Energy Dissipation Mechanisms Research Articles

An energy-based criterion for defining slope failure considering the coupling effect of groundwater table and impact loading

Slope instability poses significant risks in tunnel construction, particularly under the influence of impact loading and fluctuations in groundwater table. This study addresses the complexity of energy transformation and distribution in slopes affected by these factors. The research aims to analyze the local dynamic Factor of Safety (FOS) from the perspective of energy-based criterion, considering groundwater table, impact loading, and load position. Key findings indicate that the groundwater table is the most influential factor on slope stability, followed by load position and impact loading. The overall dynamic FOS was observed to peak at 0.35 s and trough appears at 1.0 s during impact loading, stabilizing after 2 s. The evolution of the overall dynamic FOS is explained from the energy dissipation and transformation mechanisms. These insights provide a critical basis for risk assessment and prevention in complex slope scenarios, contributing to sustainable infrastructure development in line with UN SDG 11 (Sustainable Cities and Communities).

Mechanical Failure Characteristics and Energy Dissipation Laws of the Coal–Concrete Combination under Impact Rates

Mechanical Failure Characteristics and Energy Dissipation Laws of the Coal–Concrete Combination under Impact Rates

A weight-based efficiency measure for energy dissipating devices for flexible rockfall barriers

Flexible barriers are essential passive measures which are able to protect human life, structures and infrastructures from rockfall hazards. When a barrier is impacted, a significant portion of energy dissipation is concentrated in targeted components, named brakes, which can be replaced after the rockfall event. Several technologies exist, differing in both constitutive elements and energy dissipation mechanisms, but experimental data are generally restricted by producers. The present paper compares the various technologies thanks a new efficiency index, that is the ratio between the component potentially dissipated energy and its weight. To analyse the effects of the design parameters, four of the most common brakes are analytically modelled. It is shown that the performance of the devices is variable and depends on the working mechanism and the adopted material. In particular, plastic deformation energy dissipation induced by buckling is generally more efficient than the one caused by bending. Finally, a discussion on the force that activates the brake is proposed. The proposed analyses are of paramount importance for the conceptual design of new energy dissipation devices in rockfall risk mitigation structures.

Multifunctional Triboelectric Metamaterials with Unidirectional Charge Transfer Channels for Linear Mechanical Motion Energy Harvesting

AbstractConventional triboelectric generators (TEGs) have been developed to mainly harvest the energy of linear mechanical motions and convert it usually into oscillating or pulsive, but not sustainable, electrical outputs. In this study, unidirectional charge transfer mechanisms are introduced to develop a triboelectric mechanical metamaterial (TMM) with sustainable electrical outputs. Density functional theory and experimental analyses demonstrate three minimum necessary components of TMMs fabricated by only two triboelectric materials (i.e., copper and PTFE) to generate sustainable electrical outputs. Under a wide range of compression‐tension strain of ±50%, the maximum open‐circuit voltage, short‐circuit current, and volumetric power density are 3860 V, 8 µA, and 365.3 kW m−3, respectively. Different from most conventional cellular solids, the mechanical energy dissipation of the TMMs increases quadratically with the unit cell number. High volumetric electromechanical efficiency is achieved when the unit cell is miniaturized. In addition to energy harvesting and mechanical energy dissipation, TMMs can sense the displacement by counting the number of distinctive peaks in the short‐circuit charge transfer or reaction force versus time curves. The extreme electromechanical functionalities of the TMMs facilitate their applications in intelligent suspension systems, miniaturized green power sources, and self‐sensing energy harvesters.

Strong, healable materials with bio‐like ordered architectures and versatile functionality

AbstractThe capacity of biological tissues to undergo self‐healing is crucial for the performance of functions and the continuation of life. Conventional intrinsic self‐healing materials demonstrate analogous functionality depending on the dissociation‐recombination of reversible bonds with no need of extra repair agents. However, the trade‐off relationship between mechanical strength and self‐healing kinetics in intrinsic self‐healing systems, coupled with the lack of additional functionality, restricts their service life and practical applications. Diversified highly ordered structures in organisms significantly affect the energy dissipation mechanism, signal transmission efficiency, and molecular network reconstruction capability due to their multi‐dimensional differentiated macroscopic composite constructions, microscopic orientation textures, and topologies/bonding types at molecular level. These architectures exhibit distinctive strengthening mechanisms and functionalities, which provide valuable references. This review aims at providing the current status of advanced intrinsic self‐healing materials with biomimetic highly ordered internal micro/nanostructures. Through highlighting specific examples, the classifications, design inspirations, and fabrication strategies of these newly developed materials based on integrating dynamic interactions with ordered nano/microstructures are outlined. Furthermore, the strengthening and self‐healing balance mechanisms, structure–functionalization relationships, and potential application values are discussed. The review concludes with a perspective on the challenges, opportunities, and prospects for the development, application, and promotion of self‐healable materials with bio‐like ordered architectures.

