纤维复合材料粘弹性动态性能的细观力学分析

建立了纤维增强复合材料粘弹性动态性能的细观力学模型.首先建立了树脂基体相各向同性的粘弹性模型,模型参数由纯树脂基体材料的蠕变试验获取,在此基础上分别建立了针对单向和正交铺层复合材料的横观各相同性、正交各相异性的细观粘弹性模型.对单向、正交铺层复合材料进行了静态和动态试验,分别通过试验和上述理论模型得到了其阻尼比、动态储存模量、损耗模量和损耗因子,理论预测与试验结果吻合.     

服从分数导数Kelvin本构模型的粘弹性阻尼器的阻尼性能分析及试验研究

从分数导数的定义出发,提出了在经典粘弹性模型理论中采用Abel粘壶取代传统牛顿粘壶的新观点.将高分子粘弹性阻尼器在MTS831.10材料试验机上进行动态力学行为试验,对试验结果用分数导数模型进行拟合.结果表明,分数导数Kelvin模型可以同时精确地拟合高分子材料的存储模量和损耗模量随频率变化的曲线,而且其形式简单、统一.在计算过程中需要调整的参数很少.最后将分数导数模型引入静态特性公式,得出了圆筒状粘弹性阻尼器动态刚度与阻尼的表达式.     

阻尼压筋板的动态力学性能研究

本文对一种船用压筋板进行了粘弹性阻尼处理，通过有限元模拟计算了阻尼结构的模态参数，用试验模态分析的结果进行了验证，二者所得结果基本一致，并进一步用有限元分析预测了阻尼材料模量、处理厚度等变化对压筋板动态力学性能参数的影响，探讨了粘弹性阻尼材料抑制结构共振响应的有效性。     

阻尼材料对环肋柱壳稳态响应影响的分析

利用Ｆｌｕｇｇｅ壳体理论，讨论了敷设自由层粘弹性阻尼材料的环肋柱壳受周期性径向激励的稳态响应，用复模量形式计及基壳和粘弹性阻尼材料的损耗因子，并计入流固耦合作用，讨论了粘弹性阻尼材料的物理参数和厚度对其稳态响应的影响。     

粘弹性耗能器的性能与结构减振试验研究

根据土木结构的特点和要求,选用三种国产粘弹性材料制作相应的耗能器,分别进行了变频、变温、变应变、常温与低温疲劳及极限变形等耗能器性能试验,并选用ＺＮ－２２型粘弹性材料制作的耗能器进行了结构减振模拟地震振动台试验。研究了这些材料的主要性能指标——剪切贮能模量、耗能因子的变化规律,分析了频率、温度、应变和疲劳效应等因素对粘弹性材料性能参数的影响,分析了结构减振试验的效果。在此基础上,提出了粘弹性耗能器设计和制作的一些要求以及国产粘弹性材料用于土木结构减振时进一步改性的目标。     

基于材料参数随机性的粘弹性结构振动特性分析

基于粘弹性材料的随机性对粘弹性结构的振动特性进行了分析，研究了模量模型的随机性对结构固有频率和模态损耗因子的影响，在模型的随机性中分别考察了常复数模型，Kelvin-Voigt模型和三参数标准流变学模型，结果表明，粘弹性材料参数的随机性对粘弹性结构的模态损耗因子的影响还是比较大的，因此，对粘弹性结构采取随机分析是非常必要的。     

高分子材料的粘弹性摩擦接触力学研究

采用非线性有限元方法研究了高分子材料的粘弹性摩擦接触问题,采用初应变法将粘弹性材料的蠕变应变转化为等价的虚拟节点力,并结合线性粘弹性理论对蠕变应变进行迭代修正,从而获得了粘弹性材料满足摩擦接触条件的解答。文中考虑了接触问题的边界非线性和粘弹性材料的材料非线性。并考虑了接触过程中温度,模量等级时间的增加而改变。     

麦秆发泡包装衬垫非线性粘弹性模型及参数识别

由非线性粘弹性材料的一维Volterra-Frecher积分型本构方程推导得出了非线性粘弹性材料的一维微分型本构方程,建立了麦秆发泡包装衬垫的非线性粘弹性模型。根据在一种跌落高度、一种衬垫厚度和静态应力条件下的麦秆发泡包装衬垫的动态压缩试验数据,识别出了其缓冲性能模型参数。     

