原位微拉曼测试技术在碳纳米管纤维和薄膜材料力学性能研究中的应用

利用宏观应力联合原位微拉曼测试技术对双壁碳纳米管(Carbon Nanotube,CNT)纤维和薄膜材料的力学性能进行了实验分析,探讨了拉伸加载期间纤维和薄膜内CNT的载荷响应及其与宏观力学性能的关联,揭示了两种材料力学性能差异性的微观机理。实验分析表明,CNT纤维和薄膜的拉伸变形呈现弹性、强化和损伤断裂三个阶段,但其内的CNT只发生弹性变形,没有塑性形变,且没有明显的损伤或键的断裂,纤维和薄膜呈现阶段性拉伸变形的原因可归结为滑移。纤维的弹性模量显著高于薄膜,是薄膜的4.7倍,原因是弹性阶段纤维中CNT的轴向伸长对宏观应变的贡献较大。纤维和薄膜的拉伸强度相差较小,原因是强化阶段薄膜内不断有大量CNT进入承载队伍,这也使得薄膜具有比纤维更高的韧性。     

Fourier transform mechanical spectroscopy of the sol-gel transition in zirconium alkoxide ceramic gels

The gelation of a ceramic precursor, zirconium alkoxide, has been studied using dynamic oscillatory measurements. The gelation time is controlled by varying the concentrations of zirconium propoxide, hydrolysis with water, and acetylacetone concentration which acts as a chelating ligand. Gelation times were varied from minutes to months. The gelation time varied with zirconium concentration to the –10 power, hydrolysis to the –7 power, and ligand concentration of the –17 power. The sol-gel transition was monitored using the criteria of Winter in which GG ⁿ and tan () = tan . It is shown that the use of multiple superimposed sinusoidal waves to simultaneously measure the moduli at several frequencies is faster than using individual frequency sweep experiments. The selection of rate and strain criteria for brittle network gels is discussed in detail.     

Non Linear Rheology for Long Chain Branching characterization,comparison of two methodologies : Fourier Transform Rheology and Relaxation.

In this study we compare three rheological ways for Long Chain Branching (LCB) characterization of a broad variety of linear and branched polyethylene compounds. One method is based on dynamical spectrometry in the linear domain and uses the van Gurp Palmen plot. The two other methods are both based on non linear rheology (Fourier Transform Rheology (FTR) and chain orientation/relaxation experiments). FTR consists in the Fourier analysis of the shear stress signal due to large oscillatory shear strains. In the present work we focus on the third and the fifth harmonics of the shear stress response. Chain orientation/relaxation experiment consists in the analysis of the polymer relaxation after a large step strain obtained by squeeze flow. In this method, relaxation is measured by dynamical spectrometry and is characterized by two relaxation times related to LCB. All methods distinguish clearly the group of linear polyethylene from the group of branched polyethylene. However, FTR and Chain orientation/relaxation experiments show a better sensitivity than the van Gurp Palmen plot. Non linear experiments seem suitable to distinguish long branched polyethylene between themselves.     

A hierarchical algorithm for predicting the linear viscoelastic properties of polymer melts with long-chain branching

The hierarchical model proposed earlier [Larson in Macromolecules 34:4556–4571, 2001] is herein modified by inclusion of early time fluctuations and other refinements drawn from the theories of Milner and McLeish for more quantitative prediction. The hierarchical model predictions are then compared with experimental linear viscoelastic data of well-defined long chain branched 1,4-polybutadienes and 1,4-polyisoprenes using a single set of parameter values for each polymer, which are obtained from experimental data for monodisperse linear and star polymers. For a wide range of monodisperse branched polymer melts, the predictions of the hierarchical model for monodisperse melts are very similar to those of the Milner–McLeish theories, and agree well with experimental data for many, but not all, of the branched polymer samples. Since the modified hierarchical model accounts for arbitrary polydispersity in molecular weight and branching distributions, which is not accounted for in the Milner–McLeish theories, the hierarchical algorithm is a promising one for predicting the relaxation of general mixtures of branched polymers.     

用Fourier变换莫尔法测量流体自由表面微幅波的振幅

采用一种非接触的光学方法－傅立叶变换莫尔法（Fourier transformmethod），结合数字图像处理技术，对微幅振荡的水表面波的振幅进行测量。它是对全场中每一个像素点进行测量，比较触测量法具有更高的灵敏度。它为微幅水表面波振幅的测量提供了一种手段。通过将计算机生成的周期性光栅图像经投影机直接投影到被测物体的参考平面，经CCD摄像头、图像板捕捉存储形成数字化的光栅图像，利用傅立叶变换莫尔法处理光栅图像，从而获得包含有水表面波的振幅的相位信息，再经适当的几何变换获得振幅信息。我们在垂直振荡装置上进行了不同激励频率和不同振幅的表面波的振幅测量。     

