Energy Dissipation Mechanisms Research Articles

Energy Behavior of Sandstone Containing Weak Filling Joints with Multiple Angles under Dynamic Splitting Loads

The impact of weak filling joints with multiple angles on the energy dissipation mechanism is significant for surrounding rock engineering to prevent and mitigate disasters. In the present study, the sandstone samples containing weak filling joints were prefabricated, and dynamic splitting tests were conducted under three nominal loading rates with a modified Split Hopkinson Pressure Bar system. The effects of nominal loading rates and joint angles on time-based curves and energy-based curves were investigated systematically. The test results indicated that the nominal loading rate and joint angle had remarkable influences on energy dissipation characteristics. The sample containing a larger joint angle preferred brittle failure, whereas the sample with a smaller joint angle failed with a plastic feature. Moreover, the reflection energy decreased as the joint angle increased, which was opposite to the evolution tendencies of transmission energy and absorption energy. The transmission energy and absorption energy had different sensitivities to changes in joint angle and nominal loading rate. The exponential function could excellently describe the dependence of transmission energy, reflection energy, and absorption energy on joint angles. With the incremental joint angle, the energy reflection ratio had a contrary tendency to the energy transmission ratio.

Elucidating the impact of microstructure on mechanical properties of phase-segregated polyurea: Finite element modeling of molecular dynamics derived microstructures

Phase-segregated polyureas (PU) have received considerable interest due to their use as tough, impact-resistant coatings. Polyureas are favored for these applications due to their mechanical strain rate sensitivity and energy dissipation. Predicting and tailoring the mechanical response of PU remains challenging due to the complex interaction between its elastomeric and glassy phases. To elucidate the role of PU microstructure on its mechanical properties, we developed a finite element modeling framework in which each phase is represented by a volume fraction within a representative volume element (RVE). Critically, we used separate constitutive models to describe the elastomeric and glassy phases. We developed a plasticity-driven breakdown process in which we model the glassy phase disaggregating into a new phase. The overall contribution of each phase at a material point is determined by their respective volume fractions within the RVE. We applied our modeling methods to two compositions of PU with differing elastomeric segment lengths derived from oligoether diamines, Versalink P650 and P1000. Our simulations show that a combination of microstructural differences and elastomeric phase properties accounts for the difference in mechanical response between P650 and P1000. We show our model’s ability to predict PU behavior in various loading conditions, including low-rate cyclic loading and monotonic loading over a wide range of strain rates. Our model produces microstructure transformations that mirror those indicated by small-angle X-ray scattering (SAXS) experiments. Fourier transform analysis of our RVEs reveals glassy phase fibrillation due to deformation, a finding consistent with SAXS experiments.

Energy dissipated by spherical nanoparticles debonding in nanocomposites under cryogenic and steady state conditions

In this paper, an analytical model was presented to estimate the influence of nanoparticles size and volume fraction on the debonding dissipation energy of nanoparticles/polymer nanocomposites in cryogenic temperature. A spherical representative volume element including a nanoparticle and a pure polymer phase was considered. It was assumed that the temperature is uniform within the whole RVE, i.e., a steady state temperature condition. Using the stress and displacement fields within the constituents of RVE, the dependence of the debonding dissipation energy on the nanoparticles size and volume fraction was obtained at a certain temperature. In addition to the analytical model, a finite element (FE) analysis using surface-based cohesive method was carried out to simulate the debonding process under cryogenic and steady state conditions. It was observed that the nanoparticles size has a significant effect on the energy dissipated by debonding. Moreover, the results manifested that the nanoparticles volume fraction affects the dissipation energy of debonding in nanocomposites reinforced by larger nanoparticles at cryogenic temperature. A good agreement was also found between the FE analysis results and the closed-form solution data. The conclusions obtained by this closed-form solution can be useful as a trigger for the other energy dissipation mechanisms occurred in the nanocomposites reinforced by nanofillers such as silica, alumina, titania, etc.

