三维编织复合材料力学行为研究进展

对三维编织复合材料的细观结构几何模型和力学性能的研究进展进行了综述。重点介绍近几年该领域的研究成果和作者的一些研究工作, 其中包括三维编织复合材料力学性能的实验研究和理论研究。在理论研究方面, 介绍了弹性应变能法、纤维倾斜模型、三细胞模型和有限元模型等工作。最后, 对未来的研究趋势进行了展望。      

X-cor夹层结构压缩模量有限元分析

通过两种有限元模型的对比,提出了符合实际的X-cor夹层结构压缩模量有限元计算模型,利用大型有限元软件ANSYS对其压缩模量进行了数值计算,得到了X-cor夹层结构的应力场和压缩模量.研究了Z-pin半径、密度、植入角度和体积分数的改变对模型压缩模量的影响.结果表明:X-cor夹层结构压缩模量随Z-pin植入角度增加而减小,随Z-pin半径、密度和体积分数增加而增加,且与Z-pin体积分数呈线性关系,改变Z-pin半径与改变Z-pin密度对X-cor夹层结构压缩模量影响是等效的.通过有限元模型的计算,得到了X-cor夹层结构参数对其压缩模量的影响规律,验证了所提有限元模型的合理性.     

橡胶沥青复合材料动态剪切流变特性

在橡胶沥青复合材料中加入不同的胶粉含量,其动态力学特性发生明显改变。利用三参量流变模型,推导了橡胶沥青复合材料黏弹性的动态剪切流变参数。通过Origin软件自定义拟合功能,对黏度预估模型的4个待定参数进行了拟合。采用动态剪切流变仪(DSR),在不同温度下对不同胶粉含量的橡胶沥青复合材料试样进行测试,并将实验结果与三参量流变模型得到的理论结果进行对比。结果表明,实验结果与理论结果吻合较好。随着测试温度的升高或胶粉含量的降低,橡胶沥青复合材料的黏度、储存模量和损耗模量均呈现降低的趋势,而损耗因子呈增大的趋势。     

磁性目标的单点模量测距方法

针对磁偶极子模型,提出了一种基于磁梯度张量信息的模量测距方法.该方法利用磁传感器阵列测量磁性目标的磁感应强度模信号、总梯度模信号和梯度张量模信号,从而求解阵列与目标之间的距离.本文介绍了一种十字型平面磁梯度张量测量系统,并推导了测距求解过程;根据测距模型分析了影响测距精度的因素;仿真与实验结果表明:该方法相比直接反演法,抗噪性能更好,受磁性目标姿态影响更小,更具有实际应用意义.     

沥青混合料动态模量预估模型研究进展

由于沥青路面结构受到车辆荷载、环境等因素的不断变化作用,它的实际工作状态与静态体系在材料性质等方面存在较大差距。因此,针对动态荷载作用下沥青路面结构的动态参数和动力特性的研究十分必要。沥青混合料动态模量是沥青路面设计的重要参数之一,通过室内试验测得沥青混合料不同温度、频率下的动态模量,然后绘制主曲线,可准确预测不同温度、频率及极端条件下沥青混合料的动态模量。然而,目前沥青混合料模量测试方法复杂、试验成本较高,因此寻求简便的方法获得或预估沥青混合料的模量成为近年来研究的热点。为此,已有众多学者针对沥青混合料动态模量预估模型进行了研究。典型的预估模型包括Witczak 1-37A模型、NCHRP 1-40D模型和Hirsch模型等,尽管这些模型是在大量试验数据的基础上拟合得到,但由于世界不同地区的材料、试验方法、环境条件等存在差异,致使三种经验预估模型在不同地区的适用性也不尽相同。与此同时,随着计算机技术的发展,研究人员逐渐从微观角度建立模型来预测混合料的动态模量,而在沥青混合料数值模拟方面,离散元法(DEM)具有其他数值模拟方法无可比拟的优势。在典型预估模型的适用性方面,国外针对沥青混合料动态模量的预估做了大量研究,对几种典型的动态模量预估模型的适用性进行了系统分析,并提出了具体的修正模型。但目前我国在预估模型方面的研究只集中于个别省份和地区,而全国范围内沥青混合料动态模量的综合测试较少,缺乏有效的预估模型基础数据,因此针对我国不同地区沥青混合料动态模量的预估模型有待进一步深入研究。在沥青混合料细观模型方面,基于CT图像处理技术的离散元仿真试验,可建立以真实试件为依据的虚拟几何模型,其中集料形状、分布以及空隙特征都可与实际情况一致,从而进行良好的虚拟仿真试验。本文归纳了沥青混合料动态模量预估模型的研究进展,分别对沥青混合料动态模量预估模型以及各预估模型在不同地区的适应性进行了分析,并介绍了基于DEM的动态模量预测方法。最后,分析了沥青混合料动态模量预估模型研究面临的问题并展望了其应用前景,以期为沥青混合料动态模量预估模型在我国沥青路面设计中的研究和应用提供参考。     

