Measurement of the unsteady lift acting on test structures inside wind or water tunnels is challenging because flexible test structure dynamics induce errors in base-embedded force transducers. Force reconstruction techniques attempt to mitigate such errors by inversely estimating the applied force, oftentimes by way of modal filtering of structural response measurements. A previous work by Jones and Vlajic utilized dynamic fluid non-dimensional scaling as optimization criteria to calculate modal filters for the purpose of identifying the unsteady lift acting on flexible test structures inside wind or water tunnels directly from base-embedded force transducers. In the present work, we extend the previous methodology to determine unsteady lift spatial force distributions. In the proposed technique, forces within the spatial distribution are assumed to be some fraction of the total force on the structure and to be spatially uncorrelated. Additionally, the distribution is assumed to not vary significantly over the tested range of water tunnel flow speeds. The unsteady lift on the flexible structure is first estimated by way of non-dimensional scaling optimization. Results are then used to supplement an optimization problem in which the error is minimized between modal forces estimated via acceleration response measurements and those estimated via the unsteady lift. Numerical validation is provided as proof-of-concept, while experimental results are also provided to validate the mathematical framework and test assumptions.
Rubber vibration damping is among the most widely used classical vibration mitigation structures. In this study, based on the actual service conditions of rubber vibration dampers, a dedicated axial high-cycle fatigue test fixture was developed for rubber vibration damper structures. High-cycle fatigue tests and thermal effect studies were conducted on specimens subjected to accelerated aging under temperature and irradiation conditions, as well as on specimens with 4 years of service exposure. The microscopic fatigue failure laws of rubber vibration damping structures were elucidated, and the fatigue life under various operating conditions was obtained. The results demonstrate that the fatigue failure life of rubber vibration damping structures after temperature and irradiation acceleration is superior to that of new dampers. For dampers with 4 years of service, the remaining average fatigue failure life is more than 1.5 times higher than that of new dampers from the same batch. Moreover, the fatigue heating temperatures of rubber damper structures before critical failure do not significantly affect on the fatigue life of the damping structures.
Abnormal drill string vibrations frequently lead to premature failure, particularly in air drilling operations where the absence of drilling fluid lubrication exacerbates vibrational severity. To address this challenge, this paper proposes an Air Drilling Shock Absorber (ADSA) and systematically evaluates its mitigating effects on drill string dynamics. Firstly, the structural parameters of the ADSA's elastomeric components were optimized using finite element analysis (FEA), and the structural integrity was validated through physical pressure testing. Subsequently, a comprehensive drill string dynamic model was established, incorporating the tool's working mechanism and actual downhole operating conditions. The axial displacement, velocity, and acceleration of the drill string were then obtained via numerical solutions. A comparative analysis reveals that the integration of the ADSA significantly attenuates the vibration displacement, velocity, and acceleration across various sections of the drill string. Finally, field validation using vibration data from actual drilling operations demonstrated that the ADSA effectively suppresses drill string vibrations, thereby offering robust protection for the drill string and Bottom Hole Assembly (BHA).
Measuring the aerodynamic peak pressure transients generated by high-speed trains in tunnels, has importance due to the passenger comforts and safety limits. These effects are further influenced by the interaction between train nose geometry and the confined tunnel boundaries. In this study, a combined experimental and numerical approach is used to investigate three different high-speed train nose configurations (from sharp to flat). Experiments are carried out under dynamic entry conditions at 180 km/h using a high-speed rotary scaled model (HRSM) test rig with a 1:25 train scale. In addition, a computational fluid dynamics (CFD) simulations were performed in ANSYS FLUENT, using sliding mesh technique to capture the transient interaction between the moving train surfaces and the stationary tunnel walls. The results show the ability of HRSM setup to measure the effects of nose shapes and stated that flat nose profiles producing stronger compression waves compared with elongated nose (Shinkansen type) of about 32
The investigation of fracture damage evolution in rock-like materials subjected to explosive loading is critical for advancing mine engineering blasting techniques. However, direct observation of blast-induced damage in such materials remains experimentally challenging. This study presents a novel experimental system and theoretical framework for evaluating dynamic crack propagation using transmission digital gradient sensing (DGS) methodology. The proposed theoretical model is employed to quantify crack growth parameters in poly(methyl methacrylate) (PMMA) sheets subjected to interstitial lead azide charges under controlled detonation conditions. Through this approach, we systematically analyze the dynamic crack propagation behavior and stress wave evolution during explosive fracture processes. Our results demonstrate that the theoretical model effectively captures transient stress field information, with experimentally derived crack propagation dynamics showing strong agreement with LS-DYNA numerical simulations. These findings validate the reliability of the DGS-based optical measurement technique for quantitative characterization of explosive fracture phenomena.
