Fractional-order visco-plastic constitutive model for uniaxial ratcheting behaviors

This paper proposes a novel unified visco-plastic constitutive model for uniaxial ratcheting behaviors. The cyclic deformation of the material presents remarkable time-dependence and history memory phenomena. The fractional(fractional-order)derivative is an efficient tool for modeling these phenomena. Therefore, we develop a cyclic fractional-order unified visco-plastic(FVP) constitutive model. Specifically, within the framework of the cyclic elasto-plastic theory, the fractional derivative is used to describe the accumulated plastic strain rate and nonlinear kinematic hardening rule based on the Ohno-Abdel-Karim model. Moreover, a new radial return method for the back stress is developed to describe the unclosed hysteresis loops of the stress-strain properly.The capacity of the FVP model used to predict the cyclic deformation of the SS304 stainless steel is verified through a comparison with the corresponding experimental data found in the literature(KANG, G. Z., KAN, Q. H., ZHANG, J., and SUN, Y. F. Timedependent ratcheting experiments of SS304 stainless steel. International Journal of Plasticity, 22(5), 858–894(2006)). The FVP model is shown to be successful in predicting the rate-dependent ratcheting behaviors of the SS304 stainless steel.

Identification of structure and parameters of rheological constitutive model for rocks using differential evolution algorithm

To determine structure and parameters of a rheological constitutive model for rocks,a new method based on differential evolution(DE) algorithm combined with FLAC3D(a numerical code for geotechnical engineering) was proposed for identification of the global optimum coupled of model structure and its parameters.At first,stochastic coupled mode was initialized,the difference in displacement between the numerical value and in-situ measurements was regarded as fitness value to evaluate quality of the coupled mode.Then the coupled-mode was updated continually using DE rule until the optimal parameters were found.Thus,coupled-mode was identified adaptively during back analysis process.The results of applications to Jinping tunnels in China show that the method is feasible and efficient for identifying the coupled-mode of constitutive structure and its parameters.The method overcomes the limitation of the traditional method and improves significantly precision and speed of displacement back analysis process.

A bounding surface visco-plasticity model considering generalized spacing ratio of soils

The non-unique critical state of soils with time-dependent behaviors is a significant issue in geotechnical engineering problems.However,previous bounding surface plasticity models cannot predict accurately the non-unique critical state of soils,because the distance between the compression line and critical state line charged by strain-rate effect is basically neglected.To fill this gap,a generalized spacing ratio of soils is defined in the elasto-viscoplastic framework,and a bounding surface visco-plasticity model is formulated and verified,which can consider the generalized spacing ratio.Specifically,the generalized spacing ratio of soils reflects the distance between the compression line and the critical state line of soils with time-dependent behaviors.Then,the generalized spacing ratio is introduced into an improved anisotropic bounding surface.A new expression of the visco-plastic multiplier is derived by solving the consistency equation of an anisotropic bounding surface.In the expression,a strain rate index is proposed to account for the strain-rate effect on visco-plastic strain increment,and a visco-plastic hardening modulus is derived to predict the visco-plastic response of soils in overconsolidation conditions.The model is then verified through constant strain rate tests and creep tests.Notably,it can capture the non-unique critical states of soils with time-dependent behaviors due to the generalized spacing ratio and the creep rupture of soils due to the visco-plastic multiplier that considers the stress ratio and visco-plastic strain rate.

A new shear rheological model for a soft interlayer with varying water content

The rheological behavior of a soft interlayer is critical to understanding slope stability, which is closely related to the water content of the soft interlayer. This study used the soft interlayer of the Permian Maokou Formation in Southwest China as an example to perform ring shear creep tests with different water content amounts. The effect of water content on the creep properties of the soft interlayer was analyzed, and a new shear rheological model was established. This research produced several findings. First, the ring shear creep deformation of the soft interlayer samples varied with the water content and the maximum instantaneous shear strain increment occurred near the saturated water content. As the water content increased, the cumulative creep increment of the samples increased. Second, the water content significantly affected the long-term strength of the soft interlayer, which decreased with the increase of water content, exhibiting a negative linear correlation. Third, a constitutive equation for the new rheological model was derived, and through fitting of the ring shear creep test data, the validity and applicability of the constitutive equation were proven. This study has developed an important foundation for studying the long-term deformation characteristics of a soft interlayer with varying water content.

