Murat Şen

This study investigated the dynamic behavior of AA7075 plates joined by Friction Stir Welding (FSW), focusing on the influence of key process parameters, rotation, and traverse speeds, on the resulting dynamic characteristics. Experimental Modal Analysis (EMA) was performed under free boundary conditions to determine resonance frequencies, mode shapes, and damping ratios, revealing that an increase in traverse speed consistently led to a decrease in natural frequencies across most modes, thereby indicating reduced joint stiffness attributed to insufficient heat input. Furthermore, localized weld defects caused significant damping variations, particularly in low-order modes. To complement the experimental findings and enable simultaneous, multi-output prediction of these coupled dynamic parameters, a Co-Active Neuro-Fuzzy Inference System (CANFIS) model was developed. The CANFIS architecture utilized spindle speed and feed rate as inputs to predict natural frequency and damping ratio for multiple vibration modes as tightly coupled outputs. The trained model demonstrated strong agreement and high predictive accuracy against the EMA experimental data, with convergence analysis confirming its stable learning and excellent generalization capability. The successful integration of EMA and CANFIS establishes a robust hybrid framework for both physical interpretation and intelligent, coupled prediction of the dynamic behavior of FSW-welded AA7075 plates.

This study investigates the dynamic properties of aluminum plates repaired with composite patches, focusing on how natural frequencies change after repairs on plates with various crack configurations. To predict these changes, an Artificial Intelligence (AI) model was developed using data from 2000 Finite Element (FE) analyses conducted in ANSYS. A Deep Neural Network (DNN) was trained using this dataset, which included 2000 damage scenarios based on four parameters: defect length ( L ), radius ( r ), depth ( h ), and the defect region. The optimal network configuration (11-[15-15-5]-4) was trained to predict the first four natural frequencies of these single-sidedly patch-repaired, cracked plates. The model’s accuracy was rigorously validated using an unseen test sample (Region 6, L = 35 mm, r = 2.5 mm, h = 5 mm) not included in the training data. The AI’s predictions were compared against both numerical results and an Experimental Modal Analysis (EMA). The results confirmed the high success rate of the model, showing minimal differences from the numerical simulations (max 0.39% error) and experimental results (max 3.15% error).

This study comprehensively investigates the dynamic vibration behavior of multilayer carbon nanotubes with stepped cross-sectional geometries under various boundary conditions, which is crucial for their advanced engineering applications. The methodology integrates classical molecular dynamics simulations to determine the bending stiffness of single-walled and multi-walled atomistic structures, which are subsequently utilized in the Euler–Bernoulli beam theory based on nonlocal elasticity for vibration analysis. The research focuses on elucidating the influence of the μ/L ratio (a key length parameter) and different support conditions on the natural frequencies and mode shapes of these nanostructures. Key findings reveal that the cross-sectional geometry significantly impacts the vibrational characteristics. A consistent trend observed across all examined boundary conditions is a decrease in natural frequencies as the μ/L ratio increases, indicating that increased free length or reduced fixed length leads to lower stiffness and, consequently, reduced natural frequencies. The study presents Frequency Response Functions (FRFs) and the first four mode shapes, which visually confirm these dynamic characteristics. Graphical representations further reinforce the sensitivity of natural frequencies to both the μ/L ratio and support conditions. The systematic analysis presented in this work provides vital data for predicting resonance phenomena, optimizing structural stability, and enabling precise control over the vibrational response of these advanced nanomaterials in diverse engineering applications.

This study investigated the dynamic properties of a spherical sandwich composite structure made of carbon fiber face sheets and a Nomex honeycomb core. The structure was produced using the hand lay-up method. The results from Experimental Modal Analysis (EMA) and the numerical model created in ANSYS showed high consistency. The natural frequency difference was only 0.73% for the second mode, with the largest discrepancy of 6.5% was observed in the first mode. These differences are thought to be related to structural variations from the manufacturing process, such as resin distribution, carbon fiber fabric stacking, and air voids and the experimental challenges such as double hit errors, measurement resolutions related to force sensor and accelerometer and environmental noise. The vibration damping capability of the sandwich structure was investigated. Some modes exhibited high damping, while others had relatively lower values. The highest and the lowest damping ratios were obtained as 0.83% for the third mode and 0.23% for the fourth mode. A numerical equivalent model of the structure was created in ANSYS to determine its natural frequencies and vibration modes, confirming its effectiveness in modeling complex structures.

This study investigates the vibrational characteristics of multi-layered graphene sheets with variable thickness (VTGSs) by using molecular dynamics (MD) simulations. It is aimed to determine how the natural frequencies and vibration damping ratios of variable-thickness graphene change with respect to temperature. Atomistic models for six distinct geometries (1L, 3LT, 3LTB, 5LT, 5LTB, and 9LTB) were generated to analyze the influence of structural design and temperature on their natural frequencies. The simulations were performed using the Large-Scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) with an AIREBO potential to represent interatomic carbon interactions. Natural frequencies of all atomistic models were extracted by applying the Fast Fourier Transform (FFT) method to the Velocity Autocorrelation Function (VACF) data obtained from the simulations. In addition, the analysis was conducted at three different temperatures: 250 K, 300 K, and 350 K. Key findings reveal that an increase in the number of graphene layers results in a decrease in the fundamental natural frequency due to the increased mass of the structure. Moreover, it was noted that natural frequencies decrease with increasing temperature. It is attributed to the reduction in structural rigidity at higher thermal energies. These results provide critical insights into how geometric and thermal variations affect the dynamic behavior of complex multi-layered graphene structures.

