High Frequency Ultrasonic Investigation for Ceramic Materials to Test the Manufacturing Process

Abstract

High frequency ultrasonic techniques for nondestructive tests of fine grained ceramic materials are presented. Green and partially sintered are considered. To this purpose, ultrasonic velocities and attenuation were measured and correlated to the porosity degree reached in different phases of the manufacturing process. A physical understanding of the experimental results is achieved by comparing them with the theoretical predictions provided by a self consistent scattering theory introduced in the 1980s. Finally, porosity maps are proposed since they give a comprehensive view of the process quality.     

碳纤维复合材料孔隙率超声衰减测试研究

探讨和分析了碳纤维复合材料孔隙率检测的各种方法以及理论方面的研究,指出材料内部孔隙形状与孔隙含量存在着相关性,孔隙含量超声衰减测量应考虑孔隙形貌因素,超声波频率因素对超声衰减孔隙含量测量存在着影响,不同频率超声波影响着超声衰减孔隙含量计算公式的具体形式,复合材料孔隙率检测的难点在于破坏性实验及孔隙特性不能与实测中超声信号充分点点对应,不能有效充分考虑孔隙特性,提出了一种基于孔隙特征的多分段拟合孔隙率超声衰减测试方法,并以一简单例子对多分段拟合结果进行了分析.     

基于核磁共振和超声波探伤技术的混凝土耐久性分析

针对核磁共振试验过程中试件尺寸受限问题,采用超声波探伤技术对混凝土内部孔隙率的变化进行表征.采用冻融循环试验加速混凝土的退化,结合超声波探伤技术测得的超声波波速和核磁共振技术测得的T2谱对试件内部孔隙率的变化进行表征.研究结果表明:混凝土在冻融循环退化过程中,T2谱中有三个波峰,其中表示试件内部微细小裂缝的主峰面积占总...     

含孔隙复合材料超声衰减分析的细观有限元模型

基于DIGIMAT/FE建立含孔隙复合材料细观模型,模型涵盖纤维、树脂和孔隙三相,有效反映了复合材料真实的微结构和细观材料属性,结合通用的ABAQUS/EXPLICIT对细观模型施加超声波激励。通过提取超声波在材料内传播云图,建立了单向连续纤维增强复合材料超声衰减和孔隙率的关系。以T800/环氧树脂复合材料体系为例,研究孔隙尺寸对超声衰减系数模拟结果的影响,并将数值模拟结果与解析模型得到的经验关系进行对比,验证了模型的有效性。该方法能够有效地指导实验过程,为降低复合材料孔隙率、提高其性能提供理论依据。     

Nondestructive Porosity Assessment of CFRP Composites with Spectral Analysis of Backscattered Laser-Induced Ultrasonic Pulses

The laser-ultrasonic method for nondestructive quantitative local porosity assessment for CFRP composites is proposed and realized experimentally for only one available flat surface of a specimen or a product. This method combines the laser thermoelastic generation and the high-sensitivity piezoelectric detection of broadband pulses of longitudinal ultrasonic waves and does not require the detection of the backwall echo ultrasonic signal. The generation and the detection of ultrasonic pulses is carried out with the specially designed laser-ultrasonic transducer, which allows one to obtain both the temporal profile and the frequency spectrum of a part of the ultrasonic signal backscattered by gas voids in a composite specimen. The frequency spectrum of backscattered ultrasonic pulses is analyzed for three sets of CFRP specimens with different epoxy matrix fractions and porosity. The empirical relation between porosity of CFRP specimens and the spectral power (structural noise power) of ultrasonic signals backscattered by voids is obtained for porosity values up to 0.15. This relation allows one to evaluate the local porosity from measured structural noise power both for CFRP specimens and products fabricated from the same composite material. The proposed laser-ultrasonic setup demonstrates a basis for a system of CFRP porosity assessment in field conditions. It can be very useful especially for nondestructive detection of structural changes of composite materials that will allow evaluation of products during their life time.     

