Numerical Simulation of Elastoplastic Multi-scales Model for Magnesium Alloy Under Tensile Load

In order to investigate the macroscopical mechanical performance of magnesium alloy material containing pore and the mechanism during distorting destructing, an accurate finite element model of magnesium alloy using the multiscales method was developed, and the macroscopic properties of material under the macroscopic tensile load using the developed constitutive model of multi-scales and finite element method was obtained. By analyzing the distortion results of meso-model through the multi-scales method, with macroscopical load increasing, the difference demonstrated on the macroscopic is very small, however, with the increase of the load step, the phenomenon that the ability of plasticity deformation of the meso-models which includes the cuboid pore decreased gradually remarkable and the phenomenon of stress centralized is more severity than the meso-models including cylindrical pore could be obviously observed during the process of deformation on the meso-models.     

红层泥岩桩岩接触面本构模型试验及数值模拟

桩-岩（土）接触面力学特性的研究是桩基承载机理研究的基础。通过红层泥岩桩岩接触面大型直剪试验,研究了红层泥岩桩岩接触面的力学特性,结果表明：接触面剪应力先随剪切位移增大而增大,在达到峰值后,剪应力随着剪切位移增大而降低,并最终趋于稳定值,应力应变曲线呈现出应变软化的特征。根据剪切试验结果,推导出桩岩接触面应变软化本构方程。利用fish语言对FLAC^3D中自带的理想弹塑性接触单元进行二次开发,并应用开发的模型对桩岩接触面直剪试验进行了数值模拟,分析剪应力与剪切位移之间的关系,证明了该本构能够较好地模拟接触面间的应变软化特性。     

Calculation of Properties of Fracture for Magnesium Alloy AM50 and Experimental Certification

The strain-stress curve and the stress intensity factor are carried out using the machine MTS for Magnesium alloy AM50.Energy release rates(G)are evaluated based on the virtual crack closure technique and Griffith potential energy.Based on the relationship between Energy release rate(G)and stress intensity factor(K).And then stress intensity factor(K) is got.Comparison of stress intensity factors(K) of between the calculated values and experimental values is made,showing that they are in good agreement.     

Damage Constitutive Relationship of Coupled Plasticity-creep for Magnesium Alloy

Based on a simple mechanical model and an appropriate definition of generalized time,a constitutive equation is obtained for coupled plasticity and creep behavior of materials.A damage evolution based on a spherical void model for mixed hardening materials is obtained by means of Gurson's model.The damage evolution law is embedded in the adopted constitutive equation,and a damage constitutive equation is obtained for coupled plasticity and creep behavior of die-casting magnesium alloy.The response of magnesium alloy subjected to cyclic loads is analyzed.The validity of the proposed model is demonstrated by the satisfactory agreement between the experimental and calculated results.     

施工阶段大跨径预应力混凝土刚构桥腹板开裂机理

进行了大跨径预应力混凝土刚构桥腹板开裂机理研究,基于弹性力学平面问题分析方法,推导了集中荷载作用下的板件应力函数表达式,绘制了不同受压边长与集中荷载长度比（d/a）下的横向应力曲线,拟合了集中荷载作用下构件的横向应力求解函数,构造了混凝土刚构桥腹板在预应力集中荷载作用下等效压力矩形的选取方法,并基于平面应力的表达式提出了在三维情况下沿预应力轴线的横向应力计算方法。通过建立某预应力混凝土刚构桥0~3#段实体有限元模型,分析施工过程中刚构桥混凝土腹板在不同等级预应力作用下的开裂情况。结果显示：有限元裂缝模拟与实桥腹板开裂范围一致,有限元应力分析结果下限值与推导的横向应力求解函数计算结果接近,变化趋势一致,印证了横向应力函数求解方法的正确性。     

Nonlinear Stiffness Matrices of Plane Beam Element Including Initial Stress and Strain Item

There were often happened cases for beam elements with initial stress or initial strain while the geometrically nonlinear analysis was performed for the plane structure. The deduction of stiffness matrices was awfully difficult because the nonlinear stiffness matrices included node displacement vectors and extensive matrix operations. Based on the nonlinear geometric equation of plane beam element and general elastic relationship of stress-strain including initial stress and initial strain,the tangent stiffness matrix was derived. All explicit formula of stiffness matrices including initial stress and strain item have been developed by use of the MATLAB Mathematical Tools. The results are of great significance to the nonlinear finite element programming for plane beam elements.     

Finite element analysis of the LX150 motorcycle crankcase box

The wall thickness and strengthen muscle of motorcycle crankcase box influences its structure intensity directly. The static model of crankcase box of a magnesium alloy material is established by finite element method. The structure is analyzed with I-DEAS, the reason the crankcase box is crazed is pointed out. The structure is rebuilt, the intensity is increased remarkablely, the cost of manufacture is reduced largely. And the capability of a originally material, i.e. aluminium alloy is validated.     

