Internal Friction Of Material Research Articles

Wedge-Shaped Hopper Design for Milled Woody Biomass Flow

The bioenergy industry has been challenged by unstable flow and transport of milled biomass in material handling operations. Handling issues such as hopper clogging and auger jamming are attributed to knowledge gaps between existing handling units designed for bulk solids and their suitability for milled biomass with high compressibility. This work investigates various flow behaviors of granular woody biomass in wedge-shaped hoppers. Hopper flow physical experiments and numerical simulations are conducted to study the influence of the critical material attributes and critical processing parameters on the flow pattern, arching, and throughput. The results show that (1) the preferred flow pattern, mass flow, can be achieved by controlling the material’s internal friction angle, hopper inclination, and hopper wall friction; (2) hopper arching, governed by the competing gravity-driven force against flow resistance from material internal friction and material–wall friction, can be controlled by the hopper wall friction angle and the inclination angle; and (3) flow throughput can be accurately estimated from our empirical equation with inputs of hopper outlet geometry and particle-scale to bulk-scale material attributes. This study elucidates woody biomass flow physics and provides guidance for industrial equipment design.

Identification of limiting damping mechanisms in a high quality factor hybrid resonator of space application gyroscope

• Studied hybrid gyroscope resonator damping mechanisms with imperfection sensitivity. • Realized thin film coated high precision resonator with few millions quality factor. • Limiting damping mechanisms are identified at each stage from design to realization. The performance of Hemispherical Resonator Gyroscopes (HRG) is decided by the mechanical resonator’s Quality factor ( Q factor). The Q factor is a measure of energy dissipation. A Q factor of few millions is needed to realize fine resolution millimeter size of the HRG for future interplanetary satellite missions. The objective is to carry out a detailed study of thermoelastic damping (TED), anchor loss, surface loss, material internal friction and fluid damping. A hybrid resonator is designed with very low TED. One of the major contributions of the present work is the study of the effect of thin film coating and different coating configurations on TED. Extensive simulations have been carried out on the effect of different fabrication deviations on anchor loss. A unique sensitivity study of mode interactions and mass unbalance pattern on frequency split and anchor loss mismatch is also done. Based on this, dimensional and geometric tolerances are derived for precision fabrication and the precision hybrid configuration resonator is realized. Surface loss and material internal friction are estimated. Also, surface characterisation has been done using nanoindentation techniques. Q factor of few millions is obtained in a fabricated precision resonator with thin film coating. Based on the estimation of different damping mechanisms and measurements, the limiting mechanisms are identified at each stage from the design to the realization. The Q factor of an uncoated resonator is limited by the surface loss while that of a coated resonator is limited by the coating induced additional TED, the coating material internal friction and the surface loss.

Design to Operational Parameters Dependency on Quality Factor of Sensor Mechanical Resonators

The critical functional part of any high performance resonance based sensor is a mechanical resonator. The performance is measured by resonator quality factor (Q-factor). Damping mechanisms such as thermoelastic damping (TED), anchor loss, surface loss, material internal friction, fluid damping and electronics damping are covered in this review with more focus on gyroscope resonators. Dissipations can be reduced by different means. Hence, the effects of various design to operational parameters on the Q-factor for different configurations, sizes and materials are reviewed in detail. Micro scale ring resonators can achieve a Q-factor of the order of hundreds of thousands. Macro scale hemispherical resonators are suitable for ultrahigh Q-factors. High temperature sensor operation is not preferred because of TED, while sub-zero operation is limited by material internal friction. Few orders of dissipation increase are seen with thin film metallic coating due to TED and coating material internal friction. High precision fabrication is mandatory to achieve the designed minimum anchor loss as it is highly sensitive to fabrication imperfections. Q-factor sensitivity to operating pressure is different for different resonator configurations. This review study helps to build a comprehensive mechanical resonator design, realization and operation strategy to achieve high sensor performance. A roadmap on future research requirements for developing compact mass producible CVG type sensors with ultrahigh Q-factor is also highlighted.

