.

ACPs consist of two thin aluminum sheets enclosing a core material, which can be made of polyethylene (PE) or a fire-resistant, mineral-filled composition. This structure provides a unique balance of strength, flexibility, and thermal stability, making ACPs an ideal choice for both exterior and interior applications. These panels are particularly valued for their outstanding resistance to weathering, corrosion, and mechanical impact, ensuring long-term performance in various environmental conditions.

Beyond their mechanical and protective properties, ACPs offer significant advantages in design flexibility. Their lightweight nature reduces structural loads, simplifying transportation, handling, and installation while lowering overall costs. Available in a broad spectrum of colors, finishes, and textures, they enable architects and designers to achieve highly creative and modern facades with seamless visual appeal. The exceptional flatness and smooth surface quality of ACPs are crucial for high-end cladding applications, where precision and aesthetic consistency are required.

Additionally, ACPs contribute to enhanced energy efficiency through thermal insulation and sound-dampening properties, improving indoor comfort and reducing energy consumption. In response to growing fire safety concerns, fire-resistant ACP variants have been developed, incorporating noncombustible mineral cores to comply with strict fire regulations, particularly for high-rise buildings and public infrastructure. Moreover, ACPs offer low maintenance requirements, ensuring long-lasting aesthetic and functional performance with minimal upkeep. Their ability to withstand environmental stressors, combined with their ease of installation and customization options, has solidified their position as a preferred material in contemporary construction and architectural innovation.

Alucobond panels are widely employed in building facades, interior cladding, signage, and artistic installations due to their blend of aesthetic appeal and functionality. Their mechanical properties, including tensile, flexural, and shear strength, determine their suitability for various applications. Tensile strength, primarily contributed by the aluminum layers, ensures resistance to pulling forces, while shear strength maintains structural integrity by resisting sliding forces between layers. These properties make Alucobond panels a reliable choice for modern construction and architectural needs. The mechanical characterization of these panels involves experimentally assessing formability, which reflects stiffness; a higher Young’s modulus indicates a stiffer material, as noted by Kim et al. Adjusting the core material and its thickness can tailor the panels for specific applications, taking into account maximum load and deformation limits. These parameters are crucial for selecting the appropriate panel for specific uses, ensuring safety, durability, and aesthetic appeal in various environments.

Furthermore, the development of materials that offer flexibility, lightness, and a balance between strength and durability has been a longstanding goal. This has led to the study of foam cores, with researchers comparing the deformation characteristics of aluminum foam cores with thermoplastic facings to those of polymer foam core sandwich structures under four-point bending. For example, Ahkami et al. examined the limit deep-drawing ratio (LDR) of Al3105/PP/Al3105 sandwich sheets, validating their experimental results through simulations using the Gurson-Tvergaard-Needleman damage model. Numerous studies have explored plates, shells, and laminated composites in the form of sandwich structures investigated the impact of skin and core layer thickness on forming potential using finite element modeling. , Therefore, Mussa and Salih demonstrated that integrating 30% wood fibers into a plastic matrix could reduce the thermal conductivity of the resulting ACP by approximately 25%, leveraging the natural insulating properties of wood.

Recent research by Bendarma et al. analyzed the behavior of Alucobond composite structures under ballistic impact, conducting tensile and compression tests at various strain rates on a composite made of AW5005 aluminum and Low-Density Polyethylene (LDPE). These studies revealed that the mechanical properties of these materials vary with strain rate and temperature. Finite element simulations of fracture behavior in ACP samples have been used to study how the material’s stiffness degrades under tensile loading, assuming a stable and progressive fracture. Incorporating actual tensile test data enhances the accuracy of these simulations, as demonstrated by Hossain et al. using ABAQUS. Simulation has also played a key role in processing laminated sandwich structures (AA5182-O/PP/AA5182-O), with studies examining the impact of design parameters on springback. Liu et al. developed a model to explore the compatibility of failure criteria between aluminum and polymer in a three-layered sandwich panel, effectively assessing the safety of plastic forming processes and critical failure in composite sandwich panels.

