Dissipation Research Articles

Seismic performance and calculation method for plastic hinge length of RC pier reinforced with UHPC

Piers are highly vulnerable load-bearing components, and their seismic performance determines the integral seismic resistance of bridges to a certain degree. They play crucial roles in evacuation during earthquakes and post-earthquake rescue. The manner in which piers meet the seismic performance requirements after reinforcement has become a popular research topic. In this study, ultra-high-performance concrete (UHPC) and HTRB600E high-tensile reinforcements were used to expand the cross section of a cast-in-place square pier with severe bending damage. The earthquake-resistant behaviour indicators of the pier were compared and analysed by conducting pseudo-static tests on a reinforced concrete pier before and after reinforcement. These indicators included the hysteretic curve, skeleton curve, energy dissipation curve, rigidity degradation, residual displacement, and pier body curvature. Based on the results of the seismic reinforcement quasi-static tests, a finite element model (FEM) of the bridge pier was constructed using the ABAQUS software, and the accuracy of the FEM was averaged. The impact of the reinforcement layer height, thickness, longitudinal strength and axial compression ratio on the equivalent plastic-hinge length of the reinforced pier was analysed, and the formula for the equivalent plastic-hinge length of the reinforced pier was obtained based on multiple linear regression fitting. The analysis results demonstrated that the broadened section method, utilising UHPC and high-tensile reinforcement, significantly enhanced the flexural capacity, energy dissipation, and first rigidity of the bridge pier. The earthquake-resistant behaviour of pier was effectively restored and improved, and the seismic reinforcement effect was significant. The equivalent plastic hinge length of the pier after reinforcement is proportional to the height of the reinforcement layer, the thickness of the reinforcement layer, the strength of the longitudinal reinforcement, and inversely proportional to the axial compression ratio.

Experimental Study and Analysis of the Static and Dynamic Mechanical Properties of Graphene Oxide Cement Soil Under Composite Salinity Erosion

In coastal and saline-alkali regions, cement soil materials face significant challenges from salt erosion and both dynamic and static loads, threatening their structural stability. To enhance the mechanical properties of cement soil, this study explores the incorporation of graphene oxide (GO). We subjected GO cement soil specimens to various concentrations of a composite salt solution (with a NaCl to Na2SO4 mass ratio of 1:1) in erosion experiments lasting 7 and 30 days. The specimens were analyzed through unconfined compressive strength tests, split Hopkinson pressure bar (SHPB) tests, and scanning electron microscopy (SEM) to examine changes in stress-strain curves, peak stress, and energy dissipation. The results indicate that the dynamic and static peak stresses, energy absorption, and energy absorption efficiency of the GO cement soil specimens are inversely related to the concentration of the mixed salt solution. Notably, in a 4.5g/L erosion environment after 7 days, an increasing trend was observed in static peak stress, energy absorption, and energy absorption efficiency. Additionally, when the salt concentration was fixed, these properties showed a positive correlation with impact gas pressure. SEM analysis revealed that the nucleation effect of GO and its strong bonding with the cement matrix significantly improved the microstructure of the specimens by reducing pores and defects, thus enhancing density and overall performance. Furthermore, in an 18g/L erosion environment, a notable presence of ettringite (AFt) was identified in the GO cement soil specimens.

Seismic performance of precast concrete shear wall with treatments of connecting reinforcement defects in grouted sleeves under combined axial tension and cyclic horizontal load