压力与温度对炭黑填充丁苯橡胶复合材料动静态性质影响的分子模拟

采用分子动力学模拟研究了不同压力与温度对炭黑填充丁苯橡胶复合体系动静态性能的影响。结果表明,复合体系的玻璃化转变温度随着压力升高呈现线性上升;体系自由体积与分子链尺寸随着压力上升或温度下降而减小,这也导致了分子链平动扩散与旋转动力学的降低。通过计算材料储能模量、损耗模量与损耗因子,发现材料储能模量与损耗模量随着压力上升或温度下降而上升,而材料损耗因子随着压力上升或温度下降而逐渐减小。这些结果为理解水声材料在大压力宽温域环境下的性能演变提供了微观机理。     

分数算子描述的粘弹性材料的本构关系研究

从分数导数的定义出发,提出了在经典粘弹性模型理论中采用Abel粘壶取代传统牛顿粘壶的新观点.将有机硅高分子材料在MTS831.10材料试验机上进行动态力学行为试验,对试验结果分别用经典粘弹性模型和分数导数模型进行拟合.结果表明,分数导数Kelvin模型可以同时精确地拟合高分子材料的存储模量和损耗模量随频率变化的曲线,而且其形式简单、统一,在计算过程中需要调整的参数很少.     

Effect of nonlinear response of concrete on its elastic modulus and strength

The purpose of this paper is to investigate the effect of nonlinear response of concrete on the relationship between modulus of elasticity at static and dynamic loading as well as on its strength. The obtained relationships are based on the thermofluctuation strength theory coupled with a nonlinear stress–strain material model. From the corresponding equations it was found that the ratio of the static to the dynamic modulus of elasticity depends on the strength of concrete, its temperature, rate of loading. Also it was confirmed that the dynamic modulus is greater than static modulus of elasticity. These equations explain the influence of the value of applied stress on the value of the static or dynamic modulus of elasticity. Comparative study shows substantial agreement with existing experimental results and the general equations given in standard BS 8110, Part 2:1985, and ACI documents. Based on the obtained relationships new methods for evaluating the static modulus of concrete and its strength from the results of dynamic tests are described subsequently.     

Quantitative mapping of surface elastic moduli in silica-reinforced rubbers and rubber blends across the length scales by AFM

The surface elastic moduli of silica-reinforced rubbers and rubber blends were investigated by atomic force microscopy (AFM)-based HarmoniX material mapping. Styrene–butadiene rubbers (SBR) and ethylene–propylene–diene rubbers (EPDM) and SBR/EPDM rubber blends with varying concentrations of silica nanoparticles (0, 5, 10, 20, 50 parts per hundred rubber, phr) were prepared to investigate the effect of different composition on the resulting morphology, filler distribution and elastic moduli of a specific rubber or rubber blend sample. For SBR, the elastic modulus values varied from 0.5 MPa for unfilled SBR to 5 MPa for 50 phr reinforced SBR with the increase in the concentration of filler. For EPDM, the corresponding values increased from 1.4 MPa for unfilled EPDM to 4.5 MPa for 50 phr reinforced EPDM. Local stiff and soft domains in silica-reinforced SBR and EPDM rubbers and rubber blends were identified by HarmoniX AFM imaging. While the stiff silica particles show modulus values as high as 2 GPa, the rubber matrix reveals modulus values in the range of ca. 30 MPa for the rubber blends to ca. 300 MPa for the unfilled rubbers. The lower value of elastic modulus of the EPDM phase in the blend, compared to the blank EPDM compound can be attributed to the presence of Sunpar oil in the compound which has a very good affinity with EPDM and decreases the rubber modulus. The elastic moduli maps revealed an increase of the areal fraction of silica particles showing an intrinsic surface modulus value with rising silica content in the compound preparation mixture. HarmoniX AFM measurements revealed the formation of larger silica aggregates in EPDM in contrast to SBR where isolated silica particles were observed. For silica-reinforced rubber blends a phase separation into a soft (ca. 40 MPa) and a significantly harder phase could be observed (ca. 500 MPa–1.5 GPa) indicating the incorporation of silica particles in the SBR phase. Using HarmoniX AFM imaging significantly higher surface elastic moduli were observed compared to those obtained by bulk tensile testing. Possible reasons for the observed differences between bulk modulus values and those measured by AFM are discussed in detail, including the aspect of different averaging procedures like inherent to surface probing by AFM versus bulk tensile testing, different filler distributions in SBR and EPDM and the AFM modulus calibration procedures.     

