Potential Aerospace Applications Research Articles

Composite Panel Damage Classification Based on Guided Waves and Machine Learning: An Experimental Approach

Ultrasonic guided waves (UGW) are widely used in structural health monitoring (SHM) systems due to the sensitivity of their propagation mechanisms to local material changes, i.e., those induced by damage. Post-processing of the signals gathered by piezoelectric sensors, typically used for both the excitation and the sensing of UGW, is a fundamental step to extract all the peculiar features that can be related to both damage location and severity. This research probes the efficacy of machine learning (ML) models in discerning damage location (R-Classification) and size (S-Classification). Seven supervised ML classifiers were examined: Ensemble-Subspace K-Nearest Neighbors (KNN), Ensemble-Bagged Trees, KNN-Fine, Ensemble-Boosted Trees, Support Vector Machine (SVM), Linear Discriminant, and SVM-Quadratic. The experimental dataset comprised measurements from varied reversible damage configurations on a composite panel, represented by wooden cuboids of single and three different sizes. Signal noise was minimized by performing a low-pass filter, and sequence forward selection-aided feature selection. The optimized ensemble classifier proved to be the most precise for R-Classification (95.83% accuracy), while Ensemble-Subspace KNN excelled in S-Classification (98.1% accuracy). This method offers accurate, efficient damage diagnosis and classification in composite structures, promising potential applications in aerospace, automotive, and civil engineering sectors.

Experimental study on delamination identification in tapered laminated composite plates using damage detection models

Delamination frequently occurs in composite laminates composed of fibre-reinforced polymer (FRP) and is considered a typical type of failure. The structural health monitoring (SHM) of structures with composites can be assessed by utilising changes in dynamic responses caused by a reduction in structural stiffness resulting from delamination. However, to ensure successful SHM, an inverse problem solution is required. Solving inverse problems can be computationally expensive and time-consuming, especially for large and complex structures. This study examined the efficiency of different damage identification techniques in detecting delamination in tapered composite plates. Four damage detection algorithms were tested, including the mode shape curvature (MSC), gapped smoothing method (GSM), mode shape curvature square (MSCS), and the gapped smoothing method square (GSMS) were implemented as damage index (DI) and curvature damage factor (CDF). A tapered composite plate composed of glass-fibre reinforced polymer was subjected to experimental modal analysis, including one undelaminated plate and three artificially delaminated plates. The delamination areas in the artificially damaged composite plates ranged from 1.5% to 8% of the plate area and were located at different interfaces. The results showed that statistical treatment further enhanced the damage identification, the CDF using the GSMS method performed the best overall, particularly in identifying the size and locations of delamination. The study also found that adding more modes to the averaging process increased CDF sensitivity and reduced uncertainty. This study suggests that the CDF method using GSMS is a promising approach for detecting delamination in tapered composite plates, with potential applications in aerospace, automotive, and civil engineering.

Facile and eco-friendly fabrication of superhydrophilic and superhydrophobic SiC surfaces by nanosecond laser treatment

Superhydrophobic silicon carbide surfaces have garnered substantial attention for their potential applications in aerospace, ship domain, military, etc., fields. In this work, we used a nanosecond laser (λ = 1065 nm) and fluorine-free N-octyltriethoxysilane (OcTES) to fabricate SiC surfaces capable of transitioning from superhydrophilic to superhydrophobic. Superhydrophilic surfaces were produced within minutes through laser treatment, and the time required to convert it to superhydrophobic surfaces is only 1 h. The apparent water contact angle (WCA) of superhydrophilic SiC could reach the saturated Wenzel regime. The number of hydrophilic polar bonds on SiC surfaces increased while nonpolar bonds of hydrophobicity decreased due to oxidation during laser treatment. After OcTES treatment, the SiC surface transformed from superhydrophilic to superhydrophobic (WCA of 153° and roll-off angle of 0°). These results indicate that surface roughness and chemical compositions are critical for superhydrophobicity. It was discovered that Si–O–Si groups were formed on SiC surfaces in the atmosphere, thereby enhancing the material surface's hydrophobicity. Superhydrophobic SiC surfaces also have excellent low-adhesion and anti-icing properties, making them of potential interest for functional ceramic surface applications.

