Internal Friction Parameter Research Articles

Slope Deformation Mechanisms and Stability Assessment under Varied Conditions in an Iron Mine Waste Dump

The instability of geological slopes in mining environments poses a significant challenge to the safety and efficiency of operations. Waste Dump#2 at the Ziluoyi Iron Mine in China is a notable case study that highlights the challenges associated with sizable base slopes and large step heights. To address hidden hazards in the mine and the above issues, an inclusive investigation is carried out to examine the physical and mechanical properties of the soil–rock slope through indoor testing and analyze the deformation mechanisms of the slope using numerical simulations, taking various factors into account. The study reveals that the stability of Waste Dump#2 is deeply affected by weight, groundwater conditions, earthquake loading, and rainfall. To this end, the cohesion and internal friction parameters of the soil–rock slope are first determined through direct shear tests, which show a cohesion of 6.215 kPa at the top of the slope and an internal friction angle of 34.12°. By adopting GEO-SLOPE, 3D Mine, and AutoCAD software, stability calculations of the slope are performed, which give stability coefficients of 1.547 under normal conditions, 1.276 in rainfall, and 1.352 in seismic conditions. These results meet safety standards and ensure the safe and efficient operation of the mine.

OPTIMIZATION OF THE DC MOTOR MODEL COMPLEXITY LEVEL SELECTION FOR THE SYSTEM USING A NEURAL NETWORK

A mathematical and computer model of the torque control system of a DC motor with independent excitation was built using the NARMA 2 neurocontroller. NARMA - a nonlinear moving average autoregressive model is one of the basic structures of a discrete and nonlinear model. The task was to conduct a comparative analysis of the operation of the neurocontroller-based control system using plant model of varying complexity. For the experiment, three models of the object were built with different degrees of detail, and therefore the reliability of the object. The full model includes an independently excited DC motor model that takes into account all the main parameters of the DC machine, internal friction parameters, excitation circuits, etc. The simplified model is a linear approximation of the DC motor by a second-order system that takes into account both mechanical and electrical time constants. The simplest model is a linear approximation of a DC motor by a first-order aperiodic link that takes into account only the mechanical time constant. The neurocontroller was trained using the above object models and an experiment was conducted to process the reference torque signal by the system. For each of the three training cases, the neurocontroller was set to 1000 epochs, since further training performance improvement is unnecessary due to the huge loss of computation time. The NARMA-L2 neurocontroller, which is also called feedback linearization control, was used. This controller can be implemented using a pre-identified NARMA-L2 object model. Neural networks that are trained on simplified object models do not take into account most of the electrical processes in a DC motor, especially the excitation winding is not modeled at all. The obtained results were compared with the use of a neurocontroller as a torque regulator. Further research in this direction involves the study of the necessary computing power for the microprocessor implementation of the neurocontroller.

Improving a technique to calculate strength of cylindrical rock samples in terms of uniaxial compression

Purpose is to improve analytical technique to calculate strength of cylindrical rock samples taking into consideration standard horizontal stresses. Methods. Mathematical modeling of cylindrical rock sample breakage under the truncated-wedge destruction was performed taking into consideration the standard horizontal stresses using four experimental characteristics (i.e. k being shear strength; fс and μ being contact and internal friction coefficients; and Е being elasticity modulus) as well as comparing the design strength with experimental data obtained in the process of uniaxial compression. Findings. The technique makes it possible to identify both maximum strength and residual strength of cylindrical rock samples using four indicators of properties which can be simply defined by experiment. Comparison of the analytical strength limits and experimental data, obtained in terms of uniaxial compression, supports the idea of high efficiency of the proposed technique. Originality. For the first time, analytical modeling of cylindrical rock sample breakage has been performed in terms of the truncated-wedge destruction taking into consideration the standard horizontal stresses as well as contact and internal friction parameters. Practical implications. The technique advantage is to apply promptly the calculation results in the context of industrial enterprises since their environment helps apply simple procedures to define indices of physiсomechanical characteristics of rocks for determination of stability of underground structures and reduction of energy consumption while disintegrating in open pits and mining and processing complexes.