Energy Dissipation During Prey Capture Process in Spider Orb Webs

Abstract Capture of a prey by spider orb webs is a dynamic process with energy dissipation. The dynamic response of spider orb webs under prey impact requires a multi-scale modeling by considering the material microstructures and the assembly of spider silks in the macro-scale. To better understand the prey capture process, this paper addresses a multi-scale approach to uncover the underlying energy dissipation mechanisms. Simulation results show that the microstructures of spider dragline silk play a significant role on energy absorption during prey capture. The alteration of the microstructures, material internal friction, and plastic deformation lead to energy dissipation, which is called material damping. In addition to the material damping in the micro-scale modeling, the energy dissipation due to drag force on the prey is also taken into consideration in the macro-scale modeling. The results indicate that aerodynamic drag, i.e., aero-damping, plays a significant role when the prey size is larger than a critical size.

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

Predicting the critical outlet width of a hopper using a continuum finite element method model

In this work, the critical outlet widths (COWs) for continuous bulk solids flow predicted by Jenike's theory, the McLean correlation, Enstad's theory, and Finite Element Method (FEM) analysis are compared. The FEM predictions use a Mohr-Coulomb elasto-plastic constitutive model. Unlike Jenike's theory and the McLean correlation, Enstad's theory and the FEM model show that the COW depends on the material height. The effects of the material internal friction angle, slope of the flow function, wall friction angle, and hopper half angle on the COW predictions are explored. Comparisons to experimental COWs from the literature show that the FEM model provides, by far, the best predictions. The primary advantage of using an FEM model for COW predictions are that complex materials and hopper geometries may be simulated, where simplifying assumptions of the standard theoretical models are not valid.

Evolution of a hillslope by rock avalanches: insights from analog models

Rock avalanches are among the most hazardous processes on hillslopes because of high velocity, great dimensions, and long run-out distance. For this reason, understanding the dynamics and factors of rock avalanches and their role in hillslope evolution is crucial. Studies evidenced that occurrence and evolution of these phenomena are influenced by lithological, structural, and climatic factors. Statistical analysis on natural cases demonstrated correlations between slope geometry and rock avalanche volume. Most of the studies referred to experimental tests which represent powerful tools to understand these landslides. Many models focused on the mechanism leading to high velocity and long run-out, but few studies discuss the role of rock avalanches in the evolution of a bedrock hillslope. The influence of slope geometry and physical properties of the substratum on the dynamics of rock avalanches is poorly constrained. We present results from analog models of a hillslope evolving by base level lowering. We tested several slope widths and two analog materials. The experimental apparatus allowed for checking the mass of mobilized material at each step and for taking a 3D scan of the whole surface. Our results, coupled with a statistical analysis, indicated that hillslope evolution is influenced by the material internal friction and by the friction with box walls (i.e., valley walls) when the slope is narrow. Widening the slope, the influence of lateral friction disappears, confirming observations in other models and nature. These results represent a new contribution to understand the dynamics of rock avalanches on bedrock hillslopes.

Size-Effect Law for Scratch Tests of Axisymmetric Shape

AbstractThis paper presents a theoretical and experimental framework for the application of size-effect analysis to microscratch testing as a means to quantify the fracture properties and internal friction of materials at the microscale. The energetic size-effect law (SEL) for microscratch tests is developed for a general monomeric probe shape in terms of an intrinsic size function. The fundamental idea of the proposed approach is to rescale the scratch response to that of the flat punch, a conjecture that allows one to compare the SEL for different probe geometries, and thus solve for the asymptotic fracture toughness and effective process zone length from scratch tests done on homogenous (acetal homopolymer resin and polycarbonate resin) and inhomogeneous materials (mica ceramic and gas shale). As a material of current interest for controlled fracture studies, two samples of gas shale cored from the Marcellus and Eagle Ford formations are tested and analyzed to quantify all material properties that may ...

