Piezoelectric energy harvesting from roadways, which converts ambient vibration energy of roads into electric energy, has a wide range of potential applications in intelligent transportation systems. ...On-site open-traffic tests revealed that energy harvested by piezoelectric energy harvester (PEH) units embedded in roadways is far less than the value in laboratories, which may be because the parameters of traffic flow load (frequency, distribution, wave shape, etc.) and the road structure are significantly different from the pre-established conditions in laboratories or even on-site tests with only one vehicle passing. To address this issue, an analytical model for piezoelectric energy harvesting from roadways under open-traffic conditions was proposed to examine the mechanical response of the road structure and the electrical performance of the stack PEH units embedded in the road. The influence of all parameters in the energy-harvesting system was then obtained with the scaling law method, revealing that the energy harvested by PEH units is determined by the energy coefficient, the system’s intrinsic parameter, normalized parameters of roadways, and the normalized embedded position of PEH units. It is found that that the energy-harvesting system’s intrinsic parameter should be approximately 0.8 to ensure maximum energy-harvesting efficiency. Meanwhile, the pavement with lower bending stiffness and higher linear density while the foundation with small stiffness and smaller damping coefficient would be more suitable for energy harvesting. Furthermore, the lateral embedded position of PEH units should be carefully chosen, since the units embedded in an optimal position can harvest three times more than that embedded in other positions. The concise criteria presented in this study will be used as a reference not only for material selection, dimension optimization, and embedded positions determination of PEH units but also for choosing of the optimal roadways to achieve maximum piezoelectric energy harvesting efficiency under open-traffic conditions.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
A compact, stable, sustainable, and high‐energy density power supply system is crucial for the engineering deployment of mobile electromechanical devices/systems either at the small‐ or large‐scale. ...This work proposes a spiral‐based mechanical energy storage scheme utilizing the newly synthesized 2D diamane. Atomistic simulations show that diamane spiral can achieve a high theoretical gravimetric energy density of about 564 Wh kg−1, about 14 500 times the steel spring. The interlayer friction between diamane is found to cause a strong stick–slip effect that results in local stress/strain concentration. As such, the energy storage capacity of the diamane spiral can be tuned by suppressing the influence from the interlayer friction. Simulations affirm that higher gravimetric energy density can be achieved by reducing the turn number or adopting a low friction contact pair. The fundamental principles that dominate the energy storage capacity of the spiral spring are theoretically analyzed, respectively. The obtained insights suggest that the 2D vdW solids can be promising candidates to construct spiral structures with a high gravimetric energy density. This work should be beneficial for the design of reliable, stable, and sustainable nanoscale mechanical energy storage schemes that can be used as an alternative low‐carbon footage energy supplier for novel micro‐/nanoscale devices or systems.
A 2D diamane‐based planar spiral is proposed as an alternative low‐carbon footage energy supplier for micro‐/nanoscale devices/systems based on its mechanical deformation. Supported by the theoretical analysis, atomistic investigations reveal that its gravimetric energy density can reach 2.03 MJ kg−1 or 564 Wh kg−1, about 14 500 times that of steel spring.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Residual stress is ubiquitous and indispensable in most biological and artificial materials, where it sustains and optimizes many biological and functional mechanisms. The theory of volume growth, ...starting from a stress-free initial state, is widely used to explain the creation and evolution of growth-induced residual stress and the resulting changes in shape, and to model how growing bio-tissues such as arteries and solid tumors develop a strategy of pattern creation according to geometrical and material parameters. This modelling provides promising avenues for designing and directing some appropriate morphology of a given tissue or organ and achieve some targeted biomedical function. In this paper, we rely on a modified, augmented theory to reveal how we can obtain growth-induced residual stress and pattern evolution of a layered artery by starting from an existing, non-zero initial residual stress state. We use experimentally determined residual stress distributions of aged bi-layered human aortas and quantify their influence by a magnitude factor. Our results show that initial residual stress has a more significant impact on residual stress accumulation and the subsequent evolution of patterns than geometry and material parameters. Additionally, we provide an essential explanation for growth-induced patterns driven by differential growth coupled to an initial residual stress. Finally, we show that initial residual stress is a readily available way to control growth-induced pattern creation for tissues and thus may provide a promising inspiration for biomedical engineering.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Recently, the mechanical behavior of micro-/nano-structures has sparked an ongoing debate, which leads to a fundamental question: what steps can be taken to investigate the mechanical characteristics ...of these structures, and characterize their performance? From the standpoint of the non-classical behavior of materials, size-dependent theories of micro-/nano-structures can be considered to analyze their mechanical behavior. The application of classical theories in the investigation of small-scale structures can lead to inaccurate results. Many studies have been published in the past few years, in which continuum mechanics models have been used to investigate micro-/nano-structures with different geometry such as rods, tubes, beams, plates, and shells. The mechanical behavior of these systems under different loading – resulting in vibration, wave propagation, bending, and buckling phenomena – is the focus of the review covered in this work. The present objective is to provide a detailed survey of the most significant literature on continuum mechanics models of micro-/nano-structures, and thus orient researchers in their future studies in this field of research.