活体状态下人脸皮肤力学性能原位测量研究

人类面部皮肤力学性能对面部手术、整容和表情形成机理等研究工作具有重要意义,但目前对面部皮肤力学性能的研究尚不完善,特别是实验方法和实验设备开发等方面还存在较多问题。本文提出一种适用于面部皮肤的加载装置,可精确实现直线运动,并通过微力传感器测量探针与皮肤之间的接触力,得到接触力-探针位移曲线,测得面部皮肤有效弹性模量E*为5.6~11kPa,皮下组织的厚度直接影响着皮肤的有效弹性模量,皮肤组织较薄的颧骨区域E*为9.3~11kPa,较厚的嘴角及脸颊区域E*为5.6~8.9kPa。此外,利用3D-DIC(三维数字图像相关技术)对皮肤表面变形场进行测量,其变形场特征充分体现出皮肤的各向异性。结果为深入研究面部皮肤本构关系打下了基础,也可为面部生物力学研究提供实验数据支持。     

陶瓷再生粗骨料混凝土力学性能研究

采用硅烷偶联剂KH-550溶液浸泡陶瓷再生粗骨料,改变其表面性能,从而增强陶瓷骨料-水泥石界面的粘结性能。使用处理后的陶瓷骨料制备陶瓷再生混凝土,并对其进行了立方体抗压强度试验和弹性模量测试。结果表明:随着陶瓷粗骨料掺量的增加,再生混凝土的强度降低;当掺量为60%时,再生混凝土的弹性模量较原碎石混凝土提高了3.2%;当掺量为100%时,再生混凝土抗压强度仍然满足要求。     

基于纳米压入法Sn-Ag-Cu无铅焊料高温力学性能的研究

无铅化和微型化已经成为电子封装的发展趋势,温度对无铅焊点的可靠性产生了不可忽视的影响。本文对Sn96.5Ag3Cu0.5无铅焊料进行回流处理,采用纳米压入法研究其在实际工况下的高温力学性能。结果表明,温度对焊料试样的力学性能影响显著。随着温度的升高,弹性模量和硬度逐渐降低,焊料发生软化;较高温度下的蠕变应力指数较小,焊料的蠕变抗力降低,其相应的蠕变激活能为76kJ/mol。由此可知,随温度的升高,焊料的蠕变机制由位错攀移逐渐转变为晶界滑移。     

基于纳米压痕法无铅焊锡连接各层材料力学性能的研究

利用SMT全自动回流焊机和高温恒温试验箱,制备出经2次回流焊时效20天的Sn-0.7Cu/Cu焊点试件.采用纳米压痕法,对其焊点金属间化合物力学性能进行测试.根据OliverPharr算法,利用接触刚度连续测量技术得到该化合物(IMC)的弹性模量及硬度,并与同种工况下的焊料及铜进行对比,发现其硬度明显大于二者.并得到了Sn-0.7Cu焊料、金属间化合物和Cu的室温蠕变速率敏感指数,对三者的蠕变性能做了对比分析,发现Sn-0.7Cu的室温蠕变速率敏感指数明显大于IMC和Cu.     

钢纤维掺量对活性粉末混凝土力学性能的影响

通过实验研究了活性粉末混凝土的基本力学性能(抗压强度、劈拉强度和抗折强度),分析了钢纤维掺量对活性粉末混凝土力学性能的影响,拟合得到了抗折强度与劈拉强度之间的关系表达式。在实验分析的基础上,建立了不同钢纤维体积含量活性粉末混凝土受压应力-应变全曲线的数学表达式。研究结果表明：钢纤维体积含量在1.0%～3.5% 之间时,活性粉末混凝土的抗压强度、劈拉强度和抗折强度均随着钢纤维掺量的增加而增大;当钢纤维体积含量超过3.5% 后,活性粉末混凝土抗压强度下降,劈拉强度略有提高,而抗折强度仍有明显的提高。     

On the convergence and causality of a frequency domain method for dynamic structural analysis

Venanico-Filho et al. developed an elegant matrix formulation for dynamic analysis by frequency domain (FD), but the convergence, causality and extended period need further refining. In the present paper, it was argued that: (1) under reasonable assumptions (approximating the frequency response function by the discrete Fourier transform of the discretized unitary impulse response function), the matrix formulation by FD is equivalent to a circular convolution; (2) to avoid the wraparound interference, the excitation vector and impulse response must be padded with enough zeros; (3) provided that the zero padding requirement satisfied, the convergence and accuracy of direct time domain analysis, which is equivalent to that by FD, are guaranteed by the numerical integration scheme; (4) the imaginary part of the computational response approaching zero is due to the continuity of the impulse response functions. The English text was polished by Yunming Chen     