Additive Manufacturing of Silicon Oxycarbide Ceramics with Minimal Surface Structures

The traditional ceramic powder sintering forming method severely limits the performance of the fabricated parts. Many new solutions have been achieved by precursor derived ceramics (PDC). Silicon oxycarbide ceramics as one of them has many performance advantages such as excellent mechanical properties, low density, excellent thermal stability, low thermal conductivity, and resistance to thermal shock and corrosion. In this paper, a photosensitive polysiloxane resin (PPR) with excellent light curing properties was prepared, which has high precision in the process of additive manufacturing. In addition, samples with minimal surface features in different porosity were fabricated. The compressive strength of the structure with 85%, 75%, and 65% porosity was about 9.51 MPa, 13.76 MPa, and 21.69 MPa, respectively. These porous silicon oxycarbide ceramics are likely to have a wide range of potential applications in aerospace, aviation, and other fields.

Fused deposition modeling of carbon‐reinforced polymer matrix composites: A comprehensive review

AbstractCarbon‐reinforced polymer matrix composites (PMCs) have been thoroughly applied in different fields because of their benefits, such as low specific gravity, corrosion resistance, good electrical conductivity, and robust mechanical properties. Especially, with the emergence of fused deposition modeling (FDM) technology has further promoted the application of such materials in complex structural components. Recently, FDM printing carbon‐reinforced PMCs have become a hot topic in composites research, and many promising results have been achieved around related research. In order to help readers have a comprehensive and systematic understanding of the latest research progress of FDM printing carbon‐reinforced PMCs in terms of material modification, processing, material properties, and application levels, this paper reviews the properties and processes of FDM printed carbon‐reinforced PMCs and their potential applications in aerospace, flexible sensing, electrochemistry, and biomedical fields. The effects of commonly used carbon reinforcing materials on the performance of FDM printed PMCs were contrasted and analyzed. Moreover, the process optimization of printing carbon‐reinforced PMCs was introduced and highlighted. Finally, the current challenges and future research directions of FDM printing carbon‐reinforced PMCs were analyzed and prospected.

Influence of annealing temperatures on the microstructure and deformation behavior of a CrCoNi based medium-entropy alloy

The pursuit of strong and ductile synergy is a key objective in the development of metals and alloys. Medium entropy alloys (MEAs) have emerged as a highly promising structural material, with potential applications in high-speed trains, aerospace, and defense fields. This study systematically investigates the effect of annealing temperature on the mechanical properties of a CrCoNi based MEA, namely (CrCoNi)97Al1Ti2 MEA. The (CrCoNi)97Al1Ti2 MEA was fabricated by cold rolling reduction of 40% and subsequently annealed at 820 ℃ for 1 h to achieve a heterogeneous structure that exhibits an excellent combination of strength and plasticity. Scanning electron microscopy and transmission electron microscopy were used to characterize the samples before and after tensile deformation, and to reveal the underlying deformation mechanisms. The results show that annealing at 820 ℃ for 1 h introduces a large number of precipitation phases, which are not observed at other annealing temperatures. During plastic deformation, the fine recrystallized grains contribute to the good ductility of the (CrCoNi)97Al1Ti2 MEA, while deformation twinning and dislocation densities enable it to maintain good strength. The precipitation phase formed by annealing at 820 ℃ also significantly improves the strength of the (CrCoNi)97Al1Ti2 MEA. Overall, this study provides insights into the mechanical properties of (CrCoNi)97Al1Ti2 MEA, and highlights the importance of annealing temperature in achieving an optimal combination of strength and plasticity. The findings of this study have important implications for the design and development of MEAs for various applications in structural engineering.

EFFECT OF TIG WELDING ON ALUMINIUM MATRIX COMPOSITE

Metal Matrix Composite has evoked a keen interest in potential applications in aerospace and automotive industries, owing to their superior strength-to-weight ratio and temperature resistance. Nowadays, welding strength on composite materials is more essential. So, in this project, we consider the effect of TIG welding on aluminium matrix composite (Al & Sn). The TIG welding on aluminium alloys like (Al 6061& Al 6063) has lost its welding strength by around 30% in Al 6063 & 50% in Al 6061. To regain the welding strength, we need a heat treatment process like hardening and tempering, which is a more costly and time-consuming one. To eradicate this problem, we will mix the malleable Tin (Sn) in different ratios of 90:10 and 85:15 for the aluminium alloys (Al 6061 & Al 6063). Then analyzing the effect of TIG welding on the aluminium metal matrix, the welding strength of the aluminium metal matrix composite is increased by 5% compared to the previous material.

