Based on the fundamental principles of the thermodynamics of irreversible processes and continuum damage mechanics, this paper describes and experimentally substantiates a generalized phenomenological model of damage accumulation kinetics for fiber-reinforced composite materials. The main mechanisms of damage development are systematically analyzed: in the fibers, in the matrix, and due to shear within and between the layers of the composite. In doing so, the technological features of layer placement, the angle of inclination of the reinforcing fibers, and the sequence of their arrangement are considered. The introduction of threshold mechanisms for the initiation of various types of damage at the micro- and meso-levels of the reinforced composite, in conjunction with power-law and exponential patterns of their accumulation, allows for an adequate reproduction of the characteristic stages of this complex and multifaceted process, namely: initiation, stable growth, and accelerated degradation of the structure. To determine the parameters of the damageability model, a framework for experimental studies was developed that allows for the quantitative characterization of the composite’s initial physical and mechanical properties and the evolution of its damageability under static and cyclic loading. A series of experimental studies on the damage behavior of the reinforced composite under various lamination schemes was conducted. This allows, by varying the orientation and sequence of layers, to specifically identify the dominant damage mechanisms (fiber, matrix, shear, and interlaminar).
A charged air cooler is one of the most important components applied in a turbocharger system. This study aimed to investigate the damage characteristics of a charged air cooler using a broken intercooler as the research object. Various experiments were conducted to analyze the microstructure at the damage point. The fluid–structure coupling interaction simulation was performed to determine the temperature field of the equipment under the given operating conditions. Finally, the reason for the damage was proposed based on the experimental findings. The results showed that the welding process and high temperatures led to the growth of the precipitated phase during equipment manufacturing and operation, reducing material strength. In addition, the silicon and oxygen elements within the material contributed to crack initiation and damage. The findings of this study provide theoretical guidance for improving the design of the equipment.
This study numerically determines the deformation limits of an electro-thermo-compliant (ETC) microactuator designed for microelectromechanics. Prior investigations have not explored the structural integrity limits of microactuators based on thermo-mechanical-electrical properties, stress-strain-temperature, and stress-voltage relations. A comprehensive 3D multiphysics structural-thermoelectric finite element model was designed. All the mechanisms of heat dissipation for conduction, convection, and radiation were thoroughly considered. We established that the quantity of tip displacement (or put force) can be precisely adjusted by relating it to the applied voltage, grounded on thermomechanical considerations, thus improving the control and efficacy of microactuators. The numerical findings were confirmed by referencing published experimental data. Tip deflection and achievable maximum temperature curves showed nonlinearity for potential differences applied to the anchors. While a linear stress-strain curve was demonstrated, a nonlinear 2nd order voltage effect on stress was shown. The critical voltage level for the melting temperature of silicon at 1750 K was determined. A brittle failure type was observed at approximately 1600 MPa with a 1
Maraging steels are widely used in aerospace, mold manufacturing, and high-end equipment manufacturing due to their high strength, good toughness, and excellent processability. Selective laser melting (SLM), a common metal additive manufacturing (3D printing) technology, offers a novel approach to fabricating maraging steel components with complex geometries. However, the SLM process parameters significantly influence the final microstructure and properties of the formed parts. This study systematically investigated the effects of key process parameters, including laser power, scanning speed, layer thickness, and volumetric energy density (VED), on the microstructure, mechanical properties, and defect formation of 18Ni300 maraging steel. The results show that optimizing the VED to 107.78 J/mm3 can synergistically improve molten pool stability, suppress defects such as lack of fusion and porosity, and refine grains. Consequently, the material achieves a relative density of 8.06 g/cm3, a peak impact toughness of 75.2 J/cm2, and high yield strength, realizing an excellent strength–toughness balance. Optimizing VED can significantly enhance material density, refine the grain microstructure, and improve overall mechanical properties. This study provides a theoretical basis and practical guidance for parameter optimization in the SLM processing of maraging steels.