With the purpose of investigating the influence of connecting reinforcement defect in grouted sleeves and corresponding strengthening schemes on the seismic performance of precast concrete shear walls under combined in-plane axial tension and cyclic horizontal load, four full-scale precast concrete shear wall specimens and one monolithically cast-in-place concrete shear wall specimen as a reference, were designed and tested. The seismic performance, including failure mode, seismic load bearing capacity, ductility, stiffness degradation and energy dissipation capacity, of all specimens were selectively emphasized. The test results revealed that under combined axial tension and cyclic horizontal load, the precast shear wall with reliable connecting via grouted sleeves technology would achieve the satisfactory seismic performance, approximately parallel to that of monolithically cast-in-place shear wall. However, the ultimate seismic load bearing capacity and ultimate deformation of precast shear wall with reinforcement connection defect in grouted sleeves decreased by around 44.1%, 171.6% respectively, compared with that of precast shear wall with reliable connecting via grouted sleeves. In terms of strengthening specimens, the seismic load bearing capacity, peak deformation, flexural stiffness and energy dissipation basically recovered to the identical level of seismic performance with monolithical shear wall under coupling action of axial tension and cyclic horizontal load. Differently, the post-peak deformation ability of strengthening specimens severely decreased due to the stress concentration and further premature fracture of steel rebars resulting from the presence of UHPC in strengthening region. Finally, the portion of shear deformation and failure mechanism of precast concrete shear walls with reinforcement defect in grouted sleeves, and those employing different strengthening schemes were well discussed and analyzed under coupling action of axial tension and cyclic horizontal load as well.

A rate-dependent crack bridging model for dynamic fracture of CNT-reinforced polymers

Carbon nanotubes (CNTs) improve the fracture toughness of polymer-based matrix composites by bridging the crack growth path. This research presents a finite element (FE) rate-dependent crack bridging model of Mode-I dynamic crack growth in CNT-reinforced polymers accounting for rate of loading and rapid crack growth. Two distinct CNT bridging and matrix cracking damage mechanisms are taken into account in the fracture process zone (FPZ) accounting for the dissipation of fracture energy. A viscoelastic-viscoplastic material model is adapted for the matrix phase to capture the strain rate effects. The crack in the matrix phase is modeled using cohesive zone elements characterized by experimental data. A rate-dependent traction-separation law obtained from CNT pull-out simulation at relevant crack opening speeds is used to simulate the CNT bridging in the FPZ. Considering the given traction-separation law as a constitutive equation, the CNTs are replaced with non-linear spring elements to facilitate the FE simulation of crack bridging with numerous CNTs in the FPZ. The proposed rate-dependent FE model for crack bridging enables the study of the effect of key CNT factors such as length, orientation, waviness, volume fraction, and agglomeration on fracture energy dissipation at various crack speeds. The developed model can simultaneously consider the interactive effects of all CNT parameters which is useful for considering all processing-induced uncertainties in analyzing the effects of CNTs on the dynamic fracture toughness of nanocomposites.

Sunflower pith inspired dual-gradient cellular polyurethane architecture with amplified mechanical functions

Artificial cellular materials with various mechanical functions are attracting increasing attentions from aerospace, transportation, and industrialization. However, many artificial cellular materials, despite of the hierarchically ordered structures and even unique performance to some, still lag behind many natural ones in amplification of mechanical functions owing to the limitations in intrinsic mechanical performance and sophisticated structural design. Herein, inspired with lightweight and high strength of sunflower piths, we proposed a dual-gradient structure consisting of pore size gradient and wall thickness gradient to engineer cellular architectures with desirable mechanical performance by harnessing vat photopolymerization 3D printing of double crosslinking networks polyurethane elastomer. The double-gradient cellular polyurethane architecture displays more exceptional capability in load-bearing and energy absorption compared with non– and single gradient structures. Besides, the specific compressive strength and energy absorption of the dual-gradient cellular architectures are 4 times higher than those of traditional mechanical metamaterial structures such as octet-truss lattice, gyroid lattice, and porous structure prepared with the same material. Potential mechanisms such as dual-gradient cellular structures to obtain selective flexural deformation behaviour increasing their energy absorption and dissipation capacity are fully elucidated. As the potential paradigms, we demonstrated the mechanical functions of biomimetic mechanical cellular architectures for efficient impact protection and noise isolation, which offered a promising perspective toward developing soft metamaterials with excellent mechanical functions for potential soft machines and engineering applications.

