Энергия деформирования в слоистой среде при ударном нагружении (на примере автомобильных дорог)

An anomaly in the necking and fracture behaviour of polyethylene under constant uniaxial tensile loading has been reported in several papers1–3. At a certain stress level, the almost instantaneous fracture of the neck formed at high loads was replaced by the formation of a neck that resisted fracture for a considerable time. This marked transition was observed for high density polyethylenes of comparatively high molecular weight. A hypothesis has been proposed to explain the appearance of the marked transition: 1. At high strain rates, large stresses concentrate to the taut tie chains between the crystallites, favouring fracture processes. At lower strain rates, the molecules rearrange in a way that distributes the local stresses more evenly over the structure which then deforms further rather than fracturing. 2. Owing to the high concentration of the chains in the high density, high molecular weight polyethylenes, the transfer of stresses and deformations between adjacent crystallites is very efficient. Therefore the structure has a good resistance towards fracture and the deformation of different lamellar regions occurs cooperatively. 3. The marked transition is a result of both (a) the rapid formation of high strength fibrillar structure, which is partly due to reasons given in item 2 of this hypothesis, and (b) the influence on the strength of the strain rate in accordance with item 1 of the hypothesis. At the marked transition, the maximum in the local strain rate is about the highest tolerable for the actual structure without macroscopic fracture. When an element of the specimen passes the maximum in local strain rate the probability for fracture of this element decreases due to the decreasing strain rate and to the continuous formation of a high strength fibrillar structure. In addition, e.g. the rise in local temperature in the neck caused by dissipation of deformation energy,may affect the necking and fracture behaviour.

This research delves into the transfer and loss of energy in a discrete mass when subjected to forced vibration. Using discrete element method (DEM), we analyzed the dynamic behavior of regular spherical granular assemblies and the energy distribution characteristics under different excitation frequencies and reduced accelerations. Moreover, the energy transfer and dissipation process of granular assemblies under different vibration states are studied using an experimental method. The results show that the granular assemblies will produce collision energy dissipation, thermal energy dissipation, acoustic energy dissipation and other forms of energy dissipation in the forced vibration state and the proportion of different energy dissipation under different excitation is given. The collision and friction of granular assemblies are the key to affecting other forms of energy dissipation. When the excitation increases, the energy dissipation forms are generated inside the granular assemblies, and the proportion of collision energy dissipation of the granular assemblies increases. The acoustic energy above 20 kHz occupies the main part of the acoustic energy dissipation. Thermal energy consumption always exists, which takes a long time to play a role. The granular also have other forms of energy loss, which is hard to be measured, including Rayleigh waves generated by granular collision. In this study, the relationship between the forced vibration state of the granular assemblies and the energy loss distribution is established. Various types of energy transfer and conversion distribution which further enriches the energy dissipation of discrete element calculation of the granular assemblies is discussed and provides a reference for the energy loss analysis of the granular assemblies.

This paper investigated into the application of fiber-enhanced asphalt mixture in surface layer of the large longitudinal slope pavement of Xi-Sang Highway. Asphalt mixture with and without polyester fiber were used. Focus is on resistance of deformation at high temperature and flexibility at low temperature. Fiber-enhanced asphalt mixture with dynamic stability above 7000 passes/mm indicated excellent rutting resistance. The high temperature dynamic modulus of fiber-enhanced asphalt mixture was much higher than conventional SBS modified asphalt mixture. Three-point blending test result indicated that the maximum flexural strain of fiber-enhance asphalt mixture reached 4180μm/m. It was concluded that fiber-enhanced asphalt mixture was suit to be used in surface layer of the large longitudinal slope pavement of Xi-Sang Highway.

