Swelling and mechanical properties of radiation crosslinked Au/PVA hydrogel nanocomposites

Hydrogel nanocomposites of polyvinyl alcohol (PVA) filled with gold nanoparticles (Au NPs) were synthesised using gamma irradiation technique. Structural, optical, and morphological characterisation was performed using powder XRD, UV-vis, FESEM, and TEM techniques. Inclusion of Au NPs at the time of crosslinking may have reduced the binding sites of PVA matrix, which resulted in high-swelling capacity of Au/PVA hydrogel nanocomposites. The increase in mechanical stability of the Au/PVA hydrogel nanocomposites has been observed and it may be due to increase in the crystallinity percentage with increased Au NPs in PVA matrix. These nanocomposites may fulfil the increasing demand for multifunctional hydrogel with enhanced swelling and mechanical properties.     

Characterization of mechanical and geometrical properties of a tube with axial and circumferential guided waves

Guided waves propagating in cylindrical tubes are frequently applied for the characterization of material or geometrical properties of tubes. In a tube, guided waves can propagate in the axial direction and called axial guided waves, or in the circumferential direction called circumferential guided waves. Dispersion spectra for the axial and circumferential guided waves share some common behaviors and however exhibit some particular behaviors of their own. This study provides an investigation with theoretical modeling, experimental measurements, and a simplex-based inversion procedure to explore the similarity and difference between the axial guided waves and circumferential guided waves, aiming at providing useful information while axial and circumferential guided waves are applied in the area of material characterization. The sensitivity to the radius curvature for the circumferential guided waves dispersion spectra is a major point that makes circumferential guided waves different from axial guided waves. For the purpose of material characterization, both axial and circumferential guided waves are able to extract an elastic moduli and wall-thickness information from the dispersion spectra, however, radius information can only be extracted from the circumferential guided waves spectra.     

超声探头的响应特性及暂态回波模型

建立检测系统的数学模型,可以更好地理解超声检测的物理本质。分析了超声波从产生、介质中传播、缺陷耦合以及接收的全过程,将缺陷回波表示为探头响应函数与缺陷响应的时域卷积。利用空间脉冲响应和基尔霍夫近似建立了超声波与平面型缺陷的耦合模型,用大平面试块底面回波和大平面响应进行反卷积求得了探头的响应函数,并详细分析了探头在不同偏置位置时不同大小缺陷响应的特点,发现缺陷回波由直达回波和边缘回波组成,直达回波和边缘回波极性相反,且直达回波的幅值远远大于边缘回波。     

超声无铆静力学性能强化试验与机制研究*

无铆连接是一种薄板材料连接新技术,可在无需预成孔和表面预处理情况下,实现同种、异种、多层薄板材料高效连接,但由于无铆接头静力学性能较低,极大地限制了该连接技术的推广与发展。为解决这一难题,本文选用5A06铝合金与TA1钛合金进行同种金属无铆铆接,并在此基础上进行了超声金属焊接复合实验,基于静拉伸测试和扫描电镜分析,探究超声焊对无铆接头力学性能的强化机制。试验结果表明：超声焊可有效提升无铆接头力学性能,特别是对于铝合金无铆接头;超声焊使得铝合金板塑性提高,钛合金板则得到硬化;超声焊后无铆接头的受力形式发生改变,从颈部受力变为先焊合区受力再颈部受力,这是超声焊复合强化的根本原因;超声焊可使铝合金无铆接头内部形成一定深度的固相焊,使铝合金接头力学性能得到大幅提升;TA1钛合金无铆接头内部固相焊较浅,力学性能提升相对较低。     

A physics-based temperature model for ultrasonic vibration-assisted pelleting of cellulosic biomass

Temperature in ultrasonic vibration-assisted (UV-A) pelleting of cellulosic biomass has a significant impact on pellet quality. However, there are no reports on temperature models for UV-A pelleting of cellulosic biomass. The development of a physics-based temperature model can help to explain experimentally determined relations between UV-A pelleting process variables and temperature, and provide guidelines to optimize these process variables in order to produce pellets of good quality. This paper presents such a model for UV-A pelleting of cellulosic biomass. Development of the model is described first. Then temperature distribution is investigated using the model, and temperature difference between the top and the bottom surfaces of a pellet is explained. Based on this model, relations between process variables (ultrasonic power and pelleting duration) and temperature are predicted. Experiments were conducted for model verification, and the results agreed well with model predictions.     

