Energy Dissipation Processes Research Articles

Energy balance and acoustic emission in titanium Grade 2 under fatigue

This work is devoted to the study of fatigue crack propagation features in titanium Grade 2 in order to develop effective methods for fatigue crack detection and prediction of its propagation rate. Two characteristic stages of heat dissipation are identified during fatigue crack growth. Also the stored energy during fatigue crack propagation is calculated by experimental data of mechanical work and heat dissipation. The stored energy rate is smoother than heat dissipation rate and it slows down when approaching the moment of damage. Cluster analysis of the signal allows us to identify two most probable clusters. The correlation between the acoustic emission energy and heat dissipation was found to be a harbinger of the approaching transition from stable to unstable crack growth. The relation between fatigue crack growth rate and the processes of energy dissipation and acoustic emission can be used in development of intelligent monitoring systems for assessment of current state of structure.

Synthesis and photophysical properties of photostable 1,8-naphthalimide dyes incorporating benzotriazole-based UV absorbers.

We developed a series of blue-emitting 1,8-naphthalimide dyes covalently attached to 2-(2-hydroxyphenyl)-2H-benzotriazoles that retard photodegradation of the fluorophore. The dyes displayed weaker fluorescence emissions than the parent 1.8-naphthalimide. Quantum chemical calculations suggested that the decreased fluorescence was caused by the nonradiative deactivation promoted through the excited state intramolecular proton transfer (ESIPT) in benzotriazole components. The dyes' phosphorescences in a degassed solution at 77 K were more efficient than that of the parent 1.8-naphthalimide, indicating a possible deactivation pathway through intersystem crossing. PMMA films doped with these dyes showed higher resistance against photoaging than the film doped with an equimolar mixture of constituent 1.8-naphthalimide and the benzotriazole derivatives. Thus, the covalently linked benzotriazole units slow fluorophore degradation not only by preferential absorption of harmful UV light, which is found in the film with a simple mixture of two components, but also by the nonradiative deactivation involved in benzotriazole units.

Transient Superdiffusion of Energetic Carriers in Transition Metal Dichalcogenides Visualized by Ultrafast Pump-Probe Microscopy

Because of the strong Coulomb interaction and quantum confinement effect, 2-dimensional transition metal dichalcogenides possess a stable excitonic population. To realize excitonic device applications, such as excitonic circuits, switches, and transistors, it is of paramount importance for understanding the optical properties of transition metal dichalcogenides. Furthermore, the strong quantum confinement in 2-dimensional space introduces exotic properties, such as enhanced phonon bottlenecking effect, many-body interaction of excitons, and ultrafast nonequilibrium exciton–exciton annihilation. Exciton diffusion is the primary energy dissipation process and a working horse in excitonic devices. In this work, we investigated time-resolved exciton propagation in monolayer semiconductors of WSe 2 , MoWSe 2 , and MoSe 2 , with a home-built femtosecond pump-probe microscope. We observed ultrafast exciton expansion behavior with an equivalent diffusivity of up to 502 cm 2 s −1 at the initial delay time, followed by a slow linear diffusive regime (20.9 cm 2 s −1 ) in the monolayer WSe 2 . The fast expansion behavior is attributed to energetic carrier-dominated superdiffusive behavior. We found that in the monolayers MoWSe 2 and MoSe 2 , the energetic carrier-induced exciton expansion is much more effective, with diffusivity up to 668 and 2295 cm 2 s −1 , respectively. However, the “cold” exciton transport is trap limited in MoWSe 2 and MoSe 2 , leading to negative diffusion behavior at later time. Our findings are helpful to better understand the ultrafast nonlinear diffusive behavior in strongly quantum-confined systems. It may be harnessed to break the limit of conventional slow diffusion of excitons for advancing more efficient and ultrafast optoelectronic devices.

