超声波实时监测乙烯基酯树脂固化反应过程

采用超声波纵波透射法对乙烯基酯树脂固化反应过程进行了实时在线监测,准确测量了超声波在树脂体系中的传播速度及振幅衰减,研究了不同厚度树脂的固化反应过程及其储能模量和固化度的变化。实验显示,随着固化反应进行,超声波声速增加,振幅衰减先增大后降低。超声波声速变化与固化过程中体系力学性能的变化有关,通过声速与振幅衰减能实时获取体系的储能模量、凝胶时间及固化度。结果表明,超声波技术能够实时监测树脂体系的固化过程和性能变化,对树脂类复合材料的制备工艺和性能研究有重要的指导作用。     

超声波法表征纤维增强树脂基复合材料固化行为

采用超声波法对乙烯基酯树脂、玻璃纤维/乙烯基酯树脂、碳纤维/乙烯基酯树脂3种体系的固化反应过程进行了实时监测, 准确测量了超声波在3种体系中的传播速度及振幅衰减随体系固化反应时间的变化, 研究了纤维对树脂体系凝胶时间、固化过程体积储能模量及反应活化能的影响。结果表明, 玻璃纤维/树脂体系的反应活化能较纯树脂体系减小14 %, 固化速率加快; 而碳纤维/树脂体系的反应活化能较纯树脂体系增大15 %, 固化速率较纯树脂体系慢。超声波技术能够实时在线监测并量化纤维/树脂复合体系的固化行为, 为复合材料的制备工艺和性能研究提供了一种重要的量化手段。      

超声波改性有机膨润土及其对苯的吸附研究

为了提高有机膨润土对苯的吸附能力,采用超声波辐照处理膨润土改性合成有机膨润土.通过研究不同的改性条件对苯吸附量的影响,获得了最佳工艺条件为:超声处理时间20min、固液比1:10、十六烷基三甲基溴化铵(HTAB)加量120mmol/100g及超声波功率600 W.在此条件下制备的有机膨润土对苯的吸附平衡研究表明,在开始30rain内吸附非常快,吸附150min后基本达到吸附平衡,其对苯的吸附量达51.28mg/g.     

超声波在线监测环氧树脂固化反应过程

采用超声波技术成功地对环氧树脂固化过程进行了在线监测。超声波横渡与纵波及其波峰衰减反映了固化体系剪切模量的变化、凝胶点和固化终点。固化剂含量为9％时有利于体系的完全固化。超声波法在线监测技术将为研究聚合物固化反应提供了一种简单、实用的技术手段。     

Modeling of transient ultrasonic wave propagation using the distributed point

Transient ultrasonic waves in a fluid medium generated by a flat circular and a point-focused transducer of finite size are modeled by the distributed point source method (DPSM). DPSM is a Green's-function-based semi-analytical mesh-free technique which is modified here to incorporate the transient loading from a finite-sized acoustic transducer. Conventional DPSM solves acoustic problems in steady-state frequency domain. Here, DPSM is extended to the time domain without the fast Fourier transform (FFT) but using the Green's function in the time domain. This modified method is denoted t-DPSM. Harmonic point sources of DPSM are replaced by time-dependent point sources in t-DPSM. Generated t-DPSM results are compared with the finite element (FE) results for both focused and flat circular transducers. The developed method is used to solve the transient problem of wave scattering by an air bubble in a fluid as the bubble is moved horizontally or vertically from the focal point of the focused transducer. The received energy signal is compared for different eccentricities.     

Characterization of 2-dimensional crack propagation behavior by simulation and analysis

Crack propagation behavior in 2-dimensional polycrystals is simulated and analyzed as a function of the fracture toughness of the grain boundary. The path of a crack impinging on a grain boundary is determined by the competition theory between intergranular and transgranular propagation. With decreasing boundary toughness, the tendency of intergranular propagation increases and the apparent fracture toughness of the polycrystal decreases. The results of the 2-dimensional analysis are compared with the simulation, and the advantages and limitations are discussed. The grain boundary toughness is evaluated by comparing the simulated crack paths with direct observations, resulting in a reasonable value for alumina ceramics. The fracture behavior is characterized in a macro-scale by the percentage of transgranular fracture and also in a micro-scale by the distribution of crack deflection angles.     

