Non-destructive 3D grain imaging in aeroengine materials by diffraction contrast tomography

传统的x射线图像依赖于衰减对比，这意味着x射线照片的某些区域看起来很亮，因为它们比其他区域衰减更多的x射线。目前，几乎所有的实验室扫描仪利用这种对比机制。有许多材料，如碳纤维复合材料和柔软的生物组织，只含有低衰减材料。在这种情况下，很难看到感兴趣的关键特征，如缺陷、裂缝和癌组织。虽然这些软材料显示出很少的衰减对比，但它们确实通过折射率的差异影响x射线的相位。通常，这些相位变化不能成像，但对于高相干源，如同步加速器源，相位对比正迅速成为一种主要工具。然而，实验室x射线系统通常具有很少的相干性，因此该方法的应用并不简单。作为该项目的一部分，将研究在实验室x射线成像中显示相衬的新方法，目的是开发一个原型相衬成像计算机断层扫描（CT）系统，以及重建相衬图像所需的软件。这个原型成像系统将被开发、改进和测试，使用一些关键的演示材料科学问题。其中第一个将是大型碳纤维复合板的检查。制造损伤和几乎不可见的冲击损伤是复合材料工业特别是航空航天领域的主要问题。特别是，异常大的颗粒被认为是许多限制寿命的影响的途径，例如航空发动机材料的居住疲劳。这严重影响了航空发动机部件制造和寿命方面的生产率。这位博士将是第一个应用相衬技术来发现、成像和跟踪这些颗粒的降解效应，并使用罕见事件的数学来精确地生活这些部分的人。相衬技术的应用也可用于其他软固体样品（例如可能的软组织样品）。

Traditionally X-ray images rely on attenuation contrast which means that some regions of a radiograph appear light because they attenuate more of the X-rays than others. At present, nearly all lab scanners exploit this contrast mechanism. There are many materials such as carbon fibre composites and soft biological tissue which contain only lowly attenuating materials. In such cases it is difficult to see key features of interest such as defects, cracks and cancerous tissue.While these soft materials show little attenuation contrast, they do affect the phase of the X-rays through differences in refractive index. Normally these changes in phase cannot be imaged but for highly coherent sources such as synchrotron sources phase contrast is fast becoming a major tool. Laboratory X-ray systems however typically have little coherence and so the application of this method is not straightforward. New methods for revealing phase contrast in lab X-ray imaging will be investigated as part of this project with the aim of developing a prototype phase contrast imaging computed tomography (CT) system, along with the software required to reconstruct the phase contrast images.This prototype imaging system will then be developed, advanced and tested using a number of key demonstrator materials science problems. The first of these will be the examination of large carbon fibre composite panels. Both manufacturing damage and barely visible impact damage are a major concern for the composite industry especially in aerospace. In particular, unusually large grains are believed to be the route of a number of life-limiting effects, such as dwell fatigue in aeroengine materials. This significantly affects productivity in terms of aeroengine component manufacture and life. This PhD will be the first to apply the phase contrast technique to find, image and follow the degrading effect of these grains and use the mathematics of rare events to accurately life such parts. The application of the phase contrast technique can also be used on other soft solid samples (possible soft tissue samples for example).