Aluminum Structures Research Articles

Analysis of the Influence of Adhesive, Geometry, and Manufacturing Processes on Mixed Mode Stress Ratio in Single Lap Shear Adhesive Joint Structures of Aluminum and Composite Plates

In aircraft structures, composite plate joints often present significant challenges. Mechanical fastenings such as pins, bolts, or rivets require holes to be drilled in the plates, which reduces the strength of the laminate due to stress concentrations around the hole edges. These joints frequently become sources of structural failure in aircraft. Therefore, the design of composite plate joints is crucial to maintain structural integrity. Adhesive joints offer several advantages over mechanical joints, including the ability to join two different materials, more uniform stress distribution along the joint, and reduced weight since no bolts or rivets are needed. The most common adhesive joint design is the Single Lap Joint (SLJ), which is popular due to its simple geometry and high structural efficiency. However, the main drawback of the SLJ is load eccentricity, which leads to secondary bending and undesirable normal stresses along the adhesive edges. The hypothesis of this study is that SLJ conditions with optimal shear strength can be achieved through the right combination of adhesive type, bond surface preparation, and joint configuration. This study analyzes the influence of various adhesive materials, joint designs, and manufacturing methods using numerical modeling methods, validated with analytical approaches and ASTM standard testing. Numerical modeling is conducted using the finite element method with a cohesive zone model (CZM) approach to examine stress distribution in various cases, such as the impact of geometry, adhesive thickness, and joint length. The normal and shear stress distribution along the joint is found to significantly affect the strength of the SLJ, highlighting the importance of careful design and material selection in these applications.

On the role of local reinforcement in an adhesively bonded AL/CFRP energy absorber under axial loading: A theoretical investigation and optimization

AbstractThis paper aims to develop a novel theoretical model that incorporates the effects of local composite reinforcement using adhesive bonding on the energy absorption of aluminum structures under axial loading. The goal is to optimize energy absorption prior to any connection failures and to prevent uneven structural deformation. Moreover, it strives to reduce the structure's weight and material usage, achieving superior results compared to traditional global reinforcement techniques. The theoretical model was validated through experimental testing and finite element analysis, demonstrating good agreement with the predicted results. The results reveal that increasing the CFRP fiber angle, layer thickness, and number of layers generally leads to improved energy absorption capacity. An optimization analysis was performed to determine the optimal design parameters, yielding a fiber angle of 80°–90°, composite thickness of 1.5 mm, and aluminum thickness of 2.5 is the best configuration, offering the highest specific energy absorption and adequate peak load capacity for maximized energy absorption. The proposed model offers significant improvements over existing approaches, enhancing the predictive capabilities and practical applicability of energy absorption predictions in engineering design.Highlights A novel theoretical model for energy absorption in locally reinforced hybrid AL/CFRP structures. The influence of design parameters, such as CFRP layer count, fiber orientation, and thickness ratio. Optimization to maximize the average crushing force while meeting weight and geometric constraints. Findings can inform the design of safer and more efficient energy‐absorbing structures in various applications.

Influence of the stoichiometric ratio of barrier layer alumina on the transport properties of Josephson junctions

In the field of quantum computing, the Josephson junction is one of the main components for generating superconducting qubits. The material defects present in the junction affect the stability and reproducibility of qubits, which consequently limits the performance of quantum computing. In this paper, we conduct a detailed study of the crystal structure of alumina at different stoichiometric ratios and its electrical properties using density-functional theory (DFT). Additionally, we simulate the amorphous structure at various stoichiometric ratios using molecular dynamics methods. Our results show that a decrease in the oxygen content in the crystalline alumina material leads to a linear reduction in the bandgap. We then construct Josephson junction models with different stoichiometric ratios of the barrier layer based on our study, and calculate the equilibrium conductance for each model using the Non-equilibrium Green’s Function (NEGF) method. Our results indicate that the structure of the barrier layer significantly affects the electrical properties of the Josephson junction. Moreover, the stoichiometric ratio of alumina is a critical parameter that results in exponential variations in the equilibrium conductance. In summary, we seek to elucidate the role that variations in the stoichiometric ratio of the oxide play in the transport properties of the junction. Our findings provide a theoretical basis for improving the stability and performance of superconducting qubits.

