芯砂粘模性的测试方法

芯砂粘模性的测试方法哈尔滨工业大学（哈尔滨１５０００１）吉林工业大学（长春１３００２５）第一汽车集团公司石晶玉＊何镇明王强于殿峰关键词：芯砂粘模性脱模芯砂粘模是铸造生产中常见的现象，它会引起砂芯掉肉、起模困难等问题。合理地芯盒设计和选用适当的粘结剂并...

冷硬呋喃树脂砂防粘模技术的研究

就冷硬呋喃树脂砂使用过程中常见的粘模问题进行了较系统的研究．通过对木质芯盒和铝芯盒采用不同的脱模剂进行的一系列试验表明，自制的Ｊ—Ｂ溶液是较理想的一种脱模剂．

粘模的各种因素及防止措施

用冲压成形模具加工薄钢板中伴随滑动所产生的粘模是由于薄钢板和模具金属接触引起的烧粘,在模具或薄钢板表面将出现严重伤痕现象。在汽车车体的薄板冲压加工中,在使用普通钢板时已出现粘模现象。最近由于使用了高强度钢板,有大量发生粘模现象的趋势,所以人们希望对此采取防止措施。目前,粘模试验方法还没有实现标准化,每个研究人员应该抓住目的和特征值的关系,

Local existence and uniqueness of solutions to the evolutionary model for magnetoviscoelasticity

In this paper,we prove the local existence and uniqueness of solutions to the evolutionary model for magnetoviscoelasticity in R^(2),R^(3).This model consists of an incompressible Navier-Stokes,a regularized system for the evolution of the deformation gradient and the Landau-Lifshitz-Gilbert system for the dynamics of the mag-netization.Our approach depends on approximating the system with a sequence of perturbed systems.

FEM tire model oriented to virtual experiment of off-road vehicle trafficability

In order to estimate the trafficability of off-road vehicles, the linear relationships between the pressure and the stiffness of the tire and the action of the vertical tire force with the viscoelasticity are analyzed. The method to improve the precision of the model by the coefficients is presented. The constitutive equation of the three-parameter linear model and the stiffness matrix of four-node isoparametric elements are derived to construct the FEM （finite element method） tire model in plan stress. A demarcation and verification system is designed based on the six-dimensional wheel force transducer and the vertical tire force is measured under different velocities. The results show that the model and the method proposed are reasonable.

BISQ model based on a Kelvin-Voigt viscoelastic frame in a partially saturated porous medium

Taking into account three important porous media mechanisms during wave propagation （the Biot-flow, squirt-flow, and solid-skeleton viscoelastic mechanisms）, we introduce water saturation into the dynamic governing equations of wave propagation by analyzing the effective medium theory and then providing a viscoelastic Biot/squirt （BISQ） model which can analyze the wave propagation problems in a partially viscous pore fluid saturated porous media. In this model, the effects of pore fluid distribution patterns on the effective bulk modulus at different frequencies are considered. Then we derive the wave dynamic equations in the time-space domain. The phase velocity and the attenuation coefficient equations of the viscoelatic BISQ model in the frequency-wavenumber domain are deduced through a set of plane harmonic solution assumptions. Finally, by means of numerical simulations, we investigate the effects of water saturation, permeability, and frequency on compressional wave velocity and attenuation. Based on tight sandstone and carbonate experimental observed data, the compressional wave velocities of partially saturated reservoir rocks are calculated. The compressional wave velocity in carbonate reservoirs is more sensitive to gas saturation than in sandstone reservoirs.

Modeling and analysis of azimuthal AVO responses from a viscoelastic anisotropic reflector

We propose a method for mOdeling azimuthal AVO responses from a fractured i reflector. The method calculates the integrated reflected wavetrains, and the wavetrains contain elastodynamic information including the contrast in impedance and anelasticity i across interfaces, the intemal anisotropic propagation, the dispersion and attenuation along i the wave path, and tuning and interference. The results suggest that for large angles of incidence, the velocity dispersion and attenuation increase the amplitudes of PP waves from the top and decrease those from the bottom. For azimuthal responses at specific angles of incidence, the reflected wavetrains of PP waves tend to have longer duration with increasing azimuth. In contrast, model-converted PSV and PSH reflections show stable azimuthal features and are less affected by the reflector thickness. The amplitudes of PSV reflections increase with increasing azimuth; moreover, the waves have no reflection energy at 0° and 90° azimuth and maximum amplitude at 45° azimuth.