Constitutive model depending upon temperature and strain rate of carbon constructional quality steels

The basic factors relating to the rheological stress in the constitutive equations were introduced.Carbon constructional quality steels were regarded as a kind of elastic-viscoplastic materials under high temperature and the elastic-viscoplastic constitutive models were summarized.A series of tension experiments under the same temperature and different strain rates,and the same strain rate and different temperatures were done on 20 steel,35 steel and 45 steel.52 groups of rheological stress-strain curves were obtained.The experimental results were analyzed theoretically.The rheological stress constitutive models of carbon steels were built combining the strong points of the Perzyna model and Johnson-Cook model.Comparing the calculation results conducted from the model with the experiment results,the results proves that the model can reflect the temperature effect and strain rate effect of carbon constructional quality steels better.

A new general rheological model for rheological lubrication

Limitation and deficiency of main thcoogical models at present are descrital and analyzed, and seteralgeneral rheological models are discussed and compared with each other, and basic demands for a general model aresummarized. The constitutive eqUation is proposetl for a new general theobocal model. The general medel feaaressimple structure and wide coverage, and can take the Place of many edsting thcofogical ed. The whel has suc-cessfully been used for Elastohydrodynamic lubrication calculation.

Traction rheological properties of simulative soil for deep-sea sediment

The traction capacity of the mining machine is greatly in?uenced by the traction rheological properties of the deep-sea sediments. The best simulative soil was prepared for substituting the deep-sea sediment based on the deep-sea sediment collected from the Paci?c C-C mining area. Traction rheological properties of the simulative soil were studied by a home-made test apparatus. In order to accurately describe the traction rheological properties and determine traction rheological parameters, the Newtonian dashpot in Maxwell body of Burgers model was replaced by a self-similarity spring-dashpot fractance and a new rheological constitutive model was deduced by fractional derivative theory. The results show the simulative soil has obvious non-attenuate rheological properties. The transient creep and stable creep rate increase with the traction, but they decrease with ground pressure. The fractional derivative Burgers model are better in describing non-attenuate rheological properties of the simulative soil than the classical Burgers model. For the new traction rheological constitutive equation of the simulative soil, the traction rheological parameters can be obtained by ?tting the tested traction creep data with the traction creep constitutive equation. The ground contact length of track and walking velocity of the mining machine predicted by the traction rheological constitutive equation can be used to take full advantages of the maximum traction provided by the soil and safely improve mining effciency.

RHEOLOGICAL BEHAVIOURS OF CAST STEEL DURING SOLIDIFICATION

The stress-strain relation for cast low alloy carbon steel at solidification temperature has been examined by the authors' own desingned apparatus for rheological properties measurement.The rheology model,the stress-strain constitutive equation and the rheological parameters therefrom of the cast steel were proposed.Thus the theoretical basis and calcula- ting data for computerized s#nulation on the stress-strain relation and thermal cracking of the cast steel were suggested.

Rheological properties of surrounding rock in deep hard rock tunnels and its reasonable support form

Second lining stability, which is the last protection in tunnel engineering, is critically important. The theological properties of the surrounding rock heavily affect second lining stability. In this work, we used laboratory triaxial compressive rheological limestone tests to study nonlinear creep damage characteristics of surrounding rock mass in construction projects. We established a nonlinear creep damage constitutive model for the rock mass, as well as a constitutive model numerical implementation made by programming. Second, we introduced a new foam concrete with higher compression performance and good ductility and studied its mechanical properties through uniaxial and triaxial tests. This concrete was used as the filling material for the reserved deformation layer between the primary support and second lining. Finally, we proposed a high efficiency and accuracy staged optimization method. The minimum reserved deformation layer thickness was established as the optimization goal, and the presence of plastic strain in the second lining after 100 years of surrounding rock creep was used as an evaluation index. Reserved deformation layer thickness optimization analysis reveals no plastic strain in the second lining when the reserved deformation minimum thickness layer is 28.50 cm. The results show that the new foam concrete used as a reserved deformation layer filling material can absorb creep deformation of surrounding rock mass, reduce second lining deformation that leads to plastic strain, and ensure long-term second lining stability.

