Gillespie David I, Hamilton Andrew W, Atkinson Robert C, Bellekens Xavier, Michie Craig, Andonovic Ivan, Tachtatzis Christos
Department of Electronic and Electrical Engineering, Royal College Building, University of Strathclyde, 204 George Street, Glasgow G1 1XW, UK.
Collins Aerospace, Prestwick, 1 Dow Avenue, Prestwick International Aerospace Park, Ayrshire KA9 2SA, UK.
Sensors (Basel). 2020 Dec 17;20(24):7227. doi: 10.3390/s20247227.
Delaminations within aerospace composites are of particular concern, presenting within composite laminate structures without visible surface indications. Transmission based thermography techniques using contact temperature sensors and surface mounted heat sources are able to detect reductions in thermal conductivity and in turn impact damage and large disbonds can be detected. However delaminations between Carbon Fibre Reinforced Polymer (CFRP) plies are not immediately discoverable using the technique. The use of transient thermal conduction profiles induced from zonal heating of a CFRP laminate to ascertain inter-laminate differences has been demonstrated and the paper builds on this method further by investigating the impact of inter laminate inclusions, in the form of delaminations, to the transient thermal conduction profile of multi-ply bi-axial CFRP laminates. Results demonstrate that as the distance between centre of the heat source and delamination increase, whilst maintaining the delamination within the heated area, the resultant transient thermal conduction profile is measurably different to that of a homogeneous region at the same distance. The method utilises a supervised Support Vector Classification (SVC) algorithm to detect delaminations using temperature data from either the edge of the defect or the centre during a 140 s ramped heating period to 80 °C. An F1 score in the classification of delaminations or no delamination at an overall accuracy of over 99% in both training and with test data separate from the training process has been achieved using data points effected by transient thermal conduction due to structural dissipation at 56.25 mm.
航空航天复合材料中的分层问题备受关注，它出现在复合材料层合结构内部，表面却没有明显迹象。基于传输的热成像技术使用接触式温度传感器和表面安装的热源，能够检测热导率的降低，进而检测出冲击损伤和较大的脱粘情况。然而，使用该技术无法立即发现碳纤维增强聚合物（CFRP）层之间的分层。利用CFRP层合板区域加热引起的瞬态热传导剖面来确定层间差异的方法已得到验证，本文在此方法的基础上进一步研究了分层形式的层间夹杂物对多层双轴CFRP层合板瞬态热传导剖面的影响。结果表明，在将分层保持在加热区域内的同时，随着热源中心与分层之间距离的增加，所得的瞬态热传导剖面与相同距离处均匀区域的剖面有明显差异。该方法利用监督支持向量分类（SVC）算法，在140秒升温至80°C的加热过程中，使用缺陷边缘或中心的温度数据来检测分层。使用受56.25毫米处结构耗散引起的瞬态热传导影响的数据点，在训练和与训练过程分开的测试数据中，分层或不分层分类的F1分数在总体准确率超过99%的情况下均已实现。