Solar air heaters (SAH) serve as effective, sustainable thermal systems for low- and medium-temperature applications, yet air's limited heat transfer properties constrain their performance. This study examines the thermal and thermo-mechanical performance of four distinct SAH configurations using computational fluid dynamics (CFD) and experimental methods. The configurations analyzed include a basic flat-plate SAH, a honeycomb-structured absorber plate, a 26°-tilted SAH, and a nano-coated absorber plate with Al2O3 particles. Experimental validation conducted at mass flow rates of 0.004 kg/s and 0.006 kg/s demonstrated satisfactory concordance with CFD predictions, exhibiting deviations of 10–15
This study simulates a single strike by a standard explosive UAV (drone) on a third-level protective structure (in accordance with the “Krayina-Fortetsia” concept). The impact-explosive load, applied as a pulse at three points, is considered, with the parameters determined in accordance with UFC 3-340-02. Modeling and calculations were performed in the LIRA-FEM software package to determine the forces in the roof slab, main beams, and columns. The primary assessment of reinforced concrete elements involved determining the required reinforcement contribution, highlighting the importance of using fiber-reinforced concrete under high loads. Despite this, the columns required an increase in their cross-section, indicating the need for more rational, modern solutions. The developed calculation model has demonstrated the high resistance of the third-level protective structure to single impact-explosive loads.
Optimal design and kinematic parameters of elastic sectional screws of conveyors have been determined to ensure the operating characteristics of the bulk material transport process. New designs of the elastic sectional screw of conveyor have been developed, and their optimal parameters have been substantiated to ensure the conveyance of bulk materials along curved paths. Analytical relationships for a section of an elastic sectional screw under contact between the ball and the surfaces of the sockets have been obtained, depending on the load and the design parameters of the conveyor. The relationship between the magnitude of the torque arising between the loaded sections of the screw and their spatial arrangement has been evaluated, which is a prerequisite for improving the operating characteristics of flexible screw conveyors.
This study investigates the static bending response of simply supported laminated composite plates by developing and comparing three four-variable refined plate theories. The proposed models incorporate an exponential variation of transverse shear stresses through the plate thickness, thereby inherently satisfying the zero-traction boundary conditions at the top and bottom surfaces without requiring empirical shear correction factors. The first formulation (RPT1) employs a conventional displacement field, while the second (RPT2) introduces an extension component to the transverse displacement, and the third (RPT3) further accounts for thickness-stretching effects. Governing equilibrium equations are systematically derived via Hamilton’s variational principle and solved analytically via the Navier solution based on a double Fourier series expansion for anti-symmetric cross-ply laminates under sinusoidal loading. The predictive accuracy of the proposed theories is rigorously validated against three-dimensional elasticity solutions, classical plate theory, and established higher-order shear deformation models. Numerical assessments reveal that all three formulations yield highly accurate in-plane stresses and deflections, particularly for thin to moderately thick plates. Notably, RPT3 captures the parabolic variation of transverse displacement induced by thickness stretching, whereas RPT1 and RPT2 predict a uniform through-thickness deflection. A critical limitation is identified in RPT2: while it improves displacement predictions, it fails to enforce zero transverse shear stress at the free surfaces when evaluated through constitutive relations. Overall, the exponential shear function framework demonstrates exceptional computational efficiency and precision, offering a robust analytical tool for the design and optimization of advanced laminated composite structures.
Welded structure’s stress corrosion cracking (SCC) is the primary environmental damage phenomenon in water reactors, and the crack-tip strain rate is the most important mechanical parameter, but quantitative evaluation is very difficult. This paper establishes a numerical model of SCC crack-tip creep using compact tension specimens, analyzing various macrostructural parameters, including the effects of mechanical parameters influencing material plasticity and the variation in crack-tip stress intensity factors on crack-tip creep behavior. The functional relationship between macrostructural parameters and the crack-tip creep rate has been established, and a quantitative calculation method based on crack-tip creep has been developed, laying the foundation for the predictive capability of the SCC model.
A pressing scientific and applied problem has been solved: the mechanisms of premature brittle fracture of cubic boron nitride (CBN) cutting inserts during the machining of high-manganese steels (equivalent to ISO GX120Mn13) have been elucidated. A comprehensive approach was applied, combining the vibroacoustic concept of tool condition diagnosis with the methodological foundations of Griffiths’ fracture theory, and based on spectral analysis of tool vibrations and an assessment of spectral component energy using Parseval’s theorem. Laboratory experiments have established that up to 80
The appearance of foreign-made high-pressure cylinders for technical gases on the Ukrainian market requires appropriate experimental testing of their quality to justify their purchase. Experimental studies of the strength parameters of a test batch of high-pressure cylinders (seven sizes, five cylinders of each type), manufactured from seamless tubes, established that two cylinder sizes failed to withstand standard cyclic pressure tests. The probable cause of failure is a manufacturing defect resulting from non-compliance with the regulatory document regarding the radius of curvature of the concave bottom and significant deformations under cyclic test pressure loading. Significant cyclic deformations of the cylinder bottoms contributed to the initiation and propagation of fatigue cracks in the stress concentration zone in the circumferential direction, which led to failure due to the action of longitudinal stresses. The following mechanisms of cylinder failure during standard testing have been experimentally established. Under static loading with increasing internal pressure, failure occurs due to the action of hoop stresses in the longitudinal direction of the cylinders via a quasi-static mechanism with signs of accumulated strain limitation. Under cyclic loading with test pressure, failure occurs due to longitudinal stresses via a low-cycle fatigue mechanism resulting from the initiation and growth of fatigue cracks to critical sizes in the stress concentration zone.