Models equivalent in damping in experiments for determining the parameters of internal friction in materials

The work is devoted to improving the methods of experimental determination of internal friction parameters in materials. The aim of the laboratory experiments is to obtain physical parameters of the material that allow to take into account the damping forces in a uniaxial stress state. The research is focused on the internal friction model, which is based on the use of the generalized Prandtl model, that gives frequency-independent internal friction and allowing for the dependence of internal friction on the level of time-varying stresses. Damped oscillations during pure bending are recorded on a specially made laboratory installation. The description of the installation, the reference points of which coincide with the fixed points of the realized form of natural oscillations, is provided. The algorithm of cameral processing of experimental data is obtained. It is proposed to use a virtual system equivalent in damping. This is a system with one dynamic degree of freedom. The involvement of an imaginary system permits, after performing tests of the sample for pure bending, to acquire data corresponding to stretching - compression. The technique grants the use of long samples, which reduces the negative effect of stress concentration in the anchorages. The damping equivalent scheme makes it possible to use samples with an arbitrary cross-section. The found damping parameters for low-carbon steel are given.

Damping properties of innovative NiTi elements: development of proof of concept and demonstrators

Thanks to their functional properties, NiTi and NiTi-based shape memory alloys (SMAs) exhibit both pseudo-elastic and intrinsic damping ability finding applications in several fields. The use of these alloys in damping devices or systems allows the attenuation of different kinds of vibration such as noise or more intense oscillations. In this work, the damping behaviour of different NiTi semifinished products has been evaluated by means of dynamic thermomechanical measurements in order to have a preliminary indication for the integration of these SMA elements in damper demonstrators. The evolution of the internal friction parameter with respect to temperature, frequency and strain extent is evaluated. Moreover, some possible demonstrators’ concepts, i.e. a cladding panel, some dampers and a shock absorber, are proposed and characterized. The investigated SMA elements are a plain-woven mesh made of NiTi and steel thin wires, wave-shaped NiTi ribbons and NiTi single-turn wave springs. The elements have been thermally treated in order to achieve the required shapes and thermomechanical conditions. The perspectives and potential of these semifinished products in the field of damper devices are investigated by a preliminary characterization and discussed.

Rouse model with fluctuating internal friction

A coarse-grained bead-spring-dashpot chain model with the dashpots representing the presence of internal friction is solved exactly numerically for the case of chains with more than two beads. Using a decoupling procedure to remove the explicit coupling of a bead’s velocity with that of its nearest neighbors, the governing set of stochastic differential equations are solved with Brownian dynamics simulations to obtain material functions in oscillatory and steady simple shear flow. Simulation results for the real and imaginary components of the complex viscosity have been compared with the results of previously derived semi-analytical approximations, and the difference in the predictions is seen to diminish with an increase in the number of beads in the chain. The inclusion of internal friction results in a nonmonotonous variation of the viscosity with shear rate, with the occurrence of continuous shear-thickening following an initial shear-thinning regime. The onset of shear-thickening in the first normal stress coefficient is pushed to lower shear rates with an increase in the internal friction parameter.

Dynamic coarse-graining of polymer systems using mobility functions

We propose a dynamic coarse-graining (CG) scheme for mapping heterogeneous polymer fluids onto extremely CG models in a dynamically consistent manner. The idea is to use as target function for the mapping a wave-vector dependent mobility function derived from the single-chain dynamic structure factor, which is calculated in the microscopic reference system. In previous work, we have shown that dynamic density functional calculations based on this mobility function can accurately reproduce the order/disorder kinetics in polymer melts, thus it is a suitable starting point for dynamic mapping. To enable the mapping over a range of relevant wave vectors, we propose to modify the CG dynamics by introducing internal friction parameters that slow down the CG monomer dynamics on local scales, without affecting the static equilibrium structure of the system. We illustrate and discuss the method using the example of infinitely long linear Rouse polymers mapped onto ultrashort CG chains. We show that our method can be used to construct dynamically consistent CG models for homopolymers with CG chain length N = 4, whereas for copolymers, longer CG chain lengths are necessary.

Ultrasonic Characterization of Nanoparticle-Based Ceramics Fabricated by Spark-Plasma Sintering

Resonant ultrasound spectroscopy was used to determine elastic constants and internal friction parameters of bulk nanoparticle-based ceramic materials compacted by spark plasma sintering. Boron nitride-based and boron carbon nitride-based materials were studied, and the results were compared with similar bulk materials prepared from graphene nanoplatelets. The results showed that such nanoparticle-based materials can be strongly anisotropic, and can have very different elastic constants depending on the nanoparticles used. From the temperature dependence of the internal friction parameters, the activation energy for sliding of the individual monolayers along each other was determined for each material. Very similar values of the activation energy were obtained for boron nitride, boron carbon nitride, and graphene, ranging from 15 to 17 kJ/mol.