This study examines the mode-dependent changes in the critical stress intensity factor of AA6061 aluminum alloy processed by up to three passes of Equal Channel Angular Rolling (ECAR). Tensile tests, modified Arcan fracture experiments at 0° (mode-I), 45° (mixed-mode), and 90° (mode-II), and finite element simulations were conducted to determine the critical stress intensity factors. ECAR increased yield strength by 32.6
For the scientific and quantitative assessment of the comprehensive damage power of blast - fragmentation warheads, by considering the attenuation of the shock wave pressure peak and fragment velocity with the increase of the detonation center distance, the variable weight idea is introduced. The comprehensive damage power evaluation model of the blast fragmentation warhead is proposed based on variable weight and criteria importance through intercriteria correlation (CRITIC). The static explosion tests of blast fragmentation warhead with equal volumes of 3,4-Dinitrofurazanylfuroxan (DNTF) and trinitrotoluol (TNT) were carried out, and the power parameters were tested, such as shock wave pressure and fragment velocity, and the variation law of each power parameter is analyzed. Combined with the measured data and the comprehensive power evaluation model proposed in this paper, taking the ground-reflected pressure peak, free field pressure peak, and total pressure peak as the evaluation indexes of shock wave power, respectively, and combining with the fragment velocity, the comprehensive damage power of the DNTF charge blast-fragmentation warhead was evaluated, it is obtained that the maximum TNT equivalent ratios are 1.78, 2.13, and 2.31, and the minimum is 1.57, 1.69, and 1.73. This method can scientifically and objectively calculate the weight of the shock wave and fragment at different distances from the explosion center and can accurately evaluate the comprehensive power of the blast-fragmentation warhead, which can provide an important reference for warhead design.
This paper presents the development, numerical analysis, testing and qualification of long and slender bellows for sodium cooled fast reactors especially in in-vessel fuel handling mechanism. Bellows of SS316L material are used to prevent the entry of the sodium in the annular space between concentric gripper tubes of the mechanism. Based on the space requirements, the length to diameter ratio of the bellows is more than 3 which is beyond the recommended value in EJMA. Commonly such bellows are manufactured with intermediate squirm rings with circumferential seal welds. Failure of any single weld including L-seam weld can lead to loss of leak tightness of the system. An improved design with 2 plies with each ply independently capable to carry the pressure loading and with a tangent type lip seal weld configuration was developed. An in-house experimental facility was developed for testing of such long and slender bellows addressing their bucking under compression and column instability under internal pressure. Fractographic investigation of the tested bellows at the fracture location showed striations and confirmed that the failure mode was fatigue. The methodology proposed in this work can also be used for developing slender bellows such as in large size sodium valves.
Photoelasticity is a reliable experimental technique for analysing stress distribution in machine components with complex geometries. Conventional model preparation using metal moulds is often labour intensive and suffers from limitations related to surface finish, dimensional accuracy and replicability. Although additive manufacturing has improved fabrication flexibility, issues such as residual stresses, anisotropy and optical scattering persist. This study presents a comparative evaluation of three model-making techniques: wooden moulds, 3D-printed moulds and silicone rubber moulds used for photoelastic analysis. A hybrid approach combining additive manufacturing for pattern generation with conventional epoxy casting is explored to improve model quality while reducing fabrication complexity. The performance of each method is assessed through qualitative photoelastic observations under identical experimental conditions, focusing on transparency, dimensional fidelity, leakage behaviour, ease of demoulding and residual stress patterns. The results indicate that silicone rubber moulds prepared using 3D-printed patterns provide superior transparency, minimal residual stresses, and improved repeatability, making them well suited for accurate and reliable photoelastic experiments.