Largely enhanced damping performance of nitrile rubber/ethylene–vinyl acetate blends via phenolic resin-induced phase separation

The low glass transition temperature (Tg) and narrow effective damping temperature range (EDTR) greatly restrict the application of common vulcanized rubbers in fields relating to high temperature environmental condition due to the greatly reduced damping performances. In this work, phenolic resin (PR) was incorporated into nitrile rubber/ethylene–vinyl acetate (NBR/EVM) blends through melt-compounding processing, and the microstructure and damping performance changes induced by PR were comparatively investigated. The results show that PR induces the phase separation of the blends and most of PR particles selectively locate in the NBR component. Molecular dynamics simulation confirms that more hydrogen bonds form in the ternary blends, and reduced free volume fraction is also achieved. The ternary blends show good high-temperature damping performances, and apparently enhanced Tg (up to 17.7 °C) and EDTR (82.6 °C, from −2.6 to 80 °C) are also achieved. Additionally, the ternary blends exhibit good mechanical properties, including higher ductility and larger fracture energy, and better energy dissipation ability. This work provides an alternative resolution way to enhance the damping performances of the common vulcanized rubbers at high temperatures.

Multi-axial fatigue of high-strength concrete: Model-enabled interpretation of punch-through shear test response

This paper aims to fill the gap in multi-axial fatigue characterization of concrete by presenting a comprehensive numerical analysis of data from the punch-through shear test (PTST), which allows control over combined shear and compression loads in the tested ligament. To accurately reproduce the degradation process in this multi-axial configuration, a material model must capture two key effects: (i) dissipative behavior at the inter-aggregate level during subcritical pulsating loading and (ii) fatigue-induced tri-axial stress redistribution in the test ligament. The recently published MS1 model by the authors effectively incorporates these features, thereby enabling a deeper interpretation of the experimental data. The former effect is seamlessly integrated into the model using the Lemaitre-type fatigue hypothesis, facilitating the direct derivation of general evolution equations. The latter effect is efficiently represented through the microplane homogenization framework. The model’s predictions for PTST response under monotonic shear loading with varying levels of radial confinement align well with experimental results. Similarly, the simulated fatigue response accurately reproduces the experimentally observed S-N (Wöhler) curves. Further studies demonstrate the model’s ability to predict the effect of fatigue loading sequence. A thermodynamically-based formulation provides an energetic interpretation of this effect, offering a quantitative breakdown of energy dissipation attributed to individual dissipative mechanisms over the lifetime of the material. The studies show that damage-induced dissipation remains almost constant regardless of different fatigue loading histories.

Influences of Strain Rate and Density on the Dynamic Material Properties and Energy Dissipation Characteristics of Iron Tailing Porous Concrete

Influences of Strain Rate and Density on the Dynamic Material Properties and Energy Dissipation Characteristics of Iron Tailing Porous Concrete

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.

Measurement While Drilling Method for Estimating the Uniaxial Compressive Strength of Rocks Considering Frictional Dissipation Energy

Measurement While Drilling Method for Estimating the Uniaxial Compressive Strength of Rocks Considering Frictional Dissipation Energy

Fatigue-induced alterations in force production, trajectory and performance in alpine skiing

ABSTRACT In giant slalom, the ability to apply a high amount of force in the radial direction is essential for performance. A race is characterized by repeated turns performed at high velocity, potentially inducing fatigue. Therefore, this study aimed to assess the effect of fatigue on performance, trajectory characteristics, and force production capacities onto the snow. Twelve skiers ran a 4-turn section with (FATIGUE) and without pre-induced fatigue (CONTROL). Knee extensor maximal voluntary contraction (MVC) was performed before the experiment and after both conditions. Section time, energy dissipation, path length, total force output, force application effectiveness, and EMG activity of the main lower-limb muscles were compared between conditions. Multiple linear regressions were used to understand whether interindividual variability in the kinematic, kinetic and EMG between conditions explains variability in performance changes with fatigue. MVC was lower after FATIGUE (−19.1 ± 6.4%, p < 0.001) but did not change after CONTROL. FATIGUE was associated with longer section times (+0.21 ± 0.11 s, p < 0.001), energy dissipation (−0.78 ± 1.05 J.s.kg.m−1, p = 0.026), path length (+1.1 ± 1.6 m, p = 0.033) and lower force application effectiveness (−0.1 ± 0.1, p = 0.017). This study experimentally demonstrates that fatigue in giant slalom results in lower force application effectiveness, inducing over-dissipation of mechanical energy and longer path length, leading to lower performance.