The plastic core of sandwich structures can be foam-based, as demonstrated by recent studies. Giannini et al. optimized AFS panels by predicting sound transmission loss (STL) using deterministic-statistical energy analysis for both single and double panels. Neu et al. studied industrial Autoclaved Fiber Cement Sandwich (AFS) panels for car bodies by using X-ray radiography to identify weak points in the foam core, proposing it as an alternative for lightweight automotive bodywork. Moreover recent studies highlight advancements in carbon fiber-reinforced polymer (CFRP) sandwich structures. One enhances mechanical properties and formability through additive manufacturing-induced anisotropies, Rithika and Sudha. Another investigates the clinching of CFRP/aluminum alloy sheets with a composite sandwich structure to ensure mechanical integrity, Wang et al.

The innovation in ACP design lies primarily in the shaping and refinement of the plastic core between two aluminum sheets, creating a rigid and durable material for various applications while maintaining standardized thicknesses. Standardized core thickness ensures consistent manufacturing and uniform mechanical properties, which are essential for mass production and large-scale applications. This approach also facilitates customization to meet specific functional needs, such as energy absorption, impact resistance, or weight reduction, while ensuring compatibility with existing industrial processes. By improving the core material and thickness, manufacturers can achieve a balance of strength, lightness, and durability, making ACPs highly adaptable for diverse industries. For example, in the automotive industry, lightweight yet durable ACPs can be used for vehicle body panels, reducing overall weight and enhancing fuel efficiency while maintaining safety standards. In aerospace, ACPs can be employed for interior cabin components or exterior structures, with AA surface strengthening techniques like shot peening to ensure high strength-to-weight ratios. , Similarly, in marine engineering, ACPs offer excellent corrosion resistance and durability, making them ideal for shipbuilding. ,

This paper presents an experimental and numerical study of the tensile strength of Aluminum composite panel AA-PE-AA specimen, tested both individually and in bonded with configurations. The goal is to identify the optimal core thickness of the plastic material to achieve an ideal balance between performance, durability, and material efficiency. The enhancement process is based on a comprehensive evaluation, ranging from elastic deformation and plastic behavior to specimen failure. The combination of aluminum and polyethylene in the material structure adds complexity to the study, requiring advanced modeling techniques to capture the interactions between the layers and accurately predict the mechanical response under different configurations.

2. Materials and Methods

2.1. Materials

The Aluminum Composite Panels (ACP) used in this study have a sandwich composition of Aluminum/Polyethylene/Aluminum (AA/PE/AA). The panels were commercially acquired, and the following material specifications are provided to clarify their structural characteristics.

The AW5000 series refers to aluminum–magnesium (Al–Mg) alloys known for their excellent corrosion resistance, high strength, and good weldability. These alloys are widely used in marine, aerospace, transportation, and structural applications due to their durability and resistance to harsh environments. This aluminum alloy (AA) is a non heat-treatable aluminum–magnesium alloy known for its excellent corrosion resistance, good weldability, and moderate strength. It has a magnesium content of approximately 0.5–1.1%, which enhances its mechanical properties while maintaining good formability. With a tensile strength of around 100–200 MPa and a yield strength of approximately 60–160 MPa, AW5005 is suitable for applications requiring lightweight yet durable materials. It exhibits good anodizing properties, making it an ideal choice for architectural applications, decorative finishes, and signage, Table . Additionally, its density of about 2.7 g/cm³ ensures a high strength-to-weight ratio, while its melting point of around 600 °C provides good thermal stability. The designed AA is also highly resistant to atmospheric and marine corrosion, making it widely used in transportation, roofing, and paneling applications. Its good electrical conductivity allows it to be used in electrical enclosures and busbars, while its ease of fabrication supports bending, forming, and welding processes.

1. Mechanical Properties of the AW 5005 Aluminum Alloy (AA) .

Modulus of Young (MPa)	Yield Stress (MPa)	Tensile Strength (MPa)	Poisson ratio	Elongation (%)
69000	45	110	0.33	15