The fracture failure of three-dimensional concrete structures subjected to concentrated loadings using the Boundary Element Method

Abstract This study applies the Boundary Element Method (BEM) for the fracture failure modelling of three-dimensional concrete structures subjected to concentrated boundary conditions. The non-requirement of domain mesh by the BEM enables high accuracy in the domain fields assessment in addition to less complex remeshing procedures during crack propagation. However, concentrated boundary conditions often occur in fracture mechanics. The Lagrangian version of the BEM enforces such boundary conditions approximately by small length elements, which lead to numerical instabilities or even inaccurate problem representation. This study proposes a formulation for representing properly concentrated boundary conditions within the Lagrangian BEM framework. Nonlinear fracture mechanics describes the material failure processes herein. The classical cohesive crack approach governs the nonlinear energy dissipation processes, in which constant and tangent operators solve the resulting nonlinear system. Three applications demonstrate the accuracy of the proposed formulation, in which the BEM responses are compared against numerical and experimental results available in the literature.

4-Pole Hybrid HVDC Circuit Breaker for Pole-to-Pole (PTP) Fault Protection

Numerous problems have emerged with the development of HVDC transmission technology. One of them is the fault current that occurs when there is an issue in the line. In particular, in the case of a PTP (pole-to-pole) fault, a DCCB design suitable for the direction is required because the fault current flows through the positive and negative poles. In the case of PTP fault, a fault current of the same value occurs in the opposite direction, and in the case of DCCB, the breaking efficiency may be reduced or even impossible to break due to a mistake in the emission direction or a wrong design. In particular, when designing using several unidirectional DCCBs, it is cheaper and consumes less area than typical DCCBs, so it is economical, but this problem may be more prominent. To solve this problem, this paper proposes a 4- pole Hybrid HVDC circuit breaker to solve this problem. This circuit optimizes the DCCB internal components through quantitative analysis of the fault current to reduce the influence of the residual fault current as well as the previously most important parameter, Zero-Cross Time (ZCT). We also verified the circuit’s energy dissipation process to increase reliability. The circuit in this paper is simulated based on the VSC-based HVDC transmission link. Physically analyze the derived results and described the circuit mechanism.

The Ballistic responses of thread-quilted plain weaves with increased yarn–yarn​ friction

This paper investigates the influence of quilting on the ballistic performance of plain weaves. The friction between the fabric-forming yarns was increased due to the constraint imparted by thread quilting. Ballistic impact tests were performed to characterize the ballistic protection of the quilted and the un-quilted samples, and FE simulation was used to study the mechanisms of energy absorption. It was found that the quilted fabrics outperform the un-quilted plain weave in terms of energy absorption. The most significant improvement in energy absorption capability exhibits a specific energy absorption over two times greater than that of un-quilted plain weaves. In addition, it was found from the images obtained from the high-speed camera that yarn quilting is effective in resisting yarn pull-out during a ballistic event, enabling more energy to be absorbed by the fabric system. Numerical predictions showed that thread quilting enlarges the area of stress distribution and the transverse deflection, and consequently enable the quilted systems to absorb more energy than the unquilted system shortly after impact. When the constituent layers were quilted together in a panel, the system acted as integrity during the energy dissipation process even though the individual layers were damaged by the projectile.

Ускоренная оценка влияния технологических факторов на прочностные характеристики Ti-6Al-4V И Al-Cu-Mg