An investigation of the hydration of calcium aluminate through ultrasonic wave propagation

The hydration process of a high alumina cement was investigated through ultrasonic wave propagation techniques. A correlation between wave amplitude and velocity and breaking strength of the cement is demonstrated. The wave behaviour through hydrating cements was found to be a function of the cement-to-water ratio between values of 2 and 4. Changes in the temperature of the hydrating samples were found to exhibit a similar dependence.     

CFRP复杂几何结构区相控阵超声检测建模与声传播规律

为厘清碳纤维增强树脂基复合材料(Carbon fiber reinforced plastics,CFRP)复杂几何构件相控阵超声检测中声传播规律,围绕CFRP材料R区开展了弹性特性表征、有限元建模、声场计算及实验验证工作。基于超声液浸背反射法和模拟退火算法求解了CFRP单向板刚度矩阵反问题,并借助Bond变换实现了R区弹性特性的定量描述。结合微观组织分析等获取材料、几何特征,建立了虑及曲面形状、叠层、弹性各向异性的R区相控阵超声检测有限元模型,计算了R区相控阵超声检测A、B扫描信号,发现存在结构噪声和缺陷伪像。在此基础上研究CFRP材料R区瞬态声场并与CFRP平板、弹性各向同性R区和0°单向板R区情况对比,阐明了结构噪声和缺陷伪像的形成机制:弹性各向异性叠层结构导致倾斜入射的超声波发生反射和折射,与沿肋板传播的快速波混叠在R区形成结构噪声,同时多向板R区两侧肋板反射导致缺陷伪像,即材料弹性各向异性与构件曲面叠层结构耦合共同影响缺陷的精准辨识。      

Numerical simulation of ultrasonic wave propagation in anisotropic and attenuative solid materials

The axisymmetric elastodynamic finite element code developed is capable of predicting quantitatively accurate displacement fields for elastic wave propagation in isotropic and transversely isotropic materials. The numerical algorithm incorporates viscous damping by adding a time-dependent tensor to Hooke's law. Amplitude comparisons are made between the geometric attenuation in the far field and the corresponding finite element predictions to investigate the quality and validity of the code. Through-transmission experimental measurements made with a 1 MHz L-wave transducer attached to an aluminum sample support the code predictions. The algorithm successfully models geometric beam spreading dispersion and energy absorption due to viscous damping. This numerical model is a viable tool for the study of elastic wave propagation in nondestructive testing applications.     

双马来酰亚胺改性环氧树脂固化反应行为及性能研究

采用双马来酰亚胺（BMI）改性环氧树脂（TDE-85）／芳香胺（DAMI）固化体系。用差式扫描量热法（DSC）对树脂体系的固化反应行为与固化动力学进行了分析，考察了BMI含量对改性体系性能的影响。结果表明，随着体系中BMI比例的增加，体系固化放热峰向高温区移动，总反应热减小，固化物的耐热性和力学性能明显提高；根据Kissinger方法求得改性前后体系固化反应的表现活化能△E分别为52．46和57．72kJ／mol；根据Crane理论计算得到改性体系的固化反应级数n为0．88，固化反应过程为多级反应。     

Identification of parametric models for ultrasonic wave propagation in the presence of absorption and dispersion

Acoustic wave propagation in an absorptive and dispersive medium is usually described using models derived from a nearly local form of the Kramers-Kronig relationship, e.g., Q- and relaxation models. A modeling approach based on rational transfer function models for the generalized Hooke's law is presented. The assumptions and restrictions of models based on the nearly local absorption-dispersion relations and rational transfer function models are discussed. Using identification techniques, it is experimentally shown that the rational transfer function models explain the ultrasonic wave propagation in an absorptive-dispersive medium much better than the classical Q-models.     