Polyethylene (PE) is a versatile thermoplastic polymer known for its lightweight, durability, and chemical resistance. It has a low density (0.91–0.96 g/cm³), making it one of the lightest plastics available. PE exhibits excellent impact resistance and high flexibility, even at low temperatures, which makes it ideal for applications requiring toughness and resilience. It has a melting point ranging from 105 to 135 °C, depending on the grade, and possesses low moisture absorption, ensuring stability in humid environments. PE also demonstrates good electrical insulation properties, making it suitable for wiring and cable applications. Additionally, it offers strong resistance to most acids, bases, and organic solvents, contributing to its widespread use in chemical storage containers and piping. However, PE has relatively low mechanical strength and poor UV resistance, which can be improved through additives or reinforcements. Common types of polyethylene include Low-Density Polyethylene (LDPE), High-Density Polyethylene (HDPE), and Ultra-High-Molecular-Weight Polyethylene (UHMWPE), each tailored for specific applications, ranging from packaging films to heavy-duty industrial components. Table summarizes the key mechanical properties of the HDPE, providing essential parameters for evaluating its structural performance.

2. Mechanical Properties of the HDPE .

Modulus of Young (MPa)	Yield Stress (MPa)	UTS (MPa)	Poisson Ratio	Density (g/cm3)
965	10	29	0.4	0.953

2.2. Methods

2.2.1. Experimental Setup

A tensile study of aluminum composite panels (ACP), such as Alucobond AA/PE/AA, provides valuable insights into their mechanical behavior, focusing on properties like tensile strength, elongation at break, and the modulus of elasticity. These properties are evaluated using carefully prepared specimens, with their geometry and dimensions standardized to ensure consistency. Rectangular strips are cut from larger ACP sheets, and precise measurements are taken to maintain uniformity across all samples.

The specimens are tested in a Universal Testing Machine, specifically an INSTRON model, equipped with clamps and an extensometer to accurately monitor deformation. The UTM applies a uniaxial tensile load at a controlled rate, gradually increasing the load until the specimen elongates and ultimately fails, Figure . This process generates critical data on the material’s response to stress, including its ability to withstand tension and deformation before failure. It features advanced load cells, a high-capacity frame with a load range of 10 kN to 50 kN, and user-friendly software for precise tensile, compressive, and flexural testing. Capable of real-time data acquisition, it accurately measures stress–strain behavior, load–displacement curves, and mechanical properties, making it ideal for evaluating Aluminum Composite Panels (ACP) under controlled conditions.

1.

Experimental setup and specimens used for the tensile test: (a) 1 ACP, (b) 2-bonded ACP, (c) 3-bonded ACP.

Each specimen is carefully cut using a CNC router to achieve precise dimensions and smooth edges, eliminating imperfections that could lead to inaccuracies in the results. Critical dimensions, such as gauge length, are clearly marked on each specimen to enable precise positioning in the testing machine. This attention to detail ensures consistency and reliability in the testing procedure, leading to accurate and repeatable results.

Accurate specimen dimensions are critical for obtaining reliable tensile test results. Specimens are cut into standardized rectangular strips with a consistent cross-section to ensure uniform stress distribution during testing. The specimen thickness matches the ACP material being tested, falling within the range of 4 to 11 mm. The effect of loading on the performance of the sandwich panels was also evaluated.

2.2.2. Computer Modeling

Computational FEM provides a reliable alternative to experimental methods, with the unique ability to assess the local mechanical response of materials and determine the direct impact of specific parameters. In this study, finite element simulations were carried out using Abaqus/Explicit (SIMULIA, Dassault Systèmes, version 2023) to account for material nonlinearities and to simulate the tensile test up to failure. A three-dimensional model was constructed to represent the composite specimens panels (AA/PE/AA).

The specimen geometry was modeled to closely match the real structure and dimensions. The 3D models were partitioned to differentiate between the aluminum and polymer components (Figure ). Contact between the aluminum and polymer regions was defined as fully tied. The tie constraint was used to model perfect bonding between the aluminum skins and the polyethylene core, based on the manufacturing process of the ACPs, which ensures strong adhesive bonding. No interfacial failure or debonding was observed during the experimental tensile tests, supporting this simplification.

2.

Studying bonding specimens 1, 2, and 3 (a) and the effect of PE thickness (t _PE) from 3 mm to 10 mm (b).

An 8-node linear hexahedral with reduced integration elements (C3D8R) are used for meshing. Mesh refinement was applied in regions of high stress concentration to ensure numerical accuracy, with a finer mesh applied to the central region. Boundary conditions were defined to replicate experimental setups, with one end of the specimen fixed and the other subjected to a gradually increasing tensile displacement.