A numerical study of Mullins softening effects on mode I crack propagation in viscoelastic solids

This paper presents a finite element analysis of steady-state crack propagation in viscoelastic soft solids exhibiting Mullins softening. A cohesive-zone model is employed to simulate the localized processes at the tip of a Mode I crack in materials governed by viscoelastic behavior and damage-induced Mullins effects. The study numerically evaluates the intrinsic dissipation characteristics of typical rubber-like materials, focusing on the influence of key factors such as Mullins damage, relaxation modulus, and relaxation time. The impact of these factors on material toughening is examined, with particular emphasis on their role in crack propagation. The results reveal that crack propagation velocity is highly sensitive to the interplay between energy dissipation mechanisms. Specifically, Mullins damage parameters are shown to increase fracture toughness by raising the local energy release rate threshold at the crack tip. Additionally, the relaxation modulus enhances viscous dissipation, further elevating this threshold and subsequently reducing crack propagation velocity. Interestingly, an inverse relationship between relaxation time and crack propagation velocity is observed. The study provides a detailed analysis of the dissipation mechanisms at the crack tip, offering valuable insights for improving material toughness.

Recent Experimental Advances in Solid–Liquid Composites for Impact and Blast Mitigation

The development of high-performance composites for mechanical energy dissipation during impact or explosive events is of vital importance for the safety of personnel and infrastructures. Solid–liquid composites are an emerging class of energy absorbers where a liquid-phase filler is seamlessly integrated into a solid matrix to enhance the impact resistance of the protection target. This innovative approach leverages the distinct properties of both phases and the unique interactions between them to achieve superior performance under high-impact conditions. This paper aims to review the liquid-phase materials used in solid–liquid composites, ranging from neat liquids to complex fluids, including liquid nanofoam and shear-thickening fluids, to provide an in-depth analysis of the fundamental physics underpinning the resulting solid–liquid composites, and to explore how their unique properties contribute to enhanced impact resistance and energy absorption. Furthermore, this paper evaluates the advantages and limitations of these solid–liquid composites and offers insights into future directions for the development of solid–liquid composites in various fields, including personal protective equipment, automotive safety systems, and structural protection.

Investigation of the transient characteristics of the Francis turbine during runaway process

Transient hydraulic phenomena, including flow separation, vortex structure and high amplitude pressure fluctuation, occur in the turbine during runaway process, significantly affecting the safe and stable operation. To clarify the unsteady flow characteristics in the runaway process, this paper focus on a low head model Francis turbine, examining the transient flow dynamics from rated speed to runaway speed. Numerical simulations show good agreement with experimental test results for the runaway speed and discharge. Results identify that two typical cavitation vortex structures within the runner: A cloud cavitation vortex near the hub on the pressure side and a columnar cavitation vortex on the suction side. Further analysis reveals that the pressure fluctuation induced by the former are low-frequency (0.08fn and harmonics), whereas those induced by the latter are high-frequency (1.16fn and harmonics). Entropy production analysis in homogeneous flow indicates that energy dissipation mainly occurs in the runner and draft tube during the runaway process. Turbulent entropy production within the turbine comprises a significant portion of the total entropy production. Additionally, areas around the recirculation zone exhibit considerable high entropy production, indicating that the energy of the fluid is dissipated by cavitation vortex structures generated in these areas. Additionally, the analysis indicates that the entropy production rate correlates with vapor generation, underscoring the cavitation vortex as the primary cause of energy dissipation. This investigation can provide valuable insights into the energy dissipation mechanisms during the runaway process.

Investigation of dynamic impact behavior of bighorn sheep horn

The horn of the bighorn sheep is composed of keratin-based biological material that has a tubule-lamella structure, which gives it anisotropic hardening properties under impact loading. This paper aims to investigate the energy dissipation mechanisms inherent in bighorn sheep horns by developing a numerical material model that accounts for the horn’s anisotropic features and strain-rate effects. To this end, a transversely isotropic constitutive model, which includes both anisotropic hardening and strain-rate effects, was formulated to accurately predict the mechanical behavior of bighorn sheep horns. Material characterization was conducted through uniaxial compression tests that were conducted under quasi-static and dynamic conditions. The developed constitutive model was implemented into LS-Dyna via a user-defined material subroutine and was validated against empirical data. The validated numerical model was used to investigate the horn’s mechanical responses under dynamic loading conditions. The paper focused on impact energy dissipation mechanisms, including energy absorption and transition, stress distribution, and displacement wave propagation. The insights gained from this paper are expected to significantly contribute to the development of novel artificial materials with enhanced energy absorption and impact mitigation properties.

