Energy Dissipation Theory Research Articles

Damage Constitutive Model Based on Energy Dissipation for Frozen Sandstone Under Triaxial Compression Revealed by X-Ray Tomography

A series of triaxial compression tests, with real-time computed tomography (CT) scanning performed in the loading process, were conducted on frozen sandstones at confining pressures of 0, 1, 2, and 3 MPa at different temperatures of −2, −6, −10, and 20 °C, respectively. The experimental results indicate that the strength of frozen sandstone increases with a decrease in temperature. The strength of frozen sandstone increases with an increase in the confining pressure at freezing temperatures. In the loading process, the evolution law of the CT value of the whole sandstone is explored, and three-dimensional reconstruction of CT images, which denote postfailure models of frozen sandstone, is also performed. According to energy dissipation theory, an isotropic damage variable is introduced. Based on the CT value of the whole sandstone, the concept of the compaction coefficient K, which describes the compaction degree, is proposed to modify the damage model obtained by Lemaitre’s strain equivalence hypothesis. The validity of the model is verified by comparing its computed results with the experimental results obtained from triaxial compression tests. The results indicated that the modified damage model can adequately predict the stress-strain relationship of the frozen sandstone.

Dynamic fracture and energy consumption characteristics of coal-series sandstone after heat treatment

In this paper, the dynamic loading tests of sandstone after heat treatment at 25-800?C are carried out by using the split Hopkinson pressure bar test system. Combined with the theory of energy dissipation, the dynamic fracture and energy consumption characteristics of coal-series sandstone are systematically studied. The test results illustrate that the dynamic fracture and energy consumption characteristics of sandstone are mainly related to the changes of internal moisture and cementing materials.

Study on Catastrophe Instability of Support System in Gypsum Goaf Based on Energy Dissipation Theory

The stability of the goaf support system is the key to safe production in gypsum mines. Therefore, this study constructed a pillar-beam support system which contained pillar plastic zones. In this support system, the beam and pillar were taken as energy releaser and energy dissipater, respectively. Through establishing a cusp catastrophe model based on energy theory, the new criterion for instability was obtained which is related with geometric stiffness and system energy dissipation. The results indicate the instability of the support system is caused by the incompatibility of energy release, dissipation, and geometric deformation. When K > 1, the energy released by the support system is compatible with geometric deformation. The support system experiences a quasistatic process from the static state in bottom page to the static state in top page along Path I. When K < 1, the energy released by the support system cannot be in tune with geometric deformation. The support system experiences a catastrophe process along Path II. The evolution from the static state in bottom page to the static state in top page is not progressive, but catastrophic. The redundant energy released in this process leads to mechanical instability of the support system. This study provided theoretical foundation for the mining and treatment of mines. Based on actual engineering examples, the sensitivity of the geometric parameters of the support system was analyzed as well. These parameters are ranked by their sensitivity from high to low, as is shown below: beam thickness, plastic zone width, room span, pillar width, and pillar height. Then, the goaf was classified according to the geometric parameters. Energy catastrophe theory was applied to analyze the stability of the support system in different classes of goaf. The analysis results showed that Class D goaf should be labeled as the unstable zone, which was consistent with the result of field research. To conclude, energy catastrophe theory can be used to demonstrate the nonlinear mechanical mechanism of support system instability in room-pillar mining goaf.

Prediction of electrical contact endurance subject to micro-slip wear using friction energy dissipation approach

Fretting wear is a common cause of failure of an electrical contact (EC). In this study, we analyzed in detail the failure of EC induced especially by sliding using the representative electrical terminals. Furthermore, combining the friction energy dissipation theory, we proposed a prediction model to evaluate the electrical connector endurance (ECE) based on the contact stress and geometrical changes during the wear process obtained from a numerical model. The study helps establish that the friction energy dissipation theory is a powerful tool to analyze a contact failure due to wear. The proposed model proves to be effective in predicting the ECE for all considered cases such as micro-slip amplitude, contact force, overturning angle, superficial layer thickness, and friction/wear coefficients.