Internal Friction Parameter in Shape Memory Alloys: Correlation Between Thermomechanical Conditions and Damping Properties in NiTi and NiTiCu at Different Temperatures

Among the different functional properties provided by shape memory alloys (SMA), the damping attracted increasing interest in the last decades. Particularly, the exploitation of pseudo-elastic properties to damp or prevent the oscillations of physical systems has received wide attention in civil engineering. In this context and in other practical applications, intrinsic damping properties at low strains are not yet well explored. To fill this gap, in this work, a systematic approach was taken to study the internal friction (IF) coefficient of several NiTi and NiTiCu SMA by tuning the microstructural condition through different thermal treatments. The changing of IF with respect to temperature in tensile, flexural and torsional configurations has been considered; tests have been accomplished at a solicitation strain in the order of 10−4 and at four frequencies (0.5, 1, 10 and 50 Hz). Results allow a broad overview of the intrinsic properties of the considered alloys with encouraging prospect for future applications. A reference scheme was reported in order to individuate the best SMA candidate in the light of the requirements in a wide range of possible applications, being a helpful guideline for the ideation and the design of novel devices.

THE INFLUENCE OF THE STIFFNESS OF THE ELEMENTS OF RAIL DAMPING ON THE PARAMETERS OF THE MULTI-MASS WAGON–TRACK VIBRATORY SYSTEM

The task of achieving the increase in the weight and velocity of trains being core objective for most railways is inherently associated with solving problems of improving the dynamic qualities of wagons and locomotives during their interaction with the upper structure of the railway track. The strength and stability of rolling stock against derailment in various climatic zones should be ensured together with minimizing operating costs.Analysis of the reliability and performance of the wagon–track system can be conducted based on multivariate dynamic calculations of mathematical models and through experimental studies of dynamic vibrations. Currently, the issues of the influence of changes in the elastic-hysteresis properties of various impact absorber materials under the action of temperature factors on the elements of a multi-mass vibratory system remain insufficiently studied. The purpose of the research described in the article was to analyze the dynamic processes taking place in a multi-mass wagon–track vibratory system under the influence of changes in stiffness and internal friction coefficients of a damping rail component depending on a type of structural material and ambient temperature.The research resulted in elaborating model of multi-mass vibratory wagon–track system. Multivariate model calculations were carried out regarding various stiffness and internal friction parameters of damping elements situated under the rail; the parameters being selected from experimentally constructed dynamic hysteresis. The work presents results of calculations of the reaction forces and deviations in the elements of the vibratory system depending on temperature, type of material, thickness and design of damping elements.

Cyclic-Dependent Damage Evolution in Self-Healing Woven SiC/[Si-B-C] Ceramic-Matrix Composites at Elevated Temperatures.

Cycle-dependent damage evolution in self-healing, 2.5D woven Hi-NicalonTM SiC/[Si-B-C] and 2D woven Hi-NicalonTM SiC/[SiC-B4C] ceramic-matrix composites (CMCs) at 600 and 1200 °C was investigated. The cycle-dependent damage parameters of internal friction, dissipated energy, Kachanov’s damage parameter, and broken fiber fraction were obtained to describe damage development in self-healing CMCs. The relationships between cycle-dependent damage parameters and multiple fatigue damage mechanisms were established. The experimental fatigue damage development of self-healing Hi-NicalonTM SiC/[Si-B-C] and Hi-NicalonTM SiC/[SiC-B4C] composites was predicted for different temperatures, peak stresses, and loading frequencies. The cycle-dependent damage evolution of self-healing Hi-NicalonTM SiC/[Si-B-C] and Hi-NicalonTM SiC/[SiC-B4C] composites depends on temperature, testing environment, peak stress, and loading frequency. For the Hi-NicalonTM SiC/[Si-B-C] composite, temperature is a governing parameter for the fatigue process. At an elevated temperature of 600 °C in an air atmosphere, the internal frictional parameter of Hi-NicalonTM SiC/[Si-B-C] composite decreases first and then increases with applied cycle number; however, at an elevated temperature of 1200 °C in an air atmosphere, the internal frictional parameter of Hi-NicalonTM SiC/[Si-B-C] composite decreases with applied cycle number, and the interface shear stress at 1200 °C is much lower than that at 600 °C. For Hi-NicalonTM SiC/[SiC-B4C] composite at 1200 °C, loading frequency is a governing parameter for the fatigue process. The degradation rate of interface shear stress is much higher at the loading frequency of 0.1 Hz than that at the loading frequency of 1 Hz.