Magnetic chimeras in voltage-driven nano-oscillators

The emergence of spatiotemporal coherence is ubiquitous in nature. Intriguingly, in systems with uniform energy injection and dissipation mechanisms, coherent regions can be neighboring zones with non-coherent (e.g., chaotic or quasi-periodic) motions, giving rise to the so-called chimera states. This article studies the chimeric self-organization of magnetic nano-oscillators coupled with dipolar fields under energy losses and injection. The chimera states arises from an alternating voltage that, in the presence of insulating barriers, modulates the magnetic anisotropy fields, an effect known as voltage-controlled magnetic anisotropy. This field allows the efficient manipulation of the magnetization because it can produce magnetic switching and resonances, among other dynamic responses, while avoiding the Joule heating. In the classical limit, magnetization dynamics are governed by the Landau–Lifshitz equation. We consider three setups composed of N={4,6,10} interacting oscillators, each one of them regarded as a macrospin that moves rigidly. Our main results are Small magnetic chimeras, Weak magnetic chimeras, and a meta-chaos state. Chimera states are composed of a synchronized and a chaotic group of oscillators, both sets typically having hundreds of units; on the other hand, small chimeras are composed of a few – usually around five – oscillators dividing into coherent and non-coherent regions. A weak chimera has two or more sets of coherently oscillating units, but the groups possess different frequencies. Finally, the meta-chaos state is a chaotic transient. Beyond the previous zoology, fully synchronized states are also present, as the bifurcation diagram reveals.

Cyclic fatigue responses of double fissure-contained marble: Insights from mechanical responses, energy conversion and hysteresis characteristics

The intermittent fissures are widely distributed in rock mass, rock bridge segment among the fissures are crucial to the mechanical properties and stability of rock mass. The static mechanical behaviors of fissure-contained rock were well understood, yet the fatigue mechanical properties were poorly investigated. This work aims to reveal the influence of rock bridge length on rock mechanical responses, energy dissipation and hysteresis characteristics in lab-scale. Marble samples with rock bridge length (RBL) of 10, 20, 30, and 40 mm were prefabricated as parallel pattern, and they are subjected to multi-level fatigue loading paths. Testing results show that the rock bridge between the fissures resists rock deformation and the terminal volumetric strain decreases with increasing RBL. In addition, the hysteresis energy density and damage evolution are influenced by the rock bridge length. The strain energy density development aligns with deformation pattern results. Deterioration in the rock bridge structure causes reduced capacity and higher energy consumption. More energy is required to drive damage progression and crack connectivity in rocks with a larger RBL. Ultimately, two hysteresis indices are introduced to characterize fatigue damage evolution. These indices exhibit nearly opposing trends throughout the loading process. It is proposed that extending the rock bridge length results in a roughly linear trend for both hysteresis indices.

A Thermal Model for a Hybrid Gas Bearing System in Oil-Free Turbochargers

Abstract With little drag friction, gas bearings operate at high rotor speed and high temperature and thus enable long operating life along with material damping for mechanical energy dissipation. However, most computational tools for modeling gas bearings are not accessible to bearing manufacturers or potential end-users, and the models are restricted to specific geometries and operating conditions or are missing important features, thus limiting their utility. This paper presents the thermal energy transport in a hybrid gas bearing (HGB) for oil-free turbochargers (TCs) with integrated heat and fluid flow models to produce a comprehensive thermohydrodynamic analysis predictive tool and to design and evaluate air-lubricated gas bearings by predictions and experiments. An efficient algorithm couples the solution of the Reynolds equations and the thermal energy transport equations in the film between the rotor and a pad of the hybrid gas bearing and updates the temperature-dependent viscosity and film thicknesses during the iterative process. The balance of the bulk-flow thermal energy transport is that the summation of drag power losses plus heat convection into the film equals to the thermal energy advected by the film. The predictions show that the film temperature varies along circumferential and axial directions by following the balance of the energy flows and shows high film temperatures corresponding to the small film thicknesses and thus large film pressures. The predicted result also shows that the peak temperature of the film occurs at the exit side of the film near the trailing edge of each pad. Thermocouples installed axially at the leading and trailing edges of each pad measure temperature of the film to validate the thermal module. The test repeats and averaged for each rotor speed from 2 krpm to 22 krpm at intervals of 2 krpm, for supply pressure varying along 25 psi to 100 psi, and predicted film temperature matches well with the measured one. The parameters of interest in this analysis include the gas supply condition, bearing configuration, and the gas properties at high altitudes and high rotation speeds. The parametric study results show that the density and kinematic viscosity are the most dominant properties of the gas lubrication for the film temperature.

