Breakage of anisometric rod-shaped particles

In this experimental study, behavior of dry granular layers of monodisperse cylindrical particles (8?×?1?mm) under uniaxial compression in piston die arrangement was investigated. The layer compressibility and particle size distribution (PSD) were measured. It was found that neither the piston speed nor the layer size were relevant, within the experimental range. The compressibility and PSD were affected mainly by the applied load. At the single compression, with the increasing pressure, PSD moves toward smaller sizes of broken particles always leaving some initial particles intact. At the repetitive compression, the pressure had more destructive effect, resulting in larger particle fragmentation.     

Influence of Punch Velocity on the Compressibility of Granules

Abstract

The influence of punch velocity over the range 1-30 mm/min on the compressibility of granules and particles was studied using a modified Kawakita equation. Granule strength (S_t) increased with increasing concentration and viscosity of binder solution as well as increasing mean molecular weight of binding agent. The compressibility of powders was evaluated by the modified Kawakita equation (K). For the granules, the relationship between pressure and reciprocal of porosity (I/ε) showed an inflection point, but for the particles, no such inflection point was found. The slope of low compression stress in the stage of densification by powder slippage and rearrangement was the constant K₁; and slope of high compression stress in the stage of elastic, plastic deformation and plastic fracture of particles was the constant K₂. The K₁ values decreased with increasing punch velocity. An approximately linear relationship was observed between reciprocal of compressibility constant (I/K₂) and granule strength (S_t). For crystalline lactose, K values decreased with increasing punch velocity, indicating that compressibility was lowered. Thus, compressibility was shown to be dependent on type of crystal. The quantity of stress relaxation increased with increasing punch velocity. Especially, constant a and b values in a cellulose system (HPC) were greater than those in a noncellulose system (PVP). As a good relationship was found between constants a, b and constant K₂, materials which undergo plastic deformation and fragmentation have great stress relaxation. The radial tensile strength (σ_t) increased with increasing granule strength (S_t). We concluded from these findings that the σ_t value was affected by the contact area rather by than the number of contact points.     

Enhanced compressibility tomography

We are interested here in the inversion of data leading to high quality imaging of physical parameters. We deal with ultrasonic diffraction tomography and first show how far field diffraction measurements of an incident plane wave give access to the spatial Fourier transform of a composite object. In the case of an acoustic model (soft tissues), this object is characterized by two parameters, e.g., the compressibility and density, each being affected by its own point spread function. The development of quantitative imaging proceeds from the separation of each parameter contribution. This can be done by measuring the scattered field over an arc for several transmitter positions around the object. This allows us, under specified conditions, to reconstruct either the compressibility, or the velocity, or the impedance maps. We have focused on compressibility imaging for which we propose a novel algorithm based on a redundant reconstruction procedure. We present tomograms of biological phantoms obtained with our experimental set-up     

Properties of the Anisimkin Jr.' modes in quartz plates

Dispersion curves, surface displacements, and displacement profiles over the plate thickness are numerically calculated for acoustic plate modes, propagating in fused and Y-rotated, X-cut quartz samples with thickness h/lambda in the range 0-4.5 (h, thickness; lambda, wavelength). The Anisimkin Jr.' modes with velocity v(n) close to that of longitudinal bulk wave v(L) and the dominant longitudinal displacement u1 distributed uniformly through the plate thickness are found in quartz crystals with cut angles mu = 120 degrees-140 degrees and plate thickness h/lambda = 0-0.36, 0.94-1.78, 2.32-3.08, and 3.64-4.44. The same modes in fused quartz are not found, except in a narrow region near zero thickness.     