A four-tensor momenta equation for rolling physics

Relativistic four-tensor equation dJ μ ν = M μ ν dt is developed to analyse linear translation with rotation processes. The postulated cause-effect four-tensor equation, a relativistic generalisation for classical angular-impulse–angular-momentum variation equation dJ = Mdt, includes the Poinsot-Euler rotation (angular-impulse–angular-momentum variation) equation, Newton’s second law (linear-impulse–linear-momentum variation equation), and thermodynamics first law (work–energy equation). This four-tensor formalism is applied to describe three linear translation with rotation processes: a ring rolling on the floor by a horizontal force linear impulse and torque, fulfilling the rolling condition (mechanical energy conservation), a spinning ring placed on the ground until achieved the rolling condition (mechanical energy dissipation by friction), and a fireworks wheel ascending an incline (mechanical energy production by decreasing a thermodynamic potential).

Three‐Dimensional Particle‐In‐Cell Simulations of Electron‐Only Magnetic Reconnection Between Laser‐Produced Plasma Bubbles

AbstractElectron‐only magnetic reconnection, a novel type of reconnection where only electron dynamics is involved, has recently been observed in turbulent plasmas in the Earth's magnetosphere. In this letter, using particle‐in‐cell simulations, we demonstrate that electron‐only reconnection can be created via laser‐plasma interactions. The reconnection current sheet is carried by electrons, and its width is at the electron inertial scale. Moreover, only electron outflow is observed, while the ion outflow is negligible. The duration of the reconnection is found to be within the electron scale, thus there is no sufficient time for ions to respond. The energy conversion during electron‐only reconnection mainly occurs in the vicinity of the X‐line, and is dominated along the perpendicular direction. By analyzing the Poynting flux patterns, we find that the reconnection electric field dominates the whole energy conversion. This study advances our knowledge of the energy dissipation mechanism in the electron‐only reconnection regime.

Type 2 diabetes impairs annulus fibrosus fiber deformation and rotation under disc compression in the University of California Davis type 2 diabetes mellitus (UCD-T2DM) rat model

Abstract Understanding the biomechanical behavior of the intervertebral disc is crucial for studying disease mechanisms and developing tissue engineering strategies for managing disc degeneration. We used synchrotron small-angle X-ray scattering to investigate how changes to collagen behavior contribute to alterations in the disc’s ability to resist compression. Coccygeal motion segments from 6-month-old lean Sprague-Dawley rats ( n=7) and diabetic obese University of California Davis type 2 diabetes mellitus (UCD-T2DM) rats ( n=6, diabetic for 68±7 days) were compressed during simultaneous synchrotron scanning to measure collagen strain at the nanoscale (beamline 7.3.3 of the Advanced Light Source). After compression, the annulus fibrosus was assayed for nonenzymatic cross-links. In discs from lean rats, resistance to compression involved two main energy-dissipation mechanisms at the nanoscale: (1) rotation of the two groups of collagen fibrils forming the annulus fibrosus and (2) straightening (uncrimping) and stretching of the collagen fibrils. In discs from diabetic rats, both mechanisms were significantly impaired. Specifically, diabetes reduced fibril rotation by 31% and reduced collagen fibril strain by 30% (compared to lean discs). The stiffening of collagen fibrils in the discs from diabetic rats was consistent with a 31% higher concentration of nonenzymatic cross-links and with evidence of earlier onset plastic deformations such as fibril sliding and fibril–matrix delamination. These findings suggest that fibril reorientation, stretching, and straightening are key deformation mechanisms that facilitate whole-disc compression, and that type 2 diabetes impairs these efficient and low-energy elastic deformation mechanisms, thereby altering whole-disc behavior and inducing the earlier onset of plastic deformation.

