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。     

On Mooney viscosity and Mooney stress relaxation. I

Mooney relaxation is highly nonlinear, strongly differs from stress relaxation at small strains, and can be described by Wagner's nonlinear rheological model for polymer melts. In the practical evaluation, the Mooney Stress Relaxation slope is more accurate than quantities such as t₈₀. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1207–1219, 1999     

A Nonlinear Magneto-Mechanical Coupled Constitutive Model for the Magnetostrictive Material Galfenol

In order to predict the performance of magnetostrictive smart material and push its applications in engineering, it is necessary to build the constitutive relations for the magnetostrictive material Galfenol. For Galfenol rods under the action of the pre-stress and magnetic field along the axial direction, the one-dimensional nonlinear magneto-mechanical coupling constitutive model is proposed based on the elastic Gibbs free energy, where the Taylor expansion of the elastic Gibbs free energy is made to obtain the polynomial forms. And then the constitutive relations are derived by replacing the polynomial forms with the proper transcendental functions based on the microscopic magneto-mechanical coupling mechanism. From the perspective of microscopic mechanism, the nonlinear strain related to magnetic domain rotation results in magnetostrictive strain changing with the pre-stress among the elastic strains induced by the pre-stress. By comparison, the predicted stress-strain, magnetostrictive strain, magnetic induction and magnetization curves agreed well with experimental results under the different pre-stresses. The proposed model can describe not only the influences of pre-stress on magnetostrictive strain and magnetization curves, but also nonlinear magneto-mechanical coupling effect of magnetostrictive material systematically, such as the Young’s modulus varying with stress and magnetic field. In the proposed constitutive model, the key material constants are not chosen to obtain a good fit with the experimental data, but are measured directly by experiments, such as the saturation magnetization, saturation magnetostrictive coefficient, saturation Young’s modulus, linear magnetic susceptibility and so on. In addition, the forms of the new constitutive relations are simpler than the existing constitutive models. Therefore, this model could be applied conveniently in the engineering applications.     

基于冻融循环作用的纤维混凝土配比优化试验研究

基于对聚丙烯纤维混凝土的快速冻融试验,结合不同的配合比参数和聚丙烯纤维掺入量对其冻后力学性能进行了测试分析,得到了不同配合比与纤维掺量对混凝土冻后各项性能的影响结果.研究分析试验结果表明:细骨料比例的提升会加强冻融后纤维混凝土的力学性能;冻融后混凝土强度随聚丙烯纤维掺入量的增大而非线性变化,且抗拉强度的变化幅度大于抗压强度,纤维掺入量存在一个最优范围使得混凝土的力学性能出现峰值.最后基于遗传算法,在试验结果的基础之上建立了混凝土配合比的优化模型,并验证了优化模型的有效性.     

基于区间值模糊集的模糊区域拓扑关系模型

在GIS实际应用领域中,采样点的属性数据往往不是精确的数值,而是一个区间范围,对此类空间数据的建模、分析和推理越来越受到相关领域研究者的重视.利用区间值模糊集描述由不确定属性数据所圈定的模糊区域,基于区间值和区间值模糊集的运算性质,给出了模糊区域间拓扑关系的分析模型.该模型改进了基于经典模糊集及其截集的拓扑关系模型,对模糊区域拓扑关系的分析结果更符合人们的认知习惯,可以利用区间值结果进行推理和决策,能够有效地分析由区间值属性所确定的模糊区域间的拓扑关系,在地理信息系统和空间数据库等领域具有实际应用价值.     

城市特征新论

城市本身是一个辩证的对立统一体,以往对城市系统单个特征的认识或强调是片面的,需要从对立统一规律的角度来重新审视城市特征.笔者认为,城市的特征主要有:集聚与扩散作用的共存性及交替主导性、溢出效应与乘数效应的互动性、公共性与经营性的兼容性、多样化与两极分化的并存性、线性关系向非线性关系的递进性等.     

Characteristics of polyurethane adhesives with various uretonimine contents in isocyanate and average alcohol functionalities

Polyurethane adhesives are found in a variety of applications. To ensure durability and functionality, a polyurethane adhesive is required to possess good adhesive properties and thermal stability. In this study, polyurethane adhesives were fabricated using isocyanate and polyols of various type and functionality (f_av). It was found that peel strength of an adhesive is strongly related to the f_av of a polyol and uretonimine content. At high uretonimine content, the probability of forming hydrogen bonded component increases and as a result the adhesive's peel strength increases. At high f_av and molecular weight of a polyol, an adhesive's wettability decreases so does its adhesion to a substrate. Therefore, designing for a functional adhesive, high uretonimine content and low f_av of polyol are desired. Thermal stability of a polyurethane adhesive also improves with uretonimine content. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43737.     

循环稳定材料的棘轮行为:I.实验和本构模型

在实验分析结果的基础上,对循环稳定材料的室温单轴和非比例多轴循环棘轮行为进行了本构描述,建立了一个简单而合理的、便于工程应用的粘塑性循环棘轮本构模型。给出了模型参数的确定方法,并根据实验获得的单拉应力-非弹性应变关系曲线确定了针对U71Mn 轨道钢材料的参数值。在此基础上,通过对该材料棘轮行为的本构模拟检验了发展模型的预言能力。结果表明,模型具有很好的预测效果,模拟结果与对应的实验结果符合得很好。     

离心钢管混凝土的等效本构关系

在现有离心钢管混凝土本构关系分析的基础上,将离心钢管混凝土简化为同一尺度的横观各向同性体,利用在弹性状态下应变能相等原理和弹塑性状态时应力—应变呈二次抛物线变化的假定,提出了离心钢管混凝土这种组合结构新的等效本构关系。实例分析表明,模型与试验结果吻合较好,且该本构关系能客观地反映了离心钢管混凝土构件的物理力学关系,为离心钢管混凝土结构进行数值分析奠定了基础。     

岩体结构面切向循环加载本构关系研究

回顾岩体结构面切向循环加载的力学试验和数值模型,并建立新的本构模型。在粘接状态下,结构面切向本构关系表示为由双曲线和直线段组成的滞回曲线。在接触状态由粘接变为滑移的过程中,峰值摩擦角以双曲线函数逐渐降低至残余摩擦角,体现出峰值剪切特性。考虑结构面切向与法向耦合的剪胀关系,建立相应的接触刚度矩阵,并引入初始剪胀角和残余剪胀角来建立分段抛物线形式的剪胀曲线。循环加载导致的磨损对结构面的摩擦和剪胀特性均产生影响,通过以切向塑性功指数函数表示摩擦角和剪胀角的磨损过程。模型在物理意义上反映了切向循环加载的特性,计算结果能较好地拟合试验曲线。