A composite particle model for non-spherical particles in DEM simulations

This paper presents a composite particle model with sphere clumps for modelling non-spherical particles in discrete element method (DEM) simulations. The formulation of the sphere clumps uses random selections of particle radii and positions, thus it can theoretically simulate all possible non-spherical particles encountered in engineering projects. In this study, the generation of sphere clumps in space was discussed in detail, and different particle non-sphericities were compared. This numerical model has been employed to study the shear behaviour of granular assemblies under undrained triaxial compression conditions. It is evident that the use of composite particle model in the DEM can largely increase the shear strengths of granular assemblies. For granular samples consisting of various types of sphere clumps, different mechanical responses have been observed. In particular, the sphere clumps with high non-sphericity can lead to very high peak/residual shear strength, and high material internal friction angle. The use of sphere clumps mixture can modulate the shear behaviour, with its mechanical properties being close to those of real quartz sand grains.

Flow performance of ground biomass in a commercial auger

The flow performance of preprocessed biomass plays an important role in biomass transportation and handling. The research as presented here investigated how the Angle of Repose (AOR) of miscanthus and switchgrass is related to flow performance of biomass particles in an auger that was originally designed to convey corn and soybeans. The flow performance metrics were the specific energy consumption (SEC), energy efficiency (EE), volumetric efficiency (VE), volumetric flow rate (VFR) and mass flow rate (MFR).The results showed that the EE and MFR while conveying miscanthus and switchgrass particles ground through 6.35-, 9.53-, 12.7- and 25.4-mm milling screens were much lower than those of corn. However, the differences in VFR between corn and biomass were much smaller than that in SEC and mass flow rate (MFR). This result implies that the low bulk density of biomass feedstock is a more pronounced limiting factor in biomass handling than the conveying mechanism used.The AOR of miscanthus and switchgrass particles was found proportional to particle size and moisture content. While AOR is an indicator of the material's internal friction, in this study, the AOR of miscanthus and switchgrass was not significantly related to the energy/volumetric efficiency of the auger. By comparing the measured auger power consumption to predictions from empirical equations developed for corn and soybean, it became evident that these equations do not perform well for biomass feedstock.

An exercise on slope stability and perfect elastoplasticity

In this paper the stability of an infinitely long granular slope is addressed in the framework of small-strain perfect elastoplasticity. The problem is approached by discussing the condition of strain localisation and, through a reinterpretation of the concept of ‘angle of natural repose', a modified strategy for evaluating the slope safety factor is introduced. The angle of natural repose is demonstrated to differ substantially from the material internal friction angle (as this can be determined from standard triaxial tests). The role of non-associativeness is critically discussed and simple shear stress paths are numerically simulated: pseudo-hardening and pseudo-softening regimes are described. The influence of the loading history on the overall ductility/brittleness of the system mechanical response is analysed. To stress the dependency of the angle of natural repose on the material ductility/brittleness, additional simple shear numerical results are illustrated for the case of a strain-softening constitutive relationship. Finally, the stability of the stratum under undrained conditions is critically tackled with reference to the phenomenon of static liquefaction of loose sands.

Memory-efficient displacement-based internal friction for wave propagation simulation