DNA超分子水凝胶的粗粒化建模与模拟

DNA超分子水凝胶在生物、医学领域具有广阔的应用前景,基于计算模拟技术研究其分子结构与其宏观性能关系具有重要意义.归因于其复杂的结构和较大的相关时间空间尺度,目前针对DNA水凝胶的分子建模与模拟研究比较缺乏.本文建立了一种DNA水凝胶的粗粒化模型,采用分子动力学模拟的方法针对一种模块化纯DNA水凝胶进行了研究.模拟结果表明其凝胶态介观结构为多孔海绵状,其交联度与水凝胶的浓度成正相关,并得出了其转变温度的范围等.模拟结果与相关实验定性或半定量符合,表明该模型可能用于该模块化DNA水凝胶等类似系统的结构功能关系研究.     

Effects and mechanism of ultrasonic irradiation on solidification microstructure and mechanical properties of binary TiAl alloys

In spite of their high temperature and reactivity, the binary TiAl alloys are successfully imposed by the ultrasonic irradiation and the microstructure evolution, solidification behaviors and mechanical properties are elaborately investigated. After ultrasonic irradiation, a high quality ingot without shrinkage defects and element segregation is obtained and the coarse dendrite structure is well modified into fine non-dendrite globular grains. The coarse lamellar colony and lamellar space of Ti44Al alloy is refined from 685 μm to 52 μm and 1185 nm to 312 nm, respectively (similarly, 819 μm to 102 μm and 2085 nm to 565 nm for Ti48Al alloy). For Ti48Al alloy, the α peritectic phase is simultaneously precipitated from the melt as well as the β primary phase before the peritectic reaction and the solidification is transformed into the mixed α-solidifying and β-solidifying. Ultrasonic irradiation promotes the peritectic reaction and phase transformation completely and the phase constituent becomes more close to the equilibrium level. The compressive strength of Ti44Al and Ti48Al alloys are increased from 623 MPa to 1250 MPa and 980 MPa to 1295 MPa, respectively. The grain refinement and dendrite transformation enhance the grain boundary sliding improving the plastic deformation ability. Ultrasonic irradiation significantly accelerates the melt flow and solute redistribution and the main grain refinement mechanism is the cavitation-enhanced nucleation by inclusion activation and heightened supercooling.     

液态簧振动力学谱在蛋白质水凝胶脱水变性过程的应用研究

本文用液态簧振动力学谱(RMS-L)方法, 对典型蛋白质水凝胶鸡蛋清的脱水变性过程进行了测量, 结果表明, 随水含量的减少, 鸡蛋清至少存在4个力学谱的显著变化过程. 基于此结果并结合力学谱的理论分析, 作者推测, 随水含量的减少, 鸡蛋清可能依次存在下述4个状态: 1) 类体水(bulk-likewater) 的蛋白质水凝胶态; 2) 键合水 (bond water) 的蛋白质水凝胶态; 3) 键合水和键合蛋白质(bonding protein) 的混合态; 4) 键合蛋白质态. 而蛋白质的空间构型(spatial configuration)转变即变性, 主要发生在拥有键合水的蛋白质通过失水向键合蛋白质转变的混合态. 这表明RMS-L对鸡蛋清脱水变性过程的检测是有效的, 所得结果对蛋白质变性机理、以及蛋白质水凝胶态的深入研究也应具有参考价值. 关键词： 力学谱 蛋白质水凝胶 蛋白质变性     

用于测量流量和含沙量的超声波液位测定系统

本文介绍了实验室内用于测量流量和含沙量的超声波液位测定系统，此系统采用气介式方案，选用复合材料高频换能器作为超声波发射／接收器件，结构简单，静态测量时测量误差在１５０ｍｍ范围内不超过１ｍｍ，并可与微机进行远距离通讯。     

超声空化去毛刺的理论分析及数值仿真

随着制造业的不断发展,对产品的加工精度要求愈来愈高,然而微小毛刺的去除仍然是十分困难的。毛刺虽小但危害巨大。因此,有效去除毛刺已成为加工中不可或缺的工序。而超声波去毛刺法可以有效快速的去除复杂零件的微小毛刺,具有很高的实用价值。尽管超声波的相关理论日趋完善,但是超声去毛刺机理以及空化产生的高压对毛刺的影响缺乏一些理论参考。此文阐述了超声波去毛刺的基本原理,利用有限元软件ABAQUS对单个空化泡在毛刺上的溃灭过程进行数值仿真,证明了超声波去毛刺的可行性,通过实验验证,超声波能够有效的去除毛刺。其研究结果为进一步研究超声波去毛刺的理论提供了参考。     

Alternate stresses and temperature variation as factors of influence of ultrasonic vibration on mechanical and functional properties of shape memory alloys

