The failure behavior and energy absorption performance of star-shaped zero Poisson’s ratio honeycomb core with aluminum face-sheet sandwich beams under three-point bending are experimentally and numerically studied. A numerical model that accounts for the nonlinear mechanical behavior of phenolic resin-impregnated aramid paper is developed, and its accuracy is validated using experimental stiffness and peak load data, yielding maximum errors of 13.40% and 3.26%, respectively. The influence of key geometric parameters on the load-carrying capacity, energy absorption and failure mechanisms of honeycomb sandwich beams is systematically analyzed. Results demonstrate that increasing the face-sheet thickness, honeycomb core height, honeycomb cell wall thickness or reducing the side length of the honeycomb cell can improve both the structural loadcarrying capacity and energy absorption. When the core height is held constant, the initial failure mode transitions progressively from face-sheet indentation to core shear failure with increasing face-sheet thickness. Furthermore, the overall bearing capacity of the sandwich beam is improved with the increase in core height, ranging from 2335 N at d = 16 mm to 2943 N at d = 22 mm. However, core height effect on structural stiffness is less pronounced compared to that of the face-sheet thickness. It is worth noting that core shear consistently dominates the failure response across all specimens regardless of variations in core height.
This paper establishes a coupled, electromechanical nonlinear model with formulation for a complex piezoelectric energy harvester using Hamilton’s principle based on both Timoshenko and Euler-Bernoulli beam theories. The coupled nonlinear governing equations are derived and it incorporates geometric, inertial, damping, material and electromechanical coupling nonlinearity effects. The Galerkin method is applied to reduce the nonlinear partial differential equations, while the method of multiple scales is used to yield approximate analytical solutions for displacement, output voltage, and power amplitude. Comparison between the two beam theories under varying length-to-thickness ratios reveals that material nonlinearity significantly enhances the system nonlinear dynamic response. Accounting for shear deformation and rotary inertia, the Timoshenko beam theory demonstrates superior accuracy, particularly for short, thick beams with low length-to-thickness ratios. The results show effective reduction of natural frequency and broadening of low-frequency applicability. Additionally, optimizing load resistance matching improves output stability and energy conversion efficiency under low-frequency resonance conditions.
During tunnel construction in weak strata, the coupled effects of ground rheological behavior and stress release significantly influence both construction progress and safety. As a critical support measure in tunneling engineering, the time-dependent mechanical interaction between rock bolts and the surrounding rock under such complex conditions remains insufficiently understood. To elucidate the time-dependent interaction mechanism between rock bolts and surrounding rock under these challenging engineering conditions, this study develops an analytical solution for bolted tunnels that explicitly couples tunnel excavation-induced stress release and ground rheology. The rheological behavior of the ground is characterized using classical Maxwell and Kelvin-Voigt creep models, while the stress release effect is represented through the virtual support pressure method. A closed-form analytical solution is ultimately derived via integral transforms. The solution accounts for two types of rock bolts: end-anchored rock bolts and fully grouted rock bolts, which are distinguished by modifying the contact conditions at the boltrock interface. Numerical simulations verify the validity and engineering applicability of the proposed analytical method. Furthermore, parametric studies are conducted to examine the influence of bolt parameters and stress release parameters on surrounding rock deformation. The proposed analytical approach provides researchers and engineers with an improved theoretical understanding of the interaction between rock bolts and tunnel surrounding rock in weak strata.
As a significant improvement and supplement to the element-free Galerkin (EFG) method, the complex variable element-free Galerkin (CVEFG) method and its improved versions introduce complex variable basis functions when constructing shape functions. These methods are used not only to approximate vector functions but also to approximate scalar functions by using only the real part of the shape functions. They demonstrate higher accuracy than the EFG method in solving linear and nonlinear mechanics problems, positioning them as an important direction for improving the EFG method. This paper reviews the advances in the complex variable moving least-squares (CVMLS) approximation and its further improvements, as well as those of the CVEFG methods based on these CVMLS approximations. The formulas for the CVMLS approximation and its improvements are provided, along with those for the CVEFG and improved methods. Several numerical examples are presented to demonstrate the effectiveness and advantages of the improved CVEFG methods. Finally, relevant conclusions and future prospects are discussed.