Numerical simulation of viscous liquid sloshing by moving-particle semi-implicit method

A meshless numerical simulation method, the moving-particle semi-implicit method （MPS） is presented in this paper to study the sloshing phenomenon in ocean and naval engineering. As a meshless method, MPS uses particles to replace the mesh in traditional methods, the governing equations are discretized by virtue of the relationship of particles, and the Poisson equation of pressure is solved by incomplete Cholesky conjugate gradient method （ICCG）, the free surface is tracked by the change of numerical density. A numerical experiment of viscous liquid sloshing tank was presented and compared with the result got by the difference method with the VOF, and an additional modification step was added to make the simulation more stable. The results show that the MPS method is suitable for the simulation of viscous liquid sloshing, with the advantage in arranging the particles easily, especially on some complex curved surface.

Vertical vibration of a floating pile in a saturated viscoelastic soil layer overlaying bedrock

An axisymmetrical analytical solution is developed to investigate the vertical time-harmonic vibration of a floating pile in a saturated viscoelastic soil layer overlaying bedrock. The soil is described by porous medium model established by Boer, while the pile is described by a beam vibration theory. By using separation theory of differential operator and variables to solve the dynamic governing equations for the soil, the fundamental solutions for the soil reactions on side and bottom of the pile are obtained. The dynamic impedance of the pile head is then derived by solving the vibration equation for the pile according to the compatibility condition between the pile and the soil. The proposed model is validated by comparing special cases of our model with the existing results. Numerical examples are presented to analyze the vibration characteristics of the pile.

Influence of features of natural soft clay on behaviour of embankment

The influence of different features of natural soft clays,namely anisotropy,destructuration and viscosity,on modelling the time-dependent behaviour of Murro embankment was investigated.The newly developed elasto-viscoplastic models were enhanced for determining viscosity parameters in a straightforward way and adopted for the finite element analysis.The same set of common parameters determined from conventional triaxial and oedometer tests was employed for all models,with additional parameters required for representing different soil features.The finite element predictions by using models coupled with BIOT's consolidation theory were compared with each other and with field data for settlement,horizontal displacement and excess pore pressures.In addition,the stress paths under the embankment loading were also compared with each other to improve the understanding of the effect of different soil features.All simulations demonstrate that all three features significantly influence the predictions.As a consequence,accounting for soil features needs to be carefully considered when they are applied to a construction site.

Laparoscopic resection of an adrenal pseudocyst mimicking a retroperitoneal mucinous cystic neoplasm

Adrenal pseudocysts are rare cystic masses that arise within the adrenal gland and are usually non-functional and asymptomatic. Adrenal pseudocysts consist of a fibrous wall without a cellular lining. We report a patient with a 9 cm, left-sided suprarenal cystic mass who presented with abdominal discomfort of 2 years＇ duration. A 38-year-old woman was referred to our service for evaluation of abdominal discomfort and gastrointestinal symptoms. Routine laboratory tests were within normal limits. An abdominal computed tomography scan showed a 9 cm × 8 cm × 8 cm well-defined cystic lesion displacing the left kidney. Magnetic resonance imaging showed a cystic lesion with low signal intensity on the Tl-weighted image and high signal intensity on the T2-weighted image. A laparoscopic left adrenalectomy was performed to diagnose the lesion. The final pathology showed an adrenal pseudocyst without a cellular lining. The patient had no postoperative complications and she was discharged four days after surgery.

Numerical Simulation of Viscous Flow Through Spherical Particle Assemblage with the Modified Cell Model

The cell model developed since 1950s is a useful tool forexploring the behavior of particle assemblages, but it demandsfurther careful development of the outer boundary conditions so thatinteraction in a particle swarm is better represented. In this paper,the cell model and its development were reviewed, and themodifications of outer cell boundary conditions were suggested. Atthe cell outer boundary, the restriction of uniform liquid flow wasremoved in our simulation conducted in the reference frame fixed withthe particle.

Bulk and bubble-scale experimental studies of influence of nanoparticles on foam stability

Influence of silicon oxide(SiO_2) and aluminum oxide(Al_2O_3) nanoparticles on the stability of nanoparticles and sodium dodecyl sulfate(SDS) mixed solution foams was studied at bulk and bubble-scale. Foam apparent viscosity was also determined in Hele-Shaw cell In order to investigate the foam performance at static and dynamic conditions. Results show that the maximum adsorption of surfactant on the nanoparticles occurs at 3 wt% surfactant concentration. Foam stability increases while the foamability decreases with the increasing nanoparticle concentration. However, optimum nanoparticle concentration corresponding to maximum foam stability was obtained at 1.0 wt% nanoparticle concentration for the hydrophilic SiO_2/SDS and Al_2O_3/SDS foams. Foam performance was enhanced with increasing nanoparticles hydrophobicity. Air-foams were generally more stable than CO_2 foams.Foam apparent viscosity increased in the presence of nanoparticles from 20.34 mPa·s to 84.84 mPa·s while the film thickness increased from 27.5 μm to 136 μm. This study suggests that the static and dynamic stability of conventional foams could be improved with addition of appropriate concentration of nanoparticles into the surfactant solution. The nanoparticles improve foam stability by their adsorption and aggregation at the foam lamellae to increase film thickness and dilational viscoelasticity. This prevents liquid drainage and film thinning and improves foam stability both at the bulk and bubble scale.