It is known that the main factors in a variation in the shape memory alloy properties under insonation are heating of the material and alternate stresses action. In the present work the experimental study of the mechanical behaviour and functional properties of shape memory alloy under the action of alternate stresses and varying temperature was carried out. The data obtained had demonstrated that an increase in temperature of the sample resulted in a decrease or increase in deformation stress depending on the structural state of the TiNi sample. It was shown that in the case of the alloy in the martensitic state, a decrease in stress was observed, and on the other hand, in the austenitic state an increase in stress took place. It was found that action of alternate stresses led to appearance of strain jumps on the strain–temperature curves during cooling and heating the sample through the temperature range of martensitic transformation under the constant stress. The value of the strain jumps depended on the amplitude of alternate stresses and the completeness of martensitic transformation. It was shown that the heat action of ultrasonic vibration to the mechanical behaviour of shape memory alloys was due to the non-monotonic dependence of yield stress on the temperature. The force action of ultrasonic vibration to the functional properties was caused by formation of additional oriented martensite.     

Elastic and ultrasonic properties of single crystalline nickel nanowires

In the present paper, we have theoretically calculated the non linear elastic constants of single crystalline Ni NWs at very broad temperature range 20–300 K validating simple interaction potential model. The temperature dependent ultrasonic attenuation and other related properties are determined using their second and third order elastic constants (SOECs/TOECs). Where possible, the results are compared with experiments from literature. There is a correlation between the thermal conductivity and ultrasonic attenuation in the temperature range 100–300 K. Also, a correlation between the resistivity and ultrasonic attenuation in the temperature range 40–100 K has been established validating the theoretical approach.     

Separation of viscothermal losses and scattering in ultrasonic characterization of porous media

This paper presents a method for separating viscothermal and scattering losses in ultrasonic characterization of porous media. This method is based on variations of the static pressure of the saturating fluid. Experimental results were already presented in previous papers and the losses separation was verified experimentally. The aim of this paper is to present an analytic justification of this losses separation in the case of this experimental method and to show that it is possible to estimate acoustic parameters without the knowledge of scattering characteristics. The standard scattering length is used to renormalize speed and transmission through the porous medium, described as an equivalent fluid. Under certain assumptions corresponding to a weak scattering regime, it is shown how viscothermal and scattering losses can be separated easily without knowing scattering characteristics. Application of this model is presented in the case of weak scattering in a polyurethane foam and in the limit case of stronger scattering in a glass beads sample.     

Comparison of frequency domain and time domain methods for the numerical simulation of contactless ultrasonic cavitation

The use of a top-mounted electromagnetic induction coil has been demonstrated as a contactless alternative to traditional ultrasonic treatment (UST) techniques that use an immersed mechanical sonotrode for the treatment of metals in the liquid state. This method offers similar benefits to existing UST approaches, including degassing, grain refinement, and dispersion of nanoparticles, while also preventing contact contamination due to erosion of the sonotrode. Contactless treatment potentially extends UST to high temperature or reactive melts. Generally, the method relies on acoustic resonance to reach pressure levels suitable for inertial cavitation and as a result the active cavitation volume tends to lie deep in the melt rather than in the small volume surrounding the immersed sonotrode probe. Consequently, (i) with suitable tuning of the coil supply frequency for resonance, the treatment volume can be made arbitrarily large, (ii) the problem of shielding and pressure wave attenuation suffered by the immersed sonotrode is avoided. However, relying on acoustic resonance presents problems: (i) the emergence of bubbles alters the speed of sound, resonance is momentarily lost, and cavitation becomes intermittent, (ii) as sound waves travel through and reflect on all the materials surrounding the melt, the sound characteristics of the crucible and supporting structures need to be carefully considered. The physics of cavitation coupled with this intermittent behaviour poses a challenge to sonotrode modelling orthodoxy, a problem we are trying to address in this publication. Two alternative approaches will be discussed, one of which is in the time domain and one in the frequency domain, which couple the solution of a bubble dynamics solver with that of an acoustics solver, to give an accurate prediction of the acoustic pressure generated by the induction coil. The time domain solver uses a novel algorithm to improve simulation time, by detecting an imminent bubble collapse and prescribing its subsequent behaviour, rather than directly solving a region that would normally require extremely small time steps. This way, it is shown to predict intermittent cavitation. The frequency domain solver for the first time couples the nonlinear Helmholtz model used for studying cavitation, with a background source term for the contribution of Lorentz forces. It predicts comparable RMS pressures to the time domain solver, but not the intermittent behaviour due to the underlying harmonic assumption. As further validation, the frequency domain method is also used to compare the generated acoustic pressure with that of traditional UST using a mechanical sonotrode.     

