Meccanica最新文献

This paper presents a dynamic continualization technique for a multi-layer beam-lattice metamaterial with an alternating chiral microstructure, where each layer is reciprocally interconnected through the insertion of pins. The study analyzes the dispersive properties of the system and its potential applications as a meta-filter, highlighting how the enhanced continualization technique introduced can capture the dispersive properties of stratified systems with chiral geometry. This approach makes it possible to derive higher-order gradient-type continuum models that yield dispersion spectra close to those obtained through a discrete Lagrangian treatment, without encountering dynamic instability effects due to thermodynamic inconsistency. These aspects are further investigated through the presentation of application examples, specifically concerning a stratified tetrachiral waveguide. A key finding of the studied examples is related to the passive/active tunability of the system, specifically in relation to the stiffness of the pin which determines significant influences on the dispersion spectra. To complete the analysis, a further example is finally proposed in which the waveguide is subjected to harmonic excitation, revealing how variations in the parameters can affect wave polarizations.

The rolling soft robot usually uses circular or ellipse-like configurations but the factors influencing the robot configuration have not been sufficiently investigated. This study presents a theoretical model for investigating the morphology evolution of a thin elastic ring under gravity. The ring exhibits an ellipse-like morphology under gravity, with this morphology governed by the ratio of gravity to bending stiffness. An increase in the ratio of gravity to bending stiffness results in a flatter ellipse-like structure, accompanied by an enhanced contact length with the ground and a concomitant reduction in its gravitational moment on the slope. The ellipse-like structures calculated by the theory are in good agreement with the experiment and simulation. This study provides a theoretical basis for the material selection and geometry determination of the configuration design of required rolling soft robots.

Lattice-like cellular materials, with their unique combination of lightweight, high strength, and good deformability, are promising for engineering applications. This paper investigates the energy-absorbing properties of four truss-lattice structures with two defined volume fractions of material in static compression experiments. The mass-specific energy absorption is derived. The specimens are manufactured by SLA printing of viscoelastic polymeric material. Sustainability implies that the lattice structures can withstand multiple loads and return to their original state after some recovery. Additionally, we present finite element simulations of our experiments and show that these calculations are, in principle, able to predict the different responses of the lattices. Like in the experiments, the truncated octahedron-lattice structure proved to be the most effective for energy absorption under strong compression.

We introduce the energy-stepping Monte Carlo (ESMC) method, a Markov chain Monte Carlo (MCMC) algorithm based on the conventional dynamical interpretation of the proposal stage but employing an energy-stepping integrator. The energy-stepping integrator is quasi-explicit, symplectic, energy-conserving, and symmetry-preserving. As a result of the exact energy conservation of energy-stepping integrators, ESMC has a 100% acceptance ratio of the proposal states. Numerical tests provide empirical evidence that ESMC affords a number of additional benefits: the Markov chains it generates have weak autocorrelation, it has the ability to explore distant characteristic sets of the sampled probability distribution and it yields smaller errors than chains sampled with Hamiltonian Monte Carlo (HMC) and similar step sizes. Finally, ESMC benefits from the exact symmetry conservation properties of the energy-stepping integrator when sampling from potentials with built-in symmetries, whether explicitly known or not.

The temperature rise of the tooth surface in spiral bevel gears plays a crucial role in lubrication performance and surface failure. However, existing studies primarily investigate scuffing by analyzing tooth surface temperature through experiments and simulations, without using similarity theory to examine comparable systems. By leveraging similarity theory, researchers efficiently translate insights from controlled experiments to real-world applications, fostering innovation while conserving resources. Similarity theory is used in the study to analyze the temperature rise of the tooth surface, and it is possible to determine that gears in different systems may exhibit analogous thermal behavior under specific scaling conditions. A thermal fluid–structure coupled model is employed to conduct a precise analysis of the original system for thermal assessment and experimental validation. Similarity theory effectively predicts tooth surface temperature rise and optimizes lubrication strategies. Notably, the temperature rise is more pronounced near the tooth crest. The maximum temperature in the similarity model reaches 140.59 °C, while that in the original model is 134.5 °C. The deviation between simulation and experimental results for the original model is 6.43%, and the discrepancy between the original and similarity models remains within 4.53%. This similarity-based modeling approach accurately captures the thermal behavior of analogous systems, significantly reducing the cost of manufacturing test gears and the workload associated with tooth surface temperature experiments and simulations.