Design and development of smart AI-based voice assistive ergonomic commode wheelchair for mobility and rehabilitation

This study focuses on enhancing assistive devices for the elderly and disabled, primarily addressing the challenges associated with traditional wheelchairs. While wheelchairs are widely used for basic mobility, the research identifies several issues in existing products, such as a lack of attention to ergonomic features, anthropometric principles, and limited technological interventions. One major concern is the discomfort experienced by users over extended periods, especially when essential design elements like height and back adjustments are neglected. Another challenge highlighted is the issue of defecation, particularly in the absence of a caregiver. This dependency on caretakers can be mentally burdensome for users, raising privacy concerns during such personal activities. To address these issues, this research proposes a solution that integrates ergonomic features and incorporates low-cost technological interventions, including artificial intelligence-based voice assistance. The ultimate goal of this paper is to design and introduce an AI-based voice-assisted ergonomic wheelchair that not only supports basic mobility but also ensures comfort over extended periods. The proposed solution aims to incorporate a commode feature for defecation within a smart ergonomic wheelchair equipped with voice assistance and provide comfort to the user(s). The design prioritizes anthropometric dimensions, ensuring comfort and convenience for users across various age groups. Employing SolidWorks software, a stable and robust model has been designed, and its durability was assessed through stress analysis using the SolidWorks simulation tool by applying a 981 Newton load on the wheelchair's frame using two different materials (steel and aluminum). The maximum stress value is less than the yield strength, and the deformation is 2.57 e+00 mm for the steel frame, indicating that the design is stable and durable compared to the aluminum structure. The proposed voice-assistive, ergonomic, AI-based wheelchair with a commode cavity is a revolutionary development for the healthcare sector in terms of innovation.

Atomic-scale investigation on the structures and mechanical properties of metastable grain boundaries in aluminum

Grain boundary (GB) structural transition in pure metals open up new possibilities for material microstructure design. By managing the distribution of ground-state and metastable GB structures, the beneficial effects of GBs on materials can be maximised. However, the application of GB transitions to develop high-performance aluminum is limited by the inadequate understanding of the metastable GB structure in aluminium and its associated plastic deformation mechanisms. In this work, we firstly used a high-throughput GB generation method to construct multiple GB structure for a given misorientation angle, and screen out the ground-state and metastable GB structures according to the energy principle. Six typical symmetrically tilted GBs were investigated, including Σ5(210), Σ17(410) and Σ17(530) GBs around <001> tilt axis, and Σ9(221), Σ11(332), Σ17(223) GBs around <110> axis. Then, molecular dynamics simulations were carried out to perform uniaxial tensile tests on the six GBs and their corresponding metastable GBs at different temperatures. The results show that the tensile strength of <001> metastable GBs differs slightly from the ground-state GB at various temperatures, but for <110> GBs, the strength of most metastable GBs is significantly stronger or weaker compared to that of ground-state GB at 10 K. An increase in temperature reduced this difference in tensile strength of <110> GBs. According to atomic analysis of the GB structural characteristics, it was found that stress and temperature-induced GB structural transition, GB strain localization, and the prevention of dislocation nucleation or propagation from the dissociated structure are the main causes of the differences in tensile responses between the ground-state and metastable GBs.