Non-Amontons frictional behaviors of grain boundaries at layered material interfaces

Against conventional wisdom, corrugated grain boundaries in polycrystalline graphene, grown on Pt(111) surfaces, are shown to exhibit negative friction coefficients and non-monotonic velocity dependence. Using combined experimental, simulation, and modeling efforts, the underlying energy dissipation mechanism is found to be dominated by dynamic buckling of grain boundary dislocation protrusions. The revealed mechanism is expected to appear in a wide range of polycrystalline two-dimensional material interfaces, thus supporting the design of large-scale dry superlubric contacts.

New insights into impact-induced removal of the deposited droplet

This paper presents a comprehensive investigation into the collision dynamics of equal and unequal-sized nanodroplets on a flat surface using molecular dynamics simulations, revealing new insights into scaling laws and energy dissipation mechanisms. The simulations, conducted with the Large-Scale Atomic/Molecular Massively Parallel Simulator software, involved an initially stationary droplet on the surface and a suspended droplet with varying diameter ratios (λ) and impact velocities. The results show that at low Weber numbers (We < 24.15), the droplets tend to deposit after impact, while at higher Weber numbers (We ≥ 24.15), they undergo spreading and retraction, ultimately rebounding. The study reveals that the dimensionless contact time (t*) and maximum spreading factor (βmax*) in collisions between droplets of different sizes do not follow the same scaling relationship observed in single nanodroplet impacts. By redefining the Weber and Reynolds numbers (Re), the new scaling relationships t* ∼ We2/3Re−1/3λ−1/3 and βmax* ∼ We2/3Re−1/3λ−1/3 are proposed and validated. This work represents a further in-depth study of previous research on single nanodroplet impact, introducing for the first time the diameter ratio in unequal droplet impacts into the variation patterns of contact time and maximum spreading diameter. Moreover, these findings highlight the importance of revisiting and potentially revising classical theories to accommodate the unique physical phenomena that emerge at smaller scales.

Chemical regulation of lignin spatial conformation for a multifunctional soft material with a novel energy dissipation mechanism

An eternal and important challenge for soft materials is the occurrence of creep behavior, meaning they cannot maintain original structure and shape under continuous or repeated external forces, which will seriously affect the service life and value of soft materials. In this work, the inspiration comes from the multi-level structure of wood cells in trees, which can absorb external forces through the transformation of macromolecular spatial conformation to prevent occurrence of irreversible deformation. The conformational evolution of lignin in different solvent environments is investigated by all-atom molecular dynamics (MD) simulations. Biomass macromolecule lignin with three-dimensional spatial structure is formed into polyurethane modified lignin by 1,6-diisocyanate in different solvent environments polymerisation reaction to regulate its molecular spatial conformation to meet the needs of energy dissipation mechanisms under different external forces. The creep behavior of obtained hydrogels can be effectively improved by the introduction of lignin molecules with precise regulation of spatial conformation. After 20 cycles of 500% stretching amplitude loading–unloading, the dissipation energy is still maintained at more than 95% of the first cycle, and compressive strength reaches more than 85% of the first cycle after 20 cycles of 60% compression amplitude loading–unloading. Furthermore, the obtained hydrogel exhibits strong antibacterial properties, stress sensing in harsh environments, and wound healing promoting properties. These findings break through the conventional notion that the energy dissipation mechanism of hydrogels depends on sacrificial bonds and are expected to expand the application potential of natural biomass macromolecules to a multifunctional hydrogel sensing platform.

Mechanism of airborne sound absorption through triboelectric effect for noise mitigation

Mitigating broadband noise with passive airborne sound absorbers has been a long-lasting challenge, particularly for low-frequency anthropogenic sounds below kilohertz with long wavelengths, which require bulky materials for effective absorption. Here, we propose a strategy that utilizes local triboelectric effect and in-situ electrical energy dissipation mechanism for airborne sound absorption. This approach involves a fundamentally different mechanism that converts airborne sound into electricity for energy dissipation, in contrast to conventional mechano-thermal energy conversion mechanisms. We establish an equivalent acoustic impedance model to provide theoretical analysis of the underlying sound absorption mechanisms, with a theoretical maximum mechano-electro-thermal coupling efficiency approaching 100% under optimal conditions. We design fibrous triboelectric composite foam materials accordingly and show their substantially boosted acoustic absorption performance experimentally, where the adoption of diverse triboelectric material pairs validates that a larger difference in material charge affinities intensifies the local triboelectric effect and results in higher acoustic absorbing performance.

