Small Internal Friction Research Articles

Impact experiments on granular materials under low gravity: Effects of cohesive strength, internal friction, and porosity of particle layers on crater size

Impact craters on the surface of asteroids provide information about their surface properties and evolutionary processes. Investigating how crater size depends on these physical properties is important for establishing a crater-size scaling law. We conducted high-velocity impact experiments at 1 G and at simulated low gravity on dry particle layers with different physical properties. The crater diameter was larger for targets with smaller internal friction. Also, for similar internal friction, the crater diameter was larger for targets with lower porosity. The crater diameter for targets with particle diameters of several hundred micrometers was proportional to the gravitational acceleration to the power of −0.16 to −0.18. However, the crater diameters for targets with particle sizes of ∼40 μm showed little or no difference between 1 G and low gravity. Although the results for targets with particle sizes of ∼40 μm at 1 G showed a relationship in the gravity regime, the results under low gravity deviated from this tendency. We obtained the condition for the transition between the gravity- and strength-dominated regimes: the ratio of the cohesion Ycoh to the term ρtgD, or the ratio of the effective strength YEFF to ρtgD, where ρt, g, and D are the target bulk density, gravitational acceleration, and crater diameter, respectively. The values of Ycoh/ρtgD and YEFF/ρtgD for targets with particle sizes of ∼40 μm were 0.22–0.27 and 0.11–0.60, respectively. This study provides basic experimental data for comparison with numerical simulations.

Introduction to Modelling the Correlation Between Grain Sizes of Feed Material and the Structure and Efficiency of the Process of Co-Rotating Twin-Screw Extrusion of Non-Flammable Composites with a Pla Matrix

Abstract Co-rotating twin-screw extrusion is an energy consuming process that is generally not fully optimised to a specific polymer. From the point of view of the efficiency of the extrusion process, the starting material should be characterised by small grain sizes in comparison to the screw channel area, small surface area to volume ratio and small internal friction between the pellets. To develop a model describing the effect of polylactide (PLA) grain size on the extrusion efficiency, a series of experiments with a twin-screw extruder were carried out during which the energy consumption; torque on shafts and temperature of the melt on the extruder die were monitored. As feed material, both the neat PLA with different grain sizes and the PLA with expandable graphite fillers and phosphorous-based flame retardants were used. Morphology and dispersion quality of the composites were examined using scanning electron microscopy (SEM); flammability, smoke production, mass loss and heat release rates were tested using cone calorimetry; and melt flow rate was determine using a plastometer. Moreover, the thermal properties of the obtained composites were determined using differential scanning calorimetry (DSC). The results show that the choice of the starting material affects both the efficiency of the extrusion process and the flame retardancy properties of the composite materials.

Seismic barriers filled with solid elastic and granular materials: Comparative analysis

A comparative study of the vertical seismic barriers intended for protecting from Rayleigh seismic waves and filled with (1) homogeneous linearly elastic materials and (2) granular metamaterials, is done by the finite-element (FE) modeling. The granular metamaterial obeys the Mohr–Coulomb plasticity model with the associated flow rule, low cohesion value, and small internal friction and dilation angles. The performed numerical analysis reveals a principal ability achieving much higher reduction ratios for magnitudes of accelerations along with much longer shadow zones behind the barrier for barriers filled with metamaterials in comparison with the purely elastic homogeneous barriers.

Effect of interface types on the static and dynamic mechanical properties of 3D braided SiC/SiC composites after oxidation

For applications in thermal structure engineering, static and dynamic mechanical properties of 3D braided SiC/SiC composites after oxidation were investigated and the effects of interface between fibers and matrix were revealed. The results showed that composites with combined (PyC + SiC) multilayer interface (denoted as K–C/S) were superior to those with a single interlayer or without an interlayer. After oxidation, K–C/S showed the least weight changes, the highest flexure strength, small internal friction, and highest storage modulus. The outside SiC interface of K–C/S protected the PyC interface from further oxidation. Thus, K–C/S showed highly advantageous with regard to both static and dynamic properties after oxidation.