Effect of Styrene–Butadiene Rubber Latex on Mechanical Properties of Cementitious Materials Highlighted by Means of Nanoindentation

Abstract: In this paper, micro‐mechanical properties of styrene–butadiene rubber (SBR) latex‐modified cement pastes identified by means of the nanoindentation (NI) technique are related to macro‐mechanical properties of SBR latex‐modified mortars obtained from standard test methods, considering an SBR latex/cement ratio varying from 0% to 20%. For this purpose, the average value of the hardness and the so‐called indentation modulus of the different material phases of the cement paste, i.e. calcium–silicate–hydrate (CSH), portlandite, anhydrous cement, etc., obtained from NI are compared with the compressive and flexural strengths, on the one hand, and the dynamic elastic modulus of SBR latex‐modified mortars, on the other hand. This comparison revealed a linear correlation between the dynamic elastic modulus and the indentation modulus and between the compressive strength, flexural strength and hardness. Thus, the obtained results clearly indicate the finer‐scale origin of the macroscopic elastic and strength properties, linking the mechanical properties at the so‐called mortar scale to the cement‐paste scale.     

Preparation and properties of the powder SBR composites filled with CNTs by spray drying process

Carbon nanotubes (CNTs) filled powder styrene-butadiene rubber (SBR) composites were prepared by spray drying of the suspension of CNTs in SBR latex. The powder was spherical like and uniform with an average diameter of less than 10 μm. The dispersion of CNTs in the rubber matrix was improved remarkably compared with that in the rubber composites obtained by the conventional mechanical mixing method. Further study about the effect of CNTs on the prepared SBR composites was performed by analyzing the vulcanization process of the SBR powder, thermal and mechanical properties of the vulcanized SBR composites. Differential scanning calorimeter (DSC) analysis indicated that the glass transition temperatures of SBR composites increased with the increasing ratio of CNTs. The vulcanization process showed that CNTs could decelerate the vulcanization of the SBR composites. Dynamic mechanical analysis indicated that the storage modulus of the composites was improved with the CNTs additions, especially when the CNTs addition exceeded 30 phr. Compared with pure SBR composites, the hardness, tensile and tear strengths of the composites filled with 60 phr CNTs enhanced 73.9%, 327.7% and 191.1%, respectively, which should be ascribed to the excellent mechanical properties of CNTs and uniform dispersion of CNTs in the rubber matrix.     

Pulsatile newtonian frictional losses in a rigid tube

Analytic expressions for the instantaneous average velocity and friction factor have been obtained for pulsatile Newtonian laminar flow with mean flow. Experimental pulsatile pressure gradients were found to be complex wave forms whose characteristics strongly influenced the experimental pulsatile average velocity and friction factor. Experimental and theoretical reduced instantaneous friction factor histories varied in a non-sinusoidal manner throughout the pulse cycle and exhibited extremum points. At high pulsation pressure ratios, substantial deviation occurred in the portion of the pulse cycle where the instantaneous average velocity approached zero. At low pulsation pressure ratios, the experimental and theoretical time average friction factor equaled unity and was independent of pulsation modulus. One potential application of this result is in the study of blood flow through small blood vessels.     