In this study, both the aluminum skins and the polyethylene (PE) core are modeled as ductile materials capable of undergoing damage and progressive failure under tensile loading. Ductility and toughness were considered as key properties governing the overall mechanical response of the bonded aluminum composite panels (ACPs), particularly in delaying localized failure and preventing brittle fracture.

To replicate the experimental tensile tests, a quasi-static explicit simulation incorporating ductile damage initiation and evolution was employed. The ductile fracture model was based on a phenomenological damage criterion that defines the onset of fracture through the accumulation of equivalent plastic strain. Material degradation was simulated by element deletion, where elements are progressively removed from the mesh once the damage variable reaches its critical value (D = 1), indicating complete material failure.

3. Results and Discussion

The tensile testing process using the UTM was conducted in multiple phases to evaluate the material’s behavior under various conditions, ensuring a thorough understanding of its mechanical properties. To guarantee the reliability and accuracy of the results, each test was repeated twice, ensuring data consistency and statistical significance. This repetition was crucial for verifying the reproducibility of the observed trends and confirming the reliability of the conclusions drawn from the tests. The methodology allowed for a detailed exploration of the material’s tensile properties across different configurations, including varying strain rates and specimen arrangements.

The results of these tensile tests are essential for evaluating the mechanical performance of ACPs and their suitability for various structural applications. They provide insights into the material’s reliability under real-world conditions, ensuring it meets the required standards for load-bearing structures. This information is crucial for developing safer and more efficient building materials.

To investigate the effect of thickness on mechanical behavior, Alucobond specimens were prepared in two- and three-layer configurations. Special care was taken to ensure durability and prevent slipping between layers during testing. Tensile tests were conducted for each configuration, with the materials stressed until failure occurred.

3.1. Reproducibility of Experimental Measurements

The curves presented in Figure illustrate the load–displacement relationship, revealing how the ACP specimen responds to an applied tensile force. Five tensile tests were performed, and only the two extreme curves were presented. In the test, the specimen is pulled at a strain rate of 20 mm/min, with the load gradually increasing until the specimen fractures. The resulting elongation is measured simultaneously.

3.

Reproducibility of tensile tests of ACP specimen at V = 20 mm/min.

The load–elongation curve details the behavior of the ACP specimen under tensile stress. Initially, in the linear region (elastic deformation), the load and elongation exhibit a linear relationship, where the slope corresponds to the material’s stiffness. As the load increases to 700 N, the specimen reaches the yield point, marking the onset of plastic deformation, where the relationship between load and elongation begins to deviate from linearity.

The consistent replication of the tensile curves across both test repetitions indicated a high degree of reliability in the data, confirming that the testing process was robust. However, despite the consistency in the overall tensile curve, variations in fracture behavior were observed between specimens. These discrepancies can be attributed to the nonuniformity of the core material, a characteristic often found in composite materials like aluminum composite panels (ACP). Nonuniformities in the core materials such as uneven distribution of fillers, variations in resin content, or inconsistent curing during the manufacturing processcan result in localized weak points. These inconsistencies can lead to differential stress distribution within the material, ultimately affecting how the specimen fractures under tensile loading as mentioned by Kroon et al.

3.2. Effect of the Strain Rate

The strain rate influences the mechanical behavior of materials, particularly their transition between ductile and brittle states. At higher strain rates, materials tend to exhibit a reduced capacity for plastic deformation. This is especially critical in applications involving rapid deformation, where unexpected failures can occur if the material’s response to high strain rates is not properly understood.

In the case of Alucobond, which consists of a metal reinforcement and a central polymer core, the combination of two different materials makes mechanical behavior prediction more complex. The metal exhibits strain-rate-dependent plasticity, while the polymer core, being viscoelastic, responds differently to varying loading speeds.

To assess the effects of crosshead speed variations, tensile tests were conducted on Alucobond at two loading speeds: 20 mm/min and 50 mm/min (Figure ). The results indicate that increasing the strain rate primarily affects the maximum stress and the yield strength. However, the apparent Young’s modulus remained relatively unchanged, indicating that the elastic behavior of the material was not significantly affected.

4.

Effect of load velocity on the ACP specimen.