Stability analysis of anchored slopes based on a peak shear-strength criterion of rock joints

A new three-dimensional shear-strength criterion (3DSSC) considering the three-dimensional (3D) roughness of rock joints and the internal friction angle of rock masses is discussed. Two methods for transforming the parameters of the 3DSSC into the linear Mohr–Coulomb failure criterion parameters are proposed. The calculation method of the anti-sliding safety coefficient of a rock slope controlled by a single anchored rock joint is derived, and anchoring parameter analysis is carried out. Compared with the equivalent linear fitting method and tangent equivalent method for obtaining the Mohr–Coulomb shear-strength parameters, the 3DSSC can be directly applied to calculate the rock slope stability controlled by a single rock joint. The change in the characteristics of the anti-sliding safety coefficient of the slope with the changes in the 3D roughness parameters, shear rate, and internal friction angle are discussed. The sensitivity of these factors to the slope stability is analyzed. It is suggested that for rock slopes with high roughness and a small internal friction angle, the weakening effect of the anchoring force angle on the anti-sliding stability of the slope should be taken into account.

Silica Glass for High-Q Mechanical Resonators

This paper addresses issues related to the choice of materials for the fabrication of high-Q mechanical resonators. It has been shown that the best material combining a low level of thermoelastic losses and small bulk internal friction is silica glass. Given its excellent dissipative characteristics and relatively low cost, silica glass prepared via high-temperature hydrolysis of silicon tetrachloride in an oxygen–hydrogen flame is the most promising material for such resonators.

Tunnelling outburst potential affected by mechanical properties of coal seam

Coal and gas outburst is greatly affected by the stress distribution in front of the heading face when tunnelling in high gassy coal seam. In this paper, the FLAC3D software and Mohr-Coulomb failure criterion are used to study the stress differences in front of the heading face. A total of 31 homogeneous models are built to study the stress differences affected by the coal seam mechanical properties. And another 8 kinds of heterogeneous models are built to study the stress differences affected by the abruptly changes of coal seam mechanical properties.When tunnelling in homogeneous coal seam, the large elastic modulus of coal seam will increase the stress peak value in front of the heading face, but do not change the stress peak position. The small internal friction angle will push the stress peak far away from the heading face. Therefore, the range of stress-relief zone in front of the heading face could significantly increase. The small cohesion of the coal seam will also push the stress peak far away from the heading face, but will result in an increase in the stress peak value. The Poisson ratio and tensile strength of the coal seam have little influence on the value and position of stress peak. As the elastic modulus decreases, cohesion and internal friction angle can greatly increase the displacement of the coal in front of the heading face. Taking into account both the mechanical properties of coal seam and the corresponding stress peaks, gas outburst is not easy to occur in the homogeneous coal seam.When tunnelling in heterogeneous coal seam, the abrupt change of coal seam elastic modulus greatly affects the stress concentration peak. If the cohesion of the coal seams also changes greatly with the elastic modulus, the stress peak will be enhanced. The abrupt change of coal seam cohesion and Poisson ratio have a slight influence on the stress concentration, while the abrupt change of internal friction angle of coal seam have little effect on the stress concentration. An outburst accident is most likely triggered when the cohesion and elastic modulus of the coal seams change greatly at the same time.Outcomes of this study is very beneficial for the prediction and prevention of coal and gas outburst. Meanwhile, this study provides a reference for the setting of mechanical properties of the coal seam and rock layers in the numerical simulation of mining.

Stability analysis of irregular cavities using upper bound finite element limit analysis method

Underground cavities mainly exhibit irregular forms in nature. Due to the difficulties in describing the geometrical shape of irregular cavities and theoretically analyzing such cavities, irregular cavities are generally simplified as regular circular, elliptical or polygonal shapes in most studies. The purpose of this paper is to quantitatively describe the shape of irregular cavities using Fourier descriptors from inverse discrete Fourier transform (IDFT) theory and to translate the generation process of irregular cavity contours into a conversion between discrete frequency-domain and time-domain signals. Based on this approach, the stability analysis of irregular underground cavities is conducted using the upper bound finite element limit analysis (UB-FELA) method. The upper bound stability numbers (γcrD/c) and collapse mechanisms are presented for a series of irregular cavity depth-to-diameter ratios (H/D), internal friction angles (φ) and geometrical shape descriptors (D2, D3 and D8). The obtained results demonstrate that the stability numbers increase with increasing φ and decrease with increasing H/D and descriptor values (D2, D3 and D8). The failure mechanisms are significantly asymmetrical due to the contour fluctuations of the irregular cavity. Specifically, interlaced shear bands form between the adjacent fluctuations on the surface of the irregular cavity, which considerably differs from the failure mechanism of regular cavities. Local shear failure is the main failure form for the soil around the cavity. An obvious bottom bulge phenomenon is observed in the cavity at small internal friction angles.