Preliminary tests on additive-manufactured Al-Sc specimens for the setup of a numerical model for Laser Shock Peening

Aluminum-Scandium alloys offer a great potential in aerospace applications due their high corrosion resistance and improved strength properties. Furthermore, these alloys have been qualified for laser additive manufacturing (AM), producing parts with static strengths rivalling their conventionally manufactured counterparts. However, laser processing also results in large residual stresses that can severely affect fatigue properties and result in geometric distortion. A proven method for reducing the fatigue-related problems in metallic structures is to drive compressive residual stresses into the affected area by means of Laser Shock Peening (LSP). This surface treatment is very effective in bulk structures, improving life performances of fatigue-sensitive aeronautical components, such as jet engines turbine blades or helicopter gearboxes. On the other hand, quite a limited number of studies has been presented on the effect of LSP on fatigue crack growth in thin components and laser AM structures. This work presents first the results of preliminary tensile tests on additive manufactured Al-Sc specimens. The tensile strengths of as-built and heat-treated samples are compared. Then, a reliable and computationally time-effective numerical model of laser peening is reviewed, referring to case studies investigated earlier. In view of applying LSP to additive manufactured Al-Sc components, the effects of different laser parameters and geometries are discussed. Finally, the possible drawbacks of the LSP treatment are addressed, in order to exploit its full potential in increasing the fatigue life of AM components.

MXene/CNTs/Aramid Aerogels for Electromagnetic Interference Shielding and Joule Heating

It is a considerable challenge to develop a composite material with ultra-light and high electromagnetic interference (EMI) shielding efficiency for the next generation of electronic equipment. MXenes have received extensive attention in composite aerogel EMI shielding due to their abundant surface groups and ultra-high conductivity. However, the poor mechanical properties make them difficult to apply on a large scale. Here, we demonstrate a simple method to construct ultra-light conductive Ti3C2Tx MXene/aramid nanofibers (ANFs)/carbon nanotubes (CNTs) aerogels with a “sandwich” structure. CNTs and MXene absorb and reflect electromagnetic waves, while ANF aerogel provides good mechanical strength. Our composite aerogels with an extra-high EMI shielding efficiency of up to 69.0 dB at the X-band, despite their thickness and density being only 2 mm and 0.0428 g/cm3, respectively. At the same time, the composite aerogel with a low 0.0488 W/(m·K) thermal conductivity shows extraordinary flame resistance, heat preservation, and insulation ability. Besides, MXene/ANFs/CNTs aerogel can reach 104 °C in 3 s under an 8 V voltage and shows long-term Joule heating stability. This work provides a forward-looking idea for building multifunctional EMI shielding materials. The obtained aerogels have potential applications in aerospace, portable electronic devices, and defense industries.

Two-Dimensional Carbon Networks with a Negative Poisson’s Ratio

Low-dimensional materials with a negative Poisson’s ratio (NPR) have attracted lots of attention for their potential applications in aerospace, defense, etc. Although graphene and monolayer h-BN have been reported to have NPR behavior under external strains, the mechanism is not clear, and the critical strains of the occurrence of a NPR are relatively larger. Here, we propose that the origination of the NPR phenomena in the 2D honeycomb structures can be explained by the variation of the zigzag chains under strains. Our calculations clarify that a NPR occurs along the armchair-chain direction rather than the zigzag-chain direction in these materials. Furthermore, a series of two-dimensional carbon networks including zigzag chains have demonstrated that there is NPR phenomena in them. In some of the networks, a NPR can be found under a small external strain. Our study not only deepens the understanding of the origin of NPR in honeycomb systems but also offers guidance to design auxetic nanostructures.

Residual stress mitigation in directed energy deposition

Directed Energy Deposition (DED), a class of additive manufacturing techniques, has seen rapid growth over the last decade for potential applications in aerospace, medical devices, and energy systems. Despite notable progress in the research and development of AM, control and mitigation of residual stress during DED remains a challenge. In this work, we propose a novel approach that can be used for the mitigation of residual stresses in additively manufactured components. Specifically, we propose to mitigate the residual stress state of as-deposited components using alloy design, engineering of solid-state transformations, and the introduction of both hard and soft metallic phases. We demonstrate this strategy with a model system consisting of pure Fe and Fe–Cu. Experimental results indicate that residual stresses can be successfully manipulated by adjusting the alloy composition as a soft metallic phase can accommodate plastic deformation. Moreover, our findings suggest that the solid-state transformations experienced by the Fe and Fe-rich phases contribute to the observed differences in magnitude and location of residual stresses. This study is the first to suggest using residual stress as an engineering criterion in the design of alloys for metal additive manufacturing.