The characterization of anelastic losses due to material internal friction has become increasingly important in geophysical exploration and other seismological applications, as these losses greatly affect the amplitude and dispersion of seismic waves. Anelasticity is usually specified in terms of the material’s quality factor, [Formula: see text]. Different viscoelastic models have been used to represent [Formula: see text] as a function of frequency. Most of these models are defined in terms of stresses and strains as the primary variables. Thus, in three dimensions, a separate model needs to be associated with each of the six strain components. We introduce an internal friction model that uses, instead, displacements as primary variables. For a fiber, the proposed model consists of a set of three distinct elements in parallel with different relaxation mechanisms: namely, two elements that consist of a spring and a dashpot in series (Maxwell) and a third element that consists of a spring and a dashpot in parallel (Voigt). In addition to saving memory, this formulation is particularly suitable for finite-element schemes. The model exhibits an almost constant quality factor within the frequency range of interest, with a tolerance of 5% with respect to the target [Formula: see text] value, and provides a close approximation to the variation of the phase-velocity with frequency—as has been observed in empirical data. The extension of this model to 3D anelastic problems and its use in idealized cases, such as an infinite-space, a half-space, and a layered half-space, and the comparison of results with semi-analytical reference solutions obtained from theory and previous, similar studies, corroborates the validity of the proposed model for incorporating anelastic losses in wave propagation problems.

Parameter Estimation of Particle Flow Model for Soils Using Neural Networks

A calibration process is developed to determine the parameter values. Three-axial compressions tests in laboratory and neural network are used to determine the material internal friction angle and stiffness, respectively. These tests are repeated numerically using PFC models with different sets of particle friction coefficients and particle stiffness values. Three-axial compressions tests are found to be dependent on both the particle friction coefficient and the particle stiffness. The compression test results can be used to determine a unique set of particle friction and particle stiffness values. The calibration process is validated by modelling filling process of head chamber of shield machine. It is shown that the parameter estimation procedure proposed in the paper can accurately predict the deformation characteristics and flow patterns of conditioned soils.

Calibration of granular material parameters for DEM modelling and numerical verification by blade–granular material interaction

The discrete element method (DEM) is a promising approach to model blade–granular material interactions. The accuracy of DEM models depends on the model parameters. In this study, a calibration process was developed to determine the parameter values. The particle size was the same as the real material and the particle shape was modelled using two spherical particles rigidly clumped together to form a single grain. Laboratory shear tests and compressions tests were used to determine the material internal friction angle and stiffness, respectively. These tests were replicated numerically using DEM models with different sets of particle friction coefficients and particle stiffness values. The shear test results are found to be dependent on both the particle friction coefficient and the particle stiffness. The compression test results show that it is only dependent on the particle stiffness. The combination of shear test and compression test results can be used to determine a unique set of particle friction and particle stiffness values. The calibration process was validated experimentally and numerically by modelling a blade moving through granular material. Results show that the forces acting on the blade can be accurately modelled with DEM and the maximum error is found to be 26%. The relative particle-blade displacements were used to predict the position and shape of the shear lines in front of the blade. A good qualitative correlation was achieved between the experiments and the DEM simulations.

Calibration of discrete element parameters and the modelling of silo discharge and bucket filling

The discrete element method (DEM) is a promising approach to model machine–granular material interaction. The accuracy of DEM models depends on the model parameters. In this study a calibration process is developed to determine the parameter values. Laboratory shear tests and compressions tests are used to determine the material internal friction angle and stiffness, respectively. These tests are repeated numerically using DEM models with different sets of particle friction coefficients and particle stiffness values. The shear test results are found to be dependent on both the particle friction coefficient and the particle stiffness. The compression test results show that it is only dependent on the particle stiffness. The combination of shear test and compression test results can be used to determine a unique set of particle friction and particle stiffness values. The calibration process is validated by modelling silo discharge and bucket filling. It is shown that DEM can accurately predict the silo discharge rate and flow patterns. It is also shown that DEM can predict bucket forces, fill rates and fill patterns.

Prelimiting Plastic Deformation of Loose Medium in a Rotary Drum

A problem on behavior of loose medium in a rotary drum is solved with taking into account the dilatancy and internal friction of material, as well as the elastic and prelimiting plastic strains. It is shown that when the drum rotation angle increases, material may be deformed in two modes. Under the first mode, prelimiting state is reached at the material and drum interface, and the material displaces as a rigid whole. Under the second mode, prelimiting state is reached near the free surface of the material, and a flow sets on in the upper layer, which leads to mixing. The fields of displacements and stresses are constructed, and the regions of active loading and elastic unload are determined.