Role of molecular damage in crack initiation mechanisms of tough elastomers

Tough soft materials such as multiple network elastomers (MNE) or filled elastomers are typically stretchable and include significant energy dissipation mechanisms that prevent or delay crack growth. Yet most studies and fracture models focus on steady-state propagation and damage is assumed to be decoupled from the local stress and strain fields near the crack tip. We report an in situ spatial-temporally resolved 3D measurement of molecular damage in mechanophore-labeled MNE just before a crack propagates. This technique, complemented by digital image correlation, allows us to compare the spatial distribution of both damage and deformation in single network (SN) elastomers and in MNE. Compared to SN, MNE have a wide-spread damage in front of the crack and, surprisingly, delocalize strain concentration. A continuum model, where damage distribution is fully coupled to the crack tip fields, is proposed to explain these results. Additional measurements of time-dependent molecular damage during fixed grips relaxation in the presence of a crack reveal that the less localized damage distribution delays fracture initiation. The observations and exploratory modeling reveal the dynamic fracture mechanism of MNE, providing guidance for rational design of high-performance tough elastomers.

Polymerization-Induced Self-Assembly Providing PEG-Gels with Dynamic Micelle-Crosslinked Hierarchical Structures and Overall Improvement of Their Comprehensive Performances.

Polymer gels are fascinating soft materials and have become excellent candidates for wearable electronics, biomedicine, sensors, etc. Synthetic gels usually suffer from poor mechanical properties, and integrating good mechanical properties, adhesiveness, stability, and self-healing performances in one gel is more difficult. Herein, polymerization-induced self-assembly (PISA) providing PEG-gels with an overall improvement in their comprehensive performances is reported. PISA synthesis is carried out in PEG (solvent) to efficiently produce various nanoparticles, which are used as the nanofillers in the subsequent synthesis of PEG-gels with dynamic micelle-crosslinked hierarchical structures. Compared to hydrogels, PEG-gels show excellent long-term stability due to the nonvolatile feature of PEG solvent. The hierarchical PEG-gels (with nanofillers) exhibit better mechanical and adhesive properties than the homogeneous-gels (without nanofillers). The energy dissipation mechanism of the PEG-gels is analyzed via stress relaxation and cyclic mechanical tests. High-density hydrogen bonds between the micelles and PAA matrix can be broken and reformed, endowing better self-healing properties of the dynamic micelle-crosslinked PEG gels. This work provides a simple strategy for producing hierarchical structural gels with enhanced properties, which offers fundamentals and inspirations for the designing of various advanced functional materials.

Paddle-wheels, friction, and moving-boundary work

Abstract Moving-boundary work, also called pressure-volume work or expansion work, is perhaps the main form of work discussed in introductory courses about thermodynamics. Here, we take a particular definition of this kind of thermodynamic work. On this basis, we show with simple reasoning that significant phenomena involving dissipation of mechanical energy, often mentioned as well in those courses but with a vague formalization, can be traced back right to moving-boundary processes. We refer in particular to the conversion of external work into internal energy in paddle-wheel experiments such as the one conducted by J. P. Joule in 1850, and to other processes involving friction.

Translaminar fracture in (non–)hybrid thin-ply fibre-reinforced composites: An in-depth examination through a novel mini-compact tension specimen compatible with microscale 4D computed tomography

Translaminar fracture toughness is pivotal for notch sensitivity and damage tolerance of fibre-reinforced composites. Hybridisation offers a promising pathway for enhancing this parameter in thin-ply composites. Three novel mini-compact tension specimen geometries were investigated for their competence in microscale characterisation of translaminar fracture using in-situ synchrotron radiation computed tomography (SRCT). Only “mini-protruded” design resulted in stable crack propagation with adequate crack increments. Based on this design, five baseline and hybrid cross-ply configurations incorporating low- and high-strain carbon fibres were studied. Crack propagation in low- and high-strain baseline configurations was stable. For interlayer and intrayarn fibre-hybrid configurations, a correlation between load–displacement curves and delamination is observed. The SRCT data confirmed that 90° ply-blocks cushion the interaction between 0° plies, enabling independent fracture. Additionally, crack fronts in 90° plies advance further than those in 0° plies. Moreover, mechanical interlocking and bundle bending within 0° plies serve as supplementary mechanisms for energy dissipation.