This study aimed to investigate the dynamic characteristics of shafts joined by friction welding and to update their finite element models. The first five bending mode resonance frequencies, damping ratios, and mode shapes of SAE 304 steel beams, friction-welded at three different rotational speeds (1200, 1500, and 1800 rpm), were determined using the Experimental Modal Analysis method. This approach allowed for an examination of how the dynamic properties of friction-welded beams change at varying rotational speeds. A slight decrease in resonance frequency values was observed with the transition from lower to higher rotational speeds. The largest difference of 3.28% was observed in the first mode, and the smallest difference of 0.19% was observed in the second mode. Different trends in damping ratios were observed for different modes. In the first, second, and fourth modes, damping ratios tended to increase with increasing rotational speeds, while they tended to decrease in the third and fifth modes. The largest difference was calculated as 52.83% in the third vibration mode. However, no significant change in mode shapes was observed for different rotational speeds. Based on the examined Modal Assurance Criterion (MAC) results, cross-comparisons of the mode shapes obtained for all three different speeds yielded a minimum similarity of 93.8%, reaching up to 99.9%. For model updating, a Frequency Response Assurance Criterion (FRAC)-based method utilizing frequency response functions (FRFs) was employed. Initially, a numerical model of the welded shaft was created using MATLAB-R2015a, based on the Euler–Bernoulli beam theory. Since rotational coordinates were not used in the EMA analyses, static model reduction was performed on the numerical model to reduce the effect of rotational coordinates to translational coordinates. For model updating, experimentally obtained FRFs from EMA and FRFs from the numerical model were used. The equivalent modulus of elasticity and equivalent density of the friction weld region were used as updating parameters. Successful results were achieved by developing an algorithm that ensured the convergence of the numerical model’s FRFs and natural frequencies.

The aim of this study was to examine the alterations in the dynamic properties of damaged aluminum plates following repair with carbon fiber composite patches. Initially, cracks of varying lengths (10, 20, 30, 40, and 50 mm) were introduced at different locations (mid-straight, mid-diagonal, corner-straight, and corner-diagonal) on 1.8 × 200 × 200 mm aluminum plates. Subsequently, these induced defects were repaired using single-sided and double-sided patches produced via the vacuum infusion method. The research then focused on analyzing how the resonance frequencies, vibration mode shapes, and damping ratios of the plates changed after these repairs. The dynamic properties of the plates were determined using the Experimental Modal Analysis (EMA) method. The results indicate significant changes in the dynamic properties of the plates due to crack formation and patch repairs. The first five modes of the plates were analyzed, and variations in resonance frequencies, influenced by crack length, location (middle or corner regions), and application type (single-sided or double-sided), reached up to 6.07%. While no substantial change was observed in the vibration mode shapes, particularly at lower frequencies, the fifth vibration mode showed the highest variation at 8.8%. Additionally, remarkably high changes in vibration damping ratios, up to 37.39%, were observed. The findings were presented in a comparative and elucidative manner, aiming to contribute to the literature.

Composite patches (CPs) are used to increase fuel, oil and gas resources efficiency, and improve performance in sectors such as aviation and automotive due to their lightness and durability. These materials strengthen structures thanks to their high strength and contribute to the extension of the life of structures by being used in areas such as marine and construction due to their resistance to corrosion. One of the most important advantages of CPs is that they can be produced in the desired shapes and sizes. This feature provides engineers with flexibility in design and offers ideal solutions for structures with complex geometries. In addition, there is no need for processes such as drilling holes or weakening the existing structure when applying CP. In this way, cracks are prevented from progressing and structural integrity is maintained. This review study presents a thorough investigation of the aspects of the methodology, materials, applications, performance, monitoring and evaluation of CP repairs of composite and metallic structures with investigation of the recent studies on this special area.

Friction stir welding (FSW) is the most widely used solid-state joining method for sheet and plate-like materials, valued for being a highly adaptable, environmentally sound, and energy-efficient process. The literature has repeatedly shown that FSW is a reliable joining technique for high-demand technological applications, particularly for high-strength aluminum and titanium alloys used in aerospace, which are difficult to join with traditional fusion welding methods. To describe the microstructural changes caused by solid-state FSW, many studies analyze mechanical parameters of FSW joints, including tensile strength, bending, torsion, elasticity, and fatigue responses. In recent years, the push to expand FSW's use, broaden the range of compatible alloy systems, and improve the resulting mechanical properties has led to significant advancements in this joining method. Accordingly, this review study provides a comprehensive investigation into the methodology and the materials relevant to this specific field.

Pump systems are widely used in engineering applications and are meticulously designed using numerous engineering calculations. Engineers strive to produce safer and more efficient pumps. These systems are dynamic, incorporating moving components such as shafts, impellers, and bearings, all subject to various dynamic effects. During the design phase of such systems, understanding how their dynamic characteristics will evolve with the design is crucial for ensuring safe and high-performance operation. In this study, modal analysis and rotordynamic analysis were performed on a rotor system, consisting of the shaft, impeller, and bearings, of a centrifugal pump system. A numerical model of this system was created using MATLAB. The moving rotor of the centrifugal pump was modeled using the Euler-Bernoulli beam theory. The impeller was represented as an equivalent disk after creating its 3D solid model, taking into account its polar and diametric moments of inertia. The ball bearings supporting the rotor were modeled using linear spring and damping elements. It is investigated how the natural frequencies and critical speeds of the rotor system changed for different distances between the two ball bearings used for shaft support and for various bearing stiffness values. Additionally, the presence of anti-resonance frequencies in the transfer frequency response functions between the impeller and the bearings was identified, and their variations with parameter changes were analyzed. The conducted parameter variations revealed that the natural frequencies and critical speeds changed significantly, and these changes exhibited different tendencies depending on the mode shapes. The results demonstrate that constructional design parameters in pump system rotors significantly impact the system's dynamic characteristics.