Pulsed eddy current stimulated thermographic NDE

脉冲涡流热成像技术是一种新型的无损检测技术，它采用红外摄像机来检测缺陷，通常是组件表面的裂纹，通过成像它们对脉冲涡流加热系统产生的组件加热的影响。迄今为止，使用传统的涡流加热系统，在一个简单的，两个或三个匝，环绕线圈的测试件中产生了50- 200khz范围内的涡流。裂纹阻断了涡流的流动，并显著地改变了其附近的电流流动路线。由涡流引起的焦耳加热可以通过红外摄像机成像，提供了一种通过成像它们对涡流分布的特征效应来检测裂纹的方法。这种方法比需要逐点扫描的传统超声波或涡流检测技术要快得多。虽然在少数实验室中取得了令人印象深刻的结果，但该系统，特别是激励，还需要工程设计。需要对系统的可靠性进行调查，因为担心组件上某些位置的缺陷可能会被遗漏；这是励磁系统在元件表面产生的涡流密度的函数。此外，迄今为止的结果是相当定性的，几乎没有缺陷可检测性或其依赖于系统，缺陷或试件参数的指示。本提案旨在对可靠的涡流激发热成像检测系统的涡流激励要求和测量进行科学研究，以确定该系统的缺陷检测能力。该计划是一个两个人一年的项目，其中第一年将在纽卡斯尔进行，工作重点是涡流励磁系统需求的建模，以及研究合适系统的设计和建造。第二年将以巴斯为基地，该系统将用于研究缺陷检测能力。本文将研究两种励磁系统。一个用于测试可放置在环形线圈内的小组件，另一个用于测试较大组件，这些组件将使用线圈在组件的局部区域产生加热来逐步测试。实用的样品将由工业合作伙伴劳斯莱斯和阿斯顿电力公司提供。该项目将涉及对试样表面产生的涡流密度及其在不同方向和位置设置的不同尺寸裂缝中的加热效应进行深入建模。在涡流线圈内改变试样方向的影响将被模拟，以建立检测测量，从而检测出试样内所有方向上的缺陷。实验研究了该系统在检测和成像不同尺寸、形状和方向缺陷方面的性能。该技术的性能将与其他热成像NDE方法进行比较：光学刺激、传统瞬态热成像和声刺激热超声。该项目的总体目标是对一项有前途的新濒死技术进行彻底的科学调查，在该技术成功引入工业之前，这是必要的。

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.