Curing behavior and kinetic analysis of epoxy resin/multi-walled carbon nanotubes composites

The effect of multi-walled carbon nanotubes (MWNTs), both amino-functionalized (f-MWNTs) and unfunctionalized (p-MWNTs) on the curing behavior of epoxy resin (EP) cured with triethanolamine (TEA), was investigated using differential scanning calorimetry (DSC). Because the triethylenetetramine (TETA) grafted on the f-MWNTs could act as curing agent and the produced tertiary amine as negative ionic catalysts of curing reaction of EP, so the activation energy of the EP/TEA system was decreased by the addition of f-MWNTs. Viscosity played a key role in the curing behavior of the EP/TEA/MWNTs system, for high viscosity of the EP/TEA/MWNTs system could hinder the motion of the functional groups. The curing heat in EP/TEA/f-MWNTs (weight ratio 1/0.1/0.01) system was higher than the neat EP/TEA (weight ratio 1/0.1) system, while the curing heat in EP/TEA/p-MWNTs (weight ratio 1/0.1/0.01) was lower than the neat system. When the content of f-MWNTs was increased to 2 phr (weight ratio of 1/0.1/0.02), the curing heat became lower than that of the neat EP/TEA system, which was the result of the higher viscosity of the EP/f-MWNTs/TEA system. Since the curing heat indicated the curing degree of the system generally, the addition of the f-MWNTs was thought to increase the curing degree of the epoxy matrix at a relatively low content.     

Control of hydration rate of polymer modified cements by the addition of organically modified montmorillonites

The addition of polyvinyl alcohol (PVA) in concrete causes a delay in the hydration rate of Portland cement paste. Three different montmorillonites (MMTs) (Cloisite Na, 30B, and Nanofil) were previously mixed with PVA in order to control this delay. A comparison between the hydration rate of Portland cement paste and Portland cement paste modified with PVA and the different MMTs was made by means of semi-adiabatic calorimetry, thermal gravimetric analysis and contact angle measurements. Different rates of hydration were obtained with each MMT. The paste with PVA and Nanofil behaves almost the same as the unmodified cement paste. Mechanical properties were also studied. An increase in the flexural strength and a decrease in the compression strength were found, which is expected for a Portland cement paste modified with PVA. The addition of MMT to the cement paste with PVA hardly affects the mechanical properties.     

一种灌封结构用环氧树脂的固化行为表征和模拟

以中高温固化的E39D环氧树脂为研究对象,基于顺序耦合热传导-固化和应力位移模块的数值仿真方法,选择合适的实验方法测试环氧树脂的固化性能,引入相关假设,推导与热传导-固化和应力位移模块相关的树脂固化性能参数和模型;然后,建立典型E39D树脂灌封结构的数值模型,模拟结构内部观测点在固化过程中的温度和应力演变,并基于FBG...     

Temperature dependences of longitudinal ultrasonic wave propagation velocity in gallium arsenide and indium phosphide single crystals

Results are considered for experimental studies of the longitudinal ultrasonic wave propagation velocity in gallium arsenide <001> and indium phosphide <100> single crystals in the temperature range 200–355 K with measurements made through each 0.5–1 K. Measurements were made by the ultrasonic echo-pulse procedure using calibration marks of time. The frequency of the sounding signal is 10 MHz.Translated from Problemy Prochnosti, No. 11, pp. 48–49, November, 1991.     