Numerous aircraft accidents involving bird flocks have occurred in aviation. Existing literature and the airworthiness certification standards are primarily focused on single bird-strike assumption. The present study addresses the possibility of bird flock incident and investigates the crashworthiness of NASA Common Research Model wing subjected to single and multiple bird strikes, using a coupled Finite Element Method and Smooth Particle Hydrodynamics approach. The numerical bird model is validated and the influence of equation of state (EOS) models, porosity and contact loads variation against the target structure’s shape, is reported. Two locations along the span i.e. towards the wing root and the wing tip, are considered for impact investigation, with emphasis on comparative penetration, energy absorption capability and potential damage to the main spar. Results revealed that the impact loads and impulse for the curved leading-edge section to reduce by more than half compared to the flat plate. The Gruneisen EOS provided a good correlation with experimental data, while adding porosity to the Polynomial EOS significantly reduced pressure peaks. Analyzing different flock orientation scenarios, the vulnerability of wing tip to multiple bird strikes was observed, leading to main spar damage. While single bird strikes may not cause critical damage, bird flocks pose a significant threat to aircraft safety, emphasizing the need for incorporating bird flock scenarios into aircraft design considerations.

The seismic fragility of free-standing rigid blocks under earthquake excitation is investigated, focusing on the combined effect of rocking and sliding in their dynamic response. A variational-based formulation of the non-smooth contact dynamics method is employed for the problem solution, requiring the solution of a quadratic programming problem at each time step in the three unknown block scalar velocities. Such an approach efficiently captures all possible block response modes, including rocking, sliding, rocking-sliding, and free flight. The seismic fragility of both slender and stocky blocks is evaluated through a multiple-stripe analysis, introducing overturning-sliding fragility curves that account for overturning and excessive-sliding limit states. Numerical validation against benchmark results confirms the accuracy of the proposed formulation, showing that while a no-sliding assumption is reliable for slender blocks, it may prove unsafe for stocky blocks, even assuming high friction at the foundation. The resulting overturning-sliding fragility curves highlight the dependence of the block response on the normalized friction coefficient, defined as the ratio of the friction coefficient to the block slenderness. Blocks with a normalized friction coefficient below unity exhibit an isolation effect, preventing overturning at the cost of significant sliding. Conversely, blocks with normalized friction coefficient above unity undergo rocking-sliding or pure-rocking motion, which can lead to overturning. Accordingly, the overturning-sliding fragility curves are determined by the interplay between overturning and excessive-sliding limit states, as governed by a prescribed sliding displacement capacity. For typical values of the friction coefficient at the block-foundation interface, slender blocks are largely unaffected by sliding, whereas overturning-sliding or sliding fragility curves are crucial for accurately assessing the seismic performance of stocky blocks.

Due to the nature of grain boundaries, it is challenging to simulate the transgranular and intergranular fractures in polycrystalline materials. In this contribution, to model the crack propagation inside grain’s boundaries, e.g., intergranular fracture, we introduce additional relations between tensile strength at boundary and grain, which regard to the work in Riad et al. (Finite Elem. Anal. Des., 2021), to our previous anisotropic damage model, Vuong et al. (Theor. Appl. Fact. Mec. 2022). The developed damage model can smoothly simulate interfacial fracture without requiring an expensive mesh for interface regions. Furthermore, the interplay between transgranular and intergranular fractures is well captured through numerical tests. Several reported interfacial fracture phenomena are reproduced to show the accuracy of the developed technique.

We present an initial study on the use of contaminated soils, effectively treated through a solidification and stabilization (S/S) process that renders them inert, as encapsulated aggregates in the creation of novel metaconcretes. Several mix designs of solidified and stabilized soils are carefully examined, and their physical and mechanical properties are characterized experimentally. These properties are crucial for determining how these treated soils can be effectively incorporated into metaconcretes, a class of materials known for their unique ability to attenuate mechanical waves through resonant structures. The frequency bandgap response of metaconcretes incorporating rubber-coated aggregates made from solidified soils is studied using analytical formulations. The results indicate that the proposed reutilization technique for contaminated soils not only ensures their safety but also offers significant potential for applications in the construction of blast-protective structures and seismic-shielding metamaterials.

This paper uses a novel numerical approach to investigate the fracture of porous media in laminar duct flow. Combining Peridynamics with Navier–Stokes equations through an Immersed Boundary Method (IBM), we achieve a comprehensive analysis of fluid dynamics while considering fracture mechanics. The study presents results from numerical simulations exploring the breakup of six distinct configurations of porous media, varying in porosity from 0.55 to 0.8 and considering different fracture energy releases. Phenomenologically, we observe that fluid-induced stress lead to the breakup of the solid matrix, initiating rapid crack propagation and fragment generation. Detailed analyses of temporal evolution, including porosity and permeability, are provided, alongside Probability Density Functions (PDFs) of an equivalent stress distribution within the porous material. Additionally, a criterion for porous media breakup under laminar duct flow is proposed, employing Griffith’s theory of fracture mechanics. The authors believe that these results contribute to a deeper understanding of such complex multiphysical phenomena and offer insights into fracture mechanics within porous media in duct flow.