Low-frequency Vibration Inspection of Sandwich Composites

使用低频振动方法可以成功地对某些复合材料结构（蜂窝、轻木和泡沫芯夹层）进行单侧在用检测，但缺陷检测有限，目前还不支持缺陷分类。数据采集设备在20年里几乎没有什么进步，除了从模拟到数字，直到Baugh和Weedon公司的新型“Bondcheck”债券测试系统。这提供了在每个位置的全波形捕获，具有扩展到传感器阵列的潜力，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，改进的俯角捕获探针设计可以提高分辨率和频率范围，而全频率捕获的使用为缺陷分类、深度和尺寸估计提供了潜力。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，并根据与一系列具有不同缺陷类型的结构的模拟低频（5 kHz -100 kHz）响应的比较，确定其深度、位置和大小。布里斯托尔在声学建模和使用模拟响应的反演方法方面都有丰富的经验。对于该项目，最初将使用数据库方法与多维优化相结合，以反转数据并确定缺陷的类型和3D位置，并有可能以各种方式改进该方法。该学生将在布里斯托尔大学的超声波和无损检测小组工作，然后搬到位于赫里福德的Baugh & Weedon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.