Numerical simulation on fracture resistance and factors affecting toughness for welded joint of low-alloy steel

Crack propagation resistance for welded joint was numerically simulated by ABAQUS software, where compact tensile (CT) specimens with different thickness and depth of side groove were taken to discuss the variation and reliability of results. It is found that the critical fracture toughness Jc increases with the thickness and then decreases gradually to the plane strain fracture toughness. The equivalent thickness Beq was put forward by numerical simulation. Strain energy density and the volume of plastic deformation zone were calculated to explain the effect of thickness on Jc based on the theory of energy dissipation. The simulated results revealed that another critical geometry factor like the depth of side groove up to 25% of total thickness contributed to a smaller J integral distribution gradient. The CT specimen with suitable geometry size was obtained according to the numerical results, which helps in guiding the experimental test of fracture toughness. The simulation results of fracture resistance demonstrate a good consistency with experiments, showing that numerical model is of high reliability, and stable Jc could be achieved at suitable specimen size.

Microscopic Theory of Energy Dissipation and Decoherence in Solid-State Quantum Devices: Need for Nonlocal Scattering Models.

Energy dissipation and decoherence in state-of-the-art quantum nanomaterials and related nanodevices are routinely described and simulated via local scattering models, namely relaxation-time and Boltzmann-like schemes. The incorporation of such local scattering approaches within the Wigner-function formalism may lead to anomalous results, such as suppression of intersubband relaxation, incorrect thermalization dynamics, and violation of probability-density positivity. The primary goal of this article is to investigate a recently proposed quantum-mechanical (nonlocal) generalization (Phys. Rev. B 2017, 96, 115420) of semiclassical (local) scattering models, extending such treatment to carrier–carrier interaction, and focusing in particular on the nonlocal character of Pauli-blocking contributions. In order to concretely show the intrinsic limitations of local scattering models, a few simulated experiments of energy dissipation and decoherence in a prototypical quantum-well semiconductor nanostructure are also presented.

Experimental study on energy dissipation characteristics of adiabatic shear evolution in high-speed machining of U75V steel

As one of the main characteristics in high-speed machining process, the adiabatic shear evolution induced energy dissipation influences the development of serrated chip and tool failure, which was further investigated experimentally in this work. Through the high-speed machining experiment of U75V rail steel by applying the cemented carbide insert, the development of chip morphology accompanying with the adiabatic shear evolution and tool failure with the cutting speed increasing were investigated microscopically. Based on the adiabatic shear saturation limit analysis, the energy dissipation theory was further proposed to evaluate the energy dissipation accumulation and energy dissipation rate of adiabatic shear evolution. The influences of energy dissipation characteristics related to physical and mechanical properties on the tool failure were revealed and discussed. It was concluded from the analysis of experimental results that the energy dissipation of adiabatic shear evolution from adiabatic shear banding to fracture, resulting in the thermal and mechanical coupling, mainly influenced the mechanisms of tool failure on the rake face. The occurrence of adiabatic shear fracture weakened the friction effect on the rake face. The energy dissipation theory of adiabatic shear evolution reasonably assessed the tool failure characteristics in high-speed machining process.

A NOVEL EVALUATION APPROACH FOR SHALE BRITTLENESS INDEX

Brittleness index (BI) is a key parameter used for reservoir fracability evaluation and "sweet spot" search in shale gas exploration. The existing assessment methods cannot guide the fracturing design and field treatment due to their insufficient theoretical foundation and neglect on the influences of engineering factors. This study aims to solve this problem by using the thermodynamics criterion in nonlinear fracture mechanics. First, the quantitative relationship between energy loss and rock brittleness was investigated during fracture propagation. The nonlinear plastic deformation at the crack tip was then simplified into an ideal line elastic condition by using the equivalence principle. In addition, the numerical equation for surface pressure was fitted by the monadic regressive method. A case study was conducted to compare the obtained BI using common methods and the proposed one. Results demonstrate that energy dissipation theory is recommended to describe the essence of nonlinear rock deformation. Moreover, a higher BI indicates more occurrences of microseismic events. The monitoring data fitted with the conclusion well, which verify the applicability of the proposed evaluation method. Furthermore, the average BIs of the two wells used in this study are 48% and 62%, which shows obvious positive correlation with production. The proposed model can be regarded as a good reference for BI evaluation in shale reservoirs. Keywords: Brittleness index, Shale gas, Hydraulic fracturing, fracability

Linking chloroplast relocation to different responses of photosynthesis to blue and red radiation in low and high light-acclimated leaves of Arabidopsis thaliana (L.).