THE CALCULATION OF MULTILAYER LINING OF TUNNELS, CONSTRUCTED IN A TECHNOLOGICALLY DIVERSE OF MASSIF SOIL

Addressing urban transport is a very timely matter, especially in the capital Hanoi and Ho Chi Minh City. In order to solve this problem, a solution has been proposed for the construction of overhead tram and subway lines. In fact, when constructing subway lines through historical sites, high population density, many surface structures, etc., the method of open construction is not feasible, it is necessary to use the method Underground construction. These areas are often weak soil, the physical parameters of the soil detrimental to the tunnel construction work; Such as small stickiness, small internal friction angle, high porosity, high permeability coefficient, high water saturation, short shear strength etc. These factors create complex geological conditions in Construction tunnel. With that in mind, the calculation of the selection of the tunnel casing structure is necessary, which is timely.This paper provides a solution to the problem of stress state of multilayer lining supporting the tunnel of circular cross-section, constructed in a technologically heterogeneous array. The tunnel lining and surrounding soil mass are considered as elements of a united deformable system.

Prediction of mass discharge rate in conical hoppers using elastoplastic model

Precise evaluation of mass discharge rate (MDR) in hoppers is an important topic in many industries. Facilitated by an Eulerian-formulation finite element method (FEM), this paper uses an elastoplastic model to investigate the MDR in conical hoppers and evaluates its applicability in various cases of hopper geometries and material properties. The obtained flow field complies with the scaling of outlet velocity Vy~gD0 and that of the discharge rate MDR~gD05/2 universally. The MDR is basically independent of the fill height and silo width, but a strong height dependency may emerge for very small internal friction angle of granular material, similar to the fluid-like discharging observed in previous DEM simulation. As for the material properties, the MDR is mainly controlled by the plastic parameters such as internal friction angle and dilation but is insensitive to the elastic modulus. The quantitative accuracy of the model is verified by comparing experimental measurements and discrete simulation over a wide range of hopper half angles. The existing correlations are often conditionally applicable in describing MDR – some for steep hoppers while others mainly suitable for shallow ones. An empirical correlation is formulated based on the FEM results to achieve a general applicability, which may help to improve the hopper design in practical applications. The needs for future research are also discussed.

Impact of a multilayer structure on initiation and evolution of strain localization in porous rocks: Field observations and numerical modeling

Networks of localized conjugate compactive shear bands with large dihedral angles (corresponding to so-called shear-enhanced compaction bands) were generated in 3-layer plane strain finite-difference models. The central layer has elastic–plastic properties with a small positive internal friction coefficient, negative dilatancy factor, and the hardening modulus reducing during the deformation. The two other layers are elastic. The spatial organization of the networks in the central layer, resulting from the elastic–plastic instability of the 3-layer system, was shown to be dependent on the contrast of the elastic stiffness of the layers and on the friction between them. When the stiffness E of the elastic layers and/or the friction are small, the networks are rather symmetric (the bands of both orientation families are distributed homogeneously within the layer). An increase in E at high friction, results in the clustering of the bands of one orientation along a layer segment which is followed by another segment filled with the bands of the other orientation. Different network types are characterized by different band spacing which is smaller in the clustered networks. The intensity of inelastic deformation and hence of porosity reduction within the bands are also smaller in this case. The obtained band networks are very similar to those in nature where the same variability of the network organization is observed. Available geological and mechanical data confirm the conclusions from the modeling about the origin of this variability.