Introduction. The network of highways is one of the factors ensuring sustainable development of both plain and mountainous territories. Effective monitoring of road condition using modern non - destructive methods is an integral element of ensuring their normative condition. One of the promising ways to improve nondestructive testing methods is the energy approach based on the indicator of dissipation of deformation energy. Methods. The mathematical model considered in this paper is based on the solution of the system of dynamic Lame equations in displacements. The solution is constructed by applying the properties of the Fourier transform, and methods of discrete harmonic analysis. The output data are the amplitude - time and amplitude - frequency characteristics of the displacements on the pavement surface. The elastic properties of pavement layers are described by the elastic moduli and Poisson’s coefficients of the layer materials, and the viscous properties by the tangents of the loss angles of longitudinal and transverse waves. Results and discussion. A numerical experiment was carried out to investigate the influence of elastic and viscous characteristics of pavement layers on the value of strain energy dissipation. The values of strain energy dissipation were calculated by dynamic hysteresis loops obtained by superimposing the amplitude - temporal characteristic of the shock loading impulse on the amplitude - temporal characteristic of displacements on the pavement surface. It was found that varying the elastic modulus of asphalt concrete has the greatest effect on the amount of energy dissipation in the zone from 0 to approximately 1.8 m from the point of impact load application. The modulus of elasticity of the base layer affects the change in energy dissipation in the entire study area, gradually converging to zero at a distance of 2.1 m from the point of impact loading. The modulus of elasticity of the working layer of the subgrade has a significant effect on the energy dissipation in the whole investigated area. Viscous characteristics have much less influence on the energy dissipation value in some cases leading to qualitative changes in its distribution. Conclusion. The obtained results can serve to improve the existing methods of nondestructive testing of road pavements, in particular, when developing effective procedures for correcting the parameters of the calculated response relative to the experimental one.

This report documents the research performed under NCHRP Project 1-43. It describes the work activities undertaken in the study and presents the results of those activities toward the development of the Guide for Pavement Friction. The information provided in this report serves as the basis for many of the guidelines and recommendations contained in the Guide. The information will be of interest to highway materials, construction, pavement management, safety, design, and research engineers, as well as others concerned with the friction and related surface characteristics of highway pavements. Using information collected through detailed literature reviews and surveys/interviews with state highway agencies, this report discusses a variety of aspects regarding pavement friction. It describes and illustrates the importance of friction in highway safety, as well as the principles of friction, as defined by micro-texture and macro-texture. It identifies the factors affecting friction and examines the ways that friction can be measured (equipment and procedures) and expressed (reporting indices). Most importantly, it presents valuable information on (a) the management of friction on existing highway pavements and (b) the design of new highway surfaces with adequate friction. This information focuses on techniques for monitoring friction and crashes and determining the need for remedial action, as well as identifying combinations of aggregate (micro-texture) and mix types/surface texturing methods (macro-texture) that satisfy friction design requirements. The report includes various conclusions and recommendations based on the results of the study, and it features five appendixes containing supplemental information on friction.

The phenomena of elastic aftereffects during loading/unloading of viscoelastic and capillary-porous bodies, relaxation of their stresses is accompanied by the energy accumulation and dissipation to be taken into account in the theory of oscillations which also considers the behavior of materials when the force is applied to them. The elastic aftereffect and stress relaxation forms ostensibly opposite energy processes. In the first case, under constant load deformation, the work increases in course of time, and in the second case, under constant load deformation, the work (energy) decreases. While researching on the energy dissipation in the conditions of oscillations application, i.e. within the frame of internal friction theories, one can find that some theories are based on the dependence of friction on the oscillations’ velocity, other ones establish the dependence of friction on the amplitude. Research papers are based on the hypothesis of M.M. Davydenkov, according to which the energy when subjected to oscillations depends on the amplitude and does not depend on the velocity. According to E.S. Sorokin, the theory of internal friction is poorly consistent with the theories describing the inherited properties of materials (viscoelastic and capillary-porous ones). A tendency is observed: the better a theory reflects hereditary properties, the worse this theory is adapted to describe energy losses due to oscillations.In this paper, an attempt has been made to harmonize both these theories and numerous experiments on the destruction of materials described in the academic literature. It turns out that in order to remove contradictions, it is necessary to take into account the dependence of body deformation changing in the course of time.It is shown that the hierarchy of times determining shear and bulk relaxation in viscoelastic/capillary-porous medium has a fractal (scale-invariant) structure. It was observed that the presence of time fractality eases the modeling of viscoelastic/capillary-porous bodies resulting in the universal relaxation function of a rather simple kind. In particular, for the scale-invariant distribution of relaxation characteristics medium, the application of algebraic relaxation law for viscoelastic/capillary-porous materials is possible: this resulting in rheological models and state equations with the derivatives of fractional order.