活性粉末混凝土力学性能及冻融性能研究

活性粉末混凝土具有优异的力学性能和耐久性,本文按照正交设计方法设计了9组不同配合比的活性粉末混凝土,通过试验研究了其基本力学性能及抗冻融性能,分析了水胶比、硅灰水泥比和钢纤维含量等因素对活性粉末混凝土力学性能及抗冻融性能的影响规律。研究表明,水胶比是影响活性粉末混凝土力学性能及抗冻融性能最主要的因素,钢纤维含量对活性粉末混凝土抗折和劈裂强度影响较为显著,对其抗压强度和抗冻融性能的影响不明显。本文根据试件破坏的现象对钢纤维作用的机理做了初步的探讨。     

冻融循环次数和含水率对尾细砂力学性质的影响研究

为研究冻融循环次数和含水率对尾细砂力学性质的影响,利用GDH-2005B型高低温试验箱对尾矿砂试样进行冻融循环,并通过FST-200型应变控制式三轴剪力仪开展五种冻融循环次数(1次、3次、5次、7次、9次)和五种含水率(11%、13%、15%、17%、19%)尾矿砂试样常规三轴试验。研究表明:(1)相同含水率时,随着冻融循环次数的增大,变形模量逐渐减小,内聚力和内摩擦角均呈现降低的趋势;经历9次冻融循环后,内聚力降低至17.4kPa,内摩擦角降为14.82°。(2)相同冻融循环次数条件下,随着含水率的增大,尾矿砂的峰值应力降低,对应峰值应变增大;围压100kPa时,含水率19%的尾矿砂在经历9次冻融循环后应变为18.21%,应力为139.37kPa;各冻融循环次数下的尾矿砂抗压强度均呈现下降的趋势,内聚力和内摩擦角均随着含水率的增大而减小。研究成果可为尾矿砂物理力学性质理论的丰富以及尾矿砂相关工程的安全运营提供参考。     

Fourier Representation of Intermittent Flow in a Porous Medium

The field measurements and numerical results for intermittent flow regime in a sandy soil show that the time distributions of the soil water flux q(z, t), and the soil water content θ(z, t)at various depths are periodic in nature, where t is time and z is the depth (i.e., at the surface z = 0 and at depths z = − 5, − 10, − 15 cm, etc). The period of q(z, t) and θ(z, t) variations are generally determined by the sum of the duration of pulse and the duration between the initiation of two consecutive pulses of water at the soil surface. Fourier series models have been given for q(z, t) and θ(z, t) variations. The predicted Fourier results for these variations have been compared with the experimentally verified numerical results—designated as observed values. The results show that the amplitudes of these variations were damped exponentially with depth, and the phase shift increased linearly with depth.     

聚氯乙烯弹性体静动态力学性能及本构模型

为揭示聚氯乙烯弹性体在静、动态载荷下的力学性能,采用万能材料试验机和改进的分离式霍普金森压杆实验装置获得了材料在应变率为0.001、0.01、0.1、1 510、2 260和3 000 s⁻¹下的应力应变曲线,并以屈服强度为整形器优选参数,对比了紫铜、铜版纸和铅等3种整形器材料的整形效果。使用修正的ZWT非线性黏弹性本构模型描述聚氯乙烯弹性体在静、动态载荷下的力学性能。结果表明：聚氯乙烯弹性体在静态载荷下具有应变率效应和显著的超弹性特性,动态载荷下表现出较明显的应变率效应和较强的抗变形能力,且静动态载荷下的力学行为受应变历史影响较大。3种整形器材料中铜版纸的整形效果最好。修正后的ZWT非线性黏弹性本构模型能够得到统一参数的本构表达式,且各应变率下的拟合结果与实验结果具有较好的一致性。

     

Mechanical behaviour of the upper layers of a sandy loam soil under shear loading

The mechanical behaviour of the upper layers of a sandy loam soil was studied under standard triaxial compression and direct shear box tests. Variations of soil material properties were investigated at four different initial dry bulk densities of 1410, 1520, 1610 and 1670 kg/m³. Soil deformation and volume change under the triaxial compression loading were also studied at these bulk densities. Results from the two tests showed increases in the soil mechanical properties with the initial dry bulk density. The internal friction angle values measured with the triaxial compression apparatus exceeded those measured with the direct shear box. In contrast, the soil cohesion values measured with the direct shear box exceeded those measured with the triaxial compression apparatus. Under the triaxial compression test, the loose soil samples underwent contraction and volume reduction, whereas the dense samples swelled and failure cracks appeared clearly at various planes. The soil contraction for the former case characterizes the occurrence of soil compaction, whereas the cracks propagation and volume increase in the latter case characterizes the breaking up and loosening of soil during tillage operations. For the loose and moderately compacted states, the engineering Poisson's ratio increased with the axial strain until loading was completed. It also increased at the compacted and very compacted states until reaching given loading stages, after which its value started to decrease. This shifting in the engineering Poisson's ratio during loading may provide another identification of the moment of soil failure occurrence, in addition to that of the maximum shear stress.     