A highly stretchable, adhesive, and antibacterial hydrogel with chitosan and tobramycin as dynamic cross-linkers for treating the infected diabetic wound

Diabetic wounds pose a significant challenge due to their susceptibility to bacterial infection in a high-glucose environment, which impedes the wound healing process. To address this issue, there is a pressing need to develop suitable hydrogels that can promote the regeneration of diabetic wounds in clinical practice. In this study, we designed and fabricated a highly stretchable, adhesive, transparent, and antibacterial hydrogel through a one-pot radical polymerization of N-[Tris (hydroxymethyl) methyl] acrylamide (THMA) and acrylic acid (AA), and with chitosan and the antibiotic tobramycin as the dynamic physical crosslinkers. The copolymer contains a large number of carboxyl and hydroxyl groups, which can form an interpenetrating network structure with chitosan and tobramycin through multiple dynamic non-covalent bonds. This hydrogel exhibited over 1600 % elongation through an energy dissipation mechanism and strong adhesion to various surfaces without any chemical reaction. In vivo, studies conducted on a staphylococcus aureus-infected full-thickness diabetic skin wound model demonstrated that the hydrogel loaded with tobramycin as one of the crosslinkers had a long-lasting antibacterial activity and effectively accelerated wound healing. Therefore, the antibiotic-loaded adhesive hydrogel we proposed holds great promise as a treatment for bacteria-infected diabetic wounds.

High-performance epoxy nanocomposites via constructing a rigid-flexible interface with graphene oxide functionalized by polyetheramine and f-SiO2

Graphene oxide (GO) is an ideal reinforcement for improving mechanical properties of epoxy (EP) and reducing its coefficient of thermal expansion (CTE). However, the poor interfacial interaction between GO and polymer matrix seriously hinders the reinforcing effect of GO. To improve their interface, we first functionalized GO with flexible polyetheramine (PEA) and f-SiO2 rigid nanoparticles, obtaining PEA-GO and SiO2-PEA-GO hybrids, respectively. Then the PEA-GO and SiO2-PEA-GO were incorporated into EP to obtain nanocomposites with flexible interphases and rigid-flexible interphases, respectively. The interfaces were tuned by two PEA molecules (D230 and D2000) with different chain lengths. The effects of the different interface structures on the mechanical properties and CTE of the GO/EP nanocomposites with a 0.25 wt% filler loading were investigated. It was found that the effects of SiO2-PEA-GO on strengthening and toughening EP matrix and on reducing its CTE were much better than those of PEA-GO, because the rigid-flexible interfaces provided higher bonding strength and better energy dissipation mechanisms than the flexible interfaces. Moreover, the D230-GO/EP nanocomposite containing shorter PEA (D230) molecules exhibited higher strength but lower toughness and CTE than the D2000-GO/EP nanocomposite. However, the SiO2-D2000-GO/EP nanocomposite showed greater strength, toughness and CTE than the SiO2-D230-GO/EP nanocomposite. This indicated that the longer PEA molecules in rigid-flexible interphases produced higher improvement in strength and toughness but smaller decreases in CTE. This work provides a promising strategy of constructing an adjustable flexible-rigid interfacial structure and opens an avenue for developing GO/EP nanocomposites with high mechanical properties and low CTE.

Acoustic characterization of natural areca catechu fiber‐reinforced flexible polyurethane foam composites

AbstractThe development of acoustic absorbers from natural resources is a novel approach in acoustics. In the current study, the effect of unprocessed raw areca fiber (AF) particle reinforcement on the sound absorption (SA) behavior of polyurethane (PU) foam composites is investigated. Influences of fiber weight percentage and graded distribution of fiber with varying fiber weight percentage on the SA coefficient (SAC) of the composite foams are examined through the impedance tube approach. Morphological studies are carried out with the help of FESEM images to investigate the acoustic energy dissipation mechanism of PU foam and its composites. It is found that the SA capability of the composite foam is enhanced by increased fiber weight percentage, graded distribution of fiber wt%, varying sample thickness, and air cavity length. In general, PU‐AF composite specimens show a peak SA value of 0.95 around 450 Hz, which is not the case for other natural fiber results available in the literature. Theoretical results predicted using the JCA (Johnson‐Champoux Allard) model agree with the experimental results.