Low light (LL) and high light (HL)-acclimated plants of A. thaliana were exposed to blue (BB) or red (RR) light or to a mixture of blue and red light (BR) of incrementally increasing intensities. The light response of photosystem II was measured by pulse amplitude-modulated chlorophyll fluorescence and that of photosystem I by near infrared difference spectroscopy. The LL but not HL leaves exhibited blue light-specific responses which were assigned to relocation of chloroplasts from the dark to the light-avoidance arrangement. Blue light (BB and BR) decreased the minimum fluorescence ([Formula: see text]) more than RR light. This extra reduction of the [Formula: see text] was stronger than theoretically predicted for [Formula: see text] quenching by energy dissipation but actual measurement and theory agreed in RR treatments. The extra [Formula: see text] reduction was assigned to decreased light absorption of chloroplasts in the avoidance position. A maximum reduction of 30% was calculated. Increasing intensities of blue light affected the fluorescence parameters NPQ and qP to a lesser degree than red light. After correcting for the optical effects of chloroplast relocation, the NPQ responded similarly to blue and red light. The same correction method diminished the color-specific variations in qP but did not abolish it; thus strongly indicating the presence of another blue light effect which also moderates excitation pressure in PSII but cannot be ascribed to absorption variations. Only after RR exposure, a post-illumination overshoot of [Formula: see text] and fast oxidation of PSI electron acceptors occurred, thus, suggesting an electron flow from stromal reductants to the plastoquinone pool.

Shearing Performance of Lime‐Reinforced Iron Tailing Powder Based on Energy Dissipation

The resource utilization of iron tailing powder is an effective measure to reduce the risk of tailing stacking. Based on the research findings on lime soil, a method for using lime to strengthen iron tailing powder was proposed. F-s curves and c and φ values of iron tailing powder with 0%, 2%, 4%, 8%, and 10% lime were obtained through direct shear tests. The back propagation (BP) neural network algorithm was used to fit the F-s curve, and the fitting equation that met the accuracy requirement was obtained. Based on the energy dissipation theory, the shear failure energy dissipation of iron tailing powder with different lime doses was achieved in the form of definite integrals under different normal stresses of 100 kPa, 200 kPa, 300 kPa, and 400 kPa, respectively. It was concluded that the addition of lime could increase the shear energy dissipation of iron tailing powder. The shear energy dissipation of iron tailing powder first increased and then decreased with the increase in lime dose. The maximum value was reached with 4% lime, and the energy dissipation increased linearly with increasing normal stress. In this study, the shear performance of lime‐reinforced iron tailing powder was studied through the direct shear test combined with the energy dissipation theory, providing a theoretical basis for the resource utilization of iron tailing powder.

Estimation of Crack Initiation and Propagation Thresholds of Confined Brittle Coal Specimens Based on Energy Dissipation Theory

A new energy-dissipation method to identify crack initiation and propagation thresholds is introduced. Conventional and cyclic loading–unloading triaxial compression tests and acoustic emission experiments were performed for coal specimens from a 980-m deep mine with different confining pressures of 10, 15, 20, 25, 30, and 35 MPa. Stress–strain relations, acoustic emission patterns, and energy evolution characteristics obtained during the triaxial compression tests were analyzed. The majority of the input energy stored in the coal specimens took the form of elastic strain energy. After the elastic-deformation stage, part of the input energy was consumed by stable crack propagation. However, with an increase in stress levels, unstable crack propagation commenced, and the energy dissipation and coal damage were accelerated. The variation in the pre-peak energy-dissipation ratio was consistent with the coal damage. This new method demonstrates that the crack initiation threshold was proportional to the peak stress (σ p) for ratios that ranged from 0.4351 to 0.4753σ p, and the crack damage threshold ranged from 0.8087 to 0.8677σ p.

