板岩渐进剪切破坏各向异性及其数值模型研究

层理面是导致岩石试样在变形和力学特性上表现出各向异性的根本原因。为研究层理弱面影响下板岩的渐进破坏模式,揭示其各向异性的力学机制,选取贵州东部的层状板岩开展不同加载空间位置关系下的直剪试验。结果显示:剪切强度各向异性是由其破坏机制控制的,层理面与剪切面平行时,属于沿层理面的剪切滑移破坏;层理面与剪切面垂直且其交线与剪应力方向也垂直时,属于剪切作用下层理面的张拉和基质体的剪切破坏;层理面与剪切面垂直而其交线与剪应力方向平行时,垂直于层理面方向试样在泊松效应作用下产生拉伸破坏,剪应力方向试样发生基质体的剪切破坏,此时强度最大。基于层理结构的本构关系,构建层理体系的材料模型,并采用数值模拟研究层理结构对板岩破坏模式的影响,模拟结果与试验结果吻合较好,进一步解释了层状板岩破坏模式各向异性的产生机制。

二维格构模型在岩石类材料开裂模拟中的应用

采用二维格构模型来模拟岩石类非均质材料的开裂过程。该方法能较好地反映材料微结构对开裂的影响。该模型中 ,岩石类连续介质被离散为由弹性杆或梁组成的二维格构。单元的属性根据某种概率分布而变化 ,以体现材料的随机不均质性 ,材料的开裂破坏通过单元的断裂来实现。算例表明 ,该模型能较好的模拟出岩石类材料的开裂过程及其荷载 -位移曲线。

Fatigue analysis of closed-cell aluminium foam using different material models

The fatigue analyses of AlSi7 closed-cell aluminium foam were performed using a real porous model and three different homogenised material models:crushable foam model,isotropic hardening model and kinematic hardening model.The numerical analysis using all three homogenised material models is based on the available experimental results previously determined from fatigue tests under oscillating tensile loading with the stress ratio R=0.1.The obtained computational results have shown that both isotropic and kinematic hardening models are suitable to analyse the fatigue behaviour of closed-cell aluminium foam.Besides,the kinematic hardening material model has demonstrated significantly shorter simulation time if compared to the isotropic hardening material model.On the other hand,the crushable foam model is recognized as an inappropriate approach for the fatigue analyses under tension loading conditions.

Deformation characteristics of surrounding rock of broken and soft rock roadway

A similar material model and a numerical simulation were constructed and are described herein. The deformation and failure of surrounding rock of broken and soft roadway are studied by using these models. The deformation of the roof and floor, the relative deformation of the two sides and the deformation of the deep surrounding rock are predicted using the model. Measurements in a working mine are compared to the results of the models. The results show that the surrounding rock shows clear theological features under high stress conditions. Deformation is unequally distributed across the whole section. The surrounding rock exhibited three deformation stages： displacement caused by stress concentration, theological displacement after the digging effects had stabilized and displacement caused by supporting pressure of the roadway. Floor heave was serious, accounting for 65% of the total deformation of the roof and floor. Floor heave is the main reason for failure of the surrounding rock. The reasons for deformation of the surrounding rock are discussed based on the similar material and numerical simulations.

Numerical simulation on the risk of roof water inrush in Wuyang Coal Mine

Water-inrush in mine is one of the mine disasters caused by mining.In order to assess the risk of roof water-inrush in Wuyang Coal Mine based on the geological material of the coal mine,we built numerical models for the roof fracture and seepage development rule by using RFPA2D and COMSOL respectively,to analyze the changes in fracture zone,stress,water pressure and seepage vector with the advancement of working face,and compared the results with the field investigated data.The numerical simulation results indicate that:(1) with the advancement of the working faces,the stress relief range and fracture zone in the overlying strata increased rapidly up to about 90 m,and then tended to remain constant,reaching a final height of about 95 m which agrees with the field investigation;(2) the seepage flow constantly increased with a larger flow volume both in the front and rear area,where the stress concentration are the most serious.

Numerical model and experimental observation for distribution of SiC_p in electromagnetic-centrifugally cast composites

A two-phase numerical model coupled with heat transfer was presented to describe the radial distribution of SiC particles on centrifugally-cast metal matrix composite,and a transverse static magnetic field was concurrently imposed to induce electromagnetic stirring of the melt as it revolved with the mold.Meanwhile,experimental observations were also carried out to examine the radial distribution of SiC particles in pure aluminum.The effects of the imposed magnetic field,particle size and the matrix metals were discussed.The computational results show that the particles tend to be congregated by the centrifugal force,and both increasing the imposed magnetic field and decreasing the particle size tend to result in even distribution of the particles.With the magnetic field varying from 0 to 1 T and the particle size from 550 to 180 μm,a uniform distribution of the particles in the aluminum matrix can be obtained among the computational results.The matrix metal can also influence the particle distributions due to the difference in physical properties of metals.Experimental observation shows similar tendency of particle distributions in aluminum matrix influenced by magnetic field and particle size.However,the chilling effect from the mold wall results in an outer particle-free zone,which is not involved in the numerical model.