Experiments and FE Modeling on the Seismic Behavior of Partially Precast Steel-Reinforced Concrete Squat Walls

This paper proposed an innovative precast steel-reinforced concrete (PPSRC) squat wall to simplify on-site construction. In PPSRC squat shear walls, the hollowly precast RC wall panel can be assembled on-site through the pre-erected steel shapes, and the boundary cores will be filled using fresh concrete together with the slab system. The seismic performance of PPSRC squat walls, influenced by different construction techniques (cast-in-place vs. precast) and steel ratios, was examined through pseudo-static experiments on three specimens. Some key performance indicators, including hysteretic behavior, skeleton curves, stiffness degradation, energy dissipation, and load-carrying capacity, were analyzed in detail. The test results indicated that all the PPSRC squat walls failed in typical shear failure, and no significant slippage between the precast and fresh concrete sections was observed during the loading process, indicating that the composite action could be fully achieved via the novel throat connectors. In addition, the PPSRC squat walls could achieve comparable seismic performance compared with that of cast-in-place SRC shear walls (the peak load of the PPSRC squat wall only increased by 0.26% compared with the control specimen), and the load-carrying capacity and deformability could be enhanced by increasing the steel ratio in the boundary elements. Finally, an elaborate finite element model was developed and validated using ABAQUS software. The parametric analysis of the concrete strengths of precast and cast-in-place parts and the axial load was conducted further to investigate the seismic performance of PPSRC squat walls.

Balancing Interfacial Toughness and Intrinsic Dissipation for High Adhesion and Thermal Conductivity of Polymer-Based Thermal Interface Materials.

In recent years, adhesive thermal interface materials have attracted much attention because of their reliable adhesion properties on most substrates, preventing moisture, vibration impact, or chemical corrosion damage to components and equipment, as well as solving the heat dissipation problem. However, thermal interface materials have a huge contradiction between strong adhesion and high thermal conductivity. Here, we report a polymer-based thermal interface material consisting of polydimethylsiloxane/spherical aluminum fillers, which possesses both adhesion properties (adhesion strength of 3.59 MPa and adhesion toughness of 1673 J m-2 and enhanced thermal conductivity of 3.90 W m-1 K-1). These excellent properties are attributed to the modified chain structure by introducing acrylate accelerators into the polydimethylsiloxane network, thereby striking a balance between interfacial toughness and intrinsic dissipation. The addition of thermally conductive aluminum fillers not only increases the thermal conductivity but also improves the bulk energy dissipation of the thermal interface material. This work provides a novel strategy for designing a novel thermal interface material, leading to new ideas in long-term applications in high-power electronics.

Evaluation of Inherent Damping Feature of Beam Structure Based on Complex Modulus

Structural damping, which has been widely used to quantify the energy dissipation of engineering structures, plays an important role in dynamic analysis during the design phase and the assessment of existing structures. However, the development of an accurate damping model remains an open question due to the unclear mechanism. In this study, structural damping was identified based on loss factors for beam structures, which were used for presenting the damping behavior during vibrations. The equation of motion for the bending deformation of a Timoshenko beam was derived, accounting for the material damping. To identify the loss factor of the beam from the response signals at a limited number of measurement points, an inverse algorithm based on wave coefficient estimation was developed, considering the numerical stability for data interpretation. Based on the proposed loss factor identification method, several beam models with different shapes of cross-sections were investigated, focusing on the feasibility of the method of varying cross-section cases. Comparing the spectral element model with the loss factor and the finite element model with Rayleigh damping, it was confirmed that the loss factor can better describe the actual energy dissipation behavior of the structure. It provides a more accurate theoretical model for estimating structural damping in practical engineering.