Influence of particle breakage on the dynamic compression responses of brittle granular materials

The dynamic compression responses of dry quartz sand are tested with a modified spilt Hopkinson pressure bar (MSHPB), and the quasi-static compression responses are tested for comparison with a material testing system. In the experiments, the axial stress–strain responses and the confining pressure of the jacket are both measured. Comparison of the dynamic and the quasi-static axial stress–strain curves indicate that dry quartz sand exhibits obvious strain-rate effects. The grain size distributions of the samples after dynamic and quasi-static loading are obtained with the laser diffractometry technique to interpret the rate effects. Quantitative analyses of the grain size distributions show that at the same stress level, the particle breakage extent under quasi-static loading is larger than that under dynamic loading. Moreover, the experimental and the theoretical relationships of the particle breakage extent versus the plastic work show that the energy efficiency in particle breakage is higher under quasi-static loading, which is the intrinsic cause of the strain-rate effects of brittle granular materials. Using the discrete element method (DEM), the energy distributions in the brittle granular material under confined compression are discussed. It is observed that the input work is mainly transformed into the frictional dissipation, and the frictional dissipation under dynamic loading is higher than that under quasi-static loading corresponding to the same breakage extent. The reason is that more fragmentation debris is produced during dynamic breakage of single grains, which promotes particle rearrangement and the corresponding frictional dissipation significantly.     

Measurement of acoustic reflection coefficients by an ultrasonicmicrospectrometer

An ultrasonic microspectrometer (UMSM) was developed in order to evaluate the elastic properties of a solid specimen at a small spot on its surface. In this system, spherical-planar-pair (SPP) lenses were used, by which the acoustic reflection coefficient of a liquid/solid interface was measured as a function of the incident angle in the frequency range from 20 to 140 MHz. Using a specimen of fused quartz whose material constants were well known, the measurement accuracy was examined. The phase velocity of a leaky Rayleigh wave was obtained from the phase change of the reflection coefficient with 0.4% accuracy in this frequency range. For a specimen of steel with a large acoustic attenuation, bulk attenuation factors and their frequency dependence were successfully estimated by computer-fitting of the reflection coefficient. As an example of anisotropic materials, the reflection coefficient of X-cut quartz was also measured. Measured phase of the reflection coefficient was in good agreement with numerical calculation     

脉管制冷机光纤结构回热器特性的模拟与分析

提出采用基于多孔光纤技术的以熔融石英为材料的回热器构想,其流道水力半径可以达到比高目数不锈钢丝网更小的尺度,然后就635目不锈钢丝网(rh=8μm)和熔融石英多孔平行管(rh=8μm、5μm、1μm)等4个算例进行模拟计算和优化分析。结果显示,在相同的高频工作环境下,采用熔融石英多孔管回热器脉管制冷系统的COP高于采用635目不锈钢丝网系统的COP,并在一定范围内随着石英多孔管水力半径的减小而增高。     

An analysis of nonlinear vibrations of coupled thickness-shear and flexural modes of quartz crystal plates with the homotopy analysis method

We investigated the nonlinear vibrations of the coupled thickness-shear and flexural modes of quartz crystal plates with the nonlinear Mindlin plate equations, taking into consideration the kinematic and material nonlinearities. The nonlinear Mindlin plate equations for strongly coupled thickness- shear and flexural modes have been established by following Mindlin with the nonlinear constitutive relations and approximation procedures. Based on the long thickness-shear wave approximation and aided by corresponding linear solutions, the nonlinear equation of thickness-shear vibrations of quartz crystal plate has been solved by the combination of the Galerkin and homotopy analysis methods. The amplitude frequency relation we obtained showed that the nonlinear frequency of thickness-shear vibrations depends on the vibration amplitude, thickness, and length of plate, which is significantly different from the linear case. Numerical results from this study also indicated that neither kinematic nor material nonlinearities are the main factors in frequency shifts and performance fluctuation of the quartz crystal resonators we have observed. These efforts will result in applicable solution techniques for further studies of nonlinear effects of quartz plates under bias fields for the precise analysis and design of quartz crystal resonators.     

Plastic buckling analysis of a circular cylinder considering plastic compressibility

In this study the plastic buckling analysis of a circular cylinder under axial compression is carried out considering plastic compressibility. For the stability analysis, the linearized finite element equation is derived and the general elastic-plastic constitutive equation is formulated. The Drucker-Prager plastic potential is used to describe the plastic compressible yielding and the strength-differential effect. The influence of plastic compressibility on the buckling load is investigated for a circular cylinder.     