Nonlinear dynamic vibration absorbers have been extensively utilized for controlling vibrations in structures. A beam-type nonlinear dynamic vibration absorber (BNDVA) is proposed and investigated. A nonlinear dynamic model of the coupled single-degree-of-freedom system is established to systematically evaluate its vibration suppression performance. First, the effects of excitation amplitude on vibration reduction efficiency, effective suppression bandwidth, and oscillator’s response characteristics are examined through theoretical analysis. The effects of nonlinear parameters on the efficiency of vibration suppression and the response of the oscillator are examined. It is shown that a relatively high vibration reduction efficiency can be maintained under different excitation conditions, while a non-monotonic variation is observed with increasing excitation amplitude. The nonlinear effect is shown to effectively suppress the oscillator’s response and broaden the high-frequency operating range. Meanwhile, a mathematical model is constructed using machine learning. The model maps vibration reduction efficiency and nonlinearity performance index in the parameter space of excitation amplitude and primary system frequency. Rapid prediction of performance and identification of effective vibration reduction regions are achieved. Finally, an experimental platform is established, and the absorber’s performance under different excitation amplitudes is tested. The experimental results agreed closely with theoretical results. The reliability of the theoretical analysis is effectively validated by the experimental results. The proposed theoretical and machine learning models provide a systematic basis and experimental reference for the performance evaluation, design optimization, and engineering application of nonlinear vibration absorbers.
Wave propagation in a viscoelastic medium over an inviscid fluid layer has been extensively studied due to its applications in environmental and ocean modeling, particularly in the context of ice-covered seas. This work examines wave dispersion in a thick viscoelastic medium overlying an inviscid fluid, with additional in-plane compression applied at both the free surface and the interface. The dispersion relation governing this configuration is derived and the dispersion characteristics along with the group velocity are analysed for both elastic and viscoelastic cases. Shallow- and deep-water approximations are also obtained from the derived dispersion relation and their behavior is examined. A critical buckling load is identified, and a relation connecting the governing parameters with this critical load is obtained under the shallow-water approximation, which distinguishes the stable and unstable regions of wave propagation. The analysis is further extended to the viscoelastic case, where the effect of viscosity on the dispersion characteristics is investigated. A critical viscosity is identified, beyond which the behavior of the compression-induced mode changes significantly. These findings enhance our understanding of wave dispersion in a two-layer system consisting of a viscoelastic medium over an inviscid fluid, which serves as an idealized model for ice-covered domains and surface layers such as oil spills in the ocean.
The ability of shape memory polymers (SMPs) to undergo significant deformations and still regain their initial shape or another desired shape under the action of particular stimuli has led to their recent application in many domains, particularly in biomedical devices and even space applications. Their use in structural members, however, has been limited due to their low strength and other poor mechanical properties. Incorporating reinforcing fibers or particles into SMPs significantly enhances their mechanical properties but reduces their intrinsic shape memory properties. This paper investigates the shape deformation, shape fixity, and recovery performance of thermally stimulated glass fiber/epoxy woven roving mat (WRM) reinforced SMP laminate beams using finite element analysis relative to unreinforced neat SMP beams. The SMP used in the study is an in-house realized material with optimized constituents to have a high glass transition temperature. The increase in stiffness of the shape memory polymer composite (SMPC) beam and a corresponding reduction in shape memory properties is observed and quantified for different number of layers of the WRM reinforcement and compared with the neat SMP beam. The study contributes valuable insight into optimizing SMPC structures for aerospace applications where a balance is required between superior mechanical properties without much reduction in the shape memory behavior.
This study presents an integrated finite element (FE) and artificial neural network (ANN) framework for predicting the modal frequency response of damaged agar-based hydrogel plates under varying geometry, boundary conditions, and damage severity. The aim of the work is to develop a computationally efficient hybrid methodology in which validated FE simulations are used to generate a reliable dataset, and ANN-based surrogate models are subsequently employed for rapid frequency prediction. The hydrogel material parameters were obtained from experimental compression data through curve fitting using an Ogden-type hyperelastic model. Thereafter, the frequency characteristics were computed using ABAQUS-based FE analysis, and the numerical consistency was ensured through mesh convergence and validation studies. A systematic parametric investigation was conducted by varying stiffness-sensitive parameters, namely aspect ratio, thickness ratio, boundary conditions, and damage length, to establish physically consistent frequency trends. Unlike earlier studies that mainly focus on either numerical simulation or data-driven prediction independently, the present work combines FE-based modal analysis with ANN surrogate modelling for frequency-based assessment of damage-induced stiffness degradation in hydrogel plates. Based on the generated dataset, five ANN surrogate configurations were trained and compared to identify the most efficient prediction model. The proposed FE-ANN workflow enables rapid frequency estimation and reduces the need for repeated FE simulations. The frequency increased from 6.4977 Hz to 30.093 Hz when the aspect ratio changed from 1 to 3.