Deep learning has been increasingly applied to impact-echo (IE) signals for automatic detection of internal defects in concrete structures. Existing studies typically convert IE signals into a single time–frequency map and focus on optimizing convolutional neural network (CNN) architectures. However, it remains unclear whether the classification performance is mainly determined by the CNN structure or by the time–frequency representation of the signal. This study systematically compares four representative time–frequency representations—STFT, bump, morse, and amor wavelet transforms—combined with four lightweight CNN models under identical datasets, training settings, and noise conditions. IE signals collected from a concrete slab containing defects at different depths were converted into time–frequency images for classification. The results show that the choice of time–frequency representation has a more significant influence on classification performance than the CNN architecture. Morse and amor wavelets consistently provide clearer feature patterns and stronger noise robustness than Bump and STFT. Among all combinations, the amor–MobileNet model achieves the best performance with an accuracy exceeding 99
Given the necessity of strengthening concrete columns that may suffer from accidental disasters, aging, or human-induced damage, this study presents an experimental investigation of the pre-damaged reinforced concrete (RC) columns jacketed using square corrugated steel sheets under axial compression. The influence of corrugated steel thickness, corner connection type of the jackets (welding vs. bolting), as well as pre-damage level, are investigated based on ten short RC columns. The strain and stress development in the corrugated steel jacket are analyzed in detail, revealing the confinement effect in the square section and load-carrying contribution of different parts. Although severer damage leads to the loss in the ultimate load-bearing capacity of original RC section, the transverse expansion is effectively restrained by the passive confinement provided by the corrugated steel jacket, which indirectly reduces the lost strength. As a result, the corrugated steel jacket can contribute to increasing the ultimate bearing capacity of the damaged RC specimens by 34.6
This paper presents experimental, analytical, and numerical models to predict the response of multi-layered sandwich composite panels under low-velocity impact loading. The sandwich panels’ skin consists of a twill carbon-reinforced epoxy resin, whereas the core comprises a 2D Nomex honeycomb. The panels are then subjected to transverse impact loading to investigate their impact behaviour. Analytical models were developed based on a spring-mass system to predict the dynamic behaviour of the striker-multi-core-sandwich plate domain and, finally, to determine the contact force history, which represents the main novelty of this research. The analytical models incorporate the effect of variable core and skin distribution to identify the most suitable combination for four designs under impact loading. These experimental results are then used to verify analytical and numerical models constructed in LS-Dyna. The finite element models of the honeycomb-reinforced sandwich panels are also investigated using MAT-054 and MAT-26 material cards in LS-Dyna to find the most economical computational approach. Finally, the energy-absorption characteristics calculated by analytical models are used to evaluate the performance of the multi-layered sandwich composite and to provide design recommendations. The specific energy absorption (SEA) under low-velocity impact (8.8 J) was compared across designs, revealing that the single-core panel achieved the highest SEA (78 J/kg), while multi-core and thicker builds provided higher stiffness and peak loads but reduced mass efficiency.
Performance of viscous dampers used in transmission towers is susceptible to long-term high-temperature service conditions. In this study, an improved viscous damper is developed through a synergistic design strategy integrating a polytetrafluoroethylene (PTFE)-based composite sealing system, and multi-layer protective reinforcement to mitigate leakage-induced degradation. This study conducts accelerated ageing tests based on temperature and heating duration to systematically evaluate the durability of the novel viscous dampers. It assesses their conventional mechanical properties and fatigue performance after ageing. The results show that the present viscous damper maintains stable damping performance and energy dissipation capacity under high-temperature conditions, demonstrating effective resistance to thermal ageing within the tested range and confirming its suitability for reliable long-term service in high-temperature environments.
Optical Coherence Tomography (OCT) vibrometry provides sub-nanometer displacement sensitivity and has become a key technique for mapping complex vibration patterns, particularly in hearing research where frequency-dependent motion of middle-ear structures is central to diagnosing pathology. However, at high frequencies, OCT measurements often approach the noise floor, degrading the accuracy and interpretability of reconstructed displacement fields, which is especially critical for fast and reliable assessment. We introduce a robust, regularized finite-element (FE) global reconstruction framework that utilizes higher-order shape functions and L-curve optimization to recover continuous, high-fidelity displacement fields. Through comprehensive simulation and experimental validation, we demonstrate that this method significantly outperforms traditional unregularized filters. Statistical validation via two-sample t-tests indicates that the regularized approach achieves significantly lower mean reconstruction errors compared to lower-order methods (p < 0.01). Most importantly, variance testing proves that regularized filtering always improves the variance (p < 0.01), consistently reducing noise-propagation while preserving the underlying accuracy of the reconstructed field. This workflow provides an objective, reproducible method for quantitative vibration analysis, bridging the gap between raw OCT data and high-fidelity mechanical modeling.
Creep is a phenomenon occurring in materials subjected to constant stress or load for a prolonged period of time on the scale of weeks, months, or years. In this work, we introduce a novel high-throughput technique to perform multiple creep tests simultaneously. The method works by coupling four specimens in series and loading them simultaneously. Although all specimens experience the same force, each has a different cross-sectional area, and thereby experiences a different stress. The resulting strains are then monitored using Digital Image Correlation, which facilitates the independent assessment of creep deformation in each specimen. To validate the technique, we use commercial 316 L stainless steel machined to 1/5 scale ASTM-E8 pin-loaded specimens. Two different sets of experiments are conducted at 650 °C and 325 MPa, 300 MPa, 275 MPa, and 250 MPa: (i) single-specimen tests to provide a benchmark measurement; and (ii) four specimens connected in series, to demonstrate the high-throughput technique. Successful validation showed that the high-throughput technique is capable of conducting up to four times as many creep tests within the same timeframe, thus significantly expediting the characterization of new alloys for creep resistance.