•Size-dependent continuum mechanics models for micro/nano-structures are reviewed.•Vibration, wave propagation, and buckling/post-buckling analysis are thoroughly discussed.•Classification of the problems in linear and nonlinear models.•Providing a detailed survey to help researchers in their future studies in this field.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The multiplicative decomposition model is widely employed for predicting residual stresses and morphologies of biological tissues due to growth. However, it relies on the assumption that the tissue ...is initially in a stress-free state, which conflicts with the observations that any growth state of a biological tissue is under a significant level of residual stresses that helps to maintain its ideal mechanical conditions. Here, we propose a modified multiplicative decomposition model in which the initial state (or reference configuration) of a biological tissue is endowed with a residual stress instead of being stress-free.
Releasing theoretically the initial residual stress, the initially stressed state is first transmitted into a virtual stress-free state, thus resulting in an initial elastic deformation. The initial virtual stress-free state subsequently grows to another counterpart with a growth deformation, and the latter is further integrated into its natural configuration of a real tissue with an excessive elastic deformation that ensures tissue compatibility. With this decomposition, the total deformation arising during growth may be expressed as the product of elastic deformation, growth deformation and initial elastic deformation, while the corresponding free energy density should depend on the initial residual stress and the total deformation. Three key issues including the explicit expression of the free energy density, the predetermination of the initial elastic deformation, and the initial residual stress are addressed.
Finally, we consider a tubular organ as a representative example to demonstrate the effects of the proposed initial residual stress on stress distribution and on shape formation through an incremental stability analysis. Our results suggest that the initial residual stress exerts a major influence on the growth stress and the morphology of biological tissues. The model bridges the gap between any two growth states of a biological tissue that is endowed with a certain level of residual stresses.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•Concurrent multiscale design for piezoelectric actuators is conducted.•Both macrostructures and microstructures are optimized to maximize the actuation.•Influence of material distribution across the ...scales for design is investigated.•Transmitted displacement increases with the increase of microscale material.
As an important component of smart structural devices, piezoelectric composites have strong macroscopic electromechanical coupling properties which often depend on their microstructural geometries and material parameters. Therefore, optimizing the microstructural design is crucial for achieving the desired macroscale effective properties. To this end, this paper conducts a concurrent multiscale topology optimization (TO) to optimize the material distribution of piezoelectric actuators, aiming to maximize the electrical and mechanical energy transmission to meet specific engineering requirements. Firstly, an energy method is used to homogenize the microstructures and obtain the effective parameters of the piezoelectric material. Then, the piezoelectric material with penalization and polarization (PEMAP-P) approach in conjunction with the adjoint method is employed to calculate the sensitivity of objective and constraint functions. The sensitivities at both the macroscale and microscale are obtained by considering the interscale coupling effects. Finally, the concurrent bi-level iteration based on the optimality criteria (OC) or the method of moving asymptotes (MMA) is conducted. Through this research, we have illuminated the relations between the optimized performance of the actuator and the material volume fractions at each scale. We have also compared in detail the differences between two-scale and single-scale designs, as well as the differences between the simplified half-symmetric geometric model and the full geometric model. We find that a larger volume fraction of material either at the macroscale or microscale generates a larger transmitted displacement magnitude under the same applied electric field, and for a given total material, the transmitted maximum increases with increasing microstructural volume fraction.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
This work offers a comprehensive overview of how gravity affects soft materials, with a particular emphasis on gravity‐induced instability. Soft materials, including biological tissues, elastomers, ...and gels, are characterized by low elastic moduli and the ability to undergo significant deformations. These large deformations can lead to instabilities and the emergence of distinctive surface patterns when even small perturbations are introduced. An in‐depth understanding of these gravity‐induced instabilities in soft materials is of paramount importance for both fundamental scientific research and practical applications across diverse domains. The underlying mechanisms governing these instabilities are delved in and elucidate the techniques employed to study and manipulate them. Further, the gravity‐induced wrinkling and the Rayleigh‐Taylor (RT) instability in soft materials are zoomed in, highlighting how altered gravity environments impact natural and synthetic systems. Lastly, current and potential applications are underscored where gravity‐induced instabilities are already making an impact or may hold promise in the near future. In sum, the exploration of gravity‐induced instabilities in soft materials paves the way for innovative applications and advancements in a wide range of fields.