蜂窝芯层等效参数研究综述

蜂窝芯层等效参数的相关研究是蜂窝夹层结构设计和计算的重要基础,深入研究蜂窝芯层的力学特性具有重要的应用意义。对蜂窝芯层等效参数的研究进行了综述,首先介绍蜂窝芯层面内等效参数的研究进展,主要基于经典梁理论和均匀化理论,从线性和非线性两方面展开综述。然后介绍芯层面外等效参数研究,围绕各种计算方法、等效力学模型、线性和非线性等效,以及各自的优缺点等问题进行总结和评述。此外还对一些解析公式的精度和适用范围进行了比较,以方便工程应用。最后,指出了这一领域需要进一步研究的若干问题。     

玻纤增强酚醛树脂复合材料的粘弹性——材料储能模量模型的建立

利用DMA分析技术考察了玻纤增强酚醛复合材料的储能模量在升温过程中的变化。由于后固化和热分解反应的发生,材料的储能模量在温度高于玻璃化转变温度后出现了先上升随后下降的趋势。以三元件标准线性固态模型为基础建立了材料储能模量变化的数学模型,模型计算值与实验实测值吻合较好。     

X-cor夹层结构拉伸模量有限元分析

通过分析X-cor夹层结构中Z-pin端部的细观结构,提出Z-pin端部树脂区椭圆形态的基本假设并建立X-cor夹层结构拉伸模量的有限元模型,利用大型有限元软件ANSYS对其拉伸模量进行了数值计算。研究了Z-pin植入角度、直径和密度的改变对X-cor夹层结构拉伸模量的影响。结果表明:X-cor夹层结构的拉伸模量随Z-pin植入角度增加而减小,随Z-pin直径和密度增加而增加。通过有限元模型的计算,得到了X-cor夹层结构参数对其拉伸模量的影响规律,数值计算结果误差范围是±10%,验证了所提的有限元模型的合理性,说明该模型可用于预测其拉伸模量。     

公路路基检测技术

本文介绍了既有路基调查目的及特点,分析了路基调查内容和路基质量控制指标,重点阐述了土基的回弹模量检测方法,供大家参考。     

低模量高强度钛合金的研究进展

介绍了近年来低模量高强度钛合金的成分选择、设计方法及研究进展，讨论了合金元素添加量对合金力学性能的影响，并对这种低模量高强度钛合金的应用前景作出了展望。     

塑料合金关于温度-频率-振幅的本构模型

以经典Kelvin分数导数理论为基础,建立新型BTG塑料合金的改进Kelvin分数导数动态本构模型,该模型综合描述了温度、频率和振幅与BTG塑料合金模量的关系.通过动态热分析仪DMA242,获取了BTG塑料合金几个温度下,振幅恒为30μm时的频率扫描和几个频率下的恒温幅值扫描的动态存储模量和损耗模量实验数据.首先分析频...     

Fractional derivative viscoelastic model for frequency-dependent complex moduli of automotive elastomers

Finite element modeling has been used extensively nowadays for predicting structural vibration and noise radiation of automobile engines and subsystems. However, many elastomeric components on the engines or subsystems are often omitted in the FE models due to primarily the lack of material properties at higher frequencies. The present paper describes a form of fractional derivative viscoelastic model for characterizing frequency-dependent complex moduli of elastomers. The model is used to predict the high frequency complex moduli of some fluoroelastomers with varying durometers. Excellent correlations between testing and prediction are obtained.     

Pricing Model for Convertible Bonds: A Mixed Fractional Brownian Motion with Jumps

A mathematical model to price convertible bonds involving mixed fractional Brownian motion with jumps is presented. We obtain a general pricing formula using the risk neutral pricing principle and quasi-conditional expectation. The sensitivity of the price to changing various parameters is discussed. Theoretical prices from our jump mixed fractional Brownian motion model are compared with the prices predicted by traditional models. An empirical study shows that our new model is more acceptable.     

分数指数模型的热力学分析及其应用

本文论证了两种经典粘弹性固体模型的等价性并指出了其存在的问题。给出了热力学对分数指数模型 ^[1]参数的限制条件。计算与实验结果比较表明:因为该模型具有适当多的参数,采用同一组参数可以做到同时与同一材料的蠕变和松弛试验结果很好吻合;并能做到松弛模量和蠕变柔量的Stieltjes卷积近似等于单位阶跃函数;在很宽广的频率范围内能同时很好地模拟真实材料的存储模量和损耗模量。由于其计算速度快,能与大多数真实材料的性能实验结果相拟合,可以广泛应用于工程实际中的粘弹性静力和动力问题的计算。     

On the numerical handling of fractional viscoelastic material models in a FE analysis

The paper presents the finite element (FE) implementation of linear and nonlinear fractional viscoelasticity models. To this end, a short introduction on fractional calculus is given. In addition to the fractional operators, this includes analytical and numerical solution schemes for selected fractional integral and differential equations. The presented rheological model is based on state of the art approaches and has been adopted to model the strain rate dependent material behavior of polymers. To this end, two approaches with constant and overstress dependent viscous properties resulting in linear and nonlinear evolution equations are discussed. The uniaxial constitutive relations are generalized to the multiaxial case and processed to be implemented in a FE code. The model behavior of both approaches is demonstrated and compared for selected uniaxial and multiaxial load cases.     