Introduction. The strength of construction materials when used under cyclic loads is of great importance in design engineering. A significant number of factors that affect the fatigue resistance have predetermined the creation of numerous methods that consider such influence. Nondestructive methods that are based on the connection of the physical degradation of material with strain properties enable evaluating experimentally the fatigue properties of materials. Purpose of study: the analysis of the processes of energy dissipation and strain accumulation during the inelastic cyclic strain of samples, using the VT6 (Ti-6Al-4V) titanium alloy and the D16 (Al-Cu-Mg) aluminum alloy before and after the technological impact. The work experimentally investigates the physical processes of degradation of the VT6 and D16 alloy samples that accompany the process of fatigue failure in materials with homogeneous and inhomogeneous stress-strain states in the concentrator (in the form of a hole and a weld). Typical modes are used to reach the fatigue testing that determine the critical stress in a material sample – the stress at which physical properties (temperature, strain) change without reaching the fatigue failure of samples. Critical stress amplitudes in the cycle, based on the data obtained during the experiment and the results of mathematical simulation, are compared. The effect of stress concentrators on critical loads that a detail can withstand after a unit operation is estimated by the finite-element method (FEM). As a result, the effect of the operational and technological factors on critical stress determined by strain and temperature is estimated. Comparative tests of the VT6 and D16 alloy samples with and without stress concentrators showed that the amplitudes of critical stress decrease by more than 30% in comparison with the ones that are without stress concentrators. The low-cycle fatigue tests of the D16 alloy samples are carried out. Mathematical simulation of the cyclic strain of the samples is carried out using MSC.Marc package. The results of the cyclic loading tests, which show that the characteristics of the technological process reduce the amplitudes of the critical stress of the VT6 and D16 alloys and affect the fatigue properties of the D16 aluminum alloy, are discussed. Mathematical simulation corresponded positively to the experimental data. Such correspondence indicates the possibility of conducting qualitative numerical assessments of the beginning of the inelastic strain accumulation process in structures with stress concentrators under the cyclic stress and the increasing stress amplitude, using the typical sample made of hardening elastoplastic material.

Thermodynamic modeling of stress–strain behavior of saturated sand considering temperature effect

Based on the thermodynamic process of granular matter, considering the influence of temperature on energy dissipation at the mesoscopic level, a thermodynamic constitutive model, which can describe the thermal properties of saturated sand, is proposed in this paper. The model adopts the idea of double entropy theory, which introduces the concept of granular entropy to reflect the energy dissipation at the mesoscopic level. The energy dissipative structure composition and the related migration coefficient relationships are determined theoretically. Combined with the thermodynamic differential equation and the conservation and entropy increase equations, the thermodynamic identity is established; then, the mathematical expression of effective stress, plastic deformation, and granular temperature motion including the temperature effect are deduced accordingly. The relationship between the mesoscopic energy dissipation process caused by temperature change and macro-mechanical behavior is established by means of migration coefficient relationships and the energy function model. In addition, the dilatancy equation considering the state parameters is combined with the model parameters, so the stress–strain behavior of saturated sand considering the temperature effect can be described. The ability of the model to describe the thermal properties of saturated sand is verified by comparing the simulation results with the heating-induced volume change and triaxial undrained shear test results.

Negative Aspects Regarding the Ductile Seismic Design Concept of the Pure Moment Resisting (MR) Reinforced Concrete (RC) Frame Systems (A Theoretical Study)

Abstract Seismic activity in the last two decades validate the urgent improvement requirement of the ductile seismic design concept for the MR RC frame structures. This necesity of improvement comes from the unfavorable recorded seismic response of the MR RC frame structures required to on-site seismic actions. The same observations and conclusions (regarding the soft storey (Ground Floor (GF) or Current Floor (CF)) mechanism development and the seismic energy dissipation process in the RC columns marginal zones) were registered in the analytical research and the experimental studies on seismic platforms. The fragile rupture mechanism of the vertical structural elements produces the segmentation of the superstructure into rigid and fragile segment portions. In these conditions, the fundamental seismic response mechanisms and the seismic design elements of the MR RC frame structures found in current practice and considered in actual seismic design standards are specified through comparative methods. In the final chapter of the current theoretical research study, it were specified the main conclusions and immediate improvement necessity of the ductile seismic design concept for MR RC frame system.

Seismic design of reinforced concrete frame structure based on structural energy analysis

Different from the traditional seismic design method based on bearing capacity and displacement, the energy method can consider the cumulative plastic damage caused by earthquake duration, which is a relatively perfect seismic design method and has attracted wide attention. Based on the principle of energy balance, through the analysis of hysteretic energy consumption and its interlayer distribution, we can find out the weak parts of the structure and make an effective qualitative evaluation of the seismic performance of the structure. By calculating the inter-story damage index of the structure, the seismic performance of the frame structure can be effectively and quantitatively evaluated. Example analysis shows that the energy response distribution of the structure is closely related to the selection of damping model, and the seismic response and damage process of the structure are closely related to the energy absorption and dissipation process of the structure.