Mechanical Behavior of Water Deionizing Granular Material Bed for Space Life Support Systems

AbstractOne of the most critical components in the oxygen-generation and water-processing assemblies for human habitation in space is the deionizing (DI) bed—a packed bed of ion-exchange resin beads—that purifies water. The DI bed shrinks during the course of its operation, and therefore, for the bed to work satisfactorily, it must be kept properly compressed. To understand the force-transferring mechanism along the bed, sets of experimental programs were developed and conducted on the individual particles and bed samples of a DI granular material, Amberlite IRN-78. The presence of water reduced the load-bearing capacity of the individual particles, because most of the wet (water submerged) particles tested failed under relatively small crushing force, whereas the dry particles withstood a much higher load. The particle crushing force was found to be closely represented by normal and Weibull distributions. The DI material bed has a relatively small internal friction angle (shear strength). The lateral pre...

Conductive knitted fabric as large-strain gauge under high temperature

An intrinsically conductive knitted fabric-based electrical resistive strain gauge is developed to measure in-plane or out-of-planar large strain under high temperature. Electro-mechanical properties, which governor the sensitivity of the gauge, are analyzed theoretically by a model of weft plain fabric. The contacting electrical resistance ( R c), resulted from two overlapped yarns, is attributed to be the key factor contributing to the resistance–strain response while the fabric structure determines the sensitivity of the gauge. Two structures are fabricated making use of the properties of contacting resistance to find the key factors governing the sensitivity, repeatability and accuracy of the sensors. The effects of strain-rate and temperature on the sensitivity of the gauge are analyzed experimentally. From the experimental results, fabric gauges made from carbon fibers display a higher sensitivity, repeatability and accuracy than those made by stainless steel due to its small internal friction and intrinsic physics properties. Meanwhile, tubular structure has high maximum strain level than single warp structure but exhibits lower sensitivity than the latter. Temperature exhibits greater effect on the sensitivity than the strain-rate.

Analysis of slug tests in bypassed wells

In Berlin many wells are constructed with an additional small diameter bypass tube flanged on to the large diameter casing and running parallel to the later upward to the surface. The response to a slug test conducted in such a well is usually characterised by significant water level oscillations developing inside the branched pipe system. In the present paper, a general non-linear model is developed for the analysis of slug tests performed in bypassed wells. The model includes skin effects, non-linear head losses due to internal well bore fluid friction, minor losses originating at radius changes along the flow path inside the well, and inertial effects of the water columns contained within the primary casing and the bypass. Pipe flow inside the branched tubing system is described by the one-dimensional conservation law of the mechanical energy of the well bore fluid. Aquifer flow is quantified by a convolution-type approach. The coupled well-aquifer system is governed by an integro-differential equation representing the mean mechanical energy of the total well bore fluid and, coupled to it, by a non-linear ordinary differential equation which accounts for mechanical energy fluctuations between the water columns inside the main casing and the bypass. Both equations are solved by finite difference approximations coupled to point iterative numerical techniques. An application of the model to field data suggests that non-linear hydraulic head losses originating inside the well bore may cause the measured head responses to depend on the initial displacement. A packer used to initiate a slug test can induce these non-linear distortions through the combined effect of minor losses originating at the inlet and the outlet of a small diameter packer flow-through tube and internal fluid friction potentially developing inside that packer passage. As classical linear theories do not allow for the analysis of such phenomena, a model accounting for these non-linear processes should be used if field data show significant dependencies on the initial slug height.

The bufferness phenomenon in distributed mechanical system

Self-excited oscillations of weakly non-linear systems with distributed parameters are investigated. From the unified standpoints of the Lyapunov-Poincaré perturbation method, the limit cycles are determined in a constructive manner and conditions are found for the existence and stability of “quasi-linear” self-excited oscillatory modes of behaviour for two classes of mechanical objects, namely, a model of the transverse vibrations of a rotating thin shaft of circular cross-section, taking into account small internal and non-linear external viscous friction, and a two-dimensional model of the linear vibrations of a string connected at its midpoint to a self-excited oscillating circuit (an oscillator) of the Van der Pol type. In both models a “bufferness phenomenon” is established: the systems may have several stable limit cycles, depending on the values of the parameters (the angular velocity of rotation of the shaft or tension forces in the string) and corresponding to different oscillatory modes of distributed systems.

