High frequency guided ultrasonic waves for hidden fatigue crack growth monitoring in multi-layer model aerospace structures
High frequency guided ultrasonic waves for hidden fatigue crack growth monitoring in multi-layer model aerospace structures
复制标题
DOI：
10.1088/0964-1726/24/2/025037
复制
发表时间：
2015-02-01
影响因子：
4.1
通讯作者：
Fromme, Paul
中科院分区：
文献类型：
--
作者：
Chan, Henry;Masserey, Bernard;Fromme, Paul
特别是对于老化的飞机，由于应力集中和变化的负载条件而在紧固件孔处产生疲劳裂纹构成了重大的维护问题。高频导波在具有经过验证的缺陷检测灵敏度的局部批量超声波测量能力与低频导波的大面积覆盖之间提供了潜在的折衷方案。高频导波的能量分布在样本厚度的所有层中，原则上允许隐藏（第二层）疲劳损伤监测。为了集成到结构健康监测系统中，必须确定从远处检测多层组件难以接近的位置中隐藏的疲劳损伤的灵敏度。研究的多层模型结构由两个带有环氧密封剂层的铝板条组成。在循环加载期间，监测紧固件孔处的疲劳裂纹扩展。使用标准超声波楔形换能器选择性地激发特定导波模式（基本 A(0) 和 S-0 兰姆模式的组合）高于更高模式的截止频率。在缺陷附近进行非接触式激光测量，以验证铝层中的疲劳裂纹对导波散射的影响。使用激光干涉测量法进行疲劳裂纹扩展监测显示出良好的灵敏度和可重复性，可以可靠地检测小的四分之一椭圆形裂纹。采用标准超声波脉冲回波设备从一定距离监测隐藏的疲劳损伤，而无需接触损坏的样品层。验证了检测位于难以接近的铝层中的疲劳裂纹的足够灵敏度，原则上允许对疲劳裂纹扩展进行实用的原位超声波监测。
Especially for ageing aircraft the development of fatigue cracks at fastener holes due to stress concentration and varying loading conditions constitutes a significant maintenance problem. High frequency guided waves offer a potential compromise between the capabilities of local bulk ultrasonic measurements with proven defect detection sensitivity and the large area coverage of lower frequency guided ultrasonic waves. High frequency guided waves have energy distributed through all layers of the specimen thickness, allowing in principle hidden (2nd layer) fatigue damage monitoring. For the integration into structural health monitoring systems the sensitivity for the detection of hidden fatigue damage in inaccessible locations of the multi-layered components from a stand-off distance has to be ascertained. The multi-layered model structure investigated consists of two aluminium plate-strips with an epoxy sealant layer. During cyclic loading fatigue crack growth at a fastener hole was monitored. Specific guided wave modes (combination of fundamental A(0) and S-0 Lamb modes) were selectively excited above the cut-off frequencies of higher modes using a standard ultrasonic wedge transducer. Non-contact laser measurements close to the defect were performed to qualify the influence of a fatigue crack in one aluminium layer on the guided wave scattering. Fatigue crack growth monitoring using laser interferometry showed good sensitivity and repeatability for the reliable detection of small, quarter-elliptical cracks. Standard ultrasonic pulse-echo equipment was employed to monitor hidden fatigue damage from a stand-off distance without access to the damaged specimen layer. Sufficient sensitivity for the detection of fatigue cracks located in the inaccessible aluminium layer was verified, allowing in principle practical in situ ultrasonic monitoring of fatigue crack growth.