The aluminum reinforcement, typically ductile, exhibited reduced plastic deformation capacity at higher strain rates due to restricted dislocation mobility, making it more prone to early failure. Meanwhile, the viscoelastic polymer core showed increased stiffness with higher strain rates, reducing its ability to absorb energy and leading to a more brittle failure mode. These findings underscore the importance of considering strain rate effects in the design of composite materials, particularly for applications subjected to dynamic loading.

3.3. Assessing the Effect of Specimen Number on Tensile Behavior

3.3.1. Experimental Investigation

To examine the effect of varying Aluminum Composite Panel (ACP) thickness, a specimen-stacking approach was employed, bonding multiple specimens to simulate increased thickness. Two specimens were initially bonded and tested to assess the adhesive interface’s influence on tensile strength and elasticity. These tests revealed critical insights into load distribution and deformation behavior at the bonded interfaces.

Subsequent tests involved three bonded specimens, further increasing thickness and introducing an additional interface. This allowed a systematic analysis of the combined effects of thickness and multiple interfaces on mechanical properties, including stiffness, yield strength, and elongation at break. The findings highlighted how additional layers influenced structural performance and deformation characteristics.

All tensile tests were carried out at a constant crosshead speed of 20 mm/min, with specimens aligned along the same direction. Adequate clamping pressure was applied to prevent specimen slippage, ensuring cohesive behavior and accurate simulation of varying thicknesses under realistic conditions. This stacking methodology provided a controlled means to study the mechanical behavior of ACP, offering valuable insights into how thickness influences key properties such as tensile strength, elasticity, and load-bearing capacity. These findings are essential for applications in protective coatings, structural reinforcements, and load-distribution layers.

Figure illustrates the force–displacement response for one, two, and three bonded specimens, highlighting the effect of specimen number on load-bearing behavior. In all cases, the curves begin with an initial linear region at small displacements, corresponding to elastic behavior, followed by a nonlinear regime characterized by gradual stiffness reduction. The maximum force increases with the number of specimensapproximately 700, 1300, and 2000 N for one, two, and three specimens, respectivelydemonstrating near-proportional scaling of load capacity. Prior to failure, a plateau region is observed, suggesting plastic deformation or load redistribution. At large displacements, the force abruptly decreases, indicating progressive damage accumulation and final structural failure.

5.

Experimental response of the bonded specimens under tensile testing force–displacement.

In the plastic zone, the material exhibited a plateau characterized by significant elongation at maximum load, demonstrating its ductility and ability to undergo substantial deformation without failure. This plateau underscores the material’s capacity to redistribute stress and delay fracture, a critical feature for applications requiring both strength and flexibility. Fracture consistently occurred after approximately 16 mm of elongation, with variations in fracture behavior influenced by the core material’s structure (PE). These results emphasize the core material’s role in shaping mechanical performance and suggest that enhancing its composition could improve resilience and elongation capacity. −

Microscopic observations performed before and after the mechanical test show no evidence of debonding at the aluminum/PE interface. Interfacial adhesion is preserved throughout the loading process, including at the failure stage. As illustrated by the microscopic images, the interface remains intact, indicating effective bonding between the two materials and confirming that failure is not governed by interfacial damage (Figure ).

6.

Microscopic observations of the aluminum/PE interface before and after mechanical testing.

3.3.2. Analysis of Apparent Modulus Variation

The apparent Young’s modulus E _app versus number of bonded ACP for each configuration (1ACP specimen, two and three ACP bonded specimens) was determined by analyzing the initial elastic deformation phase and calculating the slope of the corresponding stress–strain curve. This approach reflects the material’s stiffness and resistance to elastic deformation under applied load. Table summarizes the apparent Young’s modulus E _app values for each test, demonstrating the consistency of elastic properties across different bonded specimens and thicknesses, as well as the reliability of the bonding process.

3. Experimental Apparent Young’s Modulus E _app versus Specimen Number.

Number of ACP (n)	1 ACP specimen	2 ACP specimens	3 ACP specimens
E app (MPa)	2108.05	1919.45	1788.81

These findings provide key insights into the mechanical behavior of bonded specimens, emphasizing the interplay between thickness, elastic properties, and core material structure. This knowledge is essential for developing composite materials tailored to specific performance demands, particularly in applications requiring a balance of strength and deformation capability.