孔隙率对碳纤维复合材料超声衰减系数和力学性能的影响

复合材料的工艺过程对最终产品的力学性能具有决定性影响,但其机理十分复杂。通过设置一系列固化压力历程以产生不同水平的孔隙率,采用超声C扫描、显微镜分析和酸解法对孔隙的分布、形状、尺寸和体积含量进行了定性和定量表征。讨论了孔隙率对层压板层间剪切性能、弯曲性能和拉伸性能的影响规律,获得了性能下降的临界孔隙率值。结果表明:孔隙率对性能的影响只受孔隙含量、分布、尺寸和形状等的影响,而与产生方式没有直接联系。本文作者的研究将工艺参数、孔隙率和性能有机地联系起来,体现了复合材料设计、制备与性能一体化的特点。      

X70管线钢板超声波探伤不合格原因分析

用扫描电镜观察与能谱分析方法研究了X70管线钢板超声波探伤不合格的原因。试验分析表明：超声波探伤缺陷是由数量较多、尺寸为100μm以上的气孔与缩松经轧制变形压合而形成的;气孔是由原X70管线钢坯连铸时下水口保护浇铸的氩气所引起,缩松是由连铸拉速过大所致。关闭下水口保护浇铸的氩气,并降低拉速可使X70管线钢板超声波探伤合格率达到100％。     

光催化剂纳米TiO2改性技术的研究进展

综述了纳米TiO2光催化剂与吸附剂、粘土、碳黑、强氧化剂、过氧化氢、表面超强酸化、表面多孔化和冲击波活化等新型提高光催化活性的技术,介绍了近年来新发展起来的超声波、微波、等离子体、电化学、生物化学与光催化反应结合的几种高效光催化的研究现状与进展,并对今后的研究进行了展望.     

不同厚度碳纤维布/环氧树脂复合材料孔隙率超声衰减模型

复合材料中孔隙的存在造成了材料性能的下降,因此,对材料孔隙的检测至关重要。本文利用异丙醇(IPA)添加量的不同,制备了不同层数、不同孔隙率含量的碳纤维(CF)布/环氧树脂层合板试件。采用脉冲反射法测试计算了CF布/环氧树脂层合板试件的超声衰减系数,通过金相显微分析对孔隙的分布、形状及尺寸进行了表征,运用MATLAB对金相显微图进行分析得到试件的孔隙率。讨论了孔隙率对材料的声速、声阻抗及超声衰减系数的影响规律,利用4组不同层数样本试件的孔隙率和超声衰减量的试验数据,给出了基于模型的孔隙率与材料层数、超声衰减量的拟合公式。结果表明,随着IPA添加量的增加, CF布/环氧树脂层合板(2 mm)孔隙率从1.09%增加到4.16%,材料的声速和声阻抗均下降,超声衰减系数从2.51 dB/mm增大到5.34 dB/mm。孔隙率为1%时,厚度从2 mm (8层)增加到5 mm(20层),衰减系数增大了0.54 dB/mm。     

Synthesis of La-Doped CaTiO3 Perovskite Powders from the Mixture of Metal Salt Solutions by Ultrasonic Mist Combustion/Pyrolysis Processes

The CaTiO₃ and La-doped CaTiO₃ [Ca_1–x (La) _x TiO₃, x = 0.05–0.3] powders were prepared from aqueous solutions by the ultrasonic mist pyrolysis and ultrasonic mist combustion processes. Glycine provides carboxylic acid and amine groups as a fuel in the ultrasonic mist combustion process. In ultrasonic mist pyrolysis, the particles with hollow sphere morphology were obtained; whereas, particles prepared by the ultrasonic mist combustion process had a dense solid morphology with low porosity. The ultrasonic mist combustion process using metal nitrates and glycine as the fuel for a starting material has proved to be a simple and unique approach to preparing dense CaTiO₃ powder and a solid solution of CaTiO₃ with lanthanum.