Reduced Internal Friction by Osmolyte Interaction in Intrinsically Disordered Myelin Basic Protein.

Urea is a strong denaturing osmolyte that disrupts noncovalent bonds in proteins. Here, we present a small-angle neutron scattering (SANS) and neutron spin-echo spectroscopy (NSE) study on the structure and dynamics of the intrinsically disordered myelin basic protein (MBP) denatured by urea. SANS results show that urea-denatured MBP is more compact than ideal polymers, while its secondary structure content is entirely lost. NSE experiments reveal concomitantly an increase of the relaxation time and of the amplitude of internal motions in urea-denatured MBP as compared to native MBP. If interpreted in terms of the Zimm model including internal friction (ZIF), the internal friction parameter decreased by a factor of 6.5. Urea seems to not only smooth local energy barriers, reducing internal friction on a local scale, but also significantly reduces the overall depth of the global energy landscape. This leads to a nearly complete loss of restoring forces beyond entropic forces and in turn allows for larger motional amplitudes. Obviously, the noncovalent H-bonds are largely eliminated, driving the unfolded protein to be more similar to a synthetic polymer.

The use of fixed points in experimental research of the internal friction of material

The aim of the work. The work is devoted to experimental research of internal friction parameters of the material. Methods. The research of internal friction is carried out by consideration of damped oscillations of the experimental system that consist of rigid plates and a specimen in a state of pure bending. We propose to locate bearings in the fixed points to minimize energy losses in support fastenings. Fixed points are determined by using a finite element complex with consideration of free oscillations of the loose model. Results. Damping curves were determined, which demonstrate a very small logarithmic decrement of oscillations and frequency independence of inertial friction. The main result of the work is the tested improvements of the experimental technique, among which the main one is the use of fixed points for determining the places of fastening of the laboratory installation

Traditional and new materials for the reeds of woodwind musical instruments

Cane (Arundo donax L.) is the traditional material for reeds of woodwind musical instruments of classical symphony orchestra—clarinet, saxophone, oboe and bassoon. Cane is a natural material, and its structure is influenced by the growth conditions of the plant or by fungal attacks. The mode of vibration of reeds is affected by the quality of cane. In this article, physical, acoustical and mechanical properties of this material are described. These properties are characterized by a large natural variability. The physical properties of special interest are the swelling and the shrinkage of cane and the density (specific gravity). Mechanical properties of interest for the behavior of cane during playing are the elastic constants—moduli of elasticity and the corresponding parameters of internal friction. Acoustical properties are expressed by the velocity of propagation of elastic waves. The aging of reeds is due to various factors, among them are the repeated wet–dry and dry–wet cycles and the “continuous” playing. These factors modify the structural response of cane and have an irreversible effect on the quality of reeds. Statistical correlations between the quality of reeds and the descriptors of musical sounds are discussed. New synthetic materials of the group of polypropylenes have been developed for reeds having a better long-term behavior.

Express evaluation method of internal friction parameters in molding material briquettes

The purpose of this work is to develop an express method of evaluating the coefficient of internal friction and cohesive strength of molding material briquettes. Advantages and disadvantages of modern evaluation methods of internal friction parameters in particulates have been considered, and the need to improve them has been substantiated. An alternative method based on measuring the position of shear planes and the briquette cracking pressure in uniaxial compression strength tests has been proposed. The theoretical justification of the method has been provided, and examples of implementation have been given. The research results may be used in the process of educating students of technical specialties, as well as at research and design organizations.

Macroscopic framework for viscoelasticity, poroelasticity, and wave-induced fluid flows — Part 2: Effective media

Sedimentary rocks possess complex microstructures and require simplified descriptions in terms of averaged, or effective mechanical properties. Most conventional approaches to effective media use the concept of viscoelastic moduli to describe the frequency-dependent wave velocities and attenuation. However, for rock containing pore fluids, a single pair of bulk and shear moduli does not account for slow P- and S-waves and for reflections and conversions in heterogeneous media. To overcome these limitations, we use the general linear solid (GLS) theoretical framework to derive multiphase models of effective media. Two types of models are considered. First, for sandstone containing thin layers saturated with brine and gas, two-phase effective-medium relations are derived in a (relatively) closed form for the density and elasticity, and the parameters of internal friction are inferred by fitting the dispersion spectra of both fast and slow P-waves. In the second application, we consider the generalized standard linear solid (GSLS) medium, which is broadly used in numerical simulations of seismic wavefields. The GLS point of view suggests that (petro)physical significance should always be sought for the mathematical variables usually assumed in GSLS models. Inertial effects and interactions between internal variables cause additional wave modes in a GSLS medium. Contrary to what is often thought, with inertial effects and fuller interactions between the internal variables, near-zero or negative velocity dispersion can occur in a medium with band-limited attenuation.