Wave Energy Dissipation in a Shallow Coral Reef Lagoon Using Marine X‐Band Radar Data

AbstractA novel approach for estimating wave energy dissipation on a coral reef barrier is studied using X‐Band radar technology. The prominent features of coral reefs, including the delineation of reef morphological structure, wave energy dissipation and wave transformation processes are obtained in a reef lagoon in San Andres Island, Colombia. Results show that reef attenuates incident waves by approximately 75% due to both frictional processes and wave breaking, with an equivalent bottom roughness of 0.20 m and a wave friction factor of 0.18. These parameters are comparable with estimates reported in other shallow coral reef lagoons as well as at seagrass meadows obtained using in‐situ measurements. Also, the mean height of the reef elements Hbed and its standard deviation σb are also estimated in the entire radar coverage area. Hbed and σb (0.5 and 7.66 cm respectively) are in the same order of magnitude of measured data reported by previous studies and in good agreement with the geometric parameters proposed by in‐canopy flow models for branched species, such as Stylophora and Pocillopora, which are also common in the coral carpets of San Andres Island. This work proposes a completely novel use for X‐Band radars by describing prominent features in barrier‐reef systems including the delineation of the reef structure and wave energy dissipation.

Slope threshold for overland flow resistance on sandy soils

AbstractRecent research on rill flows recognised that an 18% slope can be used to distinguish between ‘gentle’ and ‘steep’ slope cases for the detected differences in hydraulic (flow depth and velocity) and sediment transport variables (flow transport capacity, actual sediment load). The effects of slope on flow velocity, friction factor and transport capacity and their interactions affect process‐based erosion modelling. The main aim of this paper is to investigate, for the first time, how slope affects the overland flow resistance on sandy soils, which are characterised by loose particles readily available to be transported and deposited. Using literature measurements carried out in sandy soils for both gentle and steep slopes, a theoretical overland flow resistance equation, based on the integration of the power velocity distribution, is tested. The relationship between the velocity profile parameter Γ, the channel slope, the Reynolds and Froude number is calibrated using measurements characterized by a wide range of hydraulic conditions and distinguishing between gentle (5.2%–13.2%) and steep (17.4%–42.3%) slope conditions. The analysis demonstrated that: (1) the parameter Γ can be accurately estimated by Equation (15) in which the exponents are independent of slope condition; (2) the coefficient a of Equation (15) is equal to 0.8750 and 0.8984 for the gentle and steep slope condition, respectively; (3) the estimations of the Darcy–Weisbach friction factor f (Equation 19) are accurate and characterised by errors less than or equal to ±5% for 97.2% of cases; and (4) in the range of steep slopes, the flow resistance law calibrated for the gentle slope condition (Equation (19) with a = 0.8750) systematically overestimates the f value. In conclusion, this study allowed the recognition, for an unlimited soil detachment condition and an overland flow, of how the energy dissipation processes and the estimate of the friction factor are affected by slope.Highlights A theoretical overland flow resistance law is tested by data obtained on sandy soils. Differences between gentle and steep slope conditions are investigated. The Darcy–Weisbach friction factor estimate by the flow resistance law is accurate. The law calibrated for gentle slopes overestimates f in the range of steep slopes.

Viscosity Approximation of PDMS Using Weibull Function.

The viscosity of a fluid is one of its basic physico-chemical properties. The modelling of this property as a function of temperature has been the subject of intensive studies. The knowledge of how viscosity and temperature variation are related is particularly important for applications that use the intrinsic friction of fluids to dissipate energy, for example viscous torsional vibration dampers using high viscosity poly(dimethylsiloxane) as a damping factor. This article presents a new method for approximating the dynamic viscosity of poly(dimethylsiloxane). It is based on the three-parameter Weibull function that far better reflects the relationship between viscosity and temperature compared with the models used so far. Accurate mapping of dynamic viscosity is vitally important from the point of view of the construction of viscous dampers, as it allows for accurate estimation of their efficiency in the energy dissipation process.

