Pulsed eddy current stimulated thermographic NDE

脉冲涡流激发热像仪是一种新型的无损检测(NDE)技术，它使用红外相机来检测缺陷，通常是部件表面的裂纹，通过成像它们对脉冲涡流加热系统产生的部件加热的影响。到目前为止，50-200 khz范围内的涡流已经在使用带有简单的两圈或三圈环绕线圈的传统涡流加热系统的试件中产生。裂缝阻碍了涡流的流动，并显著改变了附近的水流流线。由涡流引起的焦耳加热可以通过红外相机成像，从而提供了一种通过成像裂纹对涡流分布的特征影响来检测裂纹的方法。该方法比传统的需要逐点扫描的超声波或涡流检测技术要快得多。虽然在少数实验室取得了令人印象深刻的成果，但该系统，特别是励磁系统，需要工程设计。需要调查系统的可靠性，因为担心可能会遗漏部件上某些位置的缺陷；这是励磁系统在部件表面产生的涡流密度的函数。此外，到目前为止，结果相当定性，几乎没有缺陷可检测性的迹象，或者它对系统、缺陷或试件参数的依赖。该提案旨在对可靠的涡流激发热像检测系统的涡流激励要求进行科学研究，并进行测量以确定此类系统的缺陷检测能力。该计划是一个为期两年的项目，第一年将以纽卡斯尔为基地，工作重点是涡流励磁系统要求的建模和研究合适系统的设计和建造。第二年将设在巴斯，该系统将在那里用于研究缺陷检测能力。将研究两种类型的励磁系统。一种用于测试可放置在环绕线圈内的小部件，另一种用于测试较大的部件，这些部件将使用线圈逐步测试，以在部件的局部区域产生热量。劳斯莱斯和Astom Power将提供实用的样本。该项目将涉及对样品表面感应的涡流密度及其在部件不同方向和位置设置的不同大小裂缝的加热效应进行深入模拟。改变样品在涡流线圈内的取向的影响将被模拟，以建立检查测量，该测量应导致检测在样品内的所有方向设置的缺陷。实验研究了该系统对不同尺寸、形状和方位缺陷的检测和成像性能。该技术的性能将与其他热成像无损检测方法进行比较：光激励、传统的瞬时热成像和声激励热超声。该项目的总体目标是对一种有前景的新无损检测技术进行彻底的科学调查，该技术在成功地引入工业之前是必要的。

Pulsed eddy current stimulated thermography is a novel non-destructive evaluation (NDE) technique that employs an infrared camera to detect defects, typically cracks at the surface of a component, by imaging the effects that they have on the heating of a component produced by a pulsed eddy current heating system. To date, eddy currents in the 50-200 kHz range have been generated in a test-piece using a conventional eddy current heating system with a simple, two or three turn, encircling coil. Cracks block the flow of eddy currents and significantly alter current flow lines in their vicinity. The Joule heating caused by the eddy currents can be imaged by an infrared camera, providing a means of detecting cracks by imaging the characteristic effects that they have on eddy current distribution. The method is considerably quicker than conventional ultrasonic or eddy current inspection techniques that require point by point scanning. Whilst impressive results have been achieved in a small number of laboratories, the system, particularly the excitation, needs engineering. The reliability of the system needs to be investigated as there is concern that defects in some locations on a component may be missed; this is a function of the eddy current density that is generated across the surface of a component by the excitation system. In addition, results to date are rather qualitative with little indication of defect detectability or its dependence on system, defect or test-piece parameters. This proposal is for a scientific investigation of the eddy current excitation requirements for a reliable eddy current stimulated thermography inspection system and measurements to determine the defect detection capabilities of such a system. The plan is for a two person-year project in which the first year will be based at Newcastle with the work focussed on the modelling of the requirements of the eddy current excitation system and on researching the design and construction of a suitable system. The second year will be based at Bath where the system will be used to research defect detection capabilities. Two types of excitation system will be investigated. One for the testing of small components that can be placed within an encircling coil and the other for the testing of larger components which will be progressively tested using a coil to produce heating in a localised region of the component. Practical specimens will be provided by the industrial collaborators, Rolls-Royce and Astom Power. The project will involve in-depth modelling of the eddy current density induced in the surface of a specimen and its heating effect at cracks of different size set at different orientations and locations across the component. The effects of changing the orientation of a specimen within the eddy current coil will be modelled to establish inspection measurements that should lead to the detection of defects set at all orientations within the specimen. Experimental studies will be made of the performance of the system in detecting and imaging defects of different sizes, shapes and orientation. The performance of the technique will be compared with the other thermographic NDE methodologies: optical stimulated, conventional transient thermography and acoustically-stimulated thermosonics. The overall aim of the project is to perform a thorough scientific investigation of a promising new NDE technique that is needed before the technique can be introduced successfully into industry.