On strain-rate independent damping in continuum mechanics

Strain-rate independent damping is a theory of energy dissipation in solids. It is based on the assumption that an increase or decrease in the strain-energy density correlates with a multiplication of 1+η or 1-η respectively, of the material stiffness matrix, with 0≤ η <<1 with η either a constant or a function of the strain-energy density.This type of damping has a loss (Watt m-3) of η times the absolute value of the rate of change of the strain-energy density. For uni-axial strain and a suitable function of the strain-energy density, the energy dissipation (Joule m-3) due to an infinitesimal change of the strain is strain-rate independent and proportional to the absolute value of the strain raised to a power ranging from 1 to 2. This is an idealization of tests results, based on forced harmonic strain cycles, with an energy dissipation (Joule m-3 cycle-1) found to be nearly frequency independent and almost proportional to the strain amplitude raised to a power ranging from 2 to 3.The PDEs derived for strain-rate independent damping can be solved for 1, 2 or 3 dimensions via direct integration, provided that the software supports PDE coefficients that are functions of the solution and its space and time derivatives. A 3D problem with 22,000 DOF's and 10,000 time steps was solved successfully and convincingly.

Effect of surface mechanical attrition treatment on low cycle fatigue properties of an austenitic stainless steel

In order to study the influence of surface mechanical attrition treatment (SMAT) on low cycle fatigue (LCF) properties of an austenitic stainless steel AISI 316L, cyclic loading responses and fatigue lifetime are investigated using fully reversed tension-compression LCF tests under total strain control. The results reveal that SMATed material exhibits higher cyclic stress amplitude due to higher strength of the SMAT affected region. During cyclic loading, untreated material is hardened under high strain amplitude (±0.8%, ±1.25%), but softened under low strain amplitude (±0.5%). In contrast, SMAT affected region undergoes cyclic softening. Furthermore, SMAT mainly affects cyclic behavior of the early stage of LCF, and its effect is gradually reduced as cyclic loading goes on. Fatigue lifetime analysis indicates that SMAT could decrease the fatigue lifetime of material under cyclic loading with high strain amplitude (±1.25%). Based on analysis using Coffin-Manson law and energy dissipation theory, this lifetime decrease is considered to be due to the decrease of ductility and fatigue damage capacity.

An Entropy-Assisted Shielding Function in DDES Formulation for the SST Turbulence Model

The intent of shielding functions in delayed detached-eddy simulation methods (DDES) is to preserve the wall boundary layers as Reynolds-averaged Navier–Strokes (RANS) mode, avoiding possible modeled stress depletion (MSD) or even unphysical separation due to grid refinement. An entropy function fs is introduced to construct a DDES formulation for the k-ω shear stress transport (SST) model, whose performance is extensively examined on a range of attached and separated flows (flat-plate flow, circular cylinder flow, and supersonic cavity-ramp flow). Two more forms of shielding functions are also included for comparison: one that uses the blending function F2 of SST, the other which adopts the recalibrated shielding function fd_cor of the DDES version based on the Spalart-Allmaras (SA) model. In general, all of the shielding functions do not impair the vortex in fully separated flows. However, for flows including attached boundary layer, both F2 and the recalibrated fd_cor are found to be too conservative to resolve the unsteady flow content. On the other side, fs is proposed on the theory of energy dissipation and independent on from any particular turbulence model, showing the generic priority by properly balancing the need of reserving the RANS modeled regions for wall boundary layers and generating the unsteady turbulent structures in detached areas.

Gravitational Effect on a Fiber-Reinforced Thermoelastic Medium with Temperature-Dependent Properties for Two Different Theories

A general model of equations of the three-phase-lag model and thermoelasticity without energy dissipation theory was used to study the effect of the gravity field on a fiber-reinforced thermoelastic half-space. The material is a homogeneous isotropic elastic half-space. Normal mode analysis was used to get the exact expressions for the displacement components, force stresses and temperature. The variations of the considered variables with the horizontal distance were illustrated graphically. Comparisons were made with the results of the two theories in the absence and presence of the gravity field as well as the reinforcement. A comparison was also made between the results of the two theories with and without temperature-dependent properties.

