Energy Dissipation Mechanisms Research Articles

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 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.

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

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

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.

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.

Simplified assessment of structures with clutching inertia-friction systems by equivalent linearization methods

The innovative Clutching Inertia System (CIS), has garnered increasing recognition for its effectiveness in mitigating structural vibrations. To enhance the efficiency of passive CIS, introducing suitable energy dissipation mechanisms for the rotation inertia component is imperative. This study delves into the dynamic behavior of CIS, augmented with additional friction damping. Initially, the influence of supplementary friction damping within the CIS framework is examined through a dynamic model of a Single-Degree-of-Freedom (SDOF) system, integrated with the CIS and incorporating the Coulomb friction model. Subsequently, to streamline the dynamic analysis of the CIS and optimize the friction force thereby enhancing control efficiency while minimizing inactive durations, the paper introduces two distinct Equivalent Linearization Methods (ELMs). Furthermore, an assessment of the CIS’s dynamic performance, subjected to various external excitations, is presented. The findings highlight the crucial role of supplemental friction damping in reducing the inactivity of CIS and enhancing its overall control effectiveness. The employed ELMs demonstrate commendable accuracy and practicality for both response assessment and CIS performance optimization. In essence, the CIS, when integrated with supplemental friction damping, exhibits superior performance in suppressing structural displacement responses across diverse excitations, particularly in longer-period structures. Conversely, a more pronounced efficacy in managing structural acceleration responses is observed in structures with shorter periods. The study concludes that for specific structural applications, enhancing supplemental friction damping is more advantageous for vibration control than increasing the CIS’s inertia.

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.

Comparative Insights into Photosynthetic, Biochemical, and Ultrastructural Mechanisms in Hibiscus and Pelargonium Plants.

Understanding photosynthetic mechanisms in different plant species is crucial for advancing agricultural productivity and ecological restoration. This study presents a detailed physiological and ultrastructural comparison of photosynthetic mechanisms between Hibiscus (Hibiscus rosa-sinensis L.) and Pelargonium (Pelargonium zonale (L.) L'Hér. Ex Aiton) plants. The data collection encompassed daily photosynthetic profiles, responses to light and CO2, leaf optical properties, fluorescence data (OJIP transients), biochemical analyses, and anatomical observations. The findings reveal distinct morphological, optical, and biochemical adaptations between the two species. These adaptations were associated with differences in photochemical (AMAX, E, Ci, iWUE, and α) and carboxylative parameters (VCMAX, ΓCO2, gs, gm, Cc, and AJMAX), along with variations in fluorescence and concentrations of chlorophylls and carotenoids. Such factors modulate the efficiency of photosynthesis. Energy dissipation mechanisms, including thermal and fluorescence pathways (ΦPSII, ETR, NPQ), and JIP test-derived metrics highlighted differences in electron transport, particularly between PSII and PSI. At the ultrastructural level, Hibiscus exhibited optimised cellular and chloroplast architecture, characterised by increased chloroplast density and robust grana structures. In contrast, Pelargonium displayed suboptimal photosynthetic parameters, possibly due to reduced thylakoid counts and a higher proportion of mitochondria. In conclusion, while Hibiscus appears primed for efficient photosynthesis and energy storage, Pelargonium may prioritise alternative cellular functions, engaging in a metabolic trade-off.

Nacre‐Mimetic Multi‐Mechanical Synergistic Ceramic Aerogels with Interfacial Bridging and Stress Delocalization

AbstractElastic ceramic aerogels are exceptionally suitable for thermal insulating applications, but lacking multi‐mechanical synergistic high strength remains a deficiency. Inspired by the robust protective shells of mollusks in nature, which feature distinct hierarchical ordered structures, exhibiting strong and tough mechanical properties, a system construction and structural governing strategy is proposed to allow the nanostructure to assemble strong and flexible ceramic aerogels. Through the design of a hierarchical multi‐arched structure configurated binary‐soldering‐assemble interfacial topology interlocking, concentrated stress is effectively discrete. This biomimetic strategy enables the effective dissipation of mechanical energy, resulting in ceramic aerogels with exemplary compressive resilience, bendability, tensile resistance, and their strength exceeding that of other nanofibrous aerogels by up to tenfold. Additionally, the flexible aerogels also show remarkable thermal resistance from −196 to 1100 °C and superior thermal insulation capabilities (39.72 mW m−1 K−1), making them more suitable for the applications.

Mechanochemically responsive polymer enables shockwave visualization

Understanding the physical and chemical response of materials to impulsive deformation is crucial for applications ranging from soft robotic locomotion to space exploration to seismology. However, investigating material properties at extreme strain rates remains challenging due to temporal and spatial resolution limitations. Combining high-strain-rate testing with mechanochemistry encodes the molecular-level deformation within the material itself, thus enabling the direct quantification of the material response. Here, we demonstrate a mechanophore-functionalized block copolymer that self-reports energy dissipation mechanisms, such as bond rupture and acoustic wave dissipation, in response to high-strain-rate impacts. A microprojectile accelerated towards the polymer permanently deforms the material at a shallow depth. At intersonic velocities, the polymer reports significant subsurface energy absorption due to shockwave attenuation, a mechanism traditionally considered negligible compared to plasticity and not well explored in polymers. The acoustic wave velocity of the material is directly recovered from the mechanochemically-activated subsurface volume recorded in the material, which is validated by simulations, theory, and acoustic measurements. This integration of mechanochemistry with microballistic testing enables characterization of high-strain-rate mechanical properties and elucidates important insights applicable to nanomaterials, particle-reinforced composites, and biocompatible polymers.

Self-contact snapping metamaterial for tensile energy dissipation.

Mechanical metamaterials for energy dissipation have received significant attention for vibration and impact mitigation. However, existing designs often neglect energy dissipation in the tensile direction, which is crucial for attenuating tensile load and controlling falling descent. Importantly, current energy-dissipating mechanisms including plastic deformation and friction mechanisms, suffer from drawbacks such as reversibility and self-recovery, restricting their effectiveness under tension. To address these limitations, we propose a novel mechanism utilizing self-contact snap-through buckling to develop an energy-dissipating metamaterial. Unlike previous metamaterials, the self-contact snapping metamaterial (SCSM) achieves tensile energy dissipation with fewer unit cells while exhibiting reusability, self-recovery, and low reliance on material selection. A theoretical model is established to explain its energy-dissipating mechanism from the perspective of buckling mode transition. Moreover, the proposed SCSM exhibits sequential snapping behavior and effectively mitigates tensile impacts, as demonstrated through quasi-static and dynamic tests. This work opens new avenues for achieving tensile energy dissipation and inspires future research on energy conversion employing self-contact interactions.