Mathematical Model of a Nonlinear Electromagnetic Circuit Based on the Modified Hamilton–Ostrogradsky Principle

This paper presents a mathematical model of a typical lumped-parameter electromagnetic assembly, which consists of two subassemblies: one includes a magnetic circuit and the other with selected elements of electric circuits. An interdisciplinary research approach is used, which assumes the use of a modified integral method based on the variational Hamilton–Ostrogradsky principle. The modification of the method is the extension of the Lagrange function by two components. The first one reflects the dissipation of electromagnetic energy in the system, while the second one reflects the effect of external non-potential forces acting on the electromagnetic system. This approach allows for the avoidance of the inconvenience of the classical theory, which assumes the decomposition of the entire integrated system into individual electrical subsystems. The state equations of the electromagnetic subassembly are presented solely on the basis of the energy approach, which in turn allows taking into account various latent motions in the system, because the equations are derived based on non-stationary constraints between subsystems. The adopted theory allows for the formulation of the model of the system in a vector form, which gives much more possibilities for the analysis of higher-order electromagnetic circuits. Another important advantage is that the state equations of the considered electrical object are given in Cauchy normal form. In this way, the equations can be integrated both explicitly and implicitly. The results of computer simulations are presented in graphical form, analysed, and discussed.

Wave–Tide–Surge Interaction Modulates Storm Waves in the Bohai Sea

Typhoons, extratropical cyclones, and cold fronts cause strong winds leading to storm surges and waves in the Bohai Sea. A wave–flow coupled numerical model is established for storm events observed in 2022 caused by three weather systems, to investigate how storm waves are modulated by wave–tide–surge interaction (WTSI). Wave response is basically controlled by water level change in coastal areas, where bottom friction or breaking dominates the energy dissipation, and determined by the current field in deep water by altering whitecapping. Wave height increases/decreases are induced by positive/negative water level or obtuse/acute wave–current interaction angle, leading to six types of field patterns for significant wave height (Hs) responses. For the three storm events, Hs basically changed within ±5% in central deep water, while the maximum increase/decrease reached 160%/−60% in the coastal area of Laizhou Bay/Liaodong Bay. Based on maximum Hs and its occurrence time, WTSI modulation is manifested as the superposition effect of wave–tide and wave–surge interactions in both space and time scales, and occurrence time depends more on tide than surge for all three storms. The enhancement/abatement of WTSI modulation happens for consistent/opposite changing trends of wave–tide and wave–surge interaction, with the ultimate result showing the side with a higher effect.

Vibration Suppression and Energy Harvesting of Nonlinear Energy Sink-Based Piezoelectric System with Combined Damping and Bistability Properties for Nonlinear Oscillator

Nonlinear energy sink (NES) as a new type of dynamic absorber has received widespread attention due to its broadband vibration suppression capability, but it has a certain requirement of energy triggering threshold. In this work, a bistable NES-based piezoelectric system with combined damping (BCPNES) and low threshold requirement is proposed. Electromechanical-coupled equations for the nonlinear oscillator coupled with BCPNES (NO-BCPNES) are established. The vibration suppression and vibration energy harvesting performance for the coupled system are investigated numerically and analytically. The frequency–energy plots of the conservative system are investigated using the complex-variable averaging method and the electromechanical decoupling method. The influence of circuit parameters on the target energy transfer threshold and harvested energy is discussed through the equivalent stiffness and damping of the circuit. The vibration suppression performance and the target energy transfer characteristics are analyzed in terms of the time–history response, the time–frequency response and the slowly varying dynamic flow, respectively. The results show that the electromechanical coupling coefficient affects the skeleton curve of frequency–energy plots in the form of equivalent stiffness. The NO-BCPNES system exhibits higher energy dissipation performance and better targeted energy transfer form under various excitations. From the phase perspective, NES-based piezoelectric system achieves vibration suppression of the main structure through the phase locking phenomenon. The mechanism of the influence of piezoelectric device parameters on the energy harvesting performance of the systems is clarified.