Damping of liquid sloshing by floating balls

Sloshing in partially filled containers is a key phenomenon for the design of offshore structures such as liquefied natural gas carriers, floating production storage and offloading platforms, crude oil carriers, and floating liquefied natural gas vessels, due to large sloshing force acting on container's walls. Hence, violent sloshing motion needs to be mitigated for the safe operation of the floating structures. This study is focused on the experimental investigation of a sloshing damping device based on floating balls. The free-surface sloshing waves are generated in a rectangular tank filled with water, the free-surface of which is covered by a layer of floating balls. Three important sloshing regimes, namely, shallow, intermediate, and finite-water depth sloshing, are considered for investigation. Frequency responses of sloshing with and without balls are obtained to comprehend the effects of floating balls on damping of sloshing odd modes (first, third, fifth, and ninth modes). Further, physical processes enhancing damping mechanisms are also investigated in detail. It is found that the floating balls dampen shallow-water sloshing effectively. Different motions of the balls, ball–ball interactions, motions of ball–liquid interfaces, and liquid shear-flow motion between the tank wall and balls cause the dominant mechanism of energy dissipation.

Anisotropic characteristics of layered backfill: Mechanical properties and energy dissipation

Layered backfill is commonly used in mining operations, and its mechanical behavior is strongly influenced by delamination parameters. In this study, 13 specimens with different numbers of delamination and delamination angle were prepared to investigate the anisotropic mechanical behavior, energy dissipation characteristics and crack development of backfill. P-wave velocity, uniaxial compression, scanning electron microscope (SEM), and acoustic emission (AE) experiments were conducted. The results indicate that: (1) The P-wave velocity has linear and elliptical relationships with the number of delamination surface and delamination angle, respectively; the strength, delamination parameters and P-wave velocity show a high degree of coincidence in terms of their function relationship, which can realize the rapid prediction of strength. (2) The microstructure of the delaminated surface is looser than that of the matrix, leading to a decrease in strength and an increase at the pore-fissure compaction stage. The number and angle of delamination increase linearly with the anisotropy coefficient. (3) The energy evolution in angle-cut backfill can be divided into four stages, with a decrease in the proportion of elastic energy at the initiation stress and peak stress with increasing number of delamination planes and delamination angle. (4) Crack development increases with the number of delamination surface and delamination angle, resulting in a decrease in energy dissipation coefficient and peak AE energy. These findings provide valuable insights for the design of filling materials and processes in mining operations.

Structure of a diatom photosystem II supercomplex containing a member of Lhcx family and dimeric FCPII.

Diatoms rely on fucoxanthin chlorophyll a/c-binding proteins (FCPs) for their great success in oceans, which have a great diversity in their pigment, protein compositions, and subunit organizations. We report a unique structure of photosystem II (PSII)-FCPII supercomplex from Thalassiosira pseudonana at 2.68-Å resolution by cryo-electron microscopy. FCPIIs within this PSII-FCPII supercomplex exist in dimers and monomers, and a homodimer and a heterodimer were found to bind to a PSII core. The FCPII homodimer is formed by Lhcf7 and associates with PSII through an Lhcx family antenna Lhcx6_1, whereas the heterodimer is formed by Lhcf6 and Lhcf11 and connects to the core together with an Lhcf5 monomer through Lhca2 monomer. An extended pigment network consisting of diatoxanthins, diadinoxanthins, fucoxanthins, and chlorophylls a/c is revealed, which functions in efficient light harvesting, energy transfer, and dissipation. These results provide a structural basis for revealing the energy transfer and dissipation mechanisms and also for the structural diversity of FCP antennas in diatoms.

Energy Dissipation into the Solvent during Proton Transfer Occurs via Acoustic Phonons.

In photochemistry, rapid energy dissipation into the solvent is mandatory to prevent radiation damages. By optical pump THz spectroscopy, we are able to follow the details of the energy dissipation mechanism upon photoexcitation of the photoacid to the hydrogen-bonded network of water: Based on the frequency maps subsequent to photoexcitation, we propose that energy transfer takes place via propagation of an acoustic phonon. The dissipation into the solvent can be rationalized by an initial first hydration shell response followed by energy dissipation via an acoustic phonon. Surprisingly, for the first 10 ps, the propagation in the water network can be described by a wave packet with a constant group velocity, indicating a long-range correlation. After 300 ps, thermalization in the liquid jet is reached and the THz spectrum reflects a Boltzmann population, corresponding a temperature increase of ΔT = 0.5 °C.