Modelling of closed-cell aluminum foam using Weaire–Phelan unit cells

AbstractDesign and testing of real materials is a costly process and usually requires some specific equipment. To alleviate this task numerical methods can be leveraged. In this work we show possible modelling technique for closed-cell material structure using Weaire–Phelan unit cells. As an example existing aluminum structures were used and modelled parametrically, allowing to establish different geometrical models for different applications. Numerical simulations for compression was also done on the developed models to reveal the material response. The influence on the cell wall thickness and the friction between the material and the compression plate was investigated. It was found that the friction coefficient has no significant effect on the material response, except in the case where bonded connection was assumed. It was also demonstrated that material response and the porosity controlled by cell wall thickness have an approximately linear relationship with each other. This method proved to be a flexible and alternative solution of real laboratory tests and targeted to reduce costs of material design.

A non-melting additive approach to structural repair of aluminum aircraft fastener holes

The damage to fastener holes in aerospace aluminum structures presents significant challenges for aircraft durability, and conventional bushing methods for repairing oversized holes often fall short due to the lack of metallurgical bonding and limited edge distance availability. This study investigates additive friction stir deposition, a non-melting additive process, as a viable alternative for the structural repair of aerospace fastener holes. The repair process, demonstrated on AA7050 (Al-Zn-Mg-Cu-Zr) hole structures, involves filling oversized holes with new material and machining to restore the original hole size. The repaired hole coupons are defect-free and exhibit good fatigue performance under fully reversed tension-compression loading (R = -1). At a nominal stress amplitude of 123.5 MPa, the average number of cycles to failure is 12,666 for unrepaired baseline coupons and 17,372 for effectively repaired coupons. Restoring complex geometries without compromising fatigue performance has been difficult in aerospace applications; this study marks the first demonstration of additive repair that consistently outperforms the unrepaired baseline coupons. Notably, the result is achieved through a low-energy, cost-effective solution without the need for post-repair heat treatment. Except for a few outliers, the post-repair fatigue performance generally remains inferior to that of undamaged, pristine coupons, likely due to precipitate evolution in AA7050 caused by the thermomechanical processing nature of additive friction stir deposition. This evolution weakens the repair region and the adjacent base material, leading to faster crack initiation and growth compared to the properly aged base material, AA7050-T7451.

Heteronuclear Fe-Mn Cyclopentadienyl Complexes Supported on Boehmite. Thermochemistry and Thermodynamics of their Decomposition

Boehmite samples with compounds of the composition (C5H5)2FeMnX2(μ-CO)n, where X=Cl, Br and n=1.2, precipitated at room temperature from tetrahydrofuran solutions and then heated in an air flow up to 873 K were obtained and characterized using X-ray diffractometry, infrared Fourier spectroscopy, electron magnetic resonance and temperature-programmed desorption methods. It was shown that the thermal decomposition of these compounds applied to the boehmite samples in the range from room temperature to 873 K occurs stepwise and consists of at least two stages. The first stage of thermal decomposition occurs in the range of 453–753 K, and the second – in the range of 813–843 K. The XRD data show that when calcining at 873 K the boehmite samples with the applied compounds of the above composition and containing these compounds less than 10 wt.%, the diffraction patterns show only reflections characteristic of poorly crystallized aluminum oxide. However, the electron paramagnetic resonance (EPR) spectra of these samples clearly show intense signals characteristic of superpara/ferromagnetic particles of iron and manganese oxides, as well as EPR signals from isolated Fe3+ substituting Al3+ ions in the aluminum oxide structure. EPR spectra most of the iron and manganese is stabilized on the surface of poorly crystallized aluminum oxide in the form of nanostructured iron and manganese oxides.

Poliface: A Multi-pose Synchronous Imaging System

To enhance the accuracy of face recognition technology in real-world scenarios, it is necessary to train deep learning models on datasets that contain a large number of labeled human face images under multiple poses, lighting, and accessory variations. In this paper, we introduce a novel acquisition system named the Poliface. This system can capture multiple high-resolution images simultaneously around the human head. We designed this system with a well-built aluminum structure, control electronic circuits, and high-performing in-house software. The results demonstrate the precise operation and exceptional stability of this system. Using this Poliface system, we have collected over 6 million photos, which can be used to train and evaluate facial recognition models, and exploited for three-dimensional (3D) virtual face reconstruction.