This article investigates the effects of gravity on soft materials. It unveils the mechanisms behind gravity‐induced instability, with a focus on their significance in both natural and synthetic systems for various gravity scenarios. The paper also highlights practical and potential applications where gravity‐induced instabilities are already making an impact or may hold promise in the near future.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
•The circumferential, 2D, and axial patterns observed in human intestine are reproduced in bilayer soft tubes by manipulating geometric incompatibility.•Theoretical analysis gives the 3D ...morphological phase diagram for pattern selection in geometrically incompatible bilayer tubes.•Both quantificational experiment and FE simulation show good agreement with our theoretical prediction.•Linear stability analysis can be employed to predict roughly the number of creases in tubular soft matter.
Surface morphological instability, induced by geometric incompatibility, is ubiquitous in nature and plays a pivotal role in maintaining specific biological functions in organs. In this study, we experimentally reveal that geometric incompatibility effectively regulates the morphological instability of bilayer tubes. Building upon these experimental findings, we develop a theoretical model to elucidate the underlying mechanical mechanism of the observed morphological instability. Theoretical analysis demonstrates that by manipulating geometric incompatibility, various patterns including circumferential, two-dimensional (2D), and axial patterns can be generated in bilayer tubes. Specifically, as the axial geometric incompatibility parameter increases, the instability pattern transitions from the circumferential pattern to the 2D pattern and eventually to the axial pattern. Furthermore, we conduct a series of quantitative experiments and finite element simulations to validate our theoretical model. Both the numerical simulations and experimental observations show excellent agreement with our theoretical predictions, demonstrating that linear stability analysis can be employed not only to predict wrinkles but also to determine the number of creases in tubular soft materials roughly. This study significantly advances our understanding of the morphological instability of geometrically incompatible bilayer tubular tissues and provides valuable insights for the fabrication of morphology-related multifunctional surfaces.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Accelerated molecular dynamics enables atomistic investigation on vacancy diffusion.•The increased hydrostatic pressure inhibits vacancy diffusion in nickel.•Diffusion becomes anisotropic under ...uniaxial stress.•Vacancy diffusion is preferred along the compressed direction under uniaxial stress.
Vacancy diffusion is involved in a variety of destructive failure processes in metals, whose impact becomes more magnificent in real engineering applications with external thermal and/or mechanical loadings. Here we examined the vacancy diffusion in nickel under a wide range of pressure and temperature with the aid of collective variable-driven hyperdynamics (CVHD), which is challenging for traditional molecular dynamics (MD) due to its intrinsic femtosecond time step. In line with previous studies, the vacancy diffusivity in nickel decreases when the hydrostatic pressure increases. Interestingly, the total diffusion rate increases when the uniaxial stress is applied, and the diffusion becomes anisotropic. Additionally, vacancy diffusivity becomes less dependent on either hydrostatic pressure or uniaxial stress when the temperature increases. This work provides in-depth atomistic insights into the diffusion phenomenon in nickel, which could be beneficial for unveiling the damage mechanisms and the design of next-generation Ni-based high-temperature alloys.
Vacancy diffusion becomes anisotropic under uniaxial stress in nickel, and the diffusion is impeded along the direction with tensile stress. Display omitted
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