To enhance the structural performance of fiber-reinforced composites, this study proposes a framework for concurrent topology and fiber orientation optimization. This method employs an embedded bar model to represent fibers, thereby establishing a composite unit cell structure. Taking minimum compliance as the objective function, the method defines the relationship between the macro- and micro-scales and derives the sensitivity formulas for the two-dimensional unit structure. Furthermore, it adopts Gaussian quadrature to accurately calculate the stiffness matrix of anisotropic elements. Numerical examples validate the effectiveness of the proposed parallel topology optimization approach. The results of the Michell beam example demonstrate that, compared with the optimized structure using isotropic material, the single-scale optimized structure achieves a 30.48% improvement in stiffness. In addition, compared with the single-scale optimized structure, the multi-scale optimized structure yields a further 13.99% improvement in stiffness. Multi-scale optimization fully exploits the properties of fiber materials and mitigates stress concentration. This research provides a reference for the development of topology optimization techniques for fiber-reinforced composites.
This study numerically investigates the high-velocity impact response of aluminum plates under varying thicknesses and inclination angles, with comparative analyses against steel targets to identify material-dependent penetration behavior. Penetration analyses were performed to examine energy partition, failure mode, and ballistic resistance as functions of target thickness, impact obliquity, and material properties. Aluminum plates exhibited larger dynamic deformation and a greater transient kinetic energy component than steel, particularly in thinner plates, where frictional dissipation associated with relative sliding was more pronounced. Within the investigated thickness range, steel showed petaling, whereas aluminum failed by plugging, highlighting clear differences in penetration characteristics according to material type. A critical inclination angle was identified for each thickness, significantly influencing energy dissipation and penetration resistance. Ballistic limit velocities extracted using the energy-based Recht-Ipson relation showed consistent thickness-dependent trends and physically reasonable transition behavior. These findings provide insight into impact energy transfer mechanisms and offer a foundational basis for energy-equivalent plate modeling in high-velocity structural response assessment.
The dynamic fracture of brittle geomaterials shows strong heterogeneity and stochastic variability, challenging safety assessment in hydraulic fracturing, underground energy extraction, and large-scale structures. This study develops a non-intrusive polynomial chaos expansion (PCE) framework coupled with a dynamic phase-field model to quantify the effects of material and geometric randomness on crack initiation and propagation. Two cases are studied: (i) hydraulic fracturing of sandstone and limestone with varying pre-crack inclinations, and (ii) crack evolution in a concrete dam under rising reservoir pressure. The results show the fracture energy as the dominant factor, with Young’s modulus having secondary interaction effects, while density and Poisson’s ratio are marginal. Sandstone fractures via stress concentration and gradual dissipation; limestone exhibits energy accumulation and sudden release. The PCE–phase-field framework reproduces experimental crack paths and dynamic responses with an order-of-magnitude reduction in computational cost, offering a robust tool for uncertainty quantification and reliability assessment in dynamic rock fracture.
Bioinspired structures are well-known for their specific wavy geometry and outstanding dissipating energy capacity. This paper aims to introduce a hybrid geometry inspired by biological suture patterns to show the ability of these geometries to absorb impact load energies. The longitudinal wave propagation in one-dimensional waveguides is investigated. The evaluation process begins with sinusoidal geometries, which include three configurations. The wave propagation analysis in these nonhomogeneous geometries is conducted using the Wave Element Method (WEM), investigating the effectiveness of each geometry on selected parameters. In the next step, four periodic muti-phase geometries are considered. Among them, the ones that cause significant reduction in wave group speed and vibration amplitude are identified. In the next section, combinations of sinusoidally varying geometries and multi-phase ones are introduced, and the best one that has the most significant influence on the selected parameters is chosen. New elements with quasi-periodicity are then introduced and added to the system. Finally, a non-uniform rod is considered, and the hybrid geometry with the best performance is inserted in the middle of the rod. It is shown that the proposed hybrid geometry can result in a 76% reduction in the wave amplitude. The novelty of this paper is the introduction of a new hybrid geometry similar to irregular suture interfaces and solving problems in the time domain, which are introduced for the first time in this paper. This paper's findings could help us understand the impact-reduction mechanism in animals like woodpeckers and design impact-resistant vibration systems.