Study on Methane Flow Regularity and Secondary Stress and Deformation of Coal Bady around Penetration Boreholes in Coal Seam

A new mathematical model for the coefficient of variable permeability affected by coal body, secondary stress & pressure in coalseam & a constitutive equation for gas migration are improved on the basis of the secondary stress & deformation of coal body around boreholes in coalseam. Using this model and equation,the gas flow field belongs to the 20102 experimental zone in BaiJiao coal Mine is computed & this verifies that the model & constitutive equation are both agreeable to practical results. Simultaneously, a comparison between the variable and constant permeabilities is carried out.     

Energy-absorbing Properties and Crushing Flow Stress Equation of Lightweight Foamed Concrete

Lightweight foamed concrete is a new arresting material for arresting overrun aircraft. To reveal its compression properties and mechanism of deformation and destruction, a study on lightweight foamed concrete with different density, 0.21 and 0.31 g/cm 3 respectively, has been carried out. Experiment system include CSS4410 electronic universal testing machine and Dynatup9250 drop-hammer testing machine and VHS8800 high strain rate system. Then, extrusion strength under different indenter area is predicted with a theoretical model, and a crushing flow stress constitutive equation is proposed. The results show that it is characterized by the movement of crushing driving interface during the process of deformation, crush to compaction of the material, and the deformation is notably in local. The compression strength is relevant to density and impact velocity. Moreover, theoretical model can predict the extrusion strength under different indenter area exactly, and the crushing flow stress equation can describe mechanic properties of compression well.     

On the Type of Stress-strain Relation Curves and the Critical State for Soils

In order to discuss the influence of stress history on the constitutive relations for soils,a series of drained conventional triaxial compression tests for normally consolidated and overconsolidated clays have been carried out.It is found through comparing the stress-strain relation curves under the different stress histories that the overconsolidated ratio is the determining factor for volumetric strain.The volumetric strain is less sensitive to consolidation pressure,however.For the shear capacity,the consolidation pressure is the determining factor,but the influence of the overconsolidated ratio can not be neglected since it determines whether there will be strain hardening or strain softening as well as the grade of strain softening.Despite that,the soil specimens will finally reach a unified critical state and approximately the same residual strength.According to the principle of interaction between plastic volumetric and shear strains,the mechanism of generating two types of stress-strain relation curves for clays is explained.It is shown that the critical state is a pure process of shearing deformation in which the interaction between plastic volumetric and shear strains completely disappears.The critical state is independent of the previous stress history.     

INCREMENTAL FORM OF ENDOCHRONIC CONSTITUTIVE EQUATION AND ITS APPLICATIONS

An incremental formula is derived from integral form of endochronic plastic constitutive equation, which greatly reduces the error caused by the one which was directly obtained from differential form of the constitutive equation. An elastoplastic matrix is then proposed, based on which a stiffness finite element approach is developed. The analysis of the residual stress at the inner skin of an autofrettaged thick-walled cylinder agrees well with the experimental result. The calculated stress-strain fields of a double - edge - notched plate subjected to cyclic zero-to-tension loading are also quite reasonable. The numerical process is steady and quickly convergent, and the developed approach can easily be applied to practical engineering analysis.     

Finite Element Analysis of Shear Behavior of Super High Strength Reinforced Concrete Beam

On the basis of testing results of shear behavior from 18 super high strength reinforced concrete restrained beams with web reinforcement, with the cube compressive strength ranging from over 100Mpa, in this paper, the nonlinear finite element analysis procedure was formulated and the analysis of the specimen tests was carried out with the parameters obtained from the experiments and improved constitutive model and failure criteria of materials. Based on the simulated shear resistance test results and practical measured data of eighteen super high strength concrete restrained beams under point load, the equation to compute the shear resistance capacity of such beams was thus obtained by regression. The analytical results agree well with those of experiments.     

Experimental Study on Influence of Stress Path on the Constitutive Relations for Reshaped Clay

In order to study the influence of stress path on the constitutive relations for reshaped clay,the triaxial compression tests under stress paths with drainage in cases of increased,constant and decreased mean normal stress and undrained conventional triaxial compression test have been carried out,the stress-strain relations under the four stress paths are obtained.Through visualization the three-dimensional surfaces of shear and volume strain in the whole stress field under the four stress paths are given respectively by numerical modeling.In addition,the four families of shear and volume yield loci are plotted respectively.It is found through comparing the deformation results under the four stress paths that there are obvious differences in the stress ranges,the strain peaks,the shapes of strain surfaces and the trends of variation of volume yield loci,however,for the four families the shear yield loci are similar.These results demonstrate that the influence of stress path on the constitutive relations of clay is considerably large and could not be neglected,and it relates to the effective mean normal stress closely.     