The possibility of rapidly assessing the uniaxial compressive strength of rock directly at industrial sites using samples of arbitrary shape and size is considered. The necessity of using non-destructive methods is substantiated, as the relationship between the informative parameter and strength is weakly dependent on the rock type when these methods are applied. Direct uniaxial compression strength tests were conducted under laboratory conditions on regular-shaped samples for a group of rocks. The strength of the rocks ranged from 19 to 113 MPa. For this group of rocks, two non-destructive testing methods were also used on samples of arbitrary shape: ultrasonic and impact pulse. For the ultrasonic method, the optimal operating frequency and the appropriate testing range were experimentally determined. For the studied set of rocks, with the exception of coal, a relationship close to linear was established between the longitudinal wave velocity and the uniaxial compressive strength. For the rapid determination of rock strength under industrial conditions, portable, domestically manufactured ultrasonic equipment is recommended. In the developed version of the shock pulse method, the duration of the elastic interaction between the spherical impactor and the rock serves as the informative parameter. An advantage of the method is the weak dependence of this informative parameter on the impact force. It has been established that the relationship between the value of this parameter and rock strength under uniaxial compression is also satisfactorily described by a linear function. Coal is also an exception to this established relationship. Both methods can be used for rapid assessment of the strength of rock samples of arbitrary shape, as well as for an approximate assessment of strength directly in the rock mass under appropriate measurement conditions. The recommended equipment cannot be used in mines and other underground structures where there is a risk of gas or dust.
The interlaminar fracture toughness in Mode I was investigated using DCB-type specimens made of carbon fiber-reinforced plastic (CFRP) based on balanced fabric 3752, according to ASTM D5528, using the compliance calibration method. To reduce errors in determining this parameter, the compliance of the testing machine’s force chain was accounted for. Calculations of the necessary correction factors, as well as the cube root of the normalized compliance of the specimens as a function of delamination length, were performed for cases of failure along the midplane of the specimens, their asymmetric delamination, and failure of the carbon fabric layer. For these cases, the characteristics of changes in the aforementioned parameters were established. A strong relationship was observed between the cube root of the normalized compliance of DCB specimens and the current delamination length, with a correlation coefficient of 0.9975. Additionally, the fracture toughness during delamination development in the specimens was determined using the classical beam theory method. For each set of calculated fracture toughness values during delamination development in the specimens, a linear regression equation was fit for each method. As a result, it was established that the calculated fracture toughness in Mode I using the conventional beam theory method is 11
To enhance the high-temperature erosive wear resistance of AISI 304 austenitic stainless steel, WCNiCrBSiFe composite coatings with varying WC loadings were fabricated on 304 stainless steel substrates via laser cladding in this work. A systematic investigation was conducted to examine the influence of WC content on the microstructure, microhardness, high-temperature erosion mass-loss rate, and the corresponding wear mechanism of the laser-cladded coatings. The experimental results demonstrate that as the WC content increased, the microstructure of the laser-cladded coatings was significantly refined, accompanied by a corresponding improvement in microhardness. The 25
In recent years, engineered bamboo has gained attention for its potential use in sustainable construction, offering an alternative to traditional materials such as concrete and steel. However, the fracture behavior of engineered bamboo, particularly under Mode I loading conditions, remains underexplored, and reliable methods for predicting its critical load are scarce. This study aims to fill this gap by utilizing machine learning (ML) to predict the critical load for Mode I fracture in engineered bamboo. Three gradient-boosting models, namely extreme gradient boosting (XGBoost), light gradient boosting machine (LightGBM), and categorical boosting (CatBoost), were trained using a database that included key features such as specimen dimensions and material properties. Shapley additive explanations (SHAP) were employed to interpret the influence of each feature on the model predictions. The results reveal that specimen thickness is the most influential feature, while features such as tensile strength perpendicular to the grain and bending elastic modulus also contribute, though to a lesser extent. This study provides a data-driven approach for predicting the fracture behavior of engineered bamboo, offering valuable insights for the design and application of this material in structural engineering.