Tiny yet tough: Maximizing the toughness of fiber-reinforced soft composites in the absence of a fiber-fracture mechanism

Tiny yet tough: Maximizing the toughness of fiber-reinforced soft composites in the absence of a fiber-fracture mechanism

Experimental studies of the energy dissipation processes at the tops of fatigue cracks in the elements of bridge structures

In the article, the authors investigated the possibility of using the thermal control method for diagnosing fatigue cracks in the metal superstructure, determined the necessary parameters for that control method. The studies were conducted during cantilevered steel samples fatigue tests simulating the superstructure beam wall operation, reinforced with stiffening ribs. To carry out the experiments were developed a test setup and a loading procedure at the various intensity of exposure. An electric motor with eccentrics is used as a loading device. The sample surface heating was recorded by thermal imagers with 0.03 K and 0.05 K temperature sensitivities and 60 frames/s and 9 frames/s shooting speed, respectively. Was confirmed the possibility of determining crack presence before its emergence to the surface namely at the stage of its initiation, and also were determined the self-heating zone dimensions at the tip of a crack. The conducting a laboratory experiment technique on the dissipative processes study in the metal superstructure elements is described.

Relativistic mechanics and thermodynamics. III. Rotation

A covariant four-tensor rotation equation—for bi-dimensional composite body—, by generalising cross product to four-vectors, is obtained. From it, a relativistic angular impulse-angular momentum variation equation (Poinsot–Euler rotation equation) and its pseudo-work-rotational kinetic energy variation equation (Poinsot–Euler pseudo-work equation), are obtained for a body spinning—with constant angular momentum direction—by external torques. Two rotational processes are analysed by using this four-tensor formalism—completed by a four-vector fundamental equation (Newton’s second law and thermodynamics first law)—: a rotating body subjected to conservative and friction forces torque—a mechanical energy dissipation process—, and a device spinning by torque produced by chemical reactions—a mechanical energy production process.

Development of quality control and structure parameters determination methods for large size products from sintered hard alloys WC-(Co+Ni+Cr) based on analysis of the ultrasonic oscillations spreading parameters

The object of research is hard alloys with a morphology of the carbide phase skeleton structure, in which particles contact with each other, and the gaps between them are filled with a binder phase. The mechanical and service characteristics of such materials depend on the degree of development of the skeleton structure. One of the most problematic areas is the lack of non-destructive methods for determining the parameters of the structure. The introduction of such techniques will allow obtaining objective information on the structure of the material and using it to evaluate the quality of products. In the course of the study, the parameters of the scattering of elastic vibrations in inhomogeneous media were determined. The main hypothesis of the study is the assumption that the processes of energy dissipation occur both in the structural elements themselves (carbide grains and bond areas) and at their boundaries. Therefore, the evaluation of dissipation processes will allow obtaining a quantitative estimation of the alloys structure parameters, and will allow assessing the quality of the material. The following characteristics were chosen as the parameters characterizing the propagation of ultrasonic oscillations: the speed of the oscillations propagation, the scattering background level in relation to the amplitude of the bottom reflection, the oscillations attenuation coefficient. The parameters were determined and compared with the characteristics of the quality of the products and the parameters of the microstructure, which were determined by the methods of quantitative metallography and the statistical characteristics of the relationship between the parameters, were determined. As a result, new quality control procedures for carbide products have been developed. The contiguity characteristics of the carbide skeleton of the sintered cemented carbide were determined by measuring the propagation speed of ultrasonic oscillations. The assessment of the level of porosity with a pore size of less than 1 mm was carried out according to the results of measuring the relative amplitude of the background scattering of ultrasonic oscillations. The proposed methods are non-destructive and are carried out in one cycle with ultrasonic flaw detection, to which 100% of the products are subjected. These techniques have been introduced in the production of carbide rolls by the method of controlled hot vacuum pressing. They have become an integral part of the quality control system for carbide rolls.

Rigidity Bridging Flexibility to Harmonize Three Excited-State Deactivation Pathways for NIR-II-Fluorescent-Imaging-Guided Phototherapy.