芳纶纤维对炭黑/丁苯橡胶复合材料疲劳行为的影响

使用短芳纶纤维（AF）增强炭黑/丁苯橡胶（CB/SBR）复合材料,研究AF对复合材料疲劳行为的影响。在应力控制条件下,少量AF的加入使缺口试样的疲劳寿命提高了25.5倍;疲劳使试样的储能模量（G'）降低,AF的加入使疲劳后试样的Payne效应降低,G₀'/G₁₀₀'值降低10.5%;复数模量随疲劳周期增加而降低,但少量纤维能使复合材料的复数模量保持在较高的水平,30 000周疲劳下AF-CB/SBR的复数模量仍为CB/SBR的1.73倍;疲劳后AF-CB/SBR复合材料的100%和300%定伸应力随疲劳变形量的增加而先增大后降低,断裂伸长率有所下降。试样疲劳后相对于拉伸变形量,纤维的增强作用产生滞后效应,相对界面滑脱能随疲劳应变幅度的增加而降低; SEM结果显示,疲劳后橡胶基体出现一定的剥离,纤维与橡胶界面受到损伤。     

废丁苯胶乳/废聚酯纤维高强高模复合材料的制备与性能

采用液相高剪切混合、共沉预处理技术改善纤维在橡胶基体中的分散及其界面结合,制备了废丁苯胶乳/废聚酯纤维高强高模复合材料,并系统研究了复合材料的硫化特性、力学性能、动态力学性能和断面微观形貌。结果表明,当纤维的质量分数为60%时,复合材料具有最佳的力学性能,其拉伸强度为23.2 MPa,而未填充纤维的硫化胶强度仅为9.3MPa;同时,室温下材料的储能模量提高了约19倍。     

蒙脱土填充补强丁苯橡胶及对橡胶硫化特性的影响

以十八烷基三甲基溴化铵为插层处理剂改性蒙脱土。分别采用有机蒙脱土(C₁₈-MMT) 和Na-蒙脱土(Na-MMT) 填充补强丁苯橡胶, 用XRD 和TEM 对复合材料的结构进行表征。结果表明: 蒙脱土在橡胶基体中的分散取决于蒙脱土的亲油性, 亲油性越强, 蒙脱土的片层在橡胶中的分散越均匀, 完全有机化处理的蒙脱土能够被剥离成厚度为20 nm 左右的片层并均匀分散在橡胶基体中。蒙脱土的存在对橡胶的硫化反应有一定的影响, 有机蒙脱土对橡胶硫化反应有催化作用, 但不改变硫化反应的活化能; Na-蒙脱土片层阻碍了橡胶的硫化交联, 使交联反应对温度的敏感性降低, 导致表观活化能减小。有机蒙脱土填充补强丁苯橡胶, 由于提高了橡胶的交联密度, 同时有机蒙脱土具有高比表面积和滑移性, 大大提高了橡胶的机械性能, 其拉伸强度和300 %定伸应力与炭黑N330 补强橡胶相当, 而断裂伸长率较炭黑补强橡胶有大幅度的提高, 在替代炭黑作为橡胶的补强剂方面具有广泛的应用前景。      

Synergistic effect of carbon black and nanoclay fillers in styrene butadiene rubber matrix: Development of dual structure

Styrene butadiene rubber (SBR) based hybrid nanocomposites containing carbon black (CB) and organo-modified nanoclay (NC) was prepared. X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed the presence of intercalated, aggregated, and partially exfoliated structures. Incorporating 10 phr NC to the control SBR containing 20 phr CB resulted 153% increase in tensile strength, 157% increase in elongation at break and 144% stress improvement at 100% strain, which showed synergistic effect between the fillers. The dynamic modulus reinforcement of nanocomposites was examined by the Guth, Modified Guth, and Halpin–Tsai equations. For predicting CB filled nanocomposite modulus, the contribution of modified intercalated structure of clay and the ‘nano-unit’ (dual structure) comprising CB–NC should be considered.     

Styrene butadiene rubber/aluminum powder composites—mechanical,morphological and electrical behaviors

Different weight fractions of aluminum (Al) powder viz., 10, 20, 30, 40, 50, 60 and 70 phr were incorporated into styrene butadiene rubber (SBR) matrix. The Al powder filled and vulcanized SBR composites have been characterized for mechanical properties such as tensile strength, tensile modulus and surface hardness. A drastical improvement in tensile strength and tensile modulus with increase in filler content of the composites was noticed. The electrical properties such as dielectric constant, tan delta and dielectric loss were measured for all the four compositions. The effect of volume fraction (0–70 phr) of conducting filler, frequency (100 kHz–30 MHz), temperature (25–75°C) and relative humidity on dielectric constant, dielectric loss and tan delta values of the composites were studied.