Performance Evaluation of Inerter and Negative Stiffness-Based Dampers for Seismic-Induced Vibration Response Control of a Cable-Stayed Bridge: A Comparative Study

The excessive main girder displacement responses of the large-span cable-stayed bridges during seismic events may precipitate collisions between the main girder and the approach bridge. The viscous dampers (VDs) have been extensively employed in the seismic response control of long-span bridges, yet their effectiveness is limited. To augment the seismic-induced vibration control performance of the VD, inerter element, negative stiffness (NS) element, and spring element have been incorporated into the VD to achieve energy dissipation capacity enhancement. The equations of motion for the simplified cable-stayed bridge-damper systems are established under stochastic seismic excitation, and the design parameters of inerter and NS-based damper are optimized by using the genetic algorithm. The seismic control performance of the VD and five types of dampers are systematically compared, demonstrating that these dampers can substantially enhance the main girder displacement mitigation performance in cable-stayed bridges. Owing to the NS characteristics attributes of the inerter element and NS element and the tuning effect of the spring element, the tuned viscous mass damper (TVMD) with NS achieves a 24.56% higher efficiency in control performance compared to the VD.

Sub‐assemblage testing and fragility analysis of connections of continuous‐plasterboard suspended ceiling systems

AbstractPast earthquake reconnaissance reports highlighted extensive seismic damages to suspended ceiling components and connections, including instances of complete ceiling failures. The seismic qualification of these nonstructural elements typically requires comprehensive evaluation through full‐scale shake table testing. However, such experimental evaluation is ordinarily not possible for every change made in various components and connections of ceiling systems due to the cost and effort involved. A feasible alternative is to obtain the behavior of components and connections from sub‐assemblage testing and incorporate them in appropriate numerical ceiling models to derive mechanical responses for developing alternative or new installation schemes. This paper considers critical connections of three continuous‐plasterboard suspended ceiling systems that were evaluated using shake table‐generated motions. The connections were classified according to their attachment to typical floors and walls of building structures, and sub‐assemblage testing was conducted using both monotonic and cyclic displacement loading. The observed failure modes in each connection were detailed, and appropriate damage states were assigned as the basis for constructing connection fragility curves. The results of the sub‐assemblage testing were presented in terms of the hysteresis responses, envelope curves, nonlinear backbone curves, and cumulative energy dissipation curves. Additionally, multilinear models of the connections were derived by approximating nonlinear backbone curves’ initial‐ and post‐yield behaviors. These multilinear models were further idealized to derive three equivalent linearized models for simplified yet reasonably accurate results for linear structural analyses. Finally, fragility curves were derived for all connections, considering their cyclic displacement failure capacities.

Hot deformation behavior of an ignition resistance Mg–6Zn-0.6Zr-1.2Ca magnesium alloy

The addition of Ca could enhance the ignition point of magnesium alloys but impairing their workability, so it is essential to study the hot deformation behavior of new Ca-containing ignition resistance magnesium alloys. The hot deformation behavior of a new ignition resistance Mg–6Zn-0.6Zr-1.2Ca alloy was investigated by compression experiment in the temperature range of 240 °C–360 °C, strain rates of 10−3 s−1-1 s−1 and height reduction of 10%–60%. The true stress-strain curves show that flow stress decreases as the deformation temperature increases or the strain rate decreases. Microstructure analysis shows that higher temperatures and lower strain rates are favorable for DRX, while higher strain rates promote the fragmentation of the Ca2Mg6Zn3 phase. Meanwhile, the existence of Ca2Mg6Zn3 phase make the DRX process be dominated by the particle-induced subgrain nucleation mechanism. By superposition of the power dissipation map and the instability map, a hot processing map of true strain of 0.6 is generated. According to analyses on the processing map and microstructure evolution, the instability of processing map can be attributed to the greater dislocation motion resistances, insufficient DRX, and Ca2Mg6Zn3 phase with low-melting point. Conversely, the optimal processing parameters for the alloy were determined as 280–360 °C/0.001–0.01 s−1 in safe zone with a high η above 0.3, which can be due to the apparent DRX and good deformation coordination.