Currently, there is no established rigorous method for validating measurement techniques in solid mechanics. This paper presents the appropriate statistical approach for this purpose. Validation must compare measurements obtained using different techniques, considering their standard uncertainties. The use of the measurement uncertainties is essential for the metrological rigor of the validation, which is achieved through a statistical hypothesis test based on the chi-square distribution. A similar test is also possible to define for the identification of outliers. The method is simple and easy to apply, and is presented in the form of a procedural guide. Its applicability has been shown with an example of stress measurements by photoelasticity, which have been compared with the results of a finite element analysis.
Burners that channel a gaseous methane-air mixture through a porous sintered matrix are widely used to produce flat flames with controlled inlet and boundary conditions. Such environments are essential for studying combustion phenomena and validating physical and chemical models. However, this study shows that even nominally identical McKenna burners with a 25 mm stainless steel sintered matrix exhibit significant deviations from ideal uniformity. Detailed measurements of the spatial and temporal temperature fields within the matrix, as well as surface flow velocities, reveal substantial non-uniformities: velocity deviations of up to ± 50 % across the burner surface and temperature differences exceeding 70 ^∘ C between center and edge of the matrix. Furthermore, the burner housing temperature increases steadily during operation, reaching over 70 ^∘ C after 60 minutes, indicating limited heat removal and pronounced cooling defects. These findings demonstrate that even under nominally steady operating conditions, uniform inflow and boundary conditions cannot be assumed, which is highly relevant for many experimental combustion researchers relying on consistent burner behavior. The results highlight the necessity of accounting for such gradients when using flat flame burners to investigate sensitive combustion phenomena, such as thermo-diffusive instabilities and flame pulsation onset. To facilitate this, the 2D temperature and velocity profiles presented herein can be directly utilized by the community as realistic boundary conditions for future computational fluid dynamics (CFD) simulations of burner-stabilized flames on sintered burners.
The railway industry currently lacks unified testing standards for modal parameter acquisition of freight cars, and the influence mechanisms of different test methods, support conditions, and loading states on modal parameters remain unclear, resulting in significant variations in test results that hinder effective vehicle structural optimization design, fatigue life assessment, and vibration control. This study aims to establish a comprehensive understanding of how different testing methodologies affect modal parameter identification of railway freight cars and to develop systematic criteria for test method selection and support condition assessment. A hierarchical progressive experimental approach was implemented on a C70E general-purpose gondola car using five distinct excitation methods (impact hammer, electromagnetic exciter, hydraulic exciter, shaking table, and track testing), with progressive boundary conditions and four loading states designed based on orthogonal experimental principles, utilizing optimized placement of 56 measurement points to identify modal characteristics. The shaking table method demonstrated superior identification capability with 100
Honeycomb sandwich constructions with composite face sheets are extensively used in aerospace structures. The face sheets are generally made as a combination of unidirectional and bi-directional plies. The modulus of the face sheets plays an important role in the design of the structural component. They are determined from the modulus of the individual ply, applying the lamination theory. Modulus of the individual ply is determined through the testing of the laminates as per ASTM standards. In this work, it is shown experimentally that the modulus of unidirectional ply when it is a part of a face sheet in a honeycomb sandwich construction manufactured through co-curing process is significantly less compared to the value of modulus obtained from the tests on laminates. This is because the parameters involved in the co-curing process of manufacturing honeycomb sandwich panels are different from the parameters used in the manufacturing of the laminates. In the absence of this work, higher modulus than the actual will be used in the structural design of honeycomb sandwich type structure, resulting in large error in the predicted strain as well as the natural frequency of the fundamental lateral mode of spacecraft.
This study addresses the multi-field coupling errors induced by geometric distortion and pile-up effects during tilted micro-indentation testing of 6005 A-T6 aluminum alloy. To mitigate these errors, an indentation analysis correction function was developed by combining a geometric correction of the contact area with a pile-up compensation algorithm based on plastic work. Furthermore, cubic spline interpolation under physical constraints was employed to perform small-sample data augmentation. Based on these analyses and the plastic work conservation equation, a Support Vector Regression (SVR) model was constructed. The micro-indentation experiments were designed with five tilt angles (0°–4°, in 1° increments) and four indentation depths (20–50 μm, in 10 μm increments), resulting in 20 groups of baseline small-sample tests. On this basis, physically consistent spline interpolation and small perturbation expansion were applied, ultimately yielding 63 datasets, of which 43 were augmented. Experimental results demonstrated that the corrected indentation analysis model substantially improved the prediction accuracy of hardness and elastic modulus, exhibiting outstanding performance. Specifically, the prediction of hardness achieved a mean squared error (MSE) as low as 0.04, a mean absolute error (MAE) of 0.05, and a mean absolute percentage error (MAPE) of only 2.2
