Low-frequency Vibration Inspection of Sandwich Composites

某些复合材料结构（蜂窝，轻木和泡沫芯夹层）的单侧在役检测可以成功使用低频振动方法，但缺陷检测是有限的，目前不支持缺陷分类。在Baugh和韦登推出新的“Bondcheck”键合测试系统之前，数据采集设备在20年里几乎没有进步，除了从模拟转向数字。这提供了在每个位置的全波形捕获，并有可能扩展到一系列传感器，为结构分析算法和与建模响应的比较开辟了更大的潜力。先前的工作表明，改进的一发一收探头设计可以提高分辨率和频率范围，而全频率捕获的使用可以为缺陷分类、深度和尺寸估计提供潜力。该项目将使用低频振动对夹层复合材料中的缺陷进行分类，并根据与具有不同缺陷类型的一系列结构的模拟低频（5 kHz-100 kHz）响应的比较来确定其深度、位置和大小。布里斯托在使用模拟响应的声学建模和反演方法方面具有丰富的经验。在这个项目中，一个数据库方法加上多维优化来反演数据并确定缺陷的类型和3D位置将被初步使用，并有可能以各种方式改进该方法。该学生将在布里斯托大学的超声和无损检测组工作，然后搬到位于赫里福德的Baugh &韦登办公室。

One-sided in-service inspection of certain composite structures (honeycomb-, balsa- and foam-core sandwich) can be successful using a low-frequency vibration method but defect detection is limited, and classification of defects is not currently supported. Data-acquisition equipment had hardly advanced in 20 years, bar moving from analogue to digital, until the new 'Bondcheck' bond testing system from Baugh and Weedon. This offers full-waveform capture at every location, with the potential to expand to an array of sensors, opening up greater potential for structure analysis algorithms and comparison with modelled responses.Prior work has showed the potential for improved pitch-catch probe design to enhance the resolution and frequency range, whilst the use of full-frequency capture offered the potential for defect classification, depth and size estimation. This project will use low-frequency vibration to classify defects in sandwich composites and determine their depth, location and size, based on comparison with the modelled low-frequency (5 kHz -100 kHz) responses of a range of structures with different defect types. Bristol has considerable experience of both acoustic modelling and inversion methods using modelled responses. For this project a database method coupled with multi-dimensional optimisation to invert the data and determine the type and 3D location of defects will be used initially, with potential for refinement of the method in a variety of ways.The student will be based at the Ultrasonics and Non-Destructive Testing Group at the University of Bristol before relocating to the Baugh & Weedon's offices in Hereford.