3.3.3. Numerical Investigation

Numerical study was performed for each case using Abaqus to simulate the tensile deformation behavior of aluminum composite panel (ACP) specimens, specifically AA/PE/AA composites. The analysis aimed to provide a detailed understanding of the mechanical response, focusing on predicting key properties such as the Young’s modulus and characterizing the transition from elastic to plastic deformation up to failure, as illustrated in biomechanics by Ketata et al. in the case of an artificial knee. Particular attention was given to identifying the plateau of plastic deformation, a critical phase where the material sustains maximum stress variation, signifying the onset of structural instability and marking the conclusion of the tensile test.

3.3.3.1. Effect of the Number of Specimens on Tensile Behavior

Figure shows a strong agreement between numerical load-deformation curves and experimental data for the specimen configurations : One, bonded Two, and bonded Three. This validates the accuracy of the computational models. The slope of the elastic domain, derived from numerical simulations, matches closely with experimental measurements from UTM machines. This confirms the reliability of the method in predicting the material’s elastic properties. Moreover, the fracture of bonded specimens occurs consistently within a displacement range of 14 mm to 16 mm. This indicates high reproducibility in both numerical and experimental approaches. The consistency highlights the robustness of the model in capturing critical failure points. It also reinforces its use for assessing the mechanical performance of composite materials. This alignment between simulated and experimental results shows the potential of the numerical approach. It enables reliable predictions of material behavior in practical engineering applications.

7.

Numerical and experimental force–displacement curves for bonded ACP specimens.

3.3.3.2. Stress Distribution

The analysis of von Mises stress distribution allows for a comparison of the three configurations: a single specimen, two bonded specimens, and three bonded specimens (Figure ). The results reveal distinct behaviors in terms of stress distribution, particularly between the internal and external layers of the composite. Considering a single specimen, aluminum, which has the highest stiffness compared to polyethylene (PE), bears a greater load and experiences stresses around 52 MPa during specimen elongation. At the point of fracture, as observed experimentally, aluminum undergoes premature rupture, while PE undergoes further elongation before breaking.

8.

Effect of specimen number von Mises stress distribution during deformation up to failure.

In the two-bonded and three-bonded specimen configurations, a decrease in stress is observed in the internal layers compared to the single specimen configuration. This reduction is particularly evident in the von Mises stress distributions, indicating that the AA internal layers are subjected to less intense loading. This redistribution of stress suggests that the AA external layers now bear the highest load, leading to a better distribution of stress within the structure.

Furthermore, examination of the internal AA layers reveals that these are subjected to even lower stresses than the external layers, especially in the two-bonded and three-bonded configurations. This phenomenon shows that the internal layers play a secondary role in carrying the applied load. This observation opens the way for material refinement: it could be beneficial to replace the internal AA layers with a thicker core material, such as PE, without compromising the mechanical integrity of the composite. Such a modification could not only improve material efficiency by reducing costs and the use of unnecessary materials but also increase the composite’s energy absorption capacity under tensile loads.

This analysis highlights the importance of optimized material design to maximize the performance of bonded composite structures, particularly in terms of stress distribution and mechanical strength.

3.3.3.3. Effect of PE Core Thickness

The proposed design modification involves increasing the thickness of the polymer in the sandwich structure and studying its effect on the mechanical behavior of the panels, which are suitable for advanced building applications.

Figure presents the force–displacement response curve for AA-PE specimens of different thicknesses. This analysis allows for the evaluation of the influence of thickness of PE on the mechanical properties of the material.

9.

Force–displacement curves as a function of PE core thickness variation in ACP specimens.

We observe that increasing the core thickness leads to a higher maximum applied force, as a larger cross-sectional area allows the material to sustain greater loads before failure. The yield force also increases with thickness, indicating a higher initial resistance to plastic deformation. This trend is approximately linear, with each additional millimeter of thickness increasing the maximum force by about 170 N.

Interestingly, the displacement at failure remains close to 18 mm for all specimens, suggesting that the material maintains a similar deformation capacity regardless of thickness. This indicates that the overall ductility of the composite is relatively unaffected by the core thickness, which is beneficial for predictable structural behavior in engineering applications.