Analysis and Experimental Study for Fatigue Performance of Wing-Fuselage Connection Structure for Unmanned Aerial Vehicle

(1) Background: As the principal structural element of an unmanned aerial vehicle (UAV), a lightweight, high-performance wing-fuselage connection structure plays an important role in UAV structural integrity. Previous studies focused on the static strength characteristics of aluminum and high-strength steel wing-fuselage connection structures. With the widespread usage of titanium material in aviation, research should address the fatigue performance of titanium wing-fuselage connection structures. This paper aims to investigate the fatigue performance of the titanium wing-fuselage connection structure by using analysis and experimental methods, and to develop a reliable fatigue assessment method based on the experimental results. (2) Methods: General and detail finite element models were established, and the stress distribution at the detail fatigue design point was obtained via finite element analysis. Based on the equivalent life curve theory, a dimensionless value, detail fatigue value (DF), was proposed to characterize the fatigue performance for structure. By using detail fatigue value (DF) method, the theoretical fatigue performance value was calculated. The fatigue test of the wing-fuselage connection structure was conducted, and the fatigue life was determined according to the test results. (3) Results: For the wing joint with fatigue failure in the test, the test fatigue performance was close to the theoretical value. It can be concluded from the DF value that the analysis and test results are consistent, and the values obtained from the analysis are more conservative than test results. (4) Conclusions: The error between the test DF value and the theoretical analysis DF value is small, and the theoretical analysis of fatigue performance can represent the fatigue characteristics of the wing-fuselage connection structure. The detail fatigue value (DF) method can predict the fatigue performance of the structure quite well.

Experimental investigation on composite patch repair for cracked aluminum structures

Experimental investigation on composite patch repair for cracked aluminum structures

Enhancement of the electrical conductivity of APPD manufactured copper conductors integrated into aluminium WAAM structures

Abstract Copper conductors - manufactured by atmospheric plasma powder deposition, insulated by alumina layers and integrated into aluminium structures - were analysed with regard to their electrical conductivity. Variations of a novel electrical post-processing were studied in comparison to standard heat treatment. Both of them showed significant improvement of the specific electrical resistivity.

Structure and properties of aluminoborosilicate glasses for OLED display substrate

The effects of Al2O3/SiO2 and B2O3/SiO2 substitution on the network structure and properties of high aluminium and low boron alkali-free aluminoborosilicate glasses used as OLED display glass substrate were investigated. A more polymerized network within 3 mol.% substitution for Al2O3/SiO2 was obtained, represented by the decreasing value of NBO/T from 0.14 to 0.08, as well as the opposite result for B2O3/SiO2 substitution. Q3 and Q4 units held the vast majority of Si groups, and the tetrahedral [AlO4] occupied the majority among Al groups, while [AlO5] and [AlO6] was too low or even too tiny to be detected obviously in the investigated glass system. [BO4] concentration decreased from 59.04 % to 52.74 % with the increase of B2O3 content, and [BO3] increased accordingly, which indicated that [BO4] was not the preferential borate group in this glass system even if (RO-Al2O3)/B2O3 > 1. Higher [BO3] at lower (RO-Al2O3)/B2O3 value (>1) indicated the low conversion efficiency from [BO3] to [BO4] in the investigated glasses. The glass network between the bulk sample and glass melt was also investigated, and some differences in Al groups could be concluded from the test of the glass melt. Finally, samples with satisfied properties for OLED display substrate were acquired.