A constitutive model of frozen saline sandy soil based on energy dissipation theory

A series of triaxial compression tests are carried out for frozen saline sandy soil with Na2SO4 contents 0.0, 0.5, 1.5, and 2.5% under confining pressures from 0 MPa to 16 MPa at −6 °C, respectively. The test results indicate that, the Critical State Line (CSL) of frozen saline sandy soil is curve and is not through the origin in (p,q) plane, and the soil particles have the properties of initial anisotropic rotational angle and loaded anisotropy in process of loading. In order to describe the deformation properties of frozen saline sandy soil, a new double yield surface constitutive model is proposed based on the triaxial compression tests in this paper. The proposed model contains the influence of salt contents on mechanical characteristics, so it is suitable for describing the stress–strain relation of frozen saline soil. The proposed model has the following properties: (1) By defining a modified effective stress p∗, a critical state strength envelope function is established according to the Modified Cam Clay model. The envelope approximates a straight line under low confining pressures, but it is curve downward under high confining pressures due to pressure melting. (2) The effect of the initial anisotropic rotational angle and loaded anisotropy, during process of loading under plastic volumetric compression mechanism, on yield surface of rotational hardening is taken into account. (3) A paraboloid yield surface function, including the rotational hardening law induced by loading, is proposed under plastic shear mechanism. The universality of the proposed model is verified by the test results of frozen saline sandy soil under different stress paths. Finally, in order to further study the applicability of the proposed model in this paper, the stress–strain relation of the cemented clay is simulated by it. And the influences of the pressure melting phenomenon and the rotational hardening rule on the calculated results of the proposed model are investigated. The research results indicate that the proposed model can simulate not only the mechanics properties of materials whose CSL is straight but also those of materials whose CSL is curved, other than predict the deformation regularity of frozen saline sandy soil well.

Influence of the mechanical force and the magnetic field on fibre-reinforced medium for three-phase-lag model

AbstractA new theory of generalised thermoelasticity has been constructed by taking into account the deformation of a fibre-reinforced isotropic thermoelastic medium. A general model of the equations of the formulation in the context of the three-phase-lag model and Green–Naghdi theory without energy dissipation theory are applied to study the influence of a mechanical force, temperature dependent and a magnetic field on the wave propagation within a fibre-reinforced isotropic thermoelastic medium. The exact expressions of the displacement components, temperature and stress components are obtained using normal mode analysis. The variations of the considered variables with the horizontal distance are illustrated graphically for different values of a mechanical force. Comparisons are made between the results of the two theories in the presence and absence of a magnetic field as well as temperature-dependent properties.

Energy-Saving Analysis of Fly Ash Autoclaved Aerated Concrete Block Filler Wall

Taking a six-story glass bead thermal insulation concrete frame structure building in Kangding, Sichuan as model, to design filler wall composing of fly ash autoclaved aerated concrete block. Utilizing energy dissipation theory analyzes the building energy consumption. Conclusion: The glass bead thermal insulation concrete frame structure of fly ash autoclaved aerated concrete block filler wall meets the requirement of Sichuan residential building energy-saving code.

On the theory of two-temperature thermoelasticity without energy dissipation of Green–Naghdi model

This work introduces one-dimensional numerical application of an elastic and isotropic half space in which the governing equations have been taken in the context of the two-temperature thermoelasticity without energy dissipation theory to show the effects of the two-temperature parameter on all the studied fields and to stand on the contributions of this theory. The results of this work confirmed that the two-temperature thermoelasticity without energy dissipation is valid when the thermo-dynamical temperature and the temperature of the heat conduction are not coinciding.

The Reinforcing Mechanism of Recycled Glass Fibers and Milled Glass Fibers in Polypropylene Composites

A great amount of work has been done over the past few years to use the glass fibers reinforcing polypropylene (PP) composites. Due to the sharp resources recovery, and the global demand for fiber materials, there has been growing interest in the use of the recycled glass fibers (GF) (RGF) as an alternative. This work focuses on the reinforcing mechanisms of the glass fibers in PP composites. The reinforcing mechanism is evaluated by scanning electron microscopy (SEM) on the basis of the energy dissipation theory. The GF are the excellent supporting bodies. Interfacial debonding, fiber pullout and breakage dissipate tremendous energy. These factors cause improvements in the strength of the RGF/PP and MGF/PP composites.