The numerical analysis offers a detailed visualization of the stress distribution across the composite material, utilizing the von Mises criterion. The stress maps presented in Figure reveal distinct behaviors for the different components of the aluminum composite panel (ACP). Three PE thicknesses (t _PE = 3 mm, 6 mm, and 9 mm) are selected to evaluate the stress distribution at four displacement levels in different domains: (A) in the elastic domain at U = 0.2 mm, (B) at the beginning of plastic deformation at U = 5.6 mm, (C) at the end of the plastic flow domain at U = 16 mm, and (D) the post fracture zone at U = 18 mm. The selected PE thickness influences the stress distribution across these four displacement levels, revealing critical transitions from elasticity to plasticity. These layers undergo a shift from the elastic region to the plastic deformation plateau, where irreversible strain accumulates under sustained loading, significantly influencing the structure’s mechanical response. Furthermore, the behavior observed in these four zones (A, B, C, D) provides valuable insights into stress distribution patterns, structural performance, and potential failure points. For low deformations (A), the von Mises stress level remains low in both the PE and AA regions. The specimen with t _PE = 9 mm in domain (B) exhibits greater stiffness and higher tensile resistance, reaching up to three times that of the t _PE = 3 mm specimen. The AA outer layers experience stress ranging from 35 to 52 MPa, demonstrating relatively high stress levels that highlight their critical role in distributing and bearing the applied load. This stress concentration in the outer layers confirms their function as the structure’s primary load-bearing components. At U = 16 mm (C), the t _PE = 3 mm specimen exhibits localized deformation, leading to premature failure compared to the thicker specimens, which still maintain tensile resistance. At U = 18 mm (D), all specimens have reached failure. These findings emphasize the importance of enhancing the design and material properties of the outer layers, whether by selecting high-performance alloys or refining layer thickness ratios, to enhance the structure’s overall load-bearing capacity and durability.

10.

Von Mises stress distribution in ACP specimens with various PE core thicknesses (t _PE = 3 mm, 6 mm, and 9 mm) at various displacement levels: (A) U = 0.2 mm, (B) U = 5.6 mm, (C) U = 16 mm and (D) U = 18 mm.

This distinct behavior underscores the composite nature of the ACP, where the elastic PE core provides support and stability to the stiffer AA outer layers, which bear most of the deformation and energy absorption. The numerical results offer valuable insights into the mechanical interaction between the ACP’s core and outer layers, highlighting the composite’s design efficiency under tensile stress.

Further numerical investigations have shown that variations in core thickness significantly influence the load-bearing capacity of the panels. The analysis demonstrated that increasing the core thickness not only enhances the structural stability of the composite but also establishes a foundation for manufacturing thicker, more robust ACPs capable of withstanding higher stress levels. This finding underscores the critical role of core refinement in composite design.

This relationship between core thickness and mechanical behavior can be quantitatively modeled using an empirical regression approach, providing a predictive framework for future ACP development and ensuring their adaptability across a wide range of engineering and architectural applications.

Through numerical simulations conducted on bonded AA/PE/AA specimens, the study successfully optimized the plastic core thickness, paving the way for the development of sandwich panels with superior mechanical properties. A thicker plastic core would enable the panels to support higher loads while maintaining the lightweight and cost-effective characteristics essential to their functionality. Additionally, by keeping the aluminum thickness unchanged and adjusting the polymer composition, it is possible to use recycled polymers, thus contributing to a more sustainable and environmentally friendly approach.

This approach aims to enhance the overall structural performance of aluminum composite panels (ACPs) by increasing their rigidity and load-bearing capacity, making them more suitable for demanding construction environments.

3.4. Determination of the Equivalent PE Core Thickness

Among the most important parameters in the study of composite materials is the evaluation of the Young’s modulus. The apparent Young’s modulus is a fundamental mechanical property that characterizes the overall stiffness of composite materials, such as AA/PE/AA sandwich panels. Unlike the intrinsic Young’s modulus of individual layers, the apparent modulus reflects the combined influence of the different material layers and their respective thicknesses. In sandwich structures, this property is significantly impacted by the elastic behavior of the AA skins and the PE core, as well as the quality of the interface bonding between the layers.