Geothermal wellbore stability in deep formations is governed by pronounced thermohydromechanical (THM) coupling, in which seepage-induced pore pressure diffusion plays a critical yet frequently underestimated role. Many existing thermoelastic models neglect seepage processes or treat pore pressure as a simplified boundary condition, thereby restricting their predictive capability in deep, high-temperature geothermal reservoirs. To overcome this limitation, this study develops a three-dimensional thermo-elasticity model with explicitly coupled seepage effects to investigate stress redistribution around geothermal wells under complex anisotropic loading conditions. The proposed framework incorporates depth-dependent mechanical, hydraulic, and thermal parameters, enabling a more realistic characterization of deep formation behavior. The results demonstrate that seepage-driven pore pressure diffusion fundamentally reconfigures near-wellbore stress evolution, with stress perturbations intensifying with burial depth due to enhanced hydraulicthermal gradients and anisotropic stress amplification. Overall, this study establishes a rigorous thermo-elastic analytical framework with explicit seepage coupling, providing improved predictive capability for geothermal wellbore stability and highlighting the importance of integrating hydraulic and thermal regulation into deep geothermal drilling design.
The interactive influence of disturbances and ground stress causes the failure behavior of deep rocks to exhibit a dynamic adjustment of brittleness and ductility. Excessive brittle behavior results in wellbore instability and damage to the surrounding formations in petroleum engineering. Peak and residual strength criteria applicable to such environments are proposed to establish a theoretical foundation for drilling safety assessment. The strength criterion is developed based on the CS (Cowper–Symonds) and slip-crack models. A brittle–ductile transition (BDT) index [Formula: see text] is established from the relation between residual and peak strengths. A large amount of experimental data within the ranges of [Formula: see text] s[Formula: see text] strain rate (SR) and 0–230[Formula: see text]MPa confining pressure (CP) was used to verify the reliability of this strength criterion. The correlation coefficients are close to 0.99 for peak and residual strength fittings. The errors of the BDT index are within 10% for all rock types except coal. The results indicate that rock strength increases with both CP and SR. However, the enhancing influences of SR and CP exhibit mutual suppression under coupled conditions. This phenomenon ultimately manifests as a variation in rock brittleness and ductility. Higher SRs correspond to larger values of [Formula: see text] and [Formula: see text], whereas [Formula: see text] decreases. The rates of change of the three parameters under high SR conditions are much greater than those at other SRs. The variation trends of these parameters provide a macroscopic physical explanation for the BDT. This theoretical framework has significant value for safety and risk assessment in drilling engineering under complex geological conditions.
Asymmetric sandwich structures incorporating an elastomer are developed to improve ballistic performance. The mechanism of enhancement remains unclear due to diverse structural failure modes associated with asymmetric configurations. Comprising a rubber layer, two aluminum face-sheets, and an aluminum foam core, some asymmetric sandwich plates incorporating an elastomer are designed with different thickness distributions of the face-sheets. The ballistic performance of asymmetric sandwich plates incorporating an elastomer is numerically investigated using a three-dimensional Voronoi-based approach and verified against previous experimental results. The role of the rubber layer, the structural response history, failure modes, and energy absorption characteristics of each component are thoroughly analyzed. It indicates that the enhancement effect of the elastomer depends on the structural asymmetric design and the failure mode of the elastomer. When the elastomer fails primarily through stretching, it promotes synergistic interaction between the face-sheet and foam core, reducing the residual projectile velocity by 36.4% and increasing the energy absorption capacity by 233.98%. Conversely, when the failure mode shifts to shearing-dominated failure, the enhancement effect is significantly reduced. In addition, the failure mode of the elastomer depends on the interaction between its local stiffness and the initial velocity. This study provides a fundamental understanding of the mechanisms by which elastomers enhance the performance of asymmetric sandwich structures, offering valuable insights for the design and optimization of multilayer protective systems.
To elucidate the nonlinear dependence of bonding strength on adhesive thickness, scarf angle, and temperature, uniaxial tensile tests were conducted on cylindrical aluminum alloy scarf joints. Load–displacement curves, fracture surface morphologies, and stress–strain data were systematically analyzed to evaluate the effects of adhesive thickness (t a , 100–1000 μm), scarf angle (θ, 15°–90°), and temperature (T t , 20–60 °C) on joint mechanical performance. The present work demonstrates that the relationships between these parameters and bonding strength are strongly nonlinear. Results show that reducing t a from 1000 μm to 100 μm increases peak load by approximately 83.7% and fracture displacement by about 60%, with the failure mode transitioning from interfacial debonding to cohesive failure. Decreasing θ increases the peak load but reduces the bonding strength per unit area, with the strength failure surface gradually deviating from a perfect circular arc. As the temperature rises to 60°C, the peak load decreases by 20–30% on average; however, the degradation is significantly less than that of the bulk adhesive. Moreover, increasing t a or θ mitigates high-temperature strength loss, with thicker adhesive layers providing buffering against thermal degradation. This study quantitatively characterizes the nonlinear bonding behavior of aluminum alloy scarf joints under the coupled influence of geometric and thermal factors, providing valuable insights for adhesive joint design, interface optimization, and the calibration and validation of cohesive zone models.