Sonochemical effect and pore structure tuning of silica xerogel by ultrasonic irradiation of semi-solid hydrogel

Silica xerogels were prepared by the sol-gel method under ultrasonic irradiation, using tetraethylorthosilicate (TEOS) as the starting material. Hexamethyldisiloxane (HMDSO) was used as the hydrophobizing agent. When preparing silica xerogel, it is necessary to perform aging and hydrophobization to suppress shrinkage during ambient pressure drying, however, such treatments are time-consuming. In this study, the semi-solid hydrogel was irradiated with ultrasonic for the first time in order to accelerate aging and hydrophobic treatment, and the effect of ultrasonic frequency on structure was investigated. Firstly, ultrasonic irradiation was performed at frequencies of 100 kHz and 500 kHz, followed by hydrophobic treatment at a frequency of 500 kHz, in order to promote aging. The results identify optimum conditions for ultrasonic irradiation to promote aging and hydrophobization reactions, and it was found to be possible to prepare silica xerogels in less than 1/5 of the conventional time. The silica xerogels had a low density and the shrinkage was suppressed. In this study, it was found that ultrasonic irradiation of semi-solid hydrogel was very effective for promoting the reaction.     

Dielectric and ultrasonic investigation of phase transition in cuinp2s6 crystals

Investigation results of dielectric and ultrasonic properties of layered CuInP₂S₆ crystals are presented. At low frequencies, dielectric spectra are highly influenced by the high ionic conductivity with the activation energy of 7357.4?K (0.635?eV). The high-frequency part of the spectra is determined by relaxational soft mode. The critical slowing down and Debye-type dispersion show the order–disorder type of the phase transition. The temperature dependence of the relaxational soft mode and dielectric contribution show a quasi-one-dimensional behaviour. Ultrasonic velocity exhibits critical slowing down which is accompanied by attenuation peaks in the phase transition region. Layered CuInP₂S₆ crystals have extremely large elastic nonlinearity in the direction perpendicular to layers. The nonlinear elastic parameters substantially increases at the PT temperature.     

Numerical modelling of ultrasonic waves in a bubbly Newtonian liquid using a high-order acoustic cavitation model

To address difficulties in treating large volumes of liquid metal with ultrasound, a fundamental study of acoustic cavitation in liquid aluminium, expressed in an experimentally validated numerical model, is presented in this paper. To improve the understanding of the cavitation process, a non-linear acoustic model is validated against reference water pressure measurements from acoustic waves produced by an immersed horn. A high-order method is used to discretize the wave equation in both space and time. These discretized equations are coupled to the Rayleigh-Plesset equation using two different time scales to couple the bubble and flow scales, resulting in a stable, fast, and reasonably accurate method for the prediction of acoustic pressures in cavitating liquids. This method is then applied to the context of treatment of liquid aluminium, where it predicts that the most intense cavitation activity is localised below the vibrating horn and estimates the acoustic decay below the sonotrode with reasonable qualitative agreement with experimental data.     

基于超声波测量技术的颗粒尺寸分布模型的研究

提出了一种利用单颗粒背向散射信号来进行粒径分布估算的超声波测量技术,系统阐述了其 理论基础及基本工作原理。被测颗粒的散射信号幅度与它在探测区中的位置、颗粒尺寸和形状有关。 通过理论分析,建立了一个可用于描述散射信号幅度概率分布与颗粒系尺寸分布之间关系的数学模 型,对该模型的反演计算便可得到颗粒系的尺寸分布信息。为了避免求解过程中的病态系数矩阵问 题,将模型求解转化成了易于解决的最优化问题。仿真实例结果验证了该技术的可行性。     

An ultrasonic method for measuring the elastic properties of human tibial cortical and cancellous bone

Ultrasonic techniques have been used to measure the elastic properties of bone. Eight human tibiae were used to determine and map the elastic properties of cortical and cancellous bone. The present study shows cortical bone to be at least orthotropic in its material symmetry. The mechanical properties of cortical bone are more homogeneous along the length than around the circumference. The variations in the properties around the quadrant of cortical bone are small, less than 10%, while differences in the properties around the circumference of cancellous bone are more apparent, approximately 5 times those of cortical bone. The elastic properties of cancellous bone exhibited inhomogeneity and some consistency pattern along both the length and the circumference.     

MR/PVA薄膜的SP和PP偏振存储特性的比较

用两正交偏振光(SP)和两P偏振光(PP)作为记录光(λ=532nm)，记录光的功率均为5mW，用He—Ne激光器632．8nm红光作为读出光，分别得到两种记录条件下甲基红掺杂聚乙烯醇薄膜(MR／PVA)样品的光栅生长曲线．发现用两P偏振光作为记录光时，光栅生长曲线分为快、慢2个过程；两正交偏振光作为记录光时，光栅生长曲线只有一个过程，前者的慢过程和后者过程的响应时间近于相同．