冲击压缩下A95陶瓷动态力学特性数值模拟

采用ANSYS/LS-DYNA数值模拟了平面冲击波压缩下A95陶瓷的自由面质点速度历程,将数值模拟结果与平板冲击压缩实验结果进行了对比分析.数值模拟结果表明采用JH-2材料模型能够较好地模拟陶瓷类材料在强动载荷作用下的物理力学性能.     

Evaluation of Era-Tab as a Direct Compression Excipient

The physical and compressional properties of a modified rice starch, Era-Tab, were evaluated and compared with those of 4 commercially available direct compression excipients, namely, microcrystalline cellulose (Avicel PH-101), partially pregelatinized starch, spray-dried lactose (Super-Tab Lactose), and granular dicalcium phosphate dihydrate (Emcompress). It was found that Era-Tab possessed high flowability and adequate compressibility. The compacted material made with Era-Tab has a higher crushing strength and a lower friability than 3 other direct compression excipients, except microcrystalline cellulose. Tablets containing terfenadine of the same degree of hardness (10 kg) were also prepared using different direct compression excipients. The disintegration time of the tablets made with Era-Tab was approximately 2.5 min. The maximum of the accumulated percentage of terfenadine released from the tablet reached 90%, and 63.2% of it was released within 20 min. Both the powder characteristics and tablet properties show that the modified rice starch, Era-Tab, is a useful product as a direct compression tablet excipient.     

一种高压缩性水雾化铁粉生产工艺的探讨

高压缩性水雾化钢铁粉末市场需求日益扩大,研发高压缩性水雾化生产工艺势在必行,根据实际生产情况,理论结合实践,改善提高生产条件,在生产过程中不断摸索合适生产因素,在不影响粉末整体使用性能的前提下,逐步提高水雾化粉压缩性能,为广大制品用户提供优质可靠的原料。     

A model for predicting uniaxial compression behavior of fused fibrous networks

Fused fibrous networks are increasingly being used for emerging industrial applications ranging from thermal/sound insulation, fluid filtration/separation, and energy conversion to tissue scaffolds. Majority of these applications need a deeper understanding of fused fibrous networks under compression loading. In this research work, a compression model of fused fibrous networks has been proposed by defining two distinct regions displaying the bending of free fiber segments between the fiber-to-fiber contacts followed by the transverse compression of fiber contacts through classical Hertzian contact mechanics approach. The mechanistic models developed in this study, have clearly elucidated the main fiber and structural parameters that control the compression behavior of fused fibrous networks. A comparison has also been made between the theoretical and experimental pressure–strain curves of randomly and preferentially aligned fused fibrous networks.     

Isochoric Compressibility of Solid 4He

We have performed experiments in which we inject atoms into hcp, solid ⁴He contained in a cell of fixed volume at pressures greater than the bulk melting pressure. We measure the change in pressure of the solid in response to the injection, which gives a measure of the isochoric compressibility. We show that at T??700?mK the solid undergoes very little growth and is incompressible. With decreasing temperature the compressibility rises, saturates near T??400 mK and may show weak evidence of a decrease near T??250 mK. Measurements at lower temperatures are necessary to fully test the predictions.     

Dynamics of the Moving Load Acting on the Hydro-elastic System Consisting of the Elastic Plate,Compressible Viscous Fluid and RigidWall

The subject of the paper is the study of the dynamics of the moving load acting on the hydro-elastic system consisting of the elastic plate, compressible viscous fluid and rigid wall. Under this study the motion of the plate is described by linear elastodynamics, and the motion of the compressible viscous fluid is described by the linearized Navier-Stokes equations. Numerical results are obtained for the case where the material of the plate is steel, but the fluid material is Glycerin. According to these results, corresponding conclusions related to the influence of the problem parameters, such as fluid viscosity, plate thickness, fluid depth, fluid compressibility and initial stresses on the inter-phase normal stress and normal and tangent velocities of the fluid caused by the load which moves with constant velocity, are made. In particular, it is established that the influence of the fluid viscosity of the aforementioned quantities becomes more considerable under lower velocities of the moving load. Moreover, it is established that there exists a critical velocity of the moving load under which a resonance type event takes place.     