Hilbert-Huang变换方法在Duffing方程和圆柱尾迹流分析中的应用

本文采用N．E Huang最近提出的Hilbert-Huang变换方法分析了使用三阶Runge-Kutta方法数值求解的Duffing方程的性质和圆柱绕流尾流特性,分解得到了有限阶经验模态（Empirical Modes）,给出了相应的Hilbert谱。结果表明,Hilbert-Huang变换得到的主要含能模态物理意义清晰,相应的瞬时频率存在着明显的波内频率调制,很好地刻画了信号的时空局部特性。     

Molecular dynamics of the glass relaxation process of the soft phase in block copolymers: effect of molecular architecture

To determine the impact of molecular architecture on the molecular dynamics of the glass relaxation processes of soft blocks in different types of block copolymers, model block copolymers with a variation in both molecular architecture and chemical composition were studied. Four block copolymer models, namely, two styrene–butadiene–styrene (S-B-S) block copolymers and two styrene–styrene butadiene–styrene (S-SB-S) were chosen. In each pair of block copolymers, one is linear triblock and the other is star asymmetric. For the sake of comparison, two polybutadiene (PB) homopolymer samples, having similar chain lengths of the PB blocks present in the S-B-S block copolymers, have been investigated. Dynamic mechanical measurements have been carried out for the real and imaginary parts of the complex shear modulus (G′, G”) in the temperature and frequency ranges from −110 to 30 °C and from 10⁻² to 15.9 Hz, respectively. Complete master curves have been constructed for all samples investigated. Moreover, broadband dielectric spectroscopy has been carried out to cover wide temperature and frequency windows, −120 to 0 °C and 10⁻¹ to 10⁷ Hz, respectively. The results showed that the molecular dynamics of the glass relaxation process of the PB or statistical PSB soft phases in the block copolymers is dramatically changed when compared to the PB homopolymer. In addition, the molecular architecture is found to be an important factor in determining the molecular mobility of the soft blocks. The results are discussed in terms of the applied confinement of the counter PS hard phase, block lengths, domain thicknesses and the type of end-to-end junctions between the different polymeric blocks. Paper presented 3rd Annual European Rheology Conference (AERC 2006) April 27–29, 2006, Crete, Greece.     

Some tests of constitutive equations for entangled polymers based on planar-extension flow histories in a periodically constricted channel

Stress and velocity were determined locally by birefringence measurements and laser Doppler velocimetry for a mildly entangled polystyrene solution flowing at steady state in a rectangular channel with sinusoidally varying wall spacing. Having measured both the velocity and stress fields, we were able to test constitutive equations locally, i.e., without solving the equations of motion for the entire flow. Four were examined for the periodic planar extensions on the channel centerplane: the Newtonian model, the Lodge network model, the Doi-Edwards tube model, and the Wagner-Schaeffer modification of Doi-Edwards. High enough Weissenberg and Deborah numbers were reached to produce sizable departures from the Newtonian predictions. The Doi-Edwards model underpredicted the stress, as did Wagner-Schaeffer, although to a lesser extent. Predictions of the Lodge model were best of all, a surprising result in view of its inadequacy for simple shear deformations. The predictions of the Lodge model, without parameter adjustment, agreed remarkably well with the planar extension data over the accessible range for our apparatus: Deborah numbers up to 2.0, extensional Weissenberg numbers up to 6.5, and a maximum extension ratio of about 2.3.     

On the time-dependency of the flow-induced dynamic moduli of a liquid crystalline hydroxypropylcellulose solution

Some unusual rheological features of a liquid crystalline solution of hydroxypropylcellulose (HPC) in water have been investigated. Measurements have been performed by using a variety of different apparatuses with cone and plate geometries. Particular attention has been devoted to the experimental procedures, including the use of different sealing techniques, which are necessary to avoid solvent evaporation during the very long transients. Shear fracture effects, and their dependence on the type of sealing agents have also been studied. In steady shear, the HPC solution shows some rheological features which are common to other lyotropic systems, such as a three-region viscosity curve, and a double sign change in the first normal stress difference vs shear rate curve. The structural changes which take place after cessation of shear flow have been investigated by following the evolution of the dynamic moduli as a function of the time elapsed after the shear flow is stopped. It was found that the rate of the previously applied shear strongly affects both the kinetics and the asymptotic, long time values of the dynamic properties. Possible explanations for such behavior in terms of microstructure evolution are presented and discussed.