Laser‐Induced Graphene Enabled Additive Manufacturing of Multifunctional 3D Architectures with Freeform Structures (Adv. Sci. 4/2023)

3D Printing In article number 2204990 by Fu Liu, Yan Gao, Sida Luo, and co-workers, a laser-induced graphene based additive manufacturing (LIG-AM) is developed to print bulk 3D graphene with freeform shapes such as variable-section turbine structures. By investigating particle-sintering and graphene-converting dual-mechanism as well as process dependent properties, multifunctional 3D LIG architectures are further demonstrated its potential applications in aerospace and future manufacturing field.

Innovative Ceramic Forming Techniques for High-Strength, Low-Density Components

The development of high-strength, low-density ceramic components is a critical area of research in the field of material sciences and mechanical engineering, with potential applications in aerospace, automotive, and biomedical industries. In this paper, we present innovative ceramic forming techniques that enable the fabrication of high-performance ceramic components with unprecedented mechanical properties. We introduce a novel hybrid approach that combines the advantages of both additive manufacturing and traditional ceramic forming methods, such as slip casting and injection molding. By utilizing a customized ceramic slurry formulation and a modified 3D printing process, we successfully produced complex-shaped components with a uniform microstructure and enhanced mechanical properties. The resulting ceramic components exhibited a significant increase in flexural strength and fracture toughness compared to conventionally processed ceramics, while maintaining a low density. Furthermore, we conducted a comprehensive microstructural analysis using scanning electron microscopy (SEM) and X-ray diffraction (XRD) to elucidate the underlying mechanisms responsible for the improved mechanical performance. The findings of this study provide valuable insights into the potential of innovative ceramic forming techniques for the development of high-strength, low-density ceramic components, and pave the way for their widespread adoption in various engineering applications.

First-principles study of impurity diffusion coefficients in Niobium

Nb based alloys have potential applications in aerospace due to their good high temperature strength and low temperature plasticity. It is very important to study the atomic diffusion properties for understanding the dynamic process of Nb-based alloys. However, the diffusion data of some elements in Nb are still unknown. In the present work, the impurity diffusion coefficients of ten different elements (Si, Ti, V, Ta, Ru, Cr, Te, Tc, Ir, and Y) in BCC Nb was studied by first-principles calculation based on density functional theory and nine frequency model. The climbing image nudged elastic band (CI-NEB) method was used to find the minimum energy path and the related saddle point structure during diffusion. The atomic jump frequency was calculated through the Vineyard’ s transition state theory. The results are consistent well with the exiting experimental and previous calculation results.

Effect of Mg Powder's Particle Size on Structure and Mechanical Properties of Ti Foam Synthesized by Space Holder Technique.

Titanium foam has been the focus of special attention for its specific structure and potential applications in purification, catalyst substrate, heat exchanger, biomaterial, aerospace and naval industries. However, the liquid-state foaming techniques are difficult to use in fabricating Ti foam because of its high melting temperature and strong chemical reactivity with atmospheric gases. Here, the fabrication of Ti foams via the powder metallurgy route was carried out by utilizing both magnesium powders and magnesium particles as spacer holders, and Ti powders as matrix metal. The green compacts containing Ti powder, Mg powder and Mg particles were heated to a certain temperature to remove the magnesium and obtain the Ti foam. The results show that the porosities of the obtained Ti foam are about 35-65%, and Young's modulus and yield strength are found to be in the ranges of 22-126 MPa and 0.063-1.18 GPa, respectively. It is found that the magnesium powders play a more important role than the magnesium particles in the deformation and the densification of the green compact during the pressing, and the pore structure of Ti foam depends on the amount and the size of the magnesium spacer holders after sintering.

Additive manufacturing and characterization of high temperature thermoplastic blends for potential aerospace applications

Here, we study the thermomechanical and microstructural properties of a carbon fiber (CF)-reinforced blend of poly ether ketone (PEEK) and polyether imide (PEI) used in the Fused Filament Fabrication (FFF) additive manufacturing (AM) process. The reinforced PEEK/PEI blend material was prepared by melt mixing in an extruder and used as filament feedstock for FFF printing and for the injection molding of test specimens for comparison purposes. The effect of the manufacturing process, CF reinforcement and mechanical testing temperature were investigated through mechanical tensile testing and microstructural analysis. Reinforced specimens printed in longitudinal direction demonstrated the highest modulus, 17.9 GPa, which was slightly more than the value of 16.9 GPa obtained for the injected specimens. The measured modulus was mostly constant up to 120 °C, while the ultimate tensile stress (UTS) showed an important drop from 129 MPa at 120 °C to 77.3 MPa at room temperature. Micro-tomography was executed, depicting porosity, carbon fiber length and orientation, for deeper understanding of the material microstructure and their effect on the mechanical performance. The microstructural analysis revealed that the porosity of the blend is ∼4%, the maximum fiber length is ∼600 μm, and the CFs are mainly aligned along the printing direction. According to our experimental measurements, our composite blend material shows a very strong potential for the aerospace sector, even for operating temperatures up to 120 °C.