Dynamic mechanical properties and energy dissipation of frozen weakly cemented red sandstone under high strain rate loading

Dynamic mechanical properties and energy dissipation of frozen weakly cemented red sandstone under high strain rate loading

An Investigation of Particle Motion and Energy Dissipation Mechanisms in Soil–Rock Mixtures with Varying Mixing Degrees under Vibratory Compaction

Soil–rock mixture (S–RM) is a heterogeneous granular material commonly used in engineering applications, but achieving uniform particle mixing is challenging. This study investigated the effect of mixing homogeneity on the compaction of S–RM using the discrete element method (DEM). Specimens with varying degrees of mixing were modeled under realistic vibration loading. The results showed that a higher degree of mixing resulted in a smaller void ratio after compaction. The analysis of particle motion and energy dissipation revealed that not all particle motion during vibration compaction was aligned with the direction of the particle system. However, rotation was more prevalent and contributed to densification. Dashpot energy dissipation did not solely promote changes in the void ratio, while slip energy dissipation did lead to changes in the void ratio, but not entirely towards compaction. Rolling slip energy dissipation primarily occurred during the stage of void ratio changes and significantly promoted compaction. The change in strain energy aligned with the trend of the void ratio but did not directly contribute to its promotion.

Composite nanofillers with a locust-like cushioned half-moon structure to improve the impact resistance of polyurethane

Developing a highly impact absorption properties polyurethane elastomer with exceptional strength and toughness is crucial in the realm of polyurethane impact protection. Inspired by the energy dissipation structure of the soft and hard bonding in the hind limb of locusts, the paper fixed the dynamic disulphide bonds commonly found in bioproteins after hydroxy-functionalized on SiO2 by quaternization reaction, and is creatively applied in the field of impact resistance as soft and hard sacrifice micro-regions into the polyurethane. Benefiting from the multi-scale energy dissipation approach formed by the breakage of dynamic disulphide bonds, the stress obstruction by rigid particles, and the strong bonding interface between the composite filler and the matrix, polyurethane composite have demonstrated great efficiency in energy absorption and impact protection. The static compression strength of IPS@SiO2/PUE is 148.8% higher compared to neat PUE. Furthermore, the dynamic impact energy absorption of the composite PUE was increased by 109.36%, nearly twice that of the original polyurethane. This study proposes that this strategic approach has the potential to offer a novel method for material design, which facilitates bionic design of high-impact protective elastomers utilizing different energy dissipation mechanisms.

Study on the mechanical properties and energy dissipation characteristics of concrete subjected to high strain rate and sulfate attack

Marine structures, such as cross-sea bridges, port constructions, and offshore drilling platforms, are not only subjected to sulfate erosion, but also to various dynamic loads. Analyzing the damage evolution process of concrete under sulfate erosion and impact loads is the key to improving the lifespan of concrete. In order to study the damage evolution process of eroded concrete under high strain rates, the energy dissipation characteristics, basic physics and mechanical properties, and micro-fracture mechanism of sulfate-eroded concrete at different sulfate concentrations (C=0, 3%, 6%, and 9%) under high strain rate ranging from 70/s to 85/s are systematically studied by using the split Hopkinson pressure bar (SHPB) test system, X-ray diffractometer and SEM scanning electron microscope. The research results indicate that an increase in sulfate concentration leads to a decrease in Ca(OH)2 content and an increase in Ettringite (AFt) content in concrete specimens; As the sulfate concentration increases, the dynamic peak strength and dynamic elastic modulus of concrete specimens gradually decrease, while the dynamic peak strain of concrete specimens gradually increases; The degree of macroscopic fragmentation in concrete specimens subjected to impact compression becomes increasingly severe with rising sulfate concentrations; As the sulfate concentration increases, the proportion of reflected energy and dissipated energy gradually increases, while that of transmitted energy gradually decreases, and the energy absorption capacity of the sample is significantly improved; The results of the SEM test shows that with the increase of sulfate concentration, a large amount of AFt is generated at the joint fissures and the interface of cement aggregates, the expansion of AFt and the crack development of concrete reduce the integrity and stability of concrete. This study holds significant guidance for the application of concrete in impact situations under a sulfate attack environment.

