Aerospace Defense

Abstract Introduction: Multilayered composite structures are widely used in aerospace and engineering applications due to their high strength-to-weight ratio. However, their structural performance is highly sensitive to manufacturing defects, particularly matrix cracks, which can significantly reduce the critical load-bearing capacity and accelerate buckling failure under shear loading. Therefore, developing accurate analytical models capable of accounting for damage-induced stiffness degradation is essential for reliable structural design.
Methods: An advanced analytical model was developed to predict the critical shear buckling load of thick laminated composite plates containing matrix cracks. The formulation is based on a higher-order shear deformation theory (HSDT) with 11 degrees of freedom, which accurately captures the parabolic distribution of transverse shear stresses and transverse normal strain effects without requiring shear correction factors. Stiffness degradation parameters resulting from matrix cracking were directly incorporated into the model using experimental tensile test data. The governing equations were derived through the principle of minimum potential energy and solved using the Galerkin method.
Findings: The effects of matrix crack density (0–1 crack/mm), plate thickness-to-length ratio (a/h = 5–100), and fiber orientation angle (θ = 0°–90°) on the normalized critical shear buckling load and its reduction percentage were investigated. The results demonstrated that matrix cracking substantially decreases the buckling resistance of composite plates. For the [±45]s laminate configuration, a crack density of 1 crack/mm resulted in a reduction of up to 64% in the critical shear buckling load. Furthermore, the proposed analytical predictions showed excellent agreement with three-dimensional elasticity solutions and finite element simulations.
Conclusion: The developed HSDT-based analytical model provides an accurate and efficient tool for evaluating the shear buckling behavior of damaged thick composite plates. The results highlight the significant influence of matrix crack density on structural stability and demonstrate the necessity of considering experimentally determined stiffness degradation in buckling analyses of composite structures.

Abstract In this study, the performance of anticorrosion coatings was evaluated through an integrated approach combining standards analysis, IRIA F operational data, and aircraft case studies. The results of potentiodynamic polarization and EIS tests in a 3.5 wt.% sodium chloride solution showed that the epoxy coating containing mandarin peel extract achieved protection efficiencies of 94% and 93% for aluminum alloys 2024 and 7075, respectively. Microscopic analyses and FTIR confirmed the stability of the coating, while MD simulations revealed the inhibitor adsorption mechanism. Based on these findings, practical guidelines were proposed for inspection, application of anticorrosion coatings, and optimization of storage conditions to enhance aircraft service life and operational readiness.

Abstract The security and survivability of defensive structures against extreme dynamic loads such as blast waves and impacts is a fundamental priority in modern design. Sandwich panels, due to their exceptional strength-to-weight ratio and high energy absorption capacity, are among the primary candidate materials in this field. This research investigates and compares the influence of two widely used core types the porous core and the viscoelastic core on the natural frequencies of a sandwich beam structure. The main objective of this study is to assess the potential of these cores to enhance the strength and safety of defensive structures through the analysis of their vibrational behavior. The present research employs analytical modeling to perform the natural frequency analysis. Using three-layer sandwich beam theory and applying Hamilton's principle, the governing equations of the system are derived. The resulting equations are complex partial differential equations (PDEs). To solve these equilibrium equations, the semi-analytical Navier method is utilized in the spatial domain. To validate the accuracy of the obtained results, comparisons are made with existing solutions for specific cases. Finally, the influence of various parameters such as carbon nanotube volume fraction, porosity coefficient, porosity distribution pattern, geometric and dimensional ratios on the natural frequencies of the sandwich structure is examined. This investigation covers structures with both porous and viscoelastic cores and nanocomposite face sheets. A key finding of this research is that, in most instances, the viscoelastic core exhibits higher natural frequencies and greater strength compared to the porous core.

Abstract This article examines the design of active isolators using the optimal algorithm (LQR). For this purpose, the dynamic model of the satellite launch vehicle as 6 degrees of freedom has been considered. Because the satellite carrier structure has a shell with reinforced ribs and stringers, Stiffness Calculation Methods(SCM) for reinforced shells were used. Also, to calculate the final frequency of the system, the equations of motion obtained from the dynamic model of the satellite launch vehicle were used. For damp vibrations generated with a vibration amplitude of less than 100 Hz, no method in the research conducted has been proposed. In this research, for the first time, a combined system of passive and active isolators to damp vibrations introduced into the energy supply block was used. The results of the present study show that combining these two systems improves the performance of each of the passive and active systems.In this combination, according to the results obtained by this system, vibrations with a vibration amplitude of less than 50 Hz are damped by up to 88 percent, and vibrations on the energy supply block with a vibration amplitude between 50 and 500 Hz by up to 96 percent are damped.

Abstract The experimental and numerical study on flexural behavior of new type sandwich structures with glass-epoxy skins and a combinatorial core consist of foam and corrugated composite with rectangular geometry was investigated in this paper. After sample production by vacuum assisted resin transform molding technique; samples were tested according to standard and then the related load-deflection curves were obtained. Finite element analysis was applied for determining maximum deflection of samples by ABAQUS software. In experimental three series of samples with combinatorial core and three different thicknesses for rectangular shape corrugated composite in a foam core and one series of sample with simple foam core; have been product. In order to experimental accuracy of problem; three same samples have been product in each case and the average data have been used for results. It has been shown that the flexural stiffness was increased with increasing in thickness; and the flexural stiffness to mass ratio was increased so on; but the rate of this increasing was decreased from 3 to 5 layers of corrugated composite laminate in PVC foam. Finally the experimental and numerical results were compared and a reasonable agreement between them has been observed.