In this study, the near-field pressure dynamics of cylindrical explosives in underwater explosions are systematically investigated using computational modeling and empirical validation. A three dimensional finite element model based on the Arbitrary Lagrangian-Eulerian (ALE) algorithm is developed to simulate detonation processes in infinite water domains, with model accuracy confirmed through comparisons against experimental data. Focusing on the poorly understood extreme near-field region, the influence of explosive geometric parameters (length-to-diameter ratio, L/D) and detonation asymmetry on pressure distribution is analyzed. Key findings reveal that in the extreme near-field, peak pressure is initially more pronounced in the axial direction, but transitions to radial dominance with increasing standoff distance, a behavior that is more pronounced in high-L/D configurations (e.g., L/D = 5 exhibits a 44.4% slower axial-to-radial transition than L/D = 3). Non-central detonations of cylindrical explosives introduce significant pressure directivity, enhancing local peak pressures by up to 26.9% and inducing deviations from axisymmetric wavefronts. To characterize these effects, a semi-empirical engineering model integrating explosive mass loss and centroid trajectory is proposed, complemented by a scaling law regression method to quantify directional intensity. Specifically, this framework provides directional upper and lower bounds for peak pressure in the extreme near-field by coupling time-resolved mass consumption with dynamic centroid migration, and serves as an engineering tool for preliminary assessment of pressure directivity under cylindrical charge UNDEX loading.
With the booming application of ultrafast heating technology (e.g., laser ablation, etc.) to the processing/fabricating of metallic materials/structures, the transient thermo-mechanical responses analysis is particularly important to the active vibration control. Nevertheless, in such extreme non-isothermal conditions, the influences of the inherent high-order temperature-dependent characteristics of materials on structural heat-impact responses are still not reported. To address such a deficiency, this work aims to establish a unified nonlinear non-Fourier thermoelasticity model based on the Lord-Shulman (L-S), Green-Lindsay (G-L), and Green-Naghdi (G-N) theories with high-order temperature-dependent material properties. The virtual work principle is applied for formulating a nonlinear time-domain finite element method to solve the nonlinear governing equations directly. The proposed theoretical model and numerical method are applied to investigate transient impact thermo-mechanical responses of 2D homogeneous isotropic cylindrical copper-metallic plate subjected to ultrafast laser heating. The numerical results reveal that the high-order temperature-dependent specific heat substantially lowers the temperature maximum magnitudes and harmful thermal stresses, whereas the temperature-dependent thermal modulus exacerbates stress concentration. This finding provides new insights and guidelines into controlling transient thermo-mechanical responses for metallic structures in ultrafast laser processing.
Double network (DN) hydrogels have emerged as a transformative class of soft materials, successfully resolving the trade-off between high water content and mechanical robustness. Their exceptional toughness stems from a sacrificial mechanism wherein a rigid network fractures to dissipate energy, while a ductile matrix network maintains structural integrity. Despite progress in synthesis, fully capturing the complex, nonlinear mechanical behaviors of DN gels often requires advanced characterization techniques and even computational modeling. To address this, this review systematically summarizes recent advances in experimental and computational methods for studying the mechanical behavior of DN gels. We discuss experimental techniques ranging from standard macroscopic tests to emerging non-contact methods, alongside computational methods such as molecular dynamics, network simulations, finite element methods and machine learning. The paper concludes by identifying current challenges and outlining future directions for the field.
Vascular stents play a crucial role in managing vascular pathologies with high mortality and disability rates. New opportunities for cerebrovascular stent design are offered by biodegradable materials. However, current design methodologies rely heavily on empirical trial-and-error. A systematic theoretical framework is still lacking. A closed-form analytical mathematical model, which differs from existing models by targeting the specific flexibility requirement of tortuous cerebrovascular anatomies, is presented in this study. The model is established based on cantilever beam theory, energy conservation and Castigliano's theorem. The model is built to correlate stent structural parameters with mechanical flexibility. Numerical calculation is performed with MATLAB. Validation is conducted via finite element analysis (FEA), with a coefficient of determination R-2 = 0.997 for the core parameter strut width (w) and an overall average R-2 of 0.917 for all structural parameters after dimensionless normalization. Key findings are revealed: stent flexibility is inversely proportional to the cube of strut width (w) and thickness (t). A more significant effect on flexibility is exerted by w than t. The transition of cerebrovascular stent design from empirical-driven approaches to theory-guided reasoning is realized by this work.