Small organic phototherapeutic molecules of the second near-infrared (NIR-II) window (1000-1700 nm) serve as promising candidates for theranostics. However, developing such versatile agents for fluorescence-guided photodynamic/photothermal therapy remains a demanding task stirred by competitive energy dissipation pathways, including radiative decay, internal conversion, and intersystem crossing. To the best of current knowledge, the current paradigm for addressing the issue has deliberately approached the optimum balance among three deactivation processes through offsetting from each other, possibly leading to a comprehensively compromised theranostic efficacy. Few reports aim to modulate the three deactivation pathways excluding sacrificing any one of them. Herein, a molecular design strategy to construct a phototherapeutic organic fluorophore CCNU-1060, armed with NIR-II luorescence-guided phototherapeutic properties, is rationally developed. With a flexible motor, tetraphenylethene, bridged to the rigidified coplanar core boron-azadipyrromethene, the desired CCNU-1060 is subsequently encapsulated into an amphiphilic matrix to form CCNU-1060 nanoparticles (NPs), which match or transcend its precursor NJ-1060 NPs in the three energy dissipation processes. CCNU-1060 NPs are utilized to realize high-spatial vessel imaging and effective NIR-II fluorescence-guided phototherapeutic tumor ablation. This study unlocks a viewpoint of molecular engineering that simultaneously regulates multiple energy dissipation pathways for the construction of versatile phototherapy agents.

Numerical modelling study of a modified sandbag system for ballistic protection

Modern field fortification systems are very large and cause a logistical burden during setup, thus setting the requirement for their modification. A simulation study was conducted to study the correlation between the compaction of sand and the energy absorbed by it when impacted by a solid steel projectile at 850 m/s. Furthermore, the sandbag was modified by the addition of plates in the system to observe the change in projectile penetration and the energy absorption behaviour of the sand. The factors considered for this study were the plate thickness (15 mm, 25 mm), plate material (aluminium, concrete, plexiglass, polycarbonate, steel) and plate location (226 mm, 236 mm, 256 mm from the point of impact). It was observed that a layer of compressed sand is formed around the projectile, aiding the energy absorption and dissipation process during impact. Upon addition of the plate, it was observed that the modified system (plate and sand) absorbed maximum energy when the plate is placed closest to the point of maximum penetration without the plate. It was also noted that the addition of the plate enhanced energy absorption characteristics of the system compared to conventional sandbags because of increased compaction of sand. From the study, it was observed that the plexiglass and polycarbonate plates had the maximum energy absorption and maximum deformation. The steel plate had the least energy absorption and minimal deformation. Concrete and Aluminium had comparable areal density, energy absorption and lowest deformation, making them the preferred choice of plate material for a modified sandbag. The numerical studies were verified using a gas gun and a modified sandbag with Aluminium plates to show that the addition of a plate improves compaction behaviour of sand.

Real-time hybrid simulation framework for the investigation of soil-structure interaction effects on the vibration control performance of shape memory alloys

Shape memory alloys (SMAs) are two-phase polycrystal smart materials with hysteretic energy dissipation capacity. Under a mechanically applied strain, SMAs can transform their phases and recover large deformations in a superelastic fashion. Both the hysteretic damping and the deformation recovery are key features for new type of maintenance-free vibration control devices. Various factors influence the energy dissipation process of SMAs. Particularly rates and amplitudes of the applied deformation pattern are crucial for the damping. The studies have focused so far on the interaction between structures and SMAs. This paper goes one step further and seeks to consider the soil-structure interaction (SSI) in the treatment of the SMA control performance as well. A real-time hybrid simulation based cyber-physical methodology is developed for this purpose. Using finite-element modeling technique, a semi-infinite boundary definition is realized for the soil and the soil-foundation interaction is replicated for SMA-controlled structures. The proposed approach is applied to a shear frame structure equipped with SMA wires. The responses of the structure to historic earthquake records are assessed from a macroscopic perspective of the SMA behavior. The study shows that the material and radiation damping of the soil-foundation interaction have a significant influence on the vibration control performance of SMAs.