In this work, the displacements and stresses at any point in a transversely isotropic layered half-space under multiple horizontal loads are studied. The transversely isotropic plane is assumed to be parallel to the surface plane, and uniformly distributed circular loads with different magnitudes, radii and orientations are applied to the pavement surface. Based on the cylindrical system of vector functions in the transformed domain, the governing equations are first decoupled into two sets of equations related to the LM-type and N-type respectively. Solutions for the multilayered half-space in the transformed domain are then derived by virtue of the propagator matrix method. Solutions in the physical domain are then expressed in terms of the Bessel function integration. The method of superposition is finally utilized for multiple loads. We remark that while the propagator matrix method has been frequently used to solve the vertical loading problem in layered half-spaces, which only involve the LM-type equation, the corresponding horizontal loading problem involving multiple circular loads in a transversely isotropic layered half-space has not been addressed in the literature. A computer program has been coded by the authors' research group and numerical results obtained from this program for the isotropic layered half-space have been verified with existing ones. Further presented in this paper are the results for the transversely isotropic layered half-space, with examples elucidating clearly the effect of material anisotropy on the responses, especially on pavement failure. It is also observed that, in terms of computation, the developed program is very accurate, efficient and flexible. For instance, our program can easily handle more than 10,000 field points with more than 1,000 pavement layers.

Understanding the physics underlying energy dissipation is necessary for the effective thermal management of devices based on two-dimensional (2D) materials and requires insights into the interplay between heat generation and diffusion in such materials. We review the microscopic mechanisms that govern Joule heating and energy dissipation processes in 2D materials such as graphene, black phosphorus and semiconducting transition metal dichalcogenides. We discuss the processes through which non-equilibrium charge carriers, created either transiently through photoexcitation or at steady state by a large electric field, undergo energy relaxation with the lattice and the substrate. We also discuss how these energy dissipation processes are affected by the device configuration (heterostructure, substrate material including hexagonal boron nitride, etc) as the use of different substrates, encapsulation, disorder, etc can introduce or remove scattering processes that change the energy relaxation pathways. Finally, we discuss how the unique carrier scattering dynamics in graphene-based vdW heterostructures can be exploited for optoelectronic applications in light emission and photodetection.

The Mississippi corridor of Interstate 269 (I-269) is located in northwest Mississippi and construction of this corridor encompassed approximately 27 miles of new Interstate. This study documents I-269 as a case study of the chemically stabilized soil pavement layers. The evaluation comprises pre-construction activities (material selection, mixture design, pavement design, contract information), construction activities (processes, specifications, as-built quality), and an assessment of three cement stabilized base sections. Detailed assessment included on-site specimen preparation using the plastic mold compaction device (PM Device), core drilling, and subsequent laboratory testing for density, unconfined compressive strength, and elastic modulus. This project was able to document and quantify density variability within current Proctor and nuclear gauge practices to the point where there was noticeable agency and contractor risk. Variability is known to exist in large construction projects, but quantifiable measurements over a large project, as presented in this paper, are more valuable than general expectations for basing future decisions. This paper provides evidence that a construction quality control program where nuclear gauge and Proctor compaction practices are interconnected with mechanical property measurements taken on specimens fabricated with the PM Device is worth considering for implementation. The PM Device fared well for construction, mixture design, and pavement design activities when benchmarked relative to the density, strength, and modulus of the several dozen cores taken and assessed from I-269.