QN1803奥氏体不锈钢温热本构模型构建

基于QN1803奥氏体不锈钢在塑性变形过程中存在的马氏体相变现象,提出采用基于热激活位错运动理论的物理基Zerilli-Armstrong(Z-A)模型,构建了其温热成形时的修正本构模型。采用Gleeble-3800热模拟试验机,对QN1803奥氏体不锈钢在温度为25~200℃、应变速率为0.001~0.1 s^(-1)的变形条件下进行了温热拉伸试验,基于试验结果分析了QN1803奥氏体不锈钢的温热流变行为,构建了QN1803奥氏体不锈钢在温热成形条件下的修正Z-A本构模型,并对模型精度进行了评估。结果表明,在25~100℃范围内,随着应变速率的增加,拉伸试样中的马氏体含量迅速减少。在各应变速率下,随着温度的升高,马氏体含量也迅速减少。采用相关系数R和平均绝对相对误差E AR量化了本构模型的精确度,修正的Z-A本构模型的R和E AR的值分别为0.998和1.225%,能较好地描述QN1803奥氏体不锈钢的温热流变行为。

复合固体推进剂药浆浇铸工艺仿真及优化

为了研究HTPB复合固体推进剂药浆浇铸的最佳工艺参数,采用实验与理论模拟相结合的方法,基于HTPB复合固体推进剂药浆流变性能建立了推进剂药浆流动过程的本构模型;利用有限元软件对HTPB复合推进剂药浆浇铸工艺进行仿真,通过实验验证了仿真结果的可靠性;并对该推进剂药浆浇铸工艺进行了优化,获得了最佳浇铸工艺参数。结果表明,HTPB推进剂是典型的假塑性流体,其黏度随剪切速率增大而降低;实验与仿真对比后的气孔率及浇铸时间误差分别为12.5%和11.25%;其中,温度对浇铸时间的影响最明显,真空度对气孔率影响最明显。

固体推进剂的流变性能及工艺仿真研究进展

固体推进剂药浆是一种高固含量悬浮液,其流变性能十分复杂。基于此,介绍了用于描述固体推进剂流变性能的非牛顿本构方程,回顾了近年来固体推进剂混合、浇铸、包覆工艺过程仿真的研究进展,列举出目前推进剂工艺仿真研究中存在的问题和不足,提出进一步开展混合工艺过程中固体推进剂流变性能仿真以及固体推进剂全工艺过程仿真的建议,以期为固体推进剂工艺设计及参数优化提供参考。

水泥乳化沥青混合料路面压实工艺参数研究

为了精准预测水泥乳化沥青混合料路面达到目标密实度所需的压路机压实工艺参数组合,基于该混合料压实流变时变特性及压实Bodner-Partom(B-P)本构模型,采用数值仿真和路面压实试验相结合的方法开展研究。首先对ANSYS进行二次开发得到B-P材料模型,然后将阶段性变化的B-P模型参数代入压实组合仿真分析中,最后开展路面压实试验,进一步得到压实工艺参数优化组合。数值仿真研究结果表明:由仿真结果得到3个低频高幅高速组合,3个组合作用后沿轮宽方向的混合料竖向应变值减小幅度均较大,在路面深度6 cm处的混合料竖向应变衰减幅度值均较小,其中组合六的衰减幅度值为最小,路面目标成型厚度可控制在7 cm以下。路面压实试验表明,组合六(低频高幅高速压实6遍)的有效压实能量偏大,应将组合六的压实遍数优化为:低频高幅高速压实5遍+高频低幅高速压实2遍。

激光增材制造镍基高温合金的高温变形行为与本构模型

开展了激光增材制造镍基高温合金在7种温度下的拉伸试验,通过断口分析、数据处理等手段研究了增材制造高温合金的破坏机制及本构模型。结果表明:镍基高温合金的屈服强度、抗拉强度随着温度的升高而降低;温度高于673 K时,塑性段出现锯齿流变现象,随着温度的升高,锯齿的密度减小;试件断口表面存在大量韧窝和撕裂棱,具有显著的韧性断裂特征;通过考虑应变和温度对材料塑性行为的耦合影响,建立了以J-C和Z-A模型为基础来拟合合金流动应力的改进本构模型,拟合值和试验值吻合较好,相对误差绝对值均小于4%;将有限元仿真结果和试验的载荷-位移曲线进行对比,进一步证明了所建立本构模型的准确性。