This parameter plays a critical role in assessing the structural performance of sandwich panels under various loading conditions. It provides valuable insight into how changes in the thickness of the PE core or aluminum layers influence the overall rigidity of the composite. Furthermore, understanding the apparent Young’s modulus E _app is essential for optimizing the design of sandwich structures, especially in applications where high performance and low weight are crucial.

The calculation of the apparent Young’s modulus can be approached using empirical or analytical models, which take into account the mechanical properties of each layer. In the case of AA/PE/AA composites, the aluminum layers generally dominate the stiffness due to their higher modulus, while the PE core has a secondary role, mainly contributing to deformation and energy absorption.

Figure illustrates the decreasing trend in the evolution of Young’s modulus as a function of the PE thickness. An empirical equation has been evaluated to highlight this evolution, which can be expressed as

$$E=983.27+2462.63\exp (-0.26t_{\mathrm{P}\mathrm{E}})$$ 1

where E is the apparent Young’s modulus, t _PE is the thickness of the PE core.

11.

Fitted curve of the apparent Young’s modulus (E _app) as a function of PE thickness (t _PE) based on numerical results.

The overlay of the experimental and numerical curves shows an accurate correlation between the t _PE = 9 mm specimen and the superposition of three specimens. This result confirms the reliability of the numerical model in simulating the mechanical behavior of the composite structure. The consistency between both approaches suggests that adjusting the PE core thickness can effectively replace the traditional method of stacking specimens without compromising the accuracy of the results, Figure . These findings provide valuable insights for future ACP design, offering a more efficient and cost-effective solution while maintaining the required structural performance. Further studies should focus on validating this approach under different loading conditions and exploring the potential for even more efficient material configurations.

12.

Comparison of the mechanical behavior of ACP panels with PE core thicknesses of 6 and 9 mm relative to configurations with two and three bonded ACP specimens.

This study focused on uniaxial tensile loading, which does not fully capture the mechanical response of ACPs under more complex stress states. Future work should consider different loading directions and include flexural tests to better assess the behavior of the material under real-world conditions.

4. Conclusions

The simulations provided a detailed visualization of the deformation progression, including stress distribution, strain localization, and failure mechanisms, capturing the material’s response up to damage. This numerical approach not only confirmed the reliability of the predicted mechanical properties but also revealed critical insights into the ACP’s structural integrity under varying loading conditions. By establishing a robust correlation between numerical and experimental results, the study highlights the potential applications of AA/PE/AA composites in engineering designs requiring lightweight yet durable materials, particularly under tensile stresses.

The deformation behavior of AA/PE/AA sandwich sheets was investigated through tensile tests conducted on assembled samples with varying thicknesses. The phases of deformation, including elasticity, the plasticity plateau, and the rupture or tearing of Alucobond specimens, were systematically evaluated. Global behavior was identified, accounting for the thickness of the aluminum and the thickness variations of polyethylene layers. Apparent properties, such as Young’s modulus and stiffness, were estimated using empirical laws tailored to the thickness of the PE core. To further analyze the observed behavior and predict instability in the plastic deformation of the sandwich sheets, simulations were conducted using Abaqus, successfully replicating the experimentally measured load-deformation behavior. A precise prediction of the composite’s elastic modulus was achieved, closely matching experimental results. The elastic-plastic transition was identified, emphasizing the critical role of the PE core in load distribution and fracture delay. Stress distribution maps revealed that deformation predominantly occurred in the aluminum layers (AA), while the PE core remained largely unstressed during elastic loading. Furthermore, fracture was predicted within a strain range consistent with experimental observations, validating the model’s reliability. These findings demonstrate that the Abaqus model effectively captures the complex tensile deformation behaviors of sandwich sheets, providing valuable insights for material enhancement and composite design.

Glossary

Abbreviation

AA

Aluminum Alloy

ACP

Aluminum Composite Panels

AFS

Autoclaved Fiber Cement Sandwich

CFRP

Carbon Fiber-Reinforced Polymer

CNC

Computer Numerical Control

E _app

Young’s Modulus Apparent

FEM

Finite Element Methods

LDR

Limit Deep-Drawing Ratio

PE

Polyethylene

UTS

Ultimate Tension Test

The authors declare no competing financial interest.