Subwavelength structure (SWS) of alumina treated by aluminum dihydrogen phosphate

The subwavelength structure (SWS) surface of γ-AlOOH transformed from sol-gel derived amorphous alumina on a Ge prism and quartz and subsequently followed by the treatment of aqueous aluminum dihydrogen phosphate (AlP) was investigated by optical spectroscopy in the visible region and attenuated total reflection (ATR) infrared spectroscopy, respectively. To facilitate the mechanism of anti-reflection in the SWS based on a graded region in the refractive index, the layer of amorphous alumina was widened by using a two-layer coating and by employing the precursor’s solution with prolonged aging for 6 months. As for the treatment of aqueous phosphate, the enrichment of D2O was applied in combination with infrared spectroscopy. The anti-reflection of the SWS coating on quartz became superior by increasing the thickness of amorphous alumina up to 400 nm, which was reproduced in the simulations with an increase in width of the graded region having the principal gradient of the refractive index. By ATR infrared spectroscopy, aqueous aluminum dihydrogen phosphate was inferred to penetrate into the amorphous layer of alumina left at the interface with the substrate and reacted with it, increasing the refractive index of the amorphous layer. By the enrichment of D2O, it was revealed that there were few pores accessible by the vapor of D2O in the SWS coating treated by AlP. The reaction of the amorphous layer with aluminum dihydrogen phosphate is inferred to prevent corrosion from moisture in the optical glasses beneath in practical camera lenses.

A Proposed Non-Destructive Method Based on Sphere Launching and Piezoelectric Diaphragm.

This work presents the study of a reproducible acoustic emission method based on the launching of a metallic sphere and low-cost piezoelectric diaphragm. For this purpose, tests were first conducted on a carbon fiber-reinforced polymer structure, and then on an aluminum structure for comparative analysis. The pencil-lead break (PLB) tests were also conducted for comparisons with the proposed method. Different launching heights and elastic deformations of the structures were investigated. The results show higher repeatability for the sphere impact method, as the PLB is more affected by human inaccuracy, and it was also effective in damage detection.

Local reinforcement of adhesively bonded square shape aluminum energy absorber with CFRP under quasi-static axial loading: An experimental and numerical study

This study presents experimental and numerical investigations on the effects of composite ply angle, thickness and number of layers on energy absorption behavior of adhesively bonded carbon fiber-reinforced plastic/aluminum hybrid structure under quasi-static axial loading. This paper aims to use the advantages of adhesive bonding for the local strengthening of a square shaped aluminum energy absorber by composite and as a result achieving desirable energy absorption behavior prior to failure in the connection and without heterogeneous deformation of the structure while reducing the weight of the structure and usage of material and at the same time obtaining favorable results compared to the traditional ways like reinforcing the aluminum structure with composite globally. For this purpose, two models were made and analyzed; one reinforced with four L-shaped composites adhesively bonded using Araldite 2015 to four outside corners of the aluminum square and the other reinforced locally to four corners from within the square. Finite element model was developed for analysis of these hybrid structures. Five different ply angles for composite and multiple number of composite layers varied from 2 to 8 layers under the same and different thicknesses were investigated. Moreover an alpha factor has been determined to measure the importance of local reinforement of the square shape aluminum energy absorber by L-shaped composites. The results showed that compared to aluminum and aluminum with global composite reinforcement energy absorbers, due to the adhesive connection between aluminum and composite in the locally reinforced CFRP/aluminum specimen, the composite had better energy absorption by following the collapse pattern of aluminum and creating a continuous collapse and failure modes. The results indicated good coordination and agreement between the simulated models and the experimental tests. The findings from this experiment demonstrates significant potential for local reinforcement of structures employing adhesives. Utilizing such connections and the ability to strengthen specific areas based on arbitrary geometry and strengthening location could offer substantial opportunities in constructing lightweight structures with high energy absorption across diverse applications.

