International Journal of Mechanical Sciences最新文献

Determining the stress-strain relationship in materials that exhibit complex behaviors, such as anisotropy, is pivotal for applications in structural engineering and materials science, as the behavior of materials under stress directly impacts safety and performance. This study introduces an innovative approach that leverages Artificial Intelligence (AI) through deep learning (DL) techniques to accurately predict transversely isotropic material properties using kinematic fields. These kinematic fields are derived from Finite Element Method (FEM) computations, which can realistically be obtained through advanced image correlation techniques, ensuring high precision and applicability in real-world scenarios. The objective of this research is to precisely characterize the behavioral parameters governing transversely isotropic materials. This methodology can also be applied to other constitutive laws, extending its utility across different material models. The proposed methodology, which utilizes a multi-scale encapsulated AI architecture, not only provides nearly instantaneous analytical solutions but also achieves remarkable accuracy, with average errors in parameter identification remaining below 3 % across all parameters. This sophisticated AI model plays a crucial role in accurately ascertaining the mechanical properties of transversely isotropic materials. By offering a method that is significantly faster and more precise than traditional experimental techniques, this research advances the current understanding of transversely isotropic materials' behavior. Such improvements in analysis speed and accuracy facilitate quicker iterations in material design and testing, potentially accelerating advancements in materials science and engineering applications.

In this study, we present a novel topology-optimized design of a two-dimensional cavity-free mechanical metamaterial with a negative coefficient of thermal expansion. We challenge the prevailing hypothesis that cavities are necessary for achieving negative coefficients of thermal expansion. The proposed metamaterial is a periodic lattice of a topology-optimized unit cell comprising three distinct solid materials, analyzed using a homogenization method. To confirm the negative thermal expansion of the optimized structures, we present some numerical experiments of the optimized designs and analyze the deformation of the metamaterial under temperature variations.

The performance of concrete will decrease when subjected to external sulfate corrosion, and numerical models are effective means to analyze the mechanism. Most models cannot efficiently consider the effect between cracks and ionic transport because crack initiation and propagation are ignored. In this paper, a coupled chemical-transport-mechanical phase-field model is developed, in which the phase-field model is applied for the first time to predicate the cracking of sulfate-eroded concrete. The chemical-transport model is established based on the law of conservation of mass and chemical kinetics. The phase-field model equivalents the discrete sharp crack surface into a regularized crack, making it convenient to couple with the chemical-transport model. The crack driving energy in the phase-field model is computed by the expansion strain, which can be obtained from the chemical-transport model. The coupling of crack propagation and ionic transport is achieved by a theoretical equation, which considers both the effects of cracking and porosity. Complex erosion cracks can be automatically tracked by solving the phase-field model. The simulation results of the multi-field coupling model proposed in this paper are in good agreement with the experimental data. More importantly, the spalling phenomenon observed in physical experiments is reproduced, which has not been reported by any other numerical models yet, and new insight into the spalling mechanism is provided.

The connection between micro-level characteristics and macroscopic properties in granular heat transfer and mechanics is fundamental and crucial. This study proposes a novel discrete element approach incorporating granular heat transfer, contact bonding, and granular stress tensor models to investigate the mechanical and thermal responses of continuum media composed of constituent spheres. Eight benchmark tests were devised to bridge the long-standing gap between micro and macro properties in granular materials. Through these tests, the numerical solutions obtained from discrete element modeling match well with existing analytical or finite element solutions derived from continuum-based theory. This validation underscores the rationality and reliability of the granular heat transfer model, contact bonding model, and granular stress tensor model. Moreover, the study highlights the consistency between continuum-based theory and discontinuum-based theory. A minor distinction between continuum-based models and discrete element models emerges near the boundaries due to variations in the specification of boundary conditions. This discrepancy can be clarified by Saint-Venant's Principle, thus validating the accuracy of the microscale heat transfer and mechanics theory for granular materials. Five mono-disperse packing structures, including simple cubic (SC), body-centered cubic (BCC), face-centered cubic (FCC), hexagonal close packing (HCP), and random packing (Random), were further analyzed to examine their influence on heat transfer performance. Numerical results reveal that higher coordination numbers and solid volume fractions correspond to higher apparent thermal conductivity of granular assemblies, thus elucidating the connection between micro packing configurations and macroscopic heat transfer properties. The apparent thermal conductivity for different crystal configurations follows the sequence: HCP ≒ FCC > BCC ≒ Random > SC. To improve the accuracy and physical relevance of the proposed model, the effect of particle contact area needs to be further incorporated into the granular heat transfer model.

4H-SiC wafer with alloy backside layer is gradually applied in power devices. However, the laminated structure presents various challenges in manufacturing. In this study, a model for brittle-ductile transition in grinding of laminated materials is established and verified by grinding experiment to ensure the complete removal of the alloy backside layer while achieving ductile removal of the 4H-SiC layer. In the modeling process, the maximum unreformed chip thickness and brittle-ductile transition critical depth of each-layer in the laminated material is deriving, taking into account the laminated structure. Consider the variability in proportion of dynamic active grits during grinding, set operation is introduced to analyze the relationship between sets maximum unreformed chip thickness and brittle-ductile transition critical depth, and to predict the removal mechanism of the 4H-SiC layer. Comparing the predicted results with experimental grinding data, found that under the conditions of grinding wheel with average size of abrasive 10 μm, grinding wheel speed v_s of 74 m/s, grinding depth a_p of 10 μm, and feeding speed v_w of 2 mm/s, the alloy backside layer can complete removal while achieving ductile removal of the 4H-SiC layer. This study provides a new method for predicting removal mechanism in grinding of laminated material and theoretical guidance for optimizing machining parameters of 4H-SiC wafer with alloy backside layer.