Characterization of the viscoelastic behavior of bismaleimide resin before and after exposure to high temperatures

Creep and high strain rate mechanical properties, shrinkage strain, and thermal properties of a bismaleimide neat resin after exposure to a high temperature in air were evaluated and compared with the corresponding properties for a pristine resin. Under tension at a strain rate of 6×10^?4 s^?1, the Young’s modulus decreases and Poisson’s ratio increases with temperature, measured up to 310 °C. The tensile creep behavior was determined at stress levels of 12, 24, and 33 MPa at elevated temperatures. At each stress level, the creep compliance curves at different temperatures were shifted horizontally to form a master curve. These creep compliance master curves are nearly identical, indicating a linearly viscoelastic behavior up to 33 MPa. The bismaleimide resin was also exposed to air at other temperatures of 245, 260, and 280 °C for 1500 hours. After exposure to a high temperature, three regimes were observed in the resin through optical micrographs: an outer layer showing darker color, an interior that nearly maintained its original color, and a transition (or reacting) region in between. The average shrinkage on surface was determined as 3.4 % strain after 1500 hours of exposure to 260 °C in air. Compression at a high strain rate using a long split Hopkinson pressure bar shows that the bulk bismaleimide resin is rather insensitive to the exposure to a high temperature, exhibiting only a slight reduction in mechanical properties after 1500 hours of exposure to 245 °C. The uniaxial creep compliance of the neat resin was converted into the Young’s relaxation modulus, which was then used to calculate the Young’s modulus under tension at the strain rate and temperatures involved, and a good agreement was achieved between the calculated results and the experimental data, indicating that the rate-dependent Young’s modulus is the representation of viscoelastic properties.     

Cure kinetics characterization and monitoring of an epoxy resin using DSC,Raman spectroscopy,and DEA

The use of thick sections of fiber-reinforced polymers (FRPs) is increasing for numerous industrial applications such as wind turbine blades. In situ cure monitoring is very important to directly observe the cure process of FRPs during the manufacturing process. In this work, Raman spectroscopy and dielectric analysis (DEA) are investigated for in situ cure monitoring of an epoxy resin. The cure behavior is first characterized using differential scanning calorimetry (DSC) as a baseline comparison, and the best-fit phenomenological reaction model is determined to describe the cure behavior of the epoxy resin as well as the kinetic parameters. The relationship between T_g and degree of cure is also established. The degree of cure obtained from Raman spectroscopy and DEA under isothermal conditions is compared to that obtained from DSC. A good agreement is observed among the three methods, supporting the potential of these in situ cure monitoring methods during manufacturing. An implementation plan for in-plant monitoring is also discussed.     

有机硅改性丙烯酸树脂乳液的合成及性能研究

采用乳液聚合法,并以种子乳液法分步加料方式,将一定比例丙烯酸酯单体、自制的有机硅大分子单体进行自由基聚合,得到有机硅改性丙烯酸树脂乳液.利用单因素实验和5因素4水平正交实验优化出最佳工艺参数:MM用量为1.2%,有机硅预聚体的用量为9%,单体配比为0.76,异丙醇用量为1.5%,可获得高稳定性乳液,成膜各项性能提高.     

超声波活化处理提高纤维素选择性氧化反应性能的研究

纤维素是一种重要的可再生性天然多糖聚合物。纤维素的高度结晶性和难溶性,决定了纤维素多数的化学反应都是在多相介质中进行。为了提高纤维素对试剂的可及度及反应性能,在进行多相反应之前,纤维素材料通常要经历溶胀或活化处理。本文采用超声波对纤维素进行活化处理,研究了处理条件对纤维素选择性氧化反应的影响。结果表明,超声波处理能显著提高纤维素与高碘酸盐的氧化反应活性,缩短反应时间和高碘酸盐用量,优化反应条件。     

Modeling and simulation of curing kinetics for the cardanol-based vinyl ester resin by means of non-isothermal DSC measurements

The cure kinetics of vinyl ester-styrene system was studied by non-isothermal differential scanning calorimetric (DSC) technique at four different heating rates. The kinetic parameters of the curing process were determined by isoconversional method for the kinetic analysis of the data obtained by the thermal treatment. Activation energy (E_a = 56.63 kJ mol⁻¹) was evaluated for the cure process and a two-parameter (m, n) autocatalytic model was found to be the most adequate to describe the cure kinetics of the studied cardanol-based vinyl ester resin. Non-isothermal DSC curves, as obtained by using the experimental data, show good agreement with the DSC curves obtained by theoretically calculated data.