Magnetometry for the Muon g-2 Experiment

The Muon g-2 Experiment at Fermilab aims to measure the muon anomalous magnetic moment with a precision of 140 parts per billion (ppb). The collaboration has published the latest measurement based on the first three Runs (collected from 2018 to 2020) in August 2023 with a precision of 200 ppb. The experiment accumulated three more years of data, from 2020 to 2023, which are currently being analyzed. This additional statistic is sufficient to achieve and possibly exceed the goal of 100 ppb of final statistical uncertainty. As the statistical error reduces, increasing attention is dedicated to studying systematic uncertainties. Among them, one source is a magnetic transient generated by the fast kickers. To center the muon orbit into its final position in the storage ring, three kickers emit a 120 ns magnetic pulse of ∼240 G, right after injection. This, however, induces eddy currents in the kicker aluminum structure that last for several microseconds. To measure the 10 mG magnetic perturbations generated by the eddy currents, the INFN team developed a laser magnetometer based on the Faraday effect. This article describes the technical principles, operations, and data analysis of this very sensitive device.

Directional salt crystallization system for high-efficiency solar-driven evaporation to achieve zero-liquid discharge

Solar-driven interfacial evaporation is an efficient technology for water treatment, enabling the production of freshwater and the removal of impurities. However, achieving a high evaporation rate and a long-term stable operation is challenging due to the salt accumulation on the evaporation surface. In this study, a novel three-dimensional directional salt crystallization system is proposed. The melamine sponge modified with polydopamine and carbon black was used to transport brine, absorb sunlight, and generate steam. The non-photothermal evaporation regions were innovatively constructed by placing a thermally conductive aluminum structure with the deflector paper around the sponge, which increased the effective evaporation area of the system to accelerate the evaporation of brines from the overall system, resulting in an evaporation rate of 2.20 kg m−2 h−1 under one sun irradiation in a 15 wt% NaCl solution. Moreover, the non-photothermal evaporation regions were isolated from the evaporation interface as a salt crystallization region, which completely avoided salt accumulation at the evaporation interface and ensured the long-term stable operation of the system. Salt crystals can be easily collected by replacing the deflector paper regularly, and the salt collection efficiency is over 95 % to achieve zero-liquid discharge (ZLD) treatment. More importantly, the directional salt crystallization system achieves efficient purification of heavy metal ion wastewater and dye wastewater. Consequently, the system presents a highly efficient method for ZLD seawater treatment and wastewater purification.

Enhancing microstructural integrity and mechanical performance of thick wire-arc directed energy deposited eutectic aluminum-silicon solid structure through continuous multi-pass friction stir processing

In wire-arc directed energy deposition (waDED), fabricating larger 3D components with single-layer tracks is challenging due to limitations in track thickness, requiring the development of bead overlapping strategies. However, fusion-based 3D-printed aluminum structures often show porosity and coarse-grained microstructures, limiting their industrial applications. To address these limitations, this study employs continuous multi-pass friction stir processing (FSP) on a waDED-produced aluminum block (140 mm × 150 mm × 28 mm). The severe plastic deformation induced by FSP triggers dynamic recrystallization (DRX), promoting the formation of equiaxed grains with an average grain size 8.75 times smaller than the as-fabricated waDED sample (67.03 μm vs 7.66 μm). Transmission Electron Microscopy (TEM) revealed decreased dislocation loops post-FSP, indicating DRX and dislocation annihilation. X-ray micro-computed tomography (X-CT) examination showed complete elimination of porosity in the waDED sample, owing to the intense mechanical stirring induced during FSP. Scanning electron microscopy (SEM) images of the waDED samples showed fibrous eutectic networks disrupted by FSP, leading to a uniform distribution of broken Si particles within the α-Al matrix. Hardness decreased by approximately 38 % (86 HV0.1 vs 53 HV0.1), while the average ultimate tensile strength decreased by about 4 % in the FSP-treated samples (159.19 MPa vs 153.02 MPa). Additionally, the formation of alpha fiber and weak cube texture components during FSP enhances ductility, as evidenced by a sixfold improvement in elongation (1.93 % vs 11.59 %). This textural transformation contributes to the characteristic deeper and more uniform dimples in the FSP-treated samples, indicative of ductile fracture, compared to the premature failure patterns in as-deposited samples.

Recent trends in adhesive bonding for aluminum structures

Recent trends in adhesive bonding for aluminum structures