Study on Collision Between Two Ships Using Selected Parameters in Collision Simulation

In the present analysis, several parameters used in a numerical simulation are investigated in an integrated study to obtain their influence on the process and results of this simulation. The parameters studied are element formulation, friction coefficient, and material model. Numerical simulations using the non-linear finite element method are conducted to produce virtual experimental data for several collision scenarios. Pattern and size damages caused by collision in a real accident case are assumed as real experimental data, and these are used to validate the method. The element model study performed indicates that the Belytschko-Tsay element formulation should be recommended for use in virtual experiments. It is recommended that the real value of the friction coefficient for materials involved is applied in simulations. For the study of the material model, the application of materials with high yield strength is recommended for use in the side hull structure.

A Comparison of Different Approaches in Numerical Modeling of Pavement Granular Material

Modeling pavement granular materials have played through an experimental or numerical approach to predict the a significant role in pavement design procedure. Modeling can be granular behavior during cyclic loading. Current design process in western Australia is based on linear elastic analysis of layers. The analysis is largely performed through a well-known program CIRCLY which is applied to model bound pavement material behavior. The KENLAYER is one of the common pavement software models used for pavement design in the United State which performs non-linear analysis for granular materials. Alternatively, a general finite element program such as ABAQUS can be used to model the complicated behavior ofmultilayer granular materials. This study is to compare results of numerical modeling with these three programs on a sample constructed pavement model. Moreover, a parametric study on the effects of Poisson ratio over the surface deflection of the flexible pavement has been conducted. It is found that increase in Poisson ratio of asphalt layer will increase the surface deflection while the increase in Poisson ratio of granular layers decreases the surface deflection.

Surface Roughness of Material Processing during Milling Process

To realize full automation in machining process, Computer Numerically Controlled （CNC） machine tools have been implemented during the past decades. The CNC machine tools require less operator input, provide greater improvements in productivity, and increase the quality of the machined part. End milling is the most common metal removal operation encountered. It is widely used to mate with other part in die, aerospace, automotive, and machinery design as well as in manufacturing industries. Surface roughness is an important measure of the technological quality of a product and a factor that greatly influences manufacturing cost. The quality of the surface plays a very important role in the performance of milling as a good-quality milled surface significantly improves fatigue strength, corrosion resistance, or creep life. Consequently, the desired surface roughness value is usually specified for an individual part, and specific processes are selected in order to achieve the specified finish. Purpose of the study is to develop a technique to predict a surface roughness of the part to be machined according to technological parameters. Such technique could be achieved by making mathematical model of machining. In this study as machining process the milling process is chosen, especially for end milling operation. Additionally to the study, one of the key factors, which differ from similar studies, is that as surface parameters the 2D, 3D surface parameters are used. In this study, all the surface parameters are expressed as 2D, 3D parameters. The 2D, 3D surface parameters give more precise figure of the surface; therefore it is possible to evaluate the surface parameters more precisely according to technological parameters. The result of the study, mathematical model of end-milling is achieved and qualitative analysis is maintained. Achieved model could help technologists to understand more completely the process of forming surface roughness.

Three-dimensional Numerical Study of Laminar Confined Slot Jet Impingement Cooling using Slurry of Nano—encapsulated Phase Change Material

This Article presents a three dimensional numerical model investigating thermal performance and hydrodynamics features of the confined slot jet impingement using slurry of Nano Encapsulated Phase Change Material(NEPCM)as a coolant.The slurry is composed of water as a base fluid and n-octadecane NEPCM particles with mean diameter of 100 nm suspended in it.A single phase fluid approach is employed to model the NEPCM slurry.The thermo physical properties of the NEPCM slurry are computed using modern approaches being proposed recently and governing equations are solved with a commercial Finite Volume based code.The effects of jet Reynolds number varying from 100 to 600 and particle volume fraction ranging from 0% to 28% are considered.The computed results are validated by comparing Nusselt number values at stagnation point with the previously published results with water as working fluid.It was found that adding NEPCM to the base fluid results with considerable amount of heat transfer enhancement.The highest values of heat transfer coefficients are observed at H/W=4 and C_m=0.28.However,due to the higher viscosity of slurry compared with the base fluid,the slurry can produce drastic increase in pressure drop of the system that increases with NEPCM particle loading and jet Reynolds number.