Ta/Cu transition region in TC4/Inconel718 bimetallic structure fabricated by laser deposition manufacturing

The bimetallic structure formed by TC4 and Inconel718 has broad potential applications in aerospace. Based on the laser deposition manufacturing technique, a TC4/Inconel718 bimetallic structure was fabricated via the Ta/Cu transition layer. The test results indicated that a Ta/Cu transition region with a width of 475.0 μm was formed. The microstructure of the transition region changed from a reticular to a rod structure, and the corresponding phase compositions were β-Ta + Ti2Cu + TiCu and TiCu+γ-Cu + Cr2Ta. Owing to the formation of Ti–Cu and Cr–Ta phases in the transition region, the Vickers hardness reached 444.0 HV. The ultimate tensile strength was 280 MPa, and the fracture morphology presented a quasi-cleavage fracture, which occurred in the Ta/Cu transition region where Ti–Cu brittle phases exist.

Insights into impact interaction between graphene and High-speed atomic oxygen for aerospace protection application

Graphene has great potential in aerospace applications but is inevitably influenced by the high-speed atomic oxygen (AO) in the low earth orbit. So far, the understanding of the impact interaction between AO and graphene as well as the protection mechanisms in the literature are still inconsistent and obscure, jeopardizing the practical application of graphene in this field. Herein, by using first-principles calculation combined with experiments, we explored the interaction process between high-speed AO and graphene based on actual aerospace conditions. The ab-initio molecular dynamics simulations show that the high-speed AO will either be scattered or adsorbed by graphene, which is strongly correlated to the impacting sites and incident angles. The AO-bonding condition of different sites on graphene is the most significant determinant affecting the impacting results. Moreover, the experimental results show that scattering AO is a better protection strategy than trapping AO on the graphene surface. To achieve higher probability of scattering, it is desired that graphene directly, rather than obliquely, faces to vertical AO impact. These findings revealed useful insights into the interaction mechanisms between AO and graphene and provide a guide for using graphene as an AO impact-resistant material in aerospace applications.

Toughening effect of self-assembled thermoplastic particles on phthalonitrile containing benzoxazine and improved mechanical properties in the presence of fibers reinforcement

Phthalonitrile containing benzoxazine resin (BA-ph) was a new type of high-performance resin which could be used at high temperature by autocatalytic molding at low temperature. However, its brittleness after polymerization and weak interaction with fibers when it as the matrix of fiber reinforced composites (FRC) were obstacles to its wide application. In this study, Poly (arylene ether nitrile) containing phenolphthalein (PP-PEN) was introduced by solution blending to toughen BA-ph and its glass fiber (GF) FRC. The effects of PP-PEN on the crosslinking behavior and processability of BA-ph were studied by differential scanning calorimetry (DSC) and dynamic rheology analysis (DRA). The effect of PP-PEN on the structural strength and thermal stability of BA-ph/GF was further studied by other characterization methods. The non-notchable impact strength of BA-ph/PP-PEN/GF FRC formed at lower temperature (200 °C) could reach 148 kJ/m2, which was 91.4% higher than that of BA-ph/GF FRC. Furthermore, the fracture morphology showed that PP-PEN significantly enhanced the interfacial strength between BA-ph and GF. It has potential applications in aerospace, rail transportation and the fields requiring high-performance polymer matrix FRC.

Sustainable Fiber‐Reinforced Composites: A Review

AbstractSustainable fiber reinforced polymer (FRP) composites from renewable and biodegradable fibrous materials and polymer matrices are of great interest, as they can potentially reduce environmental impacts. However, the overall properties of such composites are still far from the high‐performance conventional glass or carbon FRP composites. Therefore, a balance between composite performance and biodegradability is required with approaches to what one might call an eco‐friendly composite. This review provides an overview of sustainable FRP composites, their manufacturing techniques, and sustainability in general at materials, manufacturing, and end‐of‐life levels. Sustainable plant‐based natural fibers and polymer matrices are also summarized, followed by an overview of their modification techniques to obtain high‐performance, multifunctional, and sustainable FRP composites. Current state‐of‐the‐art mechanical and functional properties of such composites are then surveyed, and an overview of their potential applications in various industries, including automobile, aerospace, construction, medical, sports, and electronics is provided. Finally, future market trends, current challenges, and the future perspective on sustainable natural FRP composites are discussed.