Bifurcation of a shaft with hysteretic-type internal friction force of material

The bifurcation of a shaft with hysteretic internal friction of material was analysed. Firstly, the differential motion equation in complex form was deduced using Hamilton principle. Then averaged equations in primary resonances were obtained using the averaging method. The stability of steady-state responses was also determined. Lastly, the bifurcations of both normal motion (synchronous whirl) and self-excited motion (nonsynchronous whirl) were investigated using the method of singularity. The study shows that by a rather large disturbance, the stability of the shaft can be lost through Hopf bifurcation in case the stability condition is not satisfied. The averaged self-excited response appears as a type of unsymmetrical bifurcation with high orders of co-dimension. The second Hopf bifurcation, which corresponds to double amplitude-modulated response, can occur as the speed of the shaft increases. Balancing the shaft carefully to decrease its unbalance level and increasing the external damping are two effective methods to avoid the appearance of the self-sustained whirl induced by the hysteretic internal friction of material.

Microscale technique for in situ measurement of elastic parameters of materials under reactive atmosphere

This article discusses a technique for measuring elastic bulk parameters of metallic samples of micrometric sizes (3–100 μm thick) under a controlled atmosphere. This method offers the benefit of being relatively easy to implement, relying on off-the-shelf instrumentation, while still providing an excellent sensitivity. Furthermore, this technique allows the analysis of the elastic behavior of thin film that is not possible with another approach. A small cell that holds microcantilever shaped metal has been designed to perform measurements from vacuum to several bars of reactive atmosphere such as hydrogen. Young’s modulus and internal friction of materials were measured by the flexural resonance response of the cantilever. We discuss the reliability of the continuum mechanics on a microscopic scale in order to understand the limit thickness of palladium microcantilever which was experimentally found to be 20 μm. Then, we demonstrate that the measurements of Young’s modulus of different materials (Al, Au, Cu, Fe, Pd) were accurate within 2%. This technique was found to be particularly suitable for investigating the change in elastic properties of thin materials during hydrogenation.

Impulse excitation apparatus to measure resonant frequencies, elastic moduli, and internal friction at room and high temperature

This paper presents a new apparatus to measure elastic properties and internal friction of materials. The apparatus excites the test specimen by a light mechanical impact (impulse excitation) and performs a software-based analysis of the resulting vibration. The resonant frequencies fr of the test object are determined and, in the case of isotropic and regular shaped specimens, the elastic moduli are calculated. The internal friction value (Q−1) is determined for each fr as Q−1=k/(πfr) with k the exponential decay parameter of the vibration component of frequency fr. A furnace was designed and equipped with automated impulse excitation and vibration detection devices, thus allowing computer-controlled measurements at temperatures up to 1750 °C. The precision of the measured fr depends on the size and stiffness of the specimen, and varies from the order of 10−3 (that is ±1 Hz at 1 kHz) in soft, high damping materials or light specimens, to values as precise as 10−5 (that is ±0.1 Hz at 10 kHz) in larger or stiffer specimens. The highly reproducible Q−1 measurements are accurate whenever the relation Q−1=k/(πfr) holds. The precision of the Q−1 measurement depends on the suspension or support of the specimen, and on the specimen size. Since external energy losses are relatively smaller for larger specimens, the lower limit of measurable Q−1 extends from 10−3 for small specimens (for example <1 g) down to 10−5 with increasing specimen size. High temperature tests have shown that Q−1 can be monitored up to values of about 0.1.

Device for determination of elasticity and nonelasticity characteristics of materials in vacuum at low temperatures

The article describes a device for study of the elasticity characteristics and coefficient of internal friction of materials in vacuum at low temperatures up to 10 K. As an illustration, temperature dependences of the Young's modulus and logarithmic decrement of vibrations of steel 01Kh12G9N3 with anomaly of the Young's modulus are presented.