硫化橡胶动态力学性能的分数阶微分Kelvin模型

研究炭黑填充硫化橡胶的动态粘弹性,采用Gabo Eplexor 500N对材料进行不同频率时的温度扫描测试,得到材料玻璃化转变温度Tg随频率的变化规律。在Tg~Tg+50℃范围内进行不同温度的频率扫描测试,得到材料存储模量、损耗模量和损耗因子。采用分数阶微分Kelvin模型对动态粘弹特性进行分析,确定了模型参数。结果表明,分数阶微分Kelvin模型可以较好地描述材料在不同温度和较宽频率范围内的动态粘弹性力学行为。当温度高于Tg时,随着温度的升高,材料从Tg附近的粘弹态向高温时的橡胶态转变,模型中的微分阶数相应地逐渐减小。     

Higher-order fractional constitutive equations of viscoelastic materials involving three different parameters and their relaxation and creep functions

Two higher-order fractional viscoelastic material models consisting of the fractional Voigt model (FVM) and the fractional Maxwell model (FMM) are considered. Their higher-order fractional constitutive equations are derived due to the models’ constructions. We call them the higher-order fractional constitutive equations because they contain three different fractional parameters and the maximum order of equations is more than one. The relaxation and creep functions of the higher-order fractional constitutive equations are obtained by Laplace transform method. As particular cases, the analytical solutions of standard (integer-order) quadratic constitutive equations are contained. The generalized Mittag–Leffler function and H-Fox function play an important role in the solutions of the higher-order fractional constitutive equations. Finally, experimental data of human cranial bone are used to fit with the models given by this paper. The fitting plots show that the models given in the paper are efficient in describing the property of viscoelastic materials.     

Fractional differential models in finite viscoelasticity

Summary A new class of constitutive models is derived for viscoelastic media with finite strains. The models employ the so-called fractional derivatives of tensor functions.We introduce fractional derivatives for an objective tensor which satisfies some natural assumptions. Afterwards, we construct fractional differential analogs of the Kelvin-Voigt, Maxwell, and Maxwell-Weichert constitutive models. The models are verified by comparison with experimental data for viscoelastic solids and fluids. We consider uniaxial tension of a bar and radial oscillations of a thick-walled spherical shell made of the fractional Kelvin-Voigt incompressible material. Explicit solutions to these problems are derived and compared with experimental data for styrene butadiene rubber and synthetic rubber. It is shown that the fractional Kelvin-Voigt model provides excellent prediction of experimental data. For uniaxial tension of a bar and simple shear of an infinite layer made of the fractional Maxwell compressible material, we develop explicit solutions and compare them with experimental data for polyisobutylene specimens. It is shown that the fractional Maxwell model ensures fair agreement between experimental data and results of numerical simulation. This model allows the number of adjustable parameters to be reduced significantly compared with other models which ensure the same level of accuracy in the prediction of experimental data.     

分数阶导数线性流变固体模型及其应用

采用Koeller 弹壶元件替代标准线性固体模型中的Newton黏壶, 得到分数阶导数线性流变固体模型, 给出了表征模型动态黏弹特性的存储模量、损耗模量和损耗因子以及表征模型静态黏弹特性的蠕变柔量和松弛模量。采用分数阶导数线性流变固体模型、标准线性固体模型和五参量固体模型对聚丙烯材料应力松弛特性进行分析。讨论了Mittag-Leffler函数的求和截断误差。结果表明分数阶导数线性流变固体模型能更准确描述聚丙烯材料的应力松弛行为。     

On the Fractional Order Model of Viscoelasticity

Fractional order models of viscoelasticity have proven to be very useful for modeling of polymers. Time domain responses as stress relaxation and creep as well as frequency domain responses are well represented. The drawback of fractional order models is that the fractional order operators are difficult to handle numerically. This is in particular true for fractional derivative operators. Here we propose a formulation based on internal variables of stress kind. The corresponding rate equations then involves a fractional integral which means that they can be identified as Volterra integral equations of the second kind. The kernel of a fractional integral is integrable and positive definite. By using this, we show that a unique solution exists to the rate equation. A motivation for using fractional operators in viscoelasticity is that a whole spectrum of damping mechanisms can be included in a single internal variable. This is further motivated here. By a suitable choice of material parameters for the classical viscoelastic model, we observe both numerically and analytically that the classical model with a large number of internal variables (each representing a specific damping mechanism) converges to the fractional order model with a single internal variable. Finally, we show that the fractional order viscoelastic model satisfies the Clausius–Duhem inequality (CDI).