The elastic matrices of extremal metamaterials have one or more zero eigenvalues, allowing energy-free deformation modes. These elastic metamaterials can be well approximated by manufactured microstructures. They can exhibit an unprecedented capacity to manipulate bulk and surface waves, which are unavailable with conventional solids due to the easy deformation modes, as already exemplified by pentamode materials (PMs). In this paper, we theoretically investigate a direct one-to-one correspondence of birefringent metamaterial and quarter-wave plate between optical and elastic waves based on a carefully designed quadramode material (QM). This QM metamaterial allows only two transverse wave modes, eliminating mode conversion due to the presence of the longitudinal mode. The characteristics of the elastic birefringent metamaterial and elastic quarter-wave plate are demonstrated by both homogenized and corresponding discrete models. A free space elastic wave isolator, analogous to a diode in electronics, is also proposed, which can effectively protect upstream sources or systems from back-reflected noise or interference. An additional benefit of the discrete model is also revealed for its working frequency tunability through deformation. This work provides the first study on elastic birefringent metamaterials and tunable elastic quarter-wave plate, which may stimulate applications of extremal elastic metamaterials for controlling elastic wave polarization.

In this study, inspired by the mechanical metamaterials with bandgap properties, a new type of meta-arch structure (MAS) for the attenuation of elastic waves is proposed. In this metastructure, the reinforcement cage, typically employed to enhance the tensile properties of building materials, has been redesigned and transformed into a new structure containing circular tubes with embedded resonant microstructures. The vibration reduction performance of the MAS was illustrated by the frequency response analysis in the simulation calculation, and the generation mechanism of the vibration attenuation band was revealed. The specimens of the complex MAS consisting of gypsum, reinforced steel bars, and tubes were fabricated, and the vibration response experiments were carried out to determine the dynamic properties of the novel MAS. The results show that the designed arch structure exhibits a broad vibration attenuation band without sacrificing its structural bearing capacity. Additionally, the robustness of the band gap is demonstrated by analyzing how changes in the positions of excitation and response points influence the band gap. Moreover, the MAS can be customized for specific application scenarios of vibration reduction according to the parameter analysis. Finally, the experimental results closely align with the numerical estimations, confirming the feasibility of the design method for reducing vibrations. This work provides a new method for the development of building structures for vibration and noise control.

A novel mixed finite element method is developed and implemented for analyzing the vibration and buckling behavior of general composite beams which consists both transversely layered and axially jointed materials. The governing state-space equations are derived using the Hamilton's principle, where both displacements and stresses are treated as fundamental variables. This semi-analytical method uses transfer relations in the transverse direction and finite element meshing in the longitudinal direction, overcoming the difficulties for general composite beams analysis and providing computational efficiency and analyzing flexibilities. The developed mixed finite element model ensures continuity of both displacements and stresses across the material interface, thereby resolving interfacial stress singularity issues and offering more reliable simulations of boundary conditions at both ends. The proposed method is formulated and validated for the free vibration and buckling analysis of general composite beams. Additionally, it is observed that material properties such as Young's modulus and density, as well as the stiffness of the interface connecting layers, have significant effects on the free vibration and buckling responses of the composite beams. Analysis of periodically distributed and bi-directional composite beams demonstrates the versatility of this method in handling two types of combination forms. The proposed method serves as a valuable reference for obtaining accurate vibration and buckling results while ensuring stress-compatibility for composite beams in practical applications.

Mechanical metamaterials have emerged as a promising solution for shielding against environmental vibrations and shocks. However, most existing metamaterials provide a single functionality in mechanical protection, limiting their adaptability to complex working scenarios. To address this limitation, we propose a double-strip metamaterial (DSM) that achieves both vibration isolation and shock attenuation. The DSM employs quasi-zero stiffness for vibration isolation and snap-through buckling for shock energy dissipation. Buckling mode analysis reveals that the dual-functionality of the DSM arises from its diverse buckling behaviors, with theoretical models further quantifying its mechanical response. The DSM can effectively isolate the vibration above 13 Hz and reduce instantaneous shock by up to 58 %, as demonstrated by dynamic tests. This design strategy opens new avenues for comprehensive protection in engineering applications, spanning aerospace, automotive, and logistics.

Ensuring ductile removal in a grinding process is crucial for achieving the desired finish on a hard and brittle single crystal. This study provides new insights into the material removal processes in Si and GaAs single crystals, exploring their deformation behaviour using Berkovich and Conical tips to replicate contact from a fixed abrasive grit. Experimental observations are compared with Molecular Dynamic (MD) simulations to uncover the atomistic deformation mechanisms during the ductile-to-brittle transition (DBT). Notable plastic deformation and minimal cracking were consistently observed in Si, irrespective of the tips used. MD simulations supported this observation, revealing pronounced chip formation indicative of ductile material removal. The resistance to cracking in Si was attributed to amorphization induced by localized high contact stresses. In contrast, GaAs showed a propensity for cracking, with MD simulations revealing dislocation and slip band formation, and cracks emerging in the areas of substantial plastic deformation. These findings address phenomena not previously discernible in experimental studies due to the challenge of real-time observation. Moreover, the tip geometry was shown to significantly influence stress distribution, impacting deformation and crack formation in GaAs. This study also reveals limitations in predicting the critical depth for DBT in both Si and GaAs throught the amended Bifano, Dow, and Scattergood (aBDS) models and MD simulation, offering nuanced insights into these challenges that have not been extensively explored. It was found that the experimental results exceeded predictions by an order of magnitude. These discrepancies underscore the aBDS model's disregard for essential material properties and tip geometry, while the disparities between MD simulation and experiment are primarily attributed to the inherent limitations in the simulated length scales and challenges in detecting initial subsurface cracks.