Optical in-situ analysis of the cavitation damage on technical alloys under repeated single bubbles

重复单气泡作用下技术合金空化损伤的光学原位分析

• 批准号: 451715773
• 负责人: Dr.-Ing. Stefanie Hanke
• 金额: --
• 依托单位: Lehrstuhl für Werkstofftechnik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/451715773?language=en
• 关键词: Optical; situ; analysis; cavitation; damage

With time, cavitation – that is, the formation and collapse of gas bubbles in liquids – can damage the surface even of high-strength materials. The resistance of materials to cavitation is typically investigated using ultrasound sonotrodes. Due to the large number and stochastic nature of the acoustically generated bubbles, in general the resulting damage cannot be assigned to individual bubble events. However, by means of focused laser pulses it is possible to generate individual bubbles that are precisely reproducible in location and time. Besides many studies on the fluid dynamics of the collapsing bubble, some works examine the effect of such individual bubbles on a deformable solid surface. With few exceptions, the sample is from a soft material, such that the deformation resulting from a single bubble can be correlated with its dynamics. However, it is unclear how these results can be transferred to higher-strength materials.The proposed project aims at this knowledge gap between microscopically uncontrolled damage to technical alloys by acoustic cavitation on one hand and precisely reproducible loading on soft materials by individual bubbles on the other. Series of single bubbles will provide defined, repeated stress on surfaces of technical alloys. The dynamics of each bubble are recorded by imaging, then after each bubble collapse the incremental increase in damage is recorded in situ by optical microscopy, and this is complemented by high-resolution ex-situ techniques to yield a detailed picture of the damage evolution. This enables examining the development of damage during the incubation and erosion phases in unprecedented spatio-temporal resolution, as well as correlating the details of the collapse processes with material changes. In parallel, standard tests with a sonotrode are performed to put this damage into context with what is generally known about the materials’ cavitation resistance.First, microscopy optics are integrated into an existing single-bubble experiment and synchronized with high-speed visualization of the bubbles. Using samples from a soft material, this in-situ imaging is validated by ex-situ confocal microscopy. In a second step, series of tests are carried out on NiAl bronze and 316L steel in order to develop semi-automated methods to efficiently evaluate the very large data sets and to correlate in-situ and ex-situ microscopy. Finally, these methods are used in experiments on both materials, in which the number of bubbles, their distance from the sample surface, and the bubble diameter are varied. Ex-situ, the damage mechanisms in the technical alloys are analyzed in detail by high-resolution electron microscopy and compared with samples from experiments with ultrasonic cavitation according to ASTM G32. The extensive data generated in this project will be made publicly accessible, in particular for modeling work outside of the project.

随着时间的推移，空化-即液体中气泡的形成和破裂-甚至可以损坏高强度材料的表面。材料对空化的抵抗力通常使用超声焊极来研究。由于声学产生的气泡的大量和随机性质，一般来说，所产生的损害不能被分配到单个气泡事件。然而，通过聚焦的激光脉冲，可以产生在位置和时间上精确再现的单个气泡。除了许多研究的流体动力学的崩溃的气泡，一些作品检查的影响，这样的个别气泡上的可变形的固体表面。除了少数例外，样品来自软材料，使得由单个气泡引起的变形可以与其动力学相关。然而，目前还不清楚这些结果如何可以转移到更高强度的材料。拟议的项目旨在一方面通过声学空化对技术合金进行微观不受控制的破坏，另一方面通过单个气泡对软材料进行精确可重复的加载，这两者之间的知识差距。一系列单个气泡将在技术合金表面上提供确定的重复应力。通过成像记录每个气泡的动态，然后在每个气泡崩溃后，通过光学显微镜原位记录损伤的增量增加，并通过高分辨率的非原位技术来补充，以产生损伤演变的详细图像。这使得能够以前所未有的时空分辨率检查孵化和侵蚀阶段期间损坏的发展，以及将崩溃过程的细节与材料变化相关联。与此同时，使用超声波发生器进行标准测试，以将这种损坏与通常所知的材料的抗气蚀性相结合。首先，显微镜光学器件集成到现有的单气泡实验中，并与气泡的高速可视化同步。使用从软材料的样品，这种原位成像是通过非原位共聚焦显微镜验证。在第二步中，在NiAl青铜和316L钢上进行了一系列测试，以开发半自动化方法来有效地评估非常大的数据集，并将原位和非原位显微镜相关联。最后，这些方法被用于实验中的两种材料，其中的气泡的数量，它们从样品表面的距离，和气泡的直径是不同的。通过高分辨率电子显微镜详细分析了技术合金中的非原位损伤机制，并根据ASTM G32与超声空化实验样品进行了比较。该项目中生成的大量数据将公开访问，特别是用于项目之外的建模工作。