Numerical simulation of remodeling in mandible under orthopedic loads

The research on the remodeling in mandible under the action of orthopedic loads is important for the determination of orthopedic scheme. a three-dimensional finite element model of mandible and temporomandibular joint is established. Using Cowin Remodeling Law, the finite element simulation of the remodeling in mandible during the orthopedics under the action of orthopedic loads is carried out. Comparing the numerical results after remodeling with those before remodeling, it is demonstrated that the normal remodeling greatly affects the distribution of strain and strain gradient on the surface, therefore the effect cannot be ignored in the determination of the orthopedic scheme.     

干旱胁迫条件下AM真菌对蓝莓光合特性及矿质元素含量的影响

旨在进一步明确丛枝菌根(arbuscular mycorrhizal, AM)真菌摩西球囊霉(Glomus mosseae)提高蓝莓抗旱性的机制。采用盆栽实验研究了在中度干旱胁迫条件下AM真菌对南高丛蓝莓“奥尼尔”叶片光合特性及矿质元素含量的影响。结果表明：中度干旱显著降低了蓝莓菌根侵染率、净光合速率(Pn)、蒸腾速率(Tr)、气孔导度(Gs)、PSII 原初光能转化效率(Fv/Fm)以及叶片磷(P)、镁(Mg)及铁(Fe)含量;在中度干旱胁迫条件下,AM真菌接种显著提高了蓝莓叶片叶绿素和类胡萝卜素含量、Pn、Tr、Gs、胞间CO2浓度(Ci)、Fv/Fm 以及P、Mg和Fe 含量,而对钾(K)和锰(Mn)含量并无显著性影响。可见中度干旱胁迫主要通过降低PSII 光能转化效率等非气孔因素来抑制蓝莓的光合速率;但在中度干旱胁迫条件下,AM真菌则通过气孔因素和非气孔因素来提高蓝莓的光合效率,进而有利于提高其抗旱性。     

Theoretical Analysis and Finite Element Computing for Rectangular Plates Bucking under Shear Load

By adopting the energy and finite-element methods with analysis software MATLAB and ANSYS,a detailed and complete solution process for bucking of simply supported rectangular elastic plates is provided.By increasing the triangular series for the deflection function,the amendments have been made to the K values given in references.Through finite element analysis,the expression of K value is fitted out.It is ascertained that the shear stress,taken as a critical shear stress,is reasonable according to the small deflection theory under limited plate deflection.The results of two analytical methods show that the fitting curve of K values used by finite element analysis has more comprehensive practical significance.     

Effect of phytic acid modification AZ31 magnesium alloy on the cell surface adhesion property

Phytic acid coatings on the surface of AZ31 magnesium alloys are prepared by immersion method. Then cell culture and detection of cell survival rate on treated or untreated AZ31 magnesium alloy with phytic acid is carried out by the direct method and the indirect method respectively,and surface morphology and chemical composition of coatings are studied by scanning electron microscopy with energy dispersive spectrometer. The results show that uniform phytic acid coating forms on the surface of magnesium alloy,and there is a similar cell survival rate on the treated or untreated AZ31 magnesium alloy surface. But the adhesive ability of cells on the surface of phytic acid modification magnesium alloy is significantly different. Phytic acid modification can effectively improve the cell adhesion properties of AZ31 magnesium alloy.     

a rational method for defining damage variables in one dimension

To address the issue of whether it is rational to define damage variables through the degradation of elastic modules, we essentially clarified which material module should be used to describe the damage variables in unidimensional cases, and pointed out that the reference undamaged working state of material was needed firstly in order to measure the degree of damage if the strain equivalence hypothesis was used. We maintained it was baseless to consider the linear stress strain working state as an undamaged reference state. We deduced a rational definition of elastic and elasto plastic damage variables. We stated that the degradation of an unloading module can be used to define the damage variables. To illustrate the definition of damage variables, we presented an example of establishing a damage constitutive equation of concrete in compression, validate the elastic strain equivalence hypothesis, and provide an appropriate approach for establishing a damage constitutive model.     

BOUNDARY ELEMENT METHOD FOR MULTI-BODY CONTACT PROBLEM AND ITS APPLICATION IN HUGE EXCAVATOR

A boundary integrate equation and its discrete technique for multi-body contact problem is carried out on basic equations of boundary element method and its fortran program is compiled. Using the method ,the press distribution on the roller plate of the huge excavator with capacity 16 m3 was calculated and a distroy stress analysis of caterpillar of the excavator was carried out.     

Hyperelastic Constitutive Relations and Finite Element Formulation for Porous Silicone Rubber

The strain energy density function which was decoupled into isochoric parts and volumetric parts is presented for describing mechanical behaviors of compressible porous silicone rubber material,the constitutive model is then attained.The finite element formulation for isotropic hyperelastic porous silicone rubber is developed by use of total Lagrangean method.