Diffraction of Torsional Surface Wave in a Voigt Layer Overlying a Prestressed Heterogeneous Substratum

AbstractThis paper discusses the torsional surface wave in a Voigt-type layer placed over an initially stressed heterogeneous semi-infinite substratum. The heterogeneities in the semi-infinite substratum are thought to emerge as a result of exponential variation in rigidity, density, and initial stress. A closed-form dispersion relation for the torsional surface waves under the considered geometry was obtained. The effect of various technical constants, such as internal friction parameter, stress parameter, heterogeneity parameter, dissipation factor, complex wave number, and thickness of the layer, were studied numerically by plotting various graphs between the nondimensional angular frequencies against the nondimensional real wave number for the torsional surface wave propagation. The numerical solution for the limiting case of torsional surface waves is also presented. In the absence of the considered technical constants, the obtained results are in close agreement with the results obtained by other re...

Mechanical properties of potato starch modified by moisture content and addition of lubricant

Abstract Laboratory testing was conducted to deliver a set of characteristics of structure and mechanical properties of pure starch and starch with an addition of a lubricant - magnesium stearate. Considerable influence of moisture content of potato starch was found in the case of density, parameters of internal friction, coefficients of wall friction and flowability. Elasticity was found to be strongly influenced by water content of the material. Addition of magnesium stearate affected density and parameters of flowability, internal friction and elasticity. Bulk density increased from 604 to 774 kg m-3 with decrease in moisture content of potato starch from 17 to for 6%. Addition of magnesium stearate resulted in approximately 10% decrease in bulk density. Angle of internal friction obtained for 10 kPa of consolidation stress decreased from 33 to 24º with increase in moisture content, and to approximately 22º with addition of the lubricant. With an increase of moisture content from 6 to 18% and with addition of the lubricant, the modulus of elasticity during loading decreased from approximately 1.0 to 0.1 MPa. Modulus of elasticity during unloading was found in the range from 19 to 42 MPa and increased with increase of moisture content and amount of lubricant.

Relationship between single and bulk mechanical properties for zeolite ZSM5 spray-dried particles

In this work typical mechanical properties for a catalyst support material, ZSM5 (a spray-dried granular zeolite), have been measured in order to relate the bulk behaviour of the powder material to the single particle mechanical properties. Particle shape and size distribution of the powders, determined by laser diffraction and scanning electron microscopy (SEM), confirmed the spherical shape of the spray-dried particles. The excellent flowability of the material was assessed by typical methods such as the Hausner ratio and the Carr index. This was confirmed by bulk measurements of the particle–particle internal friction parameter and flow function using a Schulze shear cell, which also illustrated the low compressibility of the material. Single particle compression was used to characterize single particle mechanical properties such as reduced elastic modulus and strength from Hertz contact mechanics theory. Comparison with surface properties obtained from nanoindentation suggests heterogeneity, the surface being harder than the core. In order to evaluate the relationship between single particle mechanical properties and bulk compression behaviour, uniaxial confined compression was carried out. It was determined that the Adams model was suitable for describing the bulk compression and furthermore that the Adams model parameter, apparent strength of single particles, was in good agreement with the single particle strength determined from single particle compression test.

Application of resonant ultrasound spectroscopy to determine elastic constants of plasma-sprayed coatings with high internal friction

We present a novel modification of resonant ultrasound spectroscopy (RUS) for analysis of elastic constants of plasma-sprayed coatings in the ‘as sprayed’ state, i.e. without removing the substrate. This modification is suitable for coatings with high internal friction (Q−1≳10−2), which cannot be measured by RUS in the free-standing state due to strong damping. In combination with through-transmission measurements, this modification is able to provide full anisotropic tensor of elastic constants of the coating. As an illustrative example, the proposed methodology is applied to two steel coatings prepared by water-stabilized plasma (WSP) spraying. In addition to the moduli, also the internal friction parameters of the coatings are obtained. The results of RUS are compared to moduli determined by four-point bending tests, and it is shown that the anisotropic elasticity of both examined materials exhibits an elliptic form of transversal isotropy with four independent elastic coefficients.