热力耦合作用下花岗岩流变模型的本构关系研究

热力耦合作用下岩石的微观结构的变化是引起宏观力学变化的主要原因,从热力耦合作用下花岗岩的流变机制研究出发,建立热力耦合作用下花岗岩的流变模型,从而推导流变本构方程是一种可行的方法。通过热力耦合作用下花岗岩的流变机制研究可知:(1)花岗岩是一种由多种成分构成的具有多晶复合介质特点的脆性坚硬岩石,具有很大的非均质性,内部微观结构可分为晶粒、晶粒边界、晶间胶结物及晶间孔隙,这样的组分和结构将决定花岗岩在热力耦合作用下的流变特性。(2)热力耦合作用下花岗岩流变现象主要是热力耦合作用下岩体内晶间胶结物及晶粒内部产生的位错及微破裂过程,即温度产生的热破裂和应力产生损伤破裂的复合破裂过程,微观结构上的变化使得标志着热力耦合作用下宏观力学特性的力学参数成为温度的函数。因此,将岩石现象流变学与物理流变学结合起来,提出热力耦合作用下岩石热黏弹塑性流变元件力学元件,在广义西原模型的基础上建立热力耦合作用下花岗岩流变模型,推导出可描述150MPa及600℃以内花岗岩的流变本构方程,用试验结果验证了其适用性和合理性。热力耦合作用下花岗岩流变模型的本构方程的建立为高温岩体地热开发钻井施工及其稳定性研究提供了依据。

泥板岩流变试验与粘弹性本构模型研究

某水电站泥板岩变形是该坝区地下洞室群和高边坡研究的主要问题,探讨泥板岩粘弹性本构模型有重要意义。选取泥板岩岩芯做成简支梁进行流变试验,在梁上取10个测点贴上应变片,在梁的中央施加集中荷载,用应变仪测定10个测点的应变片在各级长期荷载作用下随时间变化的应变量。根据所测定的应变量来反演泥板岩粘弹性本构模型,得到了符合泥板岩的粘弹性流变本构模型。

页岩卸荷流变力学特性的试验研究

岩体开挖卸荷产生的变形具有时间效应,其瞬时力学及流变力学响应都会有一定的变化。当前,对此流变行为的研究多建立在加载力学基础上的岩石流变试验,而未考虑岩石卸荷应力路径下的流变特性,往往与实际力学过程不相吻合。选取乌江彭水水电站地下厂房新鲜页岩进行恒轴压、逐级卸围压应力路径下的卸荷流变试验,对岩石的三轴卸荷流变特性进行初探。试验表明,页岩在较低应力水平下,轴向及侧向蠕变曲线呈现出衰减阶段的流变特性。基于试验成果,对H-K三元件模型参数进行非线性回归,从而得到页岩在该应力状态下的卸荷流变本构方程。研究表明,该模型能很好地描述该应力路径下页岩的卸荷流变行为。

加锚岩体流变特性及锚固控制机制分析

通过室内蠕变试验和理论分析,对加锚改善岩石流变力学特性进行了研究,并探讨了锚固控制岩石流变的力学机制。采用RLJW-2000型流变试验机,对红砂岩及其加锚试件进行分级加载(100 h以上)单轴压缩试验,结果表明,加锚后岩石的流变应力阀值提高了20%～30%c,且不同应力水平流变量均能得到一定控制,加锚使试件的长期强度增加了5%～10%c。此外,基于整体协调变形原理,建立了加锚体流变本构方程,推导出了一维B-K模型解答,算例分析表明,锚杆密度越大,对岩石流变控制效果越好,得出锚杆等效刚度是约束岩石流变的主导因素,但从技术经济角度考虑,锚杆支护密度与岩石流变参数之间存在一个合理的匹配区间。研究结果对长期使用的岩体工程锚固支护设计提供了理论依据。

参数非线性理论流变力学模型研究进展及存在的问题

对现有的参数非线性理论流变力学模型及其建立的方法进行系统的总结,归纳出处理参数非线性理论流变模型的3种方式:(1)给出非线性流变部分的本构方程,推导出整个流变模型的本构方程,并进一步推导出包括蠕变方程在内的流变模型的其他方程;(2)给出非线性部分的本构方程,推导出该部分的蠕变方程,并与常参数部分的蠕变方程叠加得到整个流变模型的蠕变方程;(3)给出非线性流变部分的蠕变方程,与常参数部分的蠕变方程叠加,得到整个流变模型的蠕变方程。这3种方式可以对今后的研究给予指导。指出一些参数非线性理论流变模型和建立方法所存在的问题甚至错误,以免在今后的研究工作中犯类似的错误。

大型滑坡滑带土剪切流变特性研究

利用重力压密原理制样 ,采用“陈氏加载法” ,对某大型滑坡滑带土剪切流变特性进行研究。选择伯格粘弹性本构模型描述滑带土的流变性状 ,获得了滑带土的长期强度值 ,并论述了长期强度在滑坡稳定性研究中的意义。