Ultrasonic Characterization of Material Interfaces and Flaws

材料界面和缺陷的超声波表征

• 批准号: RGPIN-2014-03671
• 负责人: Sinclair, Anthony
• 金额: $ 2.4万
• 依托单位: University of Toronto
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2017
• 资助国家: 加拿大
• 起止时间: 2017-01-01 至 2018-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=638536
• 关键词: Ultrasonic; Characterization; Material; Interfaces; Flaws

Ultrasonic Characterization of Material Interfaces and FlawsUltrasonic inspection has become the primary tool for industry to characterize flaws in engineering structures, and to evaluate material properties; this mirrors a parallel development of ultrasonic diagnostic techniques in the biomedical field. In its simplest form, a short mechanical impulse, with a central frequency in the MHz range is sent into an engineering component, where it interacts with defects, interfaces and other types of material discontinuities. Diffracted and reflected waves are captured, and then analyzed to determine the internal structure of the component under examination. Numerical modeling can then be used to assess the stress levels and the probability of component failure before the next inspection takes place. More advanced testing modes include resonance tests, evaluation of material anisotropy, grain size distribution assessments, and measurements of non-linear material properties.This technology is being challenged by factors such as (a) an increasing focus on product safety, (b) the use of brittle materials such as ceramics with low fracture toughness, (c) the need for inspection of very hot or radioactive components, (d) new composite materials that introduce complexities to wave propagation, and (e) a growing tendency to push engineering materials closer to their theoretical limit where even the smallest flaw can be critical. In this research program, we are developing several key elements of ultrasonic nondestructive evaluation technology to meet these challenges. Each project has active involvement from industry, with financial support coming from government granting agencies and private sponsors:(1) Development of new ultrasonic transducers for use in harsh environments of high temperature and/or gamma radiation. The key unique aspect of this project is the attenuative backing element for the piezoleectric element – we are developing a new form of porous ceramic material that has the high-temperature stability, acoustic impedance, and attenuation required for this special role. (2) New digital signal processing strategies to enhance the sharpness of ultrasonic images, such that defect size or crack depth can be measured to a fraction of a millimeter. This project takes signal processing techniques commonly used in one field of study such as biomedical imaging or geophysics, and develops them for new applications in the industrial nondestructive evaluation world. (3) Ultrasonic characterization of material interfaces, in particular those featuring partially degraded adhesion –e.g., an environmentally degraded adhesive bond; a cold shut in a turbine blade; a lapping defect in an extruded tube. In this class of problems, we are confronted with an interfacial region whose thickness is substantially less than the typical ultrasonic wavelength of ~1 mm produced by conventional transducers. A combination of techniques is required to achieve adequate imaging resolution for this class of problems: very high frequency transducers; spectral extrapolation techniques to extract high frequency components; use of angled shear waves that have a shorter wavelength and more sensitivity to weak interfaces than compression waves, frequency analysis of wave interfacial reflection and transmission. (4) Finite element modeling of wave propagation in non-homogeneous materials. This issue is concerned not just with functionally graded materials, but materials that have a strong temperature gradient such as encountered in on-line industrial inspections. Not only does the speed of sound change with temperature, but waves will “skew” onto a curved trajectory when they encounter a temperature gradient.

超声检测已成为工业上表征工程结构缺陷和评价材料性能的主要工具；这反映了超声诊断技术在生物医学领域的平行发展。最简单的形式是，一个中心频率在MHz范围内的短机械脉冲被发送到工程部件中，在那里它与缺陷、界面和其他类型的材料不连续相互作用。捕获衍射波和反射波，然后分析以确定被检查部件的内部结构。然后，可以使用数值模拟来评估应力水平和部件失效的概率，然后进行下一次检查。更先进的测试模式包括共振测试、材料各向异性评估、晶粒尺寸分布评估和非线性材料特性测量。这项技术正受到以下因素的挑战：(a)对产品安全性的日益关注，(b)使用脆性材料，如具有低断裂韧性的陶瓷，(c)需要检查非常热或放射性的部件，(d)新的复合材料引入了波传播的复杂性，以及(e)将工程材料推向其理论极限的日益增长的趋势，即使是最小的缺陷也可能至关重要。在本研究项目中，我们正在开发超声无损评估技术的几个关键要素来应对这些挑战。每个项目都得到了工业界的积极参与，并得到了政府拨款机构和私人赞助商的财政支持：(1)开发用于高温和/或伽马辐射恶劣环境的新型超声波换能器。这个项目的关键独特之处在于压电元件的衰减背衬元件——我们正在开发一种新型多孔陶瓷材料，它具有高温稳定性、声阻抗和这种特殊作用所需的衰减。(2)新的数字信号处理策略，以提高超声图像的清晰度，使缺陷尺寸或裂纹深度可以测量到一毫米的几分之一。该项目采用生物医学成像或地球物理学等研究领域常用的信号处理技术，并将其开发用于工业无损评估领域的新应用。(3)材料界面的超声表征，特别是那些部分粘附性下降的材料界面。，一种环保降解胶粘剂；涡轮叶片的冷关闭；挤压管中的研磨缺陷。在这类问题中，我们面临着一个界面区域，其厚度基本上小于传统换能器产生的典型超声波波长约1毫米。对于这类问题，需要结合多种技术来实现足够的成像分辨率：高频换能器；提取高频成分的频谱外推技术；利用比压缩波波长更短、对弱界面更敏感的角度剪切波，进行波界面反射和透射的频率分析。(4)非均匀介质中波传播的有限元模拟。这个问题不仅涉及功能梯度材料，而且涉及在线工业检查中遇到的具有强温度梯度的材料。不仅声速会随着温度的变化而变化，而且当波遇到温度梯度时，它们也会“倾斜”到弯曲的轨迹上。