Constitutive Model of Saturated Soft Clay with Cyclic Loads under Unconsolidated Undrained Condition

An equivalent visco-elastic model of saturated soft clay was studied under unconsolidated undrained (UU) condition, which can be used to evaluate the stability of ocean foundation. Cyclic triaxial compression and extension tests were conducted to study the parameters of the model. Results showed that the relationships of the damping ratio and the octahedral shear modulus with the octahedral cyclic shear strain were nearly unique, when the initial octahedral shear stress ratios of specimens were equal to 0.3, 0.5 and 0.7. The relationships of the damping ratio and the octahedral shear modulus with the octahedral cyclic shear strain determined from the cyclic triaxial compression tests were basically the same as those determined from the cyclic triaxial extension tests. Furthermore, the relationships were not related to the initial stress condition, the test stress state and the octahedral cyclic shear stress ratio. The relationships determined from the cyclic triaxial tests under no deviatoric stress were basically the same as those determined from the cyclic triaxial tests under deviatoric stress. The change of the octahedral cyclic accumulative strain with the number of cycles was unique under different tests stress states. An equivalent visco-elastic constitutive model of saturated soft clay under UU condition was initially established.

Some Magnetized Bulk Viscous String Cosmological Models in Cylindrically Symmetric Inhomogeneous Universe with Variable Λ-Term

Some cylindrically symmetric inhomogeneous viscous fluid string cosmological models with magnetic field and cosmological term A varying with time are investigated. To get the deterministic solution, it has been assumed that the expansion （θ） in the model is proportional to the eigen value σ^11 of the shear tensor σ^ij. The value of cosmological constant for the model is found to be small and positive, which is supported by the results from recent supernovae Ia observations. The effect of bulk viscosity is to produce a change in perfect fluid and hence exhibits essential influence on the character of the solution. The physical and geometric properties of the models are also discussed in presence and absence of magnetic field.

Model Test and Numerical Analysis on Long-Term Mechanical Properties of Stepped Reinforced Retaining Wall

Model tests and numerical analyses of stepped reinforced retaining wall were performed to investigate the effects of rheology of backfill and creep of geogrids on the long-term performance of the structure.The geogrid tensions,soil pressures,wall deformations and foundation pressure were measured during model construction and loading.A visco-elasto-plastic model and an empirical nonlinear visco-elastic model were utilized to simulate the stresses and deformations of geogrid-reinforced earth-retaining wall under long-term loads.By comparing test data with numerical results,it is shown that the foundation pressure distribution is nonlinear,and the lateral constraint of geogrids for backfill can cause a redistribution of foundation pressure.The curve of soil pressure is outside convex at each step initially,and it is close to the distribution for the case of vertical wall subsequently.The variation trend of geogrid tensions at different heights is obtained.Moreover,the failure mechanism and development mode of potential slip surface in retaining wall are proposed.

A triaxial creep model for coal containing gas and its stability analysis

Triaxial creep tests on CCG specimens were systematically performed using aself-made creep seepage experimental apparatus for determining the creep law of CCG.An improved triaxial creep model of CCG was established on the basis of a Nishiharamodel and another visco-elasto-plastic model,parameters of which were fitted on test data.Furthermore,the creep model is validated according to the result of triaxial creep experiments,and the outcome shows that the proposed triaxial creep model can properly characterizethe properties of various creep deformation phases of CCG,especially the acceleratingcreep phase.At the same time,the instability conditions of CCG were presentedbased on the discussion of the improved model's stability in terms of stability theories ofdifferential equation solution.

An analytic solution describing the visco-elastic deformation of coal pillars in room and pillar mine

Coal pillar deformation is typically nonlinear and time-dependent. The accurate prediction of this defor- mation has a vital importance for the successful implementation of mining techniques. These methods have proven very important as a way to excavate coal resources from under buildings, railways, or water bodies. Elastic and visco-elastic theory are employed with a Maxwell model to formulate an analytic solution for displacement of coal pillars in room and pillar mine. These results show that the visco-elastic solution adequately predicts the coal pillar deformation over time. We conclude that the visco-elastic solution can predict the coal pillar and roadway displacement from the measured geological parameters of the conditions in situ. Furthermore, this method would be useful for mine design, coal pillar support optimization, ground subsidence prediction, and coal pillar stability analysis.