Remarks on multiaxial fatigue limit criteria based on prismatic hulls and ellipsoids

This paper focuses on a class of multiaxial fatigue limit criteria where the equivalent shear stress amplitude is calculated by means of a scalar measure associated with a hypersurface enclosing the deviatoric stress history at a material point. We consider two hypersurfaces proposed by the authors, namely the maximum prismatic hull and the minimum Frobenius norm ellipsoid. Previous results obtained with elliptic and non-elliptic stress paths strongly suggested that such measures might always be the same. In this work we consider two counter-examples which show that these approaches are distinct. Fatigue limit criteria based on the linear combination of these measures with the maximum hydrostatic stress were applied to experimental data including: axial–torsional, biaxial tension and plane stress tests performed under harmonic and non-harmonic, synchronous and asynchronous waveforms. The predictions for both criteria fell within a 15% scatter band.     

Shock adiabat,phase diagram,and viscosity of mercury at a pressure up to 50 GPa

The results of measurements of shear viscosity of mercury under shock compression, obtained in [1]by the method of decay of small perturbations preassigned at the shock wave front, are considered in the light of new data on the phase diagram, isothermal compressibility, and equation of state for mercury in the high-pressure region. It is demonstrated that the measured value of viscosity η = 0.8 kPa s at a shock compression pressure of 44 GPa (which differs from the initial state under normal conditions by a factor of 5 × 10⁵) corresponds to the transition of mercury under shock compression to the solid state..     

Prediction of fracture healing under axial loading,shear loading and bending is possible using distortional and dilatational strains as determining mechanical stimuli

Numerical models of secondary fracture healing are based on mechanoregulatory algorithms that use distortional strain alone or in combination with either dilatational strain or fluid velocity as determining stimuli for tissue differentiation and development. Comparison of these algorithms has previously suggested that healing processes under torsional rotational loading can only be properly simulated by considering fluid velocity and deviatoric strain as the regulatory stimuli. We hypothesize that sufficient calibration on uncertain input parameters will enhance our existing model, which uses distortional and dilatational strains as determining stimuli, to properly simulate fracture healing under various loading conditions including also torsional rotation. Therefore, we minimized the difference between numerically simulated and experimentally measured courses of interfragmentary movements of two axial compressive cases and two shear load cases (torsional and translational) by varying several input parameter values within their predefined bounds. The calibrated model was then qualitatively evaluated on the ability to predict physiological changes of spatial and temporal tissue distributions, based on respective in vivo data. Finally, we corroborated the model on five additional axial compressive and one asymmetrical bending load case. We conclude that our model, using distortional and dilatational strains as determining stimuli, is able to simulate fracture-healing processes not only under axial compression and torsional rotation but also under translational shear and asymmetrical bending loading conditions.     

石英砂脱水性能的研究

通过大量试验结果 ,研究了各种粒度范围的石英砂的脱水性能 ,包括沉降特性、过滤性能、极限压缩浓度等 ,为进行此类产品的固液分离提供了重要的参考数据     

Validation of the photomechanical spalling test in the case of non-linear dynamic response: Application to a granite rock

In this paper, the use of the virtual fields method for the identification of a strongly asymmetric compression–tension response of rock-like materials under dynamic tensile loading is investigated. The photomechanical spalling set-up is used, which induces an indirect tensile load in a non-balanced sample, and the inertial component of the test is directly related to the measured dynamic stress with no previous assumption on the material behaviour. This experimental method provides a direct route to identifying the material asymmetric constitutive response in compression and tension under a uniaxial stress state as well as the material non-linear response after tensile strength is reached. To validate this approach, the entire measurement chain for the case of a post-peak response is investigated through simulated experiments that incorporate a damage model and synthetic grid images. Finally, the method is applied to the case of granite rock, namely, a Bohus granite, as to directly measure the material asymmetric compression–tension and the softening response after peak tensile stress.