Observed oceanic response to Tropical Cyclone Amphan (2020) from a subsurface mooring in the Bay of Bengal

Upper ocean responses to the super Tropical Cyclone (TC) Amphan and modulation of energy dissipation by internal tides were investigated using in situ observations from a subsurface mooring in Bay of Bengal (BoB). The observations showed that the entire observed water column (150–800 m) cooled significantly, up to a maximum of 2 ℃, and salinity increased significantly at 150–200 m within one week after the TC, mainly due to the TC-induced upwelling. Dynamic response was characterized by strong near-inertial oscillation above 120 m. The near inertial waves (NIWs) had a maximum velocity and kinetic energy at 112.6 m, about 0.34 m/s and 59.5 J/m3, respectively. The energy spectrum and bicoherence analysis indicated that, the nonlinear wave-wave interaction between NIWs (f) and semi-diurnal tide (D2), as well as the self-interaction of NIWs were enhanced after the passage of TC. The nonlinear wave-wave interaction processes were able to transfer energy to higher mode internal waves, thus accelerating energy attenuation. Hence, the observed e-folding time for near-inertial kinetic energy (6.2 days) was only 41 % of the theoretical e-folding time. This study provided a new evidence for the mechanism of energy dissipation of NIWs and semi-diurnal tide during a TC condition in the southern BoB.

CA and/or EDTA functionalized magnetic iron oxide nanoparticles by oxidative precipitation from FeCl2 solution: structural and magnetic study

Four samples containing magnetic iron oxide nanoparticles (MIONs) of various sizes are prepared employing a simple low-temperature method of oxidative precipitation from FeCl2∙4H2O–NaOH–NaNO3 aqueous solution. For the preparation of two samples, the usual oxidation-precipitation synthesis protocol is modified by using ethylenediaminetetraacetic acid (EDTA) chelating agent as a stabilizer of the Fe2+ ions in a solution, which results in the partial capping of the prepared MIONs with EDTA molecules. Three out of four samples are subjected to citric acid (CA) functionalization in the post synthesis protocol. Structural and magnetic properties of the synthesized MIONs are assessed using various experimental techniques (XRD, TEM, Fourier transform infrared, dynamic light scattering, Mössbauer, and SQUID). The average size of spherical-like MIONs is tuned from 7 nm to 38 nm by changing the synthesis protocol. Their room temperature saturation magnetization, M s, is in the range of 43 to 91 emu g−1. Magnetic heating ability, expressed via specific absorption rate value, which ranges from 139 to 390 W/gFe, is discussed in relation to their structural and magnetic properties and the possible energy dissipation mechanisms involved. The best heating performance is exhibited by the sample decorated with EDTA and with a bimodal size distribution with average particle sizes of 14 and 37 nm and M s = 87 emu g−1. Though this sample contains particles prone to form aggregates, capping with EDTA provides good colloidal stability of this sample, thus preserving the magnetic heating ability. It is demonstrated that two samples, consisting of 7 nm-sized CA- or 14 nm-sized EDTA/CA-functionalized superparamagnetic MIONs, with a similar hydrodynamic radius, heat in a very similar way in the relatively fast oscillating alternating current magnetic field, f = 577 kHz.

Motion of a viscous slug on heterogeneous surfaces: crossover from stick–slip to steady sliding

We present a theoretical study of viscous slug motion inside a microscopically rough capillary tube, where pronounced stick–slip motion can emerge at slow displacement rates. The mathematical description of this intermittent motion can be reduced to a system of ordinary differential equations, which also describe the motion of a pendulum inside a fluid-filled rotating drum. We use this analogy to show that the stick–slip motion transitions to steady sliding at high displacement rates. We characterize this crossover with a simple scaling relation and show that the crossover is accompanied by a shift in the dominant energy dissipation mechanisms within the system.