Elastic Properties of Thin Films

AbstractA technique has been developed for characterizing the disorder present in thin films through the measurement of their low temperature internal friction. The technique utilizes a substrate, in the form of a double paddle oscillator etched from a high purity silicon wafer, onto which the thin film of interest can be deposited. The oscillator possesses an internal friction of 3 × 10−8 at 4 K which is reproducible to within 1% upon thermally cycling to room temperature. This extremely small substrate internal friction coupled with the excellent reproducibility permits measurements of the internal friction of very thin amorphous films, with a 2 tun silica film producing a change in the internal friction of 4 × 10−9. By performing low temperature internal friction measurements on thin silica films with thicknesses ranging from 2 nm to 1000 nm, we have investigated the role of interacting defects in determining the universal nature of the anomalous low temperature thermal and elastic properties of amorphous solids. We have found no evidence for strong interactions between these tunneling defects. Other applications of the oscillator include monitoring of the crystallization of amorphous films through changes in the low temperature internal friction, internal friction measurements and vapor pressure measurements of quenched condensed rare gas solids and amorphous water ice, and internal friction studies of amorphous solids which can only be produced in thin film form.

Phase-transition-like behaviour associated with the superconducting transition in Tl2Ca2Ba2Cu3Ox and BiSrCaCu2Ox compounds

A structural instability shown in the form of a phase-transition-like internal friction peak and step-like change of lattice parameters appears at 135 K in a Tl2Ca2Ba2Cu3Ox sample with zero resistance at 115 K. It was confirmed that the structural instability at 135 K coexisted with the superconducting transition at 115 K. In addition, a small internal friction peak and an ultrasonic attenuation peak, which may be related to the lower temperature superconductive phase, were observed at 90 K in the Tl-Ca-Ba-Cu-O material.

Vibration of a Bowed String : 2nd Report, Effect of Flexural Rigidity and Internal Friction, No.1

Steady self-excited vibrations of a bowed string with flexural rigidity and internal friction subject to small air resistance are analysed by Fourier series solutions by means of series transformation method. The existence of small flexural rigidity brings about a large increase of the magnitude and fluctuation of the necessary bow force to maintain vibration. Small internal friction has an effect of mitigating these bad influences of flexural rigidity.

Study of Polymer Blends as a Vibration Damper

ABSTRACT Metallic materials have too small internal friction to damp vibration making noise, whereas plastics show remarkably large damping capacity in some characteristic temperature ranges where a considerable part of the vibrational energy is consumed as a result of molecular friction. If the two kinds of materials are combined, one can expect that the vibration of the composite materials will be damped to a greater extent than that of the metal itself. In this study dynamic mechanical properties of a variety of polymer blends were measured and those which have a broad E″ peak around 0°C were chosen from among them. Sandwich structures of Al/polymer/Al type were then constructed and the dynamic mechanical properties of the composite systems were measured by means of a vibration reed technique. It was found that the sandwich structures with these polymer blends had larger damping capacity than that with poly (vinyl acetate) or Al itself.

Dislocations, Relaxations, and Anelasticity of Crystal Quartz

By careful grinding and etching, contouring and mounting in a vacuum, very small internal friction coefficients ${Q}^{\ensuremath{-}1}$ are found in $\mathrm{AT}$ shear vibrating crystals. Various tests show that the internal friction corresponds to that of the quartz itself. The internal friction at room temperature increases proportionally to the frequency up to 100 Mc/sec indicating the presence of relaxations. These have been investigated by measuring the internal friction at very low temperatures down to 1.5\ifmmode^\circ\else\textdegree\fi{}K and two relaxations were found. One having a time constant of ${10}^{\ensuremath{-}13}$ second appears to be connected with a distorted lattice due to impurities while the other having a time constant of 7.7\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}10}$ second is thought to be connected with dislocation loops. Using equations developed previously for metals the indicated number of dislocations is $\overline{N}\ensuremath{\approx}{10}^{3}/{\mathrm{cm}}^{2}$, the average loop length about 1.8\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}3}$ cm and the ratio of Peierls force to shear modulus about 5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}8}$. Confirmation of these values is given by the time constant 7.7\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}10}$ second and the change in frequency as a function of amplitude. A long-time aging effect is thought to be due to closer pinning of dislocations by impurity atoms. It is suggested that an improved frequency standard, free from aging, can be obtained by holding the temperature of the crystal at liquid helium temperature.