Enhancing the dissipative properties of particle dampers using rigid obstacle-grids

Protein dynamics is essential for its function, especially for intramolecular signal transduction. In this work we propose a new concept, energy dissipation model, to systematically reveal protein dynamics upon effector binding and energy perturbation. The concept is applied to better understand the intramolecular signal transduction during allostery of enzymes. The E. coli allosteric enzyme, aspartokinase III, is used as a model system and special molecular dynamics simulations are designed and carried out. Computational results indicate that the number of residues affected by external energy perturbation (i.e. caused by a ligand binding) during the energy dissipation process shows a sigmoid pattern. Using the two-state Boltzmann equation, we define two parameters, the half response time and the dissipation rate constant, which can be used to well characterize the energy dissipation process. For the allostery of aspartokinase III, the residue response time indicates that besides the ACT2 signal transduction pathway, there is another pathway between the regulatory site and the catalytic site, which is suggested to be the β15-αK loop of ACT1. We further introduce the term “protein dynamical modules” based on the residue response time. Different from the protein structural modules which merely provide information about the structural stability of proteins, protein dynamical modules could reveal protein characteristics from the perspective of dynamics. Finally, the energy dissipation model is applied to investigate E. coli aspartokinase III mutations to better understand the desensitization of product feedback inhibition via allostery. In conclusion, the new concept proposed in this paper gives a novel holistic view of protein dynamics, a key question in biology with high impacts for both biotechnology and biomedicine.

Strain characteristics and energy dissipation laws of gas-bearing coal during impact fracture process

An entropy-based model of plastic deformation energy dissipation in sliding

<p>We numerically study the effects that roughness in the walls of cracks has on the P-wave modulus dispersion and attenuation due to squirt flow. We emulate the deformation caused by a seismic P-wave by applying an oscillatory relaxation test on numerical rock models having two perpendicular fluid-filled cracks interconnected and embedded in a cubic elastic background. The deformation caused by the P-wave induces a fluid pressure gradient and then, during the consequent fluid pressure diffusion process, the friction between fluid particles dissipate seismic wave energy. In this work, we consider P-wave deformation normal to one of the cracks. We first consider binary aperture distribution for the cracks to analyse where the energy dissipation process takes place. Then, more complex geometries for the roughness of the walls are also considered. In both cases, the cracks have finite length and square-shape and no contact areas between the walls of the cracks were allowed to occur. We show that the arithmetic mean of the apertures controls the P-wave modulus magnitudes at the low- and high-frequency limits. Additionally, two attenuation peaks and modulus dispersion regimes may occur associated with squirt flow. In general, at low-frequencies, the energy dissipation tends to happen inside the minimum aperture of the cracks, and consequently, the minimum aperture determines the frequency at which the low-frequency attenuation peak occurs. For the considered models, we observed that when the percentage of minimum aperture in the cracks is lower than 10$\%$, a second attenuation peak at high frequencies become dominant. The characteristic frequency of this attenuation process is controlled by an effective hydraulic aperture. Finally, we simulate an increase in confining pressure by reducing the crack apertures by a constant value, allowing for contact areas occurrence. In this scenario, the stiffness of the cracks can not longer be explained with the arithmetic mean of the aperture, as the stiffening effect of the distribution of the contact areas plays a much stronger role. In general, from the analysis of the local energy dissipation, different apertures seem to control the energy dissipation process at each frequency, which means that a frequency-dependent hydraulic aperture might be needed to describe the squirt flow process in cracks with rough walls.</p>

The fracture behavior of Au/Cr line structures formed on semiflexible and rigid-rod like polyimide film substrates has been investigated using a stretch deformation technique. The effects of metal line dimensions on the deformation behavior can be attributed to the change in the mechanical environment induced by confinement at the metal/polymer interface. Finite element analysis was employed to analyze the fracture behavior observed and found that plastic yields of the metal line and the polymer film are important in controlling the deformation behavior and energy dissipation of the delamination process. Due to the plastic yield of the metal, the interfacial stress behavior is found to be relatively insensitive as a function of the line dimension, and the edge stress concentration can not account for the delamination observed. Instead, the deformation energy is important in controlling the delamination of the metal-polymer line structure. Since the deformation energy stored in the polyimide is an order-of-magnitude higher than that in the metal, it dominates the energetics of the fracture process. The energy profile along the interface shows that maximum deformation occurs in the vicinity of the metal line edge where fracture is initiated.