Two approaches have been developed to study the thermally stressed state of functionally graded layered shallow shells in the presence of an internal heat source. The bounding surfaces of the shell layers have zero torsional curvature, and the variability of the principal curvatures is neglected. The structure is very flat, i.e., the coefficients of the first quadratic form are taken to be equal to one. It is assumed that the radii of curvature significantly exceed the thickness of the structure, and its outer surfaces have the same curvature. The imposed constraints allowed us to reduce the curvilinear orthogonal coordinate system to a planar one. In the first approach, using Reissner’s variational principle, a system of differential equations of equilibrium is formulated. For the special case of a hinged support under conditions where the thermal load is distributed from an internal energy source according to a trigonometric law, this system reduces to a system of ordinary inhomogeneous differential equations regarding the distribution of the unknown functions over the thickness of the shallow shells. The solution is obtained analytically without introducing an approximation of the unknown functions with respect to the structure’s thickness. The second approach is based on a polynomial approximation of the unknown functions with respect to the structure’s thickness. Such an approximation accounts for shear and compression by introducing corresponding unknown functions. A distinctive feature of the approach is also the definition of the displacement functions at the outer surfaces of the structure’s layers. This makes it possible, if necessary, to divide the layers into sublayers with corresponding refinement of the calculation results. The convergence of the results obtained using the two proposed approaches confirms their validity.
The effect of cold isostatic pressing (CIP) of unsintered powder blanks on the formation of the structure and mechanical properties of the hard alloy WC–8Co–0.3VC was studied. Three series of samples of the following compositions were produced: WC–8Co, WC–8Co–0.3VC and WC–8Co– 0.3VC, which before CIP was subjected to sintering. All samples were obtained from the same batch of powders under identical conditions of pressing and sintering. It was established that the alloy with 0.3 wt.
To address the challenges of evaluating structural safety margins under complex aerodynamic loads across typical operating conditions of high-speed maglev trains, this study establishes a comprehensive finite element model (FEM) of the train body, incorporating aluminum alloy loadbearing frames, sandwich structures, and connecting components. The structural strength is analyzed under four representative scenarios: tunnel entry, 500 km/h without crosswind, 500 km/h with 10 m/s crosswind, and 500 km/h with 33 m/s strong crosswind. Von Mises stress distributions of key components are obtained via simulation and compared with the yield stress of typical aluminum alloys to assess safety margins. Results show that the overall train body structure does not yield under any condition, thus meeting the static strength design requirements. However, under strong crosswind, significant stress concentrations occur in areas such as door posts, the lower front section of the train head, and floor structures, where local stresses approach the yield limit, indicating design weaknesses. Optimization recommendations for these weak regions are proposed, providing both a theoretical basis and an engineering reference for structural safety assessments under complex scenarios involving high-speed maglev trains.
Within the framework of an approach based on the equations of linearized mechanics of deformable bodies, the stress-strain state of a body containing two parallel Mode I cracks is investigated, taking into account the action of initial (residual) stresses directed along the cracks. The proposed method for solving the plane problem involves representing stresses and displacements using potential harmonic functions and applying Fourier integral transforms to them, which allows the given boundary value problem to be reduced first to a system of paired integral equations, and then to a system of inhomogeneous Fredholm integral equations of the second kind. From the analysis of the asymptotic distribution of stresses in the vicinity of crack tips, analytical expressions for the stress intensity factors are obtained, and it is shown that due to the mutual interaction of cracks, both stress intensity factors K1 and K11 take on non-zero values. For a nonlinear elastic material with the Treloar elastic potential (a neo-Hookean body), the dependence of the stress intensity factors on the initial stresses and on the crack spacing normalized by the crack length has been numerically analyzed. A resonant change in the values of the stress intensity factors was found when the initial compressive stresses reach certain critical values, which correspond, for the material under study, to a local loss of stability of the equilibrium state in the vicinity of the cracks.
This study investigates the reliability analysis of a multicomponent system in which stress and strength are modeled as dependent random variables, using progressively Type-II censored data. Both variables are assumed to follow Kumaraswamy distributions with different shape parameters, and their dependency structure is characterized via a Clayton copula. Maximum likelihood estimators (MLE) and bootstrap confidence intervals are derived for the unknown parameters and system reliability. Furthermore, Bayesian point estimates and highest posterior density (HPD) credible intervals are obtained under various loss functions. The performance of the proposed methods is evaluated through Monte Carlo simulations, and a real data analysis is presented to demonstrate the applicability of our study.
